The performance of the ion thruster depends on the discharge performance and the beam extraction, the former of which is significantly effected by the electron property such as density and energy, since ions are produced by ionization collisions between neutral atoms and electrons. In the microwave ion thruster, the discharge owes to the electron cyclotron resonance (ECR). Thus, the electron phenomenon in the microwave discharge chamber was numerically investigated by the particle simulation method. In our model, the electromagnetic wave is polarized circularly and propagates in the axial direction and electrons are moved in the microwave and static magnetic fields, colliding with neutral particles. Collision processes are taken into account by the Monte Carlo method. This simulation results show that some electrons can be heated enough to cause ionization collisions and that the density and energy distributions are peculiar to the microwave ion thrusters.
A fourth-order difference method is combined with the vorticity-vector potential formulation in the generalized coordinate. Turbulent flaws are computed in channels with the transverse riblet of convex or concave wall surface using the large eddy simulation technique with the dynamic subgrid scale model. As a result it is shown that turbulence is weakened by the concave transverse riblet and effect of drag reduction is found at the Reynolds number 8, 000 and when the interval of the riblet corresponds to the length of the Tollmien-Schlichting wave. The reason is that the fluid moves toward the concave wall and the strengthening of the streamwise vorticity is protected.
As a new procedure of a global optimization for nonlinear systems, a hybrid algorithm between a global optimization technique called a Hide-and-Seek method, a kind of continuous simulated annealing method, and a conventional local optimization technique is proposed. To show performance of this method, comparison between this and other methods are made through several bench mark and engineering optimization problems.
To investigate the unsteady structure of secondary flow of a turbulent bounded jet in both frequency and physical spaces, the wavelet auto-correlation analysis was used to analyze the fluctuating velocities at various positions in abounded jet. The wavelet auto-correlation analysis provides the auto-correlation characteristics of signals in terms of period and time delay. From the wavelet auto-correlation analysis, the branching structures in WR(a, τ) reveal that a periodic large eddy motion contains the periodic small eddy motions. In the shear layer near the wall at X/b0=8.0, Y/b0 =1.0 and Z/b0=1.9, the wavelet auto-correlation analysis may determine the period and the location of the large-scale structure and the secondary flows.
An experimental study was conducted by using the Nagoya University Shock Tunnel to examine aerodynamic interaction of a jet with the base pressure of a blunt body model in a hypersonic flow. Here in this study, we are concerned with the jet interaction at a high angle of attack, which has not been well known so far. Pressure was measured at ten pressure taps which were distributed at the base in a two coaxial rings-shaped manner;hereafter referred to as the inner and outer rings, where the jet was located between them. In this study, two parameters are employed with regard to the jet: the deflection angle and the mass flow rate. At a high angle of attack of 40 degrees, the pressure distribution shows asimilar pattern to the case of side-jet blowing to a freestream. That is, along the outer ring, the pressure is increased due to a bow shock in front of the jet, while at the inner ring, the pressure is locally decreased because of a vortex produced by the jet entrainment. This trend becomes prominent with the mass flow ratio, which is favorable for augmenting the jet thrust. By deflecting the jet toward outside, the jet becomes close to the outer ring, so that the pressure is decreased there. This is considered to be due to an entrainment effect. Integrating these pressure changes by jet interaction leads to appreciable quantity of interaction force. Under the present conditions, the maximum value of integrated base drag becomes as large as about 7.5% of the axial force of the blunt body at an angle of attack of 30 degrees.