Sharif Digital Repository

We have developed a fourth order compact finite volume method for the solution of low Mach number compressible flow equations on arbitrary nonuniform grids. The formulation presented here uses collocated grid that preserves fourth order accuracy on nonuniform meshes. This was achieved by introduction of a new fourth order method for calculation of cell and face averaged metrics. A special treatment of nonlinear terms is used to guarantee the stability of the fourth order compact method. Moreover an approach for applying this method to multi-block domains is presented for complicated geometries and parallel processing applications. Several test cases including the flow in a lid-driven cavity,... 

In this study, the hydrodynamics and noise behaviour of marine propellers are examined through finite volume method under various operational conditions. The hydrodynamics of these propellers are studied both numerically and experimentally, and the characteristic curves are produced. Sheet cavitation inception and development conditions are also considered in order to understand the impact of different rotational speeds on propeller noise. Ffowcs Williams and Hawkings equations are used to extract the total sound pressure levels under non-cavitating and sheet cavitating conditions. Finally, the impact of cavitation on increasing the propeller noise is thoroughly explored and the results are... 

There are various propulsion, maneuvering, and stabilization mechanisms in nature, which can provide inspiration for similar mechanisms in man-made vehicles. This study aims to elucidate and compare the propulsive vortical signature and performance of a foil in two important natural mechanisms of pure pitching and undulatory oscillations. Governing equations are solved with a pressure-based finite volume method solver, in an arbitrary Lagrangian-Eulerian framework domain containing a NACA 0012 foil moving with prescribed kinematics. The results show that in a given Reynolds number (Re), the undulating mechanism produces thrust at a higher Strouhal number (St) and with smaller growth slope,... 

Neutron noise induced by propagating thermal-hydraulic disturbances (propagation noise for short) in pressurized water reactors is investigated in this paper. A closed-loop neutron-kinetic/thermal-hydraulic noise simulator (named NOISIM) has been developed, with the capability of modeling the propagation noise in both Western-type and VVER-type pressurized water reactors. The neutron-kinetic/thermal-hydraulic noise equations are on the basis of the first-order perturbation theory. The spatial discretization among the neutron-kinetic noise equations is based on the box-scheme finite difference method (BSFDM) for rectangular-z, triangular-z and hexagonal-z geometries. Furthermore, the finite... 

Proper orientation of walkways, based on regional winds and local shade, provides good control over walkway ventilation. The architecture of the old town of Sirjan had experimentally orientated the city's walkways in such a manner that the shadows in the walkways produced the maximum possible natural ventilation in this hot and dry town. This study has focused on the optimum design of Sirjan city considering a natural ventilation mechanism. At first, a typical walkway with certain geometric parameters is considered. Then, considering the symmetry of the shadows cast in the walkway, the natural ventilation rate is investigated at 7 different angles and at 15° intervals. The problem is modeled... 

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... 

In this study, the hydrodynamics and noise behaviour of marine propellers are examined through finite volume method under various operational conditions. The hydrodynamics of these propellers are studied both numerically and experimentally, and the characteristic curves are produced. Sheet cavitation inception and development conditions are also considered in order to understand the impact of different rotational speeds on propeller noise. Ffowcs Williams and Hawkings equations are used to extract the total sound pressure levels under non-cavitating and sheet cavitating conditions. Finally, the impact of cavitation on increasing the propeller noise is thoroughly explored and the results are... 

Achieving more accurate reacting flow numerical solutions apparently demand employing higher-order schemes, utilizing finer grids, and benefiting from more advanced chemistry models. One major objective of this work is to extend an inclusive low-order upwind-biased scheme in the context of finite-volume-element method to predict turbulent reacting flows on coarse grid resolutions very reliably. In this regard, a low-order upwind-biased scheme is suitably extended to approximate the mixture fraction variances at the cell-faces. This scheme implements the reacting flow physics explicitly in deriving the proposed mixture fraction variance expressions. These physical implementations enhance the... 

The objective of this article is to study the estimation of an overall heat transfer coefficient in a partially filled rotating cylinder. Herein is an inverse analysis for estimating the overall heat transfer coefficient in an arbitrary cross-section of the aforementioned system from the temperatures measured on the shell. The material employs the finite-volume method to solve the direct problem. The hybrid effective algorithm applied here contains the local optimization algorithm to estimate the unknown parameter by minimizing the objective function. The data measured here are simulated by adding random errors to the exact solution. An investigation is made of the impact of the measurement... 

The finite-volume methods normally utilize either simple or complicated mathematical expressions to interpolate the fluxes at the cell faces of their unstructured volumes. Alternatively, we benefit from the advantages of both finite-volume and finite-element methods and estimate the advection terms on the cell faces using an inclusive pressure-weighted upwinding scheme extended on unstructured grids. The present pressure-based method treats the steady and unsteady flows on a collocated grid arrangement. However, to avoid a non-physical spurious pressure field pattern, two mass flux per volume expressions are derived at the cell interfaces. The dual advantages of using an unstructured-based... 

