A. Feo

Instituto Nacional de Técnica Aeroespacial, Madrid, Spain

M. Vargas

Glenn Research Center, Cleveland, Ohio

A. Sor

Instituto Nacional de Técnica Aeroespacial, Madrid, Spain

Rotating Rig Development for Droplet 

Deformation/Breakup and Impact 

Induced by Aerodynamic Surfaces

NASA/TM—2012-217721

September 2012

SAE2011–38–0087
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A. Feo

Instituto Nacional de Técnica Aeroespacial, Madrid, Spain

M. Vargas

Glenn Research Center, Cleveland, Ohio

A. Sor

Instituto Nacional de Técnica Aeroespacial, Madrid, Spain

Rotating Rig Development for Droplet 

Deformation/Breakup and Impact 

Induced by Aerodynamic Surfaces

NASA/TM—2012-217721

September 2012

SAE2011–38–0087

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

International Conference on Aircraft and Engine Icing and Ground Deicing

sponsored by SAE International

Chicago, Illinois, June 13–17, 2011
Acknowledgments

The authors wish to express their gratitude to Tom Bond, formerly Icing Branch Chief of NASA Glenn Research Center and 

presently at the FAA, for his support, interest and prominent role played at the start of the new facility development. They also 

wish to thank all the technical personnel in the INTA Experimental Aerodynamics Department for their contributions to the 

facility development, and in particular to Juan Canales for his excellent work and dedication during many years to the Facility 

improvement, to Eva Jarillo for her continuous commitment and contributions to the droplet generation system and measurement 

procedures implemented at the facility, to J. Carlos Martín for his excellent work on the implementation of all the electrical systems 

needed, to Lorenzo Plana for his lighting, optics and single imaging contributions preparing the way for future advances in this 

area and finally to Francisco Rogles for his work and continuous improvements on the droplet/model synchronization established 

in the facility. Thanks to Dr. Peter Struk for reviewing the paper. Special recognition to NASA Glenn Research Center imaging 

specialists Christopher Lynch and Quentin Schwinn for their contribution to high-speed video imaging that can be used for future 

applications in this field.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identification 

only. Their usage does not constitute an official endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217721 1

Rotating Rig Development for Droplet Deformation/Breakup

and Impact Induced by Aerodynamic Surfaces

A. Feo

Instituto Nacional de Técnica Aeroespacial 

28034 Madrid, Spain

M. Vargas

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

A. Sor

Instituto Nacional de Técnica Aeroespacial 

28034 Madrid, Spain

Abstract

This work presents the development of a Rotating Rig 

Facility by the Instituto Nacional de Técnica Aeroespacial

(INTA) in cooperation with the NASA Glenn Research 

Center. The facility is located at the INTA installations near 

Madrid, Spain. It has been designed to study the deformation, 

breakup and impact of large droplets induced by aerodynamic 

bodies. The importance of these physical phenomena is related 

to the effects of Supercooled Large Droplets in icing clouds on 

the impinging efficiency of the droplets on the body, that may 

change should these phenomena not be taken into account. 

The important variables and the similarity parameters that 

enter in this problem are presented. The facility's components 

are described and some possible set-ups are explained. 

Application examples from past experiments are presented in 

order to indicate the capabilities of the new facility.

1.0 Introduction

In-flight observations by pilots of large droplets breaking up 

when approaching lifting surfaces (Ref. 1) indicate the need to 

conduct studies of supercooled large droplets (SLD) break-up 

near large air transport airfoils, since modifications of cloud 

impinging efficiency would change the accreted ice mass and 

shape and therefore affect the aerodynamic performance of the 

aircraft.

Droplet deformation and breakup has been the subject of 

experimental research for many different applications. The 

type of disturbance defines how deformation makes progress 

and finally breaks up. Specific experimental tools have been 

used depending on the application and the objectives sought.

In shock tubes used for high-speed gas streams and shockwave studies (Refs. 2 to 12), the droplet time-dependent 

deformation is dictated mainly by the location of the release 

and the magnitude of the disturbance. Wind tunnels have been 

used for lower speed studies, with droplets injected at different 

spatial locations and directions with respect to the air stream

(Refs. 13 to 16). Recently, more wind tunnel studies have been 

performed with models included in the test section (Refs. 17

and 18). In this experimental configuration the parameters that 

may affect the deformation/breakup process are not only the 

ones related to their injection, but also include wind tunnel

turbulence intensity and model/wall interference that become 

important for model/test section area ratios above 10 percent.

Furthermore, to improve experimental simulation, it might be 

needed to measure droplet water temperatures and even to 

approximate their value to the ones existing in nature.

Past experimental studies of droplet deformation indicate 

that the last part after the deformation /breakup process may 

lead to different outcomes. One possibility is for the distorted 

droplet to hit the body surface with all of its mass. A second 

situation is when the droplet disintegrates into a fine micronsize spray before hitting the body, of which none, some or all 

may impinge onto the body. A third possibility is when part of 

the distorted droplet remains as a water mass that strikes the 

surface and the rest is converted into a fine spray of which 

again, none, some or all may re-impinge on the body surface.

For the water mass striking the surface, some remains on the 

surface, while the rest splashes back into the air flow. This is 

the well-known splashing phenomenon that has been 

extensively studied in the literature for spherical shapes and 

many different values of the parameters that dominate the 

impact. However, for other shapes there is no information in 

the public domain. Wright and Potapczuk (Ref. 19) have 

reported on a number of empirical splashing models from 

existing experiments (Refs. 20 and 21) with an upper limit of 

340 μm and velocities of 30 m/s. The results shown from two 

of the empirical models for droplets of 21 and 91 μm offer 

good comparisons with experimental collection efficiencies 

near the leading edge of the airfoil, but degrade towards the 

impinging limits. For droplets of 240 μm there are no 

collection efficiencies to compare with, but the results of the 

two models used do not agree between themselves except on 

the impinging limits. This indicated the need for additional 

experimental work on splashing by large droplets. Studies 

(Ref. 22) on single droplet impacts in a vertical wind tunnel 
NASA/TM—2012-217721 2

for droplets between 120 to160 μm and velocities of 20

to100 m/s impacting on thin water films, reported difficulties 

on the estimation of secondary droplet diameters, velocities 

and spreading diameters resulting from the impact. The 

droplet breakup and splashing dynamics for the mentioned 

complex phenomena need to be understood and measured in 

improved testing facilities and experimental configurations.

In the mid-1980s, INTA developed a small low power Rotating 

Arm Facility as part of a research effort in cooperation with 

NASA Langley Research Center on Heavy Rain on 

Aerodynamics of Aircrafts, to study the splash characteristics of 

typical spherical drops that are present in heavy rain events. The 

arm and model used were of small size, just enough to 

accommodate the drop impacts and determine the variables of the

splash that dominate the phenomenon. The maximum model 

velocity was 60 m/s and drop incidences were changed from near 

zero to perpendicular (Refs. 23 to 25). Additional development of 

the facility continued in 2007 as part of a Space Act Agreement 

research cooperation with NASA Glenn Research Center on Icing 

Physics, to offer capabilities for the study of supercooled large 

droplets (SLD) in icing cloud encounters that are subject to 

deformation/ breakup and possibly impact on the aircraft lifting

surfaces. The design requirement for the model velocity was set 

to 90 m/s and 0.5 m chord, so that the phenomena of interest had

the possibility of being observed and measured (Ref. 26). The 

present work explains the development of the facility and its 

upgrading from the capabilities of droplet splashing to the droplet 

breakup experiments.

Potential advantages of facilities that allow experiments 

with moving models (e.g., rotating arms, acceleration tracks,

etc.) include the following: smaller injection release effects on 

the droplet deformation/breakup stability; less uncertainty in

droplet temperature when reaching the target area due to 

shorter trajectory, simpler droplet control to reach specific 

target locations; easier and more effective droplet visualization 

methods to follow droplets along their the trajectories.

In the following sections details are given on the development 

of the Rotating Rig. The section are: 2.0 Variables and 

parameters defining the experiments; 3.0 Detailed description of 

the facility; 4.0 Possible experimental set-ups; 5.0 Application 

examples; and 6.0 Concluding remarks.

2.0 Problem Definition, Variables and 

Non-Dimensional Parameters

The development and use of a unique facility such as the

Rotating Arm Facility, expressly designed for experimental 

research in the field of large water droplets approaching 

aerodynamic surfaces in conditions similar to the ones 

encountered in flight, requires knowledge of the relevant 

physical magnitudes to prepare instrumentation and 

experimental techniques to be used. Due to the number of 

variables involved, the reduction and ordering of these 

variables in the form of non-dimensional groups of input and 

output parameters is appropriate.

