حجم محدود

In this paper, the heat transfer and ablation thermal insulators in solid rocket motor are investigated. Therefore, by collecting and solving the thermal ablation equations, a computer program, using MATLAB software, is developed which can predict the thermal response of insulators in different operating conditions and compare the performance of these insulators. The heat and mass transfer equations are considered in two dimensions in a solid body. We used the equations, finite volume method with implicit formulation for time dependency to solve equations. The reaction equation which written in the form of Arrhenius, is solved using Runge-Kutta method, and the density and the flux of the gas produced at each step are obtained. Also we represent a model for the rate of recession.

The solution of the heat diffusion equation in most practical applications involving complex geometry, thermophysical properties, and boundary conditions is not simply possible and there are some limitations for available numerical solutions. In this research, the finite volume Monte Carlo method was proposed for the solution of the isotropic heat diffusion equation due to two intrinsic capability of the finite volume method; first, each cell is energy conserved and second, the grid transformation is not necessary for complex geometries. The Monte Carlo method as a statistical approach based on physical simulation of the problem capable to solve heat diffusion equation with any degree of complexity was utilized in three different problems. First, a simple problem was investigated for validation of the method by comparing results with the analytical solution. Second, the prediction performance of the proposed method was evaluated in a problem with complex geometry, varying properties, and boundary conditions. Finally, the performance of the finite volume Monte Carlo method was investigated in estimating the temperature distribution of a three-layer body with different thermal conductivities and convection boundary condition. In all of the considered test cases, the predicted results were in good agreement with analytical and CFD solutions. It was also indicated that for a relatively small number of particles, it is possible to achieve acceptable accuracy with a low computational cost.

Flow in a centrifugal electrical submersible pump is simulated. The purpose of this study is to find the effect of changing the axial distance between impeller and scroll on pump’s operation. Flow in the impeller and scroll is simulated with the Fluent software. Finite volume method with SST k-ω turbulance model is used for numerical solution. In order to evaluate the simulation results, values of head, power and efficiency are calculated at the design conditions and are compared to the experimental results. Simulations are then performed with different impeller to scroll axial distances. The results show that by increasing the distance between impeller and scroll, each of the three properties, head, power and efficiency will decrease. Increasing the distance between impeller and scroll from 0.5 to 5.0 mm, head, power and efficiency will drop by 33%, 18% and 20% respectively. Also, effect of changing the axial distance between impeller and scroll on vortices created in the fluid passing through the impeller and the axial force imposed on the impeller are calculated.

In this paper, the heat transfer and ablation thermal insulators in solid rocket motor are investigated. Therefore, by collecting and solving the thermal ablation equations, a computer program, using MATLAB software, is developed which can predict the thermal response of insulators in different operating conditions and compare the performance of these insulators. The heat and mass transfer equations are considered in two dimensions in a solid body. We used the equations, finite volume method with implicit formulation for time dependency to solve equations. The reaction equation which written in the form of Arrhenius, is solved using Runge-Kutta method, and the density and the flux of the gas produced at each step are obtained. Also we represent a model for the rate of recession.

Numerical solution of conjugate heat transfer (CHT) problems in multi-region domains is a challenging issue in terms of efficiency and stability due to inherent coupling between governing equations in separate sub-domains. This paper aims at comparing two distinct strategies for coupling energy equations at interface of regions: partitioned and monolithic. While the former enforces strong coupling via iterative procedures, the latter suggests simultaneous solution of energy equation throughout all regions at once. More precisely, the primary objective of this study is to compare computational costs for three finite volume- based CHT solvers which share a same method for handling pressure-velocity coupling in the fluid, i.e. semi-implicit projection method, and are distinguished from the coupling strategy for energy equation at interface of interacting sub-domains. The first method applies simultaneous solution of energy equation across all regions while second and third ones use separate solver for each region with difference in handling iterative loops. The accuracy and convergence rate of three algorithms are assessed via transient solution of conjugate free convection in fluid and conduction in vertical wall. Finally, it is concluded that, in contrast to partitioned solver in OpenFOAM for CHT problems, employing a separate loop to enforce energy-energy coupling per iteration, can be much more beneficial in terms of computational costs.

