The ability of a weakly compressible solver to predict landing gear noise with flow-acoustic interactions

Abstract

The ability of a weakly compressible solver to solve landing gear noise with flow-acoustic
coupling is investigated. Traditionally compressible flow solvers are used to simulate flowacoustic
coupling. However, compressible solvers require greater computational resources
compared to incompressible solvers at low Mach numbers such as an aircraft on approach
to landing. While incompressible solvers are able to capture the steady aerodynamics, in this
work, their inability to capture the correct wall pressure spectra and far-field acoustics is
demonstrated for a relatively simple two wheel landing gear, i.e. the LAGOON (Landing
Gear Noise database for CAA validation) #1 geometry. This is due to the inability of
incompressible solvers to capture cavity resonances, which are important contributors to
not only tonal but also broadband noise. This is significant for landing gear noise
predictions. A weakly compressible solver is tested to determine its ability to resolve the
flow-acoustic coupling for a low Mach number flow. This solver has a similar computational
cost to an incompressible solver. The simulations are performed using a weakly
compressible solver added to OpenFOAM with a one-equation Large-Eddy Simulation
model. An incompressible simulation of the same configuration is also performed for
comparison. Results shows that the weakly compressible solver can correctly solve the
resonant tonal and broadband noise that are absent in the solution from the incompressible
solver. The weakly compressible solver maintains similar behaviour in predicting the timeaveraged
and root-mean-square flow variables. A grid sensitivity study is also included, and
consistency is compared between the two meshes of different resolutions for both near-field
pressure fluctuations and far-field acoustics. The computational cost of the weakly
compressible method for landing gear simulations is slightly less than the incompressible
solver and significantly less than other fully compressible Navier-Stokes solvers.

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