Measurement of aerodynamic noise and unsteady flow field around a symmetrical airfoil

Abstract

The purpose of this paper is to study the physics of aerodynamic noise generation from the symmetrical airfoil ofNACA 0018 in a uniform flow. The relationship between the noise spectrum and the unsteady flow field around the airfoil is studied in an acoustic wind tunnel using flow visualization and PlV analysis. The discrete frequency noise was generated from the airfoil inclined at small angle of attack to the free stream. The flow visualization result indicates the presence of attached boundary layer over the suction side and the separated shear layer over the rear pressure side of the airfoil, when the discrete frequency noise is observed. It is found from the PlV analysis that a large magnitude of vorticity is generated periodically from the pressure side of the trailing edge and it develops into an asymmetrical vortex street in the wake of the airfoil. The periodicity of the shedding vortices was found to agree with that ofthe frequency ofthe generated noise.

Preliminary Assessment of Noise Pollution Prevention in Wind Turbines Based on an Exergy Approach

“…It can be noted that the vortex is generated periodically with a counter-clockwise rotating vortex forming from the bottom of the object and the clockwise rotating vortex forming at the top of the solid object. The position of the vortices is almost equidistant along the horizontal distance, indicating a cycling nature of the vortex shedding behind the cylinder (Tomimatsu and Fujisawa, 2002). It is to be noted that the frequency of vortex shedding matches with the frequency of the fluctuation of the SPL.…”

Wind tunnel testing of shear-stress measurement by liquid-crystal coating

“…Experiments are carried out in an acoustic wind tunnel, which is described by Tomimatsu and Fujisawa (2002). The cross-sectional area of the test section is 190 mm× 190 mm and 600 mm long.…”

Measurement of pressure field around a NACA0018 airfoil from PIV velocity data

“…The planar PIV measurement of the flow field is carried out in the central section of the airfoil, which has a chord length C = 80 mm. Details of the experimental setup are described by Tomimatsu and Fujisawa (2002).…”

“…This experimental technique is non-intrusive and allows the field measurement of static pressure over the circular cylinder, so that it is well suited to the pressure measurement in wind tunnel studies. Although this approach is applicable to the evaluation of instantaneous pressure and fluid forces acting on the bluff body, the time-averaged pressure measurement is practically important in usual wind tunnel studies (Van Oudheusden et al, 2007). However, such pressure measurement has not been carried out for the flow over the complex geometry, such as airfoils.…”