bluuebunny/crossref_metadata_2025 huggingface dataset:
A Re-Evaluation of Schlichting’s Surface Roughness Experiment
Authors: Coleman H. W. , Hodge B. K. , Taylor R. P.
Published: October 2009

A re-evaluation of the skin friction coefficient and equivalent sand roughness data reported by Schlichting in 1936 on fourteen rough surfaces is presented. Several assumptions made during the original data reduction are shown to have significant effects on the final results. Additional data and analytical results published since 1936 allow the use of more precise assumptions and enable a re-evaluation of the original data. Corrected results are presented for seventy-nine runs reported by Schlichting on the fourteen surfaces containing spherical, spherical segment and conical roughness elements with various spacings. The original skin friction coefficients are shown to be higher than the corrected values by amounts ranging from 0.5 to 73 percent, while the original equivalent sand roughness values are higher than the corrected ones by 26 to 555 percent. Roughness Reynolds numbers determined using the corrected data indicate that sixteen of the runs on three surfaces were probably in the transitionally rough regime, not the fully rough regime as originally reported.
Wall Confinement Effects for Spheres in the Reynolds Number Range of 30–2000
Authors: Modi V. J. , Akutsu T.
Published: October 2009

The paper studies in detail the time history of formation, evolution, and instability of the vortex ring, associated with a family of spheres in the Reynolds number range of 30–2000 and with a blockage ratio of 3–30 percent. The flow visualization results are obtained using the classical dye injection procedure. Simultaneous measurements of pressure distribution on the surface of the sphere help establish correlation between the onset of instability of the vortex ring and the surface loading. The results suggest that the influence of the Reynolds number on the surface pressure distribution is primarily confined to the range Rn < 1000. However, for the model with the highest blockage ratio of 30.6 percent, the pressure continues to show Reynolds number dependency for Rn as high as 2300. In general, effect of the Reynolds number is to increase the minimum as well as the wake pressures. On the other hand, the effect of an increase in the blockage ratio is just the opposite. The wall confinement tends to increase the drag coefficient, however, the classical dependence of skin friction on the Reynolds number Cd,f ∝ R−1/2, is maintained. The paper also presents useful information concerning location of the separating shear layers as affected by the Reynolds number and blockage. For comparison, available analytical and experimental results by other investigators are also included. Results show that for a given blockage, separation points may move upstream by as much as 20 deg over a Reynolds number range of 100–600. In general, for a given Reynolds number, the wall confinement tends to move the separation position downstream.
Prediction of Propeller Cavitation Noise From Model Tests and Its Comparison With Full Scale Data
Authors: Bark G.
Published: October 2009

This paper deals with the prediction of propeller cavitation noise from model experiments in a cavitation tunnel. The purpose was to investigate the validity of a simple scaling formula for high frequency cavitation noise, and to get information about the influence of test parameters and analysis methods. The results indicate that the scaling formula normally used at low frequencies can, as a first approximation, be used also at high frequencies. Concerning analysis methods it is demonstrated that the noise signals in model and full scale may have different statistical properties, implying that the simple root-mean-square value of the model signal is not always a sufficient basis for prediction of full scale noise.
A Simplified Method of Using Four-Hole Probes to Measure Three-Dimensional Flow Fields
Authors: Sitaram N. , Treaster A. L.
Published: October 2009

A simplified method of using four-hole probes to measure three-dimensional flow-fields is presented. This method is similar to an existing calibration and application procedure used for five-hole probes. The new method is demonstrated for two four-hole probes of different geometry. These four-hole probes and a five-hole probe are used to measure the turbulent boundary layer on a flat plate. The results from the three probes are in good agreement with theoretical predictions. The major discrepancies occur near the surface of the flat plate and are attributed to wall vicinity and velocity gradient effects.
A Numerical Method for Solving Momentum Equations in Generalized Coordinates (Its Application to Three-Dimensional Separated Flows)
Authors: Nakayama A.
Published: October 2009

A finite difference calculation procedure has been developed for the calculations of the three-dimensional fully elliptic flows over irregular boundaries. A simple control volume analysis is introduced to reformulate the momentum equations in the generalized velocity and coordinate system, without resorting to any extensive tensor calculus. The finite difference equations are obtained by discretizing the conservation equations in this generalized system. For a practical application of the present finite difference calculation scheme, calculations are carried out on the three-dimensional separated flow in a converging-diverging rectangular duct. The calculation results reveal an extremely complex nature of the three-dimensional separated flow.
Vortex Shedding in a Linear Shear Flow From a Vibrating Marine Cable With Attached Bluff Bodies
Authors: Peltzer R. D. , Rooney D. M.
Published: October 2009

