The Influence Of Wave-uniform Flow Interaction On Hydraulic Performance Of Vertical Axis Turbine

In the actual marine environment,the marine dynamic process is complex and diverse.Tidal currents often interact with waves,causing environmental loads that combine the effects of waves and currents,which can cause immense damage to offshore structures,waterways,etc.In this paper,the second order stokes wave flume was established by numerical simulation with the vertical three-blade turbine as the research object.Under the combined action of waves and tidal currents,the hydrodynamic performance of the turbine during operation was studied,at the same time,it proposes corresponding improvenent methods for the shortcomings of turbine output energy and instability in the load of uniform flow and uniform-wave flow.The main research contents include the following points:1)Established on the basis of the second order Stokes wave equation,According to the analytic solution of traveling wave,the reasonable way of setting numerical wave boundary condition is explored.Boundary wave generation method,damped wave elimination technology and VOF free surface treatment method are adopted.Two-dimensional and three-dimensional numerical wave flume were constructed based on CFX software,and the numerical simulation of seconcd-order Stokes waves was successfully realizecd.The numerical wave has good quality and has goocd stability and periocdicity in the process of climbing and descending,which is in good agreement with the theoretical waveform.Among the errors of wave parameters,the maximum error of wave height is caused by energy dissipation cdue to wave viscous actiorn.2)Based on the wave numerical simulation method,A vertical axis ticdal current turbine is added to a three-dimensional flume to simulate and analyze the turrbine under the combined environment of second-order Stokes wave and uniform flow.The performance and irnternal flow field of the turbine under the uniform flow ancd combined wave-uniform flow conditions are compared.The results show that the wave-uniform flow coupling flow causes great fluctuation of the output energy and aggravates the instability of the unit.The internal actual flow field is an unsteady flow field that changes constantly with the coupled flow of wave and uniform.It becomes more complicated and disordered by the superposition of the waves and uniform,forming a long vortex at the tail of the blade and behind the shaft.3)In order to improve the stability of the energy output of the vertical axis water turbine under the uniform flow and combined wave-uniform flow conditions,a runner with helical triangular blade was designed to replace the traditional straight blade H-type runner,the hydraulic performance of the helical triangular impeller under uniform flow environment was studied.After comprehensive comparison,the runner with 150°helical warp angle has the best performance,which improves the energy capture coefficient and the stability of energy output.In addition,by comparing the vorticity field between the initial and modified runner,it can be found that the helical triangular blade effectively reduces the range of the wake vortex of the blade.And the amplitude of pressure fluctuation on blade surface also be reduced.All of these indicates that the helical triangular blade are conducive to the improvement of the operation stability of the vertical axis water turbine.