Study On The Aerodynamic Performance Of Impulse Turbine Used In Wave Energy

The efficient development and utilization of wave energy has important scientific value and practical significance in solving the shortage of resources,reducing environmental pollution and promoting the sustainable development of energy.As an important intermediate energy conversion device of oscillating water column wave energy system,impulse air turbine has relatively low conversion efficiency,which leads to low overall power generation efficiency of oscillating water column wave energy generation device.Based on the CFD numerical method,the effects of different blade thickness,blade rotation angle and blade incidence angle on the efficiency and aerodynamic performance of the impinging air turbine were studied.At the same time,the transient flow characteristics of the impulse turbine under the condition of regular wave reciprocating flow are also studied.The main research results are as follows:(1)The effects of blade thickness,blade rotation angle and blade incidence angle on the efficiency of impulse turbine were studied under the condition of unidirectional steady flow.It is found that the turbine input coefficient and torque coefficient decrease with the decrease of blade thickness,and the maximum efficiency occurs when the blade thickness is 16.1mm.However,the effect of blade thickness on efficiency is limited.With the decrease of the rotation angle,the torque coefficient and efficiency of the turbine increase,and the maximum efficiency of 57% occurs when the rotation angle is-6 °;when the rotation angle is negative,the input coefficient of the turbine is basically the same;when the rotation angle is positive,the input coefficient of the turbine increases with the increase of the rotation angle.With the decrease of blade incidence angle,the input coefficient and torque coefficient of the turbine increase,but the efficiency of the turbine decreases.The maximum efficiency of 45% occurs when the incidence angle is 45 °.The turbine efficiency can be significantly changed by changing the blade rotation angle and incidence angle.(2)The pressure distribution,surface load and velocity distribution of the flow field under the condition of one-way steady flow are studied.The results show that the energy loss of the blade mainly focuses on the impact loss at the inlet of the rotor blade,the return caused by the reverse pressure gradient of the suction surface of the blade,the vortex dissipation in the flow around the blade trailing edge and the vortex dissipation in the downstream guide vane channel.Reducing the thickness of blade,reducing the rotating angle and increasing the incidence angle of blade are all beneficial to reducing the negative pressure area at the inlet,making the blade surface have relatively uniform pressure distribution,thus reducing the impact loss and the reverse pressure gradient on the suction surface at the inlet,and also reducing the vortex distribution at the lower guide vane flow path,thus reducing the energy loss of the turbine.(3)The influence of blade thickness,blade rotation angle and incident angle on the frequency domain of pressure fluctuation on the surface of impact turbine blade is studied.It is found that the incident wave with time is the main reason for pressure fluctuation in the impact turbine.Therefore,the frequency of pressure fluctuation on the blade surface is mainly the frequency of incident wave or multiple of incident wave frequency.It is also found that the high-intensity pressure fluctuation is mainly the static pressure fluctuation on the blade surface.There are many high frequency components in the dynamic pressure fluctuation on the blade pressure surface,which is caused by unsteady flow near the blade pressure surface.(4)The main frequency amplitude of pressure fluctuation on blade surface under different conditions of regular wave reciprocating flow is studied.It is found that with the decrease of blade thickness,the first main frequency amplitude of pressure fluctuation decreases gradually;with the decrease of rotation angle,the first main frequency amplitude of static pressure on blade surface increases gradually,while the first primary frequency amplitude of dynamic pressure decreases first and then increases;with the decrease of incident angle,the first main frequency amplitude of static pressure on blade surface and the first main frequency amplitude of average dynamic pressure on suction surface are gradually decreased The first main frequency amplitude of the average dynamic pressure decreases gradually.