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TSI Incorporated Copyright© 2005 TSI Incorporated Laser Doppler Velocimetry: Introduction TSI LDV/PDPA Spring Workshop & Training Presented by Joseph Shakal.

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Presentation on theme: "TSI Incorporated Copyright© 2005 TSI Incorporated Laser Doppler Velocimetry: Introduction TSI LDV/PDPA Spring Workshop & Training Presented by Joseph Shakal."— Presentation transcript:

1 TSI Incorporated Copyright© 2005 TSI Incorporated Laser Doppler Velocimetry: Introduction TSI LDV/PDPA Spring Workshop & Training Presented by Joseph Shakal Ph.D.

2 TSI Incorporated Copyright© 2005 TSI Incorporated Laser Doppler Velocimetry Light Scattering Principles Fringe Formation Characteristics of Scattered Light Doppler Signals Properties of the Measurement Volume (Beam Waist) System Optics Conclusion

3 TSI Incorporated Copyright© 2005 TSI Incorporated Laser Doppler Velocimetry i(t) Signal is a Time Varying Current Photodetector (PMT) Flow Illuminating Beams Scattered Light

4 TSI Incorporated Copyright© 2005 TSI Incorporated LDV Hardware Components Signal Processor FSA Particles moving with the fluid Photo- detector No Probe in the FlowSmall Measuring Volume No Velocity CalibrationLarge Dynamic Range Desired Velocity Components High Frequency Response measured Directly Transmitting Optics Receiving Optics Laser

5 TSI Incorporated Copyright© 2005 TSI Incorporated Fringe Description dfdf d ud f x f D f    2sin = Wavelength of incident light = Frequency detected at PMT f D Transmitting Optics Actual Fringes

6 TSI Incorporated Copyright© 2005 TSI Incorporated Fringe Description uxux  Focal Length = f u d f x   2 sin K d f d f f D f Focal Distance Particle crosses a fringe Pedestal

7 TSI Incorporated Copyright© 2005 TSI Incorporated Collection Optics Location Backscatter  Receiver  Forward scatter  Transceiver Off-axis Backscatter Off-axis Forward Scatter Receiver Not Here

8 TSI Incorporated Copyright© 2005 TSI Incorporated Scattered Light Intensity Variation Log Scale Linear Scale

9 TSI Incorporated Copyright© 2005 TSI Incorporated Typical Frequency vs. Velocity Curves  nm  14    14  E E E ,000 Velocity (m/sec) Frequency, MHz = nm  = 14 0  = Typ. Frequencies Typ. Velocities

10 TSI Incorporated Copyright© 2005 TSI Incorporated Spectrum of Doppler Signal and Filtering SignalAfter high pass filter (HPF) After low pass filter (LPF) Frequency Power Pedestal DopplerHPFLPF Noise Sum Frequency

11 TSI Incorporated Copyright© 2005 TSI Incorporated Measurement Volume 1 1/e 2 Intensity d m is the diameter of the measurement volume, or in other words, the 1/e 2 waist diameter dmdm dmdm

12 TSI Incorporated Copyright© 2005 TSI Incorporated Measurement Volume Dimensions  Beam Diameter D e-2 l m = d e2 / sin   S z x y   z x 1/e 2 Contour d m Fringes l m y D e -2-2 V  6 cos 2  sin  3  /( d e2 Beams are in plane of page d e2 = 4 f /  D e-2  Focused Beam Dia. d e2 d e2 = diameter here d m = d e2 / cos 

13 TSI Incorporated Copyright© 2005 TSI Incorporated Measurement Volume Parameters f = 120mm Example: Measurement Volume Diameter  d m  m, → “small” d m ~ f / 4since  ~ 0.5  m d e2 = f4  e D 2  d m ~ d e2 / 1 d m ~ f  / 2since D e2  ~ 2.5mm Units: D m will be in  m, if in  m, f in mm, D e2 in mm since  is small (from previous slide) d m = d e2 / cos  and Diameter of Measuring Volume:

14 TSI Incorporated Copyright© 2005 TSI Incorporated Measurement Volume Parameters Example : TR-260 probe, f = 250 mm, S = 50 mm Length of Measuring Volume l m = d m / sin  Fringe Spacing dfdf f S  f S  2 sin K ~ ~ 0.5 l m = 10 d m = 620  m and d f = 2.5  m e D -2-2  f S tan  ~ sin  ~ (S/2) / f (from previous slide) so l m = 2 f d m / S = f d m / 25

15 TSI Incorporated Copyright© 2005 TSI Incorporated Measuring Volume Parameters Example N FR dmdm dfdf  4 S  e D 2  Note: N FR is independent of focal length ( f) and beam expansion N FR ~ S / 2 if S is in mm, since D e2 ~ 2.5mm for S = 50 mm, N FR = 25 (for = 2.6 mm) e D 2  4 f  /  D e2 f / S   Number of Fringes

16 TSI Incorporated Copyright© 2005 TSI Incorporated System Parameters Many of these parameters are found in the FlowSizer Run Setup -> Optics tab.

