Streamwise vortex structure induced by secondary instability of compressible shear flow was numerically investigated. Parallel shear flow with convective Mach number 0.4 was used in the present study. From linear stability analysis, existence of streamwise vortex structure components was confirmed, and scale ratio λz/λx which gives maximum amplification rate was specified. In addition, spatially evolving shear flow was investigated by three-dimensional calculation. Streamwise vortex structure similar to that gotten from linear stability analysis was observed. In the case where white-noise-like disturbance was introduced, growth rate of shear layer was estimated and effect of streamwise vortex structure on growth of shear layer was investigated. Due to streamwise vortex structure induced by secondary instability, growth rate in three-dimensional calculation was larger than the case of two-dimensional case.
In order to simulate actual behavior of bleed air flows in various air-intake operating conditions, it is necessary to consider the change in bleed mass flow rates according to the bleed plenum conditions. Wind tunnel testing was carried out for validation of the conventional Harloff’s model for the rates. The results showed that the model overestimates the bleed mass flow rates in certain cases where blowing from the bleed plenum into the main stream occurs. A new boundary condition model improved by addition of the effect of the main stream dynamic pressure is proposed and enables quantitative prediction of the bleed mass flow rates in such cases.
Flow behavior and thrust performance of MHD energy bypass scramjet engine was examined numerically. MHD generator was placed at the isolator to enhance the flow compression. Kinetic energy was converted to electrical energy in the MHD generator. Extracted electrical energy was consumed at the MHD accelerator placed at the downstream of the combustor. When MHD energy bypass system was used, the flow was decelerated and compressed in the MHD generator. Effect of velocity and Mach number on wall friction was analyzed and decrease of friction force was pointed out. Also, high pressure in the combustor resulted in increase of pressure contribution to net thrust. Despite of positive effects, decelerating Lorentz force in the MHD generator was comparably large and no significant difference in net thrust performance is observed.
An experimental study on validity and improvement of base pressure correction for a bluff-base body with hemisphere nose using MSBS (Magnetic Suspension and Balance System) has been conducted. Force and pressure distribution data on the model base were examined for several parameters; angles of attack 0–7.5º, Reynolds number ReD=7.6×104, with or without a sting and diameters of the sting. These results showed that the base pressure correction using the pressure data near the sting could have validity at the case of 0º of angle of attack only. Besides we could propose a new accurate method to calculate base-pressure axis forces.
This paper discusses an Input Shaping method for electrodynamic tether systems. The Input Shaping method is applied to generate an input current profile to reduce the induced vibration of the electrodynamic tether system in the initial phase of the propulsion. The Lorenz force and the flexibility of the tether cause vibrations of the tether system on orbit. Two different shapers are designed to suppress the two main vibration modes. The complete shaper is designed by multiplying each of the shapers together. The flexibility of the tether is described by the lumped mass model. The robustness of the shapers is discussed by sensitivity plots. The results of numerical simulations show excellent performance of vibration suppressing by the employing Input Shaping for the electrodynamic tether system.
A fundamental study for frost formation around a single cold cylinder was conducted using an experimental and numerical method. We focused on the mass transfer around the cylinder under the condition where phase change of the vapor in the flow occurs. By the experimental study, the mass transfer rate on the cold surface of the cylinder at a constant surface temperature (200–250K) was measured. The results show that the mass transfer rate decreases according to the decrease of the wall temperature below 230K, while it increases above 230K. This phenomenon can not be expressed by the common equation of Sherwood number in which the phase change of the vapor (condensation) is excluded. In the numerical study, we calculated the flow around the cylinder including the phase change of the vapor. The scheme for compressible flow was modified to be able to solve lower speed flow. As a result of the calculation we obtain same tendency as that of the experiment that the mass flux decreases at low temperatures where the phase change occurs.