A dual-scatter laser Doppler velocimeter (LDV) system designed for measuring wind tunnel flow velocity is described. The system simultaneously measures two orthogonal velocity components of a flowing fluid at a common point in the flow. Essential single-velocity component dual-scatter concepts are presented to simplify the description of the more sophisticated two-component system. To implement the two-component system three laser beams with a 0 degrees , 45 degrees , and 90 degrees polarization plane relationship are focused to a common point in the flow by the system-transmitting optics. The beams interfere to form two perpendicular sets of interference fringe planes that are orthogonally polarized. The system-receiving optics collect and separate the orthogonally polarized components of laser radiation scattered from micron-size particles moving with the flowing fluid through the ringes. The system requires no artificial seeding, since intrinsic test section aerosols are utilized for radiation scattering. The passage of each scatter particle through the interference fringes simultaneously produces two frequency-burst-type photodetected signals, the frequencies of which are directly proportional to two perpendicular components of particle velocity. The system photodetection, signal-conditioning, and data acquisition instrumentation is specifically designed to process the frequency burst information in the time domain as opposed to spectrum analysis or frequency domain processing. The system was initially evaluated in an AEDC wind tunnel operating over a Mach number range from 0.6 to 1.5. The LDV and calculated wind tunnel mean velocity data agreed to within 1.25%; flow direction deviations of a few milliradians were resolved.

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Approved for public release; distribution unlimited. '7 DISTRIBUTION STATEMENT (of the abstract entered in Block 20, II dillerenl from Report) IB SUPPLEMENTARY NOTES Available in DDC KEY WORDS (Continue on reverie side It necessary and Identity by block number)lasers cells (Bragg) signal to noise ratio speed indicators instruments (electronic) measurements aircraft density vortexes (trailing) ABSTRACT ("Continue on reverse side // necessary and identity by block number)This report summarizes a three-year analytical and experimental program to develop a dual-scatter laser velocimeter system to map the flow fields of trailing vortices stemming from the wingtips of flying aircraft. The basic design parameters ascertaining feasibility of the LV-measuring technique are presented.Included is a discussion and evaluation of a newly developed two-dimensional Bragg cell (TDBC) for resolving direc-DD i JAN"73 1473 EDITION OF 1 NOV 65 IS OBSOLETE UNCLASSIFIED UNCLASSIFIED 20. Abstracttional ambiguity. The electronics instrumentation developed for the operation of the TDBC is evaluated in detail. In addition, the development of a direct readout system yielding considerable improvement over the initial instrument is described and evaluated. A number of significant proof-of-principle experiments made at the AEDC runway of trailing vortices created by NASA-operated aircraft are discussed and evaluated. The conclusions derived from the test programs are enumerated, and a conceptual design of a mobile trailing-vortex-measuring system is described.

A newly developed signal processing and data handling system for use in laser velocimetry is described. The system provides for entry into lower signal-to-noise ratio environments for capture of data from smaller particles than was formerly practical. Experimental data from a two-component Bragg cell directional velocimeter is used in comparing the system with a conventional counter-type processor. Dramatic improvement in the ’’particle lag problem’’ is seen.

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