TSI Incorporated Copyright© 2008 TSI Incorporated Optical Systems TSI LDV/PDPA Workshop & Training Presented by Joseph Shakal Ph.D.

TSI Incorporated Copyright© 2008 TSI Incorporated Outline Beam Expansion Why Downmix? and Frequency Shifting Probe Setups for 3-Component Systems Transmitting Optics – Fiberlight & Couplers Transceiver & Transmitter Probe Design Pictures of the Optics IC Engine Probe

TSI Incorporated Copyright© 2008 TSI Incorporated Beam Expansion - Effects With a Beam Expander of expansion ratio E, the measurement region has the following effect, for a fixed focal length lens: Diameter: (f / E) 4 f dmdm = ~ 1/3 # of Fringes: Length: l m = d m / E tan k Fringe Spacing:  sin k) d f = N FR dmdm dfdf  4 f  /  D e2 E ~ f / S E   D e2 E Decreases by 1/E E tan k ~ E sin k ~ E (S / 2 f) S/2 f Decreases by 1/E Unchanged Decreases by 1/E 2 f / S E  (f / E) 2 ~ 2/3S

TSI Incorporated Copyright© 2008 TSI Incorporated Frequency Shifting Purpose: 1. To measure flow reversal 2. Extend the range of low and high velocities that can be measured by a processor 3.Maximize coincidence by equalizing the processor input frequencies among all channels (Important for 3D systems) Accomplished by: Downmixing the input signal coming into the FSA

TSI Incorporated Copyright© 2008 TSI Incorporated Problems with Stationary Fringe Pattern 10 Fringe Limit Note: Only one direction is allowed, since reversed flow would give the same frequency. Possible Particle Trajectories Not enough fringe crossings 10 Fringe Limit

TSI Incorporated Copyright© 2008 TSI Incorporated Frequency Shifting & Downmixing Bragg Cell Multimode Fiber Bragg Cell Driver PMT Outputs to FSA Signal Processor Downmixer Scattered Light Fringes Move 40MHz PDM Function of Bragg Cell and Downmixer

TSI Incorporated Copyright© 2008 TSI Incorporated Frequency Shifting & Downmixing PMT Downmixer How does Downmixing affect the Signals? 30 MHz 11.9MHz and 71.9MHz 41.9MHz Filter 2-20 MHz 11.9MHz After Bandpass Filtering

TSI Incorporated Copyright© 2008 TSI Incorporated Setting the Downmix Frequency NN F  when  = 180, for 1/,  cos  N F N 1 d m f s  (transit time) N S f s o v N  cos  N S N 1 N F N F f s f o Where: N f is the number of fringes = d m /d f N s is the # of cycles due to shift N 1 is the maximum # of cycles due to particle motion f o is the corresponding Doppler freq. f s is the shift frequency (40 - Downmix) dmdm  dfdf N N F          cos  f s f o  Transit Time o v d m  2 f o f s vovo

TSI Incorporated Copyright© 2008 TSI Incorporated Changing Downmix setting adds frequency to each and every measurement. It “shifts” the whole distribution left or right. Shift & Downmix

TSI Incorporated Copyright© 2008 TSI Incorporated Downmix Setting with 3D LDV & PDPA When doing three component LDV or PDPA measurements, one of our main objectives is to maximize coincidence. 38MHz Downmix 34MHz Downmix The result is a similar data rate and thus better coincidence on all three channels. Note the Mean Frequency is ~5MHz for all three channels.