There is not yet a comprehensive theory of large droplet 

behavior along the trajectories from far upstream to the body 

surface for the conditions existing in aircraft icing encounters.

Initial experiments (Ref. 26) showed that during the 

deformation process, the droplet presents a continuous 

geometric change from spherical to ellipsoidal and finally into 

a flattened disk without any mass loss. The droplet's breakup 

may be considered to be the last part of the deformation 

process. At this point, a transformation starts into clearly 

distinctive units such as water membranes, secondary droplets,

water rings, etc., depending upon the breakup regime (bag, 

shear or catastrophic). The facility has to be prepared to 

visualize and/or measure all the variables involved in the 

phenomena and determine what are the dominant parameters 

to understand the physical phenomena that take place for 

different input conditions. An initial assessment of the number 

of variables and non-dimensional parameters that may 

influence the final characteristics of the several phenomena 

that appear can be done based on previous experimental 

results and on dimensional analysis. In the next paragraphs the 

main variables and non-dimensional parameters that need to 

be measured in the facility are presented.

Droplet size is a key variable for trajectory determination in 

aircraft icing conditions. There are three groups of diameters 

presenting distinctive behavior as far as trajectories are 

concerned. The first is for submicron diameters that basically 

follow the air streamlines and present no problem in trajectory 

calculations. The second is for droplets between 10 and 50 μm

that are included in Appendix C regulations and their 

trajectories are calculated assuming that they behave as solid 

spheres. The third is for diameters from 50 to 3000 μm and are 

the so called “Supercooled Large Droplets” that include

freezing drizzle and freezing rain. For these droplets, the 

aerodynamic forces tend to distort their spherical shape and 

may even induce them to breakup. Droplets in these situations 

could end up impacting the body depending on conditions.

A body moving at constant velocity through still air 

determines a flow field which is a function of the following

variables: U being the incoming free stream air velocity 

magnitude respect to a frame of reference fixed at the body; ρ

the air density, μ the air viscosity coefficient and c a 

characteristic body length. Should other dimensions be needed 

to define the body geometry, they would be made nondimensional with respect to c. Also, the body attitude with 

respect to the path may be another variable, but for simplicity 

will not be considered here. The air velocity at any point in the 

field U is then a function of Ua = f (U, ρ, μ, c). Dimensional 

analysis yields:





 





μ

ρ = Uc f U

Ua (1)

Where Ua is the air velocity and (ρ ∙ U ∙ c/μ) is the Reynolds 

number based on the characteristic length c.

The droplet's motion through the air velocity field, at any 

point with air velocity Ua is a function of the following 
NASA/TM—2012-217721 3

variables: d the diameter of the droplet; xd is the distance from

the droplet to the body; td is the time it takes the droplet to get 

to the body; Ud is the droplet's velocity magnitude; ad is the 

droplet's acceleration magnitude, σw/a is the water/air surface 

tension, ρw is the water density, and μw is the water viscosity

coefficient. For convenience, the magnitude of the relative 

air/droplet velocity Udr may be used instead of Ud in some of 

the parameters. The same can be said for the droplet relative 

air/velocity acceleration adr. Any of the resultant 

characteristics (e.g., deformation geometry, secondary droplet 

diameter, etc.) denoted by C, as part of the deformation,

breakup or impact is a function of:

C = f (d, x ,t ,U ,a ,σ ,ρ ,μ ,U,c,ρ,μ) d d d dr d w a w w (2)

Dimensional analysis yields:

















μ

ρ

ρ

ρ

μ

μ

σ

ρ

σ

ρ

μ

ρ

=

U d U d d a w Uc

c

t U

c

x

c

d F

C

w

w a

w d

w a

d d dr dr dr d , , , , , , , ,

2 2

non-dimensional

(3)

Where w a

dr U d

σ

ρ 2

is the Weber number, w a

w d d a

σ

ρ 2

is the Bond 

number, and

μ

ρUdrd and

μ

ρUc are the Reynolds numbers.

In the case that some water mass hits the body surface after 

the deformation/breakup process, it will need to be

experimentally determined how much of the water will splash 

back, what its characteristics will be and how the rest of the 

water mass will be deposited on the body surface. The 

splashing process is governed by the following variables: the 

equivalent droplet diameter de; the impact velocity Ui; the 

water film thickness on which the impact takes place h; the 

surface roughness δr; the time elapsed since the start of the 

splashing process ts; the water density ρw; the water viscosity 

coefficient μw; the water/air surface tension σw/a; and the 

water/surface contact angle θ.

Thus, any splash characteristic Cs, is a function of:

= ( , , ,δ , ,ρ ,μ ,σ ,θ) s d e i r s w w w a C f d U h t (4)

Dimensional analysis yields:















 θ δ

σ

ρ

μ

ρ = , , , , ,

2

non-dimensional

e

s i

e

r

w a e

w i e

w

w i e S s d

t U

d d

U d U d h C F (5)

Where w a

w i e U d

σ

ρ 2

is the Weber number and w

wUide

μ

ρ the 

Reynolds number.

In droplet breakup and splashing experiments the main 

parameters measured or calculated are the Weber number, the 

Bond number and the Reynolds number.

3.0 Facility Description

The previous sections explained the need for experiments 

showing visualization/observation with measurements of large 

droplet behavior along the trajectory upstream of bodies that 

simulate lifting surfaces of large transport aircraft in flight. To 

accomplish this objective, the Rotating Rig Facility developed 

initially for splashing experiments was upgraded to move an 

aerodynamic body with a characteristic length of at least 0.5 m 

to a velocity up to 90 m/s. The range of droplet generation was 

increased from 100 to 3000 μm. Digital techniques using state 

of the art high speed camera and video equipment were added 

for observations and measurements. Varying the parameters, 

enough data can be generated to understand the general 

problem, with conclusions for the full scale through analytical 

calculations and/or data extrapolation. Additional modifications 

to the facility consisted in the modification of critical 

components, starting with improvements required for safety 

reasons in the room housing the Facility due to increased arm

and model dimension as well as the maximum velocity of 

operation (Figure 1) (Ref. 27). The components and equipment 

that have been upgraded or added are described below.

Figure 1.—General view of the Rotating Rig Facility.
NASA/TM—2012-217721 4

Figure 2.—Rotating Rig Support Structure.

3.1 Support Structure

A new structure has been designed to comply with the 

requirements of increasing the model velocity to 90 m/s, the 

dimension to 0.5 m and the arm length over 2 m. For the

maximum nominal velocity and model size, the maximum 

vibration detected by an accelerometer attached to the 

structure must remain below a pre-determined value for which 

an electric brake is actuated to stop the rotation. The structure 

is built with hollow steel beams of square cross section with 

the shape of a cube of 0.86 m on the lower side and of a 

truncated pyramidal shape of 0.28 m height on top (Figure 2).

The structure is welded to a steel plate attached to a concrete 

block on the floor. Internally the structure houses a new 

5.0 KW DC Electric Motor with forced ventilation and 

temperature sensor to disconnect the electric supply in case of 

overheating; the electronic control system; the transmission 

gears; the 12 channels slip rings unit and the vertical axle 

connected to the arm ́s head (Figure 3).

3.2 Arm and Counterbalance

The velocity increase and the larger model made it 

necessary to redefine the arm radius and its cross section. The 

main consideration when increasing the arm length was to

decrease the centrifugal forces on the model. Increasing the 

Figure 3.—Rotating Rig Support Structure, Internal View.

arm length has the added benefit of a smaller aerodynamic 

wake effect from the previous rotation, to the point that it may 

be neglected in the study of droplet deformation /breakup and 

impact intended for this Facility. The arm material was 

changed to aluminum, incorporating a streamlined cross 

section of 0.09 m chord and a length of 2.16 m from the 

rotation axle to the arm tip. The new conditions made the 

counterbalance weight and position critical when performing 

balancing of the model/arm operation. Small counterbalance 

variations gave large changes on the balance of the 

model/arm. Both the arm and counterbalance had to be 

supplemented with struts, to increase the unit stiffness and 

decrease horizontal and vertical vibrations (Figure 4).

3.3 Models

The model is one of the most important components of the 

rotating rig facility. Mechanical and aerodynamic elements 

enter in its design. Due to the large centrifugal forces present, 

the mass needs to be carefully adjusted to the possible 

minimum, selecting the appropriate low density material 

supplemented with light metallic materials of enough 
NASA/TM—2012-217721 5

Figure 4.—Rotating Rig Arm and Counterbalance.

