DSMC Analysis of Rarefied Gas Flow Over a Rectangular Cylinder at All Knudsen Numbers

2000 ◽  
Vol 122 (4) ◽  
pp. 720-729 ◽  
Author(s):  
Chin-Hsiang Cheng ◽  
Feng-Liang Liao
Keyword(s):  
Knudsen Number ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Flow Behavior ◽  
Cross Flow ◽  
Direct Simulation Monte Carlo ◽  
Molecular Flow ◽  
Transfer Coefficients ◽  
Numerical Predictions ◽  
Special Cases

The present study is concerned with the flow behavior of the rarefied gas over a rectangular square cylinder. Attention has been focused on the transition regime between the continuous flow (at low Knudsen number) and the molecular flow (at high Knudsen number). The direct simulation Monte Carlo method (DSMC) is employed for predicting the distributions of density, velocity, and temperature for the external cross-flow. Meanwhile the pressure, skin friction, and net heat transfer coefficients on the surfaces of the cylinder are also evaluated. The length (l) and width (h) of the cross-section of the cylinder are both fixed at 0.06 m. The Mach number (Ma) ranges from 0.85 to 8, and the Knudsen number (Kn) is in the range 0.01⩽Kn⩽1.0. Results for various parameter combinations are presented. For some special cases, the numerical predictions are compared with existing information, and close agreement has been found. [S0098-2202(00)01404-8]

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.

On the Rarefied Gas Flow in Pipes

2005 ◽  
Author(s):  
Vladan D. Djordjevic
Keyword(s):  
Knudsen Number ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Natural Extension ◽  
Slip Boundary Condition ◽  
Molecular Flow ◽  
Rarefied Gas Flow ◽  
Number Range ◽  
Average Value ◽  
Linearized Boltzmann Equation

Rarefied gas flow in a pipe is treated in the paper by modeling the slip boundary condition by means of a fractional derivative. At that the order of the derivative is conveniently chosen to be a function of the average value of the Knudsen number so that the entire Knudsen number range, from continuum flow to free molecular flow, is covered. Very good agreement with the solutions of linearized Boltzmann equation is achieved. The paper represents a natural extension of the work of the same author on the rarefied micro channel flow, published earlier.

Rarefied gas flow behavior in micro/nanochannels under specified wall heat flux

2015 ◽  
Vol 26 (08) ◽  
pp. 1550087 ◽  
Author(s):  
Mojtaba Balaj ◽  
Hassan Akhlaghi ◽  
Ehsan Roohi
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Flow Behavior ◽  
Direct Simulation Monte Carlo ◽  
Wall Heat Flux ◽  
Linear Distribution ◽  
Thermal Transpiration

In this paper, we investigate the effects of convective heat transfer on the argon gas flow through micro/nanochannels subject to uniform wall heat flux (UWH) boundary condition using the direct simulation Monte Carlo (DSMC) method. Both the hot wall (q wall > 0) and the cold wall (q wall < 0) cases are considered. We consider the effect of wall heat flux on the centerline pressure, velocity profile and mass flow rate through the channel in the slip regime. The effects of rarefaction, property variations and compressibility are considered. We show that UWH boundary condition leads to the thermal transpiration. Our investigations showed that this thermal transpiration enhances the heat transfer rate at the walls in the case of hot walls and decreases it where the walls are being cooled. We also show that the deviation of the centerline pressure distribution from the linear distribution depends on the direction of the wall heat flux.

