0


RESEARCH PAPERS

J. Fluids Eng. 1981;103(4):491-496. doi:10.1115/1.3241757.

A novel flow configuration was explored for the study of the behavior of drag reducing polymers. A screw pump consisting of a smooth cylinder and a concentrically placed screw was used to create a strongly three-dimensional but essentially laminar flow. In the first phase of the study, the static pressure head developed by the screw pump was measured as a function of polymer concentration (polyox 10 to 100 ppm in water). A large increase of the developed head was observed that behaved in an analogous manner to drag reduction as far as concentration and straining of the polymer solution was concerned. In the second phase of the study, a new apparatus was constructed and the additional parameter of a superimposed through flow was included and the degree of failure of the superposition principle was established. Sensitivity of the phenomenon to chemicals like HCl, HNO3 , and NaOH in the polymer solution was also studied. When the effect of these chemicals on the polymer solution flow behavior was presented in terms of the pH value of the polymer solution, it showed a similar trend to those observed in drag reduction.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):497-502. doi:10.1115/1.3241758.

Pressure fluctuations on a small sphere in a periodically pulsating jet are measured in relation to the study of measurements of instantaneous static pressure in unsteady flows, where the wavelength of unsteadiness is much longer than the probe dimensions and the amplitude of the velocity fluctuation is small. Both the instantaneous pressure on the sphere and the instantaneous velocity of the flow field in the absence of the sphere are measured by means of periodic sampling and averaging techniques. The measured surface pressure is expressed in terms of the measured velocity and acceleration of the flow. A simple inviscid theory is developed and compared with the experimental results. An application of the present results to the correct determination of instantaneous static pressure in unsteady flows is discussed.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):503-508. doi:10.1115/1.3241759.

In an attempt to explore the existence of large-scale coherent structures in the nearly self-preserving region of an axisymmetric free air jet, a 2.54 cm air jet at a Reynolds number ReD = 6.8 × 104 has been investigated for x/D≥40 via both long and short time-averaged space-time correlation measurements. Conventional space-time correlation data with probe separations in the stream wise direction by as much as 25 diameters suggest the passage of large-scale organized structures. The radial extent of these structures is about one local jet diameter, and the azimuthal extent is about a quadrant of the cross-section. Recurring quasi-periodic patterns are observed in the time series of short time-averaged correlations between longitudinal velocity fluctuations obtained with two arrays of hot-wires separated in the streamwise direction. These orderly patterns provide direct evidence for the existence of these structures. Quantitative details of these structures are now being investigated.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):534-542. doi:10.1115/1.3241762.

The net positive suction head (NPSH) requirements for a pump are determined by the combined effects of cavitation, fluid properties, pump geometry, and pump operating point. An important part of this determination is the temperature depression (ΔT) defined as the difference between ambient liquid temperature and cavity temperature. Correlations are presented of the temperature depression for various degrees of developed cavitation on venturis and ogives. These correlations, based on a semiempirical entrainment theory, express ΔT in terms of the dimensionless numbers of Nusselt, Reynolds, Froude, Weber, and Péclét, and dimensionless cavity length (L/D). The ΔT data were obtained in Freon 114, hydrogen, and nitrogen for the venturis and in Freon 113 and water for the ogives.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):543-549. doi:10.1115/1.3241763.

Flow conditions surrounding bubble-ring cavitation inception on hemispherical headforms are analyzed with respect to the initiation of air diffusion into microbubbles as is observed to occur at fixed positions in the boundary layer. Fairly recent observations have shown this phenomenon to occur in the laminar separation bubble on the body. The analysis shows, in agreement with the body of experimental evidence now available, that gaseous growth must be preceded by a period of vaporous growth starting in regions of low pressure upstream of the laminar separation bubble. It also appears that the most favorable condition for the initiation of gaseous growth should occur when a typical vapor bubble reaches its maximum radius as it enters the laminar separation bubble. The conditions for the initiation of subsequent gaseous growth, once the cavitation bubble is stabilized in the laminar separation zone, are more demanding. Nevertheless, it is found that the liquid in the water surrounding the bubble in the separation zone is definitely supersaturated for most flows of experimental or practical interest. Therefore, gaseous growth, as well as vaporous growth, is definitely to be associated with the onset of bubble-ring cavitation on both theoretical and experimental grounds.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):551-556. doi:10.1115/1.3241766.

