Abstract
There is a continuing trend towards building large wind turbines, especially for offshore use. Large blades will experience a wide range of Mach numbers. CFD is a promising tool for accurate wind turbine performance prediction. It is necessary to develop a CFD code that can solve incompressible and compressible flow simultaneously. A compressible Navier-Stokes code with an approximately-factored algorithm is extended for flow at low Mach numbers using the method of local preconditioning. The turbulent flow around the NREL S809 airfoil is calculated for a wide range of Mach numbers. For low Mach numbers the convergence rate and accuracy are significantly improved compared to the calculation without local preconditioning.
