A virtual boundary method for compressible flow with application to aeroacoustics of compliant trailing-edges

• Main Author: Schlanderer, Stefan Christian
• Other Authors: Sandberg, Richard
• Published: University of Southampton 2017
• Subjects: 620.2
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720213

The method is the compressible extension of the boundary data immersion method (BDIM, Maertens & Weymouth (2015)). The BDIM equations for the compressible Navier-Stokes equations are derived and the accuracy of the method for the hydrodynamic representation of solid bodies is demonstrated with challenging test cases relevant to aeroacoustic applications, including a fully turbulent boundary layer flow and a supersonic instability wave. In addition, it was shown that the compressible BDIM is able to accurately represent noise radiation from moving bodies and ow induced noise generation without any penalty in allowable time step. The newly introduced framework was employed to investigate the noise radiation from elastic trailing-edges (TE). A study employing elastic TE extensions for airfoils at angle of attack showed a noise amplification when the structural motion is close to resonance. Furthermore significant effects of the elastic TE extension on the characteristics of the laminar separation bubble on the suction side were found, resulting in a global change of the flow around the airfoil. For that reason, in an attempt to avoid changes in circulation complicating the comparison between rigid and elastic TE, a generic setup featuring a flat plate and a vortex generator was developed to investigate different material parameters for the elastic TE. Excess noise was found to be radiated in frequency bands related to the response of the motion of the elastic structure. However, a noise reduction was observed for certain frequency ranges and structural parameters. The noise reduction was associated with an attenuation of the incident pressure fluctuations. When structural damping was taken into account significant noise attenuation compared to the undamped and the rigid cases was found. The noise reduction was attributed to reduced fluctuations of the structural deflections. Finally, the simulation of a fully turbulent ow convecting over an elastic TE showed qualitatively similar behaviour to the two dimensional studies. However, the excess noise from the structural motion was relatively more important than in the two dimensional case and the overall noise reduction was reduced. The motion of the elastic TE is shown to increase the energy in the low wave number spanwise modes.