A static aeroelasticity analysis is carried out for the AGARD-B wind tunnel model. The Reynolds averaged Navier-Stokes (RANS) solution obtained by the cell-wise relaxation implicit discontinuous Galerkin computational fluid dynamics (CFD) solver is fed into the structural analysis method to iteratively determine the aerodynamic equilibrium configuration of the wind tunnel model. The effect of model deformation on the aerodynamic characteristics is examined. It is shown that an aerodynamic equilibrium configuration can be obtained within several iterations for typical supersonic flow conditions. The displacement computed at the wing tip was found to be less than 1mm for the AGARD-B model. However, the aerodynamic coefficients are shown to be altered with this small deformation.
Two methods of explaining the physical mechanism of the Magnus effect are compared with each other and fully discussed. The first method uses Bernoulli’s theorem and the fluid velocity difference between both sides of the body. The second one is based on the momentum theorem, which relates the lift force with the fluid acceleration perpendicular to the uniform flow direction, which is caused by the asymmetry of separation points. It is shown that the latter method is preferable because it can be strictly applied to the real flow field containing both the rotational and the irrotational flow regions.
Taking the engineering application of reusable booster vehicles (RBVs) as the research background, an effective navigation system scheme for rocket-powered auto-flyback RBVs is put forward in detail. First of all, the research state of RBVs in main research departments and three kinds of typically used feasible flyback options for RBVs are introduced. Based on an analysis of the characteristics of application background and engineering requirements, a feasible navigation scheme for a rocket-powered auto-flyback RBV is put forward, which consists of a strapdown inertial navigation system (SINS), global navigation satellite system (GNSS) and radio navigation equipment (radio). In order to realize navigation with high accuracy and dynamic adaptability, an improved dynamic information integration strategy is used for the navigation system, and simulation of the scheme based on a special trajectory is carried out. The theoretical analysis and simulation results indicate the effectiveness and feasibility of the navigation technologies.
A guidance law for an interceptor missile with a time-varying lateral acceleration limit is developed using differential games formulation with bounded controls. If an interceptor has axial acceleration and its lateral acceleration is generated by the aerodynamic lift, its lateral acceleration limit will vary with time due to its time-varying speed and the air density varying with altitude. This time-varying lateral acceleration limit property can also be obtained by designs of the time-varying sum of jets’ thrust when the interceptor is steered by divert reaction jets. The effect of this time-varying limit is investigated in this paper. The results indicate that the time-varying design of this limit leads to cooperation between the mid-course and terminal homing phase, and yields an improvement in homing accuracy. The effectiveness of this guidance law is demonstrated in a realistic ballistic missile defense scenario. It is shown that the proposed guidance law guarantees admissible accuracy, and is robust for the target maneuver commands and the delay in the estimation process of the target maneuvers. Furthermore, it provides better homing performance compared to the conventional law if the estimation delay is longer than a certain degree.
Rapid attitude maneuvering and high pointing accuracy are two keywords for advanced missions of next generation satellites. The single-gimbal control moment gyro (CMG) is regarded as an ideal torque generator for rapid maneuvering due to its torque amplification capability. However, singularities, unknown friction effects and its real steering resolution constrain its practical performance. This paper presents a robust attitude control approach based on variable-structure theory with a time-varying sliding surface. This approach guarantees minimum angular path maneuvering, global stability and asymptotic convergence in the presence of CMG practical restrictions, inertial uncertainties and various disturbances. By taking CMG gimbal friction as unmodeled disturbances, the approach is independent of the gimbal friction model. Furthermore, a magnetic compensation method with gimbal rate feedback is proposed to reduce torque-generated error caused by the CMG steering mechanism including singularity avoidance logic and steering resolution limits. This method also attenuates the frequent switching operation of the CMG during the stabilization phase. Numerical simulations demonstrate the validity and feasibility of the proposed approach. It is also shown that the magnetic compensation method does not only improve the tracking accuracy effectively, but also reduces the total power consumption, which is very desirable in practice.