The main objective of this work is to develop a novel moving-mesh finite-volume method capable of solving the seepage problem in domains with arbitrary geometries. One major difficulty in analysing the seepage problem is the position of phreatic boundary which is unknown at the beginning of solution. In the current algorithm, we first choose an arbitrary solution domain with a hypothetical phreatic boundary and distribute the finite volumes therein. Then, we derive the conservative statement on a curvilinear co-ordinate system for each cell and implement the known boundary conditions all over the solution domain. Defining a consistency factor, the inconsistency between the hypothesis... 

A mathematical model is presented to simulate the multiple heterogeneous reactions with complex set of physicochemical and thermal phenomena in a moving bed of porous pellets. This model is based on both heat and mass transfer phenomena of gaseous species in a porous medium including chemical reactions at interfaces whose areas vary during the conversion. This model accounts for both the exothermic and endothermic reactions which can be equimolar or nonequimolar. Furthermore it considers simultaneously the reactions in the nonisothermal transient condition. A powerful technique based upon finite volume fully implicit approach has been implemented to solve the complicated governing equations... 

The numerical solution of the fluid flow governing equations requires the implementation of certain boundary conditions at suitable places to make the problem well-posed. Most of numerical strategies exhibit weak performance and obtain inaccurate solutions if the solution domain boundaries are not placed at adequate locations. Unfortunately, many practical fluid flow problems pose difficulty at their boundaries because the required information for solving the PDE's is not available there. On the other hand, large solution domains with known boundary conditions normally need a higher number of mesh nodes, which can increase the computational cost. Such difficulties have motivated the CFD... 

Steady-state convective heat transfer around a circular cylinder embedded in porous media is studied in the range of low and moderate Peclet numbers less than 40. The cylinder is at constant temperature and the Darcy model is used for the analysis of fluid flow and heat transfer in porous media. The governing equations are discretised using finite volume approach based on staggered grids. The powerlaw scheme is used in the numerical solution and a SIMPLE-like algorithm is developed and used in the solution process. It is found that the numerical algorithm is sufficiently efficient in the range of Peclet numbers less than 40. Parametric studies are done for better understanding of the porous... 

Film cooling of surfaces appears in many applications. For instance, it is one of the most effective methods to improve the efficiency of gas turbines. As a fundamental study, two different types of film cooling (slot and discrete holes injections) are numerically simulated here. A flat surface is used to model a small portion of a gas turbine blade. Incompressible, stationary, viscous, turbulent flow is assumed using the STAR-CD software with the standard k-ε model and a cell-centered finite volume method on a nonuniform structured grid. The jet flow Reynolds number, based on the jet's hydraulic diameter, is 4.7 × 103. The study of the injection angle and the velocity ratio shows that the... 

Multiphase impeller stirred tank reactors enhance mixing of reacting species used in a variety of chemical industries. Gas-liquid mixing and mass transfer between these phases is an important application in reactor design. One such an example is hydrogenation reaction of aqueous NDMA (Nitroso dimethyl amine) solution in which one of the parameters having a significant effect on the reaction rate is mass transfer. This parameter in turn is a function of impeller shape and rotational speed, gas flow rate and reactor scale. Computational Fluid Dynamics (CFD) is a useful tool in the analysis, design and scale up of stirred tank reactors via investigating hydrodynamics of gas and liquid flow,... 

In this paper, the effect of viscosity on internal ballistics simulation of a solid rocket motor with an internal burning cylindrical grain is numerically investigated. Axisymmetric compressible Navier-Stokes equations are discretized by finite volume approach on structured mesh and are solved using upwind Roe's scheme. A quasi steady procedure is used to simulate the regression of the burning surface by using a steady flow solver. Grid resolution is studied to insure acceptable accuracy. It is finally shown that most physical phenomena are quite accurately simulated by using an Euler solver, while NS solvers do not increase the accuracy as much they increase the CPU time  

In the present study criterion for local thermal equilibrium assumption is studied. It concerns with the fluid flow and heat transfer between two parallel plates filled with a saturated porous medium under non-equilibrium condition. A two-equation model is utilized to represent the fluid and solid energy transport. Numerical Finite Volume Method has been developed for solving coupled energy equations and the Non-Darcian effects are considered for description of momentum equation. The effects of suitable non dimensional parameters as Peclet number and conductivity ratio has been studied thoroughly. A suitable non dimensional equation proposed in wide range of Peclet number and conductivity... 

In the present study criterion for local thermal equilibrium assumption is studied. It concerns with the fluid flow and heat transfer between two parallel plates filled with a saturated porous medium under non-equilibrium condition. A two-equation model is utilized to represent the fluid and solid energy transport. Numerical Finite Volume Method has been developed for solving coupled energy equations and the Non-Darcian effects are considered for description of momentum equation. The effects of suitable non dimensional parameters as Peclet number and conductivity ratio has been studied thoroughly. A suitable non dimensional equation proposed in wide range of Peclet number and conductivity... 

A computational investigation is performed to study the effects of injection velocity on the main dynamic parameters of the fuel cloud released into the open atmosphere. The volume, shape, and growth rate of the cloud, turbulence intensity, as well as the distribution of fuel concentration, temperature gradient, and self-ignition induction time are the most important parameters determining the mode of combustion that propagates through the cloud. A modified KIVA-based program is employed to fulfill the calculations. Systems of equations are solved by a finite-volume method. The k-ε model and discrete droplet model are applied for modeling gas-phase turbulence and liquid spray, respectively....