Subsonic Jet Noise Simulations Using Both Structured and Unstructured Grids

Abstract

For the last 10 years, large-eddy simulations have become a major tool for investigating jet noise sources because of their intrinsic ability to capture broadband turbulent features. However, many challenges still arise when dealing with complex geometries in terms of method accuracy and computational costs. Two different approaches to compute jet noise in an industrial context are here validated and compared. Both approaches are based on a hybrid methodology combining large-eddy simulation of jet flows for sources computations and Ffowcs Williams and Hawkings’s analogy for far-field noise prediction, but they differ on their grid topologies. The first approach uses classical block structured grids. The numerical scheme is a low-dispersive, low-dissipative finite-volume compact scheme. The second approach uses fully unstructured tetrahedral grids with a low-dispersive, low-dissipative Taylor–Galerkin finite-element scheme. Both approaches are used to compute a Mach 0.9 cold jet at the moderate Reynolds number without accounting for the nozzle geometry. Comparisons between simulations and experimental measurements highlight the need to correctly capture the initial turbulent development of the mixing layer at the nozzle exit. In the present simulations, because the nozzle geometry is not discretized, the turbulent transition is done by injecting perturbations as vortex-ring modes. Results obtained on this benchmark test case demonstrate the capability of both methods to correctly simulate and predict jet noise. The validation of the approach using fully tetrahedral grids provides a promising way to account for complex noise-reduction devices such as chevrons, realistic dual-stream nozzles, or lobed mixers.