Sharif Digital Repository

A numerical method based on the SIMPLE algorithm has been developed for the analysis of vapor flow in a concentric annular heat pipe. The steady-state response of a concentric annular heat pipe to various heat fluxes in the evaporator and condenser sections are studied. The fluid flow and heat transfer in the annular vapor space are simulated using Navier-Stokes equations. The governing equations are solved numerically, using finite volume approach. The vapor pressure and temperature distributions along a concentric annular heat pipe are predicted for a number of symmetric test cases. The vapor flow reversal and transition to turbulence phenomena are also predicted. The results are compared... 

Manta ray swimming or bio-inspiration propulsion system, as a special type of marine propulsion system, is used for submersible vehicles that require high-speed maneuverability and stability, such as glider and AUV. In a manta ray swimming, the thrust force is generated by a couple of undulation and oscillation of wing, so that the direction of undulation wave and oscillation is upright and perpendicular to the direction of thrust force, respectively. It is possible to combine these two movement modes (flapping motion) on the three-dimensional model without considering the effects of wing twisting and flexibility to simplify and better understand the physical behaviors or special study of... 

We extend a hybrid finite-volume-element (FVE) method to treat the laminar reacting flow in cylindrical coordinates considering the collocation of all chosen primitive variables. To approximate the advection fluxes at the cell faces, we use the upwind-biased physical influence scheme PIS and derive a few new extended expressions applicable in the cylindrical frame. These expressions are derived for both the Navier-Stokes and reactive flow governing equations, of which the latter expressions are considered novel in the finite-volume formulation. To validate our derived expressions, the current results are compared with the experimental data and other available numerical solutions. The results... 

In this study, a moving mesh finite-volume-based finite-element (FVBFE) method is suitably extended to simulate the effect of supercooled liquid water droplet content on ice formation and growth on wing sections. The method benefits from the advantages of both finite-volume and finiteelement methods, which promote achieving a more accurate solution and a higher efficient procedure in ice accretion calculations. The method solves the time-dependent Navier-Stokes (NS) equations on unstructured hybrid grid distributions. In this method, the convection terms are approximated at the cell faces using a physical influence upwinding scheme. We also use linear spring approach to move the hybrid mesh.... 

The receptivity of supersonic/hypersonic flows over blunt noses to freestream disturbances is performed by means of spectral collocation methods. The unsteady flow computations are made through solving the full Navier-Stokes equations in 2D. A shock-fitting technique is used to compute unsteady shock motion and its interaction with freestream disturbances accurately in the receptivity study. The computational results for receptivity of a semi-cylinder at Mach 8 is presented and validated by comparison with available theoretical and numerical results. The study shows significant effects of the viscosity on the receptivity process  

Some interface front patterns of falling droplets are studied via direct numerical solution of the full Navier-Stokes equations governing the system of droplets and the ambient surrounding media as a single-fluid model. We focus on the mutual interactions of the effects of characterizing nondimensional parameters on the formation and break-up of large cylindrical droplets. The investigation of droplet cross sections and deformation angles shows that for moderate values of the Atwood number, increasing the Eötvös number explicitly increases the deformation rate in formation and breakup phenomena. Otherwise, increasing the Ohnesorge number basically amplifies the viscous effects  

To extend a procedure to ensure the safe operation of a water reactor, we develop a numerical method to compute the high frequency pressure spikes of water hammer with liquid column separation in pipes. In this regard, we first extend a finite-volume all-speed method to solve the full one-dimensional Navier-Stokes equations. This method is capable of simulating gas and liquid phases as well as the vapor-liquid one. On the other hand, the current extended method should be capable of capturing high frequency pressure spikes, which are formed due to water hammer and column separation in pipes. The existence of such high frequency spikes has been recently reported experimentally by other... 

In this research, the problems of adiabatic film-cooling the flat, convex, and concave surfaces are investigated numerically. Two different radii of curvature and one row of vertical injection holes are considered. The Navier-Stokes equations are solved using a fine nonuniform multiblock staggered curvilinear grid and the SIMPLE-based finite volume method. The blowing rates are 0.5 and 1.0 and the mainstream Reynolds number is 10,000. The obtained results indicated that at a low blowing ratio, the cooling effectiveness enhances over the convex surface and reduces over the concave surface compared to the flat surface case. In comparison with the low blowing ratio, the curvature effects at a... 

Numerical simulations of the turbulent flow around single and side-by-side piles at different spacing ratios (centre-to-centre distance to the pile diameter) with flow Reynolds number of 105 on the fixed flat-bed are presented. The calculations are performed using the computational fluid dynamics model, FLOW-3D, which solves the Navier–Stokes equations in three dimensions with a finite-volume method. The numerical results of time-averaged flow patterns around single and side-by-side piles are validated using the available experimental measurements. At the downstream of the single pile, dimensionless vortex shedding frequency (Strouhal number) is estimated as 0.22. The maximum values of bed... 

In some diseases there is a focal pattern of velocity in regions of bifurcation, and thus the dynamics of bifurcation has been investigated in this work. A computational model of blood flow through branching geometries has been used to investigate the influence of bifurcation on blood flow distribution. The flow analysis applies the time-dependent, three-dimensional, incompressible Navier-Stokes equations for Newtonian fluids. The governing equations of mass and momentum conservation were solved to calculate the pressure and velocity fields. Movement of blood flow from an arteriole to a venule via a capillary has been simulated using the volume of fluid (VOF) method. The proposed simulation... 

In this study, the permeability for interdendritic liquid flow through equiaxial mushy zone has been modeled and experimentally measured. In the present work, by applying a virtual dendrite in a micro-domain and solving Navier-Stokes equation, flow pattern around the dendrite has been obtained and then by applying Darcy's law to this 3D domain the permeability has been determined. In this micro-model the influence of solid fraction and geometry of dendrites have been assessed. Numerically determined values of permeabilities have been analyzed by the use of SPSS statistical software. Then an experimental method is used to measure the permeability for flow through equiaxial mushy zone of Pb-Sn... 

An incompressible-smoothed particle hydrodynamics (I-SPH) formulation is presented to simulate impulsive waves generated by landslides. The governing equations, Navier-Stokes equations, are solved in a Lagrangian form using a two-step fractional method. Landslides in this paper are simulated by a submerged mass sliding along an inclined plane. During sliding, both rigid and deformable landslides mass are considered. The present numerical method is examined for a rigid wedge sliding into water along an inclined plane. In addition solitary wave generated by a heavy box falling inside water, known as Scott Russell wave generator, which is an example for simulating falling rock avalanche into... 

If the hydrodynamic diameter of a channel is comparable with the mean free path of the gas molecules moving inside the channel, the fluid can no longer be considered to be in thermodynamic equilibrium and a variety of non-continuum or rarefaction effects can occur. To avoid enormous complexity and extensive numerical cost encountered in modeling of nonlinear Boltzmann equations, the Navier-Stokes equations can be solved considering the concepts of slip flow regime and applying slip velocity boundary conditions at the solid walls. The high-order slip models can, in some cases, extend the range of applicability of the Navier-Stokes equations beyond Kn = 0.1, where the accuracy of first-order...