Search results for: Ehsan Roohi

Items from 1 to 20 out of 39 results

article

On the vortical characteristics and cold-to-hot transfer of rarefied gas flow in a lid driven isosceles orthogonal triangular cavity with isothermal walls

Ehsan Roohi, Vahid Shahabi, Amir Bagherzadeh

International Journal of Thermal Sciences > 2018 > 125 > C > 381-394

Rarefied gas flows in nano-scale isosceles triangular cavities with a motion away from the square corner are considered over a wide range of flow rarefactions regimes, i.e., 0.01 ≤ Kn ≤ 10, using the direct simulation Monte Carlo (DSMC) method. We put emphasis to the rarefaction effects on the vortical behaviors and heat transfer patterns of rarefied monatomic and diatomic gases. We show that the...

article

A generalized form of the Bernoulli Trial collision scheme in DSMC: Derivation and evaluation

Ehsan Roohi, Stefan Stefanov, Ahmad Shoja-Sani, Hossein Ejraei

Journal of Computational Physics > 2018 > 354 > C > 476-492

The impetus of this research is to present a generalized Bernoulli Trial collision scheme in the context of the direct simulation Monte Carlo (DSMC) method. Previously, a subsequent of several collision schemes have been put forward, which were mathematically based on the Kac stochastic model. These include Bernoulli Trial (BT), Ballot Box (BB), Simplified Bernoulli Trial (SBT) and Intelligent Simplified...

article

On the consequences of successively repeated collisions in no-time-counter collision scheme in DSMC

Hassan Akhlaghi, Ehsan Roohi, Stefan Stefanov

Computers & Fluids > 2018 > 161 > C > 23-32

The current paper investigates the appropriateness and consequences of avoiding successively repeated collisions usually recommended in the Direct Simulation Monte Carlo (DSMC) solvers, which use the No Time Counter (NTC) collision technique. A sensitive test case, i.e., Fourier heat transfer problem at the early slip regime, is considered in the presence and absence of the successively repeated collisions...

article

Cavitation characteristics around a sphere: An LES investigation

Mohammad-Reza Pendar, Ehsan Roohi

International Journal of Multiphase Flow > 2018 > 98 > C > 1-23

Here we examine partial and supercavitation over a sphere at a constant Reynolds number of 1.5 × 10⁶ and a broad range of cavitation numbers (0.36 <σ< 1). Large eddy simulation (LES) and Sauer mass transfer model were used to simulate the dynamic and unsteady cavitation around the sphere. Also, the compressive volume of fluid (VOF) method is used to track the cavity interface. The two-phase...

article

Regulation of anti-Fourier heat transfer for non-equilibrium gas flows through micro/nanochannels

Mojtaba Balaj, Ehsan Roohi, Alireza Mohammadzadeh

International Journal of Thermal Sciences > 2017 > 118 > C > 24-39

In this study we use the direct simulation Monte Carlo (DSMC) to elaborate on the heat transfer patterns in the pressure-driven rarefied flow through micro/nanochannels. Finite length planar micro/nanochannels are considered using with symmetrical wall heat flux boundary conditions, and the gas flow is considered to be in slip and transition regimes. When considering zero-conductive or cooled walls,...

article

Evaluation of the SBT-TAS collision scheme on treating unsteady flows

Seyyed Moein Madani, Ehsan Roohi

European Journal of Mechanics - B/Fluids > 2017 > 64 > C > 17-29

The aim of the current work is to evaluate the accuracy and efficiency of a newly suggested collision scheme in the Direct Simulation Monte Carlo (DSMC) method; Simplified Bernoulli Trials implemented over transient adaptive subcells, SBT-TAS, for two different unsteady flow test cases. First, the performance of the SBT-TAS scheme is evaluated via simulating the shock-tube test case through a broad...

article

DSMC investigation of rarefied gas flow through diverging micro- and nanochannels

Amin Ebrahimi, Ehsan Roohi

Microfluidics and Nanofluidics > 2017 > 21 > 2 > 1-12

Direct simulation Monte Carlo (DSMC) method with simplified Bernoulli trials (SBT) collision scheme has been used to study the rarefied pressure-driven nitrogen flow through diverging micro- and nanochannels. The fluid behaviours flowing between two plates with different divergence angles ranging between 0° and 17° are described at different pressure ratios (1.5 ≤ Π ≤ 2.5) and Knudsen numbers (0.03 ≤ Kn ≤ 12...

article

Collision partner selection schemes in DSMC: From micro/nano flows to hypersonic flows

