Axial Ventilator Tip Gap Noise Prediction from Discontinuous Galerkin based CAA with Stochastic Vortex Sound Sources

Abstract

A prominent noise source of axial ventilators emerges from the complex flow within the tip clearance between fan blades and surrounding encasement. To obtain an aeroacoustic fan design, an associated process must be acceptably efficient while providing a sufficiently amount of physical modeling depth. The mechanisms of noise generation as well as the sound propagation in highly inhomogeneous flow fields have to be captured. A promising method is developed at the DLR by using the in-house CAA propagation solver DISCO++ coupled with the stochastic acoustic source generator Fast Rand Particle Mesh Method (FRPM). Utilizing the Discontinuous Galerkin method the Acoustic Perturbation Equations (APE) are solved on an unstructured tetrahedral mesh, while the acoustic sources are reconstructed on a Cartesian background grid. The prediction capability of the method is evaluated by computing the noise generated by a ducted axial ventilator at two different tip clearance variations. While the trailing edge noise is well captured, the tip gap noise increase is not properly predicted in terms of spectral shape – presumably due to anisotropic length scale influence not properly recognized by the current stochastic model. First simulations based on an enhanced anisotropic length scale model will be presented and results discussed.