The present study examines the vortex street wake behavior of a flexible, helically wound, high aspect ratio marine cable in a linear shear flow. Particular attention is paid to the lock-on phenomena associated with uniform and sheared flow past the cable when it is forced to vibrate in the first mode, normal to the flow. An analysis is given of the effects on the vortex shedding and synchronization phenomena that are generated by placing distributions of spherical bluff body shapes along the span of the cable in uniform and sheared flow. The latter geometry is representative of a number of cable system deployments and has special consequencies for strumming in a shear flow. The effectiveness of these attached spheres as strumming-suppression devices is evaluated. Synchronized vibration and/or the presence of the bluff bodies significantly affected the spanwise character of the near wake cellular vortex shedding structure. The spanwise extent of the resonant, vortex-excited oscillations was significantly extended by the presence of the spheres along the cable span. This finding was particularly significant because it meant that the undesirable effects that accompanied synchronization would be extended over a longer portion of the cable span.
From Measurement Uncertainty to Measurement Communications, Credibility, and Cost Control in Propulsion Ground Test Facilities
Authors: Smith R. E. , Wehofer S.
Published: October 2009

In the past several years significant advances have been made in altitude ground test facilities with respect to measurement accuracy and measurement cost control. To a large measure, the advances have been the result of the application of comprehensive measurement uncertainty evaluation programs. This paper discusses the specific measurement evaluation process used in the Engine Test Facility, Arnold Engineering Development Center. To explain this process, the reader is guided through the measurement process for engine thrust, an extremely critical parameter for propulsion performance testing. Although this paper focuses on the measurement of engine thrust, the overall objective is the general measurement evaluation process and its uses. The approach presented can be applied to any type measurement system. First, an overview of the measurement uncertainty methodology and its application in altitude engine test cells is presented. The paper concludes with a discussion of how measurement uncertainty results can be utilized to improve measurement understanding and presents the means to identify factors that must be controlled to achieve a reliable and accurate measurement assessment.
Using Uncertainty Analysis in the Planning of an Experiment
Authors: Moffat R. J.
Published: October 2009

A simple example using convection heat transfer is used to illustrate the use of uncertainty analysis in PLANNING experiments. Major points made are: (i) the choice of test and data-reduction procedure can have important impact on the accuracy of the results, with one procedure better for some conditions and the other better in other ranges; (ii) it is important to specify carefully the level of replication (what is held constant and what varied in a given test), since otherwise an inappropriate value of uncertainty may be generated; (iii) reliable means for cross-checking and/or externally validating the results of an experiment are necessary if predicted uncertainties are to be confirmed; (iv) in experiments where data are reduced by computer, uncertainty analysis can be done by sequential perturbation, using the main data-reduction program itself.
Order of Difference Expressions in Curvilinear Coordinate Systems
Authors: Thompson J. F. , Mastin C. W.
Published: October 2009

The order of finite difference representations on general curvilinear coordinate systems is considered in some detail. It is shown that the uniform grid order is formally preserved on the nonuniform, nonorthogonal grid in the sense of the error behavior with an increase in the number of points. However, the coefficients in the series expansion may become quite large for some point distributions. Several specific distributions are evaluated.
The Instability of a Round Jet Surrounded by an Annular Shear Layer
Authors: Anderson R. , Bejan A.
Published: October 2009

A linear stability analysis of the large-scale structure of a round jet surrounded by an annular shear layer is presented. The study is limited to the developing region near the jet nozzle in the limit Re→∞. The radial dependence of the amplitudes of growing disturbances are examined in order to illustrate the extent to which the disturbances penetrate into the jet and its surroundings. The region influenced by a disturbance is found to be directly proportional to the wavelength of the disturbance. Disturbance measurements made on the jet centerline tend to select for long wavelength disturbances, while measurements made in the shear layer tend to select for short wavelength disturbances. When the shear layer thickness is small compared with the jet radius, the wavelength of the most amplified disturbance scales with the shear layer thickness. As the shear layer thickness increases, this scaling quickly breaks down. This change in scaling appears to be responsible for the transition between the “ripples” which occur near the jet nozzle and the “puffs” which are observed further downstream. Amplified disturbances exhibit a phase lag across the shear layer, which may account for the spade-like structures evident in flow visualizations of turbulent jets.
LDA Measurements in Plane Turbulent Jets
Authors: Ramaprian B. R. , Chandrasekhara M. S.
Published: October 2009

