Parallel DSMC Simulation of a Single Under-Expanded Free Orifice Jet From Transition to Near-Continuum Regime

2005 ◽  
Vol 127 (6) ◽  
pp. 1161-1170 ◽  
Author(s):  
J.-S. Wu ◽  
S.-Y. Chou ◽  
U.-M. Lee ◽  
Y.-L. Shao ◽  
Y.-Y. Lian
Keyword(s):  
Flow Structure ◽  
Three Dimensional ◽  
Direct Simulation Monte Carlo ◽  
Mean Free Path ◽  
Mach Disk ◽  
Orifice Diameter ◽  
Axial Distance ◽  
Free Jet ◽  
Barrel Shock ◽  
Dynamic Domain Decomposition

This paper describes the numerical analysis of the flow structure of a single underexpanded argon free jet issuing into a lower-pressure or vacuum environment using the parallel three-dimensional direct simulation Monte Carlo (DSMC) method employing dynamic domain decomposition. Unstructured and tetrahedral solution-based refined mesh depending on the local mean free path is used to improve the resolution of solution. Simulated Knudsen numbers of the stagnation conditions based on orifice diameter, Reynolds numbers based on the conditions at the orifice exit, and stagnation-to-background pressure ratios are in the range of 0.0005–0.1, 7–1472, and 5-∞, respectively, where “∞” represents vacuum condition in the background environment. Results show that centerline density decays in a rate proportional to the inverse of the square of the axial distance (z−2) from the orifice for all ranges of flow in the current study. The more rarefied the background condition is, the longer the z−2-regime is. In addition, a distinct flow structure, including barrel shock, Mach disk and jet boundary, is clearly identified as the Knudsen number reaches as low as 0.001. Predicted location and size of Mach disk in the near-continuum limit (Kn=0.001,0.0005) are found to be in reasonable agreement with experimental results in the continuum regime.

scholarly journals The Correctness of the Simplified Bernoulli Trial (SBT) Collision Scheme of Calculations of Two-Dimensional Flows

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 127
Author(s):  
Kiril Shterev
Keyword(s):  
Gas Flow ◽  
Three Dimensional ◽  
Direct Simulation Monte Carlo ◽  
Mean Free Path ◽  
Cumulative Distribution ◽  
Test Case ◽  
Two Dimensional ◽  
Bernoulli Trial ◽  
The Mean ◽  
Two Dimensional Flows

Micro-electromechanical systems (MEMS) have developed rapidly in recent years in various technical fields that have increased their interest in the Direct Simulation Monte Carlo (DSMC) method. In this paper, we present a simple representation of the DSMC collision scheme and investigate the correctness of the Simplified Bernoulli Trial (SBT) collision scheme for the calculation of two-dimensional flows. The first part of the collision scheme, which determines collision pairs, is presented following the derivation of the expression for the mean free path and using the cumulative distribution function. Approaches and conclusions based on one-dimensional flows are not always directly applicable to two- and three-dimensional flows. We investigated SBT correctness by using the two-dimensional pressure-driven gas flow of monoatomic gas as a test case. We studied the influence of shuffling of the list of particles per cell (PPC) before the collision scheme’s execution, as well as the minimal and maximal number of PPC, on the correctness of the solution. The investigation showed that shuffling and the number of PPC played an important role in the correctness of SBT. Our recommendations are straightforwardly applicable to three-dimensional flows. Finally, we considered the mixing of two gases and compared the results available in the literature.

scholarly journals Flow structure and cooling behavior of air impingement on a target plate

2013 ◽  
Vol 3 (3) ◽  
Author(s):  
Adnan Abdul Rasool ◽  
Faik Hamad
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Pressure Coefficient ◽  
Orifice Diameter ◽  
Complex Nature ◽  
Axial Distance ◽  
Nonlinear Behaviour ◽  
Target Plate ◽  
Pressure Coefficients ◽  
Large Orifice

AbstractAn experimental data of flow field, pressure coefficient and heat transfer of a jet impinging normally on a flat target plate are presented. The measurements of temperatures and static pressures were carried out for flow from three orifices of 5, 10 and 20 mm diameter for orifice-to-target plate distances of 5, 10, 25, 50, 70, 100 and 120 mm from the orifice exit. The axial development of flow structure of the jet from the orifice was investigated by measuring the radial jet velocity distributions at the same axial distances used to measure heat transfer and static pressure. The results show that pressure coefficients distributions on the target plate are similar to the velocity distributions in the impinging jet which indicates the strong relationship between the two parameters. The pressure coefficients from large orifice diameter are higher than the values from the small orifice diameter for same orifice-to-target plate distance. The results also show a nonlinear increase of heat transfer rate with orifice size and the ratio of axial distance to orifice diameter (X/d). The nonlinear behaviour may be attributed to the complex nature of flow structure at the stagnation region. The high velocity gradients at the stagnation zone leads to higher turbulence and comparatively higher values of heat transfer rates for large orifice diameter.

