Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1979"

A Vortex Model of the Darrieus Turbine: An Analytical and Experimental Study

Abstract: A preliminary aerodynamic performance prediction model has been constructed for the Darrieus turbine using a vortex lattice method of analysis. A series of experiments were conducted for the express purpose of validating the analytical model. These experiments were conducted on a series of two dimensional rotor configurations which were towed in a large tank of water. The use of water as a working fluid was intended to facilitate both flow visualization and the ability to measure aerodynamic blade forces while allowing operation at sufficiently high Reynolds numbers. The primary purpose of this research was to allow reasonable predictions of aerodynamic blade forces and moments to be made.

A Fundamental Criterion for the Application of Rotor Casing Treatment

Abstract: An experimental investigation has been carried out on the influence of grooved casing treatment on the stall margin of a compressor rotor. Tests were conducted with two rotor builds having different solidities (but all other parameters identical) so that one of the rotors exhibited a wall, or casing, type of stall, while the other showed a blade stall. It was found that the casing treatment, when compared to the solid casing, was very effective in increasing the stall margin of the wall stall configuration, whereas there was little or no change in the stall point of the blade stall configuration. Detailed relative frame measurements of the rotor exit flow field were also taken as part of the program. These showed that in a wall stall situation, the use of casing treatment produced a substantial decrease in the relative total pressure defect, compared with the solid casing, while this was not true for the blade stall type of blading. The results of the experiments, both in overall measurements and in the detailed relative frame traverses, support the hypothesis that casing treatment is effective only in a situation in which a wall stall exists.

Turbulent Flow Measurements by Laser-Doppler Anemometry in Motored Piston-Cylinder Assemblies

Abstract: Laser-Doppler anemometry has been used to quantify the mean velocity and turbulence characteristics of the isothermal, incompressible flow within a piston-cylinder arrangement motored without compression at 200 rpm and with idealized inlet geometries corresponding to a pipe and to an annular port located in the centre of the cylinder head. The results indicate that the pipe entry gives rise to a strong vortex near the piston as the indrawn air is deflected radially along the piston face and cylinder wall; this, in turn, gives rise to a weaker, counter-rotating vortex near the cylinder head which grows appreciably as the piston approaches bottom-dead-centre. With the annular-port entry, the inlet jet is angled and results in a flow pattern with a large vortex occupying nearly all of the flow space with much smaller vortices at the corners between the wall and the piston and cylinder heads. The effect of a piston bowl was also investigated for the port entry and is shown to be small.

The Effect of Gaseous Cavitation on Fluid Transients

Abstract: Gaseous cavitation (alternately termed gas release) is investigated for turbulent pipe flows subjected to transient wave motion. Experimental data are presented that exhibit developing 2-component flow (air or carbon dioxide and water mixtures) in a 295-m laboratory pipeline; the flow is characterized by wave dispersion due to the increase in void fraction. An analytical model based on the method of characteristics yields simultaneous solutions for pressure, velocity, and void fraction. The greatest uncertainty in the formulation is the rate of gas release; in this instance, it is allowed to depend upon the difference between saturation and instataneous line pressures. 28 references.

Experimental Study of a Jet-Driven Helmholtz Oscillator

Abstract: This paper describes an experimental study of a Helmholtz resonator driven by a round jet passing through it. This device, dubbed the jet-driven Helmholtz oscillator (JDHO), is a rigid chamber with two round openings located coaxially in two opposite walls, through which a jet is allowed to pass across the chamber. At certain jet velocities, jet instabilities couple with the Helmholtz resonance to produce very powerful chamber-pressure oscillations at a frequency slightly higher than the chamber Helmholtz frequency. The amplitude of these pressure oscillations may reach values of up to 5.6 times the jet dynamic pressure. Simultaneously, the exiting flow pulsates at the same frequency with an amplitude of up to 60 percent of the exit jet velocity, and a loud sound is emitted. The thrust of the present study was twofold: to determine the optimum range of geometrical parameters producing the maximum magnitudes, and to identify the mechanisms underlying the oscillator operation.

Prediction of Incompressible Separated Boundary Layers Including Viscous-Inviscid Interaction

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Turbulent Flow Over a Plane Symmetric Sudden Expansion

Abstract: Turbulent flow with separation and recirculation over a double backward facing step has been investigated experimentally. Time mean streamwise, transverse and cross-stream components of the velocity fluctuations, together with turbulence kinetic energy and Reynolds shear stresses, were measured using a laser Doppler anemometer, operating in the differential Doppler mode with forward scattering. Ordinary tap water was used in a closed loop flow system with a Reynolds number of 30,210 and significant changes of flow patterns, increases in turbulence kinetic energy, velocity fluctuations, and shear stresses were observed downstream of the step expansion.