In this study, the effect of heat transfers on lift and drag coefficients of two symmetric and camber airfoils with plunging motion in laminar flow is numerically investigated. The compressible Navier–Stokes equations are discretized using a finite volume method and they are solved by PIMPLE algorithm. In this simulation, fluid dynamic viscosity and thermal conductivity are considered to be variable. Also dynamic mesh method is used for oscillating motion. The results show that, by reducing the airfoil surface temperature less than the free flow temperature, lift to drag ratio increases. Moreover, influence of heat transfer on vortexes pattern at airfoils trailing edge and therefore its impact on the aerodynamic coefficients are investigated.

A Finite Volume-Lattice Boltzmann Method (FVLBM) for simulation of viscous laminar compressible flows in 2-D structured curvilinear coordinate system has been developed. In the present study, validation of the presented software and accuracy assessment of four new 2D lattices D2Q9L2, D2Q13L2, D2Q17L2 and D2Q21L2 based on increasing discrete velocities of lattice has been studied and the optimum lattice has been introduced. The presented LBM has developed using new method of circular function idea instead of expansion or correction of Maxwelian function for evaluation of equilibrium distribution functions. Moreover, in order to capture discontinuities in the flow field, 3rd order MUSCL scheme has been implemented for approximation of convective term. The laminar compressible viscous flow over the NACA0012 airfoil has been simulated in the curvilinear coordinate system for two angle of attacks, 0 and 10 Deg. The obtained results have been compared with validated N.S. solutions. Although the results have desirable accuracy in comparison of those of the N.S. solutions, limitation of the presented method and results assessment obtained by the different lattices have been investigated.

The cavity problem always has been considered as a classic and fundamental problem. Specific materials like Bingham viscoplastic which is sort of Non-newtonian fluids shows resistance in a certain range of stress, calling yield stress, and almost acts like rigid body in this limited area. In case of increase applied stress, flows like fluid. Considering heat transfer in this type of material and investigate it, yield stress and viscosity variations with temperature as in practice we face will not be far-fetched. In the present work the numerical solution of the problem of Bingham material inside lid-driven cavity, investigating fluid flow and heat transfer in view of the changes in material properties has been done and results have shown with change in dimensionless numbers and parameters of Re=10-1000, Bn=1-2000, Pr=0.01-100 and E=5000-50000. In this study, using the finite volume method to discretize governing equations and the use of collocated grid, effect of viscosity and yield stress dependence to temperature compared with independence mode and then distribution of horizontal and vertical components of velocity, yield areas and flow inside cavity, center of vortex and then heat transfer due to the stream lines next to side walls, have been analyzed.

Metal hydrides can be used for ambient cooling and heating because of their exothermic and endothermic reaction with hydrogen. This is the first attempt to investigate the cooling capacity of compressor driven metal hydride heat pumps (CDMHHP) using a two-dimensional model. In the last studies, only one-dimensional models have been used for studying the application of CDMHHPs. The simulation results have been compared with experimental results and a good agreement have been observed between them. Then the effect of compressor type and hydrogen adsorbent on the performance of heat pump have been investigated. The results show that the device efficiency significantly depends on compressor performance and using the two-stage compressor can improve the device performance compared with one-stage compressor. Also the use of LaNi5 and C5 alloys showed more cooling power in C5 alloy in the same operating condition whereas it takes more cost. Since the power consumption was equal to both alloys, the heat pump containing LaNi5 alloy with tree times larger compressor could generate the same cooling power provided by C5 alloy.

In recent years, due to population growth and the reduction of water resources, the human has forced to sweeten brackish water. While this work takes energy and high costs. Thus, the scientists studied a lot about solar desalination and the factors influencing them. In this study, we tried to have a review on the literature of numerical simulation of solar desalination systems with Assumptions: laminar natural convection, heat and mass transfer using finite volume method which presented by researchers who have been working in this field. This research is prepared for researchers who interested in this subject or those who intend to get acquainted of solar desalination systems, to have an appropriate reference for specialized study.

Aerodynamic study of flows at low Reynolds for special applications such as micro unmanned underwater vehicles, underwater robots and explorers are interested. In this paper, an improved progressive preconditioning method named power-law preconditioning method, for analyzing unsteady laminar flows around hydrofoils is presented. In this method, the 2D Navier-Stokes equations modifies by altering the time derivative terms of the governing equations. The preconditioning matrix is adapted from the velocity flow-field by a power-law relation. The governing equation is integrated with a numerical resolution derived from the cell-centered Jameson’s finite volume algorithm and a dual-time implicit procedure is applied for solution of unsteady flows. The stabilization is achieved via the second- and fourth-order artificial dissipation scheme. Explicit four-step Runge–Kutta time integration is applied to achieve the steady-state condition. The computations are presented for unsteady laminar flows around NACA0012 hydrofoil at various angles of attack and Reynolds number. Results presented in the paper focus on the velocity profiles, lift and drag coefficient and effect of the power-law preconditioning method on convergence speed. The results show satisfactory agreement with numerical works of others and also indicate that using the power-law preconditioner improves the convergence rate and decreases the computational cost, significantly.

