Septem

NASA/

Fluo

Tem

Paul M. D

Langley R

T. Lowe a

Virginia 

G. Byun 

Applied U

mber 2012

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mperatu

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Polytechnic

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 Institute an

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Particle

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ERRATA 

NASA/TM-2012-217768 

Issue Date: 11/30/2012 

Cover, Title Page, and Report Documentation Page: Author name Mark Verkamp 

corrected to read Max Verkamp. 
1

Fluorescence-Doped Particles for Simultaneous Temperature and Velocity Imaging 

P. M. Danehy, P. Tiemsin, C. Wohl, M. Verkamp*

NASA Langley Research Center, Hampton VA, 23681 

T. Lowe, P. Maisto, 

Aerospace and Ocean Engineering Department, Virginia Tech, Blacksburg, VA, 24061 

and

G. Byun, R. Simpson 

AUR, Inc., Blacksburg, VA, 24060 

Abstract 

Polystyrene latex microspheres (PSLs) have been used for particle image velocimetry (PIV) 

and laser Doppler velocimetry (LDV) measurements for several decades. With advances in laser 

technologies, instrumentation, and data processing, the capability to collect more information 

about fluid flow beyond velocity is possible using new seed materials. To provide additional 

measurement capability, PSLs were synthesized with temperature-sensitive fluorescent dyes 

incorporated within the particle. These multifunctional PSLs would have the greatest impact if 

they could be used in large scale facilities with minimal modification to the facilities or the 

existing instrumentation. Consequently, several potential dyes were identified that were 

amenable to existing laser systems currently utilized in wind tunnels at NASA Langley Research 

Center as well as other wind and fluid (water) tunnels. PSLs incorporated with Rhodamine B, 

dichlorofluorescein (DCF, also known as fluorescein 548 or fluorescein 27) and other dyes were 

synthesized and characterized for morphology and spectral properties. The resulting particles 

were demonstrated to exhibit fluorescent emission, which would enable determination of both 

fluid velocity and temperature. They also would allow near-wall velocity measurements whereas 

laser scatter from surfaces currently prevents near-wall measurements using undoped seed 

materials. Preliminary results in a wind tunnel facility located at Virginia Polytechnic Institute 

and State University (Virginia Tech) have verified fluorescent signal detection and temperature 

sensitivity of fluorophore-doped PSLs. 

1. Introduction 

This report describes progress made during Phase I of an Aeronautics Research Mission 

Directorate ―Seedling Fund‖ project supported at NASA Langley in FY11-12. The project 

focused on synthesis and characterization experiments using polystyrene latex microspheres 

(PSLs) doped with a dye or series of dyes that are mechanically bound within PSLs. This novel 

seed material would aid in the simultaneous characterization of multiple parameters in fluid flow 

environments, where only single measurements are currently performed. For example, it can 

potentially measure temperature, pressure, velocity and/or scalar concentration instead of just 

velocity. 

 

*

 LARSS Student from Rose-Hulman Institute of Technology 
2

Several authors have described efforts to dope particles, both liquid and solid, with fluorescent 

dyes and luminescent paints to measure scalar flow properties. Much work has been done to 

assess methods for doping liquid particles with dyes and temperature sensitive paints as reviewed 

by Sutton et al.1 Both Dunand et al.2 and Sutton et al.1 have indicated that two-dye techniques 

could be attractive for enhanced temperature sensitivity. Fog-based seeding is problematic in 

large scale wind tunnel facilities because of the large resulting particles and large particle size 

distribution. Emission directivity is an important phenomenon unique to droplet and particlebased fluorescence and has been discussed by various authors. As shown by Frackowiak and 

Tropea, the fluence field within a single illuminated particle is complex due to Lorenz-Mie 

scattering effects; such directivity can be exploited to optimize fluorescence signals.3

Thermographic phosphor particles or coatings have also been investigated for their potential in 

simultaneous temperature and velocity imaging.4,5,6,7,8

 However, such particles, typically 

containing rare-earth elements such as Europium, are not suitable for large flow facilities 

because of health risks. Dye doped PSLs have been fabricated, studied and used in a variety of 

applications for more than three decades.9 PSLs doped with fluorescent dyes are available 

commercially mainly for bio-medical applications but to our knowledge these have not been 

used for thermometry. These commercially available dye-doped particles are prohibitively 

expensive for large-scale wind tunnel tests. A review of the literature revealed no mention of 

PSL-based thermometry. While some researchers have used PSLs coated with pressure-sensitive 

paint10, only the current study is leveraging single-particle fluorescence signals from PSLs. 

