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#### Recommendations on performance of parallel DSMC algorithm in solving subsonic nanoflows

, Article Applied Mathematical Modelling ; Volume 36, Issue 5 , May , 2012 , Pages 2314-2321 ; 0307904X (ISSN) ; Darbandi, M ; Sharif University of Technology
2012

Abstract

We investigate the efficiency of a parallel direct simulation Monte Carlo (PDSMC) algorithm in solving the rarefied subsonic flow through a nanochannel. We use MPI library to transfer data between the processors. It is observed that PDSMC solver shows ideal speed up if sufficient workload is provided for each of processors. Additionally, this study shows that the computational time and speed up of the extended PDSMC solver do not depend (or slightly depend) on the number of cells. In contrary, increasing the total number of particles would result in a better efficiency of the PDSMC

#### Numerical study of high gradient thermobuoyant flow in a tilted cavity using a novel non-boussinesq algorithm

, Article Numerical Heat Transfer; Part A: Applications ; Volume 58, Issue 12 , 2010 , Pages 984-1003 ; 10407782 (ISSN) ; Darbandi, M ; Heidarnataj, M ; Sharif University of Technology
2010

Abstract

We study the natural convection heat transfer in a tilted square cavity with different tilt angles. The cavity is subject to a high gradient temperature resulting in high Rayleigh number flows. The fluid is air and is treated as an ideal gas. The flow is laminar. The fluid properties change with temperature variation using Sutherland's law. Because of imposing large temperature gradients to the two cavity opposite walls, there is substantial density variation in the domain. We use a novel non-Boussinesq algorithm to model the density variation fully. Therefore, the current results are considerably different from those obtained using the classical Boussinesq-based methods, which replace the...

#### Drag reduction in turbulent and laminar flows using deflectable surface

, Article 47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 5 January 2009 through 8 January 2009, Orlando, FL ; 2009 ; 9781563479694 (ISBN) ; Darbandi, M ; Schneider, G ; Sharif University of Technology
Abstract

This study is an extension of our previous work that was conducted on the aerodynamic characteristics of an ultra light weight airplane, which could be a human-powered airplane or an unmanned-aerial vehicle. One of the major aerodynamic tasks which should be done in this type of airplane is to reduce drag coefficient. The mainly effectual strategy for drag reduction is to contemplate on the components that make up the largest percentage of the overall drag and take into account that small improvements on large quantities can become significant aerodynamic improvements. Our experience showed that the use of light material in constructing human-powered airplanes and unmanned-air-vehicles has...

#### DPD simulation of non-Newtonian electroosmotic fluid flow in nanochannel

, Article Molecular Simulation ; Volume 44, Issue 17 , 2018 , Pages 1444-1453 ; 08927022 (ISSN) ; Zakeri, R ; Darbandi, M ; Sharif University of Technology
Taylor and Francis Ltd
2018

Abstract

We use the dissipative particle dynamics (DPD) method to simulate the non-Newtonian electroosmotic flow (EOF) through nanochannels. Contrary to a large amount of past computational efforts dedicated to the study of EOF profile, this work pays attention to the EOF of non-Newtonian fluids, which has been rarely touched in past publications. Practically, there are many MEMS/NEMS devices, in which the EOF behaviour should be treated assuming both non-continuum and non-Newtonian conditions. Therefore, our concern in this work is to simulate the EOF through nanochannels considering both non-Newtonian fluid properties and non-continuum flow conditions. We have chosen DPD as our working tool because...

#### Recommendations on enhancing the efficiency of algebraic multigrid preconditioned GMRES in solving coupled fluid flow equations

, Article Numerical Heat Transfer, Part B: Fundamentals ; Volume 55, Issue 3 , 2009 , Pages 232-256 ; 10407790 (ISSN) ; Darbandi, M ; Sharif University of Technology
2009

Abstract

The algebraic multigrid (AMG) algorithm as a preconditioner to the Krylov subspace methods has drawn the attention of many researchers in solving fluid flow and heat transfer problems. However, the efficient employment of this solver needs experience, because users have to quantify several important parameters. In this work, we choose a hybrid finite-volume element method and quantify the optimum magnitudes for those parameters. To generalize our results, two sets of fluid flow governing equations, the thermobuoyant flow and confined diffusion flame, are studied and the optimum values are determined. The results indicate that the AMG can be very effective if a proper storage method is chosen...

