Aerodynamic Characteristics Investigation Of Chinese Soapberry Compound Leaves

In this paper,the wind tunnel experiment perpendicular to the direction of the inflow is used to research Chinese soapberry compound leaves in the range of0m/s²2.4m/s wind speed.Analysis of deformation and vibration including changes in compound leaves states?attitude angle?bending of the axis,air resistance coefficient.Through a large number of experimental research and statistical analysis:Discovered by high-speed camera and statistical methods Chinese soapberry compound leaves at positive windward,five states and five critical wind speeds occur at wind speeds of 0m/s²2.4m/s.According to the order of appearance of different states,it can be divided into steady state 1,vibration 1,steady state 2,vibration 2,steady state 3,where steady state 1 contains the blade axis stable and the wing stable,steady state 2 contains blade fit stable,wedge stable and spiral stable;steady state 3 contains linear roll stable and staggered roll stable.Discovered by high-speed camera coordinate analysis:Chinese soapberry compound leaves at positive windward.The blade axis inclination angle is divided into stable section and vibration section in the range of wind speed 0m/s²2.4m/s,In the stable section,the inclination angle of the blade axis presents a one-to-one correspondence with the wind speed.In the range of the vibration section,the inclination angle of the blade axis fluctuates within a certain range at a certain wind speed,and the maximum difference between the maximum and minimum values of the blade axis inclination is 40°.Overall,the inclination angle of the blade axis increases with the wind speed,and finally stabilizes at around 85°.For blade inclination,can also be divided into stable segment and vibration segment,and the vibration section has a maximum difference of about 45°.Because Chinese soapberry compound leaves has a certain curvature in the natural state,Therefore,when the wind speed is 0m/s,the yaw angle of the blade axis is not 0°,and there is a yaw angle of up to 58°,as the wind speed increases,the yaw angle of the blade axis gradually decreases,and finally stabilizes at around 10°,Similar to the inclination of the blade axis,the yaw angle of the blade axis fluctuates within a certain range due to vibration.Due to the vertical relationship between the leaf veins and the axis in the natural state,therefore,the yaw angle of the blade is approximately 80°in the natural state;as the wind speed increases,the blade gradually aggregates inward,and the blade yaw angle finally stabilizes at 0°;For one compound leaf,at a certain wind speed,the more blades,the larger inclination angle of the blade axis.The blade level will decrease as the wind speed increases;As the wind speed increases,the blades will align inward,resulting in a decrease in the lateral width of the compound leaves,and the lateral width is finally stabilized at about 20%of the natural width;As the wind speed increases,the leaf axis will shift,In the range of wind speed0m/s²2.4m/s,the displacement in the x direction changes linearly,and the displacement in the z direction move as an open downward parabola,In the x-z plane,the displacement in the z direction is in the form of an open parabola with the displacement in the x direction.As a whole,the branch is spirally rising in the space.Through the statistical analysis of axis and leaves leaf axis vibration frequency is linear with V/b,blade vibration frequency is independent of V/b;The experimental study found that the critical wind speed of the blade axis vibration is a function of the axis elastic modulus E,the leaf axis density?,the axis diameter d and the axis length l;Through the statistics of the vibration of the blade front and back,found that the probability of the wind vibrating in front of is greater than the back,and the center frequency of the frontal upwind vibration is greater than the back;General theory and experimental research found that the critical wind speed U*of the blade vibration is a function of the blade width b₁,the blade length l₁,the blade thickness h,the blade elastic modulus E_l,and the blade density?_l;The experimental study found that the St-number of leaves and the vibration frequency of the leaves showed a third-order mode.Each length-to-length ratio is 10^-2,therefore,the cantilever beam optical amplification method was used to measure the elastic modulus of each branch of the compound leaf,the elastic modulus of the compound leaf in the natural state decreases from 15M to 1000MPa in each step from top to bottom,and the elastic modulus is positively correlated with density and diameter.Found by pulse dynamic analysis.The peak-to-valley value corresponds to a state change of the compound leaf,the same attitude changes the pulse power change trend is the same;Found by Fourier spectrum analysis single-frequency vibration?double-frequency and composite-frequency vibration according to the vibration frequency of the compound leaf vibration.According to the space where vibration is located,it can be divided into three-dimensional vibration and plane vibration.Analysis by force measurement of six-component balance final stable value of the drag coefficient in the x direction is relatively scattered,and is distributed at0.025,the resistance coefficient in the y direction is finally stable to 0,in the z direction is not 0 at the end;The compound leaf Vogel coefficient is distributed between-3.0 and 1.0,and the central probability density is distributed around-1.0.