| With the global climate change,the problems of energy security and environmental pollution are becoming more and more serious,and the development and utilization of new energy in various countries are increasing year by year.In the new energy structure,wind energy is highly valued by developers and researchers for its unique advantages.As an important mechanical equipment for the conversion of wind energy to mechanical energy,wind turbines are mainly divided into horizontal and vertical axes: although horizontal axis wind turbines have relatively high efficiency,they have shortcomings such as high manufacturing and maintenance costs,blade fatigue and serious noise pollution;vertical Due to its inherent structural characteristics,the shaft wind turbine has the advantages of multi-directional wind,no yaw device,stable system and strong environmental protection.It can overcome the above shortcomings of the horizontal shaft to a certain extent.However,during the rotation period of a vertical axis wind turbine,the blade’s relative angle of attack and speed change drastically,which easily causes flow separation and stall phenomena,resulting in increased aerodynamic losses and reduced wind energy utilization.Therefore,it is particularly important to slow or suppress dynamic stalls through effective flow control techniques to improve aerodynamic performance at high angles of attack.As a passive flow control method,Gurney flaps have a significant lift effect.However,traditional Gurney flaps cannot be adjusted according to changes in the external environment,resulting in increased resistance in some areas.To this end,the Gurney flap was improved to an active flow control method,so that it can reciprocate on both sides of the blade to achieve the best flow control effect.In this paper,a new dynamic Gurney flap applied to airfoil pitching motion and vertical axis wind turbines is studied by numerical methods,and its impact on aerodynamic performance and noise is analyzed.The main work and conclusions are as follows:1.A numerical model is established based on the straight-wing vertical axis wind turbine,and the reliability of the numerical parameters such as the calculation method,grid distribution,turbulence model and time step is verified,which provides effective values for the airfoil and vertical axis wind turbines that are subject to active flow control.model.2.In order to reduce the stall phenomenon during the dynamic pitch of the airfoil,dynamic Gurney flaps were placed at 10%c of the leading edge of the airfoil and the aerodynamic performance was studied.The results show that as the airfoil angle of attack increases,the leading edge Gurney flap airfoil can effectively suppress the occurrence of dynamic stall and delay the separation of the separation vortex from the leading edge of the airfoil.The dynamic Gurney flap can significantly reduce the drag coefficient while keeping the lift coefficient constant or increasing,and reduce the hysteresis effect of the airfoil during the movement;during its upward pitch,compared with the original airfoil,Airfoils with Gurney flaps can maintain a relatively high lift-to-drag ratio.3.In order to compare the effects of dynamic Gurney flaps,the effects of the aerodynamic performance and flow field structure of vertical axis wind turbines with three static Gurney flaps(outside,inside,and both sides)were analyzed.All the flaps can improve the aerodynamic performance of the whole machine.At the optimal tip speed ratio,the outer Gurney flap can increase the maximum wind energy utilization factor,and increase the maximum tangential force of the blade in the windward zone,and the inner Gurney flap can increase The moment coefficient of the blade in the leeward zone.4.Based on the periodic variation law of the angle of attack of the vertical axis wind turbine blades and the characteristics of static Gurney flap lifting,a new dynamic Gurney flap that can be reciprocated on both sides of the blade is proposed.Four different reciprocating motion laws were studied through numerical simulation.The results show that the dynamic Gurney flap has a higher wind energy utilization coefficient than the static flap,and can reduce the optimal tip speed ratio of the wind turbine and improve the operational stability;At low tip speed ratios,dynamic Gurney flaps can increase the tangential force of a single blade and increase the starting torque of the whole machine at low wind speeds;through the study of the movement mode and extension height of Gurney flaps,it is found Sinusoidal motion on both sides of the blade has the best control effect;When the height of the Gurney flap exceeds a certain range,the improvement effect of the wind energy utilization rate of the whole machine gradually decreases with the increase of the tip speed ratio,and will increase the blade fatigue load..5.Based on the sound analogy method,the influence of dynamic Gurney flaps on the aerodynamic noise of vertical axis wind turbines is analyzed.The sound source data is collected through the flow field parameters and the aerodynamic noise is analyzed.The pressure distribution on both sides of the blade leads to increased pressure fluctuation at the trailing edge;At low tip speed ratios,dynamic Gurney flaps reduce the sound pressure level in the low frequency band,while at medium and high tip speed ratios,the dynamic Gurney flap will increase the sound pressure level by 100 to 1000 Hz,resulting in aerodynamics The noise increases. |
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