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COMMENTARY

J. Fluids Eng. 1978;100(2):146. doi:10.1115/1.3448623.
Abstract
Commentary by Dr. Valentin Fuster

REVIEW ARTICLES

J. Fluids Eng. 1978;100(2):152-165. doi:10.1115/1.3448624.

Unstable flow past cavities is grouped into fluid-dynamic, fluid-resonant, and fluid-elastic categories. Fluid-dynamic oscillations are attributable to instability of the cavity shear layer and are enhanced through a feedback mechanism. Fluid-resonant oscillations are governed by resonance conditions associated with compressibility or freesurface wave phenomena. Fluid-elastic oscillations are primarily controlled by the elastic displacements of a solid boundary. Experimental information and theoretical models for the frequencies and amplitudes of each of these categories of oscillations as well as a combination of them are discussed in detail. Effects of arrangements of cavities in groups and variations in cavity shape (rectangular, circular, triangular, whistle-type, Helmholtz-type) are reviewed. Means of attenuation of oscillations via geometrical modifications and mass addition are summarized. Finally, the effects of cavity oscillations on the time-mean cavity pressure, drag, and shear-layer characteristics are discussed.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. Fluids Eng. 1978;100(2):166-176. doi:10.1115/1.3448625.

This paper describes experiments performed to measure the dynamic transfer matrices for cavitating (and noncavitating) pumps. These transfer matrices describe the relationship between small linear oscillatory perturbations in the pressures and mass flow rates at inlet and discharge from the hydraulic machine. The matrices were deduced from direct measurements of these fluctuating quantities for different modes of excitation of the machine. Results for a cavitating inducer are presented as functions of frequency and mean operating state. Though some of the trends in the data are consistent with existing theoretical models of inducer dynamics, others are not, indicating a need for further theoretical investigation of the dynamic characteristics of such flows. The results exhibit increasingly complex dynamics with increasing cavitation; it appears that the hydraulic machine deviates from an essentially passive response without cavitation to an increasingly active response as the cavitation number is reduced.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):177-179. doi:10.1115/1.3448626.

Laminar hydrodynamic entry length solutions for circular and noncircular ducts are essential in proper design of compact heat exchangers and other heat transfer and fluid flow devices. A closed form equation has been proposed to present these solutions for the circular tube, parallel plates, rectangular, equilateral triangular, and concentric annular ducts. The necessary constants are evaluated and it is shown that the proposed correlation predicts the apparent friction factors within ± 2.4 percent.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):180-186. doi:10.1115/1.3448627.

A procedure is described for computation of incompressible, steady, two-dimensional flows in fully-stalled diffusers with plenum exit. The procedure is successful in predicting pressure distributions and patterns to the accuracy of the data. The procedure employs a zonal model; this maintains close connections between the modeling and the physics thereby providing insight into critical aspects of modeling separated flows. The procedure presented is also convenient for computing unstalled flows in passages with turbulent boundary layers for either direct or indirect design problems. Computing times are well within engineering feasibility. The concepts developed can be extended to other classes of separated flows; some of these extensions have already been completed and are referenced.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):187-193. doi:10.1115/1.3448628.

The dynamics of a thin liquid film flowing through a pipe rotating about an axis perpendicular to the pipe axis are studied. Static pressure is assumed constant along the pipe and the axial flow of the film is a direct consequence of the pull of the centrifugal force. The film is pushed to one side of the pipe by a Coriolis force which is nonconservative. As a result, a secondary motion is set up in the plane normal to the pipe axis. An approximate set of equations governing the secondary flow is analyzed through an integral technique for the case of a laminar film dominated by viscous effects. A visualization experiment is carried out and the approximate theory is found to compare favorably with the qualitative observations.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):194-200. doi:10.1115/1.3448629.

A local analysis was made of the laminar throughflow between corotating disks of a Newtonian vapor containing liquid droplets. Such a flow is of practical interest in multiple-disk turbomachinery, and specifically is a model of a two-phase, single component flow (saturated vapor - saturated liquid steam) which would arise in geothermal applications of a multiple-disk turbine. Local mass conservation and momentum equations for the vapor and droplet fields were used, as well as mass conservation and energy equations for a single droplet. The vapor-droplet interaction was modeled by a drag force based on the well-known drag coefficients for flow past spheres. The governing equations were reduced to parabolic form by order-of-magnitude arguments to allow a marching-type solution. The nonlinear partial differential equations were replaced by nonlinear finite-difference equations, which were linearized. The resulting system of linear algebraic equations was solved directly. Various results are presented, including results for a set of flow parameters which are close to those applicable for multiple-disk turbines operating on geothermal steam.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):201-203. doi:10.1115/1.3448630.
Abstract
Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):204-209. doi:10.1115/1.3448631.