#### Advancement in numerical study of gas flow and heat transfer in microscale

, Article Journal of Thermophysics and Heat Transfer ; Volume 23, Issue 1 , 2009 , Pages 205-208 ; 08878722 (ISSN) ; Darbandi, M ; Sharif University of Technology
2009

Abstract

The gas flow and heat transfer in a long microscopic channel with inlet-to-outlet pressure ratio equal to 8000 is studied. The second-order slip velocity and temperature jump boundary conditions are used, which are derived using a gas-surface interface mechanisms. The inlet is discretized to 19 nodes and they are clustered near the wall, while the longitudinal dimension in discretized to 1500 divisions using a nonuniform grid distribution. The current velocity profiles are found to have a good agreement with high-order analytical solutions, indicating that the current velocity perform second-order accuracy. The pressure distributions are found to perform higher nonlinearity as the...

#### Extending the Navier-stokes solutions to transition regime in two-dimensional micro- and nanochannel flows using information preservation scheme

, Article Physics of Fluids ; Volume 21, Issue 8 , 2009 ; 10706631 (ISSN) ; Darbandi, M ; Sharif University of Technology
2009

Abstract

The kinetic-theory-based numerical schemes, such as direct simulation Monte Carlo (DSMC) and information preservation (IP), can be readily used to solve transition flow regimes. However, their high computational cost still promotes the researchers to extend the Navier-Stokes (NS) equations beyond the slip flow and to the transition regime applications. Evidently, a suitable extension would accurately predict both the local velocity profiles and the mass flow rate magnitude as well as the streamwise pressure distribution. The second-order slip velocity model derived from kinetic theory can provide relatively accurate velocity profiles up to a Knudsen (Kn) number of around 0.5; however, its...

#### Direct simulation Monte Carlo solution of subsonic flow through micro/nanoscale channels

, Article Journal of Heat Transfer ; Volume 131, Issue 9 , 2009 , Pages 1-8 ; 00221481 (ISSN) ; Darbandi, M ; Mirjalili, V ; Sharif University of Technology
2009

Abstract

We use a direct simulation Monte Carlo (DSMC) method to simulate gas heating/cooling and choked subsonic flows in micro/nanoscale channels subject to either constant wall temperature or constant/variable heat flux boundary conditions. We show the effects of applying various boundary conditions on the mass flow rate and the flow parameters. We also show that it is necessary to add a buffer zone at the end of the channel if we wish to simulate more realistic conditions at the channel outlet. We also discuss why applying equilibrium-based Maxwellian distribution on molecules coming from the channel outlet, where the flow is nonequilibrium, will not disturb the DSMC solution. The current...

#### An improved actuator disc model for the numerical prediction of the far-wake region of a horizontal axis wind turbine and its performance

, Article Energy Conversion and Management ; Volume 185 , 2019 , Pages 482-495 ; 01968904 (ISSN) ; Darbandi, M ; Sharif University of Technology
Elsevier Ltd
2019

Abstract

Actuator disc models are frequently used to provide a semi-analytical approach to estimating aerodynamic loads on rotary blades. The basic idea is to distribute the aerodynamic loads on a virtual rotating disc instead of simulating the actual rotating blade. These loads are then imposed to represent the source terms of the Navier-Stokes equations, which can be solved numerically using the computational fluid dynamic methods. The thickness of the actuator disk grid is one important factor considerably affecting calculations of the wind turbine rotor. Past researches generally considered the idea of fixed grid thickness exerting along the blade in their actuator disk modeling. However, this...

#### Numerical study of species separation in rarefied gas mixture flow through micronozzles using DSMC

, Article Physics of Fluids ; Volume 31, Issue 4 , 2019 ; 10706631 (ISSN) ; Darbandi, M ; Sharif University of Technology
American Institute of Physics Inc
2019

Abstract

This work investigates the species separation in the rarefied flow of the argon-helium mixture through convergent-divergent micronozzles. Imposing a molecular mass ratio in the order of 10, the flow of this mixture can lead to the formation of serious nonhomogeneous phenomena such as the species separation. This study is performed in the ranges of 2.0-4.0 for the geometrical expansion ratio, 200-400 K for the wall temperature, and 0.003-1.454 for the inlet Knudsen number. The effects of these parameters are examined on the separative performances of micronozzle. The direct simulation Monte Carlo method is selected as the solution method because it can provide reliable solutions in the...