TSI Incorporated Copyright© 2008 TSI Incorporated Downmix Setting for Super-Low Velocities Here we use the FSA’s variable downmixing to apply just enough shift to get us into the appropriate frequency band. The minimum input frequency is 0.3kHz for all FSAs. Say we wish to apply 1.5kHz of shift, to start. This will get us into the center of the 0.3-3kHz band. Thus: Bragg Cell Shift = 40MHz (fixed) Desired Shift = 1.5kHz 40, kHz – 1.5kHz = MHz We input MHz to FlowSizer

TSI Incorporated Copyright© 2008 TSI Incorporated Measurement Resolution When measuring a very low velocity, we may use downmixing to put us up into a higher frequency band of the processor, as discussed in the previous slide: Doppler Frequency : f o = v o /d f d f : fringe spacing Frequency Shift: f s = af o (say) a is a const. Net input Frequency to Signal Processor: f o + f s = (a + 1) f o Processor Resolution:  (percent of reading) Resolution on Measuring f o : (a + 1)  If the Doppler Frequency f o is 50kHz, and we use a 36MHz downmix setting, shift will be 4MHz. We then use the 1-10MHz band. Then a ~ 100, and our resolution is 100x worse than if kHz band was used. Using the Lowest Allowable Frequency Band Maximizes Resolution

TSI Incorporated Copyright© 2008 TSI Incorporated Probe Layouts for 1D/2D/3D Measurements 1D and 2D arrangements are simple 3D arrangements require higher flexibility Single-Probe or Two-Probe LDV systems are available from TSI Special considerations for 3D PDPA systems

TSI Incorporated Copyright© 2008 TSI Incorporated Two-Component Measurements– Perpendicular to Optical Axis 2D Probe Green Vertical Blue Horizontal + V1

TSI Incorporated Copyright© 2008 TSI Incorporated Three Component Measurements Three Component Measurements v w u (into page) 2D Probe 1D Probe Measured Components are V 1 V 2 V 3. Orthogonal Components are u, v, w. X Y Z Coordinate System (RHR)

TSI Incorporated Copyright© 2008 TSI Incorporated Three Component System Two probe arrangement Z Green (Unshifted) Green (Shifted) Probe A Probe B Blue (Shifted) V2V2  Blue (Unshifted) Front View Violet (Shifted) Violet (Unshifted) Probe A Probe B Top View Y  V3V3 V 1 (into page) Typical PDPA Receiver Location

TSI Incorporated Copyright© 2008 TSI Incorporated Three Component Measurements Non-orthogonal to orthogonal conversion If probes do not measure orthogonal velocity components, then u, v, w are obtained from transformation matrix. Z Probe A Probe B V2V2 Y (into page) Projections   X, V 1, u V3V3 (Green Vertical)

TSI Incorporated Copyright© 2008 TSI Incorporated Three Component Measurements User inputs the projection matrix, FlowSizer transformation matrix handles inversion V2V2 V3V3 V1V1 = E · v w u = e 1,x e 1,y e 1,z e 2,x e 2,y e 2,z e 3,x e 3,y e 3,z · v w u Measured Values Orthogonal Values Projection Matrix v w u = V2V2 V3V3 V1V1 · E -1 so

TSI Incorporated Copyright© 2008 TSI Incorporated Three Component Measurements cos  -sin  0 -cos  sin  Example Projection Matrices for common layouts “Y” layout shown in previous slides cos  -sin  sin  -cos  sin  0 -cos  -sin  0 -cos  sin  “Y” layout shown in previous slides, but with Probe A inclined at angle  cos  0 sin  0 cos  sin  0 cos  -sin  TR Beam Probe

TSI Incorporated Copyright© 2008 TSI Incorporated Three Component Measurements Two probe arrangements – some difficulties –Measurement in liquid flows Traversing the measuring volume The two measuring volumes do not stay overlapped Need to realign to restore coincidence –Only one small window available Large angle between the two optical axis not feasible Cannot get all the beams into a single window

TSI Incorporated Copyright© 2008 TSI Incorporated TR Component Probe 3D measurements with one probe using 3 colors G B B V G/V B G V B Green and Blue beams may be interchanged for some cases

TSI Incorporated Copyright© 2008 TSI Incorporated Effect of Small Included Angle u or v w  = 1/[  2 sin    kk

TSI Incorporated Copyright© 2008 TSI Incorporated State-of-the-art 3D PDPA System