Radiometric flow in periodically patterned channels: fluid physics and improved configurations

2018 ◽  
Vol 860 ◽  
pp. 544-576 ◽  
Author(s):  
Ali Lotfian ◽  
Ehsan Roohi
Keyword(s):  
Knudsen Number ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Thermal Characteristics ◽  
Direct Simulation Monte Carlo ◽  
Force Production ◽  
Bottom Wall ◽  
The Third ◽  
Triangular Fin ◽  
Second Category

With the aid of direct simulation Monte Carlo (DSMC), we conduct a detailed investigation pertaining to the fluid and thermal characteristics of rarefied gas flow with regard to various arrangements for radiometric pumps featuring vane and ratchet structures. For the same, we consider three categories of radiometric pumps consisting of channels with their bottom or top surfaces periodically patterned with different structures. The structures in the design of the first category are assumed to be on the bottom wall and consist of either a simple vane, a right-angled triangular fin or an isosceles triangular fin. The arrangements on the second category of radiometric pumps consist of an alternating diffuse–specular right-angled fin and an alternating diffuse–specular isosceles fin on the bottom wall. The third category contains either a channel with double isosceles triangular fins on its lowermost surface or a zigzag channel with double isosceles triangular fins on both walls. In the first and the third categories, the surfaces of the channel and its structures are considered as diffuse reflectors. The temperature is kept steady on the horizontal walls of the channel; thus, radiometric flow is created by subjecting the adjacent sides of the vane/ratchet to constant but unequal temperatures. On the other hand, for the second category, radiometric flow is introduced by specifying different top/bottom channel wall temperatures. The DSMC simulations are performed at a Knudsen number based on the vane/ratchet height of approximately one. The dominant mechanism in the radiometric force production is clarified for the examined configurations. Our results demonstrate that, at the investigated Knudsen number, the zigzag channel experiences maximum induced velocity with a parabolic velocity profile, whereas its net radiometric force vanishes. In the case of all other configurations, the flow pattern resembles a Couette flow in the open section of the channel situated above the vane/ratchet. To further enhance the simulations, the predictions of the finite volume discretization of the Boltzmann Bhatnagar–Gross–Krook (BGK)–Shakhov equation for the mass flux dependence on temperature difference and Knudsen number are also reported for typical test cases.

Study of Gas Flow in Micronozzles Using an Unstructured DSMC Method

2009 ◽  
Author(s):  
Ehsan Roohi ◽  
Masoud Darbandi ◽  
Vahid Mirjalili
Keyword(s):  
Boundary Layer ◽  
Knudsen Number ◽  
Gas Flow ◽  
Subsonic Flow ◽  
Flow Behavior ◽  
Boundary Layer Separation ◽  
Back Pressure ◽  
Viscous Force ◽  
Dsmc Method ◽  
Wide Range

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 in the divergent section of nozzles as soon as the Knudsen number increases above a moderate magnitude. In order to accurately simulate subsonic flow at the nozzle outlet, it is necessary to add a buffer zone to the end of nozzle. If we apply the back pressure at the outlet, boundary layer separation is observed and a region of backward flow appears inside the boundary layer while the core region of inviscid flow experiences multiple shock-expansion waves. We also show that the wall boundary layer prevents forming shocks in the divergent part. Alternatively, Mach cores appear at the nozzle center followed by bow shocks and an expansion region.

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.

Simulation of a Rectangular Cylinder in Cross Flow in a Microchannel Using Information Preservation (IP) Method

2007 ◽  
Author(s):  
U. Kursun ◽  
J. S. Kapat
Keyword(s):  
Gas Flow ◽  
Cross Flow ◽  
Direct Simulation Monte Carlo ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Information Preservation ◽  
Rectangular Cylinder ◽  
Characteristic Theory ◽  
Simulation Monte Carlo ◽  
Pressure Boundary Conditions

A numerical simulation is performed to study the characteristics of the gas flow over a constant temperature rectangular cylinder in a cross flow in a micro channel. The non-isothermal Information Preservation (IP) method is employed to eliminate the statistical scatter of Direct Simulation Monte Carlo (DSMC) at low Reynolds numbers. Pressure boundary conditions based on the characteristic theory are implemented in the algorithm. The simulation results are compared with the references available in the literature. This study will form a base for our future particle-atomistic hybrid computations.

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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