The present study evaluates the longitudinal stability characteristics under the influence of the wing-in-ground (WIG) effect by applying Irodov’s criteria. First, the applicability of Irodov’s criteria in estimating longitudinal stability for WIG vehicles was confirmed by derivation of the criteria and order estimation prior to usage of criteria. Second, aerodynamic analysis was conducted using the Navier-Stokes solver for the Clark-Y wing and wing-endplate combinations at various heights. Finally, longitudinal stability was evaluated using Irodov’s criteria. On analysis, four assumptions were set for the evaluation of longitudinal stability under the influence of the ground effect. The most important assumption is that the stability contribution of the horizontal tail is negligible when the ground effect is strong. Under these assumptions, the computational results satisfactorily demonstrate the stable behavior of the vehicle under the influence of the ground effect when the Clark-Y wing and wing-endplate combinations are used.
This paper describes a new pressure measurement technique for measuring the pressure over rotating blades of an industrial axial flow fan. The new technique is called the pressure sensitive foil (PS-Foil) technique. In this technique, a very thin aluminum foil is coated with pressure sensitive paint using anodization. The resulting PS-Foil can be stuck on any blade using a very thin layer of silicon. The PS-Foil technique shows a very fast time response like conventional porous anodized aluminum and can be applied to any rotor blade without fabricating the blade from aluminum. The total thickness of the aluminum foil and silicon layer is as small as 200 μm. An intensity based method and prior calibration procedures are used to obtain the calibrated PSP image. The unsteady experimental setup presented here shows that the PS-Foil time response is on the order 30 μs which is close to the conventional porous anodized aluminum method. Two applications are considered here to assess the applicability of this technique. Subsonic jet-plate impingement, and rotating blade of industrial fan. The pressure distribution over the impingement plate at different plate angles, and over the rotating blade at various speeds could be obtained with sufficient spatial resolution.
The flight test is important in the development and certification phases of an aircraft. It is composed of various tests, but the position error correction test should be performed first to determine error of the pitot-static measurement system that is the basis for evaluating flight characteristics. This paper investigates and compares recent test methods using real flight test results. The ground course and arbitrary heading method are both considered using GPS and DGPS to measure ground speed. The arbitrary heading method was most efficient and precise. In addition, new method is proposed and successfully used to determine accurate position error by comparison with DGPS results. Finally, sensitivity analysis was performed to analyze the effect of error sources. It shows that the most important error is the measured indicated airspeed following by measured true airspeed, outside air temperature, and pressure altitude.
Assuming that the sequence of the member satellites in a formation is unchanged, this paper presents a new control scheme to change the configuration of the formation from one elliptic relative trajectory (cart-wheel orbit) to another elliptic relative trajectory by using impulsive control. First, the full analytical fuel-optimal solutions of in-plane and out-of-plane orbit transfer problems using impulsive maneuver are derived, respectively. Next, the single satellite orbit reconfiguration problem is solved by using these fuel-optimal impulsive control strategies. Based on the fuel-optimal single satellite reconfiguration solutions, a new asynchronous control scheme for satellite formation reconfiguration is proposed. This new control scheme can achieve the objectives of total minimum fuel consumption of the formation, balanced fuel expenditure of the single satellite, and collision avoidance between the satellites in formation. Furthermore, this new control scheme has an analytical form, so it is simple and convenient for onboard application. The limitation of this new control scheme is that as the member satellites increases, the total reconfiguration time increases proportionally.
A 3D numerical simulation was conducted to study the effect of inlet boundary layer thickness on rotating stall in an axial compressor. The inlet boundary layer thickness had significant effects on the hub-corner-separation at the corner of hub and suction surfaces. The hub-corner-separation grew considerably for a thick inlet boundary layer as the load increased, while it diminished to become indistinguishable from the rotor wake for a thin inlet boundary layer and another corner-separation originated near the casing. This difference in the internal flow near stall also had a large effect on characteristics of the rotating stall, especially the initial asymmetric disturbance and the size of stall cells. While a pre-stall disturbance arises firstly in the hub-corner-separation for the thick inlet boundary layer, an asymmetric disturbance was initially generated in the tip region because of the corner-separation for the thin inlet boundary layer. This disturbance was transferred to the tip leakage flow and grew to become an attached stall cell, which adheres to the blade passage and rotates at the same speed as the rotor. When this attached stall cell reached a critical size, it started moving along the blade row and became a short-length-scale rotating stall. The size of the stall cell for the thick inlet boundary layer was larger than for the thin inlet boundary layer. Due to the bigger size of the stall cell, the performance of the single rotor for the former case dropped more significantly than for the latter case.
