This paper presents an experimental study of shock wave/turbulent boundary layer interaction induced by a sine shaped three dimensional protuberance. The experiments were carried out in a 8×10cm2 supersonic wind tunnel at free stream Mach number of 1.98. Corresponding free stream unit Reynolds number was 3.8×107/m. The sine shape models with height to diameter of 0.5, 0.25 and 0.1 were used in this study. Surface static pressure measurements, oil flow studies and Schlieren photographs of the flow field were made. It was found that, the upstream influence length and the maximum surface pressure decrease with the decrease of H/D, whereas the minimum pressure at the rear is insensitive to H/D. At the rear part of the model a pair of vortices appears. This is surrounded by a separation line which moves backward with the decrease of H/D. It can be said that the flow around the H/D=0.25 model differs significantly from that of the H/D=0.1 model.
Experiments have been done to investigate the transition process of the laminar separation bubble on airfoils. Measurements of the power spectrum density distribution of the streamwise velocity fluctuation was made. Three airfoils which have different steplike pressure distributions were used for measurements. A discrete spectrum and its sub and higher harmonics were observed. The frequency of the discrete spectrum was in good agreement with that predicted by the linear stability theory of the separated free shear layer. From results, it is concluded that the velocity disturbance observed initially in the laminar separation bubble for the three airfoils shows similar characteristic to that in the separated free shear layer. For the airfoil whose design pressure recovery is minimum among three airfoils, however, another kind of the discrete spectrum was also observed. This is interpreted to be caused by the interference with the external cyclic disturbance.
This parer presents an optical method for the measurement of the bending stiffness ratio of orthotropic laminates and elastic constants of orthotropic laminae. Cornu's method for the measurement of Poisson's ratio of isotropic plates is elaborated with the aid of laser holographic interferometry to measure the pure bending deformation of orthotropic laminates. A four-point bending device was made, which enables us to adjust the bending load distribution so as to eliminate distortion in the pure bending deformation. The thermoplastic plate was used in place of the photographic plate for the realtime holographic interferometry. Quadratic expressions for the fringe curves are determined by the method of least mean square. Elastic constants are determined from the coefficients of the quadratic expressions. A method is described for the confirmation of the state of the pure bending deformation. The results indicate a need for further study on the conditions for the establishment of the pure bending deformations in experiment.
A method for curing CFRP composite structures by using Joule effect is presented. Due to the presence of fiber to fiber contact, CFRP composites and their prepregs exhibit electrical conductivity in the direction transverse to fibers as well as in the fiber direction, and they can be considered as electrically homogeneous on a gross scale. Therefore, passing an electric current through a CFRP prepreg, it is self-heated due to the Joule effect. Feedback current control maintains the prepreg temperature at a desired level and makes the prepreg be cured by a specified cure cycle. Experimenal verifications have been carried out to demonstrate the feasibility of the present technique. The applications to the bonding of CFRP components and to the patch repairs of defective CFRP structures are also described.
Dynamic stability of subsonic airplanes is discussed about the relation between the dynamic stability and the weight. Linearlized, decoupled equations of motion are used and five (5) motion modes are calculated for four (4) different airplanes, which cover 107-times weight-change. The result points out that airplane dynamic stability is generally strengthened with the decrease in weight if the airplane is dynamically stable.
Spatial oscillations or “wiggles” have been encountered in many high-Reynolds number flow solutions when a central-difference method is used. As Roache demonstrates in his famous text book, it occurs even in a linear equation and the source of “wiggles” is simple. In this paper, it is clearly and mathematically shown based on the monotonicity of the solution that the “wiggles” must occur in a central-difference solution of a steady advection-diffusion equation if the cell Reynolds number is greater than 2. In order to get an accurate 3-point finite difference solution as well as to prevent such wiggles, central-upwind hybrid finite difference methods are derived.