Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1982"

An Album of Fluid Motion

Abstract: Keywords: visualisation de l'ecoulement ; tourbillon ; dynamique des : fluides ; aubes ; cylindre ; instabilite ; ecoulement : secondaire Note: moult photos Reference Record created on 2005-11-18, modified on 2016-08-08

Contributions to the Theory of Single-Sample Uncertainty Analysis

Abstract: Uncertainty Analysis is the prediction of the uncertainty interval which should be associated with an experimental result, based on observations of the scatter in the raw data used in calculating the result. In this paper, the process is discussed as it applies to single-sample experiments of the sort frequently conducted in research and development work. Single-sample uncertainty analysis has been in the engineering literature since Kline and McClintock's paper in 1953 [1] and has been widely, if sparsely, practiced since then. A few texts and references on engineering experimentation present the basic equations and discuss its importance in planning and evaluating experiments (see Schenck, for example [2]). Uncertainty analysis is frequently linked to the statistical treatment of the data, as in Holman [3], where it may be lost in the fog for many student engineers. More frequently, only the statistical aspects of data interpretation are taught, and uncertainty analysis is ignored. For whatever reasons, uncertainty analysis is not used as much as it should be in the planning, development, interpretation, and reporting of scientific experiments in heat transfer and fluid mechanics. There is a growing awareness of this deficiency among standards groups and funding agencies, and a growing determination to insist on a thorough description of experimental uncertainty in all technical work. Both the International Standards Organization [4] and the American Society of Mechanical Engineers [5] are developing standards for the description of uncertainties in fluid-flow measurements. The U. S. Air Force [6] and JANNAF [7] each have handbooks describing the appropriate procedures for their classes of problems. The International Committee on Weights and Measures (CIPM) is currently evaluating this issue [8]. The prior references, with the exception of Schenck and, to a lesser extent, Holman, treat uncertainty analysis mainly as a process for describing the uncertainty in an experiment, and end their discussion once that evaluation has been made. The present paper has a somewhat different goal: to show how uncertainty analysis can be used as an active tool in developing a good experiment, as well as reporting it. The concepts presented here were developed in connection with heat transfer and fluid mechanics research experiments of moderately large size (i.e., larger than a breadbox and smaller than a barn) and which may frequently require three

Review—Numerical Models for Dilute Gas-Particle Flows

Abstract: The significant nondimensional parameters relating to dilute gas-particle flows are defined, and a review of the essential features of gas-particle flows from the point of view of model development is presented. Also, the various models that have appeared for one-dimensional and two-dimensional flows are examined, and the advantages and disadvantages of the trajectory and two-fluid models are considered. It is concluded that the most difficult aspect of model development for gas-particle flows is the adequate description of particle dispersion due to turbulence, and that more experimental and complementary numerical work are needed in this area.

Curved Ducts With Strong Secondary Motion: Velocity Measurements of Developing Laminar and Turbulent Flow

Abstract: Two orthogonal components of velocity and associated Reynolds stresses are determined in a square-sectioned, 90 degree bend of 2.3 radius ratio by utilizing laser-Doppler velocimetry for Reynolds numbers of 790 and 40,000. Results show that boundary layers at the bend inlet of 0.25 and 0.15 of the hydraulic diameter create secondary velocity maxima of 0.6 and 0.4 of the bulk flow velocity, respectively. It is concluded that the boundary layer thickness is important to the flow development, mainly in the first half of the bend, especially when it is reduced to 0.15 of the hydraulic diameter. Smaller secondary velocities are found for turbulent flow in an identical duct with a radius ratio of 7.0 than in the strongly curved bend, although their effect is more important to the streamwise flow development because of the smaller pressure gradients. In addition, the detail and accuracy of the measurements make them suitable for evaluation of numerical techniques and turbulence models.

Transient characteristics of a centrifugal pump during stopping period

Abstract: A theoretical and experimental study has been made on the transient characteristics of a centrifugal pump during its rapid acceleration from standstill to final speed Instantaneous rotatinal speed, flow-rate, and total pressure rise are measured for various start-up schemes Theoretical calculations for the prediction of transient characteristics are developed and compared with the corresponding experimental results As the results of this study, it becomes clear that the impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between dynamic and quasi-steady characteristics of turbopump during its starting period

On the prediction of swirling flowfields found in axisymmetric combustor geometries

Abstract: The paper reports research restricted to steady turbulence flow in axisymmetric geometries under low speed and nonreacting conditions. Numerical computations are performed for a basic two-dimensional axisymmetrical flow field similar to that found in a conventional gas turbine combustor. Calculations include a stairstep boundary representation of the expansion flow, a conventional k-epsilon turbulence model and realistic accomodation of swirl effects. A preliminary evaluation of the accuracy of computed flowfields is accomplished by comparisons with flow visualizations using neutrally-buoyant helium-filled soap bubbles as tracer particles. Comparisons of calculated results show good agreement, and it is found that a problem in swirling flows is the accuracy with which the sizes and shapes of the recirculation zones may be predicted, which may be attributed to the quality of the turbulence model.

