Gasdynamic Analysis Research Articles

On shock waves in two-phase flow: effects of inter-phase heat transfer and slip

This paper is one in a series reporting on the gasdynamic analysis of two-phase flows in which a parametric treatment of the nonideal effects provides a convenient framework for analysis. The focus of this paper is on establishing the general gas dynamic relationships for normal shock waves in mixtures of a perfect gas and a nonreacting condensed phase. While the effects of slip and mixture mass fraction are examined, the main emphasis here is on the inter-phase heat transfer which occurs due to the increase in gas-phase temperature across the shock. The results show a significant influence of heat transfer on the conditions under which shocks may exist. Moderate-to-large effects in the shock downstream conditions are predicted.

Correlation between full scale and small scale steady state (S4) tests for rapid crack propagation in plastic gas pipe

The full scale and small scale, steady state (S4) tests are the principal methods for measuring the critical pressure above which rapid crack propagation can occur in a gas pressurised plastic pipe. The full scale test delivers a critical pressure which directly reflects service performance. The S4 test is less costly, but produces a critical pressure which is significantly lower than that of the full scale test. The discrepancy in critical pressures is due largely to differences in gas dynamics of the two tests. A well known gas dynamics analysis, which has previously been incorrectly applied, is used in the present work to derive a correlation function, which compares well with limited experimental data. Further experiments and analysis illustrate some other factors that influence the correlation and suggest that the application of a more precise correlation function is impractical.

Numerical simulation of electromagnetic wave attenuation in nonequilibrium chemically reacting flows

The effects of various gasdynamic phenomena on the attenuation of an electromagnetic (EM) wave propagating through the hypervelocity flow field generated by an aerodynamic body, are numerically investigated. The reacting flow field around a blunt wedge—consisting of nitric oxide ions, free electrons, and other species—is simulated using a computational fluid dynamics computer code. The computer code solves the Navier–Stokes equations including a nonequilibrium air kinetics model consisting of seven species and ten reactions, using a time-marching, explicit Runge–Kutta scheme. An EM wave, originating from within the wedge, is attenuated by the free electrons (plasma) in the chemically reacting flow. Attenuation analysis is performed separately (uncoupled) from the gasdynamic analysis using a series solution of Maxwell's equations valid for a long-wavelength plane wave and a thin (i.e. in comparison to wavelength) inhomogeneous plasma layer. The results of this computational study systematically demonstrate the importance of chemical kinetics, viscosity, mass diffusion and wall boundary conditions (adiabatic, isothermal, catalytic) for computer modeling of EM wave attenuation due to an aerodynamic plasma. Comparison is made with experimental data.

Mechanisms of absorption in pulsed excimer laser-induced plasma

This work investigates the interaction between pulsed excimer laser-induced plasma and an excimer laser beam. The optical transmissivity through the laser-induced plasma and the velocity of the plasma front are measured within the duration of the laser pulse. Based on the measured velocity of the plasma front, an analysis of compressible gas dynamics is used to compute the thermodynamic properties of the plasma layer, including temperature, pressure, and the number density of the laser-evaporated particles. The absorption coefficient of each absorption mode in the plasma is then calculated from the thermodynamic properties. By comparing the calculated and the measured transmissivity of the laser-induced plasma, we have determined the dominant absorption mechanism in the plasma plume to be photo-ionization at laser intensities in the range 90-400 MW/cm 2 .

Efficiency and gasdynamic analysis of two-phase mixtures in supersonic nozzles with inter-phase heat transfer and slip

This paper describes a gasdynamic analysis of the acceleration of a condensed phase/gaseous mixture through a converging-diverging nozzle. The model used for this analysis calculates the exit kinetic energy in terms of the mixture properties as well as the dissipative effects of heat transfer and slip between the phases. The model also calculates the nozzle efficiency by comparing the kinetic energy of the mixture at the exit to that of the ideal process. The results indicate that the efficiency decreases with both the condensed phase mass fraction and exit velocity. Inter-phase heat transfer and slip parameters produce a minimum in nozzle efficiency under conditions which are potentially encountered in rocket engines.

Drag on an ellipsoid particle in free-molecular plasma flow

Based on the analysis of molecular gas dynamics, the drag and moment acting on an ellipsoid particle of revolution X-2/a(2) + Y-2/a(2) + Z(2)/c(2) = 1, as an example of nonspherical particles, are studied under the condition of free-molecular plasma flow with thin plasma sheaths. A nonzero moment which causes nonspherical particle self-oscillation and self-rotation around its own axis in the plasma flow-similar to the pitching moment in aerodynamics-is discovered for the first time. When the ratio of axis length c/a is unity, the moment is zero and the drag formula are reduced to the well-known results of spherical particles. The effects of the particle-plasma relative velocity, the plasma temperature, and the particle materials on the drag and moment are also investigated.

