A fast and storage-saving method for direct volumetric integration of FWH acoustic analogy

Abstract

This paper proposes a new method that makes the direct volume integration of the Lighthill stress term in FWH acoustic analogy affordable in terms of both computational time and disk storage requirement. The method is based on a dual mesh concept, i.e. while a fine mesh is used in CFD, a relatively coarse mesh is used for the acoustic calculation. The terms being independent of the observer positions in the integral formula of FWH acoustic analogy are calculated on the CFD mesh and mapped onto the acoustic mesh during the simulation. These sound source terms are used for the on-the-fly acoustic computation or saved for later use in the post-processing. A formulation of the Lighthill stress tensor in cavitating flow is also derived. The method is verified with the acoustic assessment of an inclined marine propeller case. A reduction of the calculation time by 98% and disk storage by 99% is achieved while maintaining small acoustic error.