A differential game guidance law for an endoatmospheric interceptor missile steered by aero fins and reaction jets is developed in this paper with bounded controls. For a low-altitude endoatmospheric interceptor, the propellant of the reaction-jet control system (RCS) is restricted by the missile configuration. Considering propellant limits, the effect of the RCS thrust on homing performance is investigated through game space structures. Also, to use the RCS at an appropriate timing, game space decomposition is used to determine the initiating time of the RCS. Finally, the effectiveness of the guidance law is demonstrated by a realistic ballistic missile defense scenario. It is shown that the proposed guidance law provides a significant improvement in homing accuracy compared to the conditional one. Furthermore, under propellant limits, a bigger RCS thrust cannot guarantee a higher homing accuracy.
Describing the flight behavior of a helicopter is a difficult challenge in mathematical modeling. A rotorcraft can be considered as a complex arrangement of interacting subsystems, and the problem is dominated by rotor. The rotor blades bend and twist under the influence of unsteady and nonlinear aerodynamic loads, which are themselves a function of blade motion. This problem makes it more difficult to estimate the behavior of a helicopter. Furthermore, it is difficult to design a flight controller for unmanned helicopter systems. In this paper, to obtain a nonlinear dynamic model of a helicopter, parameter identification is performed using flight test data. A globally stable tracking control law for agile and precise landing of an unmanned helicopter is proposed. A near-minimum time control scheme is adopted to design the reference trajectory, and it is shown that the control law is guaranteed to be stable globally in the sense of Lyapunov. A flight test verified the performance of the proposed method. Performance can be improved by choosing the control parameters via optimization. The proposed method can be extended to a multiple output trajectory tracking problem for a precise fixed-wing UAV landing.
This paper establishes a dynamics model for deploying solar panels with clearances by using a practical method and provides a useful way to identify the effects of clearances on spacecraft systems. Considering the clearance of joints, a contact dynamic model is established using the nonlinear spring-damp model and the friction effect is considered by using the Coulomb friction model. Based on the model, numeric simulation of the deployment of a single panel with clearance on a spacecraft is presented. The effects of the clearance on attitude motion of the spacecraft as well as the deployment of a solar panel with joint clearance are analyzed. The simulation results predict the effects of clearance on the attitude motion of a spacecraft system and the deployment dynamics of solar panel preferably. It is useful for engineering design of a spacecraft control system and ground text. This work provides a valuable method for improving the dynamics of spacecraft systems.
The dynamics of flow structures in the near field of orifice plane jets with sharp-edged and right-angle exit profiles are studied experimentally. The operating velocities of the jet flow are within U0=5–20 m/s. Test results show that the evolution of the jet flow is significantly influenced by the initial orifice exit profiles. The initial fluctuating velocities of orifice plane jets are higher than the case of contoured nozzle plane jets. The vena contracta effect plays a crucial role in the flow development of the orifice plane jet. The length of potential core, mixing characteristics and turbulence properties are also extensively investigated in this paper. The energy transfer characteristics can be aptly characterized by the evolution of coherent structures. The kinetic energy gained at the immediate orifice exit is contributed to by mean energy advection. The fluctuation kinetic energy implants into the turbulent flow through turbulent energy advection at the vortex merging process because no positive value for turbulent energy production is observed there.
A novel centroid algorithm is proposed to acquire better centroid performance in a star image. Since photons incident on pixels of stars present a Gaussian point spread function (PSF), so, the centroid locations on the x and y-axis are calculated using the pixel intensity ratio and expand the Gaussian PSF to polynomials with respect to the centroid location. The angular separation error between star pairs is used to verify the proposed algorithm indirectly. The result clearly shows that the centroid accuracy achieves 1/33 of a pixel and is about two times better than the moment method, indicating the new algorithm is effective.
An unstructured grid CFD code capable of handling arbitrary polyhedra, named “LS-FLOW,” is developed for aerodynamic analyses of complex geometries. Through a series of numerical test cases, it is demonstrated that LS-FLOW can handle both structured and body-fitted/Cartesian hybrid unstructured grids successfully. Then, the code is validated by comparison with experimental data and theoretical solutions. In addition, it is shown that when a Baldwin-Lomax algebraic turbulence model is employed on the body-fitted/Cartesian grid, the portion of the body-fitted grid should be large enough to contain the whole boundary-layer. Finally, LS-FLOW is applied to a rocket configuration, and its future prospects are addressed.
A supersonic flow is achieved by a convergent-divergent Laval nozzle. A subsonic-supersonic transition is also possible in a one-dimensional isentropic flow through a uniform rotating pipe of constant cross-sectional area with a bend by the centrifugal effect. A uniform pipe with a bend lies in a meridional plane and rotates around an axis and the centrifugal force on the pipe flow has the same effect as that of an area change in a Laval nozzle. The governing equations similar to those of a Laval nozzle are derived for the one-dimensional isentropic flow in a rotating uniform pipe with a bend of constant cross sectional area, and the shock relations are also obtained.