Experimental characterization and analytical modelling of rotor tonal noise

Abstract

Rotors have played a huge role in the history of the aerospace industry. It is being widely used in small scale aircraft, helicopters, ships, wind turbines, to name a few. The study of noise generated by the rotors is an important subject of research. This project aims to characterize the open rotor tonal noise using the experimental and analytical model with a primary focus on Blade Tower Interaction (BTI) noise. The objective of the project is to implement an analytical acoustics model with input from an aerodynamics solver for calculating the noise radiation from a rotating blade. Fan noise experiments are conducted in the anechoic chamber at IMSIA, ENSTA ParisTech, France, which are used to validate the model and also characterize BTI noise. The acoustic model is based on Ffowcs-Williams and Hawkings (FW-H) acoustic analogy for moving sources. The analysis is performed in the frequency domain. The implemented model can be used to obtain noise radiations from propeller, wind-turbines or any rotating source, given the appropriate aerodynamic inputs. The implementation of the model is validated with the benchmark results in literature. The steady loading noise predicted by the analytical model matches very well with the experiments at first blade passage frequency (BPF) harmonic. The experiments offer a deep insight into the mechanism of noise radiation focusing mainly on tonal components associated with blade tower interaction. Different configurations with variation of pitch angle, blade tower distance are employed to study the impact on BTI noise. The effect of BTI noise is more pronounced at smaller blade tower distance and is almost negligible in front of the rotor when the blade tower distance is equal to the tower diameter. Further, pressure taps are used to study the pressure variations on the tower as the blade passes. An empirical model is suggested based on the pressure tap results to mimic the pressure variations on the tower. Keywords: Rotor tonal noise, Blade tower interaction noise (BTI), Fan noise experiment, Analytical modeling, Ffowcs Williams and Hawkings