This paper reports the feasibility of generating dye-doped PSLs for measurement of 

fluorescent emission in flow experiments. Also, the use of dye-doped PSLs for thermometry was 

verified. Along with enabling temperature and possibly pressure characterization, this method 

can potentially improve signal-to-noise ratios under certain circumstances compared to signals 

generated by Mie scattering. Some other important goals of this research are that the resulting 

dye-doped PSLs should be non-hazardous and inexpensive to generate so they can be used in 

large-scale wind tunnel experiments. PSLs are often used in the large scale wind tunnels at 

NASA due to their selectable, monodisperse (or uniform) diameter distribution and high index of 

refraction. Uniform, known-diameter particles have a predictable response to flow fluctuations, 

enabling prediction of lag effects in all tests, and particles of high index of refraction produce 

high-contrast scattering signals (high signal-to-noise ratio), enabling high fidelity flow 

measurements. They can also be manufactured cost-effectively, quickly and to specification inhouse. 

This report primarily focuses on the development of the method for generating the particles as 

well as some preliminary proof-of-concept measurements. Ultimately, the efficacy of these 

particles will be evaluated in wind tunnels using traditional experimental techniques (i.e., laser 

Doppler velocimetry, LDV, and particle image velocimetry, PIV) to measure a variety of flow 

characteristics possibly including the following: velocity, temperature, pressure, multi-phase 

flows, fluid mixing, etc. These measurements also may benefit from the ability to collect data 

closer to the boundary wall than is currently possible with traditional seed materials. 

This project involves three key research aspects: 

 Identifying an appropriate measurement scheme for the intended application 
3

 Identifying dyes that would meet the requirements of the measurement scheme and 

developing a method of manufacturing these dye-doped seed particles 

 Demonstrating the new measurement technique(s) on relevant flow problems 

This report focuses on the first two aspects of the research and especially the second aspect: 

identifying promising dyes and doping them into the seed materials. By way of motivation, the 

first section describes some possible measurement techniques using the fluorescent seed 

materials. The second section focuses on progress towards developing the seed materials. The 

third section describes some preliminary experiments that show proof-of-concept for temperature 

measurement using the new seed materials. 

 (c) Measure velocity from LDV and temperature from fluorescence

Figure 1. Three potential measurement schemes using dye-doped polystyrene latex spheres.
4

2. Measurement Schemes: 

Figure 1 shows examples of possible measurement schemes that could use dye-doped 

particles for different measurements in fluid flows. Laser illumination would excite fluorescence 

in the dye-impregnated PSLs which are seeded into a flow in the wind tunnel. In the first 

instance [Fig. 1(a)], the laser-induced fluorescence (LIF) intensity decreases as the temperature 

of the particles increases. Mie scattering, on the other hand, is mostly independent of 

temperature. By obtaining both Mie scattering and LIF signals, and taking their ratio, the 

temperature of the particles can be measured. Figure 1(b) gives another example of a 

thermodynamic measurement using seeded particles. In this case, a pulsed laser is used and the 

LIF intensity is measured as a function of time. The lifetime depends on the gas pressure owing 

to increases in collisions with molecules present. In Figure 1(c) the temperature approach of Fig. 

1(a) is combined with laser Doppler velocimetry to measure temperature and velocity 

simultaneously. In LDV, two crossed laser beams generate a fringe pattern. When a particle 

passes through the pattern, an oscillating time signature is collected. The frequency is 

proportional to the speed of the particle. Ratioing the LIF to Mie scattering can again provide 

temperature simultaneously with the velocity. 

The approaches described in Fig. 1 are 

single-point measurements using single 

point detectors such as photomultiplier 

tubes (PMTs). A slightly more complicated 

arrangement can allow imaging (i.e. planar 

measurements) of the flow parameters. 

