The present paper treats a supersonic panel flutter of simply-supported symmetrical laminates with a delamination. The panel flutter characteristics of composite laminates are obtained by a finite element method based on the Mindlin plate theory and a quasi-steady aerodynamics based on the linearized piston theory in this paper. The penalty function method is adopted to ensure the displacement continuity condition at the delamination front, and the linear spring model is also adopted to describe the effect between the delaminated surfaces. The panel flutter boundary is obtained by solving the eigenvalue equation as the flutter equation. The validity of the present method and the effects of the size and location of a delamination on the panel flutter characteristics of laminated plates are examined through the numerical results.
Numerical simulations of solid-solid hypervelocity impacts (HVIs) using smoothed particle hydrodynamics (SPH) method in two-dimensional axisymmetric coordinates, are performed. It is known that Gaussian kernel is adequate for the SPH method in axisymmetric coordinates, however, Gaussian kernel is computationally less efficient because of its infinite range. We propose to adopt a simple function having only even-order terms as the kernel for the SPH method in axisymmetric coordintates, to improve the computational efficiency. The equations of conservation laws, the strain rate and rotation rate are formulated by using the quadric kernel and the quartic kernel. The HVIs are numerically simulated by using the quadric kernel, quartic kernel and Gaussian kernel for comparison. Each numerical result shows a good agreement with the experimental result, and the conservation of energy is assured for each calculation. Consequently, it is found that the quadric kernel and the quartic kernel have far better computational efficiency and comparable computational accuracy to Gaussian kernel.
A new takeoff method for small airplanes was proposed. Ground-roll performance of an airplane driven by electrically-powered wheels was experimentally and computationally studied. The experiments verified that the ground-run distance was decreased by half with a combination of the powered driven wheels and propeller without increase of energy consumption during the ground-roll. The computational analysis showed the ground-run distance of the wheel-driven aircraft was independent of the motor power when the motor capability exceeded the friction between tires and ground. Furthermore, the distance was minimized when the angle of attack was set to the value so that the wing generated negative lift.
The present paper describes the influence of ground and ceiling effect on high-lift device using a circular cylinder with tangential blowing. The experiments and numerical simulations were performed under the condition of Re = 2.7× 104. In the experiments, the test, such as the time-mean surface pressure measurements on the cylinder and flow visualizations were carried out for various momentum coefficients and clearances between the cylinder and the ground (or ceiling). In the numerical simulation, a commercially available computer code, SCRYU/Tetra, was used. Qualitative agreements between the experimental and numerical results were obtained with respect to the flow fields and the lift characteristics. The experimental and numerical results show that ground effect can enhance lift-drag ratio except stalling region, and that ceiling effect can not enhance lift-drag ratio.
Concluding this series of theoretical studies, a persistent self-excitation mechanism of most unstable capillary wave at the nozzle exit is proposed on the basis of the one-dimensional model developed in the first report. It is found that, once an unstable wave travels down from the nozzle exit, the most unstable Rayleigh wave is repeatedly developed for the newly issued liquid from the capillary wave which is generated to meet the nozzle exit condition at any time. The initial amplitude of this unstable wave is the same as that of the initial unstable wave when the jet speed is equal or slower than the steady capillary wave speed. For larger jet speed, the amplitude of newly generated unstable wave decays gradually one after one, so that a periodical agitation is necessary to maintain the steady Rayleigh-type breakup of the liquid, which is usually attainable by the arrival of capillary waves from the contracting liquid jet tip to the nozzle exit.
We studied effect of ventilation ports on aerodynamics of the fuselage of a human-powered airplane and cooling performance of the pilot. An opening made in the fuselage is one of remedies for enhancing the performance of the pilot. On the other hand, the opening influences aerodynamic characteristics of the airplane, in particular the drag of the fuselage. When the ratio of inlet and outlet areas is larger than 3.0, the flux of air taken at the inlet is almost proportional to the area of inlet and depends weakly on the position and area of the outlet. Cooling of the pilot is estimated from the data of Nusselt number around the cylinder in the uniform flow at the Reynolds number defined by a velocity averaged over a cross section. An additive drag due to interaction between the injected flow from the outlets and the ambient flow around the fuselage depends strongly on the location of the outlet; the nearer to the trailing edge the outlet position moves, the less the drag increases.