Investigation of rarefied flow over backward-facing step in different rarefaction regimes using direct simulation Monte Carlo

2021 ◽  
pp. 1-28
Author(s):  
D. Nabapure ◽  
A. Singh ◽  
R.C.M. Kalluri
Keyword(s):  
Monte Carlo ◽  
Knudsen Number ◽  
Pressure Coefficient ◽  
Direct Simulation Monte Carlo ◽  
Flow Regimes ◽  
Direct Simulation ◽  
Backward Facing Step ◽  
Rarefied Flow ◽  
Simulation Monte Carlo ◽  
Velocity Pressure

Abstract Hypersonic aerothermodynamics for a re-entry vehicle approaching the earth’s atmosphere is critical in the exploration of space. These vehicles often encounter various flow regimes due to the density variations and have surface abnormalities. The backward-facing step (BFS) is one such simplified configuration for modeling anomalies around such space vehicles. The present work examines rarefied hypersonic flow over a BFS using the direct simulation Monte Carlo (DSMC) method. The purpose of this research is focused on exploring the various loads encountered by a re-entry vehicle passing through different altitudes covering different rarefaction regimes. The fluid considered was non-reacting air, with the free-stream Mach number as 25, and the Knudsen number considered ranged from 0.05-21.10. The influence of the Knudsen number on flow characteristics has been elucidated graphically in various streamwise directions. The normalised flow properties such as velocity, pressure, temperature and density showed an increasing trend with the Knudsen number due to compressibility and viscous heating effects. In all flow regimes, there was an appearance of flow recirculation. With rarefaction, the recirculation lengths decreased, whereas the boundary layer thickness showed an increase. The aerodynamic surface properties such as pressure coefficient, skin friction, and heat transfer coefficient, by and large, showed an increase with the Knudsen number. When the chemical reactions were accounted for and compared against the non-reacting flows, the velocity, pressure, and density field showed no marked variation; however, considerable variations were observed in the temperature field. Furthermore, the present study also depicts the compressibility factor contour, showing the flow regions that diverge from the ideal gas behaviour.

Modelling of chemical reactions in hypersonic rarefied flow with the direct simulation Monte Carlo method

1996 ◽  
Vol 312 ◽  
pp. 149-172 ◽  
Author(s):  
Michael A. Gallis ◽  
John K. Harvey
Keyword(s):  
Monte Carlo ◽  
Chemical Reactions ◽  
Energy Exchange ◽  
Chemical Reactivity ◽  
Direct Simulation Monte Carlo ◽  
Direct Simulation ◽  
Rarefied Flow ◽  
Rarefied Flows ◽  
Exchange Processes ◽  
Simulation Monte Carlo

In this paper the phenomenon of chemical reactivity in hypersonic rarefied flows is examined. A new model is developed to describe the reactions and post-collision energy exchange processes that take place under conditions of molecular non-equilibrium. The new scheme, which is applied within the framework of the direct simulation Monte Carlo (DSMC) method, draws its inspiration from the principles of maximum entropy which were developed by Levine & Bernstein. Sample hypersonic flow fields, typical of spacecraft re-entry conditions in which reactions play an important role, are presented and compared with results from experiments and other DSMC calculations. The latter use traditional methods for the modelling of chemical reactions and energy exchange. The differences are discussed and evaluated.

Scale Effects on Rarefied Supersonic Flows in Nanochannels

2008 ◽  
Author(s):  
Nikolaos A. Gatsonis ◽  
Wael G. Al Kouz ◽  
Ryan E. Chamberlin
Keyword(s):  
Monte Carlo ◽  
Supersonic Flow ◽  
Knudsen Number ◽  
Scale Effects ◽  
Three Dimensional ◽  
Direct Simulation Monte Carlo ◽  
Supersonic Flows ◽  
Direct Simulation ◽  
Aspect Ratios ◽  
Simulation Monte Carlo

