Aeroacoustic characteristics of multi-directional wing under the wing-in-ground effect

Abstract

Characteristics of the generation and propagation of aerodynamic noise are unique to conventional ground vehicles or aircraft due to the wing-in-ground (WIG) phenomenon. This study numerically examines the aeroacoustic characteristics of a multi-directional wing under the WIG effect with different values of clearance. The flow field was simulated by using a large eddy simulation for six groups of wings with different clearances and one group of wings in free space, at a freestream velocity of 0.3 Ma and an angle of attack of 5°. Acoustic simulations were carried out for each condition by using Möhring's analogy, and the acoustic analysis was based on details of the flow field. A multi-vortex system was generated at the trailing edge of the wing when the clearance was lower than 0.2 C. It consisted of an oscillating attached vortex that expanded and shrank with continuous changes in energy, and two periodically shedding vortices were formed that generated a strong wall-bound vortex street downstream of the wing after shedding. An analytical approach was used to simultaneously analyze different dominant frequencies in each region of the sound field. We conclude that different intensities of the WIG effect led to remarkable differences in the characteristic frequency of aerodynamic noise induced by the multi-directional wing. The characteristic frequencies of aerodynamic noise of the multi-directional wing with a low clearance (clearance ≤ 0.2 C) were mainly caused by the wall-bound vortex street while those at a high clearance (clearance ≥ 0.4 C) were mainly caused by vortices on the wingtip.