Measurements on the mean and most of the significant turbulent properties of plane isothermal and heated (but essentially “nonbouyant”) jets are reported. The velocity measurements were made using two-component, frequency-shifted Laser Doppler Anemometry (LDA) and the temperature measurements were made using fast-response resistance thermometry. A simple but effective technique was developed for obtaining accurate velocity measurements from the LDA in a nonisothermal environment. These measurements, some of which are the first of their kind, provide an independent data base with which to compare existing hot-wire data on jets. The LDA measurements indicate lower turbulence intensities and lower turbulent fluxes compared to the hot-wire data.
Vortex Shedding From Bluff Bodies in a Shear Flow: A Review
Authors: Griffin Owen M.
Published: October 2009

This paper examines the effects of velocity shear on vortex shedding from stationary and vibrating bluff bodies. Experiments with circular cylindrical bodies and other cross sections such as D-section cylinders and rectangular cylinders, which were limited to conditions with length/diameter ratios less than L/D = 15 to 20, have shown that the spanwise cellular structure of the vortex shedding is dependent upon end conditions. The vortex shedding also is influenced strongly by the shear flow steepness parameter β¯ which is based upon the incident flow velocity gradient. Experimental evidence is available to show that moderate shear levels of practical importance (β¯∼0.01 to 0.015) do not appreciably decrease the probability of occurrence of vortex-excited oscillations for flexible structures and cables. The effects of incident shear on vortex shedding from stationary and vibrating bluff structures in both fluid media should be investigated further for long cylinders which have minimal end boundary effects. More definitive bounds for and details of this fluid-structure interaction are needed for applications in the wind engineering design of buildings and structures, and in the design of marine structures and cable systems.
A Comparison of Three Critical Flow Venturi Designs
Authors: Brown E. F. , Hamilton G. L. , Kwok D. W.
Published: October 2009

Three critical flow venturi designs have been examined from the standpoint of their sensitivity to initial boundary-layer thickness, inlet flow nonuniformity, separation, and transition point location. These sensitivity studies were carried out with a finite-difference computer code which represents a coupled solution of the inviscid potential core and the viscous boundary layer. Since it makes good sense to select a design that is least sensitive to these effects, it is expected that this information will be of interest to potential users of these devices. Differences between the sensitivities of the various designs were found to be small; however, a slight advantage is seen in designs which employ a circular arc entrance section and a circular arc throat.
Coupled Parallel Flows in a Channel and a Bounding Porous Medium of Finite Thickness
Authors: Rudraiah N.
Published: October 2009

The steady laminar flow in a parallel plate channel bounded below by a porous layer of finite thickness and above by a rigid impermeable plate moving with a uniform velocity is studied. The two cases, viz., the porous medium bounded below (i) by a static fluid and (ii) by a rigid impermeable stationary wall, are considered separately. The modified slip condition involving the thickness of the porous layer is derived using the variation of velocity in the porous medium with the proper matching conditions based on the physical considerations. It is shown that when the thickness of the porous layer tends to infinity our modified slip condition tends to the slip condition postulated by Beavers and Joseph [13]. Methods to estimate the viscosity factor λ and relative permeability are discussed. The velocity profiles in the porous layer are shown to exhibit the boundary-layer type very near the porous surface; they increase with increase in depth of the porous medium and decrease with increases in λ. We find that the effect of the finite thickness of the porous medium is significant only for large values of λ and small values of the porous parameter σ.
Node Selection for Two-Point Boundary-Value Problems
Authors: Ablow C. M. , Schechter S. , Zwisler W. H.
Published: October 2009

The solutions of two-point boundary-value problems often have boundary layers, narrow regions of sharp variation, that can occur in any part of the interval between the points. A finite difference method of numerical solution will generally require more closely spaced nodes in the boundary layers than elsewhere. An automatic method is needed for achieving the irregular spacing when the location of the boundary layer is not known in advance. Several automatic node-insertion or node-movement methods have been proposed. A new node-movement method is presented that is optimal under the criterion of producing the least sum of squares of the truncation errors at the nodes. For the Keller box scheme applied to a system of N coupled first-order differential equations this truncation-error minimizing (TEM) method increases the system size to N+6 equations. The campylotropic coordinate transformation method and other published methods based on heuristically derived monitor functions are node-movement methods that involve systems of only N+1 or N+2 first order equations. A comparison is made of the accuracies of several such methods and the TEM method in the solution of a standard problem.
Instability of a Moving Cylindrical Liquid Sheet
Authors: Biswas G. , Som S. K. , Gupta A. S.
Published: October 2009

