Advancing Analytical and LES Based Predictions Of Turbulence Ingestion Noise in Complex Environments - An Experimental Study

The objectives of this study were to detail the fundamental physical processes that occur in rotorturbulence interaction to aid the development of inflow turbulence modeling and turbulence ingestion noise prediction tools. In addition, a significant goal of this project was to conduct and document detailed flow and noise measurements needed to validate computational models of this interaction. Two experimental arrangements were investigated considering ingestion of a planar turbulent boundary layer and the wake shed by an upstream cylinder. It was found that with increasing thrust turbulence distortion effects were greater in the boundary layer arrangement due to increased stretching of turbulence caused by the impermeable wall boundary condition. This produced prominent haystacking peaks about the blade passage frequency BPF and its harmonics. Also, at low advance ratios, a separation region would develop on the wall that increased the noise at harmonics of the BPF as well. In the wake ingestion case, distortion was less important. The directivity of the turbulence interaction source and its strength was found to be a function of the proportion of the rotor disk area immersed in the turbulent field and its distribution across the rotor disk area.