When temperature and pressure of the liquid and gas are raised to the critical point, they start behaving as a supercritical fluid. The supercritical fluid has the characteristics of both the liquid and the gas. These characteristics have a wide range of application to engineering process namely, the energy devices, the semiconductor washing and so on. For device development, it is necessary to have a good understanding of this phenomenon. But it is difficult to simulate flow of supercritical fluid numerically by conventional methods, due to sudden change of the physical properties depending on pressure and temperature condition. In this paper, natural convections inside a cubical cavity and Rayleigh Benard convection calculated by using numerical simulation technique of the supercritical fluid developed by Yamamoto. The effect of the density difference induced by the phase change to the flow is investigated.
A preconditioned numerical method for gas-liquid two-phase flows is applied to solve cavitating flow. The present method employs a finite-difference method of the dual time-stepping integration procedure and Roe’s flux difference splitting approximation with the MUSCL-TVD scheme. A homogeneous equilibrium cavitation model is used. The present density-based numerical method permits simple treatment of the whole gas-liquid two-phase flow field, including wave propagation, large density changes and incompressible flow characteristics at low Mach number. Two-dimensional internal flows through a backward-facing step duct, convergent-divergent nozzles and decelerating cascades are computed using this method. Comparisons of predicted and experimental results are provided and discussed.
Our research group has proposed a numerical method for supercritical fluids; Supercritical-Fluid Simulator(SFS). In this paper, supercritical carbon dioxide flows impacting on a flat plate through supersonic nozzle are calculated using SFS and the flow features changing inlet pressure, inlet temperature and the distance to the flat plate are comparatively investigated. Especially, it is noted that the density in the nozzle is rapidly changed and is deeply dependent to the inlet boundary conditions.
Unsteady 3-D wet-steam flows through three-stage stator-rotor blade rows in a low-pressure steam turbine model developed by Mitsubishi Heavy Industry (MHI) are numerically investigated. In this study, a new and simple meshing strategy is introduced to improve the prediction of end-wall flows near the shroud and the hub. Dry and wet-steam conditions are taken into account and the calculated results changing the grid system are compared with the experiments. As a practical usage, coarse-grid computations using a PC cluster are also conducted and the results are compared with those using a fine grid and a supercomputer. In addition, a super-cooled condition is assumed and the computation is further conducted. Finally, the effect of homogeneous nucleation and the nonquilibrium condensation on the present flow is evaluated.
This paper presents a numerical study for unsteady flows in a high-pressure steam turbine with a partial admission stage. Compressible Navier-Stokes equations are solved by the high-order high-resolution finite-difference method based on the fourth-order compact MUSCL TVD scheme, Roe's approximate Riemann solver, and the LU-SGS scheme. The SST-model is used for evaluating the eddy-viscosity. As numerical examples, unsteady two-dimensional flows in a partial admission stage of steam turbine are calculated. The effect of the nozzle box flange to the lift of rotors is numerically investigated. The performance of several types of partial admission stage is parametrically predicted. The efficiency was improved by the sloping flange.
This study concerns the verification of the applicability of a Super Roller Flume for Computer Aided Design of Maritime Structure (CADMAS-SURF) to specially designed long-footing caissons in an area of standing wave phenomenon through a comparison of the results of the CADMAS-SURF analysis performed for the long-footing caissons with the outcome of previous experiments. In the study, a limited amount of existing hydraulic model test data was supplemented with the calculations made with the CADMAS-SURF and the scope of application of the wave pressure formula based on the finite amplitude standing wave theory to the long-footing caissons was expanded in respect of the depth-wave length ratio and the footing length-wave length ratio.
