Samuel A. Howard

Glenn Research Center, Cleveland, Ohio

Jeremiah T. Hammer

The Ohio State University, Columbus, Ohio

Kelly S. Carney and J. Michael Pereira

Glenn Research Center, Cleveland, Ohio

Jet Engine Bird Ingestion Simulations: Comparison 

of Rotating to Non-Rotating Fan Blades

NASA/TM—2013-217904

August 2013

GT2013-95998
NASA STI Program . . . in Profi le

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientifi c and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Offi cer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major signifi cant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of signifi cant 

scientifi c and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientifi c 

and technical fi ndings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientifi c and 

technical fi ndings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientifi c and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientifi c, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientifi c and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question to help@sti.nasa.gov

• Fax your question to the NASA STI 

Information Desk at 443–757–5803

• Phone the NASA STI Information Desk at

 443–757–5802

• Write to:

 STI Information Desk

 NASA Center for AeroSpace Information

 7115 Standard Drive

 Hanover, MD 21076–1320
Samuel A. Howard

Glenn Research Center, Cleveland, Ohio

Jeremiah T. Hammer

The Ohio State University, Columbus, Ohio

Kelly S. Carney and J. Michael Pereira

Glenn Research Center, Cleveland, Ohio

Jet Engine Bird Ingestion Simulations: Comparison 

of Rotating to Non-Rotating Fan Blades

NASA/TM—2013-217904

August 2013

GT2013-95998

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Turbo Expo 2013

sponsored by American Society of Mechanical Engineers (ASME)

San Antonio, Texas, June 3–7, 2013
Acknowledgments

The authors acknowledge the support of NASA’s Fundamental Aeronautics Program—Subsonic Fixed Wing Project and 

Aviation Safety Program for supporting this work.

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

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 

This report contains preliminary fi ndings, 

subject to revision as analysis proceeds.
NASA/TM—2013-217904 1

Jet Engine Bird Ingestion Simulations: Comparison of

Rotating to Non-Rotating Fan Blades

Samuel A. Howard

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Jeremiah T. Hammer

The Ohio State University

Columbus, Ohio 43210

Kelly S. Carney and J. Michael Pereira

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

Bird strike events in commercial airliners are a fairly

common occurrence. According to data collected by the US 

Department of Agriculture, over 80,000 bird strikes were 

reported in the period 1990 to 2007 in the US alone (Ref. 1).

As a result, bird ingestion is an important factor in aero engine 

design and FAA certification. When it comes to bird impacts 

on engine fan blades, the FAA requires full-scale bird 

ingestion tests on an engine running at full speed to pass 

certification requirements. These rotating tests are complex 

and very expensive. To reduce development costs associated 

with new materials for fan blades, it is desirable to develop 

more cost effective testing procedures than full-scale rotating 

engine tests for material evaluation. An impact test on a nonrotating single blade that captures most of the salient physics 

of the rotating test would go a long way towards enabling 

large numbers of evaluative material screening tests.

NASA Glenn Research Center has been working to identify 

a static blade test procedure that would be effective at 

reproducing similar results as seen in rotating tests. The 

current effort compares analytical simulations of a bird strike 

on various non-rotating blades to a bird strike simulation on a 

rotating blade as a baseline case. Several different concepts for 

simulating the rotating loads on a non-rotating blade were 

analyzed with little success in duplicating the deformation 

results seen in the rotating case. The rotating blade behaves as 

if it were stiffer than the non-rotating blade resulting in less 

plastic deformation from a given bird impact. The key factor 

limiting the success of the non-rotating blade simulations is 

thought to be the effect of gyroscopics. Prior to this effort, it 

was anticipated the difficulty would be in matching the prestress in the blade due to centrifugal forces Additional work is 

needed to verify this assertion, and to determine if a static test 

procedure can simulate the gyroscopic effects in a suitable 

manner. This paper describes the various non-rotating 

concepts analyzed, and demonstrates the effect believed to be 

gyroscopic in nature on the results.

Introduction

Due to the large frequency of bird strike events in

commercial airliners, the FAA has established standards for 

bird ingestion for certification of aero engines (Ref. 2).

Rotating bird strike tests such as those required by the FAA 

require large-scale and expensive test facilities and 

procedures. The cost associated with these tests, make it 

difficult to assess new materials for fan designs. It is not the 

goal of this work to replace the bird strike certification tests, 

which consider aspects of a bird strike other than the direct 

impact damage (such as the ability to continue operating at a 

reduced power level) and are necessary to ensure compliance 

with certification requirements. Rather, the goal is to 

determine if simpler, less costly testing could be used for 

fundamental material development testing and still retain most 

of the physics of the rotating test. Stated another way, can a 

single non-rotating blade be impacted with a bird or simulated 

bird in such a way as to duplicate the damage that same blade 

would experience in a rotating bird ingestion test? If the 

answer to that question is yes, such a test could be used as a 

cost-effective screening test for new materials and fan designs 

that could then go further in the development cycle and 

eventually be tested in a rotating test. If the answer is no, then 

it provides a scientific rational for conducting the expensive 

rotating tests.

