Abstract:
The convective FW-H equation is widely used in far-field noise prediction. However, spurious noise arises when vortical waves pass through the unphysical permeable surface for integration purposes. This paper aims to clarify this spurious noise generation mechanism and to propose an effective suppressing method. By analyzing the thickness and the loading sources on the right-hand side of the convective FW-H equation, it is found that the material derivative operator in the thickness source and the divergence operator in the loading source enable the permeable surface sources to filter the spurious sources automatically. The spurious noise appears when solving the convective FW-H equation by the partial integral formulas derived by Farassat, which ignore some integral terms so that the automatic filtering of spurious sources in surface sources is disabled. The terms containing vortical waves are extracted from the thickness and loading sources, and the corresponding material derivative and divergence operators are retained while solving the convective wave equation to suppress the spurious noise propagation. Numerical tests are performed to validate spurious sound's generation mechanism and suppression method.