The instability of a cylindrical liquid sheet of finite thickness moving with a uniform velocity in still air is studied theoretically with the aim of throwing light on the break-up of films during atomization. It is shown that instability occurs for an axisymmetric disturbance when its wavelength exceeds the outer circumference of the sheet. For small values of the Weber number W(= T/ρaU2ra) a sheet of given thickness tends to become unstable for disturbances of large wavelengths although it is completely stabilized when W < 2.5 (approx.). The maximum growth rate for instability increases with W for fixed value of the sheet thickness. For fixed W, it is found that λ¯m (the wavelength corresponding to maximum growth rate) increases rather slowly with increase in the sheet thickness. The value of λ¯m decays rapidly from a high value as Weber number increases for a fixed sheet thickness. Further as W → ∞, λ¯m approaches asymptotically the value 10 (approx.) which agrees with the corresponding value due to Rayleigh in his study of the capillary instability of a jet.
Experimental Rayleigh-Taylor Instability in a Circular Tube
Authors: Jacobs J. W. , Bunster A. , Catton I. , Plesset M. S.
Published: October 2009

The Rayleigh-Taylor instability of an air-water system has been investigated experimentally. The instability was produced by accelerating a slug of water down a vertical circular tube of 6.25 in. inside diameter employing a pressure differential. Accelerations from 3 to 25 times gravitational acceleration with fluid depths from 5 to 20 centimeters were studied. The disturbances first observed were purely axisymmetric with wave numbers corresponding closely to the fastest growing values given by linear theory. Later stages of planform development were characterized by a series of transitions which cannot be predicted by linear theory. These transitions were correlated with disturbance height.
Adaptive Grid Generation by Mean Value Relaxation
Authors: Eiseman P. R.
Published: October 2009

A grid movement algorithm has been developed for the purpose of adaptively resolving numerical solutions to physical problems and, in addition, for grid clustering on arbitrary surfaces. Both the solutions and the arbitrary surfaces are represented by grid point data with a continuous definition provided by interpolation between points. Movement is applied relative to this representation. The algorithm comes from a local mean value construction to produce a finite difference molecule for movement. The mean value weights are of a general enough nature to provide for a generous number of clustering possibilities. The movement molecule is executed within an interative cycle in the spirit of point Jacobi or Gauss-Seidel, and as a consequence, corresponds to the solution of some elliptic partial differential equation which satisfies a maximum (minimum) principle due to the mean value construction. From this principle, the movement will always preserve nonsingularity for the continuous transformation. For the discrete representation in the form of a grid, local geometric constraints are established to maintain this preservation.
The Flow Over Two-Dimensional Surface-Mounted Obstacles at Low Reynolds Numbers
Authors: Tropea C. D. , Gackstatter R.
Published: October 2009

The flow over a fence and a block mounted in a fully developed channel flow is experimentally investigated as a function of the Reynolds number, blockage ratio and length-to-height ratio using a laser-Doppler-anemometer. The information obtained includes the location and size of the primary and secondary recirculation zones, and profiles of the mean streamwise velocity component. The experiments were carried out in a channel for a Reynolds number in the range 150 < ReH < 4500. Comparisons are drawn between the obstacle flow and the backward-facing step flow.
The Influence of Pipe Motion on Acoustic Wave Propagation
Authors: Stuckenbruck S. , Wiggert D. C. , Otwell R. S.
Published: October 2009

It is well known that the magnitude of the acoustic wavespeed in piping is influenced by properties of the fluid and the pipe material. Traditionally, derivations have been based on a quasi-static control volume model, where the pipe deformation takes place in the time the liquid acoustic wave travels a known distance along the pipe. In actuality, dilation of the piping causes axial stress waves to propagate along the pipe wall at speeds greater than that of the acoustic wave. Such axial coupling between the liquid and piping has been reported by several investigators, including Walker and Phillips [4], who developed a six-equation model with a three-wave family—radial and axial stress, and axial liquid. In the present study Walker and Phillips’ model is simplified to a four-equation one by neglecting radial inertia, a valid assumption for many practical piping system transients. An eigenvalue analysis of the hyperbolic relations reveals two axial waves—in the liquid and in the pipe wall—which are modified by the coupling action. The traditional wave speed formulations with varied coupling constraints are reviewed in light of the present development. Numerical examples are presented which show the effects of such interaction for various combinations of liquid and piping.
A Note on the Response Equations for Hot-Wire Anemometry
Authors: Swaminathan M. K. , Rankin G. W. , Sridhar K.
Published: October 2009

