Measurement and Mode Analysis of Flow Induced Noise Radiated from Forward- and Back-Step with Combined Proper Orthogonal Decomposition Analysis

In this study, two dynamic mode decomposition techniques were developed based on proper orthogonal decomposition (POD) and linear stochastic estimation (LSE) applied to the mode analysis of flow induced noise radiated from a forward-facing and backward-facing step. One used LSE to estimate radiated noise and the other used extended POD. Firstly, they were applied to the analysis of flow induced noise emitted from circular cylinder as a preliminary experiment and they were validated. There were a little difference between two analysis results obtained by two different techniques. Subsequently, simultaneous measurements of the wall pressure fluctuation on the surface of the step and far field sound pressure were performed in a low-noise wind tunnel with 30 and 50 m/s flow, and the data obtained were analyzed by the proposed methods. By using this method, the dominant mode of the surface pressure fluctuation on the forward- and backward- facing step for the noise emission was determined. Further, it was found that low-number POD modes of surface pressure fluctuation of the step related to the large-scale coherent structures had a strong impact on the emission of the noise for 30 m/s flow but higher number POD modes were important for 50 m/s flow.