1. Phase Doppler Particle Analyzer
2007 TSI LDV/PDPA Workshop & Training
Presented by Joseph Shakal Ph.D.
Copyright© 2008 TSI Incorporated

2. Phase Doppler Particle Analyzer
Light scattering principles and the phase Doppler method
Measuring the phase of the scattered fringe pattern
Validation techniques and error sources
FlowSizer Software
Measurement examples
We will begin with an optical description of the phase Doppler technique, covering the light scattering principles and how phases are obtained. Next we will cover error sources and important validation techniques. FlowSizer will be introduced here, but for practical reasons, it will be covered in the hands-on sessions. We will then look at a few recent measurement cases studies, and talk about the things we had to do in order to make those measurements possible.
Copyright© 2008 TSI Incorporated

3. Light Scattering Principles and the Phase Doppler Method
System Layout
Fringe Patterns
Reflective and Refractive Scatter
Light scattering principles will be introduced, and the importance of system layout will be discussed. We will look at fringe patterns and the two relevant scatter modes- reflection and refraction.
Copyright© 2008 TSI Incorporated

4. Schematic of Phase Doppler Optics
Particle
Optics
Receiving
Angle
Laser A 
Fringes Move
Slit B
FlowSizer C
This is a simplified schematic of the basic components. The Receiving Optics views the measurement region from three slightly different angles, using three different “viewing areas”. Using a Bragg Cell for beam splitting causes the fringes to move. The signals are detected optically by the PDM and converted to analog electronic format. The FSA digitizes these and performs burst detection and burst processing. FlowSizer software package controls the electronics, acquires the data, performs statistical analysis, and provides off-line processing.
Receiving
Optics
PDM
FireWire
FSA
Fiber-optic
Photo-detectors
Signal Processor
Copyright© 2008 TSI Incorporated

5. Actual Fringe Patterns
An actual fringe pattern is shown here. The one on the left is good, although the probe is slightly rotated counterclockwise.
The microscope was moved slightly away from the crossing to generate the image on the right.
At Crossing
Away from Crossing
Copyright© 2008 TSI Incorporated

6. Light Scattering by a Droplet Different Components
Rainbow Angle at ~140 deg
Refraction p = 1
p = 2 m
A simple description of the light scattering phenomena is illustrated in the above figure. A more rigorous description of the light scattering phenomenon is given by the Mie theory. However, the geometrical optics approach using simple ray optics provides a ready insight to the scattering phenomena used in the phase Doppler method.
Shown here are light rays, contained in a laser beam, incident on a spherical particle. To simplify the figure, only the light incident upon the lower half of the sphere is shown. At the first interface, part of the light is reflected from the surface of the sphere and these rays are referred to as p = 0. The light transmitted and refracted by the sphere is referred to as p = 1 rays and rays reflected from the interior surface and refracted in the backward direction are p = 2 rays. The relative light energy reflected from and transmitted through the sphere may be calculated using the Fresnel reflection coefficients.
The light scattering components of either refection or refraction can be measured to obtain information on the particle size. It is also possible to measure the particle size using the measured intensity of the scattered light (deflected by the sphere). However, the scattered light intensity depends upon the particle trajectory through the Gaussian beam and any optical attenuation of the light due to particles and optical surfaces in the beam path.
Rays scattered
at ~30 deg
Reflection
p = 0
Incident Beam (partially shown for clarity)
Copyright© 2008 TSI Incorporated

7. Measuring the Phase of the Scattered Fringe Pattern
Generation of Fringes by Droplets
Fringe Spacing of the Scattered Light Pattern
Reflective and Refractive Fringes
Obtaining the Phase with a Three-Detector Receiver
Detector Spacing
Next we will look at the following important concepts of phase Doppler.
One can use geometric or ray tracing optics OR a wavefront approach to arrive at the fact that a fringe pattern is formed at the detector surface.
We will look at the effect of the scattered light fringe pattern.
We will see a major difference in fringe pattern scattered by refraction and by reflection.
We will look at how the phase shift is generated by the three detector arrangement.
Lastly, we will look at important implications of the detector spacing.
Copyright© 2008 TSI Incorporated