The main objective of this paper is to provide an applied algorithm for analyzing propeller-shaft vibrations in marine vessels. Firstly an underwater marine vehicle has been analyzed at different speed in unsteady condition using the finite volume method. Based on the results of this analysis, flow field of marine vehicle (wake of stern) and velocity inlet to the marine propeller is extracted at different times. Propeller inlet flow field is applied in the boundary element code and using this code, marine propeller has been analyzed in unsteady state. In continue, main / lateral forces and moments over the propeller are extracted. Then the data obtained from the boundary element code alongwith exact geometry of the propeller and shaft have been studied, using finite element code. Natural and forced frequency of the propeller have been determined in various modes of vibration. According to obtained data from Finite Element Method (FEM) numerical analysis, maximum displacement of propeller is for displacement of the propeller tip in forced vibration state .

The use of metal hydrides is one of the hydrogen storage methods. In this research, the process of hydrogen desorption from metal hydride storages with high diameter and constant flow rate was investigated using numerical simulation. A two-dimensional model with finite volume method is applied for simulation of hydrogen desorption. Simulation results were compared with available experimental data and a good agreement was observed between them. In this study, a special design of metal hydride storage was investigated. This design allows the application of metal hydride beds with large diameter for a specific hydrogen outlet flow rate by using aluminum fins. The simulation results verified the heat transfer enhancement effect of aluminum fins and showed the storage diameter can even be increased to 60 cm by using this design. The comparison between the result of applying LaNi5 and C5 alloys revealed that the energy efficiency could be increased by using C5 alloys due to need of heating fluid with lower temperature. Moreover, the results showed that by increasing the outlet volumetric flow rate from 230 to 460 (Nlit/min), the storage diameter should be limited and therefore the smaller storage must be selected.

The panel flutter is concentrated with aerospace researchers, because of fatigue failure on structures. The usage of the numerical simulation is good company with analytical method. The 2D cylindrical panel flutter is simulated with navierstocks equations for fluid flow with finite volume theory. Also, Simulation is prepared with piston theory for analytical solution. Comparison of full numerical finite volume and assume mode method in post flutter domain is produced. Non-linear shell with the effect of in-plane load, thermal load and aerodynamic load with 3rd order piston theory is modeled to solve with assume mode method. The numerical method is 4th order rung-kutta to solve ODEs. With increasing shell camber, limite cycle oscillation change to random motion. The effect of expansion waves made decrease in second half of shell in analytical method in compare to numerical. The most important output depend on equal result for flat plate and different result on curve plate with numerical and analytical method. With increasing shell camber, limite cycle oscillation change to random motion. The effect of expansion waves made decrease in second half of shell in analytical method in compare to numerical. Amplitude of oscillation and flutter speed respectively is increase and decrease in numerical method despite of analytical one.

In this research, a finite volume-Lattice Boltzmann Method (FVLBM) for simulation of inviscid compressible flows in 1-D and 2-D structured curvilinear coordinate system is presented. In this simulation, LBM, with new method of Circular Function idea instead of expansion or correction of Maxwelian function was implemented for evaluation of equilibrium distribution functions, moreover, in order to capture discontinuities in the flow field, 3rd order MUSCL scheme was implemented for approximation of convective term. Since in lattice Boltzmann method time step is extremely limited by relaxation time (Knudsen number), we improved performance of FVLBM with a third-order IMEX Rung-Kutta scheme for temporal discretization of BGK-model for archiving greater time step and lower CPU time. Consequently, the present work can be used widely for simulation of actual engineering problems in aerodynamics. Various gas dynamics benchmark problems and applied engineering unsteady problems in curvilinear coordinate grid is solved for validation. The numerical results of the presented method are compared with experimental dates and the results of FVM Euler solutions; there is good agreement between the results of the present method and those of the references.

