Sharif Digital Repository

We have investigated the usage of a Dielectric Barrier Discharge (DBD) plasma actuator to improve the aerodynamic performance of an offshore 6 MW wind turbine. By controlling the aerodynamic load combined with pitch angles of 2, 5, and 10 degrees, we studied the plasma actuator effect on the overall harvested power. Actuators were installed in single and tandem configurations in different chord-wise locations to find the optimum design. The improved phenomenological model developed by authors was used in an analysis to simulate the interaction of the electrostatic field, the ionized particles and the fluid flow. A design software was used to estimate the harvested power of the real 3D blade.... 

The bronchial tree plays a main role in the human respiratory system because the air distribution throughout the lungs and gas exchange with blood occur in the airways whose dimensions vary from several centimeters to micrometers. Organization of about 60,000 conducting airways and 33 million respiratory airways in a limited space results in a complex structure. Due to this inherent complexity and a high number of airways, using target-oriented dimensional reduction is inevitable. In addition, there is no general reduced-order model for various types of problems. This necessitates coming up with an appropriate model from a variety of different reduced-order models to solve the desired... 

Among numerous methods which have been employed to reinforce the thermal efficiency in many systems, one is the thermal radiation which is a mode of heat transfer. Another way to improve the thermal efficiency is the utilization of the porous media. The present work includes the study of micropolar flow with allowance for thermal radiation through a resistive porous medium between channel walls. The governing coupled partial differential equations representing the flow model are transmuted into ordinary ones by using the suitable dimensionless coordinates, and then, quasi-linearization is employed to solve the set of relevant coupled ODEs. Effects of physical parameters on the flow under... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

The bronchial tree plays a main role in the human respiratory system because the air distribution throughout the lungs and gas exchange with blood occur in the airways whose dimensions vary from several centimeters to micrometers. Organization of about 60,000 conducting airways and 33 million respiratory airways in a limited space results in a complex structure. Due to this inherent complexity and a high number of airways, using target-oriented dimensional reduction is inevitable. In addition, there is no general reduced-order model for various types of problems. This necessitates coming up with an appropriate model from a variety of different reduced-order models to solve the desired... 

Among numerous methods which have been employed to reinforce the thermal efficiency in many systems, one is the thermal radiation which is a mode of heat transfer. Another way to improve the thermal efficiency is the utilization of the porous media. The present work includes the study of micropolar flow with allowance for thermal radiation through a resistive porous medium between channel walls. The governing coupled partial differential equations representing the flow model are transmuted into ordinary ones by using the suitable dimensionless coordinates, and then, quasi-linearization is employed to solve the set of relevant coupled ODEs. Effects of physical parameters on the flow under... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

Based on MRI diffusion and perfusion, a new criterion for detection and the healing progress of damaged tissue is suggested. The study is based on the ratio of capillary radii in symmetrical damaged and normal tissue neighboring spaces. The Apparent Diffusion Coefficient (ADC) and Cerebral Blood Flow (CBF) were measured in the brain tissues of six male Wistar rats utilizing suggested MRI measurement techniques. The ADC values of damaged and normal regions were (392 ± 34.1) × 10-6 mm2s-1 and (659 ± 40.7) × 10-6 mm2s-1, respectively. The CBF values of damaged and normal regions were 14.5 ± 10.13 ml/min/ 100 g and 125 ± 41.03 ml/min/100 g, respectively. The geometrical parameters of the... 

One main challenge in numerical treatment of incompressible fluid flow problems is to suppress the decoupling of pressure and velocity fields. The challenge has prompted research toward suggesting and implementing various coupling strategies. In this work, a novel strategy which suitably couples pressure and velocity in a collocated grid arrangement is presented. The current strategy develops a unique cell-face velocity expression which provides infinite cell-face velocity magnitudes in the algorithm. A smoothing factor is incorporated in the cell-face velocity expression in order to produce a wide range of velocity magnitudes. The smoothing factor provides a smooth transition from an unreal... 

The three-dimensional supersonic turbulent flows over wrap-around fin missiles have been computed using the Thin Layer Navier-Stokes (TLNS) equations to reduce the computational efforts compared to those of the Full Navier-Stokes (FNS) equations. In this research, the missile configuration is divided into multi regions to enable fluid flow simulation using Personal Computers (PC). It also makes it possible to use a different number of nodes and distribution of grids in each region to enhance the accuracy. The Thin Layer Navier-Stokes equations in the generalized coordinate system were solved using an efficient, implicit, finite-difference factored algorithm of the Beam and Warming. For the... 

In this study, in order to investigate the effect of the underlying pore-scale processes on continuum scale simulations of porous media dissolution, we improve the standard Lattice Boltzmann method using Quadtree grid refinement approach to simulate fluid flow and reactive transport through large domain sizes. Our results have shown considerable computational improvements up to 80% in simulation time together with increased numerical accuracy. The results and the added value of the new approach are discussed using comparison of our model with the conventional LBM. Moreover, we have applied a systematic analysis by increasing complexity levels and starting from fluid flow and continuing with... 

