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.
The time-averaged velocity profile of a turbulent boundary layer can be predicted combining its different trends in the inner and outer regions in a single law of the wake. A new nondimensional coordinate system that projects the time-averaged velocity profiles of the inner and the outer regions on the same non-dimensional plane is introduced, leading to a unified treatment for the mixing region. In this coordinate system, various laws of the wake are shown to be the same but a constant. The non-dimensionalization is tested on a specific law of the wake, in which the closure coefficients are regressed from wind tunnel measurements and direct numerical simulations of turbulent boundary layers under zero-pressure gradient, over a good range of boundary layer thickness based Reynolds numbers. This data fit produced profiles within 2% of the reference values. This is of practical use to numerical modellers for generating boundary layer inflow profiles.
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