Sharif Digital Repository

In this study, we present a vast boundary condition treatment to simulate gas flow through microfilters using direct simulation Monte Carlo (DSMC) method. We examine the effects of different boundary condition treatments on the density, pressure, and velocity distributions and suggest the best conditions to simulate gas flow through microfilters. We also refine the effects of upstream and downstream locations on the solution. The results show that uniform distributions can be achieved if we apply the inlet/outlet boundary condition at appropriate upstream and downstream distances. We also show that all the suggested boundary conditions suitably predict the pressure drop coefficient factor... 

A multigrid acceleration technique is suitably extended to solve the 2D incompressible Navier-Stokes equations using a fully implicit hybrid finite volume element method. As is known, the convergence of classical relaxation techniques performs an initial rapid decrease of residuals followed by a slower rate of decrease. This means that a relaxation procedure is efficient for eliminating only the high frequency components of the residuals. This problem can be overcome using a multigrid method. There are different restriction and prolongation operators to establish a multigrid procedure. An efficient operator is suitably extended in this work. It provides data during refining and coarsening... 

In this research, a multigrid formulation is suitably developed to accelerate the convergence rate for the solution of the equations arising from the discretization of the two-dimensional incompressible Navier-Stokes equations. The governing equations are treated using an implicit finite element volume method. To achieve our purpose, the solution domain is divided into a large number of quadrilateral elements. Normally, we need utilizing very fine grid resolutions to obtain solution with sufficient accuracy. Unfortunately using the standard implicit solvers on fine grids needs huge computational time. However, it is known that the rate of convergence of classical relaxation schemes reduces... 

The main purpose of the present work is to study the performance of an algebraic multigrid (AMG) algorithm as a preconditioner to the Krylov subspace methods, mainly GMRES methods. The method is used to solve the set of linear algebraic equations resulted from treating simultaneous simulation of fluid dynamics and heat transfer problems. The extended algorithm is fully implicit which results in a huge system of linear algebraic equations. Different parameters affecting the performance of the AMG are taken into account to enhance the performance of our extended algorithm. Because of high level of sparsity of the matrix of coefficients, the current results indicate that the AMG can be very... 

The use of multi-element airfoils has been known as a major approach to boost up the lift of wing without dramatic increase in its drag. In fact, the configuration helps to reduce the chance of flow separation over the airfoil. However, the use of a complicated geometry such as multi-element airfoil would normally cause complexity in flow behavior. The experience has shown that the flow field complexities cannot be properly modeled using standard two-equation k-epsilon turbulence model. Therefore, it is important to improve the accuracy of general turbulence models in specific applications and complex computational domains. In this work, we extend a suitable objective function based on...