A Wall-Flow-Direction Probe for Use in Separating and Reattaching Flows

Abstract: : The measurement of the exceedingly unsteady behavior of nominally two-dimensional, turbulent flows in regions of separation and reattachment is facilitated by the development of a new instrument; the wall-flow-direction probe which determines the instantaneous flow direction (upstream or downstream) in a thin layer of fluid very close to the wall. The probe was tested in low-speed, unsteady, separating and reattaching air flows. It appears to offer considerably more accuracy than other methods for the determination of the time mean separation and reattachment points. In addition, the probe and its control circuits are relatively inexpensive and easy to construct. (Author)

Pressure Pulse Propagation in Two-Component Slug Flow

Abstract: The simple model of pressure pulse propagation in slug flow proposed by Henry, Grolmes, and Fauske has been extended by considering wave reflection and wave transmission at gas-liquid interfaces. A frequency-response model applied to a series of idealized gas and liquid slugs yields a pulse propagation speed that approaches the homogeneous model value as the number of slugs is increased for a given void fraction. All characteristic roots from the solution to a three-equation drift-flux model are related to the velocity of the center of mass of the mixture. The pulse propagation speed relative to this velocity is exactly equal to the homogeneous model value, however. Measured pulse propagation speeds in vertically downward slug flow are, as anticipated, much less than those predicted by the simple model of Henry, Grolmes, and Fauske, but slightly greater than the homogeneous model value. Measured pressure surges produced by the rapid closure of a downstream valve in a pipeline are reasonably well predicted by the drift-flux model. For the range of void fractions, pressures, and velocities encountered in this study, it is concluded that pressure pulse speeds and the magnitude of pressure surges in slug flow can be adequately predicted by a homogeneous model.

Transport of Oils as Oil-in-Water Emulsions

Abstract: Measurements for various concentrated refined mineral oil/tap water emulsions, all prepared with a single emulsifier, 0.5Vertical Bar3< Triton X-114, with and without drag reducing additives (Dow Separan AP 273, Nalco BX-1192, Shell Neodol, and Union Carbide Polyox WSR 301) showed that oil viscosity (1.5-61.5 x 10/sup -//sup 6/ sq m/sec at 35/sup 0/C) had little effect on turbulent pressure losses of such emulsions; temperature rise from 30/sup 0/ to 45/sup 0/C also had little effect. The specific energy losses for transport of oil as oil-in-water emulsions decreased as concentration rose from 50 to 75Vertical Bar3<. Separan and Nalco were effective as drag-reducing additives but lost their effectiveness with time due to shear degradation; Polyox was completely ineffective. Nonionic surfactants such as Neodol were less effective drag-reducing agents, but their shear degradation was reversible. The energy-saving advantages (e.g., no need for heating) of pipeline transport of heavy, waxy crudes as concentrated aqueous emulsions are discussed.

Predicted Secondary Flows in Triangular Array Rod Bundles

Abstract: A one-equation turbulence model was applied to forecast the main features of fully-developed turbulent flow through infinite equilateral triangular arrays of parallel rods having pitch-to-diameter ratios of 1.12 to 1.35 and Reynolds numbers of (2.7 to 25) x 10/sup 4/. For all cases, the secondary flow was found to be a single cell of circulation for each primary flow cell of a subchannel. The strength of the secondary flow increased with Reynolds number but decreased with rod spacing. The numerical results (which included friction factors, wall shear stress variations and axial velocity distributions) are shown to be in reasonable agreement with published experimental data.

Jet Pump Cavitation With Ambient and High Temperature Water

Abstract: Cavitation characteristics of a jet pump were explored in tests with 80 C and 280 C water. A cavitation coefficient based on suction velocity and net suction head was used to correlate results. Results at low temperature compared well with results in literature. Results at high temperature and comparison of jet pump cavitation at low and high temperatures are the first to be reported as far as known. The jet pump was substantially less susceptible to cavitation at 280 C than at 80 C. The effects of cavitation, as indicated by drop-off in jet pump performance, vibration, and acoustic noise, were also much less severe at 280 C than at 80 C.

Measurements Within Görtler Vortices

Abstract: Local measurements of stream wise velocity component have been made in the laminar boundary layer on the concave surface of a water channel, supported by flow visualization. Details of the naturally-occurring Gortler vortex pattern are presented.