Preliminary Study for Quantitative Measurement of Flow Fields by Focusing Schlieren Method

Abstract

Recently a large-field and a high-brightness focusing schlieren system was developed to visualize three-dimensional density gradients in flow fields. However, a quantitative experiment seems to be still few, and the accumulation of further data is necessary to verify the quantitative measurement technique. In the present study, a diaphragmless shock tube that is expected good stability and efficiency is used to produce basic flows (utilizing a normal shock wave propagating in the test section). The aim is to apply Cook’s theory to calculate the density distribution in the shock tube flow, and discuss the characteristics of the quantitative parameter of the focusing schlieren system. The results are as follows, on the effect of the source grid (utilizing the vertical, horizontal and lattice grid) for the quantitative consideration, the results of the focusing schlieren method observed the cell structure and the shear layer in the free jet. And it seems that the characteristics of the image have same trend as well as the conventional schlieren method. The density across the incident shock wave becomes small as well as the density gradient, when the quantitative parameters β and N are increased. When the parameters are β = 0.1 and N = 3, the density distributions across the incident shock wave almost correspond to the simple theory in the present experimental condition.