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Results for “two-phase flow modeling”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Theoretical analysis of a rotating two-phase detonation in liquid rocket motors.

A nonlinear analysis to study tangential mode shock instabilities in a thin annular chamber is carried out by employing a one dimensional two phase detonation wave as a reaction model. It is assumed that phase change and reaction take place only within the wave, which is treated as a discontinuity. The annulus is unrolled and the flow is considered as two dimensional with the coordinate system fixed on the wave front. Between waves, the flow is assumed to be isentropic with no interaction between droplets and burned gases. Jump conditions across the wave are solved for two phase flow. The average pressure along the injection plate is related to the design chamber pressure by the use of overall conservation equations. The wave strength is written in terms of the design parameters of the chamber. The results compare favorably with existing experiments. Finally, the effects of drop size on the wave strength are discussed and a simple criterion which sets the lower limit of validity for this strong wave analysis, is presented.

Shen, P. I.-W.↗
NASA NTRS1976

A theoretical investigation of thermodynamic effects on developed cavitation

The results of a theoretical investigation of thermodynamic effects on developed cavitation are presented. An approximate solution to the conservation equations for a two-phase laminar boundary layer is obtained. This analysis produces an expression for the temperature difference between the liquid and vapor phases which can be applied to developed cavity flows. Experimental data of cavity temperature depressions are correlated using this result. In addition, a theoretical estimate of the Nusselt number for the cavity is made using a turbulent boundary layer cavity model proposed by Brennen. The result agrees in part with empirically determined expressions for the cavity Nusselt number.

Weir, D. S.↗
NASA NTRS1976

Non-equilibrium radiation from viscous chemically reacting two-phase exhaust plumes

A knowledge of the structure of the rocket exhaust plumes is necessary to solve problems involving plume signatures, base heating, plume/surface interactions, etc. An algorithm is presented which treats the viscous flow of multiphase chemically reacting fluids in a two-dimensional or axisymmetric supersonic flow field. The gas-particle flow solution is fully coupled with the chemical kinetics calculated using an implicit scheme to calculate chemical production rates. Viscous effects include chemical species diffusion with the viscosity coefficient calculated using a two-equation turbulent kinetic energy model.

Penny, M. M.↗
NASA NTRS1977

Assessment of analytical techniques for predicting solid propellant exhaust plumes

The calculation of solid propellant exhaust plume flow fields is addressed. Two major areas covered are: (1) the applicability of empirical data currently available to define particle drag coefficients, heat transfer coefficients, mean particle size and particle size distributions, and (2) thermochemical modeling of the gaseous phase of the flow field. Comparisons of experimentally measured and analytically predicted data are made. The experimental data were obtained for subscale solid propellant motors with aluminum loadings of 2, 10 and 15%. Analytical predictions were made using a fully coupled two-phase numerical solution. Data comparisons will be presented for radial distributions at plume axial stations of 5, 12, 16 and 20 diameters.

Tevepaugh, J. A.↗
NASA NTRS1979

Two-phase choked flow of cryogenic fluids in converging-diverging nozzles

Data are presented for the two phase choked flow of three cryogenic fluids - nitrogen, methane, and hydrogen - in four converging-diverging nozzles. The data cover a range of inlet stagnation conditions, all single phase, from well below to well above the thermodynamic critical conditions. In almost all cases the nozzle throat conditions were two phase. The results indicate that the choked flow rates were not very sensitive to nozzle geometry. However, the axial pressure profiles, especially the throat pressure and the point of vaporization, were very sensitive to both nozzle geometry and operating conditions. A modified Henry-Fauske model correlated all the choked flow rate data to within + or - 10 percent. Neither the equilibrium model nor the Henry-Fauske model predicted throat pressures well over the whole range of data. Above the thermodynamic critical temperature the homogeneous equilibrium model was preferred for both flow rate and pressure ratio. The data of the three fluids could be normalized by the principle of corresponding states.

Simoneau, R. J.↗
NASA NTRS1983

Modeling of transient two-component flow using a four-point implicit method

The four-point, centered implicit scheme that is extensively used in open channel flow simulation is shown to be applicable to rapid and slow pressure transient problems in conduits with nearly single phase and two-phase flows. It is only necessary to choose the proper weighting factor value, theta, of the Courant number. For rapid pressure transients such as waterhammer, the implicit method can yield reasonable results with limited numerical dispersion and attenuation if theta is only slightly greater than the critical value of 0.5. For slower pressure gradients in single and two-phase flows, reasonable numerical solutions may be achieved for Courant number values as high as 20.

