Sharif Digital Repository

In this paper, the ball valve performance is numerically simulated using an unstructured CFD (Computational Fluid Dynamics) code based on the finite volume method. Navier-Stokes equations in addition to a transport equation for the vapor volume fraction were coupled in the RANS solver. Separation is modeled very well with a modification of turbulent viscosity. The results of CFD calculations of flow through a ball valve, based on the concept of experimental data, are described and analyzed. Comparison of the flow pattern at several opening angles is investigated. Pressure drop behind the ball valve and formation of the vortex flow downstream the valve section are also discussed. As the... 

This paper gives details of the refinement and application of a two-dimensional horizontal model for rivers. An explicit finite-difference algorithm was used for solving the governing differential equations, which includes the conservation of mass and momentum to predict hydrodynamic parameters. The model includes different turbulence closure models - that is, constant eddy viscosity, Prandtl simple mixing length and Smagorinsky methods. An experimental programme was designed and carried out in a laboratory flume to measure the length of eddy produced at the entrance of the intake. Model predictions have been compared with experimental results for a lateral intake. The effect of different... 

A numerical code for supersonic intake design with a proper simulation of the normal and/or oblique shocks, boundary layer development, interaction of the shock and the boundary layer, as well as prediction of the flow separation is of great help to the designers. In this research, a numerical code is developed to solve the inner and outer flow fields of the intake and validated with various experimental tests. The intake is an axisymmetric external compression one. Roe scheme and new schemes, AUSM+-up (for all speed) and Advection Upstream Splitting Method with Pressure-Based Weight function (AUSMPW), are used to compute the convective fluxes. The original version of the AUSMPW scheme has... 

This study investigates the effects of wall heating and skin friction on the characteristics of a compressible turbulent flow in developing and developed regions of a pipe. The numerical solution is performed by finite-element-based finite volume method applied on unstructured grids. A modified κ-ε model with a two-layer equation for the near-wall region and a compressibility correction are used to predict turbulent viscosity. The results show that shear stress in fully developed flow is nearly constant from the centerline up to 75% of the pipe radius, then increases sharply next to the wall, and the ratio of the turbulent viscosity to the molecular one is less than 0.2. Under a uniform wall... 

The transient flow of a compressible gas generated in a pipeline after an accidental rupture is studied numerically. The numerical simulation is performed by solving the conservation equations of an axisymmetric, transient, viscous, subsonic flow in a circular pipe including the breakpoint. The numerical technique is a combined finite element-finite volume method applied on the unstructured grid. A modified K - ε model with a two-layer equation for the near wall region and compressibility correction is used to predict the turbulent viscosity. The results show that, for example, after a time period of 0.16 seconds, the pressure at a distance of 61.5 m upstream of the breakpoint reduces about...