scholarly journals DSMC Simulation of Rarefied Gas Flow over a Backward- Facing Step: Effect of Expansion ratio

2019 ◽  
Author(s):  
Deepak Nabapure ◽  
Pratijay Guha ◽  
K Ram Chandra Murthy
Keyword(s):  
Flow Field ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Expansion Ratio ◽  
Backward Facing Step ◽  
Rarefied Flow ◽  
Step Effect ◽  
Dsmc Simulation ◽  
Limiting Case

Numerical simulations have been performed to study the effect of expansion ratio on the hypersonic rarefied flow past a backward-facing step. The Direct Simulation Monte Carlo (DSMC) method is used for the present study. An opensource solver named dsmcFoam has been used for this purpose. The solver has been validated with well-established results from the literature and good agreement is found among them. Simulations have been carried out for expansion ratios (ER) of 2,4,6,8,10 in the transition regime. The different flow field properties such as velocity, pressure and temperature have been studied. The profiles have found to be influenced by the compressibility and rarefaction effects. Limiting case of ER=8 and above has no influence on the flow field properties.

DSMC Simulation of Rarefied Gas Flow Over a Wall Mounted Cube

2019 ◽  
Author(s):  
Deepak Nabapure ◽  
Ram Chandra Murthy
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Flow Behavior ◽  
Direct Simulation Monte Carlo ◽  
Temperature Fields ◽  
Gas Flows ◽  
Rarefied Gas Flows ◽  
Dsmc Simulation ◽  
Recirculation Length ◽  
Velocity Pressure

Abstract The present study investigates the flow behavior of the rarefied gas over a wall-mounted cube. The problem is studied for different cube heights (h) of 9mm and 18mm in the slip and transition regimes. The Direct Simulation Monte Carlo (DSMC) method is employed to evaluate the properties such as velocity, pressure and temperature fields. The Reynolds number (Re) ranges from 403 to 807, and the Knudsen number (Kn) is in the range from 0.05 to 0.103. A typical shock wave is formed in front of the cube. The recirculation length of the vortices normalized with respect to the respective cube heights for Kn = 0.05 and Kn = 0.103 are about 1.11 and 1.95 respectively. Similarly, the center of the vortices is located at about 3.33 and 6.11 times the respective cube heights upstream, for Kn = 0.05 and Kn = 0.103. The local temperature and pressure variations observed upstream of the cube are two orders higher in magnitude and are primarily attributed to strong compressibility effects. The present study paves the way for benchmarking, and forms a basis for understanding the rarefied gas flows over complex geometries.

scholarly journals DSMC Simulation of Rarefied Gas Flow in a Single-sided and Double-sided Lid-Driven Cavity

2019 ◽  
Author(s):  
Jayesh Sanwal ◽  
Deepak Nabapure ◽  
Sreeram Rajesh ◽  
K Ram Chandra Murthy
Keyword(s):  
Melt Spinning ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Industrial Applications ◽  
Dsmc Method ◽  
Driven Cavity ◽  
Flow Features ◽  
Dsmc Simulation ◽  
Vortex Patterns

The present study is to investigate the behavior of a monoatomic gas enclosed in a cavity with both the top and bottom walls imparting motion to the fluid. The problem is studied for single and double-sided lid-driven flow for various wall velocities as well as parallel and anti-parallel wall motions. These types of flow have many industrial applications such as drying and melt spinning. In contrast to the single-sided flows the vortex patterns obtained in the double-sided flows are different and hence it merits a thorough examination, which is studied in this paper using the Direct Simulation Monte Carlo (DSMC) method. The DSMC method proposed by G.A. Bird is based on the kinetic theory in which the molecular motion is modeled stochastically. The computational model has been implemented in OpenFOAM software using the solver named dsmcFoam. Various flow features have been examined such as eddies and vortices.

scholarly journals Investigation of Subsonic and Hypersonic Rarefied Gas Flow Over a Backward Facing Step

2019 ◽  
Author(s):  
Deepak Nabapure ◽  
Jayesh Sanwal ◽  
Sreeram Rajesh ◽  
K Ram Chandra Murthy
Keyword(s):  
Mach Number ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Flow Characteristics ◽  
Direct Simulation Monte Carlo ◽  
Primary Objective ◽  
Gas Flows ◽  
Backward Facing Step ◽  
Rarefied Gas Flows ◽  
Velocity Pressure

In the present study the Direct Simulation Monte Carlo (DSMC) method, which is one of most the widely used numerical methods to study the rarefied gas flows, is applied to investigate the flow characteristics of a hypersonic and subsonic flow over a backward-facing step. The work is driven by the interest in exploring the effects of the Mach number on the flow behaviour. The primary objective of this paper is to study the variation of velocity, pressure, and temperature with Mach number. The numerical tool is validated with well-established results from the literature and a good agreement is found among them. The flow is analyzed and some comments on the characteristics of the flow are also added.

scholarly journals DSMC investigation of rarefied gas flow through diverging micro/Nanochannels

2018 ◽  
Author(s):  
Amin Ebrahimi
Keyword(s):  
Flow Field ◽  
Cross Sections ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Pressure Ratio ◽  
Direct Simulation Monte Carlo ◽  
Divergent Channel ◽  
Uniform Cross Section ◽  
Flow Through ◽  
Simulation Parameters