Wiggert, D. C.↗
NASA NTRS1984

Dynamics of two-phase face seals

An analytic study is presented of the effects of phase change on load support for parallel and tapered face seals. Consideration is given to an adiabatic model for low Reynolds number flow. Numerical integration is carried out of the descriptive fluid equations, giving the opening force due to fluid film pressure. The loci of steady-state solutions are then plotted for water to provide curves of load support as a function of film thickness. For axial excursions of the seal rings, a quasi-steady transient analysis is made. It is found that the load support generated by fluid pressure can be multivalued for a given film thickness. Another finding is that axial disturbances of the seal rings may lead to sudden drops in load support generated by fluid pressure with three possible results. The first is that sufficient damping may permit the seal to return to the previous equilibrium operating position. The second is that the seal may collapse to an equilibrium position of smaller film thickness where face contact is more likely and a significantly higher operating temperature is assured. The third is that a limit cycle of self-sustained oscillation in the axial direction may occur if damping is sufficiently low.

Beeler, R. M.↗
NASA NTRS1983

A pumped two-phase cooling system for spacecraft

A pumped, two-phase heat-transport system is being developed for possible use for temperature control of scientific instruments on future NASA missions. As compared to a single-phase system, this two-phase system can maintain tighter temperature control with less pumping power. A laboratory model of the system has been built and tested. The measured heat transfer coefficients were approximately the same as in heat pipes, 220 Btu/hr-sq ft-F, as compared to 25 Btu/hr-sq ft-F for single-phase liquid flow. Heat shearing between experiments has been demonstrated wherein vapor generated in the cold plate of an active experiment was condensed in a cold, unheated experiment. System stability has been observed. However, additional development is needed. The use of non-azeotropic mixtures of coolants appears especially promising as a simple way to determine exit quality and thus control the flow rates to prevent dryout.

Ollendorf, S.↗
NASA NTRS1985

Comprehensive modeling of a liquid rocket combustion chamber

An analytical model for the simulation of detailed three-phase combustion flows inside a liquid rocket combustion chamber is presented. The three phases involved are: a multispecies gaseous phase, an incompressible liquid phase, and a particulate droplet phase. The gas and liquid phases are continuum described in an Eulerian fashion. A two-phase solution capability for these continuum media is obtained through a marriage of the Implicit Continuous Eulerian (ICE) technique and the fractional Volume of Fluid (VOF) free surface description method. On the other hand, the particulate phase is given a discrete treatment and described in a Lagrangian fashion. All three phases are hence treated rigorously. Semi-empirical physical models are used to describe all interphase coupling terms as well as the chemistry among gaseous components. Sample calculations using the model are given. The results show promising application to truly comprehensive modeling of complex liquid-fueled engine systems.

Liang, P.-Y.↗
NASA NTRS1985

High thermal capacity cold plate/hot plate

The results of an analytical study to determine the feasibility of a novel two-phase cold plate/hot plate (CPHP) are presented. A key feature of the CPHP is the use of capillary forces to separate the liquid and vapor phases and distribute the liquid over the evaporating/condensing surface. The liquid phase is held by capillary forces in a reservoir and is carried to the evaporating surface by a wick. The reservoir is replenished at intervals from a valved external liquid supply line. In the hot plate mode, liquid accumulates in the reservoir and is removed by an external condensate line. Performance requirements for the device were capability of handling a power density of 4 watts/sq cm, an outlet quality (percentage of vapor flow to total flow) greater than 90 percent, and operation in a 0-g environment. An analytical model of CPHP operation was developed which concentrated on the liquid and vapor flows. It was found that the liquid carrying capillary grooves of rectangular cross-section gave significantly better predicted performance than V-shaped grooves. Using the analytical model, capillary groove width and length, vapor channel dimensions, and other parameters were selected to meet the performance requirements with a 100-percent margin.

Hwangbo, H.↗
NASA NTRS1985

SSME fuel preburner phase 1/phase 2+ comparison

An analytical comparison of the predicted combustion flowfields for the Phase 1 and Phase 2+ fuel preburner configurations using an advanced CFD combustion code is currently underway at Rocketdyne. The Phase 2+ injector has a modified element design. The redesigned element provides for improved atomization through a shift in the injector element/face bleed flow split while maintaining an acceptable pressure drop. Cold-flow tests of the new design have been encouraging. As a complement to those tests, the Advanced Rocket Injector Combustor Code (ARICC) was selected to conduct a detailed combustion flowfield simulation. ARICC models two-dimensional (or axisymmetric), transient, turbulent, two-phase mixing and combustion flowfields. It is derived from a member of the Los Alamos ICEd-ALE family of codes. Unique features of ARICC include explicit representation of the coaxial LOX jet and hydrogen gas flows, distributed atomization processes, droplet breakup, and supercritical vaporation processes. Predictions of temperature and OH concentration profiles for the Phase 1 and Phase 2+ injector flowfields indicate a trend toward more uniform temperature distributions and shorter flame lengths with the Phase 2+ design.

Jensen, R. J.↗
NASA NTRS1986

Numerical analysis of confined recirculating gas-solid turbulent flows

Particle dispersion in confined recirculating turbulent flows has been investigated numerically. The present computational scheme utilizes Eulerian forms of the governing equations and allows two-way coupling between gas and solid phases. A recently developed two-phase closure model based on the multiple-scale turbulence model was used for the estimation of turbulent viscosities and diffusivities. For the particle size and loading considered in this study, the effect of particulate phase on the conveying gas is small, the nonequilibrium between the two phases is significant. Effects of recirculation, expanded chamber size and secondary annular jet momentum on the particle mixing rate are also investigated. In general, the present numerical results are in reasonably good agreement with the available experimental data.