The Impact Dynamics Group at NASA Glenn Research 

Center has been working to answer the above question and 

design a non-rotating test to simulate the damage a blade 

would sustain in a full-scale, rotating, bird-ingestion test. To 

assess whether a static test can simulate a rotating test, 3-D 

finite element simulations were performed using a gelatin bird 

model and a generic fan design. Hereafter, the term “bird” is 

used to refer to a simulated bird projectile. Numerical 

simulations were carried out with a rotating fan blade as the 

baseline case and results were compared to non-rotating blade 

numerical simulations with various concepts to apply rotatinglike loads to the blade. It is important to note that the baseline 
NASA/TM—2013-217904 2

case has not been vetted against experimental results for 

accuracy. However, the techniques and analysis tool used are 

consistent with prior work that has been shown to correlate 

well to experimental results in similar analyses (Refs. 3 to 7).

Additionally, the intent is to compare the rotating and nonrotating cases rather than focus on the accuracy of the 

predicted impact results. Furthermore, additional work is 

planned to corroborate the results obtained so far, including 

experimental validation, after which the conclusions drawn 

here can be re-evaluated.

There has been extensive work over the past several decades 

intent on modeling bird strike events on aero structures, 

including fan blades and other engine components. Together, 

Nizampatnam (Ref. 8) and Mao, et al. (Ref. 9) provide a good 

review of the representative literature. A large majority of the 

work has been focused on the development of an appropriate 

artificial bird model, including the bird shape, bird material, and 

modeling technique (Lagrangian, Euler, Arbitrary LagrangianEulerian, etc.). Considering the remainder of published work, 

few have concentrated on the rotational effect on blade 

deformation. The reports that did consider rotational effects 

either did not compare deformation between rotating and nonrotating blades, or concluded that the centrifugal forces acted to 

reduce the global deformation of the rotating blades (Refs. 3, 4,

10 to 12). Because of that finding, and independent anecdotal 

evidence from aero engine designers, it was anticipated that any 

non-rotating test techniques would need to include pre-stressing

the blade to have a chance of successfully simulating a rotating 

test condition.

Due to the above observations, early simulations were

focused on duplicating the pre-stress field near the impact 

zone. Later simulations focused on different methods for 

constraining the blade, to help determine if the method of 

applying pre-stress in addition to the magnitude is important. 

Results were disappointing, with none of the attempts 

accurately duplicating the plastic deformation of the rotating 

blade. The deformation of the rotating blade was found to be 

less than all of the non-rotating blade simulations, no matter

what pre-stress condition was present, including identically 

matching the centrifugal pre-stress condition to the rotating 

case. Therefore, there is clearly some other factor influencing 

the deformation as well. The gyroscopic effect, or the effect of 

changing the rotational inertia of the rotating fan blade, is not 

included in the non-rotating analysis and could lead to the 

over-prediction of deformation of a non-rotating blade.

This paper gives a summary of the results of the many 

simulations conducted along with a discussion of the rotating 

effects. Future plans to continue the search for a non-rotating 

material screening test are also presented.

Nomenclature

F Force

I Mass Moment of Inertia

M Moment (Vector Quantity)

m Mass

p Spin Velocity (Vector Quantity)

r Radius

t Time

θ Angle of Rotation About Spin Axis, p

Ψ Precession Angle

Ω Precession Velocity (Vector Quantity)

Methodology

LS DYNA, a general-purpose finite element program, was 

used in all the simulations reported herein (Ref. 13). The fan 

blade model used was developed at NASA Glenn Research 

Center for aero-elasticity studies and was originally for a large 

engine approximately 144 in. (3.65 m) in diameter. Since the 

fan size of interest in this study is about half that size, the fan 

blade was scaled down to about 72 in. (1.82 m) in diameter 

with a blade length of approximately 24 in. (0.6 m). Figure 1

shows a single blade mesh used in these studies. The material 

model for the blade was *MAT_PIECEWISE_LINEAR_

Figure 1.—Blade mesh showing location of bird impact and 

paths for result plots.
NASA/TM—2013-217904 3

PLASTICITY with the strain-rate dependent properties of 

Titanium 6Al-4Vgiven in Figure 2 (Ref. 14). The blade was 

modeled using LS DYNA solid element formulation 2 (8-node 

fully-integrated selective reduction).

Prior work has shown that birds can successfully be 

modeled as fluids using straight-ended cylinder, hemispherical

-ended cylinder, and ellipsoid shapes (Refs. 4, 5, and 15). 

