Proper Orthogonal Decomposition Analysis of Shear-Coaxial Injector Flows with and without Transverse Acoustic Forcing

摘要

This experimental study investigated the response of dynamic flow structures of cryogenic coaxial nitrogen jets to pressure perturbations due to transverse acoustic forcing at a pressure antinode (PAN). The role of injector exit geometry on the flow response was examined using two shear coaxial injectors with different outer-to-inner jet area ratios. Flow conditions spanning subcritical (reduced pressure of 0.44) to supercritical (reduced pressure of 1.05) chamber pressures, varying outer-to-inner jet momentum flux ratios (0.5 - 20), and acoustic pressure antinode at the jet axis location were considered. A basic application of proper orthogonal decomposition on the intensity fluctuation of high-speed images enabled the extraction of the spatial and temporal characteristics of the dominant flow structures that existed in the flow field during exposure to acoustic forcing. Regardless of injector geometry or pressure regime, low outer-to-inner momentum flux ratio flows were found to be responsive to acoustic pressure antinode forcing. With increasing momentum flux ratio, however, the flow response to forcing depended on the injector geometry.