Chen, C. P.↗
NASA NTRS1987

Liquid droplet heat exchanger studies

Recent analytical and experimental investigations of the liquid droplet heat exchanger (LDHX) concept for space power applications are described. The performance of the LDHX is compared to that of a conventional heat exchanger for heat rejection applications in a Brayton cycle, using the mass-specific heat exchanger effectiveness as a figure of merit. It is shown that the LDHX has an order of magnitude advantage over the conventional heat exchanger. Furthermore, significant improvement in cycle efficiency and power to mass ratio is possible. Two-phase flow experiments in a laboratory scale LDHX, using air and water as the two media, show very good agreement with the quasi-one-dimensional model used in the parametric studies.

Bruckner, A. P.↗
NASA NTRS1988

Computation of two-phase shear-layer flow using an Eulerian-Lagrangian analysis

A combined Eulerian-Lagrangian analysis which combines a linearized block implicit Navier-Stokes analysis for the continuous phase with a Lagrangian analysis for the discrete phase has been utilized to simulate a two-phase shear-layer flow in a two-dimensional channel flow configuration. The motion of the particles is tracked in computational coordinate space, resulting in improved computational efficiency, and interphase coupling terms for the Eulerian analysis are computed from the instantaneous distribution of the particles rather than the trajectory information. The use of the implicit Navier-Stokes analysis for the continuous phase has made it possible to efficiently use a highly stretched mesh. A low Reynolds number form of the k-epsilon turbulence model was used with near-wall resolution, thus eliminating the need to use the 'wall-function' approach. The streamwise velocity profiles for the continuous and the discrete phases have been compared with experimental data for two test cases.

Sabnis, Jayant S.↗
NASA NTRS1989

Two-dimensional analysis of two-phase reacting flow in a firing direct-injection diesel engine

The flow field, spray penetration, and combustion in two-stroke diesel engines are described. Fuel injection begins at 345 degrees after top dead center (ATDC) and n-dodecane is used as the liquid fuel. Arrhenius kinetics is used to calculate the reaction rate term in the quasi-global combustion model. When the temperature, fuel, and oxygen mass fraction are within suitable flammability limits, combustion begins spontaneously. No spark is necessary to ignite a localized high temperature region. Compression is sufficient to increase the gaseous phase temperature to a point where spontaneous chemical reactions occur. Results are described for a swirl angle of 22.5 degrees.

Nguyen, H. Lee↗
NASA NTRS1989

The modelling of heat, mass and solute transport in solidification systems

The aim of this paper is to explore the range of possible one-phase models of binary alloy solidification. Starting from a general two-phase description, based on the two-fluid model, three limiting cases are identified which result in one-phase models of binary systems. Each of these models can be readily implemented in standard single phase flow numerical codes. Differences between predictions from these models are examined. In particular, the effects of the models on the predicted macro-segregation patterns are evaluated.

Voller, V. R.↗
NASA NTRS1990

Heavy rain effects on airplane performance

The objective is to determine if the aerodynamic characteristics of an airplane are altered while flying in the rain. Wind-tunnel tests conducted at the NASA Langley Research Center (LaRC) have shown losses in maximum lift, reduction in stall angle, and increases in drag when a wing is placed in a simulated rain spray. For these tests the water spray concentration used represented a very heavy rainfall. A lack of definition of the scaling laws for aerodynamic testing in a two-phase, two-component flow makes interpolation of the wind-tunnel test uncertain. Tests of a large-scale wing are to be conducted at the LaRC. The large-scale wing is mounted on top of the Aircraft Landing Dynamics Facility (ALDF) carriage. This carriage (which is 70-foot long, 30-foot wide, and 30-foot high) is propelled with the wing model attached down a 3000-foot long test track by a water jet at speeds of up to 170 knots. A simulated rain spray system has been installed along 500 feet of the test track and can simulate rain falls from 2 to 40 inches/hour. Operational checks are underway and the initial tests should be completed by the Fall of 1989.

Dunham, R. E., Jr.↗
NASA NTRS1990

Modeling the use of a binary mixture as a control scheme for two-phase thermal systems

Two-phase thermal loops using mechanical pumps, capillary pumps, or a combination of the two have been chosen as the main heat transfer systems for the space station. For these systems to operate optimally, the flow rate in the loop should be controlled in response to the vapor/liquid ratio leaving the evaporator. By substituting a mixture of two non-azeotropic fluids in place of the single fluid normally used in these systems, it may be possible to monitor the temperature of the exiting vapor and determine the vapor/liquid ratio. The flow rate would then be adjusted to maximize the load capability with minimum energy input. A FLUINT model was developed to study the system dynamics of a hybrid capillary pumped loop using this type of control and was found to be stable under all the test conditions.

Benner, S. M.↗