Abstract:The jet in crossflow at very low Reynolds number (Re=100) with and without block is performed by means of large eddy simulation for the jet-to-crossflow velocity ratios (r) ranging from 1 to 3, and the corresponding flow characteristics are compared. The results show that the time-averaged particle trajectories of the jet are slightly changed if a block is presented, and the mixed vortices are weakened. The existence of the block also can accelerate the formation of stable counter-rotating vortex pair. At lower velocity ratio (r=1), the block has little effect on the jet in crossflow with a symmetrically positive and negative kidney shaped vortices. As the velocity ratio increases, the effect of block not only can generate an asymmetry of positive and negative kidney shaped vortices, but also it can reinforce the interaction between the positive and negative vortices in the jet in crossflow. The effect of block on the temperature field is also analyzed in detail.
Coning motion of spinning carriers is a complex rotating motion with various forms that include single circular motion, double circular motion and multiple circular motion. Due to the fact that it is difficult to describe the real coning motion of double circular motion and multiple circular motion by the common method of attack angle and sideslip angle (A-S), a cone frame and cone angles are defined to describe coning motion. Through analysis of measuring the relationship between coning motion and inertial devices such as gyroscopes and accelerometers, an inertial measuring method is proposed to build the measuring equation and resolving equation. A geometry-solving algorithm of real coning motion is derived in detail, and radiuses of large circle and real cone circle are obtained as well. A flight simulation of a spinning carrier with coning motion is designed and used to verify the measuring method and the geometry-solving algorithm. The result shows that: (1) the inertial measuring method has the same validity as A-S method to describe coning motion, but is superior to A-S method for the reason of providing the rotation information of carriers; (2) due to coupling relationship, the rotating angle is equal to the subtraction of roll angle and precession angle; (3) the real precession angle and the real nutation angle are calculated by the geometry-solving algorithm, and the real coning motion is obtained finally.
Conventional attitude algorithms have been improved for many years, but they still have attitude updating errors due to the coupling in the complicated angular motion of spinning bodies. A real-time angular motion decoupling and attitude updating method assisted by satellite navigation data is proposed in this paper. A compositive model of angular motion for spinning bodies is built to understand and analyze the trait of angular velocity. A detailed process of angular motion decoupling is addressed with the help of satellite navigation data, including a backward decoupling process and a forward decoupling angular process, to estimate angular velocity to guarantee real-time ability. A real-time attitude updating algorithm is presented in detail for determining the real attitude of spinning bodies, and the updating process of coning attitude based on rotation vector is provided. Simulations are carried out to show the coupling effect of angular motion on the conventional attitude algorithm and verify the validity of the proposed method, and flight data are used to verify the availability of engineering application. Results show that the angular motion is decoupled and attitude accuracy is improved successfully.INDEX TERMS Spinning bodies, coning motion, angular motion decoupling, attitude updating, real-time.
To solve the real-time problem of attitude algorithm for high dynamic bodies, a real-time structure of attitude algorithm is developed by analyzing the conventional structure that has two stages, and a flow diagram of a real-time structure for a Matlab program is provided in detail. During the update of the attitude matrix, the real-time structure saves every element of attitude matrix in minor loop in real time and updates the next attitude matrix based on the previous matrix every subsample time. Thus, the real-time structure avoids lowering updating frequency, though the multisubsample algorithms are used. Simulation and analysis show that the real-time structure of attitude algorithm is better than the conventional structure due to short update time of attitude matrix and small drifting error, and it is more appropriate for high dynamic bodies.
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