The various heat transfer laws describing the response of the hot-wire to the velocity normal to its axis have been evaluated on a common basis to judge their effectiveness in representing the raw calibration data. The models compared were the King’s law, the exponent power-law, the extended power-law and the polynomial heat transfer law. These models were compared in the high and low velocity ranges of 0–100 m/s and 0–35 m/s, respectively. The criteria chosen for comparison were the minimum sum of the errors squared in the velocity and the estimated uncertainties in the calibration constants evaluated. The results indicate that the differences in the various models based on the sum of the errors in velocity, are not significant. However, when an uncertainty analysis for the constants are included in the study, the extended power-law proves to be robust in both the velocity ranges besides yielding a low error in the velocity. The fourth order polynomial law produces the lowest error in velocity, but the uncertainty in the constants evaluated are considerable. The nonlinear method of calibration together with the crierion of minimizing the errors in velocity offers no significant improvement in a statistical sense as compared to the linear method and the criterion of minimizing the errors in E2.
Prediction of Incompressible Flow in Labyrinth Seals
Authors: Rhode D. L. , Demko J. A. , Traegner U. K. , Morrison G. L. , Sobolik S. R.
Published: October 2009

A new approach was developed and tested for alleviating the substantial convergence difficulty which results from implementation of the QUICK differencing scheme into a TEACH-type computer code. It is relatively simple, and the resulting CPU time and number of numerical iterations required to obtain a solution compare favorably with a previously recommended method. This approach has been employed in developing a computer code for calculating the pressure drop for a specified incompressible flow leakage rate in a labyrinth seal. The numerical model is widely applicable and does not require an estimate of the kinetic energy carry-over coefficient for example, whose value is often uncertain. Good agreement with measurements is demonstrated for both straight-through and stepped labyrinths. These new detailed results are examined, and several suggestions are offered for the advancement of simple analytical leakage as well as rotordynamic stability models.
Measurements of Confined, Coaxial Jet Mixing With Pressure Gradient
Authors: Choi D. W. , Gessner F. B. , Oates G. C.
Published: October 2009

The mixing of a subsonic confined air jet with a coaxial secondary air stream is investigated experimentally. This work differs from previous studies in that emphasis is placed on the effects of an imposed adverse pressure gradient on mixing characteristics in the initial mixing (potential core) and transition regions. The results indicate that the presence of an adverse pressure gradient promotes more rapid mixing and spreading of the shear layer in the initial mixing region, as well as elevated turbulent normal stress and shear stress levels in the outer portion of the mixing layer after the primary and secondary streams have merged. Significant radial static pressure variations occur in both the initial mixing and transition regions as a result of turbulent normal stress gradients and streamline curvature effects induced by potential core entrainment.
Impulsively Started Steady Flow About Rectangular Prisms: Experiments and Discrete Vortex Analysis
Authors: Sarpkaya T. , Ihrig C. J.
Published: October 2009

Impulsively started steady flow about sharp-edged rectangular prisms has been investigated experimentally and numerically. The forces acting on the bodies have been determined at a Reynolds number of about 20,000 for various angles of incidence as a function of the relative displacement of the fluid. The results have shown that the shedding of the first few vortices has profound effects on both the lift and drag coefficients, often resulting in a large initial rise in drag. The surface-vorticity-distribution version of the discrete vortex model has shown that the strength of the vortex clusters varies from 80 to 90 percent of the vorticity generated in the shear layers. The Strouhal number is correctly predicted but the calculated forces are somewhat larger than those measured experimentally.
A Viscous-Inviscid Interaction Procedure—Part 1: Method for Computing Two-Dimensional Incompressible Separated Channel Flows
Authors: Kwon O. K. , Pletcher R. H.
Published: October 2009

A viscous-inviscid interaction scheme has been developed for computing steady incompressible laminar and turbulent flows in two-dimensional duct expansions. The viscous flow solutions are obtained by solving the boundary-layer equations inversely in a coupled manner by a finite-difference scheme; the inviscid flow is computed by numerically solving the Laplace equation for streamfunction using an ADI finite-difference procedure. The viscous and inviscid solutions are matched iteratively along displacement surfaces. Details of the procedure are presented in the present paper (Part 1), along with example applications to separated flows. The results compare favorably with experimental data. Applications to turbulent flows over a rearward-facing step are described in a companion paper (Part 2).
Review—Mean Flow in Turbulent Boundary Layers Disturbed to Alter Skin Friction
Authors: Bandyopadhyay P. R.
Published: October 2009