An analytical method for predicting the cavitation occurrence is developed applying an analogy with the choking condition of two-phase flow. The effects of the presence of inert gas and thermodynamic depression on the inception of cavitation are estimated in various liquids such as water, freon, hydrogen, and sodium. It is clearly shown that the thermodynamic effects are remarkable in the case of low flow velocity in fluids with small Spraker’s B-factor (<1.0m−1 ). Also, the predicted values show reasonable agreement with some experimental data.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):557-563. doi:10.1115/1.3241767.

Hydrogen bubbles were generated as cavitation nuclei and their distributions were measured. The number and size distribution of bubble cavities generated on axisymmetric bodies was calculated and compared with experimental results. The measured size distribution of bubble cavities agreed qualitatively with the calculated value, but the total number of cavities was about one half of the calculation. The role of stream nuclei on the inception of sheet cavity was investigated experimentally. Without added nuclei, the value of the incipient cavitation number σi showed a large scattering, whereas with added nuclei the scattering became fairly small and σi converged to the upper limit of that when no nuclei were added. σi with added nuclei also coincided with the desinent cavitation number σd , and σd remained unchanged by adding nuclei.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):564-575. doi:10.1115/1.3241768.

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under noncavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation, depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to noncavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):577-582. doi:10.1115/1.3241772.

The present paper reviews several pertinent papers about the onset of bubble-ring cavitation on hemispherical headforms in which a laminar bubble is present. From this review, a likely sequence of events for cavitation inception, or desinence, can be discerned. When this sequence is postulated, the observational basis for each event is discussed. Once the physical aspects of the inception process have been noted, a mathematical formulation of key relationships required to establish an inception criterion can be undertaken. From these results, a quantitative criterion for the inception of bubble ring cavitation is stated and we give a discussion which interprets this possible inception criterion for future use. The use of this criterion in a theory of inception and a comparison of analytical and experimental results is left to a future publication.

Topics: Cavitation , Bubbles
Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):583-589. doi:10.1115/1.3241773.

An analytical model for the phase distribution mechanisms in fully developed turbulent two-phase flow in channels of arbitrary cross sections has been derived. The model has been applied to the special case of cylindrical pipe flow, and compared with existing data. It has been found that, for bubbly flow, it is the distribution of the liquid phase turbulence which determines the void distribution. Furthermore, the void distribution depends on the anisotropic nature of the turbulent two-phase flow.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):590-594. doi:10.1115/1.3241774.

A pressure probe which facilitates measurement of mean flow quantities in three dimensions simultaneously is described. Its main feature is a tip shaped like the frustrum of a pyramid, with three-side holes equispaced around a central hole. Flow quantities are related to the hole pressures by calibration, so that the tedious procedure of nulling or pressure balancing can be avoided. The advantages of this configuration over five-hole probes are that a simpler probe with a smaller head results, fewer pressures need to be recorded and because no redundant information is collected, determination of the dependent flow quantities is simpler and unambiguous.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):595-603. doi:10.1115/1.3241775.

It has been proposed to protect the structural walls of a future laser fusion reactor with a curtain or fluid-wall of liquid lithium jets. As part of the investigation of this concept, experiments have been performed on planar sheet water jets issuing vertically downward from slit nozzles. The nozzles were subjected to transverse forced harmonic excitation to simulate the vibrational environment of the laser fusion reactor, and experiments were run at both 1 atm and at lower ambient pressures. Linear stability theory is shown to predict the onset of the unstable regime and the initial spatial growth rates quite well for cases where the amplitudes of the nozzle vibration are not too large and the waveform is nearly sinusoidal. In addition, both the linear theory and a simplified trajectory theory are shown to predict the initial wave envelope amplitudes very well. For larger amplitude nozzle excitation, the waveform becomes highly nonlinear and nonsinusoidal and can resemble a sawtooth waveform in some cases; these latter experimental results can only be partially explained by existing theories at the present time.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):605-608. doi:10.1115/1.3241779.

A pulsed core jet is one consisting of a steady annular flow with a core, the mass flow of which is unsteady. The combined jet exhausts into a still environment. The velocity field and entrainment characteristics for such a jet have been measured for various mass flow ratios of pulsed-to-steady flow and several frequencies of pulsation. Results show the radial distribution of mean velocity to be similar to those of steady jets except very close to the nozzle, the decay of the centerline mean velocity to be less than that of steady jets, and the entrainment to be larger than that of steady jets but less than fully pulsed ones. No significant sensitivity to frequency of pulsation was observed, but the velocity field is strongly dependent on the ratio of core flow to annular flow.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):609-614. doi:10.1115/1.3241780.

