Study On Wake Model And Array Arrangement Of Vertical Axis Turbine

In recent years,some international problems,such as energy crisis,climate change and carbon neutralization,are becoming more and more serious.As a kind of clean and potential energy,renewable energy is receiving more and more attention.Vertical axis turbine(VAT)is a common energy extraction device and has many advantages,such as low operation and maintenance(O&M)costs,low noise,beautiful appearance,and no need for a yaw control mechanism.Moreover,in these years,some studies have pointed out that although the power coefficient of a single VAT is not higher than the horizontal axis turbine(HAT),the VAT array can capture more energy per unit array area and achieve higher array power density.Because of the good performance of the VAT array,and the wind turbine and tidal turbine will be arranged in the array layout in the future,the research on the VAT array is becoming more and more important.The main tool of array optimization is the wake model,which includes numerical model and algebraic model.Generally,the numerical wake model is numerical calculation with appropriate empirical correction,which can quickly calculate the wake velocity according to the different conditions.The algebraic wake model is a data-driven model,which can fit the velocity profiles at different cross sections and reproduce the flow field quickly.The numerical wake model and algebraic wake model are often used in array arrangement.However,in view of the lack of research on wake model and array arrangement of VAT,it is necessary to propose the appropriate wake model for the array arrangement.Firstly,by analyzing the characteristics of each sub method and the requirements of array arrangement for wake model,a numerical wake model based on finite vortex method and vortex particle method is proposed.In this model,the finite vortex method is used to calculate the blade load,the vortex particle method is used to calculate the wake evolution,and finally the two-dimensional wake results are modified according to the power-law function of wake velocity.According to the preliminary verification,it can be proved that the simulation results can achieve first-order accuracy,the deflection characteristics of VAT wake can be well reflected,and it is more efficient than the traditional RANS numerical model,which meet the requirements of wake model on the calculation efficiency and accuracy.According to the deflection characteristics in the wake field obtained by numerical simulation,an algebraic wake model based on Double semi Gaussian functions is proposed in this paper.It can well fit the asymmetric velocity profile of the VAT wake.Based on the momentum theorem,the relationship between turbine force coefficient(thrust)and wake parameter(peak of velocity deficit)can be constructed.And its model parameters can well correspond to the characteristic parameters of the wake.The model can reproduce the phenomenon of wake merging in case of the outer counter rotating double rotors,it can also be used to proved the self-similarity of the wake velocity profiles.Comparing the wake results of numerical model and algebraic model,the algebraic model can better meet the requirements of array arrangement on computational efficiency and accuracy.Therefore,the algebraic model is used to study array arrangement.Single rotor,inner counter rotating double rotors and outer counter rotating double rotors are the three common basic units in the VAT array arrangement.In this paper,the three kinds of VAT array are studied under the criteria of inflow velocity,power density and the combination of truncation coefficient and power density.By observing the compact arrangement of the optimal array under the power density criterion,a new array optimization method with finite region of wake influence is proposed,which takes the wake boundary as the finite region of wake influence.It takes the compact arrangement as the principle,and carries out array optimization from a geometric view.The geometric method can obtain the optimal configuration faster than the flow field method.And it can provide geometric explanation for the position parameters of optimal array obtained by the flow field method.Finally,the optimization results of single rotor and double rotors arrays are compared,and the suggestions for array arrangement are put forward.In summary,a numerical wake model is proposed,which is more efficient than the traditional RANS model.An algebraic model is proposed,which is more accurate than the traditional Gaussian and Top-hat algebraic model.An array optimization method based on finite region of wake influence is proposed,which is faster than the traditional array optimization method based on the wake field.The research methods of array arrangement are enriched,some suggestions for array arrangement are put forward,which are beneficial to the array arrangement of VAT in engineering.