Quantitative colour schlieren development

Authors: Duncan Stevenson Beric Skews

Publish Date: 2014/11/23

Volume: 18, Issue: 2, Pages: 311-320

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Abstract

This work evaluates the potential for producing quantitative data of the density field using a twodimensional colour schlieren system within the test section of a shock tube Density gradient components magnitude and direction form the basis of the quantitative evaluation These are encoded onto an imaging plane by means of a colourcoded source mask placed along the optical axis of the schlieren system Direction is indicated by the relative ratios of the three primary colours red green and blue RGB Magnitude is indicated by the relative intensities of the RGB values Sensitivity of the system is adjusted by an iris diaphragm placed in the cutoff plane The method described is applied to the focusing of a shock wave in a parabolic cavity The experimental results of the schlieren technique are compared to computational simulations with synthetic twodimensional colour and magnitude coding applied to the results The source masks designed and used proved to require a greater intensity light source and thus the design of an LED light source was developed The CFD solutions were converted into an image format directly comparable to the photographic images obtained Image processing techniques have been employed to deconstruct photographs to allow for quantitative comparisons with a calibration lens Density gradient direction has been conclusive however density gradient magnitude is not yet accurately determined due to light source constraintsThe authors wish to thank Harald Kleine Gary Settles Mike Hargather and James Taylor for input on colour schlieren systems and help with the circuits for the light source This research was supported by the South African National Research Foundation

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