Universal Airfoil Parametrization Using B-Splines

Abstract

The leading-edge noise generated by turbofan and open rotor engines due to interaction with turbulence can be a significant contributor to the total noise radiated by an aircraft. This noise source is very sensitive to the nature of the turbulence that impinges on the leading edge. Most analytical and numerical models assume that the turbulence is isotropic. This assumption produces satisfactory results for the majority of cases considered. However, there are numerous noise sources in which the anisotropy of the turbulence is significant and the resultant noise is poorly predicted with the use of an isotropic velocity spectrum. One such noise source is the ingestion of a turbulent boundary layer by an open rotor. This paper includes the anisotropic velocity spectrum of Kerschen and Gliebe in Amiet's analytical model for a translating aerofoil. Using the translating model it is shown that the axial length scale shifts the frequency at which the maximum energy in the spectra occurs and moderately alters the resulting sound PoWer Level (PWL) spectra. Conversely, altering the transverse length scale does not change the frequency at which the maximum energy occurs in the spectra but does alter the maximum PWL significantly. The analytical analysis of an aerofoil ingesting anisotropic turbulence provides an insight into how redistributing the energy in the axial and transverse energy spectra, by changing the axial and transverse length scales, can reduce leading-edge noise. The anisotropic turbulence model is compared to two real world anisotropic turbulence datasets available in the literature. These are datasets for boundary-layer turbulence obtained from experiments and direct numerical simulations of a channel flow. When the model spectra is compared to statistics obtained from these datasets, several discrepancies are observed. It is observed that the model spectrum significantly over-predicts the transverse integral length scales and energy spectra.