A rapid distortion theory-based airfoil turbulent inflow noise prediction method

Abstract

Turbulent inflow (TI) noise is reported as an important source of wind turbine (WT) broadband aeroacoustic noise, coexistent with many other sources (e.g., the airfoil self-noise). This manuscript intends to elucidate the discussion on TI noise by providing an alternative prediction method based on the rapidly distorted anisotropic turbulent velocity energy spectrum. A review on turbulent inflow noise prediction is presented, followed by the discussion on turbulence modeling and the derivation of a modified TI noise prediction expression, which allows a more detailed assessment of wind turbine noise sources. This can contribute for WT blade optimization, once it is implemented in design codes that consider noise as a constraint. Criteria for the turbulent velocity spectrum to be characterized by the rapid distortion theory (RDT) are established, and the validation methodology is carried through comparisons between the novel semi-empirical prediction method and data gathered from recent literature for a flat-plate airfoil with $$3\%$$ relative thickness and a NACA 0008 airfoil. The RDT-modified turbulent inflow noise prediction method shows better agreement with the measured data, when compared to predictions that adopt an isotropic model for the turbulent velocity energy spectrum, a condition only achieved in the absence of the airfoil in the test section of aeroacoustic facilities.