The aim of this research is to study effective parameters of incompressible، viscous and unsteady flow in Turbomachinary cascades using the Spalart-Allmaras (SA) RANS-Based Delayed Detached Eddy Simulation method. Detached Eddy Simulation is a hybrid RANS-LES method that was purposed in order to reduce LES computational cost. In this method، near wall، in boundary layer، RANS turbulence model is used and away from the wall، method automatically switches to LES. To develop original DES method (DES97)، DDES was purposed to solve modeled stress depletion problem. A new function is introduced to the DDES model to make the transition from RANS to LES grid cell size independent. The numerical method that is used for discretization is staggered finite-volume and the grid is Cartesian. Also hybrid differencing scheme (the scheme compound of central differencing scheme and upwind scheme) to discretization of convection terms in Navier-Stokes is used. The results of this study compared with the results of simulation with SA turbulence model.

Prediction of fluid-elastic instability is a great matter of importance in designing cross-flowtube bundles from the perspective of vibration. In the present paper، the threshold of fluid-elastic instability has been numerically predicted via simulation of incompressible، unsteady، and turbulent cross-flow through a tube bundle in a normal triangular arrangement. The conditions of simulation is the same as a previous experiment. A finite volume solver، based on Cartesian-staggered grid، has been implemented and the interactions between fluid and structure are solved fully coupled method of solving flow and structure equations in each time step. The fluid elastic instability was predicted and analyzed by presenting the structural responses، trajectory of flexible cylinders، and critical reduced velocities.

In this paper, the thermo-hydrodynamic analysis of incompressible fluid flow in conjunction with cell-centered finite volume-lattice Boltzmann method is developed. To demonstrate the temperature field, the double distribution function model was used. Since, instability is the most severe problem of the thermal lattice Boltzmann methods to handle flows; a stable and accurate cell-centered scheme is presented. For this purpose, the pressure and temperature based upwind biasing factors are used as flux correctors. Also, additional lattices at the edge of each boundary cell are introduced, which allow a much better description of the actual geometrical shape. The unknown energy distribution at the boundary cells were decomposed into its equilibrium and non-equilibrium parts. This treatment enlarges the domain stability and leads to faster convergence. In addition of calculating numerical viscosity, The method is applied to two dimensional incompressible thermal plane duct flow. The results show a very good accuracy and agreement with the exact solution and previous numerical results.

In this paper a two-dimensional axisymmetric numerical model with variable porosity for premixed methane/air combustion in porous media has been developed. For this purpose، multi step mechanisms such as GRI 1. 2، GRI. 2. 11، GRI. 3. 0، Skeletal and a mechanism with 17 species and 58 chemical reactions has been used and the effects of the mechanisms on the temperature profile، mass fraction of species and emission of pollutants have been investigated. This model solves the continuity، Navier Stokes، the gas and solid energy and the chemical species transport equations by using the finite volume method. The pressure and velocity have been coupled with the SIMPLE algorithm. The results showed that the combustion mechanisms have the same accuracy in predicting of temperature profile and mass fraction of species in order to the GRI. 1. 2، GRI. 2. 11، GRI. 3. 0 mechanisms are the same accuracy and also the skeletal and 17 species mechanisms are the same in predicting of temperature profile and mass fraction of species. Also the effects of increasing the inlet velocity and the volumetric heat transfer coefficient at combustion zone with variation porosity are investigated. The results showed that by increasing in inlet velocity، the peak temperature and the amount of NOx emission will be decreased and also by decreasing in volumetric heat transfer، the peak temperature will be decreased.

In this paper، the thermo-hydrodynamical analysis of incompressible flow in conjunction with cell-centered finite volume-lattice Boltzmann method (FV-LBM) was developed. To demonstrate the temperature field، the double distributions function (DDF) was used. A novel approach was applied in cell flux calculation by definition of biasing factors based on pressure and temperature. This treatment enlarges the domain stability and leads to faster convergence. A consistent open and solid boundary treatment of flow was also addressed. The unknown energy distribution at the boundary cells were decomposed into its equilibrium and non-equilibrium parts. Then، the non-equilibrium part was approximated with extrapolation of the non-equilibrium part of the populations at the neighboring nodes. Two test cases namely، thermo-hydrodynamic in a backward-facing step and around a circular cylinder inserted within the backward-facing step were carried out. The results were compared with the available solutions in the technical literature showing reasonable agreements.