Multidirection Speckle Photography of Density Gradients in a Flame

Abstract

The present investigation deals with simultaneous one-, twoand four-directional measurements of density gradients in different cross sections of an axisymmetric and a slightly asymmetric open flame, as well as with temperature profiles determined using the mesurements. The doubleexposed speckle photography methods are adopted to make measurements in an open flame. The principles of speckle field formation, of obtaining quantitative information about the test object by using the Young interference fringes, and of applying the speckle photography to study gasdynamic flows are considered. It is shown that density gradient integrals in the observation direction in a test flame are of the order of 0.1 to 3 kg/m, whereas the ultimate sensitivity of speckle photography amounts to 0.05 kg/m. The asymmetry of a test object may be estimated by imposing temperature profiles simultaneously in four directions. The main advantages of the speckle photography methods are emphasized over the traditional ones.