This paper presents a comprehensive experimental aeroacoustic investigation of a propeller under turbulence ingestion. Two turbulence-generating passive grids were utilized to quantify the effect of turbulence intensity on the aeroacoustic characteristics of the propeller. A two-component hot-wire anemometry was employed to study the flow field. The flow field results demonstrate a substantial increase in fluctuating velocity components in both axial and radial directions, concentrated at the mid-span of the blade and near the tip, respectively. Energy spectral analysis in the vicinity of the propeller blade shows significantly higher broadband energy levels with multiple haystacking peaks at the harmonics of the blade passage frequency. Far-field noise and load measurement results show that turbulence ingestion has a strong effect on the aerodynamic loading and acoustic response at the blade passage frequency. The directivity of noise radiation at low frequency shows a significant tonal noise contribution. Meanwhile, broadband noise radiation is more dominant at a higher range of frequency, especially when the propeller is operated with turbulence ingestion and at higher advance ratio settings. The far-field noise results revealed the haystacking trends in the low frequency domain of the spectra and are most significant for propellers operating in turbulent inflows.

This paper presents an experimental study on the aeroacoustics of a flat plate rig with a highly instrumented serrated trailing-edge. The role of near-field flow properties, namely, surface pressure fluctuations and spanwise coherence, in the noise suppression capability of serration is not properly understood. The results from this test rig aim to provide additional insight into the effects of the serration on the hydrodynamic field (flow field) and the scattering of the pressure waves along the trailing-edge. Despite its unconventional size, beamforming results showed a significant reduction of far-field noise over a broadband frequency range. The associated flow field is characterized by mean and spectral analyses of static and dynamic surface pressure measurements as well as hot-wire measurements. The mean pressure coefficient results and the boundary layer velocity profiles over the serrated trailing-edge showed minute differences compared to the baseline straight trailing-edge. However, the frequency-dependent energy content of the unsteady surface pressure fluctuations demonstrates an elevated energy region around the serration edges at low frequencies. Although there is an increase in the energy content of the low frequency pressure fluctuations on the serrated trailing-edge, a significant phase difference of the pressure waves is observed, which may be indicative of destructive interference. The temporal studies regarding the unsteady surface pressure fluctuations corroborate the presence of quasi-periodic large scale structures emanating from the serration edges.

Airfoil turbulence interaction noise and the flow field up to and over the porous leading edge is experimentally studied. The porous leading edges were of the same base triply periodic minimal surface structure with varying porosity to enable us to understand how the porosity, permeability, and pore size affect the generated turbulence interaction noise. The turbulent flow was generated by means of a passive turbulence grid that does not affect the normal background noise of the wind tunnel. Far-field noise results were obtained from a polar microphone array to assess the directivity of the sound as well as the narrowband frequency contributions. Far-field noise results demonstrate that increasing porosity reduces the turbulence interaction noise over low-to-mid frequencies, with a penalty of a high frequency noise increase. Flow measurement results indicate hydrodynamic penetration of the flow into the porous structure at the leading edge. Furthermore, the two-point correlation analysis of the velocity fluctuations approaching the leading edge shows that the turbulent structures approaching the solid leading edge appear to deform into more two-dimensional structures, whereas in the case of the porous leading edge, the turbulent structures appear to retain a strong spanwise coherence up to the point of hydrodynamic penetration.