#### Numerical simulation of low-mach-number laminar mixing and reacting flows using a dual-purpose pressure-based algorithm

, Article Numerical Heat Transfer, Part B: Fundamentals ; Volume 59, Issue 6 , Jun , 2011 , Pages 495-514 ; 10407790 (ISSN) ; Darbandi, M ; Hosseinizadeh, S. F ; Sharif University of Technology
2011

Abstract

Benefitting from an analogy between compressible and incompressible governing equations, a novel dual-purpose, pressure-based finite-volume algorithm is suitably extended to simulate laminar mixing and reacting flows in low-Mach-number regimes. In our test cases, the Mach number is as high as 0.00326. Definitely, such low-Mach-number flows cannot be readily solved by either regular density-based solvers or most of their extensions. To examine the accuracy and performance of the extended formulation and algorithm, we simulate two benchmark cases including the mixing natural-convection flow in a square cavity with strong temperature gradients and the premixed reacting flow through annuli with...

#### Computational zone adaptation strategy for unstructured grid users

, Article 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 4 January 2010 through 7 January 2010, Orlando, FL ; 2010 ; 9781600867392 (ISBN) ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
2010

Abstract

This paper presents an advanced grid adaptation strategy to be used by unstructured grid users. The idea behind this strategy originates from the need for automatic control of computational grids during iterative procedures utilized by fluid flow solvers. This strategy eliminates unnecessary grid computations by dividing the unstructured grid into active and inactive zones automatically. The active zones are extended automatically in order to capture the propagation of disturbances in solution domain. In this work, we focus to solve the grid deformations which are imposed in some portions of the main body and are propagated into computational domain during the iterative solutions. To achieve...

#### A directional renumbering strategy for improving unstructured grid data structure

, Article 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Orlando, FL, 4 January 2010 through 7 January 2010 ; 2010 ; 9781600867392 (ISBN) ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
2010

Abstract

A very simple and computationally low cost numerical algorithm is developed to generate a quasi-structured data structure for an unstructured grid. To achieve this purpose, the data structure in the matrices of an unstructured grid is classified to address the element layers and node lines in the computational domain. In this regard, elements and nodes of the unstructured grid are renumbered in a directional ordering-based strategy. The elements and nodes arrangement in each layer and line is accomplished in a unique direction around an interior object of the grid either clockwise or counterclockwise. Furthermore, a new searching scheme is introduced which guarantees a quick search inside...

#### Developing a unified FVE-ALE approach to solve unsteady fluid flow with moving boundaries

, Article International Journal for Numerical Methods in Fluids ; Volume 63, Issue 1 , 2010 , Pages 40-68 ; 02712091 (ISSN) ; Darbandi, M ; Taeibi Rahni, M ; Sharif University of Technology
Abstract

In this study, an arbitrary Lagrangian-Eulerian (ALE) approach is incorporated with a mixed finite-volume-element (FVE) method to establish a novel moving boundary method for simulating unsteady incompressible flow on non-stationary meshes. The method collects the advantages of both finite-volume and finite-element (FE) methods as well as the ALE approach in a unified algorithm. In this regard, the convection terms are treated at the cell faces using a physical-influence upwinding scheme, while the diffusion terms are treated using bilinear FE shape functions. On the other hand, the performance of ALE approach is improved by using the Laplace method to improve the hybrid grids, involving...

#### Study of gas flow in micronozzles using an unstructured dsmc method

, Article Proceedings of the 7th International Conference on Nanochannels, Microchannels, and Minichannels 2009, ICNMM2009, 22 June 2009 through 24 June 2009, Pohang ; Issue PART A , 2009 , Pages 417-424 ; 9780791843499 (ISBN) ; Darbandi, M ; Mirjalili, V ; ASME ; Sharif University of Technology
Abstract

The current research uses an unstructured direct simulation Monte Carlo (DSMC) method to numerically investigate supersonic and subsonic flow behavior in micro convergent-divergent nozzle over a wide range of rarefied regimes. The current unstructured DSMC solver has been suitably modified via using uniform distribution of particles, employing proper subcell geometry, and benefiting from an advanced molecular tracking algorithm. Using this solver, we study the effects of back pressure, gas/surface interactions (diffuse/specular reflections), and Knudsen number, on the flow field in micronozzles. We show that high viscous force manifesting in boundary layers prevents supersonic flow formation...

