64 Int. J. Engineering Systems Modelling and Simulation, Vol. 3, Nos. 1/2, 2011 Copyright © 2011 Inderscience Enterprises Ltd. Application of the passive control of shock wave to the reduction of high-speed impulsive noise Piotr Doerffer and Oskar Szulc* Department of Transonic Flows, Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-952 Gdańsk, Poland E-mail: doerffer@imp.gda.pl E-mail: osmark@imp.gda.pl *Corresponding author Abstract: Strong, normal shock wave, terminating a local supersonic area on an airfoil (or helicopter blade), not only limits aerodynamic performance but also becomes a source of a high-speed impulsive (HSI) noise. The application of a passive control system (a cavity covered by a perforated plate) on a rotor blade should reduce the noise created by a moving shock. This article covers details of the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes a validation against the experimental data obtained for the ONERA transonic nozzle with a flat wall. The passive control device is then applied numerically on a helicopter blade in high-speed transonic hover conditions to weaken the shock wave – the main source of HSI noise. Keywords: shock wave; passive control; perforated wall; transpiration; helicopter rotor in hover; high-speed impulsive noise. Reference to this paper should be made as follows: Doerffer, P. and Szulc, O. (2011) ‘Application of the passive control of shock wave to the reduction of high-speed impulsive noise’, Int. J. Engineering Systems Modelling and Simulation, Vol. 3, Nos. 1/2, pp.64–73. Biographical notes: Piotr Doerffer is the Head of the Department of Transonic Flows at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences. His professional interests are focused on the experimental and numerical aerodynamics of internal and external flows. He conducted his research within European projects EUROSHOCK I and II, AITEB I and II, HELIX, FLIRET, UFAST and many others. Oskar Szulc graduated in 2001 at the Technical University of Gdansk (Poland) in a specialty of fluid mechanics. Since then, his main interests are concentrated on the application of CFD methods in aviation applications, i.e., computations of flow past airfoils, wings, full aircraft models and helicopter rotors. He is also a PhD student of Prof. P. Doerffer and since 2000, he is an Assistant at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences. This paper is a revised and expanded version of a paper entitled ‘Application of the passive control of shock wave to the reduction of high-speed impulsive noise’ presented at the 4th Symposium of Applied Aerodynamics, Marseille, 2010. 1 Introduction – mechanism of passive control of the shock wave Passive shock wave – boundary layer interaction control using perforated plates was intensively investigated in the research projects Euroshock I and II. In some specific conditions application of a perforation resulted in improved aerodynamic performance of an airfoil. However, another attitude towards airfoil performance has to be considered in respect to the rotor blade of a helicopter in high-speed hover and forward flight conditions. Here, the most negative effect is the generation of a shock wave, which is responsible for a high-speed impulsive noise (HSI). To reduce the shock intensity (and noise) a cavity with a perforated plate may be located under the shock (Figure 1). Figure 1 Classical passive control of the shock wave on an airfoil (see online version for colours)