Figure 5.—DBKUP 002 Model with 0.47 m chord and 0.35 m 

span.

structural strength in the model interior to maintain its integrity 

and sustain the union to the arm. Another important aspect in 

relation with the intended simulation in the experiments is the 

aerodynamic design. The air flow forces need to be maintained 

low so that the required velocity can be attained, considering the 

power constraints imposed by the electric motor and keeping 

the associated aerodynamic wake effects to the minimum. An 

example of model design is the one shown in Figure 5, which is 

the DBKUP 002 model that was used in the observation 

experiments reported in Reference 26. It is a small aspect ratio 

wing with 0.47 m chord and 0.35 m span with a large airfoil 

thickness, to simulate as much as possible the one found on the 

leading edge of a large transport aircraft wing. It was required 

as part of model design to mount an accelerometer in its interior 

to detect undesired vibrations.

3.4 Mono-Disperse Droplet Generator

Mono-disperse droplet generators operate through vibration 

of a water jet coming out of a circular orifice (Figure 6). If a 

laminar liquid jet with a flow rate Q is vibrated at frequency f,

it produces at short distances from the orifice an equally 

spaced stream of droplets that follow the expression (Ref. 28):

d (μm) = 317 (Q(cc/min) / f (kHz))1/3 (6)

Figure 6.—Droplet Generator with Aerodynamic 

Protection.

The range of droplet sizes for a fixed orifice diameter is 

limited by the liquid jet velocity that stays in the laminar 

regime, indicating the limit of operation for that orifice. To 

increase the range of droplet diameters, larger orifice 

diameters need to be used. There is a group of frequencies 

(Raleigh frequencies) that follow the expression (Ref. 28):

fR = Uj/4.508 Dj (7)

where Uj is the water jet exit velocity and Dj is the jet diameter

(assumed to be equal to the orifice diameter), that produce a 

longer stable stream of droplets with diameter approximately 

twice the jet diameter (Figure 7). The basic system consists of 

a stainless steel water pressure container, connected through 
NASA/TM—2012-217721 6

Figure 7.—Stream of Droplets. Orifice diameter 100 μm;. fR = 20.7 KHz; flow rate 4.5 cc/min. Droplets at 

different distances from orifice.
NASA/TM—2012-217721 7

plastic tubing to a precision control valve with a manometer, 

to supply constant water pressure to the vibrating head 

directed to the exit orifice. The frequency generator prepared

for this application was a 5 MHz B&K Precision model 

4011A. While in operation with the arm and model in rotation, 

an aerodynamic protector can be attached to the vibration head 

orifice exit to minimize external air disturbances that may 

promote premature breakup of the water jet into undesirable

droplet sizes before it gets into the flow field induced by the 

model.

3.5 Lighting

Lighting equipment is another of the essential elements of 

the facility. The lighting instrumentation requirements are

imposed by higher velocities and smaller droplets. Depending 

on the test objectives, high-intensity-continuous or shortduration lights may be used. For droplet breakup and impact 

research experiments, the minimum time required is in the 

order of microseconds and the equipment used should be 

prepared to supply high intensity light during that order of 

magnitude or less. If the tests require high-speed video 

equipment, frame rates from 50,000 to 150,000 per second 

would be needed with high-intensity lighting to capture 

images in sufficient resolution. Different lighting 

configurations that have been used include: direct parallel 

light rays to the object (Shadowgraphy), parabolic reflectors,

and diffusing paper. For general type observation images, 

simple direct backlight was used to satisfy the requirement.

Examples of the equipment that have been used to provide 

short duration lighting include: Strobotac 3 μsec lamp with 

single or double variable time delay exposure; Microflash with 

microsecond spark; Nanoflash with nanosecond spark. For 

continuous lighting a xenon 2000 W lamp was used.

3.6 Imaging

Visualization is the basic technique in the Facility, from 

which measurements have to be obtained and interpreted to 

analyze the phenomena under consideration and characterize it

quantitatively. The single short duration lights need 

synchronization and time-delay systems connected to the 

camera in order to capture the images. Due to the small 

droplet sizes involved, care must be exercised in choosing the 

appropriate high quality lens, extension rings and 

magnification to achieve maximum resolution compatible with 

reasonable field of view, to permit measurement and analysis 

of the pertinent characteristics. The same considerations apply 

to high-speed video, adding frame rate selection, total number 

of frames and synchronization of the starting frame with 

model location. An example of equipment used for single 

image cases is a Hasselblad digital camera Model H3 39 with 

lens and extension rings that permit a field of view of 35- by

25-mm with a resolution of 131 pixels per mm, at a distance 

from the object of 0.6 m. Equipment for the high-speed video 

include a Photron SA 5 high speed camera used at frame rates 

from 50,000 to 150,000 with a 200 mm Micro Nikkor lens and 

a 2 plus doubler at distances from the object from 0.91 to 

0.36 m.

3.7 Additional Support Instrumentation

Variables related to the air motion due to model rotation and 

others like the breakup secondary droplet characteristics 

cannot be measured with the visualization tools mentioned in 

previous paragraphs. The air velocity outside the model's path 

may be measured with conventional pressure probes to 

understand the air rotation inside the closed room including 

the wall effects. Measurements along the model's path while in 

rotation must be done with non-intrusive techniques, such as 

Laser Doppler Velocimetry (LDV) or Particle Image 

Velocimetry (PIV) to determine model rotation upstream and 

downstream wake effects. To complete the study of model 

rotation effects, model surface pressure measurements may be 

required. This is done through ordinary pressure taps with 

transducers transmitting signals through the slip rings or 

telemetry with direct transmission to the data acquisition 

room. For characteristics of secondary droplet determination, 

resulting from either the breakup or impact processes, high 

resolution image technology or Phase Doppler Particle 

Analyzer (PDPA), traversing a pre-determined control 

volume, may be needed to obtain droplet size distributions.

4.0 Experimental Set-Ups

Depending of the objectives of the tests, different 

experimental set-ups may be used in the Facility. Three main 

test categories can be considered: 4.1 Calibration of the 

facility; 4.2 Droplet deformation and breakup; and 4.3 Surface 

droplet impact.

4.1 Calibration of the Facility

Because of the rotating nature of the experiments, some 

preliminary tests need to be made to find the limits for each 

particular application. The model's mean linear velocity and its 

standard deviation over a number of turns need to be 

measured. Instrumentation includes an opto-switch which 

captures light to be transmitted as an electric signal to an 

electronic time delay board, installed to trigger a microsecondduration high intensity light, into a parallel light conversion 

unit to obtain shadowgraph images that are to be captured on a 

digital camera for later processing. The opto-switch may be 

installed fixed to the structure near a rotating part that includes 

a reflector. The image plane of the camera must be oriented 

perpendicular to the straight line defined by the reflector 

center and the camera lens. 

The model velocity is obtained from the arc length that the 

model traverses during the time delay. The time delay is 

initiated when the model is at the position where the opto-
NASA/TM—2012-217721 8

switch is triggered. At the end of the time delay the camera is 

triggered and the position of the model is captured. Repeating 

the process a number of times at the required velocity, a group 

of model velocities is obtained from which mean and time 

standard deviation may be calculated.

An important part in the calibration of the facility is the 

determination of air motion induced by the model after 

successive rotations. There are two different groups of 

measurements that are needed to see the limitations in size for 

a type of model due to the air motion induced by it.

• The first consists of measurements within the model path 

while it is in rotation, conducted at the section where the 

droplets are designed to be released or injected. The 

precise model location is required to correlate with an 

individual piece of data, and for that particular task 

synchronization is needed. The model's circular path can 

be described in three sections: approximately one chord 

upstream of the location where the droplets are released, 

approximately one chord downstream (near the wake) of 

the location where the drops are released, and the rest of 

the circular path. Non-intrusive instrumentation must be 

used to obtain reliable data for any of the three locations. 

A simple possibility is the use of a Backscatter 1-D Laser 

Doppler Velocimeter, with the control volume at the 

model centerline, directed on the circle's tangent and 

synchronized with the model position for any of the cases. 

• The second includes measurements outside the model 

path along points located on a radial line (in the horizontal 

rotation plane) from the center of the arm rotation to the 

intersection with the location where the droplets cross the 

horizontal plane. The air motion at these locations (swirl) 

is influenced by the model position and subjected to 

interferences by the test cell room walls, floor and ceiling.

The measurements need to be synchronized and 

correlated with the model position. Measurements were 

conducted with a PIV system and can be made also with 

intrusive conventional instrumentation such as total 

pressure probes.

These two groups of measurements, after being analyzed, may 

indicate whether the results obtained in a given experiment 

can be used directly for the intended purpose, or whether some 

type or correction is needed. 