Ehsan Roohi, Stefan Stefanov

Physics Reports > 2016 > 656 > C > 1-38

The motivation of this review paper is to present a detailed summary of different collision models developed in the framework of the direct simulation Monte Carlo (DSMC) method. The emphasis is put on a newly developed collision model, i.e., the Simplified Bernoulli trial (SBT), which permits efficient low-memory simulation of rarefied gas flows. The paper starts with a brief review of the governing...

article

Nanofluid flow and heat transfer in a microchannel with longitudinal vortex generators: Two-phase numerical simulation

Amin Sabaghan, Mojtaba Edalatpour, Mohammad Charjouei Moghadam, Ehsan Roohi, more

Applied Thermal Engineering > 2016 > 100 > C > 179-189

Here we report a comprehensive numerical procedure based on the two-phase approach to simulate a rectangular microchannel consisting of six longitudinal vortex generators (LVGs). Nanofluids are used to remove heat generated within the microchannel. The simulations performed in this paper are based on the newest version of the two-phase Eulerian–Eulerian approach. The TiO₂-based nanofluids with different...

article

Heat transfer and entropy generation in a microchannel with longitudinal vortex generators using nanofluids

Amin Ebrahimi, Farhad Rikhtegar, Amin Sabaghan, Ehsan Roohi

Energy > 2016 > 101 > C > 190-201

Conjugated heat transfer and hydraulic performance for nanofluid flow in a rectangular microchannel heat sink with LVGs (longitudinal vortex generators) are numerically investigated using at different ranges of Reynolds numbers. Three-dimensional simulations are performed on a microchannel heated by a constant heat flux with a hydraulic diameter of 160 μm and six pairs of LVGs using a single-phase...

article

A novel algorithm for implementing a specified wall heat flux in DSMC: Application to micro/nano flows and hypersonic flows

Hassan Akhlaghi, Ehsan Roohi

Computers & Fluids > 2016 > 127 > C > 78-101

This paper introduces a modified version of the iterative (IT) technique called the modified iterative (MIT) technique which implements a desired wall heat flux distribution over the wall for rarefied gas simulations using the direct simulation Monte Carlo (DSMC) method. The accuracy of the MIT technique and suitable ranges of employed parameters are examined in various test cases, i.e., shear driven...

chapter

Measuring the Carbon Footprint of Business Processes

Jan Recker, Michael Rosemann, Ehsan Roohi Gohar

Lecture Notes in Business Information Processing > Business Process Management Workshops > SusBPM Workshop > 511-520

While many corporations and individuals realize that environmental sustainability is an urgent problem to address, the academic community has been slow to acknowledge the problem and take action. We contribute to the emerging academic discussion by proposing a new approach for engaging in the analysis of environmentally sustainable business processes. Specifically, we propose an approach for measuring...

article

Investigation of cavitation around 3D hemispherical head-form body and conical cavitators using different turbulence and cavitation models

Mohammad-Reza Pendar, Ehsan Roohi

Ocean Engineering > 2016 > 112 > C > 287-306

In this paper, cavitation and supercavitation around 3D hemispherical head-form body and a conical cavitator were simulated. Dynamic and unsteady behaviors of cavitation were solved using large eddy simulation (LES) and k-ω SST turbulence models, as well as Kunz and Sauer mass transfer models. In addition, the compressive volume of fluid (VOF) method is used to track the cavity interface. Simulation...

article

Simulation of three-dimensional cavitation behind a disk using various turbulence and mass transfer models

Ehsan Roohi, Mohammad-Reza Pendar, Amin Rahimi

Applied Mathematical Modelling > 2016 > 40 > 1 > 542-564

In this study, we performed numerical investigations of the cavitating and supercavitating flow behind a three-dimensional disk with a particular emphasis on detailed comparisons of various turbulence and mass transfer models. Simulations were performed using the OpenFOAM package and flows at three different cavitation numbers, (σ=0.2, 0.1, and 0.05) were considered. Large eddy simulation (LES) and...

article

DSMC simulation of hypersonic flows using an improved SBT-TAS technique

Bijan Goshayeshi, Ehsan Roohi, Stefan Stefanov

Journal of Computational Physics > 2015 > 303 > C > 28-44

The current paper examines a new DSMC approach to hypersonic flow simulation consisting of a combination between the Simplified Bernoulli Trials (SBT) collision algorithm and the transient adaptive subcell (TAS) selection procedure. The SBT collision algorithm has already been introduced as a scheme that provides accurate results with a quite small number of particles per cells and its combination...

article

A new form of the second-order temperature jump boundary condition for the low-speed nanoscale and hypersonic rarefied gas flow simulations