The supersonic flow of nitrogen into a nanochannel is investigated using a three dimensional unstructured Direct Simulation Monte Carlo (U3DSMC) method. The U3DSMC code is validated by comparisons with previous 2D DSMC simulations of flows in micron-scale channels. Rectangular nanochannels with heights between 100 nm to 1000 nm, and aspect ratios L/H of 1, 10, 100 are used in the U3DSMC investigation. The Mach 5.9 freestream has a pressure of 0. 1atm and Knudsen numbers of 0.481, 0.962 and 4.81. The nanochannel walls are assumed to be diffusively reflecting at the freestream temperature. The simulations show the development of a disturbance region upstream from the inlet that depends on the Knudsen number. For the L/H = 10 and L/H = 100 nanochannels considered the velocity decreases from its freestream value velocity decreases from its freestream value and becomes subsonic inside the nanochannel. The temperature shows an enhancement region near the inlet while the density shows an enhancement region inside the nanochannel.

Development of Object-Oriented Direct Simulation Monte Carlo Code for Modeling of Rarefied Flow around Geometries of Arbitrary Shapes

2011 ◽  
Vol 110-116 ◽  
pp. 2491-2496
Author(s):  
Sourabh Jain ◽  
Prabhu Ramachandran
Keyword(s):  
Monte Carlo ◽  
Heat Conduction Problem ◽  
Direct Simulation Monte Carlo ◽  
Object Oriented ◽  
Navier Stokes ◽  
Monte Carlo Code ◽  
Direct Simulation ◽  
Rarefied Flow ◽  
Simulation Monte Carlo ◽  
Arbitrary Shapes

Rarefied flows cannot be accurately simulated using Navier-Stokes (N-S) equations. The Direct Simulation Monte-Carlo (DSMC) technique is a particle based method for accurate simulation of flows under such conditions. A DSMC code is developed using an object-oriented (OO) approach which can simulate flows around arbitrary shapes. Hence, the flux from such boundaries can be correctly predicted. The object-oriented approach enables for easy modification of the code. For example, it is easy to use different collision models to implement different relaxation algorithm. The code is validated for the one-dimensional Fourier heat conduction problem. Results for the development of a shock due to supersonic flow over a 15 degree wedge are also presented. Inclined boundary of the wedge is correctly captured as the particles interact with the the exact shape of the boundary. Shock angle is found more than expected due to rarefaction effects.

Direct-Simulation Monte Carlo Investigation of a Berea Porous Structure

SPE Journal ◽  
2016 ◽  
Vol 21 (03) ◽  
pp. 0938-0946 ◽  
Author(s):  
Chariton Christou ◽  
S. Kokou Dadzie
Keyword(s):  
Monte Carlo ◽  
Velocity Profile ◽  
Porous Structure ◽  
Pore Diameter ◽  
Slip Flow ◽  
Direct Simulation Monte Carlo ◽  
Flow Regimes ◽  
Porous Structures ◽  
Direct Simulation ◽  
Simulation Monte Carlo

Summary Shale-gas and tight gas reservoirs consist of porous structures with pore diameter in the range of 1 to 200 nm. At these scales, the pore diameter becomes comparable to the gas mean free path. Flows in these structures fail often in the transition and slip flow regimes. Standard continuum fluid methods such as the Navier-Stokes-Fourier (NSF) set of equations fail to describe flows of these regimes. We present a direct-simulation monte carlo (DSMC) study of a 3D porous structure in an unlimited parallel simulation. The 3D geometry was obtained with microcomputed-tomography (micro-CT). The gas considered is CH4 (100%), and the gas intermolecular-collision model for the simulation is the variable hard sphere (VHS). Simulations were carried out for three different Knudsen (Kn) numbers within the transition and slip flow regimes. The results demonstrate some of the significant differences that appear in gas-flow properties depending on the Kn number and the flow regime. In addition, the velocity profile appears to depend on the Kn number. At the inlet of the porous structures, more-uniform velocity profile occurs for the three Kn numbers. At the outlet, the velocity profile varies depending on the Kn number. For Kn ≈ 0.037, a parabolic shape is observed for the velocity profile, whereas a more-uniform shape is observed for Kn ≈ 3.7.

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