PROGRAMM - DAGA 2012

Programm DAGA 2012 93or frequency dependent (realized as digital filters). One common assumptionregarding boundaries is that they should correspond to locallyreacting impedances and the global reflection coefficient therefore dependon the angle of incidence. Recent research [Excolano 2008] postulatedthat this is not the case if the boundary model is implemented asa local reflection coefficient and proposed an alternative implementation.In the work presented here, that new realization of locally reacting impedancesis analyzed. It is shown that in fact it corresponds to a frequencydependent local reflection coefficient, which can be seen as a digital filterwith a particular choice of the filter coefficients. Simulations comparingthe new approach with that used in Lambda showed no improvements.Sitzung „Strömungsakustik“Di. 14:00 titanium 2.04 StrömungsakustikMulti-Model Approach for Computational AeroacousticsM. Kaltenbacher a ,I.Sim a , A. Hüppe a und B.I. Wohlmuth ba Alps-Adriatic University of Klagenfurt; b TU München, Lehrstuhl für NumerischeMathematikSince the beginning of computational aeroacoustics (CAA) several numericalmethodologies have been proposed. Due to the practical advantagesprovided by the separate treatment of fluid and acoustic computations,hybrid methodologies still remain the most commonly used approachesfor CAA. Concerning the model approaches, we can differ betweenmodels based on acoustic perturbation equations [1], explicitly takinginto account refraction and convection effects, and the inhomogeneouswave equation of Lighthill. In our contribution we apply a multi-model approach,where we solve on the inner domain (corresponds to the maindomain of computational fluid dynamics (CFD)) an acoustic perturbationequation, and for the surrounding domain the convective wave equationof Pierce [2]. Therewith, we can reduce the number of unknowns for theouter domain from four (particle velocity and pressure) to just one (acousticscalar potential). By applying a Mortar Finite Element (FE) method,we can fully include the physical interface conditions within the overallnumerical scheme.[1] W. de Roeck, G. Rubio, M. Baelmans and W. Desmet. Toward accuratehybrid prediction techniques for cavity flow noise applications. Int. J.Numer. Meth. Fluids (2009)[2] Allan D. Pierce. Wave equation for sound in fluids with unsteady inhomogeneousflow. J. Acoust.Soc. Am. (1990)