Likewise, artificial gelatin bird models with these shapes are 

commonly used in experimental studies to simulate real birds 

(Refs. 16 and 17). The bird model used in these numerical 

simulations was a cylindrical gelatin slug with a hemispherical 

leading edge as seen in Figure 3. This shape was chosen

Figure 2.—Strain rate dependant stress strain curves for 

titanium 6V4AL.

Figure 3.—Illustration of gelatin bird model entering fan blade 

row for determination of the extent of penetration and 

velocity vectors. 

to match the shape that is typically used for in-house testing at

NASA Glenn, and has been shown to correlate well with 

analyses (Ref. 17). The formulation used for the bird was 

Arbitrary Lagrangian-Eulerian (ALE). While there are other 

common formulations, such as Lagrangian, Eulerian, and 

Spherical Particle Hydrodynamics, the ALE formulation has 

been used successfully by the authors, and the focus of this 

work was to explore potential non-rotating test configurations 

compared to rotating tests rather than finding the best bird 

formulation. The material properties for the bird were based 

on previous work with gelatin as a bird substitute (Ref. 17), 

and were somewhat similar to water.

The bird was positioned to impact the blade at 75 percent of 

the distance up from the root to the tip, as seen in Figure 1.

The rotational velocity of the fan blade was set to match the 

approximate maximum speed of a fan of this size based on 

sonic velocity at the blade tips, which corresponds to 

500 rad/sec (4775 rpm). The air speed of interest in bird strike 

events is the velocity of a given airplane shortly after take-off 

when the plane is at an altitude most likely to encounter birds.

For an airplane size consistent with a 72 in. (1.8 m) diameter 

fan that air speed is approximately 200 knots (103 m/sec).

Because the blade in a bird strike test does not translate in the 

global sense, the bird is given a velocity of 200 knots in the 

direction toward the fan blade (y-direction) as shown in

Figure 3. An assumption is made that the impact would be the 

same whether a bird travels toward a fan or a fan travels 

toward a bird, as long as the relative velocity is the same.

Following this same assumption, in the non-rotating blade 

simulations, the bird moves with a velocity of 200 knots in the 

direction along the axis of the fan (y-direction), and with a 

velocity equal to the blade leading edge velocity at the point of 

impact (730 knots, 376 m/s) in the direction toward the fan 

blade, (negative x-direction) as shown in Figure 3.

Figure 3 also illustrates the determination of the maximum 

distance the bird can penetrate into the fan before hitting the 

first blade. The blade spacing is based on the number of fan 

blades in the entire fan, which in this case is 18. Given the 

spacing of the blades at the impact zone, and the relative 

velocities of the blade and bird, one can determine that a 

maximum of 2.3 in. (58 mm) of the bird can penetrate the fan 

before being hit by the first blade if it just misses the previous 

blade. This geometry was used for all the simulations as the 

worst-case scenario. 

The criterion used to compare two different simulations is 

the plastic strain near the impact point. Hereafter, plastic strain 

and effective plastic strain are used interchangeably. Figure 1

shows a path along the leading edge and across the blade 

where plastic strain was evaluated when comparing nonrotating simulations to the rotating baseline case. Plotting 

plastic strain in the elements along these two paths gives a 

good indication of how similar two different simulations are in 

terms of permanent damage to the blade.
NASA/TM—2013-217904 4

Rotating Simulation Results and

Discussion

The first numerical simulation carried out was that of a 

rotating fan blade with a gelatin bird fired in the axial 

direction at the maximum take-off velocity. The approach 

used to develop the stress field and elastic deformation in the 

blade prior to the impact follows that used by others in 

modeling bird ingestion and also follows Test Case 5 available 

from the LS DYNA Aerospace Working Group (Refs. 3 and 

16). The method involves two separate analyses, wherein the 

first run calculates the stresses and strains using implicit 

analysis. Then, the results of that run are fed into an explicit

run as initial conditions for a secondary calculation of the 

transient impact event.

For the rotating case, the implicit pre-stress calculation 

was done with a fan blade rotational velocity of 500 rad/sec.

The 500 rad/sec velocity was maintained throughout the 

impact in the explicit analysis such that the fan blade did not 

decelerate during the simulation.

The results of the pre-stress calculations are given in

Figure 4. The top row shows the radial (z-direction) stress, 

and the bottom row shows the radial displacement, both at 

several different speeds from zero to the maximum rotation 

speed of 500 rad/sec (4775 rpm). At full speed, the stress 

generally increases from zero at the blade tip to a maximum 

in the middle of the blade at the base. 

The results of this pre-stress calculation at maximum 

speed (500 rad/sec) were then used as initial conditions for 

the transient impact analysis that followed. In the transient 

analysis, the bird model was analytically shot at the rotating 

blade at a velocity of 200 knots (103 m/sec) such that the 

blade would impact the bird at a distance 2.3 in. (58.4 mm) 

behind the leading edge of the bird as shown in Figure 3. 