This temperature-velocity imaging 

experiment is schematically shown in Fig. 

2. In this experiment, a pulsed laser is 

formed into a laser sheet to illuminate a 

flowfield. The particles seeded into the 

flow are doped with a dye which changes 

color as the particle temperature changes (as shown on the left side of the figure). Two cameras 

detect this fluorescence. The cameras have filters that pass different bands of the fluorescence 

(red and blue). The ratio of the fluorescent emission passing through the filters and detected by 

the cameras depends on temperature. Simultaneously, the image pairs can be used to measure 

the velocity of the particles using particle image velocimetry (PIV). 

Many such measurement schemes are possible, for example measuring temperature, pressure, 

or gas concentration using either continuous wave or pulsed lasers of different wavelengths. A 

variety of dyes or even combinations of dyes could be used to optimize the measurement 

techniques. Measurements could be single point (and possibly high repetition rate) or imagebased. 

3. Development and Characterization of the Seed Material: 

3.1 Particle synthesis 

The seed material generation effort involves acquisition or synthesis of candidate dye 

materials with the development of procedures to functionalize certain dye systems for chemical 

Figure 2. Schematic of the excitation scheme (left) and practical 

implementation of the setup to make simultaneous temperature and 

velocity measurements (right).
5

incorporation into PSL matrices. Research involving the direct integration of commercially 

available dye materials into PSLs has focused on two dyes: Rhodamine B and 

dichlorofluorescein (DCF, also known as Fluorescein 548 or Fluorescein 27). These were 

selected due to the capability of using these dyes for multi-parameter measurements (i.e., 

velocity and temperature). Other dyes including Kiton Red, Fluorescein, Tetraphenyl Prophyrin, 

Erythrosine, and Pyronin Y were also examined as possible candidates, but the two dyes above 

showed the most promise. 

Undoped PSLs—that is, PSLs without a fluorescent modifier—were synthesized using 

modification of a dispersion polymerization techniques developed by our group.11 The reaction 

volume for the PSLs described here was approximately 1/10 that described in the technical 

memorandum (Ref. 11). Briefly, a reaction kettle was outfitted with a gas inlet, a thermocouple, 

a mechanical stirrer, and a condensation column. A mixture of 242 mL of deionized water, 33 

mL of freshly distilled styrene, and 0.0444 g of MgSO4 were added to the kettle. This mixture 

was stirred for 45 minutes at approximately 40 RPM while nitrogen was used to purge the liquids 

of any dissolved oxygen. Next, the stir speed was increased to 250 RPM and a kettle heating 

mantle was utilized to bring the temperature up to 70 °C under a positive pressure of N2. Once 

the temperature was equilibrated, K2S2O8 was dissolved in 8 mL of 70 °C deionized water and 

rapidly added to the reaction kettle. The reaction mixture was stirred overnight under N2. The 

next day, the solution was poured through a cheesecloth filter to remove large aggregates from 

the solution. 

The synthesis of dye-doped PSLs was conducted in a similar fashion with the exception that 

the dye was dissolved in the styrene monomer prior to addition to the aqueous solution in the 

reaction kettle. This ensured that the dye would be dissolved in the organic phase prior to 

generation of the dispersion solution. 

3.2 Analysis Techniques 

The size and morphology of the 

PSLs generated in this work were 

characterized. Particle size 

measurements were conducted on a 

Particle Sizing System Model 780 

AccuSizer. The minimum and 

maximum detectable particle 

diameters for this instrument are 

500 nm and 100 micrometers, 

respectively. A typical size 

distribution is shown in Fig. 3. 

The morphology of the particles was characterized using optical and confocal microscopy. Both 

of these techniques were utilized to measure diameter variation of the PSLs in two dimensions 

with the assumption that these measurements would be representative of the variation in the third 

dimension. To measure the diameter variation, images of PSLs were fitted to rectangular shapes 

such that the perimeter of the rectangle overlaid the edges of the PSL. Variation of the length 

and width was utilized to assess the deviation of PSL circularity. Although these data are not 

shown, the rectangles fitted around the PSL images did not demonstrate a significant deviation 

from squares, at least to the resolution of the images captured. 

