Sound Generation and Radiation of an Open Two-Dimensional Cavity

Artikel i vetenskaplig tidskrift, 2009

This work studies differences in sound generation and radiation between incompressible and compressible flowfields at the corresponding Mach number of 0.15 by evaluating the two dominant dipóle terms in a temporal form of Curie's equation. The present work adds incompressible simulation results to a previously reported direct simulation of an open two-dimensional cavity oscillating in wake mode. The length-to-depth ratio of the cavity is L/D = 4, and the flow is considered to be laminar. The Reynolds number based on the cavity depth is Re D = 1500. At these conditions, the flow is characterized by large variations in the streamwise force coefficient, showing similarities to a bluff-body wake flow, which makes the present case an attractive candidate for an incompressible approach. The root-mean-square levels of the two acoustic source terms show good agreement in the vicinity of the cavity, and the agreement in the radiated sound is almost perfect when isolating the cavity walls in the surface integration. The agreement in the radiated sound for the two flowfields is equally good when isolating the downstream wall extending from the cavity trailing edge and 10D downstream. However, when the surface integration comprises both the cavity walls and the downstream wall, a major mismatch in the directivity arises, and it is shown that this mismatch is primarily caused by an almost complete cancellation of the sources at the cavity bottom and the downstream wall in the incompressible simulations.