Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E15: Rarefied Flows |
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Chair: Prakash Vedula, University of Oklahoma Room: Georgia World Congress Center B302 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E15.00001: Investigation of Interaction of Rocket Plume with Dusty Lunar Surface Shubham Karpe, Abhimanyu Gavasane, Bhalchandra Puranik, Upendra Bhandarkar When a landing module approaches a lunar surface, the plume from its rocket exhaust interacts with dust particles on the lunar surface and entrains them. These dust particles are irregular in shape and size, and also abrasive. Dust impingement on the lunar module and its thermal optical surfaces leads to several serious problems. In the present work, a 2D axisymmetric Direct Simulation Monte Carlo (DSMC) code is developed for modeling the exhaust from the rocket nozzle. The DSMC code itself is a coupled code that models the interaction of gas molecules with entrained dust particles and vice versa. For better speed, a DSMC code with only gas expansion is simulated and its results are used to track the motion of dust particles. This step essentially decouples the effect of dust particles on the gas and speeds the simulation. The present work compares the coupled gas-dust DSMC code with the decoupled one with respect to computational time and accuracy of simulation results. The decoupled code is observed to run 10 times faster than the coupled code. Additionally, a 3D DSMC code is developed to incorporate multiple nozzles. The results of a double nozzle expansion using the 3D code and 2D axisymmetric code (that does not consider 3D effects, but is faster) will also be compared. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E15.00002: Numerical analysis of nonequilibrium gas flows induced by evaporation from two-dimensional nanoscale slit arrays Ikuya Kinefuchi, Zhengmao Lu, Hiroshi Matsumoto, Hiroki Imai, Takuma Hori, Yuta Yoshimoto, Shu Takagi, Evelyn N Wang Increasing power density of electronic devices necessitates advanced thermal management technology that can dissipate high heat flux of the order of >1 kW/cm2. One of the options is a nanoporous membrane-based evaporative cooling device, where a vapor flow induced by evaporation forms a highly nonequilibrium region near the membrane, so-called the Knudsen layer. In this work, we analyze the non-equilibrium flows of polyatomic gas molecules evaporating from two-dimensional nanoscale pore arrays using the direct simulation Monte Carlo (DSMC) method and clarify the effect of the pore size and pore spacing on the flow characteristics. In addition, we present a method to deal with the Knudsen layer with the low variance DSMC (LVDSMC) method, which can drastically reduce the statistical noise at low Mach number conditions compared with the conventional DSMC method. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E15.00003: An Advanced Kinetic Description for Shock Structure under Hypersonic Conditions Mohamed Mohsen Ahmed, James Chen The one-dimensional standing shock wave has been examined theoretically and experimentally for many years since it represents the simplest flow in which non-equilibrium effects can be observed. Naiver-Stokes simulations fail to predict accurate shock profiles as the Mach number increases. Direct Simulation Monte Carlo method is considered to be the most accurate numerical method for predicting the shock structure albeit the extensiveness of required computational resources. An alternative theoretical approach to the classical Boltzmann equation, known as Boltzmann-Curtiss equation for particles with translational and rotational degrees of freedom, is considered. The first order approximate solution to the Boltzmann-Curtiss equation yield a more general stress tensor that can account for thermal non-equilibrium. Numerical simulations of a standing shock wave of argon and nitrogen in a range of Mach numbers from 1.2 to 9, reveal that the proposed model lead to significant improvements in the density profile, normal stresses and shock thickness at non-equilibrium conditions over the solution of classical Navier-Stokes equations. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E15.00004: Solution of the Boltzmann Transport Equation via Numerical Tensor Methods Arnout Boelens, Daniele Venturi, Daniel Tartakovsky High-dimensional partial-differential equations (PDEs) arise in a number of fields of science and engineering, where they are used to describe the evolution of joint probability functions. Due to the curse of dimensionality these kind of equations are notoriously hard to solve. We develop a new parallel algorithm to solve high-dimensional PDEs and apply it to the Boltzmann Transport Equation (BTE). The algorithm uses an implicit time integration scheme and is based on canonical numerical tensor methods combined with alternating least squares. We demonstrate the accuracy and efficiency of the proposed new algorithm in computing the numerical solution to a linearized version of the Boltzmann Transport Equation in six variables plus time. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E15.00005: Non-Linear Thermal Effects in Unsteady Shear Flows of a Rarefied Gas Yaron Ben-Ami, Avshalom Manela We study the response of a rarefied gas in a slab to the time-harmonic motion of its boundaries in the tangential direction. In difference from previous investigations, we consider boundaries velocities (Uw) of non-small Mach numbers (Ma = Uw/Uth, where Uth marks the mean thermal speed), which deviate the system from its low-velocity isothermal condition. The problem is studied in the entire range of gas rarefaction rates, combining limit case analyses with direct simulation Monte Carlo computations. A non-linear solution is derived in the ballistic regime for arbitrary velocity amplitudes. At near-continuum conditions, a slip-flow time-periodic solution is obtained by expanding the flow variables in a Mach power series. The results indicate that, at all Knudsen numbers (Kn = λ/L, where λ and L mark the molecular mean free path and slab width, respectively), the thermodynamic fields and normal velocity component are characterized by double-frequency time dependence, in difference from the fundamental-frequency time dependence characterizing the tangential gas velocity. System nonlinearity also results in a normal force acting on the boundaries, overcoming the tangential force with increasing Ma. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E15.00006: Transition between evaporation and condensation caused by the reflection of sound at a vapor-liquid interface Takeru Yano We study the transition processes from evaporation to condensation and vice versa by solving the Boltzmann-Krook-Welander equation numerically. The steady evaporation state and condensation state have already been well-analyzed based on the kinetic theory of gases (see, for example, book by Sone, 2007). However, unsteady evaporation and condensation phenomena, especially transition between them, still include unresolved problems. In the present study, we address the transition processes caused by the reflection of sound at a vapor-liquid interface. As a result of careful numerical analysis, we find the wave reflection law which determines the velocity and pressure in the sound wave reflected at the interface. |
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