Noise sources from a cylindrical cavity

The expansion of air traffic operations is nowadays limited by environmental constraints on noise. Advances in jet noise reduction have increased the importance of landing noise from the airframe as a significant contribution to the effective perceived noise level around airports. The most acoustically active airframe components in a civil aircraft are the high lift systems and the landing gear. Nonetheless, other components, such as fuel vents or ailerons, also contribute to the overall noise emissions. This study considers a cylindrical cavity as a low fidelity fuel vent model. Different diameter to depth ratios and inflow velocities are simulated by means of an in-house compressible Euler solver. The predictions for a diameter to depth ratio of 0.714 show an unsteady asymmetric vortex structure at the inflow Mach numbers of 0.235 and 0.3. The alternate impingement of this vortex on the right and on the left of the cavity trailing edge produces pressure waves and the flow instability is self-sustained. The simulations of a cavity with a length to depth ratio of 2.5 at the same Mach numbers show a similar self-sustained instability where the flow recirculation is symmetric about the cavity mid-plane. To identify and localize the most acoustically active regions in the inviscid flow model, the double divergence of the Lighthill stress tensor was computed from the aerodynamic predictions. This work sets the basis to perform a Ffowcs Williams and Hawkings acoustic analogy to predict the fuel vent contribution to landing noise.