The results of the bird impacting the rotating blade are 

presented in Figure 5. One can see plastic strain as it 

develops from time zero, just before the impact, to time

350 μsec in the top row of figures. The bottom rows show 

the top, side, and front views of the maximum principle 

stress as it develops in time. As mentioned earlier, the main 

parameter of interest is the plastic strain at the impact zone. 

Figure 6 gives the plastic strain along the leading edge of the 

blade and across the face according to the geometry shown 

in Figure 1. Also in the figure is a contour plot of plastic 

strain for reference.

The damage, measured in terms of plastic strain, is mostly 

localized near the impact zone. In Figure 6, one can see that 

the maximum plastic strain of about 0.21 occurs just above 

the impact point, and decreases to nearly zero 4 in. or less 

away from the impact point in all directions. The impact 

point is defined as location of first contact between the bird 

and the blade. In reality, the gelatin bird model has a 

diameter of 3.33 in. (84.6 mm), so the impact occurs over an 

area roughly that diameter. There is some plastic strain at the 

base of the blade near the leading and trailing edges, and 

some small areas at the blade tip leading and trailing edges 

as well. The plastic strain resulting from this rotating case is 

the baseline against which non-rotating bird-strike results 

will be compared.

Figure 4.—Progression of stress and displacement with increasing speed from 0 to 4775 rpm (500 rad/sec). Results 

of pre-stress calculations before the bird impact analysis.
NASA/TM—2013-217904 5

Figure 5.—Progression of plastic strain and maximum principle stress with increasing time after the impact from 0 to 350 μsec.

Figure 6.—Plastic strain as a function of distance from the 

impact point.

Non-Rotating Simulation Results and 

Discussion

A series of non-rotating blade simulations were done to 

determine the possibility of approximating the rotating blade 

damage with a non-rotating blade test. Because the damage 

was localized to the impact area in the rotating test, it was 

originally thought that good results might be possible if the 

pre-stress in the blade in the impact zone was similar to the 

rotating pre-stress. Several different methods for applying a 

load to the non-rotating blade were analyzed. 

The first method of applying a force was to pull on the 

blade with a series of cables attached at the tip of the blade. 

Figure 7 shows the analytical model of the blade with cables 

attached to the tip. By changing the diameter and length of the 

cables, and the displacement at the upper end (cable stretch), 

the force applied to the blade can be changed. The cables are 

shown as being short in the figure to conserve space, but in 

reality, the cable length is long compared to the length of the 

blade to reduce the tangential constraint of the blade tip. The 

cable stretch is set such that the pre-stress in the blade matches 

the pre-stress in the rotating case at the impact zone. In order 

to generate a pre-stress condition with the cables that matched 

the rotating case at the impact zone, many different attempts 

were made using different cable lengths and cable stretch.
NASA/TM—2013-217904 6

Figure 7.—Schematic of the non-rotating blade test 

concept using cables at the blade tips to apply a 

radial force.

Figure 8.—Top view of the blade showing the cable angle and 

resultant blade angle relative to the base of the blade.

It was discovered at this stage that the angle between the 

line connecting the tops of the cables and the base of the blade 

(called the cable angle) had a significant effect on the angle of 

attack of the blade. In other words, the blade untwisted from 

the applied radial force, which it also did in the rotating case, 

but by different amounts depending on the conditions. In order 

to simultaneously match the stress at the impact zone and the 

angle of attack, the cable angle became another important 

parameter. The sketch in Figure 8 defines the cable angle and 

the resultant blade angle (at the blade tip) relative to the base 

of the blade.

In the end, 25 different conditions were analyzed to find a 

combination of cable stretch, cable length, and cable angle that 

resulted in a pre-stress condition that closely matched that of 

the rotating blade at the impact zone. Figure 9 shows a few 

selected examples of z-direction pre-stress conditions that

were attempted, along with the rotating case z-direction prestress condition. Condition 23 resulted in the best combination 

of pre-stress and angle of attack when compared to the 

rotating baseline case, and was used for the first non-rotating 

analysis. Additional cases were studied focusing on the other 

components of stress, but the results were essentially 

independent of those components as the z-direction was the 

dominant stress component due to centrifugal forces.

The bird is given an axial velocity equal to the axial velocity 

in the rotating case combined with a tangential velocity equal 

to the velocity of the blade in the rotating case as shown in the 

velocity triangle in Figure 3. The resultant velocity of the bird 

was 1278 ft/sec at an angle 15.3° from the tangential direction. 

