The numerical code to solve axisymmetric compressible Navier-Stokes equations by the spectral collocation method was developed. It was applied to a supersonic flow about a sphere. A Residual-Dependent Filter was developed, so that the accuracy was considerably improved. The influence of filter, time step size, and grid number on accuracy is discussed. The results are compared with experiments and excellent agreement is shown.
This paper describes the flow past a two-dimensional perforated plate placed on a ground plane. The experiment was carried out in the 40cm×40cm N. P. L. -type wind-tunnel having the working section of 2m length at Reynolds number of 6.32×104. The distributions of velocity in the flowfield, the recirculation region behind the perforated plate, and the surface pressure on the ground plate were measured. The results were discussed for the various values of porosity in comparison with those of the existing investigations and the calculated value of the velocity in the mixing zone for Görtler. Consequently, the windbreak is effective for the perforated plate of porosity ratio λ=0.2.
An experimental study on the structure of the short bubble and the long bubble formed on NACA 63-009 airfoil has been made. Mean velocities, turbulent stresses and turbulent triple products were measured. Results show that the turbulent stresses attain maxima near the reattachment point for the short bubble. For the long bubble, these stresses start to increase just after the laminar separation point and attain maxima far before the flow reattaches to the airfoil surface. Turbulent energy balances were estimated from results. It is shown that the turbulent energy production term has the largest contribution to the growth of turbulent energy compared with the other terms.
Calculations of laminar-turbulent transition of boundary layers are presented with low-Reynolds number versions of k-ε model of turbulence developed for the near-wall low-Reynolds-number flows. The models are tested for the transitional boundary-layers at various levels of free-stream turbulence with and without the pressure gradient. The test calculations of flows without the pressure gradient show that the model by Launder-Sharma and that by Lam-Bremhorst to some extent are able to handle the transition phenomena within a reasonable range of initial conditions of dissipation. The former model can reproduce the observed effects of level and length scale of free-stream turbulence on the transition, though the latter fails at the lower turbulence level and for the effect of length scale. It is also noted that the applicable range of the low-Reynolds-number k-ε model is limited to a relatively small pressure-gradient condition, as the model shows an opposite trend to the experimental effect of pressure gradient on the transition.
In this paper, we discuss the method for measuring radar cross section (RCS) based on the Range-Doppler Imaging. In this method, the measured targets are rotated and the Doppler frequencies caused by each scattering element along the targets are analyzed by FFT. Using this method, each scattered power along the flighting model is measured. It is found that each part RCS of flighting model can be measured and its RCS of a main wing (about 46dB·cm2) is greater than its of body (about 20-30dB·cm2).