8. Phase Shift of Light Refracted Through a Sphere
Enlarged View 2k P m
Ray 1
This schematic shows a spherical particle located at the intersection of the two laser beams. An enlarged view of the sphere with a light ray from each beam incident upon it is also shown. A ray, which may be regarded as a representative element from each beam, is shown. Since the rays enter the sphere at different angles, they must travel on different optical paths to a common arbitrary point P in space. The particle has a different index of refraction, m, than the surroundings. Since the index of refraction is the ratio of the speed of light in the surrounding relative to the medium, the wavelength will be shorter if m>1.
Because of the different optical path lengths, the wavefronts, shown superimposed on the rays, are shifted relative to each other. The phase shifts will result in an interference pattern in the field surrounding the spherical particle. Interference fringes are bright and dark lines produced by the constructive and destructive interference of the intersecting wavefronts as they combine in phase and out of phase, respectively. The spacing of the interference fringes depend on the beam intersection angle, the light wave length, and the spacing is inversely proportional to the diameter of the sphere. If the sphere is moving, the Doppler difference frequency between the wavefronts scattered from beams 1 and 2 will cause the fringes to appear to move. The Doppler difference frequency can be related to the velocity of the sphere through the following expressions:
v = fD . df
df = l/ (2 Sin k)
where fD is the Doppler difference frequency, l is the light wavelength, and 2k is the beam intersection angle.
Ray 2
Two representative rays are pulled out of the crossing beams
Light rays enter the drop at different angles
Passing on different optical paths to reach an arbitrary point “P” results in a phase shift between the two rays
Phase shift results in constructive and destructive interference in the surrounding space
Copyright© 2008 TSI Incorporated

9. Scattered Fringe Pattern (small particle in the measuring volume)
Scattered fringe pattern (No shift) S S f AB
If the particle acts like a spherical mirror (dominant reflection) or a spherical lens (dominant refraction), it projects fringes from the measuring volume into space all around as diverging bands of bright and dark light, known as scattered fringes.
Scattered fringes as seen on a screen placed in front of the receiver are shown above.
Scattered fringes move across the receiver as the particle moves in the measuring volume, generating temporally fluctuating signals.
Two signals are shifted in phase by sAB / sf times 360°, where sf is the fringe spacing (at the receiver location) of the scattered fringes and sAB is the effective separation between the detector regions A and B.
Measured phase is inversely proportional to the spacing of the scattered fringe pattern sf .
Fringe pattern in the measuring
volume, as seen by the receiver
Copyright© 2008 TSI Incorporated

10. Scattered Fringe Pattern (large particle in the measuring volume)
Scattered fringe pattern (No shift) S S f AB
Because of their lower curvature, large particles create a scattered fringe pattern with a smaller fringe spacing (compared to that for small particles), i.e., particle diameter is inversely proportional to sf .
Measured phase is inversely proportional to the spacing of the scattered fringe pattern sf .
Hence particle diameter is directly proportional to phase shift… and THAT is phase Doppler!
Fringe pattern in the measuring
volume, as seen by the receiver
Copyright© 2008 TSI Incorporated

11. Optimized Three Detector Approach
Intensity
Pattern
Refraction
Signal A
Refraction
Signal B
Phase AB
View into
Front of
Receiver C
Signal C
Phase AC B A
Signal A
TSI utilizes the original patented concept of using three detectors in the measurement of the spacing of the interference fringe pattern produced by the scattered light. This approach has a number of advantages. The three detectors produce two pairs of redundant measurements which are then used to validate the measurements. To help distinguish reflection from refraction, the detectors are designed in an approximate 3.5:1 spacing.
As shown in the diagram, light scattered by refraction will produce a pattern that will move in the opposite direction to light scattered by reflection. The measured signals (shown as 1 bit square waves in the diagram) show how the detectors will report the passage of the signals for the two cases. The scattered fringe pattern direction is opposite that shown earlier because we now account for the Bragg cell shift.
Signal B
Reflection
Phase AB
Droplet is currently
in the Beam Waist
Signal C
Phase AC
Reflection
Copyright© 2008 TSI Incorporated

12. Optimized Three-Detector Approach
Original Detector Arrangement B
Optimized Detector Arrangement B C C
180
360
AC
AB
Phase
The original 1982 Aerometrics and later optimized TSI detector arrangements are shown here.
The general phase versus diameter curves that correspond to these detector separations is also shown. The phase difference between the signals from the closely spaced detectors, A and B follow the lower slope indicated by the dotted lines. The phase between the signals for the detectors with the larger spacing, A and C, follow the curves with the greater slope. With this arrangement, the phase may be measured for detector separations that extend over several fringes (1 fringe corresponds to a measured phase shift of 3600).
The phase of detectors A-B produces a phase measurement of phaseAB and that between A-C produce the phase measurement phaseAC. Using the phase measurement of phaseAB allows the determination of which cycle the measurement of phaseAC occurred. The example shows this logic in which the redundant measurements of phaseAB and phaseAC are made for a particle of size d1.
The two measurements are weighted according to their relative sensitivities and averaged to obtain the mean phase value for that particle. Clearly, the A-C detectors have the greatest sensitivity with the change in phase with a change in particle size being approximately three times the change for detectors A-B.
(AB) 1
(AC) 1 d1
Diameter
Copyright© 2008 TSI Incorporated