It is shown that periodic angular oscillations can be forced on a jet issuing from a nozzle based on the Coanda effect by alternate blowing from the two sides. The influence of the various geometric and dynamic parameters such as the jet width, the blowing direction, the blowing generating pressure, the jet velocity, and frequency has been investigated. The angular deflection can conveniently be controlled by the blowing pressure.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):615-623. doi:10.1115/1.3241781.

Data for smooth concentric annuli having an overall −25 to +35 percent scattter about the Colbrook prediction for smooth tubes, along with calculation techniques, are reviewed. It is shown that the accepted methods of Meter and Bird [22], and of Rothfus, Monrad, and Senecal [28] deviate substantially from the correct limit for small gaps. Further, neither correctly predicts the data trends with decreasing radius ratio. It is demonstrated that the theoretically determined laminar equivalent diameter which provides similarity in laminar flow for round tubes and concentric annuli also provides similarity in turbulent flow. The resultant equations behave correctly at both circular and flat plate limits. The combined results, when applied to objectively confirmed data, show a reduction in the observed data scatter to approximately ± 5 percent.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):624-630. doi:10.1115/1.3241782.

This paper presents experimental wind-tunnel data that show the universal logarithmic velocity profile for zero-pressure-gradient turbulent boundary layer flows is valid for values of momentum-deficit Reynolds numbers Rθ as low as 600. However, for values of Rθ between 425 and 600, the von Kármán and additive constants vary and are shown to be functions of Rθ and shape factor H. Furthermore, the viscous sublayer in the range 425<Rθ <600 can no longer maintain its characteristically small size. It is forced to grow, due to viscous effects, into a super sublayer (6-9 percent of the boundary layer height) that greatly exceeds conventional predictions of sublayer heights.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):631-637. doi:10.1115/1.3241783.

Results are presented from an experimental study of the lift, drag, pitching moment, and flow field of a series of rounded edge simple bluff bodies of various cambers and tapers. The bodies were proportioned to be similar to those of idealized ground vehicles such as automobiles, vans, and trucks. The models were tested with and without simulated wheels, underbody roughness, and proximity to a stationary and moving ground plane. The pitch angle was varied at zero yaw angle. The force and moment coefficients and flow visualization studies indicated the existence and importance of flow regimes characterized by a pair of trailing vortices on the leeward side of the body similar to those found over an inclined body of revolution and over slender delta wings. These flows can suppress bubble-type separation. The effects of a rough underbody are generally detrimental although less so if the rough surface is on the windward side. A moving ground plane was found to give significantly different lift and drag for small ground clearances characteristic of actual road vehicles.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):639-643. doi:10.1115/1.3241787.

It is shown that the method of hodograph transformation coupled with numerical calculations can be an effective method to account for the effect of gravity on certain two-dimensional potential flow problems. Specifically, the problem of a horizontal channel flow discharging an incompressible fluid through a circular-arc contraction has been worked out to illustrate the procedure. The upstream approaching flow conditions, the opening height, and also the downstream free surface flow must be compatible with each other. They must be determined through iterations. The method of iteration is also presented and discussed.

Commentary by Dr. Valentin Fuster

REVIEW ARTICLES

J. Fluids Eng. 1981;103(4):509-519. doi:10.1115/1.3241760.

A small segment of the engineering community was surveyed to obtain their judgment regarding the long-range needs for basic research in fluid mechanics. This segment consisted of approximately 600 persons active in heat transfer and fluid mechanics committees within The American Society of Mechanical Engineers. Close to 200 persons responded giving useful information relating to needed research. Of the many topics identified, six generic areas stood out: turbulence; multiphase flows; fluid structure interactions; boundary layer effects; biological, geological, and environmental fluid flow; and the need for new facilities and improved instrumentation. These six areas were summarized and an initial estimate of the research priorities presented to the DOE-ESCOE workshop on Fluid Dynamics and Thermal Processes held at the University of Kentucky on February 1–2, 1979. The priorities were modified and the final results of the workshop included herein.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):520-533. doi:10.1115/1.3241761.

Although turbulent flow separation is an old topic, little credible information is available on the flow details that must be understood to predict flows of this type. Until the last decade, there was little serious effort to develop and use experimental techniques that give unambiguous results. Consequently, flow models that are based on valid data are not well developed. Furthermore, the terminology used in discussing separation has been loosely defined, adding further confusion to the subject. This brief review presents a cross-sectional view of recent experimental techniques and results, development of models for flow prediction, efforts to define a meaningful common terminology to describe the flow, unsteady effects, and efforts to control separation.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

BOOK REVIEWS

J. Fluids Eng. 1981;103(4):644. doi:10.1115/1.3241788.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1981;103(4):644-645. doi:10.1115/1.3241789.
FREE TO VIEW
Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In