Numerical Predictions of Airfoil Acoustics with Inflow Turbulence

Abstract

The interaction of a turbulent flow with the leading edge of a foil is one of the dominant noise sources for many engineering applications, including aircraft wings, (wind) turbine blades, and non-cavitating marine propellers such as those found on tidal turbines, naval vessels and submarines. Incorporating a better understanding of the turbulence intensity on the far-field radiated noise in the early design phases can help reduce low-frequency broadband noise that is harmful to humans and (marine) wildlife. A simple framework, such as that proposed by Amiet, can provide fast predictions once validated for more complex problems. The current work assesses numerical predictions on far-field radiated noise by the leading edge of a NACA0008 airfoil for varying turbulence intensities. The flow is simulated within ReFRESCO, a partially averaged Navier-Stokes solver in which turbulence is generated using a synthetic inflow turbulence generator. Inflow turbulence and predicted far-field noise by the Ffowcs Williams-Hawkings formulations are experimentally and numerically validated, showing that the proposed method can generate realistic turbulence, pressure data on the foil surface and associated far-field noise. Variation in the turbulence intensity shows an unwanted change in the integral length scale, which did not seem to affect the far-field radiated noise. In agreement with Amiet, a linear increase in turbulence intensity leads to a near quadratic increase of the radiated noise for a receiver directly above the foil. A rapid change in scaling is seen for receivers more closely aligned with the flow direction both up- and downstream of the foil, for which the far-field noise scales with the turbulence intensity to the sixth power. Variations in the turbulence intensity between 4 % and 16 % dominate over a change in the integral length scale from 30 mm to 65 mm.