Abstract: Flutter is a dynamic instability problem represents the interaction among structural, aerodynamic, elastic and inertial forces and occurred when the energy is continuously transformed by the surrounding fluids to a flying structure in the form of kinetic energy. The study was conducted to investigate the relationship of the control surface deflection angle to the flutter speed and the flutter frequency. A wind tunnel test was performed using a flat plate wing made of composite material. It was found that by deflecting the control surface up to 45°, the flutter speed reduced almost linearly from 35.6 m/s to 22.7 m/s. The flutter frequency greatly reduced from 48 Hz without the control surface deflected to 34 Hz with the control surface deflected at 15°. After 15° deflection up to 45°, the flutter frequency reduced almost linearly.
Abstract: Experimental study of an integrated aerodynamic-ramp-injector /gas-portfire (aero-ramp/G-P) has been conducted in a hydrogen-fueled scramjet combustor. The aero-ramp injectors consisted of four flush-walled holes, arranged to induce vorticular motion and enhance mixing. For comparison, a recessed cavity with four low downstream-angled circular injector holes was also examined. The combustor models were investigated experimentally using the scramjet direct connected test facility at the Beihang University. The facility can deliver a continuous supersonic flow of Mach number 2 with a total temperature of 1200K. The hot experimental results showed that the combustion efficiency and air specific impulse of aero-ramp/G-P are 85% and 35s while the corresponding values of cavity are 92% and 34s. These results justify the feasibility of aero-ramp/G-P flame holder.
Abstract: This manuscript presents the vortex flow structure over non-slender delta wing with leading edge sweep angle, Λ=45°. A comprehensive investigation has been conducted in wind tunnel at Reynolds number ranging from, Re = 247,000 - 445,000. Seven-hole pressure probe measurements for axial vorticity, axial velocity, vortex trajectory and pressure variations are presented at various chordwise stations and angles of incidences. It was demonstrated that weak leading edge vortices are generated very close to the wing surface with strong shear layer which move upward and outboard with apex flap deflection. Reattachment line move towards wing root chord with the increase in angle of attack. Passive apex flap has been used to control the leading edge vortices and to delay the vortex breakdown. It is recognized that vortex breakdown was delayed by 8% by downward apex flap deflection.
Abstract: Transient natural convection within a 2D square cavity filled with a porous medium is numerically investigated. The left wall is suddenly heated to a constant temperature Th, while the right wall is suddenly cooled to a constant temperature Tc. Both the horizontal walls are insulated. The Finite Volume numerical method is used to solve the dimensionless governing equations. The results are obtained for the initial transient state assuaging to the steady state, and for Rayleigh number values of 102–104. It is indicated that the average Nusselt number showing an undershoot during the transient period and that the time needed to reach the steady state is longer for low Rayleigh number and shorter for high Rayleigh number.
Abstract: The effects of kinematic parameters (power input, rotational speed and initial angle of attack) of a newly proposed flapping rotary wing model on its averaged lifting force were studied experimentally. It was found that increasing the power input and wing initial angle of attack in a range (i.e. less than 15°) can increase averaged lifting force remarkably while rotational speed seems not to be a key variable determining the lift production. Besides, averaged lifting force could also be improved significantly and the wide range of initial angle of attack could be enlarged effectively to obtain higher averaged lifting force by wing structure selection properly. It was suggested that a proper selection of the wing structure, initial angle of attack (10° to 15°), and power input of the flapping rotary wing can be beneficial for a higher averaged lifting force production in the design of a micro air vehicle.
Abstract: Geometrical nonlinearity of high aspect ratio wing arises from the tip deflection which has been modeled through combined FE/modal approach. Generalized aerodynamics forces are obtained through commercial aeroelastic package. In time domain modeling, reduced frequency dependency of the aerodynamics need to be accounted. For state space time domain models this can be done through rational fraction approximation (RFA) of aerodynamics. Karpels minimum state approximation has been used in this work. Linear and nonlinear aeroservoelastic analyses of a high aspect ratio wing have been presented. Only stability and flutter issues are considered in this work while no external input has been considered.
Abstract: In this paper, the parachute opening process of finite mass situation was simulated based on ALE method. The results of structure change, the flow field change and some important aerodynamic data were obtained. Compared with the experiment, it can be found that the opening process was same with the actual opening. This method was useful in parachute designing and performance analyzing.
Abstract: In this study, a visualization experiment was performed in order to confirm the flow pattern around airfoil with relative velocity fluctuation by in-line forced oscillating in the direction of flow. An airfoil NACA0012 with attack angle of 5 degrees produce the separation in the steady state was observed by the experiments using dye streak method at Reynolds number Re=3.6x103. The investigation of the attack angle which does not separate in such low Reynolds number was performed, and it was confirmed that the separation occurs to 3 degrees. And the airfoil with attack angle of 2 degrees which does not cause separation in steady state, was forced to oscillate with two kinds of relative velocity ratio (umax/U=0.4 and 0.8, here, umax and U denote maximum moving speed of airfoil and main flow velocity, respectively.). The flow separation on the surface of airfoil with attack angle which does not produce the separation in the steady state is occurred even if the maximum moving speed of airfoil umax is in the range which does not exceed main flow velocity U.
Abstract: Refueling has become a significant part of military strategy for air forces to work at further distances from safe shores. This paper will address the concepts and requirements for applying this technique to unmanned vehicles in a military context for supporting fixed and rotor aircraft. The aerodynamics and aspects of human factors in the process are considered, reviewed and solutions proposed to allow for the first generation of designs to be developed. Furthermore, the practical and operational limitations will be addressed as part of the human factors implications.