Figure 3. Typical particle size distribution obtained from the particle sizer. 

SD is the standard deviation.
6

Four different spectral analysis techniques were available to test the resulting particles. Each 

method has advantages and disadvantages. The first method uses a low-power fixed-wavelength 

laser as the light source. In this case, the fluorescence was collected with an optical fiber and 

directed into an Ocean Optics USB2000 spectrometer where it was dispersed. A 532 nm 

blocking filter in front of the fiber blocked the laser‘s wavelength. For these laser-based 

measurements, an aliquot of the liquid/PSL particle mixture was placed on a microscope slide 

and the carrier liquid was dried, leaving the dye-doped particles behind. The temperature of the 

microscope slide could be varied using a hot plate in order to study temperature effects. 

Unfortunately, this process was not completely repeatable in absolute intensity, but it produced 

high-quality spectra and was safe and easy to use. 

The second instrument available was a spectrophotometer, which could measure the 

absorption spectrum of the dye-doped 

particles. 

The third instrument was a fluorimeter. In 

the fluorimeter, the excitation wavelength 

could be varied (and an absorption spectrum 

identified) and the emission spectrum could 

be obtained. The advantage of this 

instrument is that the sample concentration 

and optical thickness could be carefully 

controlled because the samples are liquid. 

The drawbacks of this instrument are 

twofold: First, the particles had to be studied 

in a fluid, which changed their spectral 

characteristics compared to the eventual 

application in air (for LDV or PIV). Second, light from the light source could contaminate the 

collected emission, so the spectra had to be interpreted with care. 

The final method of testing the particles was to use a high-powered continuous wave laser to 

probe the particles after they were dispersed into a gaseous flow. Fluorescence was captured by 

a lens-coupled fiber and directed to a photomultiplier tube. A filter in front of the tube blocked 

the laser‘s wavelength and transmitted the fluorescence. This final method, set up at Virginia 

Tech in Blacksburg, VA, was the most time consuming as it involved a much larger setup, a 

setup to atomize the particles, laser safety concerns, etc. Consequently, the first three methods 

were used as screening and learning tools and only promising batches of particles were tested at 

Virginia Tech using this fourth method. 

4. Results 

4.1 Incorporation of dyes into PSLs 

Dispersion/emulsion polymerization, which was the technique used to generate these dyedoped PSLs, is very sensitive to the chemical composition of the dispersion, among a myriad of 

other environmental factors. Thus, incorporation of another chemical constituent, such as a 

fluorescent dye, is likely to impact the resultant PSL size and size distribution. In some cases,

the dye is not incorporated at all. To directly address the impact on PSL characteristics, all of the 

Figure 4. Micrograph of the DCF doped particles at 80x 

magnification. Particle sizes are about 0.8 microns.
7

batches of dye-doped PSLs were synthesized with a target particle diameter of 1 micrometer 

using compositions well established in our research facility.11 Based on a review of 

commercially available dyes with spectroscopic properties relevant to existing wind tunnel 

facilities, several dyes were identified and tested. Several were chosen for low toxicity and 

temperature sensitivity. An additional dye, tetraphenylporphyrin, was identified due to the 

potential to detect pressure variations as well as modify the spectral properties readily by 

incorporation of different metallic ions in the center of the porphyrin macrocycle. Based on the 

literature, a concentration range of 0.6-0.006 mM was selected.9 As can be seen in Table 1, 

several of the dyes used did not result in significant incorporation into the particles. These 

particles did not exhibit fluorescence under illumination and were not further studied. 

Table 1. Fluorescent Dye-Doped PSL Characterization Results 

PSL Light Scattering 

Characterization

Fluorescent 

Characterization

Fluorescent 

Dye

Average 

Diameter, m

Standard 

Deviation, m



exc

, nm 

em

, nm

PSL 

Incorporation notes

No Dye 0.76 0.14 -- -- -- --

Rhodamine B 0.63 0.63 575 595 sufficient, no 

leaching

Potentially 

carcinogenic

DCF 0.77 0.17 512 526 sufficient, no 

leaching

Noncarcinogenic

Kiton Red 620 0.59 0.13 554 575 Leaching 

issues

Noncarcinogenic

Tetraphenyl 

Porphyrin 1.08 0.30 400 655 Inefficient incorporation

Tunable 

spectral 

properties

Pyronin Y -- -- 547a570 Inefficient 

incorporation

Strong 

temperature 

dependence

Erythrosine -- -- 530 a548 Inefficient 

incorporation

Noncarcinogenic 

(Food dye)

aDue to poor incorporation, the fluorescent properties could not be determined with the dye incorporated in a PSL matrix. These 

values are those determined in solution and would likely shift slightly upon incorporation into a PSL particle. 