The non-rotating blade using condition 23 is impacted with 

the bird using the above velocity vector. The damage to the 

non-rotating blade is shown along with the baseline rotating 

blade damage in Figure 10. As one can see from the figure, the 

damage, in terms of plastic strain, in the rotating blade is 

significantly less than the damage in the non-rotating blade, 

even though the pre-stress condition at the impact zone was 

similar and the impact velocity was matched. This case is 

called non-rotating concept 1. As indicated before, it was 

hoped that matching the pre-stress at the impact zone, the 

angle of attack, and the bird velocity vector at impact would 

result in similar damage whether the blade was rotating or not 

rotating. After studying non-rotating concept 1, it was thought 

that perhaps the boundary condition used to apply the load to 

the blade might have an influence on the resulting plastic 

deformation of the blade. Therefore, several different methods 

of applying a load to the blade were devised and simulated to 

determine if any methods might provide similar results to the 

rotating baseline case. For brevity, the details of each concept 

are not discussed; rather each will be described briefly, with a 

summary of all the results compiled into one plot at the end.

The second concept applies a constraint at the tip of the fan 

blade that prevents large transverse displacements at the tip, 

but does not apply a radial force. Two cables were attached at 

an angle to each other to each of the previous attachment 

points as shown in Figure 11 as concept 2.
NASA/TM—2013-217904 7

Figure 9.—Examples of various conditions analyzed in attempting to match z-direction pre-stress and angle of attack to the 

rotating baseline case. Dashed line at 75 percent of the height indicates impact zone. Condition 23 represents the best match 

of pre-stress level and angle of attack.

Figure 10.—Comparison of damage between rotating 

and non-rotating concept 1.
NASA/TM—2013-217904 8

Figure 11.—Schematic of loading concepts 2 to 5.

The next simulation, concept 3, was to apply a radial force 

at two distinct radial locations. One location was at the blade 

tip as in concept 1. The second was below the impact zone, 

where a fixture was attached to the blade, and a second set of 

cables pulled on the fixture. Since a rotating blade has a 

radially variable pre-stress, it was thought matching the prestress at just one location may not have been sufficient. With 

two load application points, the stress could be matched at the 

impact zone, and near the base of the blade. A sketch of this 

concept is shown in Figure 11 as concept 3.

Concept 4 was similar to concept 1 with the exception that 

instead of a prescribed stretch applied to the cables, the free 

end of the cables was attached to a large mass, and a body 

force (i.e., gravity) was applied to provide the radial force, see 

Figure 11. The difference between these two methods is that 

the force in concept 4 is constant and the direction of 

application of the force can change slightly since the mass is

not fixed in space. In concept 1, the free end of the cables are

Figure 12.—Plastic strain in the fan blade across the face

and along the leading edge for the rotating and various

non-rotating test concepts.

fixed after applying the pre-stress, such that as the blade tip 

moves, the force applied changes as the cables elongate or 

shrink.

Concept 5 is similar to concept 4 but with the mass fixed 

directly to the blade tip rather than through cables. The body 

force due to gravity in this case is still constant, but the large

inertia of the mass is tied directly to the blade tip as shown in 

Figure 11.

Lastly, concept 6 will be discussed shortly, but had very 

similar damage results to the other non-rotating cases.

The results of all the non-rotating experimental concepts are 

summarized in Figure 12. The rotating case is included to 

show the “correct” result (the goal). Additionally, a nonrotating case with no cables (i.e., no pre-stress) is included in 

the results for comparison. The results clearly show that none 

of the non-rotating cases result in blade damage that matches 

the rotating case sufficiently well. The other interesting result 

is that all of the non-rotating cases resulted in similar damage 

in terms of maximum plastic strain and all had very similar 

shapes, with only concept 3 having any significant deviation 

from the rest. In summary, the blade damage in the nonrotating cases near the impact is not highly dependent on the 
NASA/TM—2013-217904 9

Figure 13.—Velocity vectors for blade shooting at a 

stationary bird.

pre-stress boundary condition, but does differ significantly 

from the rotating blade case.

We propose two hypotheses to explain why the rotating 

blade deforms less than the non-rotating blade: either the 

impact dynamics are different, meaning the force profile is not 

the same, or there’s a dynamic phenomenon in the rotating 

case that is not included in the non-rotating case. In regards to 

the impact dynamics being different, one can consider the 

simple case of two rigid bodies colliding together. The impact 

force between the two bodies does not depend on the 

individual velocities of the bodies, rather it depends on the 

relative velocity of the two bodies. Extending that concept to 

this problem, it was assumed the impact forces in the nonrotating case would be the same as the rotating case as long as 

the relative velocity between the bird and blade were the same.

After observing the result shown in Figure 12, it was thought 

perhaps that assumption was incorrect, and maybe it does 

matter if the blade is moving as well. Concept 6 was analyzed 

in order to determine if the damage to the blade would be 

different if the blade was moving and the bird was stationary.