#### Wind tunnel study of the effect zigzag tape on aerodynamics performance of a wind turbine airfoil

, Article Journal of Advanced Research in Fluid Mechanics and Thermal Sciences ; Volume 41, Issue 1 , 2018 , Pages 1-9 ; 22897879 (ISSN) ; Lazim, T.M ; Darbandi, M ; Sharif University of Technology
Penerbit Akademia Baru
2018

Abstract

A wind tunnel study was performed on the FFA-W-3-270 airfoil, which form a segment of a 1.25 MW wind turbine blade, to examine the effect of fixed roughness height and position using a zigzag tape boundary layer trip strip. Tests were conducted at a Reynolds number of 1×106 over a wide range of angles of attack. The zigzag tape, as an artificial roughness device, not only triggers a premature transition in the flow whereby laminar flow regimes change to turbulent, but also increases the momentum thickness of the turbulent boundary layer and change the airfoil camber. The 60° zigzag tape of 0.5 mm and 1 mm height was placed on the suction side of the airfoil at different chord wise locations....

#### Robust 1-d fluid flow and heat transfer predictions in gas turbine cooling passages

, Article AIAA Propulsion and Energy Forum and Exposition, 2019, 19 August 2019 through 22 August 2019 ; 2019 ; 9781624105906 (ISBN) ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc, AIAA
2019

Abstract

This study describes a 1-D code, which determines the one-dimensional flow and heat transfer distributions in arbitrarily connected flow passages with multiple inlets and outlets. The procedure uses a component solver, which solves the one-dimensional compressible fluid flow and heat transfer equations inside an individual cooling passage. Also, it uses experimental correlations for the heat transfer coefficient and friction factor for each cooling passage. In addition to the component solver, there is a flow network solver subroutine, which applies the mass and energy conservation equations properly at each internal node. In order to validate this 1-D code, both the component and the flow...

#### Robust 1-d fluid flow and heat transfer predictions in gas turbine cooling passages

, Article AIAA Propulsion and Energy Forum and Exposition, 2019, 19 August 2019 through 22 August 2019 ; 2019 ; 9781624105906 (ISBN) ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc, AIAA
2019

Abstract

This study describes a 1-D code, which determines the one-dimensional flow and heat transfer distributions in arbitrarily connected flow passages with multiple inlets and outlets. The procedure uses a component solver, which solves the one-dimensional compressible fluid flow and heat transfer equations inside an individual cooling passage. Also, it uses experimental correlations for the heat transfer coefficient and friction factor for each cooling passage. In addition to the component solver, there is a flow network solver subroutine, which applies the mass and energy conservation equations properly at each internal node. In order to validate this 1-D code, both the component and the flow...

#### Effect of active feather length on aerodynamic performance of airfoils at low reynolds number flow

, Article AIAA AVIATION 2020 FORUM, 15 June 2020 through 19 June 2020 ; Volume 1 PartF , 2020 ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc, AIAA
2020

Abstract

To increase the flight endurance of a Micro air vehicle (MAVs), which operates at low Reynolds number flow, one way is to harvest energy during its flight. By inspiring from the nature when all the birds use their feathers to control and distribute their power along the flying time, a solution might be design of a piezoelectric plate as feathers, which scavenges energy directly from the fluid flow. Cantilevered beam with piezo-ceramic layer undergoing vortex-induced vibrations can convert the mechanical energy available from the ambient environment to a usable electrical power. Since a flow-driven piezoelectric composite beam takes a form of natural three-way coupling of the turbulent fluid...

#### Developing an improved 1-D thermoflow approach to analyze turbine vane temperature distribution

, Article AIAA Scitech Forum, 6 January 2020 through 10 January 2020 ; Volume 1 Part F , 6-10 January , 2020 ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc, AIAA
2020

Abstract

This study presents an improved one-dimensional approach, which is coupled with the 3D numerical flow solver, to find the temperature distribution over a typical turbine vane. The developed code solves the one-dimensional flow and heat transfer distribution in cooling flow passages inside a turbine vane. It uses our previous developed version and uses experimental correlations to predict the heat transfer coefficient and friction factor for each cooling passage. On the other hand, the hot gas flow field and conduction inside the vane material are solved using a 3D numerical solver. Our survey shows that cooling channel’s wall temperature has effect on the convective heat transfer coefficient...