Recent developments in methods of reducing drag in turbulent boundary layers have been briefly reviewed. The behavior of the mean flow in several drag reducing boundary-layer flows of current interest, viz., those over longitudinal surface riblets, outer-layer devices (OLD’s), and longitudinal convex surface curvature, has been examined. The boundary layer on a surface with longitudinal concave curvature has been studied to complement the results of convex curvature. The riblets alter the flow in their vicinity only and cause no drag penalty. However, the OLD’s disturb the entire boundary layer, and it is the slow downstream (≃150 δ0) relaxation back to the equilibrium state that produces a region of lower skin friction; a net drag reduction results when the wall-drag reduction exceeds the drag penalty due to the device. The net drag reduction achieved by the riblets and OLD’s remains a modest 10 percent compared with the more spectacular levels reached by polymer addition and microbubble injection in water. Over mild convex curvatures, the outer-boundary-layer response is a function of the curvature ratio (δ0/R), and the relaxation rate after a length of convex curvature is a function of the curved length ratio (Δs0/δi). Boundary layers exhibit an asymmetric response to streamwise surface curvatures; the response is slower to a concave curvature than to a convex. Detailed turbulence and accurate wall shear stress measurements in the altered boundary layers are needed to understand the drag-reducing mechanisms involved.
Flowfield and Performance Measurements in a Vaned Radial Diffuser
Authors: Dutton J. C. , Piemsomboon P. , Jenkins P. E.
Published: October 2009

The flow characteristics of a vaned diffuser typical of those currently used in centrifugal compressors have been determined experimentally by using a static diffuser test rig. The vortex test vehicle (VTV) portion of this rig was used to simulate the essential features of the flow leaving the impeller of an actual compressor. The mean flow phenomena at the diffuser entrance and the static pressure recovery along the diffuser passage have been determined. In addition, the flow angle and Mach number distributions at several key locations throughout the diffuser channel have been obtained. The most notable feature of the diffuser flowfield is the high degree of nonuniformity in the inlet/leading edge region.
Developing Turbulent Flow in a U-Bend of Circular Cross-Section: Measurement and Computation
Authors: Azzola J. , Humphrey J. A. C. , Iacovides H. , Launder B. E.
Published: October 2009

Laser-Doppler measurements of the longitudinal and circumferential velocity components are reported for developing turbulent flow in a strongly curved 180 deg pipe and its downstream tangent. In the bend, the mean longitudinal velocity component changes little after θ = 90 deg, but the circumferential component never achieves a fully-developed state. Similar behavior is observed in the normal stresses, with large levels of flow anisotropy arising everywhere in the bend and downstream tangent. Between θ = 90 deg and X/D = 5, the circumferential velocity profiles display reversals of the secondary flow which are essentially independent of the Reynolds number. Predictions of the flow development are presented based on a “semi-elliptic” truncation of the Reynolds equations in the main part of the flow with the standard k-ε effective viscosity model used to approximate the turbulent stress field. In the immediate vicinity of the wall a simpler treatment, PSL, is adopted that allows the inclusion of the very fine mesh needed to resolve the viscous sublayer without excessive computer storage. The calculated behavior displays reasonably good agreement with the measurements in the bend, including the secondary flow reversals. Downstream of the bend, however, the rate of recovery of the flow is too slow, which points to the same weakness in the turbulence model as found in the recovery region of the flow over a backward-facing step.
An Experimental Study of Travelling-Bubble Cavitation Noise
Authors: Hamilton M. F. , Thompson D. E. , Billet M. L.
Published: October 2009

High-frequency travelling-bubble cavitation noise generated on a Schiebe headform is analyzed with reference to several existing noise theories which are based on the collapse of a single spherical bubble. After normalizing the noise level by a bubble event rate, the normalized cavitation number based on the minimum pressure coefficient provides a reasonable scaling factor, for the noise level radiated per collapse. At frequencies above 10 kHz and for free-stream velocities between 9.1 and 12.2 mps (30 and 40 fps), the trend of noise level per collapse versus normalized cavitation number correlated well with noise theories and was constant with flow velocity for constant normalized cavitation number. The energy density spectra were flat from 10 to 100 kHz regardless of the cavitation number or free-stream velocity for the range of these experiments.
Development of Axisymmetric Laminar to Turbulent Free Jets From Initially Parabolic Profiles
Authors: Tucker H. J. , Islam S. M. N.
Published: October 2009

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.
Self-Excited Shear-Layer Oscillations in a Multi-Cavity Channel With a Steady Mean Velocity
Authors: Stephanoff K. D.
Published: October 2009

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.
The Influence of Surface Roughness on Resistance to Flow Through Packed Beds
Authors: Crawford C. W. , Plumb O. A.
Published: October 2009

