Interaction tonal noise generated by contra-rotating open rotors

Abstract

Fast and accurate prediction of sound radiation of Contra-Rotating Open Rotors (CRORs) is an essential element of design methods of low-noise open rotor propulsion systems. In the present work, a previous frequency-domain model is extended to predict CROR noise. It builds explicitly the relationship between harmonic loadings and corresponding tonal noise, by which the influential parameters to noise generation can be clearly understood. The real distributions of steady and unsteady blade loadings are calculated by the Nonlinear Harmonic (NLH) method. In the present hybrid approach, both the CFD and acoustic modules are solved in the frequency domain. To assess the accuracy of the developed method, the loading noise of a CROR is calculated and compared against results by using the time-domain FW-H module of NUMECA. The predicted sound directivities by the two methods are in good agreements. The present acoustic model in the frequency domain is proven to be accurate and have high efficiency in far-field noise prediction and data processing. Furthermore, the characteristics of the CROR interaction tonal noise are analyzed and discussed.