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 ≤ 12.7). The primary flow field properties, including pressure, velocity, and temperature, are presented for divergent micro- and nanochannels and are compared with those of a micro- and nanochannel with a uniform cross section. The variations of the flow field properties in divergent micro- and nanochannels which are influenced by the area change, the channel pressure ratio, and the rarefication are discussed. The results show no flow separation in divergent micro- and nanochannels for all the range of simulation parameters studied in the present work. It has been found that a divergent channel can carry higher amounts of mass in comparison with an equivalent straight channel geometry. A correlation between the mass flow rate through micro- and nanochannels, the divergence angle, the pressure ratio, and the Knudsen number has been suggested. The present numerical findings prove the occurrence of Knudsen minimum phenomenon in micro- and nanochannels with non-uniform cross sections.

Analysis of gas flow over a cylinder at all Knudsen numbers based on non-newtonian constitutive models

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040076
Author(s):  
Zhen-Yu Yuan ◽  
Zhong-Zheng Jiang ◽  
Wen-Wen Zhao ◽  
Wei-Fang Chen
Keyword(s):  
Constitutive Model ◽  
Gas Flow ◽  
Constitutive Relations ◽  
Constitutive Models ◽  
Direct Simulation Monte Carlo ◽  
Navier Stokes ◽  
Dsmc Simulation ◽  
Nonequilibrium Flows ◽  
Simulation Results ◽  
Better Than

This paper is focused on the gas properties over a cylinder from continuum to rarefied regimes based on the non-Newtonian constitutive model. This new constitutive model is first derived from Eu’s nonequilibrium ensemble method, which is intended for accurate description of nonequilibrium flows. Some assumptions and simplifications are made during the establishing progress of the new constitutive model by both Eu and Myong. To verify its accuracy, temperature contours and skin frictions around the cylinder are simulated by this new model. The inflow Mach number is equal to 10 and the Knudsen number ranges from 0.002 to 0.05. All simulation results are compared with Navier–Stokes (NS) and the direct simulation Monte Carlo (DSMC) methods in detail. The comparisons of friction around the surface show that the non-Newtonian constitutive models are better than the linear constitutive relations of NS equations for the prediction of nonequilibrium flow and much more close to DSMC simulation results.

A hybrid Navier-Stokes/DSMC simulation for rarefied gas flow for the deposition of nano layers for OLEDs

2015 ◽  
Author(s):  
K. Farber ◽  
P. Farber ◽  
J. Gräbel ◽  
S. Krick ◽  
J. Reitz ◽  
...  
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Navier Stokes ◽  
Rarefied Gas Flow ◽  
Dsmc Simulation

A Hybrid Fokker-Planck-DSMC Solution Algorithm for the Whole Range of Knudsen Numbers

2013 ◽  
Author(s):  
M. Hossein Gorji ◽  
Stephan Küchlin ◽  
Patrick Jenny
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Time Integration ◽  
Computational Cost ◽  
Direct Simulation Monte Carlo ◽  
Large Cell ◽  
Solution Algorithm ◽  
Rarefied Gas Flows ◽  
Knudsen Numbers ◽  
Fokker Planck

In this work, we present a hybrid algorithm based on the Fokker-Planck (FP) kinetic model and direct simulation Monte Carlo (DSMC) for studies of rarefied gas flows. A particle based FP solution algorithm for rarefied gas flow simulations has recently been devised by the authors. The motivation behind the FP approximation is purely computational, i.e. due to the fact that the resulting random processes are continuous in time the computational cost of the corresponding time integration becomes independent of the Knudsen number. However, the method faces limitations for flows with very high Knudsen numbers (larger than approximately 5). In the method presented here, the FP approach is coupled with DSMC in order to gain from the efficiency of the FP model and from the accuracy of DSMC at small and large cell based Knudsen numbers, respectively.

DSMC Simulations of Squeeze Film Under a Harmonically Oscillating Micro RF Switch With Large Tip Displacements

2012 ◽  
Author(s):  
Nadim A. Diab ◽  
Issam A. Lakkis
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Numerical Technique ◽  
Direct Simulation Monte Carlo ◽  
Squeeze Film ◽  
Rf Switch ◽  
Fluid Forces ◽  
Field Velocity ◽  
Micro Cantilever ◽  
Beam Reflection

The two-dimensional unsteady behavior of a rarefied gas film under an oscillating micro-cantilever RF switch is presented. The microbeam, undergoing a parabolic deflection profile, is allowed to oscillate harmonically between its equilibrium position and the fixed substrate underneath for large beam-tip displacements. The gas film dynamics in terms of the flow field velocity and fluid forces exerted on the oscillating microbeam are discussed. The numerical technique used to model the rarefied gas flow is the Direct Simulation Monte Carlo (DSMC) method where the Knudsen (Kn) number is greater than 0.01 (ie. non-continuum regime). Unlike previous work in literature, the beam undergoes large deflections, which requires implementation, in DSMC, of a more realistic molecule-beam reflection behavior based on the instantaneous beam’s position and velocity. The effects of inertia, both local acceleration (St) and convection term (Re), and compressibility (Ma) on the gas film dynamics are examined over ranges of oscillating frequencies, velocity amplitudes, and microbeam’s lengths.

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