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.
A Simplified Free Wake Method for Horizontal-Axis Wind Turbine Performance Prediction
Authors: Afjeh A. A. , Keith T. G.
Published: October 2009

Based on the assumption that wake geometry of a horizontal-axis wind turbine closely resembles that of a hovering helicopter, a method is presented for predicting the performance of a horizontal-axis wind turbine. A vortex method is used in which the wake is composed of an intense tip-vortex and a diffused inboard wake. Performance parameters are calculated by application of the Biot-Savart law along with the Kutta-Joukowski theorem. Predictions are shown to compare favorably with values from a more complicated full free wake analysis and with existing experimental data, but require more computational effort than an existing fast free wake method.
Measurements of Apparent Mass Torque Coefficients of Two-Dimensional Centrifugal Impellers
Authors: Tsujimoto Y. , Imaichi K. , Moritani T. , Kim K.
Published: October 2009

Apparent mass torque coefficients for fluctuations of flow rate and angular velocity are determined experimentally for two-dimensional centrifugal impellers. Nearly sinusoidal fluctuations of flow rate and angular velocity are produced by using crank mechanisms, and the resulting unsteady torque on the impeller is measured. The torque is divided into components in-phase and out-of-phase with the displacements. The in-phase components are used to determine the apparent mass coefficients. Drag torque coefficients are defined and used to represent the out-of-phase components. The tests are conducted under various frequencies and amplitudes of the fluctuations with zero mean flow rate and rotational velocity. The apparent mass torque coefficients are compared with theoretical values obtained under the assumption of a two-dimensional potential flow. The experimental values are 5 to 20 percent larger than the theoretical ones and no appreciable effects of the frequency and the amplitude are observed within the range of the experiments.
Cavitation Inception on a Circular Cylinder at Critical and Supercritical Flow Range
Authors: Ihara A. , Murai H.
Published: October 2009

Cavitation tests were performed in the critical and supercritical flow range on circular cylinders with and without boundary layer trip. Mean and fluctuating static pressures were meausred on the smooth circular cylinder from θ = 0 to 180° and on the tripped surface at θ = 104 and 106° corresponding to tripping wire location α = 38 and 40 deg. Through these measurements it was found that cavitation that closely resembles bubble ring cavitation reported on axisymmetric bodies took palce in a reattachment region of the laminar separation bubble for the critical flow range where the laminar separation bubble was present. For the supercritical flow range where the laminar separation bubble disappeared, smooth cavitation with small irregular bubbles at its rear part took place at a location about 100° from the stagnation point.
Modeling of Wall Friction for Multispecies Solid-Gas Flows
Authors: Doss E. D. , Srinivasan M. G.
Published: October 2009

The empirical expressions for the equivalent friction factor to simulate the effect of particle-wall interaction with a single solid species have been extended to model the wall shear stress for multispecies solid-gas flows. Expressions representing the equivalent shear stress for solid-gas flows obtained from these wall friction models are included in the one-dimensional two-phase flow model and it can be used to study the effect of particle-wall interaction on the flow characteristics.
Lateral Fluid Forces on Whirling Centrifugal Impeller (2nd Report: Experiment in Vaneless Diffuser)
Authors: Ohashi H. , Shoji H.
Published: October 2009

Fluid forces acting on a rotating centrifugal impeller in whirling motion are studied experimentally. A two-dimensional impeller installed in a parallel walled vaneless diffuser was forced on a circular orbital motion at various positive and negative whirl speeds. The measurements show that the fluid forces exert a damping effect on the rotor at most operating conditions, but excite positive whirl when the impeller operates at a partial discharge and rotates at speeds more than twice the whirl speed. The test results were compared with those calculated by the theory described in the 1st Report. The characteristics of whirling fluid forces are examined from both the measurements and calculations. The measured fluid forces are expressed in terms of mass, damping, and stiffness matrices.
Flow Around an Elliptic Cylinder in the Critical Reynolds Number Regime
Authors: Ota T. , Nishiyama H. , Taoka Y.
Published: October 2009

Flow around an elliptic cylinder of axis ratio 1:3 has been investigated experimentally in the critical Reynolds number regime on the basis of mean static pressure measurements along the cylinder surface and of hot-wire velocity measurements in the near wake. The critical Reynold number has been found to vary with the angle of attack α and attains a minimum around α = 5 to 10 deg. At the critical Reynolds number, the drag, lift, and moment coefficients change discontinuously, and the Strouhal number based on the upstream uniform flow velocity and the major axis length of the cylinder reaches a maximum of about 1.0 to 1.5 depending on α. It is found, however, that the universal Strouhal number based on the velocity along the separated shear layer and the wake width is nearly equal to 0.19, on average, even in the critical Reynolds number regime. The pressure distribution along with the surface oil flow pattern revealed the existence of a small separation bubble near the leading edge accompanying a turbulent boundary layer.
Analysis of Liquid and Structural Transients in Piping by the Method of Characteristics
Authors: Wiggert D. C. , Hatfield F. J. , Stuckenbruck S.
Published: October 2009

