Nonintrusive technique to measure the spectral density of a high-velocity turbulent flow

David A. Kalin; Lori C. Brooks; Bruce R. Peters; Jeffrey S. Haight

doi:10.1117/12.154891

15 September 1993 Nonintrusive technique to measure the spectral density of a high-velocity turbulent flow

David A. Kalin, Lori C. Brooks, Bruce R. Peters, Jeffrey S. Haight

Proceedings Volume 1968, Atmospheric Propagation and Remote Sensing II; (1993) https://doi.org/10.1117/12.154891
Event: Optical Engineering and Photonics in Aerospace Sensing, 1993, Orlando, FL, United States

Abstract

A simple technique has been developed to record both the high and low frequency fluctuations contained within an aerooptically distorted 2-D point spread function. A collimated beam of light from an Nd:YAG laser, operated at 1.064 jim, was passed through a high velocity wrbulent flow field and imaged on the focal plane of a 128 x 128 array CCD camera (60 jun square pixels). Extremely short duration (50 nsec) pulses from the laser, synched with a high speed (92 frames per second), video data acquisition system captured one pulse per frame and effectively froze all motion in the flow. Post test averaging of single pulsed frames made it possible to visualize the full range of frequencies contained in the Fourier plane. Investigations are currently being made into the mathematical relationship between these high resolution images and the 2-D power spectrum for the refractive index fluctuations. The technique has the advantages of being non-intrusive and capable of acquiring multiple samples in a short period of time to insure statistical validity. Experimental measurements were performed on the center of a turbulent mixing shear layer (—8 mm thick), generated by back-to-back supersonic nitrogen/argon gas nozzles, with a mean flow velocity of ''380 rn/sec. Calculations were made using horizontal scans through several frames from a single test run. Turbulent scale lengths down to 0.6 mm were resolved.

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David A. Kalin, Lori C. Brooks, Bruce R. Peters, and Jeffrey S. Haight "Nonintrusive technique to measure the spectral density of a high-velocity turbulent flow", Proc. SPIE 1968, Atmospheric Propagation and Remote Sensing II, (15 September 1993); https://doi.org/10.1117/12.154891

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KEYWORDS

Point spread functions

Collimation

Crystals

Fourier transforms

Imaging systems

Wavefront distortions

Atmospheric propagation

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