Oliver Fleig

Wind Turbine Blade Tip Flow and Noise Prediction by Large-eddy Simulation

The purpose of this research is to investigate the physical mechanisms associated with broadband tip vortex noise caused by rotating wind turbines. The flow and acoustic field around a wind turbine blade is simulated using compressible large-eddy simulation and direct noise simulation, with emphasis on the blade tip region. The far field aerodynamic noise is modeled using acoustic analogy. Aerodynamic performance and acoustic emissions are predicted for the actual tip shape and an ogee type tip shape. For the ogee type tip shape the sound pressure level decreases by 5 dB for frequencies above 4 kHz.

WIND TURBINE FLOW AND NOISE PREDICTION BY LARGE EDDY SIMULATION

The purpose of this research is to investigate the physical mechanisms associated with broadband tip vortex noise caused by rotating wind turbines. The flow and acoustic field around a wind turbine blade is simulated using compressible Large-Eddy simulation and direct noise simulation, with emphasis on the blade tip region. The far field aerodynamic noise is modeled using acoustic analogy. Aerodynamic performance and acoustic emissions are predicted for the actual tip shape and an ogee type tip shape. For the ogee type tip shape the sound pressure level decreases by 5 dB for frequencies above 4 kHz. Initial results regarding winglet simulations are shown.

LARGE-EDDY SIMULATION OF TIP VORTEX FLOW AT HIGH REYNOLDS NUMBER

Simulations using up to 300 million grid points are performed on the Earth Simulator in Japan, the fastest supercomputer in the world. The present work is the first attempt to simulate a finite blade with a tip in an incident flow and its associated tip vortex and acoustic field at a Reynolds number in the order of a million using direct compressible LES (Large-Eddy Simulation). For validation purposes, the flows around a NACA0012 blade section as well as finite blade at lower Reynolds number are simulated. It is a wall resolved simulation using the Smagorinsky eddy viscosity model. Angles of attack between 5 and 11 degrees are studied at Reynolds numbers ranging from 4.06×10 5 to 2.87×10 6 . The simulation results showed that the tip vortex plays a major role in aerodynamic noise generation. The present large-scale simulation can provide information about the physical phenomena causing tip vortex flow and tip noise at high Reynolds numbers. This information can be used in various engineering applications such as aerospace and wind energy and could help to design blade tips for reduced noise emission.

Aeroacoustics Simulation Around a Wind Turbine Blade Using Compressible LES and Linearized Euler Equations

There is a strong need to investigate aerodynamic noise caused by large and fast rotating wind turbines, especially trailing edge and tip noise. This work constitutes the first part of a project which aims to simulate the broadband tip noise emitted when the wind turbine is in operation. Several aeroacoustics methods are analyzed and their suitability for a typical wind turbine blade is assessed. A stationary wind turbine blade in an incident flow with a large region of separated flow is studied. The surface pressure fluctuations are calculated using compressible Large-Eddy simulation (LES). The aerodynamic noise perceived in the far-field is predicted by simulating the propagation of the pressure perturbations using LES and Linearized Euler equations (LEE) in the near field and Kirchhoff’s integral method in the far-field. It was found that for the present wind turbine blade with a large region of separated flow and thus relatively large fluctuations, LES with a fine enough mesh and a third-order upwind scheme is able to compute the propagation of acoustic waves as accurately as LEE with higher order schemes and separate treatment of acoustic perturbations. The method described in this paper will be used in the future to analyze a full wind turbine blade with the aim of optimizing the tip shape for reduced noise emission.© 2003 ASME