13. Optimized PDPA ReceiverB
No masks needed
No planar phases measured
Detector Areas same as Detection Areas
Collimated light input to fibers
Ideal fiber packing ratio
Non-integer detector spacing ratio → leads to non-integer phase ratio C
The TSI PDPA Receiver is optimized by having the following features:
No need for error-prone aperture masks.
Detectors are aligned perpendicular to scattering plane, eliminating “Slit Effect”
“Detector Areas” same as “Detection Areas”, we do not try to couple a narrow slit-shaped region of light into a round fiber.
Collimated light input to fibers for the lowest possible coupling losses.
Ideal fiber packing ratio for minimum interstitial space.
Non-integer detector spacing ratio -> leads to non-integer phase ratio
Higher spacing ratio extends the diameter range
TSI Optimized Receiver is not susceptible to the “Slit Effect”
Copyright© 2008 TSI Incorporated

14. Non-Integer Phase Ratio
View Into the Receiver
~ 75 Fibers A B
Detector Separation AB, DAB
If we could look into the receiver, through the slit, we would see an inverted image of the receiver bundle. Detector region A would appear on top, and C on the bottom. In fact, if you are running the PDPA, partially block off the receiver and watch the C burst signal fade away. The processor triggers off of the A signal, so blocking from the top will gradually stop data collection.
Each detector region has an optical ‘center of gravity’ which would be the theoretical centerline. The distance from the centroid of Detector A to the centroid of B will be called DAB, and the distance from the centroid of A to the centroid of C will be called DAC. A non-integer phase ratio means that the ratio of these parameters is non-integer. In practice, it will be far from integer, eg. 3.5:1, because we cannot obtain an exact numerical value even if we wanted to.
We may also point out that our receiver uses a fiber optic bundle, composed of many fibers in each detector region. Other companies use a single fiber to gather the light from each region. It can be seen that there will be large losses in coupling the rectangular region into a round fiber.
Detector Separation AC, DAC C
DAC / DAB is about 3.5 in RV series Receivers
Copyright© 2008 TSI Incorporated

15. Error Sources and Validation Techniques
Probe Volume Bias
TSI’s 3rd Generation PVC Algorithm
Mixed Mode Scattering
Intensity Validation
Phase Validation: “Diameter Difference”
Next we will look at error sources in PDPA and how we correct for them. Intensity Validation is a unique patented method of examining each diameter measurement for consistency using an independent parameter. Combined with Diameter Difference validation, these techniques help ensure accurate data.
Copyright© 2008 TSI Incorporated

16. Sample Volume or Probe Volume
Defined by the Slit
Defined by the Slit
r(di)
A(di) dw
A(di) I
This figure shows a volumetric schematic of the PDPA sample volume, at the central part of the beam waist.
The sample volume is defined by the diameter, r(di), Area, A(di), and the length, W, along the beam over which the particles may be observed.
The sample volume diameter is a function of the the particle diameter, hence the subscript i. Small particles require a greater illumination to produce a detectable signal, and are only detected in the central region shown. Larger particles can be detected out to a larger diameter. This is precisely the so-called Probe Volume Bias mentioned earlier.
The length is determined by the slit used in the receiver, and receiver angle theta.
The question is:
How do we know what these detection limits r(di) are?  W r 
Copyright© 2008 TSI Incorporated

17. Probe Volume Bias
Question: Why does the sample volume depend on measured drop size?
Answer: Larger drops can pass through the beam anywhere and still produce enough light to be detected
Scattered Intensity: Few mV up to 1000mV
This size and larger can be detected everywhere.
Typically 5 ~ 15um
I(di)m
2r(di)D ID
This slide shows the Probe Volume Bias in another way. Since particles scatter light in proportion to the diameter squared (for d >> 514nm), small particles will need to cross the beams closer to the central peak intensity to produce a detectable signal. Larger particles can pass further out on the edges of the Gaussian and still be detected.
One approach in solving this problem is to use a theoretical description of the Gaussian beam and the assumption that particles scatter light as their diameter squared to generate a theoretical description of the effect. Unfortunately, the measurement conditions vary significantly, which will lead to deviations from the theoretical predictions.
FlowSizer uses a more direct method that measures the effective beam diameter or probe volume diameter for each particle size class for each data set (run) acquired. This in-situ method automatically accounts for the changes in the sampling cross section due to the measurement environment. Details are shown in the following slides.
1/2dw = ro
More in Next Slide
Copyright© 2008 TSI Incorporated

