Determination of turbulent flow properties by a penetrating beam dynamic shadowgraph method

Abstract

The unsteady fluctuations due to turbulent flow which occur at points on the image plane of a shadowgraph visualisation system are measured using a small photodetector. The characteristics of the output signal have been investigated to determine when it has linear response to the turbulent fluctuations, and to verify that it has the expected spectral composition. It has been found that the signals are related in magnitude to the difference in density between the mixing air jet flow and the ambient air surrounding the turbulent mixing flow. Distributions of the optical shadowgraph fluctuations have been transformed by an Abel integral method to yield radial distributions of the turbulent density fluctuations within the mixing region.