Jacques C. Richard

Performance Analysis, Modeling and Prediction of a Parallel Multiblock Lattice Boltzmann Application Using Prophesy System

The Lattice Boltzmann method is widely used in simulating fluid flows. In this paper, we present the performance analysis, modeling and prediction of a parallel multiblock Lattice Boltzmann application on up to 512 processors on three SMP clusters: two IBM SP systems at San Diego Supercomputing Center (DataStar - p655 and p690) and one IBM SP system at the DOE National Energy Research Scientific Computing Center (Seaborg) using the Prophesy system. By characterizing the performance of the Lattice Boltzmann application as the problem size and the number of processors increase, we can identify and eliminate performance bottlenecks, and predict the application performance. The experimental results indicate that the application with large problem sizes scales well across these three clusters, and performance models using the coupling method are accurate with less than 4.8% average relative prediction error

Microseism and infrasound generation by cyclones

A two-dimensional cylindrical shear-flow wave theory for the generation of microseisms and infrasound by hurricanes and cyclones is developed as a linearized theory paralleling the seminal work by Longuet-Higgins which was limited to one-dimensional plane waves. Both theories are based on Bernoullis principle. A little appreciated consequence of the Bernoulli principle is that surface gravity waves induce a time dependent pressure on the sea floor through a vertical column of water. A significant difference exists between microseisms detected at the bottom of each column and seismic signals radiated into the crust through coherence over a region of the sea floor. The dominant measured frequency of radiated microseisms is matched by this new theory for seismic data gathered at the Fordham Seismic Station both for a hurricane and a mid-latitude cyclone in 1998. Implications for Bernoullis principle and this cylindrical stress flow theory on observations in the literature are also discussed.

Use of drag probe in supersonic flow

We focuse on demonstrating that the relation between a subsonic and a supersonic velocity head are the same for each drag probe. The supersonic flow impinging on the drag probe is assumed to be unidirectional

ASSESSMENT OF MAGNETOHYDRODYNAMIC LATTICE BOLTZMANN SCHEMES IN TURBULENCE AND RECTANGULAR JETS

Two lattice Boltzmann method (LBM) formulations are possible to account for the effect of the magnetic field on the velocity field in magnetohydrodynamic (MHD) flows. In the body-force formulation (BFF), the magnetic field effects manifest as an external acceleration. In the extended equilibrium formulation (EEF), the effect appears through a modified equilibrium distribution function. Further, for the velocity field itself, the available choices are the single-relaxation time (SRT) and multi-relaxation time (MRT) models. Thus, for MHD-LBM, there are four possible permutations: SRT-BFF, SRT-EEF, MRT-BFF and MRT-EEF. Numerical implementation of the first three have already been presented in the literature. In this work, we, (i) develop the numerical implementation of MRT-EEF and (ii) perform an assessment of the four possible approaches. Our results indicate that the MRT-EEF is the most robust and accurate of the MHD-LBM computational schemes examined.

Unsteady Quasi-One-Dimensional Nonlinear Dynamic Model of Supersonic Through-Flow Fan Surge

This paper presents the results of a computational fluid dynamic model of a supersonic through-flow fan (STF) in supersonic surge. The phenomenon of surge is well known for subsonic turbomachinery. However, for supersonic turbomachinery like the STF, a special type of supersonic surge occurs in which a shock oscillates through the fan, alternating locations between upstream and downstream of the fan. It is also possible for a shock to remain in a fan stage. This analysis focuses on the development of supersonic surge resulting from overpressuring the fan. A model of the STF was constructed around its steady-state experimental performance map using an existing unsteady, quasi-one-dimensional, inviscid, compressible flow code. An exit boundary condition was specified for the overpressuring that forces the shock to move upstream and interfere with normal fan operation. The effects of that interference, including a shock oscillating across the fan, are discussed.

Analysis of Laser‐Generated Impulse In An Airbreathing Pulsed Detonation Engine: Part 1

An investigation is performed on an airbreathing laser propulsion (LP) system designed to propel a 1.4 m diameter, 120‐kg (dry mass) vehicle called the Lightcraft Technology Demonstrator (LTD) into low Earth orbit, along with its opto‐electronics payload. The LTD concept led directly to the model ♯200 lightcraft — recently demonstrated in laboratory and flight experiments at White Sands Missile Range, NM at the High Energy Laser Systems Test Facility (HELSTF), using the 10‐kW PLVTS CO2 laser. The pulsed detonation wave engine (PDE) employs repetitively ignited, laser‐supported detonation (LSD) waves to develop thrust by expanding high pressure blast waves over an annular, interior shroud surface. Numerical simulation of thruster impulse is accomplished with a 1‐D cylindrical model of blast waves propagating radially outward from a laser‐generated ‘line‐source’ of high temperature, high pressure air. External airflow over the LTD structure is also analyzed to predict basic engine/vehicle drag characteristi...

