Wall-Mounted Finite Airfoil Noise Production and Prediction

Abstract

This paper presents the results of an experimental investigation of the flow-induced sound produced by a smooth, wall-mounted finite length airfoil with flat ended tip and a tripped turbulent boundary layer. Acoustic measurements have been taken in the Stability Wind Tunnel at Virginia Tech with a microphone array at a range of Reynolds numbers (ReC = 7.9 × 10 5 − 1.6 × 10 6 , based on chord), angles of attack (α = 0 − 12 • ) and for a variety of airfoil aspect ratios (airfoil length to chord ratio of AR = L/C = 1 − 3). Spectral data show the dominant noise sources are airfoil trailing edge noise and tip vortex formation noise. Acoustic data are also used to evaluate semi-empirical prediction of wall-mounted finite airfoil trailing edge and tip noise with the so-called Brooks, Pope and Marcolini (BPM) model. The prediction method employs the BPM trailing edge noise model modified to incorporate span-wise variations in flow properties in combination with the BPM flat tip noise model. Three-dimensional trailing edge noise predictions agree well with measured spectra at a Strouhal number of StC < 18, based on airfoil chord. The BPM tip noise model under-predicts the peak level and frequency of tip noise contributions at StC > 18. A new empirical model of flat tip airfoil noise is presented that provides accurate estimation of the wall-mounted finite airfoil dominant tip noise contribution to within 1.7 dB.

Experimental investigation on the structures and induced drag of wingtip vortices for different wingtip configurations

“…With regard to the external flow, as one result of the rolling up of a vortex sheet at the trailing edge of a wing, the wingtip vortex provides lift for an aircraft. However, it also plays a crucial and hazardous role on the traffic capacity, 4 aerodynamic noise 5 and safety of aircraft. 6 Motivated by these meaningful engineering problems, a large body of scientific researches have been undertaken to investigate the structure of wingtip vortex and its development from the near wake 7 to middle wake 8 and far wake.…”

On the aerodynamic and aeroacoustic characteristics of a NACA 65-410 airfoil at moderate Reynolds number

“…More importantly, they developed an empirical model to predict the trailingedge noise of an airfoil based on their extensive experimental measurements of NACA 0012 airfoils. The phenomenon and underlying mechanisms of airfoil self-noise at low to moderate angles of attack has been examined extensively from the analytical, 5-8 numerical 9, 10 and experimental [11][12][13][14][15] point of view. According to Amiet's theory, 5 the trailing-edge noise is a direct result of the scattering of turbulent structures within a boundary layer, and hence is related to both the surface pressure fluctuations and the boundary layer length scales at the airfoil trailing-edge.…”

“…Past studies often focused on the classic airfoil profiles such as flat-plate-like 13 or NACA 0012 11, 14, 16 profiles, partly due to its symmetric profile shape. Nevertheless, a cambered airfoil profile is often preferred as a 'point-of-entry' in industrial design applications, 17 and since changes in the profile shape will directly modify the development of the turbulent structures in the boundary layer and their interactions with the cambered shape, it is crucial to examine and understand the airfoil self-noise from cambered airfoils as well.…”

Correction: Broadband Airfoil-Noise Source Localization by Microphone Arrays and Modeling of a Swept Free-Tip Blade

“…3,4 For this the classical set-up including a rectangular airfoil held between two end-plates was considered as too limiting, even if many reliable results have been obtained this way in the literature of airfoil noise and of its analytical predictions. 5 The aerodynamic noise generation for a finite-span airfoil involves more features 6,7 and additional noise sources such as airfoil tip can contribute to the process. 8 Previous investigation of the wall-mounted finite length airfoil with flat ended tip was done by Moreau et al 6,7 The present contribution brings new insight into the topic.…”

“…5 The aerodynamic noise generation for a finite-span airfoil involves more features 6,7 and additional noise sources such as airfoil tip can contribute to the process. 8 Previous investigation of the wall-mounted finite length airfoil with flat ended tip was done by Moreau et al 6,7 The present contribution brings new insight into the topic. The results of the source localization with the beamforming method pointed the existence of a junction noise source at low frequencies, increasing with the angle of attack, a trailing-edge noise source dominating at middle frequencies for low angles of attack and a trailing-edge tip source observed at high frequencies.…”