An experimental and analytical investigation was conducted to determine the free surface shapes of circular jets impinging normal to sharp-edged disks in zero gravity. Experiments conducted in a zero gravity drop tower yielded three distinct flow patterns which were classified in terms of the relative effects of surface tension and inertial forces. An order of magnitude analysis was conducted indicating regions where viscous forces were not significant when computing free surface shapes. The free surface analysis was simplified by transforming the governing potential flow equations and boundary conditions into the inverse plane. The resulting nonlinear equations were solved numerically and comparisons were made with the experimental data for the inertia dominated regime.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):210-214. doi:10.1115/1.3448632.

Results are presented in dimensionless form as obtained in an experimental study of the resultant radial force variation in an eccentric annulus formed by a stationary outer cylinder and a rotating inner cylinder, through which an axial flow of oil may be pumped. Two eccentricity ratios, 0.5 and 0.9, and three axial Reynolds numbers for the flow of the fluid in the annulus, 0, 25, and 50, are considered. It is shown that the onset of Taylor vortex flow has a marked effect on the magnitude and direction of the resultant radial force. The resultant forces and attitude angles are compared with those derived from Sommerfeld’s journal bearing theory. Comparisons are also made between critical Taylor numbers for the present investigation and those available in the literature.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):215-223. doi:10.1115/1.3448633.

The Reynolds number dependence of Cf , Uo , H and other bulk flow parameters in “two dimensional” (high aspect ratio) rectangular duct flow is explored and the empirical relations Cf = 0.073 Re−1/4 and Uo /Ū = 1.28 Re−0.0116 are presented. The values A = 2.12 and K = 0.41 for the log-law constants and Π = 0.14 for Coles’ wake parameter are derived and are shown to be independent of Re. The integration of Dean’s formula for the complete velocity profile provides close agreement with all parameters when these values of A, K and Π are used and is shown to coincide with the “optimum log-law” for skin friction (which contains Π).

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):224-228. doi:10.1115/1.3448634.

Turbulence measurements were made in the separated, reattached, and redeveloped regions of a two-dimensional incompressible air flow over a flat plate with finite thickness and blunt leading edge. In the boundary layer downstream of the reattachment point, Prandtl’s mixing length and turbulent kinetic energy length scale are estimated, and the correlation between the turbulent shear stress and the turbulent kinetic energy is described.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):229-231. doi:10.1115/1.3448635.

This paper reviews the development and testing of a static pressure probe which is relatively insensitive to yaw angle. The probe averages the pressure along an equatorial line on a sphere immersed in a flowing fluid such that the average measured pressure is the static pressure. The probe can be rotated up to ± 30 deg from the velocity vector with little error in the static pressure reading.

Topics: Pressure , Probes , Yaw , Fluids , Testing , Errors
Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):232-236. doi:10.1115/1.3448637.

A simple, semiempirical method for calculating the laminar, transition, and turbulent boundary layer with arbitrary free stream pressure gradient is developed. Good correlation is obtained with data on general two dimensional turbulent flows, diffuser flows, and the cylinder in cross-flow. However only for the diffuser has the boundary layer flow been coupled with the potential core so that only the inlet conditions and geometry are required. In other cases the free stream velocity distribution must be known or calculable. Skin friction coefficient, momentum thickness Reynolds number, and free stream pressure gradient parameter correlation employs a simple lag theory. With the integral momentum equation the complete boundary layer parameters are obtained as functions of the distance along a surface.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):237-238. doi:10.1115/1.3448638.

A flow engine element is described which converts the oscillations of a flapwing, that is mounted on a crankshaft, into rotary energy. A self-starting twin model of this energy flux converter was built and tested in a moderate stream of air. Driving this device with a motor reverses it into an air blower of the hydropulser class.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):239-245. doi:10.1115/1.3448639.

The flow induced vibrations of a check valve with a spring damper to prevent slamming have been studied experimentally. Both prototype and two-dimensional model experiments were conducted to develop an understanding of the mechanism of self-excitation. The phenomenon is shown to be caused by the high rate of change of discharge at small angles of valve opening and the hysteretic hydrodynamic loading resulting from fluid inertia. As the discharge-displacement characteristics of the valve are dependent on its geometry, modifications of this geometry were examined and one found which eliminated the vibrations entirely. The phenomenon studied is considered to be the same as that causing vibrations in numerous other flow control devices when operating at small openings.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):252-253. doi:10.1115/1.3448655.
FREE TO VIEW
Abstract
Topics: Fluids , Vortices , Wind power
Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1978;100(2):253-254. doi:10.1115/1.3448656.
FREE TO VIEW
Abstract
Topics: Fluids , Vortices , Wind
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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