As detailed in the table, since most of the dyes did not incorporate into the particles or had 

leaching problems, the remainder of this report mainly focuses on the most promising dyes: DCF 

and Rhodamine B. Note that Rhodamine B is considered more toxic than DCF.

4.2 The effect of dye and salts on particle diameter 

Incorporation of fluorescent dyes was determined to impact the PSL particle diameter and size 

distribution. For most cases shown in Table 1, the presence of the fluorescent dye reduced the 

average particle diameter significantly. Similarly, the standard deviation, as a percentage of the 

particle size, increased considerably. Both of these results suggest that the fluorescent dye 

impacted the radical chain polymerization processes that generate the PSLs. A common method 

to modify PSL diameter is to change the ionic strength of the reaction solution (for example, 

changing the concentration of MgSO4). Figure 5 shows how DCF-doped particle sizes changed 

with dye concentration (a) and MgSO4 concentration, presented as ionic strength (b). Ionic 

strength is a measure of the concentration that also takes into account the charges of the ions and 

also includes the ions from the initiator (K2S2O8). Surprisingly, as seen from the graphs, neither 
8

dye concentration nor MgSO4 concentration exhibited a significant influence on the diameter of 

the PSLs. In past work11 the MgSO4 concentration significantly influenced particle size. This 

discrepancy is currently unresolved. 

(a)

(b)

Figure 5. Effect of dye concentration (a) and MgSO4 concentration (b) on particle size for DCFdoped particles. In (a), the electrolyte concentration was constant (using 0.015 mol/L water). In (b) 

the dye concentration was constant (using 0.0093 mol/L styrene).

 4.3 Spectral characterization of the resulting particles 

 Figure 6 shows a comparison of PSLs doped with Rhodamine B and DCF, both excited with 

the same 532 nm laser. The absence of signal near 532 nm was caused by the blocking filter in 

front of the optical fiber. The two spectra have peaks at different wavelengths (about 550 nm for 

DCF and 590 nm for Rhodamine B). The fluorescence from Rhodamine B is approximately 3 

times stronger than that of DCF. 

0

0.2

0.4

0.6

0.8

1

1.2

0 0.002 0.004 0.006 0.008 0.01 0.012

Diameter (um)

Dye Concentration (mol/L styrene)

0

0.2

0.4

0.6

0.8

1

1.2

0 0.005 0.01 0.015 0.02

Diameter (um)

Ionic Strength (mol/L water)
9

 

Figure 6. Comparison of fluorescence of Rhodamine B and DCF dye-doped PSLs, both excited at 532 nm 

As is well known, the spectroscopic properties of many organic molecules with large dipole 

moments are sensitive to the polarity of the environment. This property is termed 

solvatochromism. Rhodamine B is a solvatochromic dye and the influence of solvent polarity on 

Rhodamine B‘s fluorescent properties has been extensively studied.10 Therefore, to verify that 

the Rhodamine B was encapsulated within the PSLs—not simply present in solution or 

physisorbed to the surface—the fluorescent emission characteristics of the Rhodamine B-doped 

PSLs were compared to those obtained from 

Rhodamine B in an aqueous solution (Fig. 7). 

The shift in Rhodamine B‘s fluorescent emission 

to longer wavelengths confirms that it is located 

in an environment with a polarity lower than that 

of water, i.e., it is located in a styrene matrix. 

This observation was further confirmed by 

leaching studies described below. 