The role of adhesion in the mechanical properties of filled polymer composites

Filled polymer composites have been prepared in which the energetics of the filler surfaces was systematically varied in order to investigate the dependence of the mechanical properties of the composite on the interfacial strength as predicted by the thermodynamic work of adhesion at the filler-matrix interface. A high-purity silica filler was used, treated with three different organofunctional silane coupling agents (two alkylsilanes and an aminosilane) to varying degrees from zero to complete coverage. The surface energetics of the modified fillers was characterized using both inverse gas chromatography (IGC) and dynamic contact angle analysis (DCA). While the surface energy assessments from IGC were higher than those obtained with wetting measurements, as expected, the trends with fractional coverage of silane were the same for each method, and were used to evaluate the thermodynamic work of adhesion. Highly filled polymer composites were prepared by dispersing the variously treated silica fillers into the amorphous thermoplastic matrix polymers: poly(methyl methacrylate) and poly(vinyl butyral). Specimens of the composites were tested mechanically to give the yield stress. The poly(methyl methacrylate) composites all failed cohesively in the matrix, unaffected by any of the filler surface treatments. The poly(vinyl butyral) composites, however, all displayed purely interfacial failure, with the yield stress strongly dependent on the type and extent of the filler surface treatment. While all three silanes were found to decrease the filler surface energy, and consequently the thermodynamic work of adhesion, with higher surface coverage, corresponding decreases in the yield stress were found only for the alkylsilanes. For the aminosilane, the measured yield stress was found to increase with surface coverage and therefore to decrease with the work of adhesion. The difference in behavior between the two types of coupling agent is explained in terms of acid-base effects.

A Study of Multi-Dimensional Gas Flow in Engine Manifolds

In this study, a three-dimensional Navier—Stokes solver was developed based on the finite volume fluid-in-cell (FVFLIC) method. The objective was to develop a comprehensive engine simulation tool that could predict unsteady flow features in the engine manifold and gas dynamic interaction between the intake system and the engine. Therefore the geometry effect of the manifold on gas dynamics could be fully investigated and later utilized in manifold design. Being shown here are some of the latest results of the research work aiming to validate the simulation program and apply it to the analysis of gas dynamics in manifolds for future design purposes.

Shock-jump relations in a turbulent flow

The exact jump relations applying across a shock in turbulent mean flow are formulated. These are analyzed to obtain answers to the following basic questions: Is the propagation speed of a shock wave which brings about a specified compression faster or slower than its classical value when moving through a turbulent medium? What is the magnitude of the turbulence associated correction? What is the magnitude of the correction to the pressure jump? Answers to these questions are developed by combining gas-dynamic analysis with homogeneous rapid distortion approximation.

Vectorization of a Monte Carlo simulation scheme for nonequilibrium gas dynamics

Significant improvement has been obtained in the numerical performance of a Monte Carlo scheme for the analysis of nonequilibrium gas dynamics through an implementation of the algorithm which takes advantage of vector hardware, as presently demonstrated through application to three different problems. These are (1) a 1D standing-shock wave; (2) the flow of an expanding gas through an axisymmetric nozzle; and (3) the hypersonic flow of Ar gas over a 3D wedge. Problem (3) is illustrative of the greatly increased number of molecules which the simulation may involve, thanks to improved algorithm performance.

On the gas dynamics of the volcanic plumes on Io

Features of the volcanic plumes on Io observed by Voyager 1 such as the umbrella shape, the filamentary structure and the abrupt bends of the filaments, are explained based on a gas dynamic analysis. An analytic solution of the flow field between the shock and the plume top is given.

Investigations concerning plasma parameters and population inversion in laser-produced counterstreaming plasmas

We investigated the case where two laser-produced plasmas collide nearly head on. Special attention was devoted to the fundamentals necessary to realize a coherent X-ray source. A gas-dynamic computational analysis was performed to understand the evolution of the density, the temperature, and the velocity of merging plasmas. The spatial intensity distribution of selected spectral lines reveals that the interaction of plasmas of different nuclear charge and charge state is not strictly collision dominated. Using spectral line intensity ratios, we determined electron temperatures and electron number densities, as well as the intensity inversion on the 4–1 to 3–1 resonance transitions of [He]-like Al. Inversion occurs in the vicinity of the targets if identical materials are used (Al–Al) and is possibly indicated in the interaction zone for different ones (Al–Cu), too. The inversion factors (and the gain coefficient) for the 4–3 transition of [He]-like Al at about 130 Å were estimated.

Thermal sputtering as a gas-dynamic process

Thermal sputtering, which has traditionally been interpreted either as true vaporization or as vaporization from an elastic collision spike, was suggested by Urbassek and Michl to be more correctly a gas-dynamic process. We here develop a gas-dynamic analysis based on one-dimensional unsteady adiabatic expansion (UAE). We assume UAE from a system with finite extent, with an initially uniform temperature which exceeds the thermodynamic critical temperature ( T tc), and with an initially uniform density like that of the target. We take the UAE as ceasing abruptly and becoming collision-free molecular flight when the gas density falls to a critical value. We conclude that the experimental claim that the energy flux appropriate to thermal sputtering has Maxwellian form is largely acceptable given the experimental uncertainties, that the reported temperatures are also largely acceptable, and that the yields will greatly exceed those predicted for collisional sputtering. Perhaps the most important conclusion, however, is that there is nothing unphysical about the inequality T > T tc, a problem that has long beset models of thermal sputtering based on true vaporization.