18. Probe Volume Bias
All phase Doppler instruments suffer from probe volume bias.
Bias can be corrected for
May not be detected
Only larger particles detected
Bias can be corrected for
This plot shows an Intensity Validation plot with various droplet sizes shown. Inside of the 1/e^2 Gaussian beam waist, we can correct for the bias or preference towards larger droplets. Outside of the 1/e^2 Gaussian beam waist, the instrument can only detect larger and larger droplets. The smaller ones cannot be detected at all. Without a reference diameter, we cannot correct for the missed samples. The 1/e^2 diameter is commonly used to define the “measurement volume” size.
Bias is corrected for inside the Gaussian beam waist.
Small drops can only be detected in center region.
Copyright© 2008 TSI Incorporated

19. Probe Volume Correction Technique
Path Length Distribution for 2 Runs
0.14 10
Large Drops: Probe volume defined by lower intensity limit
Small Drops: Probe volume obtained from the cumulative distribution of path lengths
0.12 11
0.1
Normalized Counts
0.08
0.06
Integrated
0.04
We can measure the maximum radius (or diameter) for a droplet to be detected by processing the path length distributions of many diameter classes across the measurement range.
Note that the transit time (or Gate Time) multiplied by the velocity, offers a built in measurement scale for the measurement of the effective beam diameter for each diameter class, D(di). This is the path length.
Starting at the smallest diameters, for each size class, a path length distribution is built up for each size class, as shown in the above plot. The trajectories leading to the maximum path length indicate that these droplets passed through the center of the beam. The path length distribution is analyzed for each diameter class. The result of a proprietary algorithm gives the effective measurement diameter (indicated by the arrow above) for each size class.
For larger diameter classes we use the maximum radius defined by the lower intensity limit, or the radius defined by the path length distribution, whichever is smallest.
0.02
5.0E-05
1.0E-04
1.5E-04
2.0E-04
2.5E-04
3.0E-04
3.5E-04
Path Length (m)
Copyright© 2008 TSI Incorporated

20. Intensity Validation
Only TSI’s Intensity Validation can identify the actual flow area:
B, C B A A C
This plot shows an Intensity Validation plot with rejections below the lower cutoff limit. We may be concerned that the data quality is reduced because so many samples are rejected. This is not the case.
These rejections are caused by droplet trajectories (paths) outside of the 1/e^2 cutoff, which are thus outside the assumed beam waist diameter. Others result from reflection and phase wrap. We do not want to keep these, because we cannot do a PVC correction on them, to be sure that there is no bias towards larger droplets.
So with properly applied intensity validation, we end up with less data, but it is more reliable.
But aren’t we throwing out good data? No.
Copyright© 2008 TSI Incorporated

21. Intensity Validation Settings 1/3 Dmax Method
Find Dmax from optics setup
Arrow indicates 1/3 of Dmax
Set slope of upper limit so that it intersects saturation at 1/3 Dmax
PMT voltage & laser power are adjusted so that the data comes close to upper limit
Slope of Lower Limit is set to 1/10 Slope of Upper Limit
This method is difficult to set up if only a small part of diameter range is being used
See FAQ for more details
See Recent Support presentation for more details
So we are convinced of the benefits of Intensity Validation, but how do we set the limits?
When we raise the laser power, signals become stronger. When we raise the PMT voltage both signals AND noise become stronger. For optimum SNR, the laser power is usually increased before the PMT voltage is increased beyond ~450V. When we increase the laser power or PMT voltage, the intensity of all signals increases.
“What laser power should I use?”
“how high should I set the PMT voltage?”
Those are important questions which we know the answer to- namely, “High enough to detect all of the smallest particles.”
All the smallest particles will be detected when we set the laser power and PMT voltage according to the 1/3 Dmax rule, described above.
The method described here was developed in collaboration with Drs. Pete Strakey & Doug Talley at Air Force Research Laboratory. It has been used with success on many types of PDPA systems and ADA (Icing) probes as well.
A FAQ is available with further information.
Copyright© 2008 TSI Incorporated

22. Intensity Validation Settings D10 Stabilization Method
Here is another method to set the PMT voltage and laser power:
When we decrease the laser power or PMT voltage, we are ignoring an additional number of the smallest droplets. When we increase the laser power or PMT voltage, we are including an additional number of the smallest droplets. These are at the point of not being detected by the PDPA, because their signal is so weak (due to their small size).
For certain PDPA configurations with large dynamic diameter ranges, it is advisable to use the D10 stabilization method, given in the PDPA manual.
In the example shown here, my experience would tell me to use the 400V or 425V setting (see arrow).
This method is particularly suitable when the system has an unusually wide diameter range and only a small part is being used
See Manual for more details
Copyright© 2008 TSI Incorporated

