Instantaneous energy separation in a jet flow

“Energy separation” is the re-distribution of the total energy in a fluid flow without external work or heat, so that some portion of the fluid has higher and other portion has lower total energy (temperature) than the surrounding fluid. The mechanism of energy separation in a free jet is investigated numerically and experimentally by obtaining predictions and measurements of the instantaneous velocity and total temperature distribution. The enhancement of energy separation by acoustic excitation is also studied.; The numerical study is performed by simulating two dimensional unsteady flow and total temperature field of a plane shear layer and a circular jet with varying Reynolds number. The experimental investigation consists of the flow field measurement, flow visualization and total temperature field measurement. In the flow field measurement, the instantaneous velocity is measured to characterize the motion of the coherent structure of ring vortices and its response to acoustic excitation. The coherent structure and its response to acoustic excitation are visualized by a schlieren technique. A technique of simultaneous measurement of instantaneous velocity and total temperature is developed using two parallel constant temperature hot-wire anemometers. Comparisons of the total temperature measurement results with the flow field measurement results provide information on a link between total temperature fluctuation and the motion of the coherent structure, and the enhancement of energy separation by acoustic excitation.; The results show that the frequencies of dominant total temperature fluctuation coincide with those of velocity fluctuation which represent the passing frequencies of ring vortices at given locations. These confirm that the mechanism of energy separation is induced by the motion of the coherent vortical structure which generates pressure fluctuations within the flow field. The results also indicate that the enhancement of energy separation by acoustic excitation results from vortex pairing processes which are induced by acoustic excitation. By introducing the skewness of the total temperature fluctuation, the characteristics of energy separation can be identified.