Sharif Digital Repository

In this paper, an unsteady, two-dimensional solver is developed, based on Van Leer's flux splitting algorithm, in conjunction with the "Monotonic Upstream Scheme for Conservation Laws (MUSCL)" limiters for improving the order of accuracy. For a minimum usage of computer memory and faster convergence, the two-layer Baldwin-Lomax turbulence model is implemented for a viscous solution. Three test cases are prepared to validate the solver. The computed results are compared with experimental data and the good agreement of the compared results validates the solver. Finally, the solver is used for the flow through a multi-blade stage of an axial compressor in its design condition. The solutions of... 

An analytical procedure for supersonic flutter analysis of two-dimensional panels was developed using unsteady potential flow aerodynamic theory. The local spatial influence was considered as an integral over the plate area. The U-g method was used for flutter prediction. Results indicate a stabilizing effect of the unsteady potential flow aerodynamics theory compared to the quasi-steady first-order piston theory  

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  

The issue of entropy generation in laminar forced convection of a Newtonian fluid through a slit microchannel is analytically investigated by taking the viscous dissipation effect, the slip velocity and the temperature jump at the wall into account. Flow is considered to be hydrodynamically fully developed but thermally developing. The energy equation is solved by means of integral transform. The results demonstrate that to increase Knudsen number is to decrease entropy generation, while the effect of increasing values of Brinkman number and the group parameter is to increase entropy generation. Also it is disclosed that in the thermal entrance region the average entropy generation number... 

The entropy generation rate has become a useful tool for evaluating the intrinsic irreversibilities associated with a given process or device. This work presents an analytical solution for entropy generation in hydrodynamically fully developed thermally developing laminar flow in a microtube. The rarefaction effects as well as viscous heating effects are taken into consideration, but axial conduction is neglected. Using fully developed velocity profile, the energy equation is solved by means of integral transform. The solution is validated by comparing the local Nusselt numbers against existing literature data. From the results it is realized that the entropy generation decreases as Knudsen... 

In the present work, the second law of thermodynamics analysis has been carried out for steady-state fully developed laminar gas flow in a parallel plate microchannel with asymmetrically heated walls. The rarefaction effects as well as viscous heating effects are taken into consideration. Closed-form expressions are obtained for velocity and temperature distributions and entropy generation rates. The results demonstrate that increasing values of the wall heat fluxes ratio result in greater entropy generation for positive Brinkman numbers, whereas the opposite is true for negative values of Brinkman. However, the effect of the wall heat fluxes ratio on entropy generation becomes insignificant... 

In this work, we attempted to develop an Implicit Coupled Density-Based (ICDB) solver using LU-SGS algorithm based on the AUSM+ up scheme in OpenFOAM. Then sonicFoam solver was modified to include viscous dissipation in order to improve its capability to capture shock wave and aerothermal variables. The details of the ICDB solver as well as key implementation details of the viscous dissipation to energy equation were introduced. Finally, two benchmark tests of hypersonic airflow over a flat plate and a 2-D cylinder were simulated to show the accuracy of ICDB solver. To verify and validate the ICDB solver, the obtained results were compared with other published experimental data. It was... 

The solution for bulk fluid motion of a bidirectional coaxial vortex for application in vortex engine has been derived. The vortex engine is a novel combustion chamber in which swirl motion of reactants are used to maintain the chamber walls cool. The flow field has been considered both analytically and numerically. The model is based on incompressible, steady, axisymmetric, and non-reactive flow conditions. The governing PDEs are reduced to a system of nonlinear ODEs and then, by a coordinate transformation, their singularity has been relaxed. Solution domain has been decomposed into the inner viscous and outer inviscid regions, then, the velocity and pressure fields are obtained... 

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... 

In this paper, the truly Meshless Local Petrov-Galerkin (MLPG) method is extended for computation of unsteady incompressible flows, governed by the Navier-Stokes equations (NSE), in vorticity-stream function formulation. The present method is a truly meshless method based only on a number of randomly located nodes. The formulation is based on two equations including stream function Poisson equation and vorticity advection-dispersion-reaction eq. (ADRE). The meshless method is based on a local weighted residual method with the Heaviside step function and quartic spline as the test functions respectively over a local subdomain. Moving Least Square approximation (MLS) is employed in shape... 

The comparison of aerodynamic characteristics of circular and noncircular bodies using computational-fluid-dynamics (CFD) code and semi-emperical code was discussed. It was observed that the performance of aerodynamic coefficients was better for squared section body at different angles of attack. It was also observed from the study of the flow physics that the pressure difference between the front and back of the body that produce pressure drag was more in the circular body. Results show that the friction drag is more for the square body than the circular body as the surface area of the square body is large  

In the present study, the preconditioned incompressible Navier-Stokes equations with the artificial compressibility method formulated in the generalized curvilinear coordinates are numerically solved by using a high-order compact finite-difference scheme for accurately and efficiently computing the incompressible flows in a wide range of Reynolds numbers. A fourth-order compact finite-difference scheme is utilized to accurately discretize the spatial derivative terms of the governing equations, and the time integration is carried out based on the dual time-stepping method. The capability of the proposed solution methodology for the computations of the steady and unsteady incompressible... 

Electroosmosis has many applications in fluid delivery at microscale, sample collection, detection, mixing and separation of various biological and chemical species. In biological applications, most fluids are known to be non-Newtonian. Therefore, the study of thermal features of non-Newtonian electroosmotic flow is of great importance for scientific communities. In the present work, the fully developed electroosmotic flow of power-law fluids in a slit microchannel is investigated. The related equations are transformed into non-dimensional forms and necessary changes are made to adapt them for non-Newtonian fluids of power-law model. Results show that depending on different flow parameters... 

In this paper, combined forced and natural convection in a vertical channel containing both porous and viscous regions taking into account the influences of inertial force and viscous dissipation has been studied. In this regard, fully developed fluid flow in the porous region was modeled using the Brinkman-Forchheimer extended Darcy model. To solve governing equations of both the porous and viscous regions including thermal energy and momentum equations, a two-parameter perturbation method was applied. The velocity and temperature distributions of both the regions were obtained in terms of various parameters such as inertial force, Grashof, Reynolds, and Brinkman numbers, as well as various...