23. Intensity Validation on LDV
Rejects: Signals from large particles not tracking the flow
Sub-range out points above a threshold, eg Arrow
Count
Intensity Validation involves measurement of the strength or amplitude of the low pass filtered part of the Doppler burst (pedestal). Then, for validation of LDV signals, apply a threshold using Sub-ranges, above which samples are rejected.
Intensity Validation on LDV thus rejects signals resulting from the following unreliable sources:
Dirt or debris in the flow
Large bubbles in the flow
3) Agglomerated seed particles
Intensity
Copyright© 2008 TSI Incorporated

24. Mixed-Mode Scattering
Internal
Reflection
Reflection
Refraction
Receiver
Reflection
This figure shows schematically how the incident laser light is partitioned between the first surface reflection, a single internal refraction, and an internal reflection. There are other components but these are not shown here.
Note that light scattered by both reflection and refraction reaches the receiver simultaneously. With perpendicular incident polarization (ie electric vector perpendicular to the beam plane), the light intensity scattered by refraction will be approximately 80 times that scattered by reflection, assuming uniform illumination.
On certain trajectories through the beam, the peak intensity will fall on the region of the drop surface where the reflection will reach the receiver. This detection of the incorrect scattering component will lead to sizing errors, unless intensity validation and non-integer phase ratio is used.
Mixed-mode scattering is more prone to occur if the particle passes through the edge regions of the waist, and is similar in size or larger than the waist. That is why optical flexibility and beam expansion/contraction is far more important for PDPA than for LDV.
If the particle moves in a trajectory in the plane of the paper, the reflection and refraction will occur in serial or sequentially. This is referred to as serial scattering, a source of the slit effect.
Reflection
Refraction
Droplet is moving
into the page
Copyright© 2008 TSI Incorporated

25. Copyright© 2008 TSI Incorporated
Intensity Validation
Multiple
Particles
Region
Phase Wrap Region
This plot shows an Intensity Validation plot. Intensity Validation involves setting a minimum and maximum detectable intensity limits.
Intensity Validation gives you valuable feedback on your data, and on how well the PDPA is making measurements.
Intensity Validation relies on the fact that light scattering by reflection is much less efficient than light scattering by refraction.
Intensity Validation thus shows you the rejected signals resulting from the following sources:
Drops passing through the edges of the beam, outside the 1/e^2 waist.
Reflective Signals
Phase Wrap-Around signals
Multiple Particle events
Reflective Signals
Copyright© 2008 TSI Incorporated

26. Reflected Signals from Large Drops
This issue often comes up with dense spray measurements
Intensity validation may fail to reject these
Their effect on mass flux is not significant
Phase validation may be used to reject them via “Diameter Difference” check
Gaussian Intensity Profile
Laser Beams z y
Here is the case of a ‘large’ droplet partially outside the region we define as the waist, by the 1/e^2 intensity limit. “Large” means the droplet is larger than the waist size. Remember that we always set up the PDPA optics with the goal of having the beam waist larger than the largest drop size expected.
Notice that for a large drop on the ‘far’ side of the waist, the part nearer to the receiver is better illuminated. This will enhance the amount of reflected light scattered toward the receiver, even though the polarization is perpendicular to the beam plane, i.e. its horizontally polarized.
Intensity validation may fail to reject these, because they will show up as small drops with low intensity.
Since they appear as small drops, their effect on flux is negligible.
Phase validation may be used to help reject these measurements, however, via the diameter difference check.
To Receiver
Note that droplet is ‘large,’
non-uniformly illuminated,
and just outside the waist
Copyright© 2008 TSI Incorporated

27. Phase Validation: Integer Phase Ratio
360
Refraction
Reflection 3
Phase AC 1
Note that the ratio of Phase AC is 3x Phase AB
Let us say we have a typical RSA based PDPA system. We set it up with the receiver at 30 deg off axis for refraction. The receiver fiber bundle has a detector spacing ratio of about 3:1, nearly an integer value.
If we could generate 1000s of water droplets with diameters ranging from 1um to 1000um, ie. 1um, 2um, 3um, etc. one droplet each. We could cover the entire size range of this typical PDPA. Then, if we plot the two measured phases, we would see a plot like shown here. Namely, we would trace out the solid line for refraction.
0 deg phase corresponds to the smallest size, & larger phases corresponds to larger sizes.
Now lets say we then change to black ink and set the receiver up at 150 deg backscatter, and turn it over so that the arrow points upwards. Now we repeat the above experiment, generating 1000s of water droplets from 1um to 1000um, we would trace out the line labeled ‘Reflection’ with larger droplets having smaller & smaller phase values.
The point here is that the two lines nearly overlap. They follow one another very closely.
Plot taken from Lisbon 2000 paper by A. Naqwi, J. Shakal, & C. Fandrey
360
Phase AB
Copyright© 2008 TSI Incorporated