Numerical Study of the Mean and Filtered Characteristics of Turbulent Jets Impinging on Convex and Flat Surfaces Using LES

2012 ◽  
Author(s):  
Adra Benhacine ◽  
Zoubir Nemouchi ◽  
Lyes Khezzar ◽  
Nabil Kharoua
Keyword(s):  
Convex Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Scale Model ◽  
Wall Jet ◽  
Potential Core ◽  
Flat Surfaces ◽  
Free Jet ◽  
Eddy Simulation

A numerical study of a turbulent plane jet impinging on a convex surface and on a flat surface is presented, using the large eddy simulation approach and the Smagorinski-Lilly sub-grid-scale model. The effects of the wall curvature on the unsteady filtered, and the steady mean, parameters characterizing the dynamics of the wall jet are addressed in particular. In the free jet upstream of the impingement region, significant and fairly ordered velocity fluctuations, that are not turbulent in nature, are observed inside the potential core. Kelvin-Helmholtz instabilities in the shear layer between the jet and the surrounding air are detected in the form of wavy sheets of vorticity. Rolled up vortices are detached from these sheets in a more or less periodic manner, evolving into distorted three dimensional structures. Along the wall jet the Coanda effect causes a marked suction along the convex surface compared with the flat one. As a result, relatively important tangential velocities and a stretching of sporadic streamwise vortices are observed, leading to friction coefficient values on the curved wall higher than those on the flat wall.

The inlet flow structure of a conceptual open-nose supersonic drone

2021 ◽  
pp. 095441002098304
Author(s):  
Eiman B Saheby ◽  
Xing Shen ◽  
Anthony P Hays ◽  
Zhang Jun
Keyword(s):  
Flow Structure ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Computational Fluid Dynamic Simulation ◽  
Navier Stokes ◽  
Ansys Fluent ◽  
Navier Stokes Equations ◽  
Aerodynamic Efficiency ◽  
Performance Effects

This study describes the aerodynamic efficiency of a forebody–inlet configuration and computational investigation of a drone system, capable of sustainable supersonic cruising at Mach 1.60. Because the whole drone configuration is formed around the induction system and the design is highly interrelated to the flow structure of forebody and inlet efficiency, analysis of this section and understanding its flow pattern is necessary before any progress in design phases. The compression surface is designed analytically using oblique shock patterns, which results in a low drag forebody. To study the concept, two inlet–forebody geometries are considered for Computational Fluid Dynamic simulation using ANSYS Fluent code. The supersonic and subsonic performance, effects of angle of attack, sideslip, and duct geometries on the propulsive efficiency of the concept are studied by solving the three-dimensional Navier–Stokes equations in structured cell domains. Comparing the results with the available data from other sources indicates that the aerodynamic efficiency of the concept is acceptable at supersonic and transonic regimes.

Thermal Design of Highly-Efficient Thermoelectric Materials With Atomic-Scale Three-Dimensional Phononic Crystals

2007 ◽  
Author(s):  
Jean-Numa Gillet ◽  
Yann Chalopin ◽  
Sebastian Volz
Keyword(s):  
Thermal Conductivity ◽  
Bulk Material ◽  
Phononic Crystal ◽  
Three Dimensional ◽  
Mean Free Path ◽  
Dispersion Curves ◽  
Phononic Crystals ◽  
Thermal Design ◽  
Atomic Scale ◽  
Thermal Insulating

Owing to their thermal insulating properties, superlattices have been extensively studied. A breakthrough in the performance of thermoelectric devices was achieved by using superlattice materials. The problem of those nanostructured materials is that they mainly affect heat transfer in only one direction. In this paper, the concept of canceling heat conduction in the three spatial directions by using atomic-scale three-dimensional (3D) phononic crystals is explored. A period of our atomic-scale 3D phononic crystal is made up of a large number of diamond-like cells of silicon atoms, which form a square supercell. At the center of each supercell, we substitute a smaller number of Si diamond-like cells by other diamond-like cells, which are composed of germanium atoms. This elementary heterostructure is periodically repeated to form a Si/Ge 3D nanostructure. To obtain different atomic configurations of the phononic crystal, the number of Ge diamond-like cells at the center of each supercell can be varied by substitution of Si diamond-like cells. The dispersion curves of those atomic configurations can be computed by lattice dynamics. With a general equation, the thermal conductivity of our atomic-scale 3D phononic crystal can be derived from the dispersion curves. The thermal conductivity can be reduced by at least one order of magnitude in an atomic-scale 3D phononic crystal compared to a bulk material. This reduction is due to the decrease of the phonon group velocities without taking into account that of the phonon average mean free path.

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