The noise emitted by incoming turbulence interacting with an airfoil has many technological applications, and has accordingly received much attention in the literature. While numerous developments are focused on the determination of the airfoil response to a given incoming gust, the characterization of the incoming turbulence seems to have received less attention. An important aspect thereto is the validity of the assumptions made to describe the incoming turbulence as isotropic and homogeneous. In this work, hot wire anemometry and stereoscopic Particle Image Velocimetry are combined to obtain detailed measurements of the turbulence generated by either a grid or a rod, interacting with a NACA 0012 airfoil. A particular focus is placed on the measurement of the turbulence properties in the very close vicinity of the leading edge, in order to quantify turbulence distortion and compare the test data with Rapid Distortion Theory models. The experimental database permits to identify significant distortions of the mean velocity field, turbulence intensities, correlation lengths and turbulence spectra in a region with size comparable to the airfoil leading-edge radius of curvature. It. is demonstrated that even in cases where the flow is nearly homogeneous in the spanwise direction, small variations must be taken into account to improve the sound predictions. But the most significant effect to include in the prediction is the distortion of the incoming turbulence spectrum, here modeled using Rapid Distortion Theory, if a meaningful sound prediction is to be obtained.
展开▼
