Research On Optimization Design Of Air Turbine Performance Improvement In SCPPVC System

The air turbine in SCPPVC system is studied in this paper,Starting from the air turbine blade airfoil structure,the overall structure of the turbine,and the air circulation structure,three optimization models of the new airfoil turbine blade structure combined with the double airfoil,the air turbine with a disc,and the zoom chimney flow channel are formed.To further improve the aerodynamic performance of the air turbine.The simulation and experimental analysis from the aspects of structural parameters,aerodynamic performance,flow field streamlines etc,have verified the correctness and application feasibility of the air turbine performance improvement.Taking airfoil NACA63-215 and airfoil SD8000 as the initial airfoil,the upper surface of airfoil NACA63-215 and the lower surface of airfoil SD8000 are combined to form a new airfoil smoothly.The study found that compared with the reference airfoil,the lift coefficient of the new airfoil can be increased to more than 10%at different angles of attack,the drag coefficient is reduced and the fluctuation is smaller,the lift-to-drag ratio has been correspondingly improved,and the maximum lift is obtained at the same time.At the drag ratio,the angle of attack is the smallest among the analyzed airfoils,and the blade rotation start time is shortened.The lift coefficient of the new airfoil under different incoming wind speeds can reach over 0.9,an average increase of about 14%;the minimum drag coefficient can reduce friction and air flow along the way;the lift and drag comparison reference airfoil can be increased to more than 20%.The lift-drag ratio of the new airfoil has always been the largest under different surface roughness,which reduces the influence of roughness on the airfoil performance.The static stability of the new airfoil at different angles of attack is also optimal.Taking the designed new airfoil as the basic airfoil,based on Wilson’s theory,using Matlab software iterative solution method,the axial and circumferential induction factors at different section radii of the blade are obtained,and the chord length and torsion angle at different radius positions are obtained.Corresponding three-dimensional transformation coordinates are substituted into Soildworks software to draw,and a new model of air turbine with 3-8 blades is established.CFD software is used to establish a grid model of the entire SCPPVC system and simulate and analyze the performance and flow field of the air turbine.The influence of factors such as tip speed ratio and wind speed on the aerodynamic performance of air turbines such as torque,speed and power is analyzed.The torque of the turbine will first increase and then decrease as the tip speed ratio increases.With the increase of the blade,the tip speed ratio corresponding to the maximum torque decreases gradually.The higher the incoming wind speed,the higher the output power and energy conversion efficiency of the turbine.Both have the maximum value under 7 blades,and the minimum under 3 blades.Analysis of the cloud diagram of the flow field found that the positive pressure on the windward side of the turbine under the flow channel section is larger,while the leeward side has a smaller static pressure.The closer to the turbine,the lower the airflow velocity.The pressure difference between the blade tip and the middle of the blade under the cross section of the system is large,and the pressure difference at the blade root is small,which can make the middle of the blade and the tip of the blade generate more torque and increase the output power;as the number of turbine blades increases,The airflow area disturbed by the blades also increases,and the turbulence of the airflow between the blades is greater.In order to improve the air utilization factor of the turbine and the ability to capture wind energy,and to reduce the impact of airflow on weaker roots,a shunt circular baffle was installed in the front of the air turbine wheel pad.Analyzed the influence of the disc on the flow field of the flow channel where the air turbine is located.The results show that after the air passes through the turbine,there is obvious flow expansion.The airflow passing through the root of the blade is more skewed towards the middle and tip of the blade with strong function,and the speed of the blade root is greatly reduced;the pressure difference between the front and rear of the turbine becomes larger,and the airflow speed in the nearby flow field increases.When the ratio of the axial distance between the disc and the hub to the turbine wheel radius satisfies 5%<d/R<15%,and the ratio of the disc radius to the turbine wheel radius satisfies 12%<r/R<16%,the turbine can be improved The flow characteristics of the flow field in which it is located,and effectively improve its aerodynamic performance.And when d/R=10%and r/R=18%,the maximum wind capacity of the turbine blades is 0.7445m~3/s;when d/R=15%and r/R=16%,the maximum power coefficient of the turbine is 38.96%.In order to make full use of the incoming air and increase the output power of the turbine,the air flow channel of the chimney is designed as a scaling structure.Through orthogonal analysis,it can be concluded that the size of the inclination angle is the variable that affects the air utilization coefficient of the turbine the most,and the length of the throat has the least effect on the air utilization coefficient of the turbine.The scaling section slope Angleαis appropriately small within the allowable range,the scaling section length L and the chimney diameter D meet the L/D in 50%-75%,the throat length H and the chimney diameter D meet the H/D in 50%-60%,and the air utilization coefficient of the turbine can be significantly improved.Through experimental research,it is found that the output power of the turbine first increases and then decreases with the increase of the number of blades at a certain flow rate,and the power output of the seven-blade turbine is the most.Compared with the cylindrical channel,the scaling channel can increase the output power of the turbine by up to 22%under 7 blades.When the incoming wind speed is in the range of 2m/s-5m/s,the experimental output power of the turbine in the scaling flow passage is 22%-31%higher than that in the cylindrical flow passage.The analog power is 18-42% higher.