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RESEARCH PAPERS

J. Fluids Eng. 1986;108(3):279-288. doi:10.1115/1.3242575.

Holographic techniques are used in many fields of science and engineering including flow observation. The purpose of this paper is to review applications of holography to multiphase flow study with emphasis on gas-solid and gas-liquid two-phase flows. The application of holography to multiphase flow has been actively explored in the areas of particle sizing in particulate flows and nuclei population measurements in cavitation study. It is also recognized that holography holds great potential as a means of visualizing dynamic situations inherent in multiphase flows. This potential has been demonstrated by holographic flow visualization studies of coal combustion processes in gas-solid flows, gas-liquid two-phase critical flow measurements, and flashing flows in a nozzle. More effective and refined holographic techniques as well as efficient image processing methods are very much in need to facilitate and enhance the understanding of complex physical phenomena occurring in multiphase flows.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):289-296. doi:10.1115/1.3242576.

This paper is the result of our research into the twisted S -shaped bend diffuser—the so-called coiled bend diffuser. It is a diffuser with a centerline in the shape of a twisted “S .” Our studies show that the performance characteristics of this bend diffuser are greatly improved when interaction by the bend elements generates an adequate secondary flow inside the diffuser. Full consideration was given to the influence of the divergent angle of the bend elements, consisting of the diffuser or curvature radius ratio of the bend, on these performance characteristics. The relation between diffuser performance and internal flow also was studied. Some guidelines for designing such a high performance diffuser is given.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):297-303. doi:10.1115/1.3242577.

This paper describes the relation between bend diffuser characteristics and internal flow. Diffusers were bent into U and snake shapes within the limitation of a single plane. In these experiments, area ratio, divergent angle and curvature radius ratio of bend elements were varied. Five types of inlet velocity profiles also were used, and their effects on diffuser performance and internal flow were investigated in detail. The following is a report on the fruitful and interesting results we have obtained.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):304-312. doi:10.1115/1.3242578.

A numerical simulation of propagating stall in a linear cascade of airfoils at high Reynolds numbers is conducted using a vortex method which was first developed by Spalart [7] for this problem. In this approach, the vorticity is discretized into a large collection of vortex blobs whose motion is tracked in time by the use of a well-known vortex tracing algorithm based on the Euler equation. The near-wall effects of viscosity are accounted for by the creation of discrete vortex sheets at the boundaries of the airfoils consistent with the no-slip condition. These boundary vortices are then released into the flow field downstream of the separation points which are obtained from a boundary-layer routine. Calculations are presented for a variety of flow geometries. It is demonstrated that (for a given cascade of airfoils, disturbance wavelength, and stagger angle) several different flow regimes are obtained: Attached flow at lower angles of attack and a chaotic deep stall configuration at larger angles of attack with a narrow intermediate range of such angles where propagating stall occurs. The physical characteristics of this propagating stall are parameterized and a quantitative study of the effects of camber and imposed wavelength is conducted. Comparisons are made with previous theoretical and experimental studies.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):313-320. doi:10.1115/1.3242579.

This paper presents detailed information on the three-dimensional flow field in a realistic low aspect ratio, high turning nozzle vane design which incorporates end-wall contouring and which has been tested over a range of exit Mach number from subsonic up to the design value at mean section of 1.15. The experimental results, in the form of nozzle surface pressure distributions as well as surveys of pressure losses and flow angles at exit, are compared with those calculated by a three-dimensional flow analysis. The effects of exit Mach number on the measured nozzle performance are also presented.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):321-324. doi:10.1115/1.3242580.

Experiments were carried out on air in air axisymmetric free jets having parabolic profiles at the nozzle exit. The range of Reynolds numbers investigated was from 2342 to 11,000 and transition from laminar to turbulent flow was observed. The development of the laminar mean velocity profiles agrees well with that predicted from solution of the continuity and momentum equations using an explicit finite-difference technique of the Dufort-Frankel type. Some observations are made of the transition from laminar to turbulent flow using hot-wire turbulence measurements, and an empirical equation for the location of the transition is given.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):325-330. doi:10.1115/1.3242581.

Airflow in fully developed turbulent state between two parallel plates was accelerated through a linearly converging section, and then it flowed into a parallel-plate channel again. The Reynolds number 2hu m /ν was 10,000 and the acceleration parameter K in the accelerating section was 8 × 10−6 . Fluctuations of streamwise velocity as well as time-mean velocity profiles were measured at ten traversing stations located along the test channel by a hot-wire anemometer. It was found that the flow, partly laminarized in the accelerating section, continued to laminarize in the first part of the downstream parallel-plate section and then the reversion to turbulence occurred in the way similar to the case of natural transition in a pipe, where the transition proceeds through a regime of the so-called turbulent slug flow.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):331-337. doi:10.1115/1.3242582.

The enhancement of widening rate and turbulence intensity in a turbulent plane jet, due to an acoustic disturbance are considered. Detailed data at a representative Strouhal number suggest a well organized symmetric structural array in the initial region of the flow. These highly organized flow structures act as efficient agents in the transport of energy to the fine-grained turbulence, leading to greater diffusivity, enhanced turbulence and an increase in widening. The data also suggest significant differences in the underlying structure of the natural and excited jet flows, hence putting in jeopardy any generalization of coherent motions especially excited to facilitate their study.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):338-342. doi:10.1115/1.3242583.