TSI Incorporated Copyright© 2008 TSI Incorporated Selection of Fiberoptic Probes TM 50 series Transmitter Probe (for PDPA) Probes from 15 mm diameter to 83 mm diameter are available with working distances from 60 mm all the way up to 2m. TR 60 series Transceiver Probe (our largest probe) TR 10 series Transceiver Probe (15mm diameter, our smallest probe)

TSI Incorporated Copyright© 2008 TSI Incorporated Submersible Fiberoptic Probes TR 60 series Transceiver Probes in 3D Configuration TR 10 series Transceiver Probe (15mm diameter) TR 20 series Transceiver Probe (25mm diameter)

TSI Incorporated Copyright© 2008 TSI Incorporated State-of-the-art 3D LDV System Flow behind a rotor

TSI Incorporated Copyright© 2008 TSI Incorporated F IBERLIGHT Multicolor Beam Separator Bragg Cell Amplifier Dispersion Prism Beam Steering Mirror Shifted Unshifted Bragg Cell Input Laser Beam

TSI Incorporated Copyright© 2008 TSI Incorporated Fiberoptics- Types of Fiber  max n 1 > n 2 Fiber Core (refractive index n 1 ) Fiber Cladding (refractive index n 2 ) Acceptance Cone Fujikura SMPP Fiber Slow Axis Multimode Fiber Single Mode Fiber We will examine these in the lab.

TSI Incorporated Copyright© 2008 TSI Incorporated Optical Fibers Single mode fibers –Polarization-preserving fibers SMPP fibers Used for transmitting the beams Core diameter - SMALL! ~ 5  m Multimode fibers –Used to collect maximum scattered light –Larger diameter core ~ 100  m

TSI Incorporated Copyright© 2008 TSI Incorporated Fiberoptic Coupler X-Y Adjustment Knobs Fine Coarse Focus Adjustment Coarse Fine

TSI Incorporated Copyright© 2008 TSI Incorporated Fiberoptic Transceiver Probe Receiving Fiber to PDM Collimating Lenses Receiving Lens Transmitting Fibers Focusing Lens Scattered Light Couplers

TSI Incorporated Copyright© 2008 TSI Incorporated Fiberoptic Transmitter Probe Collimating Lenses Transmitting Fibers Focusing Lens Beam Expander Dashed lines indicate beam locations without beam expander, and with beam expander flipped over for contraction Couplers

TSI Incorporated Copyright© 2008 TSI Incorporated Fiberoptic Probes Accurate collimation of transmitting beams –The waist and focal point coincide –Fringe parallelism is measured Receiver fiber can be precisely positioned to collect light only from the focal point These steps help in making accurate –Near wall measurements –Turbulence intensity measurements Small size of probe allows specialized measurements, like with the TSI IC Engine Probe Adaptor Advantages of TSI Probes

TSI Incorporated Copyright© 2008 TSI Incorporated IC Engine Probe 240gWeight 17MPaMaximum Operating Pressure 204C (continuous)Maximum Operating Temperature 17mmDepth Adjustment Range (max) 19.05mmOuter Diameter 6.4mmClear Aperture AR Coated Fused SilicaWindow 160mmLength* mmTLN01-80EP “Long Stand-off”Lens 0-5.2mmTLN01-50EP “High-SNR” Lens Optional Measurement Distances 0 to 15.9mmMeasurement Distance (TLN01-60EP Lens) 14 x 1.25mmModel EP x 1.25mmModel EP-12 Thread Size Ideal for measuring velocity and turbulence in a unmodified IC Engine

TSI Incorporated Copyright© 2008 TSI Incorporated Conclusions Examined the effect of Beam Expansion, and what it does for us Examined downmixing and guidelines for downmix setting Looked at three-component probe layouts and saw the trade-off between third component resolution and ease of optical access Saw how measured velocities are transformed into orthogonal components Reviewed the available optics and looked at their inner workings Fiber optics allows a high degree of flexibility in measurement, even inside of unmodified IC Engines