Michiru Yasuhara

INCOMPRESSIBLE FLOW THROUGH MULTIPLE PASSAGES

In this paper, numerical simulations of incompressible flow through complicated multiple-flow passages in a container are shown. Several arrangements of multiple passages are examined. The whole region is divided into several zones for easy treatment of complicated geometry. The calculation is conducted in each zone, the results of which are connected at each boundary during calculation. An experiment was also conducted for one case to verify the calculated result. At least the qualitative agreement with experiment is good for the flow rate through each passage. The pressure distributions are also calculated, which show reasonable results. Furthermore, the thermal calculation in forced convection flow was performed for one case. Finally, an interesting flow pattern is obtained in a bifurcated channel problem along with each flow rate.

Evaluation of an RNG-based algebraic turbulence model

Abstract A new length scale and dissipation rate for a purely mathematically based algebraic turbulence model derived from renormalization group theory is proposed. The proposed length scale is developed in conjunction with an accurate characteristic length scale and the dissipation rate pertaining to the damping action due to the viscous force. In the fundamental aspect, this model is tested by applying it to a flat-plate problem to check that a simple shear layer is modeled adequately. As an application, a typical transonic flow around an airfoil is presented together with the experimental results. Comparison with other algebraic turbulence models is discussed.

Numerical calculation of hypersonic flow by the spectral method

1.INTRODUCTION Recently much attention has been paid to the hypersonic flow problem such as Space Shuttle and Space Plane. We have conducted the experiments on the hypersonic flow by using the shock tunnel with Mach number of 8 at Nagoya University. In particular, the data on the aerodynamic coefficients of the Shuttle-like body and the shape of bow shock have been collected. In parallel with the above experiments, the hypersonic flow has been numerically simulated. We have so far used the finite difference method and the finite volume method to calculate the hypersonic flow. The Euler equations, the thin layer Navier-Stokes equations, and the PNS equations have been successfully applied to this flow. Those results showed reasonable agreement with the experiment. In the present paper we employed another approach, the spectral method(1). The spectral method is a promising method to solve the fluid dynamics problem(2,3). In particular, the turbulent flow problems have so far been successfully solved. In addition to this, the Spectral method was applied to other velocity regime flow such as transonic and hypersonic flows. In the fluid dynamics problems, the finite difference method has been extensively used due to its simplicity and easy extension to higher order accuracy. Furthermore, recently the TVD method became popular to obtain the sharp shock wave in the hyperbolic type flow. However, most researchers in other fields get used to the finite element method due to its generality. Recently the finite element method has been applied to the fluid flow problems. Its strong point is that the grid can be easily generated in the complicated place. In the finite element method the interpolation function is valid within each cell. On the other hand, in the spectral method the overall region is approximated by one function which is expanded by truncated orthogonal functions. This method has several variations. One of them is referred to as the spectral element method which is similar to the finite element method. Generally, the spectral method is said to be more accurate than any other method when compared on the basis of the same number of grid points. Here we applied the collocation spectral method to the three-dimensional flow at the hypersonic flow regime. The similar flows were already simulated by several researchers where promising results were obtained. We will also show several

Diffusion effect of blast pressure in porous complex media

3 ; and sand layer with low- porosities g = 0.435 and high densities c = 1500 kg/m 3 . Peak overpressures in polyurethane foam and sand layer decrease quickly than that in air, as the blast wave is degenerated into compression waves due to its interaction with three-dimensional porosity distribution. Pres- sure attenuation caused in present complex media are in between 60 to 95 % of the peak overpressure value in air.

FLOW IN A MAGNETIC SHOCK TUBE WITH UNSTEADY MAGNETIC FIELD

Flow in a magnetic annular shock tube is analyzed, in which both the driving and applied magnetic fields vary with time. First, one‐dimensional flow is solved by the hypersonic similarity method for the case in which both fields are proportional to a power of time. Second, the local similarity approximation is described to treat more general case in which the fields are smooth functions of time. Third, a purely numerical integration using Laxs finite difference method is carried out for a flow with a sinusoidal driving magnetic field, in which a typical nonsimilar nature of the solution appears in some parts as well as locally similar ones in other parts of the flow. Next, some experiments on a magnetic annular shock tube using air as the working gas, are described with special interest paid to the effect of unsteady azimuthal magnetic field on the flow, and comparisons with theoretical predictions are reported.

The Mechanics of Flapping Wing of Rhomborrhina japonica

Investigation of unsteady flying insects is focused on low Reynolds number effect and aerodynamic properties. Interaction between flapping insect-wing and the air flow became one of important research field for development of micro air vehicle. The aim of the present work is to investigate the flow behavior of flapping wings of scarab beetle. The flapping mo- tion and flow around wing are visualized with smoke-wire method and PIV. Tethered flight of the scarab beetle shows the motion with elastic deformation of flapping wing. Measured flapping frequency is about 91 Hz and its frequency is higher than other beetles, dragonfly and butterfly. The flying beetle generates circulation of tip vortex and obtains lift by feather- ing motion, while the membrane wing adjusts to the angle of attack and the pitching angle under changes in aerodynamic force.

A calculation of the compressible Navier-Stokes equations in generalized coordinates by the spectral method

A spectral collocation method was developed in the present paper for the compressible N.S. equations written in the generalized coordinates. Comparisons between the SMC and FDM show the superiority of the former in accuracy, though it takes several times as large CPU time as the latter. Furthermore, the gas mixture model was successfully incorparated into our program code, which can become a fundation of dealing with hypersonic chemically reacting flows around blunt bodies by the spectral method.

Aerodynamic characteristics of a circulation controlled symmetrical airfoil with dual jet.

Effects of two blowing jets on aerodynamic characteristics of a 20 percent thick, non-cambered airfoil are described. Free stream wind tunnel velocity is 10m/s and the Reynolds number is 1.7×105. Section lift, drag and pitching moment coefficients are given at some effective angles of attack. The position of the second slot has a strong effect on the characteristics and the highest lift to drag ratio is given at the position of 55° measured from the first one. Two-jet system is found to be more effective in producing high lift than one-jet system at the same jet-power coefficient.