Cold high-intensity atomic hydrogen beam source

A cold atomic hydrogen beam source has been built and tested at BNL. The flow channel of the source, consisting of a discharge tube, a constricting nozzle, a thermal transition section, and an accommodator, was designed to operate in the laminar flow range. A novel feature of this source is a 0.3-mm gap between the transition Teflon tube which guides the flow and an accommodator which cools the flowing gas; across this gap the wall temperature may step from 100 K in the Teflon to 3 K in the accommodator. A record pulsed H° beam flux of 9.4×1018 H° sr−1 s−1 was obtained at an accommodator temperature of 5.8 K. The gas dynamic analysis of the system is in excellent agreement with the experimental results.

Analysis of high temperature gasdynamics in a rectangular channel using a coupled core-boundary layer model

In this paper two-dimensional steady state compressible, turbulent boundary layer equations along with the core are solved for a channel of rectangular cross-section. The behaviour of core velocity, core temperature, pressure profile, friction coefficient and heat flow for different mass flow rates and inlet pressures are analysed for combustion gases. The results are compared with experimental results obtained onzinc (zero induction channel) during the commissioning of themhd plant at Tiruchirapalli. The results match the theoretical predictions quite well.

Discrete models for the numerical analysis of time-dependent multidimensional gas dynamics

This paper explores a possible technique for extending to multidimensional flows some of the upwind-differencing methods that have proved highly successful in the one-dimensional case. Attention here is concentrated on the two-dimensional case, and the flow domain is supposed to be divided into polygonal computational elements. Inside each element the flow is represented by a local superposition of elementary solutions consisting of plane waves not necessarily aligned with the element boundaries.

An Improved Branched Pipe Model for Multi-Cylinder Automotive Engine Calculations

This paper describes a new mathematical model for calculating the behaviour of unsteady gas flow in engine manifold junctions of any configuration. The model, which allows for pressure losses at the junction, is arranged for use with engine simulation computer programs in which the gas dynamics analysis is based on the method of characteristics. Experimental coefficients obtained from steady flow tests are presented for use with existing momentum theory models and also with the generalized approach. Measured pressure-time histories and performance data for a multi-cylinder engine are compared with computer predictions using three different pipe branch calculations: constant pressure theory, momentum theory and the generalized procedure. This comparison shows the new technique gives correlations which are better than the constant pressure method but without the limitations and complexity of the model based on momentum theory.

Formulation and Assessment of a Cross-Plane Electrical Model for Magnetohydrodynamic Channels

A model for calculating cross-plane current and electric field distributions in MHD generator channels is formulated and numerically solved. The chief advantage of this model is that its solution can be implemented on the IBM 3033 digital computer in less than 1 CPU second and thus the model can be conveniently coupled to a full three-dimensional gasdynamics analysis. The model is equally valid for Faraday, diagonal-insulating-sidewall, and diagonal-conducting-sidewall channels. Accuracy of the model is calibrated by comparing its predictions with the results of three-dimensional finite-segmentation analyses. The model is found to perform best for channels with low wall temperatures and low electrode pitch-to-height ratios and when the boundary layers are thick. A discussion is given of the roles of the nonuniformity in normal current density, as predicted by the model, leading to velocity overshoots in the boundary layers, and of the transverse nonuniformity in Hall current density, generating secondary flows.

Intrinsic stellar mass flux and steady stellar winds

The conventional view that winds from stars like the Sun result from the existence of a hot corona and a low-pressure interstellar medium has recently been challeanged by R. N. Thomas and collegues. They suggest that the rates of mass loss from these and other stars are determined by conditions imposed on the flow at or below photospheric levels and that the warm chromosphere and hot corona of a solar-like star are simply consequences of this imposed photospheric flow and dissipation in the resultant stellar wind. We have examined this suggestion through the application of gas dynamic theories including dissipation. Extensive analytic and numerical calculations for both polytropic and thermally conductive flows, with viscosity included, indicate that the specification of an arbitrary intrinsic mass flux is not consistent with steady, radial, spherically symmetric flow in the absence of energy addition. We conclude that there is at present no theoretical support for the suggestion of Thomas and colleagues, and that if any such support is to be found, it will require, at the very least, a more extensive theoretical gas dynamic analysis, including explicit time dependence, spatial inhomogeneties, and/or nonclassical momentum and energy transport.

Beam-quality-determining processes in high-energy atomic iodine amplifiers

The disturbance of the optical homogeneity of high-energy, 1.315 μm atomic iodine amplifier systems by gas density changes, produced by gas-dynamic effects following nonuniform photolysis, has been analyzed for a wide range of line-broadening buffer gases. Mechanisms of photolysis gas heating and the relative merit of different buffer gases for minimizing density changes are discussed. An experimental study of the buffer gas dependence has shown good agreement with the gas-dynamic analysis. The model has been used to determine conditions for diffraction-limited amplification for varying pump times and buffer gas composition for typical large amplifier pumping profiles, showing the possibility for significantly increasing pump pulse duration.