Proceedings of Acoustics 2012 - Fremantle 21-23 November 2012, Fremantle, Australia Australian Acoustical Society 1 On the sound produced by flow interaction with a wall mounted finite length cylinder Danielle J. Moreau and Con J. Doolan School of Mechanical Engineering, The University of Adelaide, Adelaide, South Australia, 5005, Australia ABSTRACT A cylinder immersed in flow is often considered a source of unwanted sound and is relevant to a wide range of engi- neering applications including aircraft landing gear, rail pantographs and automotive side-mirrors. To investigate this flow-induced noise source, this paper examines the sound generated by a wall mounted finite length circular cylinder in cross-flow. Noise measurements have been taken in an anechoic wind tunnel at the University of Adelaide at a range of flow speeds and for a variety of aspect ratios (cylinder length to diameter ratio) to determine the influence of these parameters on noise generation. The experimental data presented in this paper give further insight into the un- derlying sound generation mechanism and can be used to validate numerical predictions of flow-induced noise from wall mounted finite length cylinders. 1 INTRODUCTION With the growing need for air, road and rail travel, more people are being exposed to transport noise and it is increas- ingly being considered an important public health issue. Aerodynamic sound is a major constituent of the noise pro- duced by modern transport vehicles and the sound generated by cylindrical objects in cross-flow is an important source of this flow-induced noise. For example, cylindrical objects are found in aircraft landing gear, rail pantographs and automo- bile appendages. In fact, cylindrical geometries are present in a broad range of engineering applications such as stacks or cooling towers, bridge piers, chimneys, masts, cables and wires. As the noise produced by flow interaction with a cyl- inder is relevant to a wide range of applications, it is impor- tant that the governing noise generation mechanism is well understood and that methods are developed so engineers can accurately predict the noise radiated into the far-field. The great majority of studies on the noise produced by flow interaction with a cylindrical object have focused on Aeolian tone generation from a two-dimensional circular cylinder (of effectively infinite length) in uniform cross-flow (Curle, 1955, Gerrard, 1955, Phillips, 1956, Schlinker et al., 1976, Cox et al., 1998, Inoue and Hatakeyam, 2002, Fujita et al., 2006, Cheong et al., 2008). Very little research has been con- ducted on the sound generated by flow over a wall mounted finite length cylinder. Experimental data sets on this topic are rare despite their importance for understanding the physical noise generation mechanisms responsible for flow-induced cylinder noise. The flow field around a wall mounted finite length cylinder is complex, three-dimensional and consists of a number of in- teracting vortex systems. In addition to the alternating span- wise vortex shedding (Kármán vortex street) observed for a two-dimensional cylinder, end effects are also present. Vor- tex structures form due to flow over the cylinder tip and at the junction of the cylinder and the wall. The vortex systems can merge and interact to produce a highly complex wake (Palau-Salvador et al., 2010). For a wall mounted finite length cylinder, the flow field structure and the radiated sound will depend on Reynolds number, aspect ratio (the ratio between cylinder length and diameter) and the ratio between the cylinder length and the wall boundary layer thickness (Becker et al., 2008). King and Pfizenmaier (2009) are one of the very few to ex- perimentally investigate flow-induced noise from finite length cylinders. Their study presents noise measurements for cylinders of various cross-section (circular, elliptical and square) and aspect ratio (L/D = 2 - 35) in a free jet at Rey- nolds numbers of Re D > 4.2 × 10 4 , based on cylinder diame- ter. Aspect ratio was found to be an important parameter in determining the peak frequency and sound level of the radi- ated noise. In addition, cylinders with an elliptical cross- section were identified as producing the lowest overall noise levels. This paper presents results of an experimental study on the noise produced by flow interaction with a wall mounted finite length circular cylinder. Far-field noise measurements have been taken in an anechoic wind tunnel at a range of Reynolds numbers (Re D = 1 × 10 4 – 1.4 × 10 4 ) and cylinder aspect ra- tios (L/D = 1.6 – 22.6). This paper aims to provide bench- mark acoustic data for a wall mounted finite length circular cylinder in cross-flow and to provide further insight into the fundamental physics of the flow-induced noise generation mechanism. It is worth noting that the results presented in this paper are the preliminary results of a much larger study examining this type of noise source. 2 EXPERIMENTAL METHOD 2.1 Anechoic wind tunnel facility Testing was conducted in the anechoic wind tunnel at the University of Adelaide. The anechoic wind tunnel test cham- ber is 1.4 m × 1.4 m × 1.6 m (internal working volume) and has walls that are acoustically treated with foam wedges to provide a reflection free environment (ideally) above 250 Hz. The facility contains a rectangular contraction with a height of 75 mm and a width of 275 mm. The maximum flow veloc- ity of the free jet is ~40 m/s and the free-stream turbulence intensity is low at 0.33%. Paper Peer Reviewed