Numerical study on the interaction between turbulent grazing flow excitation and Helmholtz cavity

In response to the problem of abnormal noise in typical aircraft structures with gaps and cavities, an experiment on a Helmholtz cavity excited by turbulent grazing flow was designed. The computational fluid dynamics software FLUENT was used to simulate the flow-induced noise of the Helmholtz cavity based on the Large Eddy Simulation (LES) method. By comparing with experimental data, the numerical simulation was validated. Meanwhile, under the given orifice size, the Helmholtz resonance effect of the cavity was studied at different velocities. It is found that the fluid oscillation frequency of the cavity orifice increases with the velocity under the given orifice size. When the fluid oscillation frequency at the cavity opening approaches the Helmholtz resonance frequency of the cavity, Helmholtz resonance occurs, leading to a significant increase in sound pressure level. Moreover, within a certain velocity range, the lock-in phenomenon occurs, and the lock-in frequency increases with the increase of inflow velocity, resulting in a frequency shift phenomenon. As the velocity increases, the lock-in phenomenon will break. This study suggests that Helmholtz coupling resonance and sound caused by the oscillatory flow with a close frequency to the cavity are one of the main causes of abnormal noise during aircraft flight.