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The interface condition provides flexibility to handle complex geometries on a set of structured grids. However, when used with a compact scheme to apply in computational aeroacoustics, its accuracy and stability may be degraded seriously by the boundary treatment that arises at a grid interface. To minimize this effect, a modified characteristic condition is incorporated in the finite difference compact scheme by using an explicit difference form at the boundary. The extension of this approach is naturally attained through the coordinate transformation of convective terms across an interface in multidimensions. The validity of current development is demonstrated through a simulation of trailing-edge noise generation from an airfoil at a low Mach number.

A new numerical simulation approach is applied to the flow around 2-D aerofoil with tonal noise generation. Two flow conditions are considered. The first case is the flow around the NACA0015 airfoil with the transition process on the suction side. The second case is the flow around the NACA0012 airfoil with the Reynolds number of about 8,000. The acoustic fields clearly show the radiation of sound waves from just after the trailing edge region. Numerical simulations also capture a separated region at the trailing edge for both cases. For the high Reynolds number case, the linear stability analysis shows the possibility of the existence of T-S waves and the most unstable frequency up to the separation almost coincides with the peak frequency. This indicates that the generation of T-S waves on the pressure side is strongly relevant to the determination mechanism of the selection of peak frequency of the tonal edge noise and that the self-excited feedback mechanism exists between just after the stagnation point at the leading edge and the trailing edge region. For the low Reynolds number case, very small sound wave is captured and the frequency is the same as that in the wake region. No development of unstable waves inside the boundary layer is observed by the stability analysis and it is still unclear whether the flow structure before the separation region around trailing edge has some effects for the determination mechanism of the selection of peak frequency of the tonal edge noise.

In practical fluid computation with structured grid around complex geometry, singular points with metric discontinuity can be frequently found. Generally, the grid singularities may cause severe numerical oscillations when some high-order finite difference method (FDM) is employed. Recently, in order to solve this problem, high-order multi-block computation technique with characteristic interface conditions (CIC) were proposed. In the previous study, the authors extended the functions of the CIC, and newly derived the generalized characteristic interface conditions (GCIC). Resultantly, numerical flexibility and robustness of the multi-block interface treatment can be further improved from a practical point of view. In this article, as a preliminary study, the GCIC are applied to multi-block large eddy simulation (LES) around complex geometry, and their practical extensibility is shown and discussed.

A new approach for the analysis of subsonic flow is proposed and the capability of capturing the detail flow properties is investigated. Especially, the natural transition phenomenon is focused on. The flows around two-dimensional aerofoil of the NACA0012 under relatively high Reynolds number conditions (Re ≃ 10 6 ) are analyzed. The development of so called T-S wave and the laminar-turbulent transition are clearly captured. Locations of transition points are compared with the experiments and agreements are excellent. The detail comparison with the linear stability analysis indicates that the most unstable disturbance in the linear unstable region is captured quantitatively by taking care of grid resolution in the chord direction. The disturbance distribution inside the boundary layer in the transitional region is examined and the phase jump is also captured.

In a practical computation with a structured grid around a complex body, singular points can be frequently found where an abrupt grid change exists. The grid singularity poses a troublesome problem when some finite difference scheme with high accuracy and resolution is applied. An excellent theory has been proposed, which solve the above singular problem by decomposing a computational domain into two blocks along a line or a surface which contains the singular points and by imposing accurate characteristic-based interface conditions at the block interface. However, the original theory has a limitation on the combination between the adjacent computational coordinate definitions. Concretely, these two coordinates have to be the same direction on the block interface. For a flexible coordinate arrangement without the restriction, the original characteristic-based interface treatment is extended and generalized. Consequently, the coincidence of the computational coordinate definitions becomes unnecessary, and a more flexible multi-block computation can be realized successfully. Numerical test analysis of vortex convection is performed for validation of the new theory, and excellent performance is confirmed as a result.

A preliminary assessment of the heating environments during a hyperbolic entry to the planet Venus is conducted in order to investigate fundamental characteristics of flows in the shock layer, and to predict the convective and radiative heat flux transferred to the entry capsule at the peak-heating point. Thermochemical nonequilibrium flows are calculated using two-dimensional Navier-Stokes equations in the axisymmetric geometry, taking into account oxidation and sublimation of the heatshield surface, and pyrolysis-gas injection. Radiative heat transfer coupled with the flow is computed by a line-by-line method with a tangent-slab approximation. Influences of uncertainties in the thermochemical models on the predicted heat flux are also examined.

New 110kW inductively coupled plasma (ICP)-heated wind tunnel in JAXA-ISTA was constructed and some performance evaluations have been conducted to simulate atmospheric reentry environment. Using this wind tunnel, initial heating tests for catalytic effect research were carried out, and new materials were tested to evaluate its characteristics including catalysis, emissivity, and so on. SiC coating samples showed comparatively low temperature, but high catalytic coating showed higher temperature. The difference was about 100 ~ 200 C, and it corresponded to 0.3 ~ 0.4MW/m 2 of heat flux. The difference of heat flux due to effect of catalytic effect was reasonable to compare with former CFD results for arc-heated wind tunnel tests. Ultra high temperature ceramic (UHTC) material was also tested, and its characteristics changed from low catalytic region to high catalytic region as the temperature increased. It was caused by changing catalytic effect and emmisivity due to oxidization.

Detailed magneto-hydrodynamic (MHD) simulations of plasma flows in an inductively coupled plasma (ICP) heater are performed with air as a working gas. The plasma flows are numerically solved by the axisymmetric Navier-Stokes equations coupled with Park’s threetemperature models and Dunn-Kang’s chemical kinetic models to take into account the thermal and chemical non-equilibrium, while induction heating in plasmas is incorporated by solving the time-averaged MHD induction equations. Computations are done by changing the operating conditions such as the input power and the background pressure to examine how the plasma properties depend on these parameters. Numerical results are compared with those of spectroscopic measurement. Good agreement is obtained in the downstream region where the flow is in local thermal equilibrium, however, qualitative discrepancy of electronic temperature between the theory and the experiment is found in the discharge chamber where Joule heating is significant.

New inductively coupled plasma-heated wind tunnel was completed and some performance evaluations have been conducted to simulate atmospheric reentry environment and to study catalytic effect and so on. Maximum power of this wind tunnel is 110 kW, and maximum total enthalpy is presently about 20 MJ/kg. The electronic excitation temperature was evaluated in the torch, and it was about 10000 K. This result was compared with real gas CFD analysis coupled with electromagnetic field. At the test section, maximum heat flux was about 1 MW/m 2 , and the obtained temperature of C/C-SiC samples was about 1500 degree C, which was same condition of actual flight. This new wind tunnel can operate more numbers of runs to obtain experimental data effectively than the existing arc-heated wind tunnel because of easiness of maintenance. This wind tunnel still has some problems, which are instability of the flow at low mass flow rate and effect of rotational flow. The modification of gas supply system might be needed as one of the idea to solve this problem.