We compared the flight stability of an airplane on Mars and on Earth. Two kinds of airplanes were used in our analysis: a centimeter-sized indoor airplane with a very thin and light main wing, and a meter-sized airplane flying outdoors. Our comparisons show the following. (1) A longer period is required to damp or diverge disturbances on Mars than on Earth. (2) On Mars, the added mass and added moment of inertia can be ignored for a light wing, whereas the added mass and added moment of inertia cannot be ignored on Earth. (3) The natural circular frequencies in the short period, the phugoid, and the dutch roll modes are smaller on Mars than on Earth. The reduced frequencies, based on the natural circular frequencies on Mars, are smaller than those on Earth. The smaller reduced frequencies and the smaller added mass and added moment of inertia imply that the significance of unsteady aerodynamic force due to fuselage motion is lower on Mars than that on Earth.
The effects of heating or cooling of the supersonic flow in a Laval nozzle have been investigated numerically. We focus on the exhaust velocity and the area ratio at given expansion ratios, which are ranged from 30 to 16,000. This range is equivalent to the area ratio from 4 to 400 at the specific heat ratio of 1.3 under isentropic expansion. Two types of heat profile are considered: pulsed heat transfer (PHT) and distributed heat transfer (DHT). The relations of Rayleigh flow and isentropic expansion are used for PHT. The exhaust velocity is higher than the isentropic value for the case where heat is provided near the throat. In other cases, the exhaust velocity is less than the isentropic value. The equivalent point of heat transfer is introduced for DHT. Using this equivalent point, the results for DHT exhibit the same trend as the results for PHT. This indicates that the effects of DHT can be predicted directly from results for PHT without numerical analyses.
To model porous walls used in transonic wind tunnels, flow through a hole is investigated using Computational Fluid Dynamics (CFD). First, we analyze the relation between flow rate and differential pressure across the hole. At low differential pressures, such as for wind tunnel porous walls, the flow rate is found to increase linearly with differential pressure. We therefore propose a new model based on a linear relationship between flow rate and differential pressure. The effects of hole shape and boundary layer conditions near the hole are then investigated. In the outflow case (i.e., wind tunnel to plenum chamber), the flow rate increases as the ratio of hole depth to diameter becomes large due to variation of the flow separation area at the hole exit. Boundary layer thickness also affects the flow field: when the ratio of boundary layer thickness to hole diameter becomes small, the flow rate decreases, because the flow along wind tunnel side wall interacts more strongly with the flow through the hole.
The traditional flight mechanics for scale helicopters uses a counter-clockwise, reduced-order rotor model that does not account for off-axis responses. The present paper deals with an improved rotor model that can set different directions of rotation and also reflects the off-axis responses of the rotor. In addition, the iterative method, which is used for rotor thrust calculations, is replaced with the dynamic inflow model. The nonlinear simulation results correlate well with the flight test results.
Carbon fiber-reinforced composites have been recently applied for engine fan blades because of their high specific strength. In the design of the fan blade, bird-strike impact is one of the greatest concerns, since impact-induced damage can lead to the engine stalling. This study presents a numerical method to analyze bird-strike impact as a soft-body impact on a cantilevered composite panel. Especially, we coupled a stabilized dynamic contact analysis, which enables appropriate prediction of impact force on the panel, with laminate damage analysis to predict the impact-induced progressive damage in the composite. This method is verified through a comparison with experimental results. With the numerical method, we investigate the effect of impact condition, blade thickness and shape on the impact-induced damage in a composite fan blade subjected to a bird strike. An intermediate blade thickness and a large blade curvature help to improve the bird-striking impact resistance of the composite.
Normal Earth observation satellites operate under a nadir-pointing stabilization mode. The effective swath width of observation is limited by the camera’s field-of-view (FOV). In order to achieve continuous and wide swath coverage, a rapid regional scanning observation mode is proposed and analyzed in this paper. Periodic maneuvering about the roll axis is needed to fulfill the mission requirement. A zigzag-like trajectory is developed as a tracking reference trajectory. A sliding mode control algorithm is exploited to achieve high-precision tracking performance. Then, a mixed steering logic utilizing two symmetric-configured control moment gyros (CMG) and three orthogonal-placed magnetic torquers (MTQ) is proposed. CMGs provide large torque for rapid roll maneuvering, and MTQs help to compensate pitch angular velocity bias introduced by the orbital motion. The feasibility of the proposed strategy is verified through numerical simulations. Moreover, this strategy will be further demonstrated on the fourth small satellite, named TSUBAME, designed by the Laboratory of Space Systems at the Tokyo Institute of Technology. TSUBAME is equipped with an ultra-small optical camera designed by the Kimura Laboratory at Tokyo University of Science.