Flow-induced noise regimes of a three-dimensional airfoil

The flow-induced noise produced by a surface-mounted three-dimensional (or finite length) airfoil is important for many aerodynamic and hydrodynamic applications. Examples include wing-fuselage junctions, turbomachinery blade, rotor tip and end-wall flows, and ship appendage and hull-junction flows. This presentation provides an overview of the three-dimensional airfoil noise program at UNSW Sydney. In general, there are four flow regimes for a three-dimensional airfoil. These are the airfoil-wall junction flow featuring a horseshoe vortex that wraps around the airfoil base; turbulent flow interaction with the leading edge; trailing edge flow whose structure depends upon the Reynolds number; and the tip flow that consists of vortices that form as the flow wraps around the free-end of the airfoil. The acoustic signature and turbulent noise sources associated with each of these flow regimes will be examined using anechoic wind tunnel measurements obtained with acoustic array, unsteady surface pressure and turbulence measurement methods

Experimental investigation of airfoil-turbulence interaction noise

Airfoil-turbulence-interaction noise, which is created whenever turbulent flow encounters an airfoil, is a major contributor of unwanted noise emitted by aircraft, turbomachinery and alike. The experimental study presented here is the precursor to a larger investigation of the impact of complex turbulence on noise generation at the airfoil's leading-edge and airfoil-wall junction. In the current study, the authors examine links between the experimentally acquired properties of isotropic turbulence and the sound radiation of the immersed airfoil. This is achieved by varying the in-flow turbulence intensity using two different turbulence grids. A NACA0012 airfoil was analysed at a range of geometric angles of attack up to 16 degrees and Reynolds numbers of 1 ∙ 105 up to 3 ∙ 105. Stereoscopic Particle Image Velocimetry (SPIV) was conducted beforehand to capture the turbulence characteristics of the free flow. Additionally, acoustic beamforming with a phased microphone array provides insight into the sound generation at the leading-edge. Pressure taps along the centre chord-line were used to measure the mean static pressure, thereby allowing for an open-jet deflection correction of the angle of attack