4.4 Effect of the dye concentration on 

fluorescence intensity 

By integrating the fluorescence in the spectral 

graphs obtained with laser excitation, a 

qualitative indication can be obtained of the 

effect of adding increasing amounts of dye to the 

PSLs. Figure 8 shows that as the DCF dye concentration was increased, the LIF intensity 

increased, though not linearly. The leveling off of LIF intensity may be caused by self 

quenching of the fluorescence or too much absorption of the laser at high dye concentrations. 

These data are considered qualitative because the process of drying a layer of particles on the 

microscope slide is not repeatable since the thickness of the layer can affect the overall intensity. 

An improved method of making these measurements quantitatively using the fluorimeter is being 

explored. 

0

100

200

300

400

500

600

700

800

500 550 600 650 700 750

Intensity (a.u.)

Wavelength (nm)

Rh B

DCF

Figure 7. Rhodamine B emission properties in an 

aqueous medium and doped in a PSL aqueous dispersion

0

0.2

0.4

0.6

0.8

1

1.2

500 550 600 650 700

Intensity, a.u.

Wavelength, nm

In Water

In PSLs
10

4.5 Leaching Studies 

In order to verify that the dye was truly contained within the PSL, leaching studies were 

conducted. In these experiments, approximately 5 g of the PSL suspension were filtered through 

a polycarbonate filter with 400 nm pores. The filtered solution was collected and visually 

analyzed for fluorescent emission. The filtered particles were re-dissolved in deionized water 

regenerating a solution of approximately the same concentration as the original solution. This 

solution was passed through another 400 nm pore-sized filter with the filtered solution again 

visually inspected for the presence of dye. 

Rhodamine-doped PSLs exhibited excellent dye retention with no detectable fluorescent 

emission from either the first or second filtered solutions (Fig. 9(a)). Kiton red-doped PSLs, 

however, demonstrated significant dye leaching, with the initial filtered solution exhibiting a 

deep red color and the second filtered solution exhibiting a pale pink color (Fig. 9(b)). Similarly, 

the filtered Kiton red-doped PSLs were nearly white upon removal of the second portion of 

solution. DCF-doped PSLs exhibited an interesting phenomenon. The first filtrate did not 

exhibit fluorescent emission, while the second filtrate did. One plausible explanation of this is 

that the pH of the initial solution was acidic—the pH was determined to be approximately 3.5—

while the second solution was neutral. Thus, dye molecules that were physi-sorbed to the 

surface of the PSL exhibited much stronger interactions with the PSL in an acidic environment 

than in a neutral environment. This hypothesis is currently being evaluated. 

0

50000

100000

150000

200000

250000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Integrated Fluorescence (counts)

Dye Concentration (g)

Figure 8. Qualitative fluorescence intensity versus DCF dye concentration doped into in PSL particles. 
11

5. Proof of concept detectivity and temperature measurement 

NASA Langley Research Center and Virginia Tech have collaborated to test the new 

fluorescent particle technologies in small benchtop experiments with a view towards 

transitioning these methods into flow rigs at meaningful conditions and scales. Benchtop 

experiments, detailed below, are being used for proof-of-concept studies 

Experiments have been conducted in a subsonic, variable-temperature round jet at Virginia 

Tech for two purposes: first to assess the single-particle LIF signal quality of Rhodamine-Bdoped PSLs described above and second, to measure the temperature sensitivity of these doped 

PSLs. The experimental setup is shown in 

Fig. 10, in which a free-space diodepumped solid state laser (Coherent, Inc., 

Verdi 18 W) emitting 5 to 6 W, continuous 

wave, 532 nm light to excite the fluorescent 

particles. Mie scattering (at a wavelength of 

532 nm) and fluorescence (at wavelengths 

greater than 600 nm) from the particles 

were collected using a lens system. The 

collected light was coupled into a 

multimode fiber optic which led to a pair of 

amplified photomultipliers, one each for the 

Mie and fluorescence signals. 

The particles were atomized inside a plenum box and mixed with dry compressed air to 

supply the jet. Cooling for jet temperature variation was achieved by placing dry ice inside the 

plenum box, and the jet temperature was measured with a thermocouple at the nozzle exit. Jet 

velocities were on the order of 10 m/s. With this setup, single-particle measurements were 

obtained with significant signals from both the Mie scattering and fluorescence. Signals from 

both Rhodamine B-doped PSLs [example in Fig. 11(a)] and un-doped PSLs [Fig. 11(b)] were 

measured to verify that fluorescence was being detected rather than Mie scattering interference. 