Two-Way Coupling Effects in Dilute Gas-Particle Flows

Abstract: A general analysis of gas-particle flows is presented using the hypotheses of a number of particles large enough to consider the solid phase as a continuum and of a volume fraction small enough to consider the suspension as dilute. It is found that the Stokes number (Sk) and the particle loading ratio (beta) are the basic parameters governing the flow. For small values of beta and large values of Sk it is possible to disregard the effect of the particles on the fluid field and simple numerical models based on one-way coupling may be used. However, for larger values of beta and lower Sk, both the fluid and the solid phase flow fields (and as a consequence the overall quantities such as pressure drop and energy dissipation) are determined to be substantially affected by the interphase coupling. A computational model accounting for two-way coupling is presented and found to provide for an accurate simulation. In addition, correlations are developed for determining the pressure drop which increases as a function of beta and Sk, and it is suggested that these correlations may be of practical interest for the investigation of flow metering systems.

Numerical Solution for Laminar Two Dimensional Flow About a Cylinder Oscillating in a Uniform Stream

Abstract: A finite difference model is presented for viscous two dimensional flow of a uniform stream past an oscillating cylinder. A noninertial coordinate transformation is used so that the grid mesh remains fixed relative to the accelerating cylinder. Three types of cylinder motion are considered: oscillation in a still fluid, oscillation parallel to a moving stream, and oscillation transverse to a moving stream. Computations are made for Reynolds numbers between 1 and 100 and amplitude-to-diameter ratios from 0.1 to 2.0. The computed results correctly predict the lock-in or wake-capture phenomenon which occurs when cylinder oscillation is near the natural vortex shedding frequency. Drag, lift, and inertia effects are extracted from the numerical results. Detailed computations at a Reynolds number of 80 are shown to be in quantitative agreement with available experimental data for oscillating cylinders.

Scale Effects in the Dynamic Transfer Functions for Cavitating Inducers

Abstract: Dynamic transfer functions for two cavitating inducers of the same geometry but different size are presented, compared, and discussed. The transfer functions for each inducer indicate similar trends as the cavitation number is decreased. The nondimensional results for the two sizes are compared with themselves and with theoretical calculations based on the Bubbly Flow Model (reference [2]). All three sets of results compare well and lend further credance to the theoretical model. The best values of the two parameters in the model (K and M) and evaluated recommended for use in applications.

Fluid dynamics of inducers - A review

Abstract: The objective of this paper is to review the experimental and analytical investigations on the fluid dynamic aspects of noncavitating inducers. Various analyses available for the prediction of the flow field, starting from the simple radial equilibrium analysis to the numerical solution of exact three-dimensional inviscid and viscid flow equations, are reviewed. The experimental data on the overall inducer performance, rotor blade passage measurements, and boundary layer on rotor blades are critically examined. Some of the available data have been reinterpreted to provide suitable guidance to the designer. The review and the concluding remarks include a global view of the state-of-the-art and applicability of the research to design, and some viewpoints on the analysis and design of inducers.

Laminar Flow in a Cylindrical Container With a Rotating Cover

Abstract: Unsteady and steady flow in a cylindrical chamber with a rotating cover has been studied for two Reynolds numbers and three aspect ratio values. The structure of the velocity and pressure fields in the apparatus is described. Primary and secondary volumetric flow rates and torque coefficients are also calculated for all six cases solved.

Diagnostic Measurements of Fuel Spray Dispersion

Abstract: Plume shape, vaporization, droplet-size distribution, and number density of a solid-cone fuel spray were studied with both conventional and novel measurement techniques. Minor differences in spray plume shape were observed by measurements with photography, pulsed laser shadowgraphy, and in-line infrared spectroscopy. Laser Mie scattering showed the dispersion of small numbers of droplets beyond spray boundaries as determined by other measurements. A new optical method for nonintrusive, local, time-averaged measurement of vapor concentration, droplet-size distribution and number density within an axisymmetric spray is introduced. For the spray studied this method showed that vapor is confined to the spray plume and that vapor concentration and the concentration of small-diameter droplets exhibit analogous behavior.

Equilibrium Parameters for Two-Dimensional Turbulent Wakes

Abstract: The parameters characterizing a plane turbulent wake in its equilibrium state of development are determined on the basis of experiment and analysis. Measurements are made in an open-circuit suction-type wind tunnel with a contraction ratio of about 10 and a test-section of about 30 cm sq and 4.27 m long. Less than 1.5% variation in wind speed along the test section is attained by applying suitable divergence for the boundary layer growth. A two-dimensional wake is created behind a twin plate configuration at a freestream velocity of 21.3 m/s. The freestream turbulence level at this speed is about 0.15%.