Study on Aerodynamic Nonlinear Characteristics of Semiclosed Box Deck Based on Variation of Motion Parameters

In order to study the nonlinear characteristics of self-excited aerodynamic forces of bluff body bridge section with the change of motion parameters, a numerical wind tunnel is established by the dynamic mesh technique of computational fluid dynamics (CFD). A state-by-state forced vibration method is used to identify the self-excited aerodynamic forces of single degree-of-freedom (DOF) heaving and pitching motion. Fast Fourier transform (FFT) is adopted to obtain frequency-domain data for analysis. The reliability of the obtained aerodynamic results is verified by wind tunnel tests. The results show that the high-order harmonic components are found in the self-excited aerodynamic forces of semiclosed box deck section, which are more significant in aerodynamic lift than in aerodynamic moment. The proportion of aerodynamic nonlinear components increases with amplitude. The effect of amplitude on the nonlinear components of heaving motion is generally higher than that of pitching motion, and aerodynamic moment is highly sensitive to the increase of vertical amplitude. The variation of the nonlinear components of the deck section with frequency is not a simple monotonic relationship, and there is a stationary point at 10 Hz frequency. The existence of wind attack angle makes the proportion of nonlinear components reach more than 30% and greatly increases the proportion of second harmonic. In addition, the high-order harmonic components, which are not integer multiples, are found at large amplitude and positive angle of attack.

Refining the aerodynamic moment of the missile based on flight test results

This research paper is intended to refine the aerodynamic moment of the missile based on an analysis of flight tests and results of gas dynamics software computations. The paper compares mathematical simulation results with flight test data in order to demonstrate an improved convergence due to the proposed refinement.

EFFECT OF AIR PERMEABILITY ON STABILITY OF SUPERSONIC PARACHUTE

A compressible air permeability model is developed to simulate the aerodynamic performance of the supersonic porous canopy. And a single-degree-of-freedom model is applied to analyse the static stability of the parachute. By using this method, the flow structure of the parachute system with big attack angle is obtained. The aerodynamic moment coefficients of porous and nonporous canopies are compared to discuss the effect of air permeability on stability of the supersonic parachute. The numerical results show that aerodynamic moment coefficient of the system with air permeability has larger oscillation amplitude and value than that without air permeability. This method can be developed as a potential method to select the supersonic parachute initially.

Effect of Aerodynamic Moment on High-Speed Maglev Train Under Complicated Conditions

As the next generation of high-speed rail transportation, the high-speed maglev train has a design speed of 600km/h, whose Mach number is about 0.49. The severe aerodynamic effect caused by this high speed has a substantial impact on the train’s stability and safety. In this paper, the aerodynamic moments of two three-carriage maglev trains passing by each other in open air are investigated by numerical simulation. To get transient moments acting on the train, this study adopted the sliding mesh method and the k-ε turbulent model, and a user-defined function was compiled to define the motion of maglev. The results show that the pitching moment is the most important factor for the steady of maglev trains running in the open air. The oscillation of the total aerodynamic moment mainly comes from the moment acting on the lower part. The coupling of the pitching moment acting on the upper and lower part of carriages make the peak of the total pitching moment behind the total yawing moment.

Numerical Simulation of the Effect of Different Number Leading Edge Winglets on the Fan-Wing Aerodynamic Characteristics

The generation of lift and thrust mainly depends on the formation of low-pressure vortices above the arc groove on the leading edge of the Fan-wing, which makes the lift and thrust have a strong coupling relationship. How to decouple and control the lift and thrust is the key to further engineering application of the Fan-wing. Normally, the geometric parameters of the Fan-wing airfoil were determined; the leading edge opening angle has the greatest influence on the aerodynamic performance. Therefore, the method of installing leading edge winglets on the leading edge of a base Fan-wing airfoil was considered to change the opening angle of the leading edge of the Fan-wing. Through numerical simulation, the effects of single, double, and triple leading edge winglets on lift and thrust of the Fan-wing at different installation angles, inflow velocities, and angles of attack were compared and analyzed. The results show that by controlling the angle of the leading edge winglet, not only the lift and thrust of the fan can be improved but also the strength and position of the low-pressure vortices can be controlled, so as to meet the active control requirements of the aerodynamic moment of the Fan-wing, and then the attitude of the Fan-wing aircraft can be controlled.

Analysis of SamSat-218D nanosatelite motion acording to trajectory measurements

The motion of the SamSat-218D nanosatellite is analyzed by trajectory measurements. Special features of nanosatellite behavior in low orbits were experimentally confirmed. These features are due to both the influence of the atmosphere and the nanosatellites’ inherent mass-inertia characteristics: the orbital lifetime of nanosatellites is shorter, whereas angular acceleration generated by the aerodynamic moment couple is much higher than that of satellites with large sizes and masses. Variation of the ballistic coefficient in time is estimated from known trajectory measurements and information on the average density of the atmosphere at the points of trajectory measurements. The ballistic coefficient of the SamSat-218D nanosatellite having the shape of a rectangular parallelepiped depends on the spatial angle of attack and the angle of proper rotation. The ratio of the maximum value of the ballistic coefficient to the minimum value is 4.75. This made it possible to evaluate the nature of possible motion relative to the nanosatellite center of mass by the behavior of the ballistic coefficient. The most probable motion relative to the center of mass of the SamSat-218D nanosatellite is the transient motion between different equilibrium positions, due to commensurate aerodynamic and gravitational moments and insignificant angular velocities.