Statistical analysis of the integrated intensity from several thousand bursts such as the example in 

Figure 9. Leaching study results for Rhodamine B (a) Kiton Red (b).

Figure 10. The flow and instrumentation setup for basic 

scattering measurements of PSL particles.  ̳V18‘ indicates the 

Verdi 18 Watt Laser..
12

Fig. 11(a) was conducted to produce the temperature sensitivity data of Fig. 11(c). Therein, the 

mean of the ratio of the LIF to Mie signal strengths, using the Mie signal as a reference for 

incident excitation intensity, is plotted versus jet exit temperature. There is a strong dependence 

of the LIF signal on temperature, evident even for the narrow temperature range studied, which 

may be leveraged in future experiments to directly measure flow static temperature. While the 

mean measurements showed temperature sensitivity, the correlation between Mie scattering and 

LIF was not repeatable on a single-shot basis, therefore preventing single-shot temperature 

measurements from being obtained. The most likely cause of this lack of correlation is particleto-particle variations in dye concentration. Future work will explore solutions to this problem. 

(a) (b) (c) 

Figure 11. Results from the single-particle measurements in cold jets. (a) and (b): single-particle Mie (solid line) and LIF 

(dashed line) photomultiplier signals from a PSL doped with Rhodamine B and an undoped PLS, respectively. (c) Ratio of the 

electronic signal strengths between Mie and LIF as a function of jet exit temperature. 

6. Conclusion 

Development of multifunctional PSL seed materials may enable a variety of experiments 

currently inaccessible to flow physics researchers. The capability of simultaneously measuring 

velocity, temperature, pressure, and/or other environmental parameters will be of paramount 

importance for furthering our understanding of variable-property turbulent shear flows, 

encompassing a wide class of applications. Applications for the new materials include studies of: 

 heated supersonic jets with the intent to reduce noise and increase performance; 

 supersonic boundary layers to obtain turbulent statistics to improve compressible 

turbulence models; 

 turbomachinery film cooling; 

 boundary layer heat transfer to hot and/or cold walls 

Beyond the measurement of pressure and temperature using fluorescence, the fluorescence 

signal may also be used to measure velocity, eliminating the interference of light scattered by 

facility walls. In such a paradigm, high Reynolds number wall flows, which exhibit very large 

gradients of velocity near the wall, may be studied for fundamental understanding of boundary 

layer development in two- and three-dimensional flows. 

In this study, various dye-doped particles have been generated and characterized. The 

presence of the dyes in the particles generally caused the particles to be slightly smaller and have 

a larger size distribution. While several of the dyes did not incorporate into the PSLs, DCF and 

Rhodamine B did produce strong fluorescence signals in the various instruments tested. In the 
13

case of Rhodamine B, the fluorescence was referenced against the Mie scattering, for singleparticles passing through a focused laser volume. As expected, temperature sensitivity was 

observed on a time averaged basis. However the correlation between Mie scattering and LIF was 

not repeatable on a single-shot basis. This approach can be extended to use a crossed-beam 

geometry so that the Mie scattering can be processed as a laser-Doppler velocimetry (LDV) 

signal to simultaneously obtain temperature and velocity in turbulent flows. Future applications 

of this technique would incorporate the temperature sensitive particles into a particle image 

velocimetry (PIV) system for simultaneous planar velocity and temperature measurements. We 

also plan demonstrations with DCF in the same apparatus to determine if it can be used instead 

of Rhodamine B. 

References: 

 

1

J.A. Sutton, B.T. Fisher, J.W. Fleming , "A laser-induced fluorescence measurement for aqueous 

fluid flows with improved temperature sensitivity," Exp. Fluids, Vol. 45, pp. 869-81, 2008. 

2 Dunand P, Castanet G, Lemoine F 2010 "A two-color planar LIF technique to visualize the 

temperature of droplets impinging on a heated wall," 15th Intl. Symp. On Application of Laser 

Techniques to Fluid Mechanics, Lisbon, Portugal, 5-8 July. 