The separation of cancer cells from a heterogeneous biological sample such as blood plays a vital role in cancer study and future treatments. In this paper, we designed and investigated two microfluidic devices for cancer cell separation, including a serpentine inertial device and an integrated inertial-magnetophoretic device. Firstly, numerical modeling was carried out to study the fluid flow, particles’ trajectories in the inertial device. Then the device was fabricated using soft photolithography and suspension of two types of microparticles with the size of 10 and 15 µm were injected into the microchannel separately to investigate the particles’ trajectories and focusing behavior at... 

Body force modeling is studied in the Generalized Newtonian (GN) fluid flow simulation using a single relaxation time lattice Boltzmann (LB) method. First, in a shear thickening Poiseuille flow, the necessity for studying body force modeling in the LB method is explained. Then, a parametric unified framework is constructed for the first time which is composed of a parametric LB model and its associated macroscopic dual equations in both steady state and transient simulations. This unified framework is used to compare the macroscopic behavior of different forcing models. Besides, using this unified framework, a new forcing model for steady state simulations is devised. Finally, by solving a... 

In this paper, a coupled hydro-mechanical formulation is developed for deformable porous media subjected to crack interfaces in the framework of extended finite element method. Governing equations of the porous medium consist of the momentum balance of the bulk together with the momentum balance and continuity equations of the fluid phase, known as [InlineEquation not available: see fulltext.] formulation. The discontinuity in fractured porous medium is modeled for both opening and closing modes that results in the fluid flow within the fracture, and/or contact behavior at the crack edges. The fluid flow through the fracture is assumed to be viscous and is modeled by employing the Darcy law... 

In this paper, the crack growth simulation is presented in saturated porous media using the extended finite element method. The mass balance equation of fluid phase and the momentum balance of bulk and fluid phases are employed to obtain the fully coupled set of equations in the framework of u - p formulation. The fluid flow within the fracture is modeled using the Darcy law, in which the fracture permeability is assumed according to the well-known cubic law. The spatial discritization is performed using the extended finite element method, the time domain discritization is performed based on the generalized Newmark scheme, and the non-linear system of equations is solved using the... 

During the past two decades, the lattice Boltzmann (LB) method has been introduced as a class of computational fluid dynamic methods for fluid flow simulations. In this method, instead of solving the Navier Stocks equation, the Boltzmann equation is solved to simulate the flow of a fluid. This method was originally developed based on uniform grids. However, in order to model complex geometries such as porous media, it can be very slow in comparison with other techniques such as finite differences and finite elements. To eliminate this limitation, a number of studies have aimed to formulate the lattice Boltzmann on the unstructured grids. This paper deals with simulating fluid flow through a... 

In recent years, some numerical models have been proposed to investigate the effects of the elastic wave such as ultrasonic on fluid flow behavior in porous media. Nevertheless, none of these models are applicable to the fractured reservoirs, especially when the fluid is a Bingham plastic. In this work, the model proposed by P. P. Iassonov and I. A. Beresnev (2003) for flow under exposure of elastic wave in nonfractured porous media is considered and used for development of a new model of steady state flow of a Bingham plastic fluid in fractured reservoirs. The Kazemi's "block and fracture" model assuming negligible vertical permeability in blocks is considered for modeling. In addition,... 

Complicated sedimentary processes control the spatial distribution of geological heterogeneities. This serves to make the nature of the fluid flow in the hydrocarbon reservoirs immensely complex. Proper modeling of these heterogeneities and evaluation of their connectivity are crucial and affects all aspects of fluid flow. Since the natural variability of heterogeneity occurs in a myriad of length scales, accurate modeling of the rock type connectivity requires a very fine scheme, which is computationally very expensive. Hence, this makes other alternative methods such as the percolation approach attractive and necessary. The percolation approach considers the hypothesis that a reservoir can... 

Relative permeability curves have practical implications in petroleum reservoir simulations. Study of the effects of reservoir wettability, pore shape geometry, and viscosity ratio of flowing fluids on the relative permeabilities is of great importance in reservoir modeling. In this paper, lattice Boltzmann method (LBM) is employed for analyzing the two-fluid flow in rigid porous media. The developed LBM code proved to be a robust numerical tool for analyzing the factors that influence the relative permeabilities of two immiscible fluids flowing through porous media. The numerically derived relative permeability curves demonstrate that in neutrally wet reservoirs, the effect of viscosity... 

Recently, a hybrid Lattice Boltzmann Level Set Method (LBLSM) for two-phase incompressible fluids with large density differences, in cases of negligible or a priori known pressure gradients, has been proposed. In the present work, the mentioned LBLSM method is extended to take into account pressure gradient effects. The lattice Boltzmann method is used for calculating velocities, the interface is captured by the level set function, and the surface tension is replaced by an equivalent body force. The method can be applied to simulate two-phase fluid flows with density ratios up to 1000 and viscosity ratios up to 100. In order to validate the method, the evolution and merging of rising bubbles...