Correlation of Flow Structures and Radiated Noise in High Speed Jets

摘要

The dynamics of large-scale turbulence structures within a high Reynolds number, ideally expanded Mach 1.3 jet were investigated during both the periods of production of strong acoustic radiation and extended periods of relative quiet that lacked such acoustic radiation. These results were acquired through a unique experiment where the sources of large amplitude sound waves were estimated with a three-dimensional microphone array and the flow field was simultaneously visualized on two orthogonal planes. The images from one of the planes were taken at a 167 kHz rate. Proper Orthogonal Decomposition (POD) was employed to create a basis of the size and distribution of large-scale structures within the two planes. These POD modes were then used to objectively determine the differences in the jet structure during noise generation and periods lacking significant noise generation. The results show that the flow during the periods of relative quiet cases is dominated by the lower order POD modes that consist of relatively large turbulence structures while it is dominated by higher order POD modes that capture the dynamic interplay of the large-scale structures during noise generation periods. For approximately one convective time scale prior to the moment of noise emission, a series of large- scale structures forms and disintegrates within the mixing layer and in the process a large amount of ambient fluid is entrained into the core of the jet. For the first time, these results show how the dynamic interplay of large-scale turbulence structures generates acoustic radiation within a high Reynolds number jet.