28. Phase Validation: Non-integer Phase Ratio
360
Refraction
Reflection
Phase AC
3.5 1
Let us say we now have a typical FSA based PDPA system, with RV series receiver. We set it up with the receiver at 30 deg off axis for refraction. The receiver fiber bundle has a detector spacing ratio of about 3.5:1, far from an integer value.
If we repeat the droplet experiments with the receiver at 30 degrees for refraction, we would trace out the solid line for refraction.
Again, 0 deg phase corresponds to the smallest size, & larger phases correspond to larger sizes.
We again then change to black ink and set the receiver up at 150 deg backscatter, and turn it over so that the arrow points upwards. We would trace out the line labeled ‘Reflection’ with larger droplets having smaller & smaller phase values.
The point here is that the two lines are rarely near each other. They follow very different paths.
Plot taken from Lisbon 2000 paper by A. Naqwi, J. Shakal, & C. Fandrey
Note that the ratio of
Phase AC is now
3.5x Phase AB
360
Phase AB
Copyright© 2008 TSI Incorporated

29. Copyright© 2008 TSI Incorporated
Phase Validation
Actual Data
Indicated measurements would appear outside our 7% limit
360
Mismatch Limit, Typ 7%
Phase AC
The above figure shows the diameter vs diameter difference (or “Epsilon”) plot for a spray, measured in refraction. Notice that the data grouping is centered on zero, indicating the phase calibration is fine.
On the right is the Phase AB -vs Phase AC plot from the previous slide. When the measurement is valid, the two phases lie somewhere on the solid zig-zag line. Setting a diameter difference mismatch limit of 0.0 would require the measurement to fall exactly on the solid line, a rarity in the real world.
Diameter Difference validation involves setting a reasonable limit (usually 7%) for diameter mismatch between detectors AB and AC.
Then, since we are in refraction, most measurements due to reflection will end up outside the 7% limits and be rejected.
360
Phase AB
Copyright© 2008 TSI Incorporated

30. Copyright© 2008 TSI Incorporated
FlowSizer 2.0 Software
New Fitting Routines
FlowSizer 2.0 LDV/PDPA software is very easy to use and comes in a single package. User customizable graphs and statistics windows means you never have un-needed clutter on the screen. Advanced programmable traverse control and power spectrum analysis are included with every system.
Flowsizer computes all the diameter statistics, performs validation checks, and allows user-specified analysis on any parameter with the Sub-range feature. Five diameter fitting routines are available, to allow easy transfer of diameter distribution functions to computational software packages.
Copyright© 2008 TSI Incorporated

31. Measurement Case Studies
Pulsed Bio-Diesel and Common Rail diesel spray (2 cases)
Flux Profile of a DI Gasoline spray
Condensing flow at a turbine outlet
Mach 2 scramjet engine flow
Aircraft based hurricane measurements
Turbine engine combustor
Nasal Inhaler Spray
Next we will look a few recent measurement examples.
Copyright© 2008 TSI Incorporated

32. PDPA Measurements by FSA 4000
Pulsed Diesel Injector
Shown here is FSA 4000 PDPA data from a pulsed Diesel injector, 8 total injections. Data overlay and running averages of axial velocity and diameter are shown for a measurement point 50mm downstream of the nozzle. The lower right plot shows a time series of diameter, indicating the 8 individual injector ‘shots’.
100% Bio-Diesel Fuel
Copyright© 2008 TSI Incorporated

33. High Density Diesel Spray
Shown here is data from a common rail type diesel injector, injected into a SF6 atmosphere.
Measurement was done 45mm downstream, 0mm off axis.
Rail Pressure was 1200bar. 1.5W laser power was used. A 25um receiver slit was used.
Velocities exceeding 100m/s are visible, data are not lost inside the spray, and the volume distribution is smooth, indicating a high quality data set.
For this spray, the Mean diameter was 15um, SMD was 21um.
It is known that ligaments and other structures may dominate the flow at the centerline of hole type injectors, so there is an upper limit to the data available to be measured.
TSI-64
Courtesy CMT – Polytechnic Univ. Valencia
Copyright© 2008 TSI Incorporated

