Computational simulation and analysis of double-swept blade in BVI noise reduction Hong Hu a, * , Leon A. Jordan Jr. a , James D. Baeder b a Department of Mathematics, Hampton University, Hampton, VA 23668, USA b Alfred Gessow Rotorcraft Center, Department of Aerospace Engineering, University of Maryland, College Park, MD 20742, USA Received 23 March 2004; revised 16 July 2004; accepted 30 July 2004 Available online 2 November 2004 Abstract The TURNS computational fluid dynamics (CFD) code with the Beddoes prescribed wake and the WOPWOP computational acoustics code is used to study blade-sweep blade–vortex interaction (BVI) noise reduction design. The CFD three-dimensional unsteady solutions of blade surface pressure distributions are used as the input to WOPWOP acoustics computational code to produce the overall sound pressure level (OASPL) on a 3-rotor radiation observer hemisphere around the helicopter rotor. To study the effects of blade sweep on BVI noise reduction, computations are performed on a baseline rectangular blade and a corresponding double-swept blade to better understand the impact of blade sweep on BVI noise reduction in relation to the interaction angle between blade leading edge and the shed tip-vortex. The present study indicates that tip-region blade forward sweep produces favorable BVI angles for dominate BVIs to reduce the maximum BVI noise level on the advancing side, while increasing noise level on the retreating side. Increasing in the noise level on the retreating side as a trade-off for decreasing in the maximum noise level on the advancing side results favorably in the reduction of the overall maximum noise level and in changing the ‘hot’ noise spots into a more desirable ‘less hot’ noise region. q 2004 Elsevier Ltd. All rights reserved. Keywords: Computational simulation and analysis; Aeroacoustics; Aerodynamics; Blade–vortex interaction noise 1. Background and objectives Blade–vortex interaction (BVI) noise reduction and modeling have been a major focus of the helicopter rotor aeroacoustics research during the past few decades. The BVI noise is the result of unsteady pressure fluctuations on the blade due to interactions with tip-vortices previously generated. The rotor BVI phenomenon is very complicated and controlled by many physical parameters, such as tip- vortex strength, miss distance between blade and shed tip- vortex, interaction angle between blade and tip-vortex, and flight conditions. Among them, the miss distance has been identified as one of most important controllable parameters in reducing BVI noise level [1]. On the other hand, the interaction geometry has been found to be one important parameter in BVI noise level and it is known that parallel or near parallel interaction can generate intense BVI noise [2]. The concept of blade tip planform modifications has been previously introduced and described [3,4] including the concept of employing a very large forward sweep region [4] either to reduce tip-vortex strength or to reduce the occurrence of parallel vortex interactions. Experimental results have shown some reduction in noise level for some of these blade tip modifications. However, since these exper- iments were mostly confined to acoustics only, a clear understanding of how the noise is affected has not been obtained. The objective of the present work is to better understand the impact of blade sweep on BVI noise reduction in relation to interaction angle between blade leading edge and the shed tip-vortex, following the lead of recent successful work [5,6] in BVI noise reduction and analysis. A high-fidelity computational fluid dynamics (CFD) method and a computational aeroacoustics method are used in the simulation and analysis of aerodynamic and acoustic fields. 0965-9978/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.advengsoft.2004.08.002 Advances in Engineering Software 36 (2005) 67–76 www.elsevier.com/locate/advengsoft * Corresponding author.