Research On Test Method Of Wind Tunnel Capture Trajectory System

The capture trajectory system is a wind tunnel special test technology used to study the separation characteristics of the aircraft,providing experimental basis for the safe and efficient separation of the aircraft and the design of the flight control system.This paper studies the key issues of the captive trajectory system in wind tunnel,including trajectory generation,kinematics of the six-degree-of-freedom mechanism and trajectory planning.Two test methods integrating measurement,aerodynamic solution and driving were designed to obtain the separation trajectory of the hypersonic vehicle.The work carried out in this paper is as follows:(1)Using Denavit-Hartenberg parametric method,the positive and negative solution algorithm for series six-degree-of-freedom mechanism is established that for displaying and controling the position of the separation body model.Using the laser tracker to detect the positioning accuracy of the six-degree-of-freedom mechanism,the results of the error are polynomial fitted and compensated to the positive and negative solution algorithm,the positioning accuracy after compensation meets the test requirements.(2)Using Newton's second law and momentum quadrature theorem to establish a set of dynamical differential equations of the separation in the separation process,using the Runge-Kutta method to solve the differential equations to obtain the actual trajectory of the separation and the moving trajectory of the separation model in the wind tunnel test section.(3)The test method of point-to-point intermittent motion and the test method of continuous motion of trajectory are designed.The former test method solves the position of the next trajectory point after stopping at the position of solved trajectory point.The latter test method solves the position of the next trajectory before moving to the solved position,and ensures the separation model continuously moves along the solved trajectory during the test.Both of these test methods use the electronic cam to achive the joint motion of all axes of the six-degree-of-freedom mechanism.The former test method uses the quintic polynomial function to plan the intermediate path between the trajectory points.The latter test method solves multiple trajectory points at a time,uses the cubic spline interpolation function and the quintic polynomial function to plan the trajectory to ensure that there is no significant fluctuation of the velocity and acceleration when the six-degree-of-freedom mechanism drives the separation model to follow the trajectory.(4)The separation trajectory under the effect of force and moment changing with time is simulated.The result shows that the designed test method has the ability to obtain the separation trajectory accurately under given initial conditions and external force.The separation trajectory under the effect of force and moment changing with position is simulated.The result shows that the trajectory obtained from continuous motion of trajectory test method is basically the same as the trajectory obtained from the point-topoint intermittent motion test method.Only a small amount of error exists when the direction of motion changes,but it has almost no effect on the separation trajectory obtained under real wind tunnel test conditions.Finally,the actual trajectories of the two test methods are analyzed,the result shows that the trajectory continuous motion test method has higher efficiency.