This work is written for the development of computational tools to predict flow-induced noise. Due to the large disparity in acoustic and hydrodynamic length scale, as well as energy levels in low MACH number flows, the aeroacoustic simulation for practical applications can only be carried out with the hybrid approach, which separates the problem into two or more parts, one describing the nonlinear generation of sound, the others describing the transmission of sound. The hybrid approach investigated in this work simulates the acoustic far-field using a two step procedure.
In the first step, the unsteady compressible flow field is computed in a computational domain comprising the acoustic sources under consideration via a compressible NAVIER-STOKES solver for the laminar flow case, and a large eddy simulation (LES) solver for the turbulent case. The time-dependent quantities of acoustic source information required in the second step are stored in a data base. In the second step, a post-processing computer program is used to extend
the dynamic near-field to the acoustic far-field, namely to calculate the far-field sound pressure based on the acoustic source information provided by the first step simulation.
The FFOWCS-WILLIAMS and HAWKINGS (FW-H) approach with a permeable (porous) control surface is chosen to carry out the second step. Three integral formulations of the FW-H approach, namely the 3D FARASSAT, 2D GUO and 2D LOCARD formulations, are implemented into the computer program. Through the comparisons among the results of the 3D and 2D formulations of the FW-H approach, the 2D approaches are suggested be an efficient way to guide and augment full 3D calculations.
The computational parameters for the aeroacoustic simulations, such as the position of the control surface, copy length in the span direction of the cylindrical control surface, spatial and temporal resolutions, and accuracies of numerical interpolation, derivation and integration, are
investigated in this work to obtain an optimization concept of the numerical calculation. The capacity of the computer program used in this work is investigated in detail with verification and validation examples. The verification examples are based on several analytical solutions.
The simulated acoustic far-field generated by an unsteady flow around a circular cylinder at Re D = 150, Ma = 0:2 (the laminar flow case) is compared with the direct acoustic simulation (acoustic DNS) of INOUE, and that at Re D = 3900, Ma = 0:2 (the turbulent flow case) is compared with the experimental results of NORBERG and SZEPESSY. Both the comparisons give a good agreement. The 2D approaches are proven to be very efficient and accurate enough
for the application of LES with a periodical condition in the span direction.