Self-excited shear-layer oscillations are observed in the cavity flows of a multi-cavity channel when the mean velocity through the channel exceeds a critical value. These coherent shear-layer oscillations appear as one or sometimes two selectively-amplified frequencies in the Fourier-analyzed signals of hot-film gauges that are sintered into the channel walls. At a constant velocity above the critical velocity, the self-excited oscillations are present in only a few cavities. Downstream from these cavities there are oscillations in the cavity flows but one or two selectively-amplified frequencies are not observed. The self-excited oscillations move upstream and the selectively-amplified frequency increases as the mean velocity through the channel is increased.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):343-347. doi:10.1115/1.3242584.

Experiments were performed to determine the effect of roughness on flow through randomly packed beds of spheres. Three different packings were investigated, one of smooth spheres, and two others composed of spheres with roughness elements added to the surface. The relative roughness, defined as the height of the added elements divided by the diameter of the smooth spheres, was .012 and .026 for these two cases. The experiments covered a range of Reynolds numbers based on the sphere diameter from near unity where the flow is dominated by viscosity to 1600 where the flow is dominated by inertia. It was found that the pressure drop is substantially increased by the presence of surface roughness over the entire range of Reynolds numbers studied. The observed behavior is quite different from that which has been proposed previously by drawing analogy with flow in rough pipes, since the flow at low Reynolds number as well as high Reynolds number was affected by roughness.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):348-353. doi:10.1115/1.3242585.

This paper presents a new method for the three-dimensional elliptic solution of the Navier–Stokes equations. It is based on the streamlike-function vorticity formulation which was developed by the authors to study the development of secondary velocities and streamwise vorticity for inviscid flows in curved ducts. This formulation is generalized for viscous flows and used to predict the development of internal three dimensional flow fields. The computed results are presented and compared with experimental measurements for the three-dimensional viscous flow in a straight duct.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):354-359. doi:10.1115/1.3242586.

The propagation of a normal shock wave into a quiescent oxygen gas seeded with carbon particles is studied. Due to the elevated postshock temperature the carbon particles ignite and burn until they disappear. For evaluating the effect of the burning carbon particles on the postshock-wave flow field, i.e., the relaxation zone, the conservation equations for a steady one-dimensional reactive suspension flow are formulated and solved numerically. The solution was repeated for a similar inert suspension flow. Comparing the two solutions revealed that the carbon burning has a major effect on the suspension properties in the relaxation zone and on the eventually reached postshock equilibrium state. For example, much higher temperatures and velocities are obtained in the reactive suspension while the pressure is lower than in a similar inert case. Longer relaxation zones are obtained for the reactive suspension.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):360-365. doi:10.1115/1.3242587.

A parametric study was conducted regarding the effects of the initial carbon concentration, the initial carbon particle diameter, the shock wave Mach number and the preshock suspension pressure on the suspension behavior in the relaxation zone. The suspension was composed of oxygen gas seeded with small carbon particles. It was found that changing either the initial carbon concentration or the shock wave Mach number has a marked effect on the suspension behavior in the relaxation zone and on the eventually reached postshock equilibrium state. Changes in the initial carbon particle diameter (at a constant shock wave Mach number and carbon concentration) has no effect on the postshock equilibrium state, but it does affect the way in which the suspension reaches this equilibrium state. Changes in the preshock suspension pressure has only minor effects on the suspension behavior in the relaxation zone.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):366-372. doi:10.1115/1.3242588.

Many recent experiments have shown the significance of cavitation nuclei, i.e., gas bubbles and/or particulate; however, progress in making quantitative predictions of cavitation depends upon some knowledge of cavitation nuclei properties such as shape, size distribution and concentration. Thus, research has also been concerned with developing measuring systems that give the statistics of the cavitation nuclei distribution. There are many different systems currently being developed; however, only the accuracy and application of the light-scattering technique initially developed by Keller is addressed in this paper. A model is formulated based on appropriate statistical analysis that defines the accuracy for a given sample size. Very good agreement has been found between microbubble distributions measured with the light-scattering system and with holography. Microbubble distribution data were obtained in the 305 mm water tunnel for different air content levels, tunnel static pressures and several tunnel velocities. These data are compared to nuclei distributions obtained at other facilities.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):373-376. doi:10.1115/1.3242589.

Cavitation phenomena were studied in the shear layer behind a two-dimensional sharp-edged plate. Observations were made under stroboscopic light and by flash photography. The first traces of cavitation appear as a series of narrow long axial “strings” suggesting that the major contributor to cavitation inception is the longitudinal (axial) secondary shear layer eddy structure. In a more developed state the cavitation takes the form of a spanwise large eddy structure but the axial “strings” are still evident. The local cavitation inception indices based on the local velocity and pressure scatter between 1.0 and 1.4 when the water is saturated with dissolved air and vary between 0.8 and 1.2 when the air content is reduced to about 30 percent of saturation. These results are in good agreement with a collection of other measurements behind sharp-edged disks that display a consistent increase of the inception index with the Reynolds number.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Fluids Eng. 1986;108(3):377-379. doi:10.1115/1.3242590.
Abstract
Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1986;108(3):379-382. doi:10.1115/1.3242591.
Abstract
Commentary by Dr. Valentin Fuster

DISCUSSIONS

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