Other important aspects for calibration are the droplet size 

and velocity of release/injection, in conditions of use similar 

to the applications. Given a droplet generator with a fixed 

diameter orifice, the water flow rate and vibration frequency 

produce a droplet stream that at small distances from the 

orifice (in the order of 300 diameters) allows theoretical 

prediction of the droplet size. At greater distances from the 

orifice, coalescence of droplets begins to take place and the 

droplet diameter changes slowly with distance. Under these 

circumstances prediction of droplet diameter is no longer 

possible and calibration is needed. 

A high-speed shadowgraph was used for calibration of the 

size of the droplets. In this method, a device calibrated by 

length (e.g., micrometer) is located where the droplet stream 

will appear. With the digital camera in the same position as in 

the tests, a correlation can be made between the pixels of the 

camera images and the size of the device used for the 

calibration. This gives the scale of the number of pixels per 

millimeter, which can then be applied to the corresponding 

tests. As a check for this type of calibration a Phase Doppler 

Particle Analyzer (PDPA) was used in a separate bench test

(Ref. 29).

4.2 Droplet Deformation and Breakup 

Processes

Once the droplets are within the upstream aerodynamic 

influence induced by the body, external forces and internal 

reactions produce shape deformation and in some conditions 

may lead to different types of fragmentation (breakup process) 

that could result in a large number of very small secondary 

droplets. The facility needs to be prepared to measure all 

important physical characteristics of both deformation and 

breakup. The deformation process for the disturbance type and 

conditions of interest has a time range measured by the 

millisecond, and the instrumentation used must be capable of 

addressing this time constraint. To follow a droplet from the 

spherical to the flattened disk final shape, a high speed digital 

video camera is needed, with frame rates per second ranging 

from 50000 to 150000 and compatible with the acceptable 

field of view and resolution. The present state of the 

technology for these cameras limits the resolution as the frame 

rate increases. To modify the magnification, the camera needs 

to be placed at different distances from the object. The shutter 

exposure time needed is very short (about 1 μsec) making it 

necessary to use a high intensity continuous light directed 

through a diffusing paper and located behind the object to 

create shadow images on the camera. 

Before the rotating arm is put into operation for a test, the 

camera needs to be aligned so that the line of sight through the 

lens towards the object coincides with the line that runs along 

the span of the model on the leading edge. The diffusing paper 

is placed perpendicular to that line of sight and the high 

intensity light is directed perpendicular to the paper. 

Synchronization of model position and starting time has to be 

defined, so that every single frame may be correlated with 

model location, since in most of the frames only the droplets 

will appear on the image.

Should the external conditions be appropriate, the droplet 

will be able to continue the deformation process at a faster rate 

with part of its mass concentrated in some particular locations 

and connected with the rest through a thin water membrane.

This configuration of the droplet is very unstable and prone to 

disintegration into secondary droplets that are of much smaller 

size than the original droplet. At this point of total droplet 

disintegration, the breakup process is considered to have ended. 
NASA/TM—2012-217721 9

All parts of the process need to be captured in images, from 

the extreme distortion into a flattened disk shape followed by 

the large deformation of the disk central region into a thin water 

membrane (bag type breakup), and ending in a spray of 

secondary droplets. For conditions that produce typical breakup 

in the rotating rig facility, the total time duration of the process 

has been observed to be in the range of 100 to 150 μsec. A highspeed video camera set up as explained earlier may be used. 

However, even with high frame rates, only a few frames are

useful because of the camera technology limitations, and the 

resolution obtained is not optimal. To improve this situation, 

high-speed video images complemented with a series of single 

short duration exposure images synchronized with the model 

are used. The first part of the set-up is the definition of the 

minimum field of view needed to capture the phenomenon, 

including the model leading edge to correlate time with the state 

of the breakup. The camera should be aligned with the model 

leading edge (when it is located at the image center) and the 

source of the short duration light. The selected camera optics 

must achieve compatibility with the previously mentioned 

requirements, with sufficient resolution to measure the 

characteristics of the breakup.

4.3 Surface Droplets Impacts

The last phase of the deformation and breakup process ends 

with impact of the full droplet mass upon the surface, except for 

the case of total disintegration. In this case, depending on the 

droplet size distribution, the mass may not impact on the surface 

location where it was supposed to impinge but may re-impinge 

at a later time on other surface locations. The droplet shape of 

interest in impact research studies ranges from spherical to 

ellipsoidal to highly distorted shapes, each with different 

outcome characteristics. These impacts take place on wetted 

surfaces where the water film thickness is one of the most 

important variables to be measured. For the higher velocities, 

the time elapsed during a perpendicular impact is in the order of 

5 to 50 μsec, for droplet diameters ranging from 100 μm to 

1 mm. The difficulty in capturing images with acceptable 

resolution using high-speed video cameras makes the use of this 

type of equipment valid only as a complement to other 

measurements of the impact resultant characteristics. Due to the 

very short time involved in the impact process, the camera field 

of view is smaller than the one used for the droplet deformation 

and break up process, and the distance from the camera lens to 

the object is shorter. 

The camera optics selected should be in accordance with the 

indicated conditions to offer maximum resolution. An 

important difference with the other processes is the ability to 

obtain 3D visualizations, created from two simultaneous views 

to capture the essential characteristics of the outcome. To 

capture two simultaneous images, two separate short duration 

light sources have to be positioned such as to produce a 

shadow (lateral image) and a plan view. Synchronization of 

droplet and model position is another distinctive feature that 

needs to be taken into account in studies of the impact process.

5.0 Application Examples

The following cases for application to droplet trajectories 

approaching a model are presented below: 5.1 Calibration of 

the Facility—Air Induced by the Model; 5.2 Droplet 

deformation and breakup; and 5.3 Droplet impact.

5.1 Calibration of the Facility—Air Induced 

by the Model

Some results are presented below on the air velocity induced 

within the model trajectory, made with non-intrusive laser 

instrumentation. A Particle Image Velocimetry System (PIV) 

was used. The results include a comparison with previous 

wind tunnel results made with a model of the same geometry 

along the stagnation line. The PIV System works by

illuminating with a laser light sheet the air flow that has been 

previously seeded with micron size particles. Images of a

double pulse of nanosecond duration each are recorded with a 

CCD camera. Correlation analysis is done to obtain the air 

velocity measurements. The model airfoil section used for this 

Calibration Program is the same as the one in Reference 26, 

but with a chord of 0.199 m and maintaining the same velocity 

of 90 m/s.

A light sheet has been generated in the vertical and 

horizontal planes with respect to the camera, which is located 

to record square fields of view of 200, 60 and 30 mm 

(Figure 8). Images are taken at different distances, from the 

model leading edge to the location where droplets are released

in a droplet breakup experiment. An image captured with the 

vertical plane and field of view of 30- by 30-mm is shown in 

Figure 9. In this figure the leading edge of the airfoil is on the 

right side (rounded dark shadow). The stagnation streamline is 

located at about y = –15 mm. Small arrows indicate the 

direction of the velocity. The magnitude of the velocity is 

color coded. The lower velocities are shown in blue, the 

higher velocities in red.

The PIV system software has the capability to extract the air 

velocities. The air velocities (external reference axis) along the 

stagnation streamline, measured for three vertical fields of 

view, are plotted in Figure 10. Previously, wind tunnel

measurements of velocities along the stagnation line were

performed with a LDV system at 40 m/s for a model of similar 

geometry and 0.047 m chord. This result is shown in Figure 11

(Ref. 30). The comparison between the velocities along the 

stagnation streamline measured with the PIV system in the 

rotating rig and the velocities measured with the LDV system 

in the wind tunnel is shown in Figure 12 (Ref. 31). The 

velocities in Figure 11 and Figure 12 are for a frame of 

reference located on the model. For this particular model the 

velocities agree well indicating no effect from the air motion 

induced by the model attached to the rotating arm.
NASA/TM—2012-217721 10

Figure 8.—Experimental setup. Vertical plane. From left to right: air flow seeding atomizer; rotating arm and 

model; PIV field of view, camera and light sheet plane.

Figure 9.—Average of 10 pairs of images processed. Vertical plane. Field of view: 30- by 

30-mm. From left to right: Isovelocity lines with lower values at left increasing to right; 

model leading edge in black with stagnation line perpendicular to model at 

approximate value Y = –20 mm; scale on right side from approximately 30 m/s (lower 

blue) to 92 m/s (higher red).
NASA/TM—2012-217721 11

Figure 10.—PIV results along the stagnation streamline. Taken for different fields of view (FOV) on horizontal (HP) and vertical

(VP) planes for model at 0.5 and 1.0 chords from leading edge to field left line (external reference).

Figure 11.—Wind tunnel measurements of horizontal velocity along stagnation streamline. Velocities 

taken with LDV along the stagnation streamline for a 0.047 m chord model (1/10 scale of DBKUP 

002) (model reference).

x / c

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Uax / U

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0
NASA/TM—2012-217721 12

Figure 12.—Comparison of rotating rig PIV measurements with wind tunnel LDV measurements. Non-dimensional velocity

comparisons along stagnation streamline (model reference).

