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A preconditioned numerical method for gas-liquid two-phase flows is applied to solve cavitating flow. The present method employs a finite-difference method of the dual time-stepping integration procedure and Roe's flux difference splitting approximation with the MUSCL-TVD scheme. A homogeneous equilibrium cavitation model is used. The present density-based numerical method permits simple treatment of the whole gas-liquid two-phase flow field, including wave propagation, large density changes and incompressible flow characteristics at low Mach number. Two-dimensional internal flows through a backward-facing step duct, convergent-divergent nozzles and decelerating cascades are computed using this method. Comparisons of predicted and experimental results are provided and discussed. [DOI: 10.1115/1.1777230]

The application of pneumatic metrology to control dimensional accuracy on machined parts is based on the measurement of gas flow resistance through a restricted section formed by a jet orifice placed at a small distance away from a machined surface. The backpressure, which is sensed and indicated by a pressure gauge, is calibrated to measure dimensional variations. It has been found that in some typical industrial applications, the nozzles are subject to fouling, e.g., dirt and oil deposits accumulate on their frontal areas, thus requiring more frequent calibration of the apparatus for reliable service. In this paper, a numerical and experimental analysis of the flow behavior in the region between an injection nozzle and a flat surface is presented. The analysis is based on the steady-state axisymmetric flow of an incompressible fluid. The governing equations, coupled with the appropriate boundary conditions, are solved using the SIMPLER algorithm. Results have shown that for the standard nozzle geometry used in industrial applications, an annular low-pressure separated flow area was found to exist near the frontal surface of the nozzle. The existence of this area is believed to be the cause of the nozzle fouling problem. A study of various alternate nozzle geometries has shown that this low-pressure recirculation area can be eliminated quite readily. Well-designed chamfered, rounded, and reduced frontal area nozzles have all reduced or eliminated the separated recirculation flow area. It has been noted, however, that rounded nozzles may adversely cause a reduction in apparatus sensitivity. [DOI: 10.1115/1.1598991]

A new probe technique is introduced for the measurement of concentration in binary gas flows. The new technique is demonstrated through application of the probe in a Mach 4 nonreacting jet of hydrogen injected into a nominally quiescent air environment. Previous concentration probe devices have mostly used hot wires or hot films within an aspirating probe tip. However, the new technique relies on Pitot pressure and stagnation point transient thin film heat flux probe measurements. The transient thin film heat flux probes are operated at a number of different temperatures and thereby provide stagnation temperature and heat transfer coefficient measurements with an uncertainty of around [+ or -] 5 K and [+ or -] 4% respectively. When the heat transfer coefficient measurements are combined with the Pitot pressure measurements, it is demonstrated that the concentration of hydrogen within the mixing jet can be deduced. The estimated uncertainty of the reported concentration measurements is approximately [+ or -] 5% on a mass fraction basis. [DOI: 10.1115/1.1595671]

An instrument for the measurement of wall shear stress in two-phase flows is described. The device, termed a Laser Interferometer Skin Friction (LISF) meter, determines the wall shear by optically measuring the time rate of thinning of a thin oil film placed on the wall of the flow channel. The LISF meter has proven to be a valuable tool for measurement of wall shear in single-phase gaseous flows but, to date, had not been applied to liquid or gas-liquid flows. This paper describes modifications to the LISF meter developed to facilitate its use in two-phase flows. The instrument's configuration, governing theory, and data reduction procedure are described. Additionally, results of validation experiments for a single-phase water flow are presented, which demonstrate the instrument's ability to accurately measure wall shear. Measurements are also presented for two-phase, water-air flows in a duct of square cross section at various superficial gas and liquid velocities within the bubbly flow regime. Results of the measurements confirm previous observations that the addition of a very small amount of the gaseous phase increases the wall shear significantly over that in a single-phase water flow. The two-phase wall shear saturates to a maximum and then declines again as the superficial gas velocity is increased. The peak two-phase wall shear increases as the liquid superficial velocity is decreased. These trends are qualitatively in agreement with previous measurements obtained in pipes using an electrochemical technique.

An experimental procedure was developed for determining both the density and flow rate of a gas from measurements of pressure drops caused by an abrupt flow area contraction in a cylindrical pipe. Experiments were carried out by varying the density and flow rate of a light gas mixture of air and helium, spanning a Reynolds number range from 0.2 x [10.sup.4] to 3.4 x [10.sup.4]. From experimental results, a procedure was then proposed for evaluating the density from pressure change measurements in the scope of light gas extraction experiments. [DOI: 10.1115/1.2953294]

This paper describes a novel in-line sensor that measures the magnitude and direction of gas flow in a tube. The sensor possesses a unique set of performance characteristics: low detection limit, little resistance to flow, and directional sensitivity. The sensor consists of two hot wire anemometers mounted in a U-shaped tube. Differences in the signals between the two hot wires under low velocity conditions are used to determine the direction of the flow. Calibration curves of flow rate versus measured velocity are used to determine the magnitude of the flow. The sensor has applications in systems that are characterized by naturally driven oscillating flows.

This paper develops a liquid film symmetry correlation and a liquid film thickness distribution model for horizontal annular gas-liquid pipe flows. The symmetry correlation builds on the work of Williams et al. (1996) (Droplet Flux Distributions and Entrainment in Horizontal Gas-Liquid Flows,' Int. J. Multiphase Flow, Vol. 22, pp. 1-18). A new correlating parameter is presented. The liquid film thickness model is based on the work of Laurinat et al. (1985) (Film Thickness Distribution for Gas-Liquid Annular Flow in a Horizontal Pipe,' PhysicoChem. Hydrodynam., Vol. 6, pp. 179-195). The circumferential momentum equation is simplified to a balance between the normal Reynolds stress in the film's circumferential direction and the circumferential component of the weight of the film. A model for the normal Reynolds stress in the circumferential direction is proposed. The symmetry correlation is used to close the model equations. The model is valid for films with disturbance waves, and is shown to be applicable to air-water flows over a range of conditions from low velocity asymmetric to high velocity symmetric annular flows. [S0098-2202(00)02102-7] Keywords: Two-Phase Flow, Annular Flow, Horizontal Gas-Liquid Flow, Liquid Film Thickness Distribution

A direct simulation Monte Carlo method (DSMC) solver, adapted to the subsonic microflow, is developed under the object-conception language (c++). Some technical details critical in these DSMC computations are provided. The numerical simulations of gas flow in a microchannel are carried out using the developed DSMC solver. Streamwise velocity distributions in the slip flow regime are compared with the analytical solution based on the Navier-Stokes equations with the velocity slip boundary condition. Satisfactory agreements have been achieved. Furthermore, the domain of the validity of this continuum approach is discussed. Simulations are then extended to the transitional flow regime. Streamwise velocity distributions are also compared with the results of the numerical solutions of the linearized Boltzmann equation. We emphasize the influence of the accommodation coefficient on the velocity profiles and on the mass flow rate. The simulation results on the mass flow rate are compared with the experimental data, which allow us to validate the 'experimental' technique of the determination of the accommodation coefficient. [DOI: 10.1115/1.3026733]