3 B. Frackowiak, C. Tropea, "Analysis of the fluorescence signal from a single droplet using a model 

based on the Lorenz Mie theory and on ray tracing methods," 14th Intl. Symp. On Applications of Laser 

Techniques to Fluid Mechanics, Lisbon, Portugal, 2010 

4 Omrane, A., Peterson, P., Aldén, M., and Linne, M. A., ―Simultaneous 2D flow velocity and gas 

temperature measurements 

using thermographic phosphors,‖ Appl. Phys. B, 92, 2008, pp.99-102. 

5 Brübach, J., Patt, A. and Dreizler, A., ―Spray thermometry using thermographic phosphors,‖ Appl. 

Phys. B, Vol. 83, 2006, pp.499-502. 

6 Omrane, A., Särner, G. and Aldén, M., ―2D- Temperature imaging of single droplets and sprays 

using thermographic 

phosphors,‖ Appl. Phys. B, Vol. 79, 2004, pp.431-434 

7 N. Jain, J. M. Seitzman , T. P. Jenkins, B. Heeg, “Characterization of Thermophosphor Particles for 

Simultaneous Imaging of Velocity and Temperature,‖ 49th AIAA Aerospace Sciences Meeting including 

the New Horizons Forum and Aerospace Exposition, 4 - 7 January 2011, Orlando, Florida AIAA 2011-

1230.

8

S. Someya, Y. Li, K. Ishii, K. Okamoto, "Combined two-dimensional velocity and temperature 

measurements of natural convection using a high-speed camera and temperature-sensitive particles," Exp. 

Fluids, Vol. 50, pp. 65-73, 2011

9 R. E. Benner, P. W. Barber, J. F. Owen, and R. K. Chang ―Observation of Structure Resonances in 

the Fluorescence Spectra from Microspheres,‖ Phys. Rev. Lett. 44, 475–478 (1980) 

10 Kimura F, Khalil G, Zettsu N, Xia Y, Callis J, Gouterman M, Dalton L, Dabiri D, Rodriguez M 

2006 "Dual luminophore polystyrene microspheres for pressure-sensitive luminescent imaging," Meas. 

Sci. Technol., Vol. 17, pp. 1254-60. 

11 Tiemsin P I, Wohl C J ―Refined synthesis and characterization of controlled diameter, monodisperse microparticles for aerospace research applications,‖ NASA technical memorandum, TM-2012-

217591 (2012). 
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Fluorescence-Doped Particles for Simultaneous Temperature and Velocity 

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Danehy, Paul M.; Tiemsin, Pacita I.; Wohl, Chrostopher J.; Verkamp, 

Ma[; Lowe, T.; Maisto, P.; Byun, G.; Simpson, R.

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14. ABSTRACT

Polystyrene latex microspheres (PSLs) have been used for particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) measurements for several 

decades. With advances in laser technologies, instrumentation, and data processing, the capability to collect more information about fluid flow beyond velocity 

is possible using new seed materials. To provide additional measurement capability, PSLs were synthesized with temperature-sensitive fluorescent dyes 

incorporated within the particle. These multifunctional PSLs would have the greatest impact if they could be used in large scale facilities with minimal 

modification to the facilities or the existing instrumentation. Consequently, several potential dyes were identified that were amenable to existing laser systems 

currently utilized in wind tunnels at NASA Langley Research Center as well as other wind and fluid (water) tunnels. PSLs incorporated with Rhodamine B, 

dichlorofluorescein (DCF, also known as fluorescein 548 or fluorescein 27) and other dyes were synthesized and characterized for morphology and spectral 

properties. The resulting particles were demonstrated to exhibit fluorescent emission, which would enable determination of both fluid velocity and temperature. 

They also would allow near-wall velocity measurements whereas laser scatter from surfaces currently prevents near-wall measurements using undoped seed 

materials. Preliminary results in a wind tunnel facility located at Virginia Polytechnic Institute and State University (Virginia Tech) have verified fluorescent 

signal detection and temperature sensitivity of fluorophore-doped PSLs. 

15. SUBJECT TERMS

Laser Doppler Velocimetry; Polystyrene Latex Microspheres

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