Grid-Generated Turbulence and Its Interference with Airfoil Leading Edges

This paper experimentally investigates grid-generated turbulence and its interference on a downstream airfoil. The grid is positioned at the nozzle exit of an acoustic wind tunnel and is defined by bar windward side width d and grid size M. The Reynolds number based on the airfoil chord length C is [Formula: see text]. The airfoil varies by replacing the solid leading edge (LE) with a wavy LE of different amplitudes [Formula: see text] ([Formula: see text]) and combined LE porosity [Formula: see text] at an angle of attack of [Formula: see text]. Noise measurements indicate that this grid-generated turbulence is primarily suitable for studying turbulence–airfoil interaction noise at low frequencies, specifically below the grid-bar vortex shedding frequency. To enhance noise measurement resolution, the airfoil is better placed downstream between [Formula: see text] and 10 (where L is the streamwise distance). In low frequencies, noise reduction efficiency improves with increasing wavy LE amplitude A and the combined normal-direction porosity [Formula: see text] under specific angle [Formula: see text]. Flow visualization reveals that the inhomogeneous vortices shed from the grid transition into homogeneous and isotropic turbulence after [Formula: see text], impinging upon the airfoil LE and generating interaction broadband noise. Force measurement results show that although the maximum lift coefficient of the airfoil with a wavy LE may decrease, the wavy LE exhibits the characteristic of delaying stall.