Magnetohydrodynamic Turbulence Decay Under the Influence of Uniform or Random Magnetic Fields

We perform direct numerical simulations of decaying magnetohydrodynamic turbulence subject to initially uniform or random magnetic fields. We investigate the following features: (i) kinetic―magnetic energy exchange and velocity field anisotropy, (ii) action of Lorentz force, (iii) enstrophy and helicity behavior, and (iv) internal structure of the small scales. While tendency toward kinetic―magnetic energy equi-partition is observed in both uniform and random magnetic field simulations, the manner of approach to that state is very different in the two cases. Overall, the role of the Lorentz force is merely to bring about the equi-partition. No significant variance anisotropy of velocity fluctuations is observed in any of the simulations. The mechanism of enstrophy generation changes with the strength of the magnetic field, and helicity shows no significant growth in any of the cases. The small-scale structure (orientation between vorticity and strain-rate eigenvectors) does not appear to be influenced by the magnetic field.

Characterization of Flow-Magnetic Field Interactions in Magneto-Hydrodynamic Turbulence

We examine the complex nonlinear flow-magnetic field dynamics in magneto-hydrodynamic (MHD) turbulence. Using direct numerical simulations (DNS), we investigate the dynamical interactions subject to the influence of a uniform applied background magnetic field. The initial magnetic and kinetic Reynolds numbers (based on Taylor microscale) are 45 and there are no initial magnetic field fluctuations. The sum total of turbulent magnetic and kinetic energies decays monotonically. With time, the turbulent magnetic fluctuations grow by extracting energy from velocity fluctuations. Expectedly, the distribution of energy between kinetic and magnetic fluctuations exhibits large periodic oscillations from the equipartition state due to Alfven waves. We perform a detailed analysis of the flow-magnetic field coupling and posit a simple model for the energy interchange. Such dynamical analysis can provide the insight required for turbulence control and closure modeling strategies.

Lattice-Boltzmann Models of Xe + Flow Through Ion Thruster Optics

The lattice-Boltzmann method (LBM) is applied to modeling the flow in electric propulsion (EP) systems such as ion thrusters. Specifically investigated are issues that affect thruster operation like the back-flow of ions that can erode the optics and reduce engine life. Historically, the transport of mass, momentum, energy, subatomic particles, etc. and the complex multi-scale physics involved, have been modeled using Direct Simulation Monte Carlo (DSMC). While DSMC has achieved great success in EP models, its connection to Boltzmann’s equation for the molecular velocity distribution function and recent developments in LBM suggest an alternate mesoscale model using LBM. To model an EP system with LBM, the Boltzmann equation is coupled with an ! .

Acceleration of a Plasma Flow by Oscillating Magnetic Mirrors

This paper explores the phenomenon of Fermi acceleration for possible application to plasma propulsion devices. The Lattice-Boltzmann Method based upon magnetohydrodynamics simulates plasma response to an externally applied magnetic field. The applied field configured as a magnetic bottle traps plasma injected into it by a rectangular jet. Moving the mirrors toward each other contracts the bottle and accelerates the plasma. Plasma loss associated with the magnetic bottle is a desired side effect constituting the propulsive mechanism for the device. Different time-varying magnetic fields, injection velocities, and magnetic Reynolds numbers are simulated. Cases demonstrating high exit velocity in the axial direction and minimal reverse flow are examined. The best cases exhibit exit flow accelerated to approximately twice its injection velocity in the axial direction and three times the injection velocity in the lateral direction. A magnetic field generated by loops with sinusoidally-varying positions shows the best results, while that from linearly-varying positions that return to their original positions in one time step is the most likely implementation for a propulsion or flow control device. Proportionally increasing injection velocity and current loop frequency is found not to increase exit velocity. The paper concludes that Fermi acceleration would be better used as a propulsion supplement and not as a stand-alone device.