Figure 13 shows the velocity vectors applied to the blade, 

which are equal in magnitude, but opposite in direction to the 

vectors applied to the bird earlier. In this manner, concepts 6 

and concept 1 are the same except that 6 has the blade 

impacting a stationary bird, and concept 1 has the bird 

impacting a stationary blade. In fact, the results are not 

identical as can be seen in Figure 12, but they are very similar.

The peak plastic strains differ by less than 10 percent.

Therefore, it seems likely that matching the relative velocity, 

but shooting a bird at a stationary blade can come close to 

simulating the impact event in terms of the contact mechanics.

This leaves the second point above that there may be 

something in the overall system dynamics that is not modeled, 

or is not included in the non-rotating cases by virtue of the fact 

that the blade is not rotating. One such dynamic effect that is 

not included in the non-rotating models is gyroscopics

(Ref. 18). When a rigid body rotates, a moment is required to 

counteract the gyroscopic effects generated whenever there is

Figure 14.—Illustration of gyroscopic effect in a spinning disk.

a precession of the rotating rigid body about any axis other 

than its principal rotation axis. For example, consider a 

spinning car tire and wheel. If the car is moving forward, the 

tire’s rotation vector points to the left. In order to turn the car 

to the right, the tire must precess, or turn, clockwise looking 

down from the top. When this happens, there is a moment 

required to keep the tire vertical with respect to the ground 

that is orthogonal to the precession direction. Figure 14

illustrates this concept, and the moment can be calculated 

according to Equation (1).

= × Ω

   M p I (1)

Where �M��⃗ is the moment vector, I is the mass moment of 

inertia of the spinning body about its rotation axis, Ω���⃗ is the 

spin vector, and �p⃗ is the precession vector (Ref. 18).

Now, consider the spinning fan blade depicted in Figure 15.

The blade spins about the y,y′-axis at the geometric center of 

the fan assembly, shown by the vector p. At time zero, the 

blade is located on the coordinate axis: x, y, z. At time δt, after 

an impact with a bird, it has rotated an angle θ to the position 

labeled with coordinates x′, y′, z′. Sometime between t = 0 and 

t = δt, a bird, travelling in the negative x-direction, struck the 

leading edge of the fan blade, and applied a force given here 

by F. Looking at a differential element of mass, δm, the force 

applied by the bird created a moment about the z-axis of the 

blade.
NASA/TM—2013-217904 10

Figure 15.—Illustration of the gyroscopic effect as it 

applies to the bird impact problem.

If that differential mass element were not part of a blade, but 

were simply a point mass, it would have precessed about the 

local x-axis according to the gyroscopic effect described 

previously. That precession would have resulted in a 

differential displacement in the positive z-direction, δz.

However, since the differential mass is connected to the 

adjacent differential mass, and so on, it is partially constrained 

in the z-direction. Therefore, the blade would behave as if it 

were stiffer than it really is. The authors believe this may be 

an explanation for the reduced deformation observed in the 

rotating case when compared to all of the non-rotating cases, 

but more work is needed to verify this.

To illustrate this effect in the present problem, a case was 

run with the pre-stress and strain calculated for a rotating 

blade as the initial condition for a non-rotating blade impact.

Therefore, at t = 0, the pre-stress and pre-strain in the blade 

are identical to the rotating case, but the dynamics when the 

bird impacts are identical to the non-rotating case. To simulate 

rotation loads in the non-rotating case after t = 0, a body force 

is applied to the blade equal to the acceleration in the rotating 

case. In other words, the pre-stress and strain and the body 

forces in the non-rotating case are identical to the rotating 

case, but the blade is not rotating, so gyroscopic effects are not 

included. Figure 16 shows a progression in time of z-direction

stress in the rotating and non-rotating blade as the bird

Figure 16.—Z-stress in the rotating blade and the nonrotating blade with body force during the impact event.

impacts. Clearly, the stress before the impact is the same in both 

cases, but as the impact event occurs, the stress field develops 

somewhat differently. Additionally, Figure 17 presents the 

plastic strain in the two cases after the impact. One can see that 

the resulting damage to the blade is quite different.

The above case demonstrates that matching the pre-stress 

condition between the rotating and non-rotating cases is not 

sufficient to simulate the impact event in a non-rotating test. 

The final case to be discussed was analyzed to determine if the 

effects of the rotating blade could be simulated without 

spinning an entire fan assembly. In this case, the blade rotates 

about its center of gravity at the same rotational velocity as in 

the rotating case, 500 rad/sec. Since the radius from the center 

of rotation to the point of impact is less than in the initial 

rotating case, the bird’s transverse velocity is adjusted to 

maintain the same impact velocity. Figure 18 gives a 

schematic of the geometry. Figure 19 shows the results of this 

final concept. Qualitatively, the damage looks very similar 

between the two cases as seen in the plastic strain contour 

plots at the top of the figure. Quantitatively, they agree very 

well also, with the maximum plastic strain within 7 percent, 

and the shape of the strain profiles along both the leading edge 

and across the face matching well. 

