Efficient Acoustic Modal Analysis for Industrial CFD

Strongoweld instabilities associated with acoustic resonance have been observed in many engineering applications. For the automotive industry noise reduction has a very high priority, while combustion driven oscillations present a serious difculty for low emissions large industrial gas turbine engines. Military engines especially have experienced major problems with low-frequencies instabilities in augmentors. To be able to predict such oscillations related with acoustic resonance, we propose here a numerically efcient and accurate engineering tool, which computes resonance frequencies and acoustic modes for any enclosure. In this algorithm sound wave propagation, reection, refraction and convection are taken into account. The formulation uses as an input the non-uniform meanow obtained from a steady-stateow solution in the domain, together with the prescribedow boundary conditions. The algorithm is implemented for full unstructured grids, to address complex industrial geometries. The present method is based on the Linearized Navier-Stokes Equations and Modal Analysis is performed using an Iterative Implicitly-Restarted Arnoldi algorithm. This offers a fast and accurate way to compute the most relevant frequencies and acoustic modes for large industrial problems. These are the modes that can resonate with the interior acoustic source processes. To validate our computational method, we present a series of simple - canonical- test cases. We also show its applicability to more complexow situations, such as sound produced by shallow cavity - typical automotive application - and oscillations inside a gas turbine combustor related with its acoustic characteristics.