5.2 Droplet Deformation and Breakup

Some results are presented for cases of droplets in the 

deformation and breakup stages as they approach the leading 

edge of an airfoil. The cases are from experiments conducted 

with the rotating rig.

5.2.1 Droplet Deformation

The case considered is one in which droplets are released 

from a mono-dispersed droplet generator falling vertically 

through the path of a model moving at a speed that is at least 

an order of magnitude larger than the droplet vertical 

velocities. Droplets being generated in these conditions may 

show oscillations as they fall before entering the model 

upstream region of influence but at all times remain within 

bounds and far of any secondary breakup instability that could 

have been produced by the monosize droplet generator. The 

vertical velocities may be interpreted as if the droplets 

approach the airfoil with a small incidence, that is something 

qualitatively similar to what happens when droplets are 

encountered in free flight. As the droplets begin to sense the 

airfoil influence, their shape begins to distort as the water/air 

surface tension and water viscosity maintain balance with the 

external air forces. The degree of distortion is dependent on 

the water properties, the drop size, the drop velocity and the 

drop acceleration that is in turn defined by the velocity field 

generated by the airfoil shape, size and velocity. The resulting 

distortions are due to the complex combination of the 

mentioned variables at each point of the flow field. They 

proceed by flattening the side of the droplet facing the airfoil 

and by elongation in the vertical direction (Figure 13).

Depending on droplet conditions, they remain in the 

deformation stage up to impact or proceed to increasing 

distortion, leading to different breakup types. 

To obtain quantitative information on droplet deformation 

along a trajectory, the use of the Rotating Arm Facility, with 

the modifications indicated in Section III, is convenient. The 

use of a high-speed imaging system is essential to accomplish 

this task. However, to provide an acceptable image resolution 

in the high-speed system, a compromise has to be reached

between frame rate and magnification, so that the magnitudes

of the distorted droplets can be determined.

The experiments presented in this sub-section correspond to 

a small aspect ratio wing with a high thickness/chord ratio 

cross section as described in Reference 26. The model has a

0.47 m chord with 40 percent thickness, a nominal velocity of 

90 m/s, and the initial spherical droplet diameter is 490 μm.

The high-speed camera rate used was 75,000 frames per 

second and the corresponding resolution in the horizontal and 

vertical directions are respectively 192 by 312 pixels.

Table I and Figure 14 show the results of an experiment that 

was conducted in the rotating rig facility and was reported in 

Reference 26. A drop deformation time sequence taken with 

the high-speed video system was used to characterize the drop 

deformation in the horizontal (d1) and vertical directions (d2).

The two magnitudes measured are presented in Table I in
NASA/TM—2012-217721 13

Figure 13.—Droplet time deformation sequence. Airfoil chord c = 0.47 m. Initial droplet diameter d = 490 

μm. Nominal airfoil velocity U = 90 m/sec. Images from Reference 26.

Figure 14.—Droplet deformation dimensions. Airfoil chord c = 0.47 m; initial droplet 

diameter d = 490 μm; nominal airfoil velocity U = 90 m/sec; d1 horizontal 

dimension (minor axis); d2 vertical dimension (major axis).
NASA/TM—2012-217721 14

non-dimensional form against non-dimensional values of time 

and distance and plotted in Figure 14. Table I also lists the 

values of the Reynolds, Weber and Bond numbers based on 

the original droplet diameter.

TABLE I.—DROPLET DEFORMATION 

ALONG STAGNATION LINE

Airfoil chord c = 0.47 m

Initial droplet diameter d = 490 μm

Nominal airfoil velocity U = 90 m/s

Droplet time to reach airfoil t

Droplet distance to airfoil x

Droplet dimension along minor axis d1 (horizontal)

Droplet dimension along major axis d2 (vertical)

t/(d/U) (x/c) Red Wed Bod (d1/d) (d2/d)

144.5 0.17 946 6.9 11.8 1.00 1.00

142.2 0.15 1013 7.3 12.0 0.91 1.14

130.0 0.14 1081 8.2 13.0 0.84 1.18

117.6 0.12 1149 9.3 14.0 0.77 1.27

105.4 0.11 1217 10.6 15.4 0.73 1.32

93.1 0.10 1284 12.1 17.1 0.68 1.36

80.8 0.08 1419 14.0 20.6 0.64 1.41

68.7 0.07 1588 16.4 27.4 0.56 1.46

56.4 0.06 1690 19.3 37.7 0.51 1.54

44.1 0.05 1825 23.2 51.5 0.46 1.64

31.9 0.03 2027 28.2 75.4 0.41 1.82

5.2.2 Droplet Breakup

The final stage of a drop deformation as it approaches the 

airfoil surface is one in which the drop rate of distortion with 

time is an order of magnitude larger than in the initial 

deformation stage.

This implies that the liquid inside is displaced, accumulating 

in a very short time at specific locations, creating conditions 

leading to instability and finally to breakup (Figure 15). One 

of the critical questions in relation to the instability onset is the 

disintegration into a fine spray of secondary droplets. This 

disintegration is very important because of the potential effect 

it has on the impinging collection efficiency over the surface 

and presents a serious challenge to the experiments.

To follow the droplet breakup process, a high-speed video 

system is an essential component. However, for the final 

outcome, including the details of the disintegration process,

resolution to characterize all the problem variables. An 

alternative such as a high resolution single image system is 

needed to complement the high-speed video. For the operation

conditions of the facility, the breakup takes place at locations 

that are near enough to the model surface so that both the 

surface and droplet can be included within the image field of 

view. The experimental conditions used to obtain the breakup 

results that are presented below are: model velocity of 90 m/s,

chord of 0.47 m and thickness of 40 percent with droplets of 

414 μm.

Measurements of the minimum and maximum droplet cross

section dimensions are taken to characterize the final stage 

leading to breakup as they change along the stagnation line 

trajectory, as was presented in Reference 26. The two 

magnitudes are presented in non-dimensional form with the 

non-dimensional time and distances to reach the airfoil in 

Table II and plotted in Figure 16. A sequence of the last stage 

of the breakup showing disintegration is presented in 

Figure 17. The sequence is for different droplets of the same 

diameter. The diameter of the droplets is 250 μm. The velocity 

of the model is 90 m/s. The model chord is 0.47 m with a 

thickness of 40 percent.

TABLE II.—DROPLET BREAKUP 

ALONG STAGNATION LINE

Airfoil chord c = 0.47 m

Initial droplet diameter d = 414 μm

Nominal airfoil velocity U = 90 m/s

Droplet time to reach airfoil t

Droplet distance to airfoil x

Minimum length d1

Maximum length d2

t/(d/U) (x/c) (d1/d) (d2/d)

31.6 0.033 0.47 1.95

21.1 0.022 0.77 2.25

15.8 0.016 0.88 2.08

10.7 0.011 1.24 2.19

5.3 0.005 1.60 2.14

5.3 Droplet Impact

Results of two cases of large droplets impacting a surface 

covered by a thin water film are presented. These are: low 

incidence impact and perpendicular impact.
NASA/TM—2012-217721 15

t = 0 μsec t = 57.1 μsec t = 85.7 μsec t = 114.3 μsec t = 142.9 μsec 

15.5 mm 10.3 mm 7.7 mm 5.2 mm 2.6 mm

Figure 15.—Droplet time deformation sequence. Airfoil chord c = 0.47 m; initial droplet diameter d = 490 μm; nominal airfoil velocity 

U = 90 m/sec. Images from Reference 26.

x/c

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035

(d1/d)

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

(d1/d)

(d2/d)

(d2/d)

Figure 16.—Droplet breakup dimensions. Airfoil chord c = 0.47 m; initial droplet 

diameter d = 414 μm; nominal airfoil velocity U = 90 m/sec; d1 horizontal axis; d2

vertical axis.

246 μm 246 μm
NASA/TM—2012-217721 16

 t = 55.5 μsec, X/c = 0.012 t = 31.1 μsec, X/c = 0.006

 t = 11.1 μsec, X/c = 0.002 t = 0 μsec, X/c = 0 

Figure 17.—Droplet Breakup. Last Stage. c = 0.47 m; U = 90 m/sec. Time sequence of high resolution images 

of (physically different) droplets of same diameter (250 μm). Each droplet is very near the airfoil surface (dark 

shadow on the right side).
NASA/TM—2012-217721 17

Figure 18.—Single Angular Drop Impact. Incidence variables 

are: U incoming air velocity; D droplet diameter; Vd droplet 

velocity; Ulocal local air velocity; k surface roughness; h water 

film thickness; Uh water film velocity; L distance from impact 

to leading edge; β droplet incidence angle.