Keeping in mind the goal of this work is to identify an 

experimental technique that can be used to simplify testing of 

a single blade while simulating the results of a full rotational 

test, this method may not be viable. It would be less difficult 

to rotate a single blade about its center of gravity than to rotate 

a full fan, but the timing of shooting a bird to hit the blade at 

just the right time and place would be more difficult.

Therefore, it may or may not be a realistic test method, but 

the results are interesting, and further support the notion that 

the rotating effects are more important than the pre-stress in 

the blade.
NASA/TM—2013-217904 11

Figure 17.—Damage comparison for rotating blade and

non-rotating blade with body force.

Figure 18.—Schematic of blade rotating about its own CG.

Figure 19.—Damage comparison for rotating blade and 

blade rotating about its CG.

Summary

Due to the high cost and complexity of impacting a rotating 

aero engine fan assembly with a bird, or simulated bird, in a 

controlled test environment, there is interest in developing a 

test method for impacting a non-rotating, single fan blade that 

reproduces similar damage results to a rotating test. The 

motivation for this type of simple test for fan blades is for 

research and development in materials for fan blades. Because 

current test methods involving rotating a fan or several blades 

of a fan are very expensive, material developers cannot create 

many samples of new materials and test them for screening 

purposes. The desire is to develop a simple, cost-effective test 

that can closely resemble to rotating test for screening 

purposes such that many different candidate materials can be 

tested and the promising materials can go on for further testing 

using more accurate and traditional methods.
NASA/TM—2013-217904 12

Using LS DYNA to analytically simulate impact events, 

several non-rotating and rotating bird impact events were 

analyzed to determine the possibility of firing a simulated bird 

at a non-rotating blade to get similar results to a rotating 

impact with the same bird model. At the outset, it was 

anticipated that the difficulty in obtaining good agreement 

between rotating and non-rotating blade damage would be in 

matching the pre-stress condition of the blade. The stress field 

in a rotating blade varies radially, and no method for 

duplicating a radial variation equivalent to the rotating case 

could be conceived. There was hope, however, that matching 

the stress condition in the blade at the impact zone may be 

sufficient because the damage was observed to be mostly local 

near the impact. For that reason, the early effort was focused 

on techniques to load the blade in a manner that would match 

the stress conditions in the rotating blade at the point of impact.

The techniques to generate a pre-stress in the blade were 

variations of two basic ideas: applying a force through cables 

attached to the blade tip and applying force through mass 

attached in some way to the blade tip. Various degrees of 

success were attained in matching the pre-stress conditions at 

the impact point. However, it was found that no matter how 

the pre-stress was generated, the blade damage was similar, 

and was always more than the rotating case.

With that un-anticipated result, suspicions arose that some 

aspect of the blade rotation was acting to stiffen the blade in 

the rotating case, resulting in less damage. At that point, two 

additional analyses were conducted. The first was a nonrotating blade that had the same pre-stress and body forces as 

the rotating blade without rotation. This condition is possible 

to simulate numerically, but would be difficult or impossible 

to recreate experimentally. However, the results verified that, 

in fact, matching the pre-stress is not sufficient to guarantee 

similar damage. The second additional case had a rotating 

blade spinning about its center of gravity impacted by a bird 

model shot with the same relative velocity as the full rotating 

case. The results of this analysis indicated that rotating effects 

are significant, and likely overshadow the pre-stress effects in 

stiffening the blade.

Future work includes more analysis to verify these finding, 

as well as some experimentation to validate the models and 

compare findings.

References

1. Blackwell, B.F., Devault, T.L., and Fernandez-Juricic, 

E., 2009, “Wildlife Collisions with Aircraft: A Missing 

Component of Land-use Planning for Airports,” 

Landscape and Urban Planning, 93, pp. 1-9. 

2. “Bird Ingestion.” 14 FAR 33.E.33.76, 2007.

3. Vasko, T.J., 2000, “Fan Blade Bird-Strike Analysis and 

Design,” 6th International LS-DYNA User’s Conference, 

Dearborn, MI, 2000.

4. Castelletti, L.L., Anghileri, M., 2008, “Birdstrike onto 

Structures in Rotational Motion,” ICAS 2008-9.4.4, 

Proc. 26th Congress of the International Council of the 

Aueronautical Sciences, Anchorage, AK, pp. 1-11.

5. McCallum, S.C., and Constantinou, C., 2005, “The 

Influence of Bird-Shape in Bird-Strike Analysis,” Paper 

Number 2C-77, Proc. 5th European LS_DYNA 

Conference, Birmingham, England.

6. Huerta-Ortecho, C.A., 2006, “Robust Bird-Strike 

Modeling Using LS_DYNA,” UMI# 1435268, Master 

Thesis, University of Puerto Rico, Mayaguez.