34. High Density Diesel Spray
Extended Diameter Statistics
Diameter Statistics
Shown here are diameter results for the common rail type diesel injector data in the previous slide.
Diameters are seen to be more normally distributed than for older plunger-type injector pumps. The question must be asked, however, as to whether these distributions hold when using the common rail system with rate-shaping injectors.
Courtesy CMT – Polytechnic Univ. Valencia
Copyright© 2008 TSI Incorporated

35. Flux Profile of a G-DI Spray
Excellent Repeatability
With TSI’s patented intensity validation and probe volume correction (PVC), we can get very accurate and reliable diameter measurements, like D10, SMD, MVD, etc. But intensity validation’s effect on zeroing in on the correct laser power and PMT voltage have a remarkable effect on flux and concentration. These values become very accurate. Shown here is a flux profile for a Gasoline Direct Injector (G-DI) spray, with the most dense center point measured first and again measured last. Results are impressive for this dense spray.
Copyright© 2008 TSI Incorporated

36. Flux Profile of a Coolant Spray
With TSI’s patented intensity validation and probe volume correction (PVC), we can get very accurate and reliable diameter measurements, like D10, SMD, MVD, etc. But intensity validation’s effect on zeroing in on the correct laser power and PMT voltage have a remarkable effect on flux and concentration. These values become very accurate. Shown here is a flux profile for a Gasoline Direct Injector (G-DI) spray, with the most dense center point measured first and again measured last. Results are impressive for this dense spray.
A New Method for Minimizing Volumetric Flux Errors Associated with PDPA Measurements in the Dilute Region of Full Cone Pressure Swirl Atomizers, ICLASS 2006, Paper #
Copyright© 2008 TSI Incorporated

37. High Density Condensing Flow
Diameter Measurement Statistics
Raw PVC
D10 (um)
D20 (um)
D30 (um)
D32 (um)
Coinc. Size Data Rate (Hz) 5737
Particle Conc.(1/cc ) 1,175,879
Measurement of a condensing flow at the outlet of a turbine.
Notice the particle size and concentration.
Waist Size 16um
Laser Power ~4W
Copyright© 2008 TSI Incorporated

38. Copyright© 2008 TSI Incorporated
High Speed Flow
This slide shows data from an aerated liquid jet in a supersonic cross-flow from Dr. Steven Lin at AFRL-Wright Patterson Air Force Base. The injected liquid was water, the freestream gas was air.
The liquid injector diameter was 0.5mm, the Jet-to-freestream momentum flux ratio was 7, the injector gas-to-liquid mass ratio was 5%, and measurements here are at 100mm downstream.
The statistics speak for themselves.
Notice the data rates, validation rates, and mean gate time.
Next slide shows a composite of many measurements in the test section of this wind tunnel.
Courtesy Dr. Kuo-Cheng Lin This work was sponsored by AFRL/Propulsion Directorate at Wright-Patterson Air Force Base
Vmean = 595m/s
Freqmean = 118.8MHz
Valid Vel = 100%
Valid Dia = 91.7%
Gate Timemean = 110nsec
Data Rate: Ch 1 = 55.8kHz, Ch 2 = 26kHz
Copyright© 2008 TSI Incorporated

39. PDPA Measurements in Supersonic Wind Tunnel (Jet in Crossflow)
Mach 1.94
d0=0.5 mm
q0=7
GLR=5%
x/d0=200
These and other results showed that aerated jets dispersed more rapidly than non-aerated jets. Atomization was complete by 100 orifice diameters downstream, after which the SMD shows much reduced variation. Moreover, it was found that normalized centerline droplet size and streamwise (x) velocity profiles collapse to universal “S” type curves. This result can be useful for modeling far-field distributions of liquid jets in supersonic cross flow environments.
More results can be found in AIAA paper
Lin, K.-C., Kennedy, P.J., Jackson, T.A., “Structures of Water Jets in a Mach 1.94 Supersonic Crossflow,” AIAA Paper , January This work was sponsored by AFRL/Propulsion Directorate at Wright-Patterson Air Force Base
Copyright© 2008 TSI Incorporated

40. PDPA Measurement of a Spray in an Acoustic Field
Water Spray
Dual Speakers
Resonance Chamber
These and other results showed that aerated jets dispersed more rapidly than non-aerated jets. Atomization was complete by 100 orifice diameters downstream, after which the SMD shows much reduced variation. Moreover, it was found that normalized centerline droplet size and streamwise (x) velocity profiles collapse to universal “S” type curves. This result can be useful for modeling far-field distributions of liquid jets in supersonic cross flow environments.
More results can be found in AIAA paper
Courtesy Prof. R.I.Sujith and K. Gurubaran, Dept. of Aerospace Engineering, IIT-Madras, India
See AIAA paper for more details.
Copyright© 2008 TSI Incorporated

