Aerodynamics and acoustics of aerofoils in simulated grid turbulence

Abstract

The interaction of turbulence with the leading edges of blades or vanes is a prominent and often dominant noise source in many applications. Although it is reasonably well understood for infinite aerofoils, the noise production of finite aerofoils has not been extensively investigated to date. This thesis presents a methodology to investigate the interaction of complex geometries, such as finite aerofoils, with homogeneous turbulent flows. A turbulence creation method for large eddy simulations, capable of generating evolving homogeneous turbulent flows, is investigated. It is shown that the method is capable of creating turbulent flows similar to those found in grid turbulence experiments and allows the turbulence production processes and development of anisotropy to be investigated. A spectral criterion to quantify the anisotropy of the energy carrying scales is presented and is shown to provide a more comprehensive description of the anisotropy than other criteria. For the purpose of validation, and to establish a baseline for the investigation of the interaction of a finite aerofoil with a turbulent flow, the problem of a thick, infinite aerofoil immersed in turbulence is studied. Results are compared against experimental and analytical methods. It is found that the numerical method is capable of capturing thickness and non-compactness effects on the far-field noise, demonstrating, for the first time, the applicability of a compressible large eddy simulation on an unstructured mesh for the investigation of aerofoil interaction noise with an evolving turbulent flow. Finally, the first investigation of a finite, thick, loaded aerofoil in a turbulent flow is presented. By comparing the distortion of the turbulent flow at the leading edge of the finite aerofoil to that of a corresponding infinite aerofoil, indications are found that the tip effects are limited to the immediate vicinity of the tip. The aerodynamics of the tip vortex interaction with the turbulence are assessed. It is found that the simulated tip vortex exhibits vortex wandering, and a wrapping of turbulent structures around the tip vortex is observed. Present results indicate that the tip vortex has an asymmetric structure in the vicinity of the aerofoil. The analysis of surface pressure spectra and cross-correlations, as well as the far-field noise emissions of subsets of spanwise sections of the finite aerofoil, suggests that while the leading edge noise is not significantly affected by the finiteness of the geometry, the tip vortex leads to a considerable attenuation of the pressure fluctuations on the suction side close to the trailing edge, and thus to a reduction of the non-compactness effects of the aerofoil sections closest to the tip.

More information

Identifiers

Catalogue record

Export record