Numerical Analysis of Bi-directional Impulse Turbine Performance for Thermoacoustic Power Generators

As a new type of acoustoelectric conversion method, bi-directional impulse turbine provides great potential for developing large scale and economic thermoacoustic power generators. In this paper, the performance of bi-directional impulse turbine with fixed guide vanes has been studied via 2D CFD modelling by commercial software Fluent. Firstly, the effects of blade structure and gas flow incident angles on the shaft power and efficiency have been investigated. Then the performance of the turbine has been studied under both steady and oscillating flow. Additionally, flow field features for the turbine in oscillating flow were presented for a better understanding. The results show that optimal flow incident angle for shaft power and efficiency are 20° and 70° respectively which indicates the difficulties in turbine design. The angles of the fluid including the gas flow incident angle and the blade angle are the most important parameter for turbine performance. The shaft power of rotor blades is more sensitive to the blade angle around the optimal incident angle region while the efficiency is not. The optimum flow coefficient is 2-3for maximum efficiency both in steady flow and oscillating flow. Increasing of the incoming flow oscillation frequency decrease the efficiency of the turbine. This loss mainly due to increased flow hysteresis effect which make the flow angle deviate from the design more.