Prediction of Contra-Rotating Open Rotor broadband noise in isolated and installed configurations

Abstract

Broadband noise is a significant part of the noise emitted by contra-rotating open rotors. Several noise sources can contribute to the total broadband sound field, with the most dominant ones probably being trailing edge noise, rotor-wake interaction noise and pylon-wake interaction noise. This paper addresses the prediction of these noise sources using analytical models based on Amiet's flat plate airfoil theory and also to empirical turbulence models, fed by input data extracted from steady and unsteady CFD RANS simulations. The models are assessed against wind tunnel tests of Rolls-Royce's rig 145 (build 1) conducted at the DNW anechoic open jet test facility using Rolls-Royce blades and Airbus pylons. The study showed promising results in terms of the ability of the models to predict acoustic power spectrum shapes, peak frequencies and absolute levels. The effects of changes in thrust on broadband wake-interaction noise are well reproduced. However, the models significantly underestimate the effect of thrust on trailing edge noise and the effect of rotational velocity on pylon interaction noise. Nomenclature

Broadband noise for rotating blades: analysis of acceleration effects in the time and frequency domains

“…Nevertheless, Amiet's method is currently being used successfully to predict broadband noise in these applications. 8 Blandeau et al 9 and Sinayoko et al 10 One way to address the low frequency problem is to focus on leading edge noise. For leading edge noise, there is no frequency constraint relative to the blade chord.…”

An analytical model for predicting rotor broadband noise due to turbulent boundary layer ingestion

“…This is challenging as open rotors have exposed fans and therefore boundary layers and wakes from the aircraft can interact with the exposed blades. An installation noise source that has been extensively studied, both experimentally and analytically, is the leading-edge noise produced due to the ingestion of a wake generated by an installation pylon [4,5,6].…”

Investigation of Wall-Pressure Fluctuations Characteristics on a NACA0012 Airfoil with Blunt Trailing Edge

“…The theoretical treatment of this noise mechanism generally relies on Amiet 2, 3 and Howe 4 theories. Accurately predicting the trailing edge noise still faces significant issues: most of the modelling involves empirical and semi-empirical models [5][6][7][8] which are essentially relying on the pressure footprint at the wall of the upstream TBL. These methods were used by Brooks and Hodgson 5 who found a good agreement of their sound pressure measurements in the farfield with the predictions of Howe 4 , derived from the wall-pressure field.…”