7. Tho, C., and Smith, M.R., 2008, “Accurate Bird Strike 

Simulation Methodology for BA609 Tiltrotor,” Proc. 

64th American Helicopter Society International Annual 

Forum 2008, Curran Associates, Inc., Alexandria, VA, 

3, pp. 2156-2167.

8. Nizampatnam, L.S., 2007, “Models and Methods for 

Bird Strike Load Predictions,” Ph.D. Dissertation, 

Wichita State University, Wichita, KS.

9. Mao, R.H., Meguid, S.A., and Ng, T.Y., 2007, “Finite 

Element Modeling of a Bird Striking an Engine Fan 

Blade,” Journal of Aircraft, 44(2), pp. 583-596.

10. Miyachi, T., Okumura, H., and Ohtake, K., 1991, “An 

Analysis of the Effect of Centrifugal Force on the 

Impact Resistance of Composite Fan Blades for TurboFan Engines,” Proc. Society of Automotive Engineers, 

246, pp. 619-626.

11. Schutte, W., 1990, “Blade Behavior During Birdstrike,” 

Proc. 5th International Conference on Science and 

Engineering on Supercomputers, pp. 145-157.

12. Shioya, T., and Stronge, W.J., 1985, “Impact Bending of 

a Rotating, Rigid-Plastic Fan Blade,” Journal of 

Propulsion and Power, 1(5), pp. 375-380.

13. LS DYNA KeyWord User’s Manual Version 971, 

Livermore Software Technology Corporation, 

Livermore, CA, 2006.

14. Carney, K.S., Pereira, J.M., Revilock, D.M., and 

Matheny, P., 2009, “Jet Engine Fan Blade Containment 

Using an Alternate Gepmetry,” International Journal of 

Impact Engineering, 36, pp. 720-728.

15. Meguid, S.A., Mao, R.H., and Ng, T.Y., 2008, “FE 

Analysis of Geometry Effects of an Artificial Bird 

Striking an Aeroengine Fan Blade,” International 

Journal of Impact Engineering, 35, pp. 487-498.

16. Olivares, G., Tufano, M., Dohle, N., Pereira, J., and 

Revilock, D.M., 2012, “Development and Validation of 

a Gelatin Bird Substitute,” Proceedings of the Aerospace 

Structural Impact Dynamics International Conference 

2012, Wichita, KS, Nov. 6-9, 2012.

17. LS DYNA Aerospace Working Group, “Test Case 5: 

Bird Strike on Rigid Plate,” awg.lstc.com.

18. Meriam, J.L., and Kraige, L.G., 1992, Engineering 

Mechanics, John Wiley & Sons, New York, NY, Chap. 

7, pp. 570-573.

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB 

control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-08-2013 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Jet Engine Bird Ingestion Simulations: Comparison of Rotating to Non-Rotating Fan Blades 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Howard, Samuel, A.; Hammer, Jeremiah, T.; Carney, Kelly, S.; Pereira, J., Michael 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 473452.05.06.02.02 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-18629-1 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2013-217904 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 37 

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

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

Bird strike events in commercial airliners are a fairly common occurrence. According to data collected by the US Department of Agriculture, over 80,000 bird strikes were 

reported in the period 1990 to 2007 in the US alone. As a result, bird ingestion is an important factor in aero engine design and FAA certification. When it comes to bird 

impacts on engine fan blades, the FAA requires full-scale bird ingestion tests on an engine running at full speed to pass certification requirements. These rotating tests are 

complex and very expensive. To reduce development costs associated with new materials for fan blades, it is desirable to develop more cost effective testing procedures than 

full-scale rotating engine tests for material evaluation. An impact test on a non-rotating single blade that captures most of the salient physics of the rotating test would go a long 

way towards enabling large numbers of evaluative material screening tests. NASA Glenn Research Center has been working to identify a static blade test procedure that would 

be effective at reproducing similar results as seen in rotating tests. The current effort compares analytical simulations of a bird strike on various non-rotating blades to a bird 

strike simulation on a rotating blade as a baseline case. Several different concepts for simulating the rotating loads on a non-rotating blade were analyzed with little success in 

duplicating the deformation results seen in the rotating case. The rotating blade behaves as if it were stiffer than the non-rotating blade resulting in less plastic deformation 

from a given bird impact. The key factor limiting the success of the non-rotating blade simulations is thought to be the effect of gyroscopics. Prior to this effort, it was 

anticipated the difficulty would be in matching the pre- stress in the blade due to centrifugal forces Additional work is needed to verify this assertion, and to determine if a 

static test procedure can simulate the gyroscopic effects in a suitable manner. This paper describes the various non-rotating concepts analyzed, and demonstrates the effect 

believed to be gyroscopic in nature on the results.

15. SUBJECT TERMS

Bird strike; Impact; Fan blades 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

20 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18