Beschreibung
The present thesis contributes to the development and the understanding of hydrodynamic/acoustic splitting (HAS) approaches in hybrid computational aeroacoustics (CAA). The discussed methods are particularly suitable for the otherwise problematic range of low Mach numbers. Approaches based on the HAS behave differently than other methods in many respects.
The basic idea of the HAS and the resulting characteristics are investigated in detail. One focus is on vortical modes of the perturbed quantities. By using a filtering of vortical components by means of the Helmholtz-Hodge decomposition, the influence of some often neglected equation terms is shown. In hybrid CAA, source data must be transferred between the flow model and the acoustics model. Among other things, it is found in the present work that the HAS approach is rather insensitive to errors made in the spatial reconstruction, but appropriate temporal reconstruction is shown to be critical.
In hybrid CAA, issues may occur if the domain of the flow simulation is smaller than the domain of the acoustics model. The arising discontinuity of the source fields on the acoustics mesh can impair the result quality. The present study shows that existing handling approaches are not always adequate. Therefore, a novel strategy to continue the flow pressure field into the outer acoustic propagation domain is proposed as an alternative.
A verification and a validation of the studied methods are presented at the end of this thesis. The case of a two-dimensional cylinder in laminar cross-flow results in a meaningful verification of the acoustics model. In a second test, the turbulent flow around a cylinder-airfoil configuration is employed, and experimental data demonstrate the validity of the basic model.
