Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1978"

A Correlation for Laminar Hydrodynamic Entry Length Solutions for Circular and Noncircular Ducts

Abstract: 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.

Experiments on the Dynamic Behavior of Cavitating Pumps

Abstract: 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.

Turbulence Measurements in Boundary Layers Along Mildly Curved Surfaces

Abstract: This paper presents results of turbulence measurements in boundary layers over surfaces of mild longitudinal curvature. The study indicates that convex wall curvature decreases both the length and velocity scales of turbulent motions, whereas concave curvature has the opposite effect. White being qualitatively similar to those brought about by stronger wall curvature, mild curvature effects are found to be much larger than what one expects from a linear interpolation between the effects of zero and strong curvature. It is also observed that curvature has a relatively larger effect on the Reynolds shear stress than on the turbulent kinetic energy. The present study, however, indicates that it is still possible to use some of the phenomenological models of turbulence (e.g., the mixing length model, the Prandtl-Kolmogorov model), provided an appropriate curvature model is available for describing the effect of curvature on the relevant length scale in the boundary layer. The present data are used to test the validity and limitations of such a curvature model (based on an analogy between streamline curvature and buoyancy) currently in use.

Vortex Sheet Analysis of the Giromill

Abstract: A two-dimensional analysis of the performance and flowfield of the Giromill is presented. The Giromill is a vertical-axis wind turbine with straight blades that are articulated to produce maximum energy extraction from the wind. It is found that the power coefficient and windwise force coefficient for the Giromill have the same limit as obtained for the horizontal-axis wind turbine. A cross-wind force is also obtained with this type of wind turbine. The cross-wind force is of second order and decreases with tip speed. Streamlines and velocity profiles are illustrated for several loading conditions.

The Computation of Optimum Pressure Recovery in Two-Dimensional Diffusers

Abstract: A method is presented for computation of optimum recovery at fixed length (Cp *) in two-dimensional diffusers with incompressible flow and turbulent inlet boundary layers. Since Cp * lies in the zone of transitory stall, the method involves computation of not only attached but also detaching and detached turbulent boundary layers. The results agree with available data to the level of the uncertainty in the data. The model is zonal in character. Results suggest that the most important feature in computing detaching flows is the treatment of the interaction between the outer (inviscid) flow and the boundary layer; the use of velocity-profile forms that represent average back-flows adequately is also important.

Effect of Polymer Additives on Cavitation Development and Noise in Water Flow Through an Orifice

Abstract: The cavitation behavior and the shock pressure were experimentally investigated in dilute aqueous solutions of polymer flowing through an orifice, and the following facts were observed: (i) Very small quantities of polymer additives effectively suppressed both the inception and the development of cavitation, (ii) nonspherical cavitation bubbles were observed at any polymer concentration tested here, and the nonsphericity tended to increase with concentration, (iii) the spectral frequencies of shock pressures were principally confined within the audio frequency range. With an increase in concentration, the energy of the pressures drastically decreased and the frequency range shifted downwards.

Symmetric Sink Flow Between Parallel Plates

Abstract: Steady, laminar, incompressible flow converging radially between two stationary disks is investigated numerically as a continuously developing flow problem under the internal boundary layer approximations. At dimensionless radii much greater than one the velocity profile becomes parabolic and invariant, but at radii less than one a typical external boundary layer evolves close to the wall with an approximately uniform core region; and the boundary layer thickness decreases from one-half the disk spacing to values proportional to the local radii as the flow accelerates. At large radii the friction factor approaches the classic value obtained for fully developed flow between infinite plates, but at small radii it approaches the constant 2.17/..sqrt..R/sub 0/, where R/sub 0/ is an overall Reynolds number based on the volumetric flow rate and the disk spacing and is independent of radius. Tabular and graphical results are provided for the intermediate range of radii, where both viscous and inertial effects are important and exact analyses are not available.