5.3.1 Low Incidence Impact

Spherical droplets with incidences such that the resultant 

droplets being ejected extend only over part of the windward 

side of the circumference on the surface where the impact is 

taking place (approximately below 12°) are considered to be 

low incidence (Figure 18) and the splash schematically looks 

as indicated in Figure 19. As time increases in the impact 

process, the droplet merges at the same rate as the normal 

impact velocity with respect to the surface, forming a thin 

water membrane with filaments from which the droplets are 

ejected. The downstream side merges smoothly with the liquid 

film underneath, without ejection of droplets. When the 

droplet flattens completely, a crater still persists and the 

remaining pressure difference at the crater base continues 

forcing ejection on the upstream side and mixing droplet 

liquid with the high velocity moving liquid film underneath, at 

the same time that a liquid film wake-like shape extends to 

large distances downstream. Crater disappearance indicates 

pressure equalization with the surrounding liquid and no more 

tendency to either form a larger crown or mix with the liquid 

film. Through the action of water viscosity, the wake-like 

liquid deposited shape will tend to extend downstream and the 

crown wall to detach from the splash-deposited wake. This 

thin water wall breaks into filaments which in turn disintegrate 

into droplets exchanging momentum and energy with the 

external air flow. No relative velocity air-liquid particles 

indicates the end of the splashing process.

The process is shown in the time sequence images of 

Figure 20. In order to obtain sufficient resolution, these 

images do not correspond to the same droplet, but to different 

generated droplets of the same size, captured with shortduration (3 μsec) high intensity lamps and controlled time 

delays. The length of arm radius used was 1.25 m; the model 

was a flat plate with a length of 200 mm, width of 100 mm 

and a thickness of 1mm, with a rounded leading edge. The 

linear velocity at the plate centerline was 60 m/s and spherical 

droplets with diameters of 4 mm falling at 4 m/s on a line at 

most 60 mm from the leading edge. The water film thickness 

was not measured in this experiment but it could be estimated,

Figure 19.—Low incidence splash relative to a fixed observer 

(drop coalescence stage). Model reference axis. W crater 

width; h1 water film thickness upstream of splash, h water 

film thickness downstream of splash, H crown wall height, d

mean ejected droplets diameters, Ud is the average 

magnitude of droplet velocities.

t = 0 μsec t = 180 μsec

t = 353 μsec t = 705 μsec

t = 1010 μsec t = 1350 μsec

t = 3300 μsec

Figure 20.—Low incidence splash (external observer's 

reference) β = 4o

, D = 4 mm, VD = 60 m/s. The figure is a 

time sequence for physically different droplets of the same 

diameter.

assuming one impact per revolution based on the generated 

droplet distances, at 10 mm in width (measured from the 

images). Adding water loss through splashing or centrifugal 

effects leads to a value for the film thickness of about 15 μm,

which yields a film-thickness to droplet-diameter ratio in the 

order of 3.75/1000. The assumption for water film thickness is 

made based on previous measuring experience, performed to 

understand the deposited water film behavior after rotating the 

model in a condition similar to the one under consideration,

h Uh

U Ulocal

VD

D

β

L

k
NASA/TM—2012-217721 18

where it was observed that when droplets were released at one 

location, the water film had a sudden increase in thickness due 

to the droplet impact, followed by a progressive decrease 

along the circumferential trajectory to reach values near the 

minimum that can be detected.

Average measurements of ejected droplet velocity 

components and ejection angles may be made by measuring

distances in each of the images from the average ejected 

droplets front location, to the point on the surface where 

contact is made at the initial time for the first signs of ejection.

Measurements of time t, distances x and y define the average 

horizontal udt and vertical udn velocities and ejected angle for 

each of the images. The magnitudes are with respect to an 

external observer axis and are presented in Table III. The 

values of this table when converted to the model reference 

axis are shown in Table IV and plotted in Figure 21 and 

Figure 22. The set of images have sufficient resolution to 

measure droplet size and, if appropriate image analysis 

software is used, a complete droplet spectrum at different 

stages of the process can be obtained. Direct inspection 

measurements indicate, from the spray of Figure 20 (last 

image), a range of diameters from 10 to 100 μm.

TABLE III.—EJECTED DROPLET MEASUREMENTS

(EXTERNAL REFERENCE)

Incident conditions Ud = 60 m/s ; d = 4 mm, β = 4°

t,

μs

x,

mm

y,

mm

udt,

m/s

udn,

m/s

γd,

°

180 3.2 1.8 17.8 10 30

353 5.6 1.9 15.8 5.1 18

705 9.0 2.4 12.8 3.4 15

1100 14.0 3.2 12.7 2.9 12

1350 15.8 3.4 11.7 2.5 11

TABLE IV.—RESULTS (MODEL REFERENCE)

Incident conditions Ud = 60 m/s; d = 4 mm, β = 4°

t/(D/VDn) ud/VD γd,

°

0.18 1.31 7

0.353 1.26 4

0.705 1.22 3

1.1 1.21 2

1.35 1.2 2

t/(D/VDn )

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

( vd /VD )

1.0

1.1

1.2

1.3

1.4

1.5

Figure 21.—Low incidence averaged ejected droplets velocities relative to model 

Vd = 60 m/s, d = 4 mm, β = 4. Impacting on a water film thickness of the order of 

10 μm. Obtained from a time sequence of single images of (physically different) 

droplets.
NASA/TM—2012-217721 19

Figure 22.—Low incidence averaged ejected droplets angles relative to model. 

Vd = 60 m/s, d = 4 mm, β = 4o

. Obtained from a time sequence of single images of 

(physically different) droplets

5.3.2 Perpendicular Impact

Spherical droplets impacting normal to the surface result in 

an axially symmetric splash configuration with respect to a 

perpendicular axis to the surface that contains the initial 

contact point droplet-surface. The physical process starts with 

the contact at high speed of the water with the surface, with 

some deformation of the sphere without any droplets being 

ejected, this being an indication of compressibility effects 

being generated inside the droplet during a few microseconds.

These high pressures are responsible for the initial high 

velocity droplets directed radially outwards (“jetting”), that 

are partially converted into trajectories with normal 

components at the edge of the crater base. They form a very 

short continuous crater wall, with water being discharged 

through it, leading to the formation of very thin filaments that 

breakup into a very small diameter droplet mist. The crater 

base grows rapidly to an appreciable size while the crater 

walls remain short and near the surface (Figure 23).

As described in previous sections, in order to obtain the best 

possible resolution for the images, a time sequence with 

different droplets of the same diameter are captured in the 

shadowgraph/lateral mode (Figure 24). A 3 μsec lamp 

triggered through synchronization and time delay was used for

model and droplet positions when their electronic pulses 

coincide within a predefined time window. The arm had a 1.25

m radius and the stagnation point model had a circular flat

surface on which the droplets were made to impact

(Figure 25). The circle diameter was 80 mm and the model 

linear velocity was 60 m/s with droplets of 4 mm. The water 

film thickness on the impact surface was estimated, based on 

the approximation of one impact per revolution extending over 

three quarters of the circular surface (from observations). It 

yields a film thickness of the order of 10 μm, an estimate

obtained following the same criterion as for the low incidence 

impacts discussed in the previous section (Ref. 32).

Measurements of the perpendicular impact that 

characterizes the splash are made directly from the time 

sequence images for its geometrical variables and the average 

values of the ejected droplet velocity magnitudes and 

direction. The variables measured are the crater diameter, the 

horizontal extension of the crown/filaments length and the 

corresponding height from the surface, the average ejected 

droplet velocity magnitude and the average ejected droplet 

angle with respect to the surface. They are measured from 

images (Ref. 33) taken simultaneously from lateral 

Shadowgraphs and frontal views (Figure 26).

t/(D/VDn)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

γd

o

0

1

2

3

4

5

6

7

8
NASA/TM—2012-217721 20

Figure 23.—Initial stage of a perpendicular spherical droplet 

splash. Impact velocity 60 m/s; droplet diameter 4 mm; water 

film thickness ~10 μm

Figure 24.—Time sequence shadow graphs of spherical 

droplet impact. Impact velocity 60 m/s; droplet diameter 

4 mm; water film thickness ~10 μm.

Figure 25.—Model attached to the rotating arm
NASA/TM—2012-217721 21

t ≈ 10 μsec t ≈ 30 μsec

 t ≈ 70 μsec t ≈ 80 μsec

Figure 26.—Simultaneous shadowgraphs and frontal images, impact 

velocity 60 m/sec, droplet diameter 4 mm, water film thickness ~ 10 μm.

