10 November 2003 Theory and application of quantitative, bidirectional color schlieren for density measurement in high speed flow
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Abstract
This paper describes a quantitative schlieren technique called Calibrated Color Schlieren (CCS) that is capable of measuring the light deflection angle in both spatial directions simultaneously and hence is able to extract the projected density gradient of a two-dimensional flow. CCS makes use of a graded color filter in combination with a square source of size whose size may be varied to change the sensitivity. A calibration polynomial is used to obtain the deflection angle from color ratios at each pixel. The technique’s performance was assessed in terms of repeatability, sensitivity and accuracy using the Prandtl-Meyer expansion fan at the wedge-plate shoulder in a supersonic flow. From the measured deflection angles the density gradient and the density are computed. The density information agrees well with Prandtl-Meyer theory. The technique is also applied to a more complex wake flow, which required the use of a color correction based on a shadowgraph image.
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David W. Watt, David W. Watt, Gerrit E. Elsinga, Gerrit E. Elsinga, Bas W. van Oudheusden, Bas W. van Oudheusden, Fulvio Scarano, Fulvio Scarano, } "Theory and application of quantitative, bidirectional color schlieren for density measurement in high speed flow", Proc. SPIE 5191, Optical Diagnostics for Fluids, Solids, and Combustion II, (10 November 2003); doi: 10.1117/12.510781; https://doi.org/10.1117/12.510781
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