Nam T.P. Le, Ehsan Roohi

International Journal of Thermal Sciences > 2015 > 98 > C > 51-59

The accuracy of numerical simulations of rarefied gas flows, in particular the Navier-Stokes-Fourier (N–S–F) equations, depends on the employed surface boundary conditions. In the literature, the combination of the second-order slip/jump conditions has primarily been used for either the Burnett or the BGK Burnett equations for hypersonic gas flows. In this work, we suggest the second-order temperature...

article

Detailed investigation of flow and thermal field in micro/nano nozzles using Simplified Bernoulli Trial (SBT) collision scheme in DSMC

Seyed Ali Saadati, Ehsan Roohi

Aerospace Science and Technology > 2015 > 46 > C > 236-255

Flow regimes through micro/nano nozzles experience the continuum behavior as well as the rarefied condition. The occurrence of broad rarefaction regimes due to unique geometry/flow conditions makes the particle-based simulation of micro/nano nozzles computationally expensive. Therefore, the primary aim of the present study is to implement the Simplified Bernoulli trials (SBT) collision algorithm in...

article

Low Mach number slip flow through diverging microchannel

Vijay Varade, V.S. Duryodhan, Amit Agrawal, A.M. Pradeep, more

Computers and Fluids > 2015 > 111 > Complete > 46-61

This paper presents experimental and three-dimensional numerical study of gaseous slip flow through diverging microchannel. The measurements are performed for nitrogen gas flowing through microchannel with different divergence angles (4°, 8°, 12° and 16°), hydraulic diameters (118, 147 and 177μm) and lengths (10, 20 and 30mm). The Knudsen number falls in the continuum and slip regimes (0.0005⩽Kn⩽0...

article

Numerical investigation of thermoacoustic refrigerator at weak and large amplitudes considering cooling effect

Ali Namdar, Ali Kianifar, Ehsan Roohi

Cryogenics > 2015 > 67 > Complete > 36-44

In this paper, OpenFOAM package is used for the first time to simulate the thermoacoustic refrigerator. For simulating oscillating inlet pressure, we implemented cosine boundary condition into the OpenFOAM. The governing equations are the unsteady compressible Navier–Stokes equations and the equation of state. The computational domain consists of one plate of the stack, heat exchangers, and resonator...

article

Effects of shear work on non-equilibrium heat transfer characteristics of rarefied gas flows through micro/nanochannels

Mojtaba Balaj, Ehsan Roohi, Hassan Akhlaghi

International Journal of Heat and Mass Transfer > 2015 > 83 > C > 69-74

In the current work, the effect of shear work due to the velocity slip on the non-equilibrium heat transfer in a pressure driven micro/nanochannel is evaluated under the constant wall heat flux boundary condition. As our simulation tool, the DSMC method is employed. Implementation of the wall heat flux in the DSMC method is performed using the “modified Iterative” technique. We investigate the effects...

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INFONA - science communication portal

Search results for: Ehsan Roohi

On the vortical characteristics and cold-to-hot transfer of rarefied gas flow in a lid driven isosceles orthogonal triangular cavity with isothermal walls

A generalized form of the Bernoulli Trial collision scheme in DSMC: Derivation and evaluation

On the consequences of successively repeated collisions in no-time-counter collision scheme in DSMC

Cavitation characteristics around a sphere: An LES investigation

Regulation of anti-Fourier heat transfer for non-equilibrium gas flows through micro/nanochannels

Evaluation of the SBT-TAS collision scheme on treating unsteady flows

DSMC investigation of rarefied gas flow through diverging micro- and nanochannels

Collision partner selection schemes in DSMC: From micro/nano flows to hypersonic flows

Nanofluid flow and heat transfer in a microchannel with longitudinal vortex generators: Two-phase numerical simulation

Heat transfer and entropy generation in a microchannel with longitudinal vortex generators using nanofluids

A novel algorithm for implementing a specified wall heat flux in DSMC: Application to micro/nano flows and hypersonic flows

Measuring the Carbon Footprint of Business Processes

Investigation of cavitation around 3D hemispherical head-form body and conical cavitators using different turbulence and cavitation models

Simulation of three-dimensional cavitation behind a disk using various turbulence and mass transfer models

DSMC simulation of hypersonic flows using an improved SBT-TAS technique

A new form of the second-order temperature jump boundary condition for the low-speed nanoscale and hypersonic rarefied gas flow simulations

Detailed investigation of flow and thermal field in micro/nano nozzles using Simplified Bernoulli Trial (SBT) collision scheme in DSMC

Low Mach number slip flow through diverging microchannel

Numerical investigation of thermoacoustic refrigerator at weak and large amplitudes considering cooling effect

Effects of shear work on non-equilibrium heat transfer characteristics of rarefied gas flows through micro/nanochannels

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