41. PDPA Measurements in a Lean Low-NOx Aircraft Combustor
SMD with Combustion
Lean Low NOx Combustor (GE CFM 56 Engine)
Aircraft makers are under pressure to reduce NOx emissions from airplanes during flight. NOx is a primary target because it is released in the upper atmosphere by the planes, and does not have a chance to undergo the cleansing action of passing through the lower atmosphere. This study aimed to refine a LES effort of the combustor by acquiring turbulence (LDV) and spray droplet size data for the operating lean low-NOx combustor. The PDPA performed well and large volumes of data were acquired.
More results are found in the paper “Flow Field Measurements in a Counter-Swirling Spray Combustor“ by J. Colby, S. Menon, and J. Jagoda, presented at the 41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibition, July 13, 2005.
Courtesy of Jonathan Colby and Georgia Institute of Technology
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42. LDV Measurements in PPL Combustor
Cold Flow
Lean Low NOx Combustor (GE CFM 56 Engine)
Combustion
This slide shows data from a premixed pre-vaporized lean (PPL) type aircraft combustor. Here, fuel efficiency and NOx emissions are the main concern. This translates into how to burn the fuel in a short amount of time, in spite of overall lean and low temperature conditions. Turbulence is the answer, and TSI’s LDV system can measure turbulence in this combustor, even with the flame present.
Courtesy of Jonathan Colby, Georgia Institute of Technology
Fuel Rate = 0.75g/s
Eq. Ratio = 0.4
Tair = 380K
Twall = 540K
Courtesy of Jonathan Colby, Georgia Institute of Technology
Copyright© 2008 TSI Incorporated

43. PDPA Measurements in Hurricane
NOAA research aircraft N43RF
A PDPA system was mounted inside a NOAA research airplane, and used to study precipitation sources during hurricanes over water. Hurricanes have high winds which cause large waves and high foaming of the sea, which generates mist. This is combined with condensation from clouds to result in heavy rainfall during hurricanes. The long-term goal is to use the PDPA for measuring size-segregated droplet concentrations and fluxes at high wind speeds in the atmospheric boundary layer (ABL) in order to understand the dynamics of droplets at high wind speeds.
See Report “Measurement of the Sea Spray Droplet Size Distributions at High Winds” filed under Award Numbers N and N (DURIP)
Hurricane Jeanne 9/25/04
Courtesy of Prof. Bill Asher and Trina Litchendorf, APL, Univ of Washington
Copyright© 2008 TSI Incorporated

44. Nasal Inhaler Spray Measurements
100ms
200ms
300ms
400ms
Measurements were made in externally triggered mode
A PDPA system was used to measure a commercially available medication packaged in a nasal inhaler (for asthma). The inhaler had a trigger signal generator to generate a TTL pulse when it was actuated, allowing time-resolved data to be taken. Here we see diameter and velocity trends within the spray event, which only lasts for a fraction of a second.
Time-averaged diameter
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45. Copyright© 2008 TSI Incorporated
Other Comments
Transient Measurements
When an electronically triggered device is being measured, it is
often interesting to look at time histories. You can use the “Sync
Pulse” input to act as an OPR signal with FlowSizer 2.0 and current FSA’s.
EB option and OPR input is the best way to trigger FSA though.
Use of a Traverse
It is easy to create and run scans through the flow, with the Traverse GUI in FlowSizer. Scans can be saved, and edited in Excel.
The FSA makes it easy to look at transient results. The benefit of going to the External Input board option is the ability to look at results using coincidence and having results overlaid in time.
Use of a traverse is simplified. Demos using a 1D traverse are encouraged, in order to promote the aspect of using the PDPA as a 1D or 2D measurement tool, rather than a point measurement tool.
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46. Copyright© 2008 TSI Incorporated
Conclusions
We have seen how the droplet scatters light
Fringe pattern is detected from three angles, resulting in phase difference
Phase is linearly related to diameter
Intensity Validation works with Probe Volume Correction (PVC) to give reliable results, even flux
Phase Validation provides backup to Intensity Validation
PDPA systems used in many applications, worldwide
We have looked at key features of the FSA based PDPA and LDV system
Intensity Validation eliminates need for arbitrary & cumbersome masks
Optimized Receiver not susceptible to slit effect
Phase Validation (Diameter Difference) provides backup support to Intensity Validation
New measurement areas are now possible – Highly dense, high speed
Copyright© 2008 TSI Incorporated