17 TSI Incorporated Copyright© 2005 TSI Incorporated Total System Parameters All these parameters and many more are found in the PDPA LDV performance spreadsheet

18 TSI Incorporated Copyright© 2005 TSI Incorporated Considerations in LDV Optimize Optics and Seeding for: –Physical Limits of Experiment –Flow Media –Laser Power Required for Good Signals (SNR) –Adequate Spatial Resolution –Required Data Density Select Signal Processor Based on: –Frequency Range Required (Maximum Flow Velocity) –Bandwidth (Dynamic Range) –Required Flow Information Next we look at some applications

19 TSI Incorporated Copyright© 2005 TSI Incorporated Turbulence Characteristics of a Swirling Jet Full turbulence statistics measured with a 3D LDV system. See AIAA paper number for details. Courtesy of Courtesy of Prof. J. Naughton and R. Semaan, Dept. of Mechanical Engineering, Univ. Wyoming.

20 TSI Incorporated Copyright© 2005 TSI Incorporated Turbulence Characteristics of a Swirling Jet Axial normalized turbulent stress distribution (uu/U 2 o ) for a swirl number of 0.39, Reynolds number of 100,000, and solid body type swirl. See AIAA paper number for details. Courtesy of Courtesy of Prof. J. Naughton and R. Semaan, Dept. of Mechanical Engineering, Univ. Wyoming.

21 TSI Incorporated Copyright© 2005 TSI Incorporated High Speed Flow V mean = 595m/s Freq mean = 118.8MHz Valid Vel = 100% Valid Dia = 91.7% Gate Time mean = 110ns Data Rate: Ch 1 = 55.8kHz, Ch 2 = 26kHz Courtesy of Dr. Steven Lin, TaiTech Inc.

22 TSI Incorporated Copyright© 2005 TSI Incorporated Analysis of a Fluttering Flow

23 TSI Incorporated Copyright© 2005 TSI Incorporated Aircraft Turbine Combustor Fuel Rate = 0.75g/s Eq. Ratio = 0.4 Tair = 380K Twall = 540K Courtesy of Jonathan Colby, Georgia Institute of Technology Lean Low NOx Combustor (GE CFM 56 Engine) Cold Flow Combustion Courtesy of Jonathan Colby, Georgia Institute of Technology

24 TSI Incorporated Copyright© 2005 TSI Incorporated Phase Discriminated LDV Wave Machine Sand is Transported off the Crests (Dispersed Phase) Use a single probe, Ar ion wavelengths NO dyes, NO wavelength filtering, NO expensive spherical particles required Uses ordinary seeding particles and ordinary sand Tracers in the Water (Continuous Phase)

25 TSI Incorporated Copyright© 2005 TSI Incorporated Phase Discriminated LDV We do not expect the typical I scatter ~ d 2 to hold for irregular particles However, regardless of particle shape, surface texture, etc. larger particles are expected to scatter more light than smaller particles “Borrow” burst intensity measurement capability from PDPA* Measured burst intensity histogram: * US Patent Sand Tracers

26 TSI Incorporated Copyright© 2005 TSI Incorporated Phase Discriminated LDV Compare intensity distribution for various measurement locations Sand Tracers In the crest region (both sand and tracers) On the bed (sand only) In the free stream (tracers only)

27 TSI Incorporated Copyright© 2005 TSI Incorporated Phase Discriminated LDV Tracers (Continuous Phase) 0.5Hz 1Hz 34cm/s Sediment (Dispersed Phase) 0.5Hz 30cm/s

28 TSI Incorporated Copyright© 2005 TSI Incorporated Probes for Underwater LDV Prism Attachments Sealed Stainless Steel Probes

29 TSI Incorporated Copyright© 2005 TSI Incorporated Conclusions Special properties of laser beams allow us to generate fringe patterns Particles are added to flow, their velocity is measured Light is scattered in all directions, but not uniformly Different lens focal lengths give different fringe spacings Fringe crossing rate of particle generates Doppler frequency Velocity is determined directly from Doppler frequency Multitude of applications


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