Application of computational fluid dynamics to turbo machinery unsteady aerodynamics and aero acoustics

Abstract

The aim of this thesis is to obtain numerical data for fan tone noise propagation and reducing the load from blade-tower interaction. By using a CFD code, MB3D, which is supplied by Professor Li He, fan tone noise transmission and wind turbine blade-tower interaction are simulated and analysed. CFD application on turbomachinery unsteady flow is introduced and the two issues, fan tone noise and wind turbine have been reviewed. The CFD code to simulate the two different problems is introduced and its computational methodology is described. By using CFD method, the sound wave transmission in cut-on and cut-off situations are simulated and analysed. The results show that when the disturbance frequency is above the cut-off frequency, the pressure wave can propagate along the duct, when the disturbance frequency is below the cut-off frequency, the pressure wave will decay along the duct. The different decay rates depend on different cut off ratio. The mesh dependency of the computational simulations has been examined. Wind turbine blade-tower interaction is also simulated by using MB3D code. Adaptively pitching blade is introduced in order to minimize this interaction. The results show that with pitching blade by half degree or so, the unsteady forces on the blade can be at least halved, which can correspondingly reduce the bending moment (hence increase the fatigue life span), and improve the average power output. Keywords: CFD, fan tone noise, cut-off, cut-on, cut-off frequency, pitch control, blade-tower interaction.