Showing papers in "Journal of Basic Engineering in 1970"

Mechanisms of Metal Removal by Impacting Dust Particles

Abstract: This is a two-part paper, which stresses the materials science approach to understanding dust erosion mechanisms. The first part is an experimental phase, studying the effects upon solid-particle erosion, of such material and environmental variables as target alloy composition and heat-treat condition; dust particle velocity, size, concentration, velocity, and kinetic energy; carrier-gas true temperature and impingement angle. All test variables and their limits were chosen to simulate the range of engineering conditions and erosive environments encountered in helicopter turbine service. Actual erosion data are compared with erosion levels predicted by existing theories on particulate erosion. The second part is a diagnostic phase, programmed to detect and study visible phenomena associated with the erosion processes, using high-magnification electron microscopy. Phenomenological evidence obtained from the erosion surfaces and erosion products are used to define probable physical models of the erosion mechanisms.

Bubble Formation Due to a Submerged Capillary Tube in Quiescent and Coflowing Streams

Abstract: The case of bubble formation in both quiescent and moving streams cine to the injection of a constant gas flow through a small tube is considered. Relationships predicting the expected size and quantity of bubbles generated are proposed. These are compared with measurements taken with stream velocities up to 9 ft/sec, while generating gas bubbles from 40 to 700 microns in diameter. For the case of generation in a quiescent stream the forces due to the virtual mass, surface tension, viscous drag, buoyancy, and the wake formed by the preceding bubble are accounted for. There still remains some question {only partly answered by a comparison with measurements) as to the proper added mass coefficient and the geometry of the bubble previous to detachment, as well as an adequate estimate of the interaction with a preceding bubble's wake. The proposed model for generation in a moving stream is in good agreement with actual measurements for co-flowing velocities between 1 and 9 fps and capillary tubes in the order of 10~ cm in dia.

Effective Drag Coefficient for Gas-Particle Flow in Shock Tubes

Abstract: : Effective drag coefficients for flows of suspensions of spherical glass particles in air were derived from simultaneous measurements of pressure and particle concentration in the flow behind weak shock waves. Average particle diameters were 29 and 62 micrometers. The instantaneous concentration was determined by light scattering, and the results agree well with earlier shock-tube data based on streak records. They exhibit several unexpected features: the correlation between drag coefficient and Reynolds number is much steeper than the generally used 'standard' curve but approaches it at Reynolds numbers of several hundred; the correlation is independent of the particle concentration over the range of experiments, that is, for particle-to-gas flow rate ratios between 0.05 and 0.36; if the Reynolds number immediately behind the shock front is changed by varying the shock strength, the points move along the correlation, but if it is changed by changing the particle size, the entire correlation is shifted although to a smaller extent than would correspond to the direct effect of particle diameter on the Reynolds number. To account for the observations, a flow model is developed which allows for microscopic longitudinal and lateral perturbations of the particle motion that are the result of various causes, such as particle interactions with wakes of other particles, lateral forces caused by particle rotation, or electrostatic forces. (Author)

Nonlinear Effects in the Collapse of a Nearly Spherical Cavity in a Liquid

Abstract: : A linearized perturbation theory was developed some time ago for the analysis of the growth of distortions in a nearly spherical cavity collapsing in a liquid. Since the distortions grow as the cavity collapses, it is of importance to determine the validity of the linearized approximation. The study gives a numerical solution of the exact nonlinear equations for the growth of a distortion. Two kinds of distortions are studied in detail: Case A is essentially a prolate ellipsoid; Case B is essentially an oblique ellipsoid. Both cases have initial large deformations from the spherical shape. The numerical solution shows that the linearized perturbation approximation remains surprisingly accurate through most of the cavity collapse. The principal effect of the nonlinear calculation is in the coupling of the various distortion modes.

Jet Pump Cavitation

Abstract: Mixing-throat cavitation in a liquid jet pump results from high jet velocities, low suction (NPSH) pressure, or low discharge pressure. Incipient cavitation at the jet boundary has no effect on jet pump efficiency, but under severe conditions it spreads to the walls. A limiting flow condition results which is independent of discharge pressure. Efficiency deteriorates rapidly and the pump head-flow characteristics can no longer be predicted by conventional theory. Eight correlation parameters (1937–1968) and their interrelations are examined. A Cavitation Index σL is recommended for correlation of cavitation-limited flow results. Limiting flow data from 14 references on water, oils, and mercury, plus additional data on three water jet pumps are compared, showing that 11 sets of data on water, oils, and mercury can be represented by the single-number index σL , with a range of 0.8 to 1.67. Conventional jet pumps are described by σL = 1.0 to 1.4 and σL = 1.35 is recommended for conservative use. The limiting flow function Y (NPSH) is shown to be a useful tool in comparing cavitation response to design changes. System design to avoid cavitation is facilitated by a simple limiting flow equation, ML (R, σL , NPSH, Vn ), and the equation is compared with recently published data. Cavitation can be avoided by reducing Vn , and R, or by raising suction port pressure. Flow passage contours, including nozzle-to-throat spacing, influence σL and the limiting flow ratio can also be improved by reducing σL (0.9 or less) through careful design. Systems handling high gas-solubility liquids can be improved by reducing gas content; fluid properties otherwise have little effect on this jet pump phenomenon.

Cavitation suppression and stress effects in high-speed flows of water with dilute macromolecule additives

Abstract: Experiments were carried out to study the effect of dilute aqueous polymer solutions on flow-generated cavitation inception. The cavitation inception on 1/4 and 1/2-in.-dia. models with a hemispherical nose in a blowdown water tunnel was inhibited at an observed range of Reynolds numbers. Reduction of the incipient cavitation number to 30 percent of its value for tap water was observed, depending on the kind of polymer used, its concentration, and the Reynolds number. Flow velocity field visualization was achieved by optical techniques, which measured the flow velocities and was used to correct values computed from venturi pressure drop. (Author)

Turbine Flowmeter Performance Model

Abstract: : The purpose of this addendum is to incorporate additional turbine flowmeter test case information that may be of interest to the user of the computer program, and also to include several minor corrections in the questionnaire (Author)

An experimental investigation of several low- area-ratio water jet pumps.

Abstract: Several low-area-ratio jet pumps were evaluated experimentally in water. Principal geometrical variables investigated were area ratio, throat length, and nozzle spacing. Diffuser geometry was also varied, but to a lesser degree. Experimental values of efficiency and head ratio were compared to a one-dimensional theoretical prediction method previously found to be applicable to moderate and high-area-ratio pumps. Two related cavitation prediction parameters were developed and compared to experimental data.