These values are measured with respect to an external 

observer frame of reference and shown in non-dimensional 

form in Table V and Figure 27, Figure 28, and Figure 29. The 

diameters of the ejected droplets cannot be obtained from the 

presented images since the ejecta appear as a compact cloud, 

where individual droplets cannot be identified in the initial 

phases of the process. For images corresponding to the last part 

of the process, the resolution is poor. The combination of these 

two difficulties indicates that challenges associated with this 

case could be so important as to make the measurements 

through this technique unfeasible. Also, due to the proximity of 

the ejecta to the surface, the use of laser instrumentation such as 

PIV or PDPA could also be a challenge. In order to estimate an 

order of magnitude for average diameters of ejecta that are 

being generated during certain amount of time, the following 

assumptions are made: 1) spherical shape, 2) the droplet inertial 

forces are entirely balanced by aerodynamic forces (drag), 3) no 

interaction between them so that the droplet Drag Coefficient 

may be taken as if the droplets were completely isolated. 

Average droplet velocities and accelerations are calculated from 

the images during the time span in terms of non-dimensional 

times based on the characteristic impact time d/Ud. For values of 

this parameter between 0 and 1, the average diameter is about 

5 μm; for values between 1 and 2, the average results are of 

about 15 μm and finally, for values between 2 and 3 the average 

value is of the order of 20 μm. Recall that these average values 

correspond to an incident droplet of 4 mm diameter with 60 m/s, 

impacting on a water film thickness of the order of 10 μm.
NASA/TM—2012-217721 22

TABLE V.—PERPENDICULAR IMPACT

SPLASH CHARACTERISTICS

D = drop diameter = 4 mm; Impact velocity = 60 m/s; 

Water film thickness ~ 10 μm

t/(D/VD) W/D W1/D H/D ud/VD γd,

°

0.16 0.5 1.25 0.38 6.66 63

0.45 1.75 5.0 0.75 5.55 52

0.77 3.0 6.25 0.88 4.66 38

1.08 3.5 7.0 0.75 4.28 35

1.23 4.0 7.5 0.50 3.96 26

1.38 4.5 8.0 0.48 3.70 25

1.54 5.0 8.25 0.46 3.50 24

1.69 5.5 9.0 0.45 3.33 24

2.77 6.5 11.0 0.44 2.22 23

3.38 7.5 12.5 0.43 2.05 23

Figure 27.—Time evolution of crater dimensions. Droplet incident velocity Ui = 60 m/s, 

droplet diameter d = 4 mm, water film thickness ~ 10 μm

t/(D/UD)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

(W/D)

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

12

(W1/D)

(H/D)

(H/D)

(W/D)

(W1/D)
NASA/TM—2012-217721 23

Figure 28.—Time evolution of average ejected droplets velocities (external observer 

reference). Droplet incident velocity Ui = 60 m/s, droplet diameter d = 4 mm, water 

film thickness ~ 10 μm

Figure 29.—Time evolution of averaged ejected droplets angle (external observer 

reference). Droplet incident velocity Ui = 60 m/s, droplet diameter d = 4 mm, water film 

thickness ~ 10 μm

t/(D/UD)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

ud /UD

0

1

2

3

4

5

6

7

t /(D/UD)

0 1 2 3 4

γ

ο

0

10

20

30

40

50

60

70
NASA/TM—2012-217721 24

6.0 Concluding Remarks

An existing small Rotating Facility was developed for studies 

on deformation/breakup and impact of water droplets induced 

by aerodynamic surfaces. Literature review has shown that there 

exists a large amount of information on droplet's deformation 

/breakup and impacts of different disturbance types but they do 

not apply to cases induced by aerodynamic surfaces in flight 

conditions. For these cases a Rotating Facility offer an 

appropriate experimental setup. The following are the main 

observations about the facility and its development:

• A Rotating Arm facility was developed at INTA. The 

recent main improvements are the increase of the arm's 

length, the power of the drive unit and structural strength 

and stability to allow model velocities up to 90 m/s and 

model dimension of the order of 0.5 m. The single droplet 

size range was extended to 100 μm from an initial range of 

1 to 4 mm.

• The room where the Rotating Arm is housed was also 

increased in size to minimize wall interference effects that 

are larger at high velocities. The ceiling supports a structure 

to attach a droplet generator system and allow to release 

droplets at any location along the circumference and also 

installation of additional instrumentation that might be 

needed for different applications.

• The model design and manufacture become one of the 

critical issues in the facility because the model must be 

have a low mass to minimize the centrifugal forces and at 

the same time have enough strength to support high 

accelerations.

• High-speed imaging visualization for parameter 

measurement and qualitative observations has proved to be 

decisive for understanding the droplet physical processes. 

Shadowgraphs of single images, using double or triple 

exposure or high-speed video has been successfully 

adapted in the facility. Simultaneous shadowgraphs with 

conventional backlight photography to obtain another out 

of plane view, has been implemented for one particular 

case (perpendicular impacts).

• Non-intrusive Laser instrumentation such as Particle 

Image Velocimetry (PIV) or Laser Doppler Anemometry 

(LDA) can be implemented for air facility calibrations or 

other general air measurements. Also Phase Doppler 

Particle Analyzer(PDPA) has been used for droplet size 

calibration complemented with shadow images.

• Several measurement samples for a number of cases have 

been presented to highlight some of the facility 

capabilities. The main results from these cases are:

○ Calibration of the air velocity for an aerodynamic 

model with an airfoil section of 0.199 m chord and 

velocity of 90 m/s. This represents a model chord

(c)/arm radius (R) of approximately 0.1 (10 percent).

Comparison of air velocity on the stagnation line with 

wind tunnel results has shown small differences from 

the leading edge up to a quarter of the chord and 

differences of the order of 2 percent up to 1.25 chords. 

This means that corrections that might be needed,

depending on the specific application for this particular 

case, are expected to be small. However, for models 

with higher (c/R) new calibration measurements must 

be made to estimate appropriate corrections or 

adequate actions needed, that will depend on test 

requirements.

○ Droplet deformation/breakup characteristics. These 

measurements were obtained with the model of 

Reference 26 at 90 m/s and 0.47 m chord. The 

deformation studies correspond to droplets of 490 μm

that start as spherical shapes and end up as flattened 

disks. This takes place at a small but constant 

distortion rate in both spheroid axis along the 

stagnation streamline at distances from the leading 

edge that go from 20 to 3 percent of the airfoil chord 

and having relatively long droplet residence times that 

are about two orders of magnitude larger than the 

droplet characteristic time defined by (d/U). The 

breakup stage that follows the distortion is separated in 

two parts. The first part is one with extreme distortion, 

showing signs that the liquid inside has larger motions 

than it had in the deformation stage and distortion

shape rates that are also larger than before, at distances 

from the leading edge from about 3 to 1.5 percent of 

the chord and residence time of only one order of 

magnitude larger than the droplet characteristic time 

(d/U). The second part is the disintegration into water 

filaments and secondary droplets. It has been observed 

in experiments when the droplets are very near the 

surface, in the same conditions as in the first part but 

with diameters of 250 μm, droplets disintegrate at 

distances from the leading edge that are about 1.5

percent of the chord and the time to reach the surface 

is still an order of magnitude larger than (d/U), with 

the observation that water filaments were not 

fragmented when the filaments touched the surface and 

therefore it could be said that complete disintegration

had not yet been achieved.

○ Droplet impacts for low and perpendicular incidences.

Experiments have been presented for very large 

droplets of 4 mm diameters at 60 m/s impacting on a 

small flat plate at zero incidence simulating a 4°

incidence and on an axially symmetric body with a flat 

surface facing the flow. The low incidence splash takes 

place in times that are of the order of the diameter over 

the normal velocity of impact, with measured ejected 

droplets mean diameters of about 20 μm at the 

beginning of the splash and 100 μm at the end. For the 

perpendicular case the splash takes place in times that 

are of the same order of magnitude as the droplet 

characteristic time (d/U) and the ejected droplet 

dimensions have been estimated from velocities in the

images to be a mean value of 5 μm at the initial steps 

of the splash to 20 μm at the end.
NASA/TM—2012-217721 25

References

1. Tan, J., Papadakis, M. and Sampath, M.K., “Computational

Study of Large Droplet Breakup in the Vicinity of an 

Airfoil,” DOT/FAA/AR-05/42, Final Report, October 

2005.

2. Engel, O.G., “Fragmentation of Waterdrops in the Zone 

Behind an Air Shock,” Journal of Research of the National 

Bureau of Standards, Vol. 60, No. 3, March 1958, pp. 245-

280.

