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摘要
Haystacked peaks in rotor noise spectra are produced by the correlated unsteady loading on neighboring blades. This noise can be predicted with knowledge of the turbulent inflow and blade response function, but this is not trivial, especially for complex turbulent inflows that are both inhomogeneous and anisotropic. This paper details the radiated noise and direct measurement of the unsteady upwash correlation in the rotating frame of a 10-bladed, 457 mm diameter rotor immersed in planar wall boundary layers of different thickness at non-thrusting and thrusting advance ratios. At low thrust conditions, the measured upwash correlation can be predicted using the fixed frame space-time correlation function of the undisturbed inflow. However, as the advance ratio is lowered, predictions progressively deviate from measurements. This is shown to be due to both the distortion of the approaching turbulence and the formation of a separation region on the wall beneath the rotor. At these low advance ratios, haystacks at the blade passage frequency and harmonics are observed in the blade-to-blade upwash coherence spectra at spanwise locations near the blade tips. Also, a lateral contraction of the turbulence is not observed in measurement of the spanwise coherence with increasing thrust. Finally, increasing the boundary layer thickness increases spectral levels of the radiated noise at higher advance ratios near zero thrust by a factor similar to the increase in boundary layer thickness. At low advance ratios, peaks in the measured noise have the same approximate magnitude for similar rotational and freestream velocities regardless of the boundary layer thickness as these are likely produced by interaction with vortex structures in the separated region.
- 出版日期2017-11-24
- 单位美国弗吉尼亚理工大学(Virginia Tech)