3. Hanson, A.R., Domich, E.G. and Adams, H.S., “Shock 

Tube Investigation of the Breakup of Drops by Air Blasts,” 

Physics. Fluids, Vol. 6, No.8, August 1963, pp.1070-1080.

4. Haas, F.C., “Stability of Droplets Suddenly Exposed to a 

High Velocity Gas Stream,” AIChEJ, Vol. 10, No. 6,

November 1964, pp. 920-924.

5. Ranger, A.A. and Nicholls, J.A. “The Aerodynamic 

Shattering of Liquid Drops,” AIAA Journal, Vol. 7,

February 1969, pp. 285-290.

6. Reinecke, W.G. and McKay, W.L. “Experiments on 

Waterdrop Breakup Behind Mach 3 to 12 Shocks,” Sandia 

Corp. Report SC-CR-70-6063, 1969.

7. Reinecke, W.G. and Waldman, G.D.A., “Study of Drop 

Breakup Behind Strong Shocks with Applications to 

Flight,” Avco Report AVSD-0110-70-77, May 1970.

8. Simpkins P.G. and Bales, L., “Water-Drop Response to 

Sudden Acceleration,” Journal of Fluid Mechanics, Vol.

55, Part 4, 1972.

9. Gel'fand, B.E. Gubin, S.A. and Kogarko, S.M., “Various 

Forms of Drop Fractionation in Shock-Waves and their 

Special Characteristics,” Inzhenemo-Fizicheski Zhurnal,

Vol. 27, No. 1, pp. 119-126, July 1974.

10. Wierzba, A. and Takayama, K., “Experimental 

Investigation of the Aerodynamic Breakup of Liquid 

Drops,” AIAA Journal, Vol. 26, No. 11, November 1988,

pp. 1329-1335.

11. Hsiang, L.P. And Faeth, G.M., “Secondary Drop Breakup in 

the Deformation Regime,” AIAA 92-0110, January 1992.

12. Hiroshara, H. and Kawahashi, M., “Experimental 

Investigation of Viscous Effects Upon a Breakup of 

Droplets in High-Speed Airflow,” Experiments in Fluids 

13, 1992, pp. 423-428.

13. Krzeczkowski, S.A., “Measurement of Liquid Droplet 

Disintegration Mechanism,” Int. J. Multiphase Flow, Vol.

6, 1980, pp. 227-239.

14. Wierzba, A., “Deformation and Breakup of Liquid Drops 

in a Gas Stream at Nearly Critical Weber Numbers,” 

Experiments in Fluids 9, 1990, pp. 59-64.

15. Kennedy, J.B. and Roberts, J., “Rain Ingestion in a Gas 

Turbine Engine,” ILASS-AMERICAS Inst. of Liquid 

Atomization and Spray Systems, 4th Annual Conference,

Hartford CT, USA, 1990, pp. 154-186.

16. Suzuki, T. and Mitachi, K., “Experimental Study on 

Aerodynamic Breakup of Liquid Droplets in TimeDependent Relative Velocity Field,” 8th. Int. Conf. Liquid 

Atomization and Spray Systems, Pasadena CA, July 2000.

17. Miller, D.R., Lynch, C.J. and Tate, P.A., “Overview of 

High-Speed Close-Up Imaging in an Icing Environment,” 

AIAA-2004-0407.

18. Tan, S.C., Papadakis, M., Miller, D., Bencic, T., Tate, P. 

and Laun, M.C., “Experimental Study of Large Droplet

Splashing and Breakup,” AIAA 2007-904.

19. Wright, W. and Potapczuk, M., “Semi-Empirical Modeling 

of SLD Physics,” NASA/TM—2004-212916.April 2004.

20. Mundo, C., Sommerfeld, M. and Tropea, C., “Droplet Wall 

Collisions: Experimental Studies of the Deformation and 

Breakup Process,” Int. J. Multiphase Flow, Vol. 21, No. 2,

pp.151-173, 1995.

21. Sammenfink, W., Elsaber, A., Dullenkopf, K. and Wittig,

S., “Droplet Interaction with Shear Driven Liquid Films:

Analysis of Deposition and Secondary Droplet 

Characteristics,” Int. J. Of Heat and Fluid Flow, Vol.20,

pp.462-469, 1999.

22. Hammond, D.W., Quero, M., Ivey, P., Miller, D., Purvis,

R., McGregor, O. and Tan, J., “Analysis and Experimental 

Aspects of the Impact of Supercooled Water Droplets into 

Thin Water Films,” AIAA 2005-77.

23. Feo, A., “Rotating Arms Applied to Studies of Single 

Angular Drop Impacts,” AIAA 87- 0257, January 1987.

24. Feo, A., “Effect of Heavy Rainfall on Aircraft 

Performance,” Von Karman Institute of Fluid Dynamics

Lecture Series “Effect of Icing, De-icing and Heavy Rain 

on Aircraft Performance”, February 1997.

25. Feo, A., “Experiments of a Perpendicular Waterdrop 

Impact in the Vicinity of an Air Stagnation Point,” ILLASS 

Conference on Liquid Atomization and Spray Systems,

Toulouse, France 1999.

26. Vargas, M. and Feo, A., “Experimental Observations on the 

Deformation and Breakup of Water Droplets Near the 

Leading Edge of an Airfoil,” NASA/TM—2011-216946, 

AIAA Paper 2010-7670, August 2010.

27. Sor, S., “Potenciación del Brazo Rotatorio,” AE-TNO 

4420-287 INTA-10.Noviembre 2010.

28. “TSI Aerometrics MDG-100 Monosize Droplet Generator 

Instruction Manual,” P/N 1990870, June 2002.

29. Jarillo, E., “ Estudio Mediante Técnica Laser PDPA de la 

Formación de Gotas en el Generador de Gotas 

Monodisperso Aerometrics MDG-100,” AE/TNO/4420/

119/INTA-06, Marzo 2006.

30. Jarillo, E., “Medidas de Velocidad en Línea de Remanso de 

un Perfil en Túnel de Viento mediante LDV,” AE-TNO 

4420-124-INTA-09, Marzo 2009.

31. Sor, S. and García-Magariño, A., “PIV Measurements on 

Airfoil Model in Rotating Arm,” AE-TNO-4420-091 

INTA-11, Febrero 2011.

32. Feo, A., “High-Speed Shadowgraphs of a Single Drop 

Perpendicular Splash,” Tech. Note N/221/510/87.017, 

INTA, November 1987.

33. Feo, A., “Waterdrop Splashback Characteristics of a 

Perpendicular Impact Near an Air Stagnation Point,” Tech. 

Note N/221/501/89.025, INTA, October 1989.

NASA/TM—2012-217721 27

Appendix.—Definitions and Abbreviations

ad droplet acceleration 

c characteristic body length

d droplet diameter 

de equivalent droplet diameter

d1 droplet dimension along minor axis (horizontal) 

d2 droplet dimension along major axis (vertical) 

fR Raleigh frequencies

h water film thickness 

h1 water film thickness upstream of splash

td droplet travel time to the body

ts splashing process time 

ud average velocity of ejected droplets

udt average tangential velocity of ejected droplets

udn average normal velocity of ejected droplets

xd distance from the droplet to the body

Bo Bond Number

C resultant body characteristics 

CCD charge-coupled device

D Diameter of impact droplet

Dj water jet diameter

H crown wall height

LDV Laser Doppler Velocimetry 

PDPA Phase Doppler Particle Analyzer

PIV Particle Image Velocimetry 

Re Reynolds Number

U incoming air velocity (free stream velocity)

Ua air velocity

Ud droplet velocity 

Udr relative air/droplet velocity

Uh Water film velocity

Ui impact velocity 

Uj water jet exit velocity

VD velocity magnitude of impact droplet

VDn normal component of velocity of impact droplet

W crater width

We Weber Number

β incident angle

δr surface roughness

γ ejecta angle

μ air viscosity coefficient

μw water viscosity coefficient

ρ air density

ρw water density

θ water/surface contact angle 

σw/a water/air surface tension
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This work presents the development of a Rotating Rig Facility by the Instituto Nacional de Técnica Aeroespacial (INTA) in cooperation 

with the NASA Glenn Research Center. The facility is located at the INTA installations near Madrid, Spain. It has been designed to study 

the deformation, breakup and impact of large droplets induced by aerodynamic bodies. The importance of these physical phenomena is 

related to the effects of Supercooled Large Droplets in icing clouds on the impinging efficiency of the droplets on the body, that may change 

should these phenomena not be taken into account. The important variables and the similarity parameters that enter in this problem are 

presented. The facility's components are described and some possible set-ups are explained. Application examples from past experiments are 

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15. SUBJECT TERMS

Aircraft icing; Aircraft safety; Aircraft control; Accident prevention; NASA programs 

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