Since liquid-filled piping systems are composed of slender elements, their transient behavior can be described as one-dimensional wave phenomena. Seven wave components are identified: coupled axial compression of liquid and pipe material; coupled transverse shear and bending of the pipe elements in two principal directions; and torsion of the pipe wall. Utilizing the method of characteristics, the combined system of difference equations for pipe elements and the pipe junction boundary conditions comprise a general mathematical tool for predicting the liquid pressure and pipe stress responses to transient excitation of either liquid or piping. The complexity of fluid-structure interaction that can take place is demonstrated.
Lateral Fluid Forces on Whirling Centrifugal Impeller (1st Report: Theory)
Authors: Shoji H. , Ohashi H.
Published: October 2009

Lateral fluid forces acting on a rotating centrifugal impeller in whirling motion are analyzed using unsteady potential flow theory. Impellers operating in diffusers with and without vanes are modeled and the fluid forces calculated for different whirl speeds and flow rates. The influences of these parameters are clarified by parametric calculations. The results for whirling impellers operating in vaneless diffusers show that the fluid forces exert a damping effect on the rotor whirling motion at all operating conditions. The results for impellers operating in vaned diffusers or guide vanes show that the time averaged values of fluid forces remain almost unchanged, while there are significant instantaneous fluctuations due to the impeller/guide vane interactions.
Experimental Determination of the Dynamic Transfer Matrix for a Pump
Authors: Stirnemann A. , Eberl J. , Bolleter U. , Pace S.
Published: October 2009

Dynamic instability in pumping systems can be the cause of a wide variety of difficulties. Analytical investigations of the dynamic behavior of such systems depend on the proper mathematical model of the dynamic performance of the pump. This paper is concerned with the experimental means and analysis procedures for obtaining the transfer matrix representing the pump as a four-pole element. Direct measurement of the pulsating flow is omitted in favor of an indirect determination utilizing multiple pressure measurements in reference pipe sections attached to the pump. The method of parameter extraction from redundant experimental data, as well as the modeling by an equivalent electrical network is shown. Results are presented for noncavitating and slightly cavitating flows. The quality of the results is an indication that the method utilized represents a successful way to determine the dynamic transfer matrix for a pump.
Velocity Fluctuations at the Walls of a Packed Bed of Spheres for Medium Re-Numbers
Authors: Bahnen R. H. , Stojanoff C. G.
Published: October 2009

A packed bed which is uniformly filled with equally large spheres is subjected to transpiration flow. The velocity component perpendicular to its surface was measured by means of Laser-Doppler-Velocimetry. Special attention is paid to the velocity fluctuations occurring at the wall of the cylindrical container and at the convex surface of rods of different diameters inserted in the bed center. The Re-numbers were between 800 and 1500. The experimental results are compared with results obtained from the literature.
An Example of Transient Laminar Countercurrent Flow
Authors: Tsanis I. K. , Leutheusser H. J.
Published: October 2009

This paper presents a numerical and experimental study of transient laminar countercurrent flow in which the pressure gradient is time-dependent. An explicit finite-difference scheme is used to solve numerically the governing equations. Experimental results are obtained with a new kind of apparatus and are found to verify the numerical predictions.
Flow Characteristics of Swirling Coaxial Jets From Divergent Nozzles
Authors: Mahmud T. , Truelove J. S. , Wall T. F.
Published: October 2009

The aerodynamic characteristics of free, swirling, coaxial jets issuing from an air model of a typical burner for pulverized bituminous coal have been studied. Detailed measurements of mean velocity and static pressure have been obtained in the region near the nozzle exit. The boundary of the reverse-flow zone has been mapped and the recirculated-mass flowrate measured in order to quantify the effects of velocity ratio and swirl in the primary and secondary jets. The influence of burner geometry (divergent-nozzle length and centre-line blockage) has also been studied. The type of flow pattern is found to depend upon the level of swirl in the primary and secondary jets. The recirculated-mass flowrate is predominantly influenced by secondary swirl. The measurements have been compared with predictions obtained by numerical solution of the governing conservation equations in orthogonal curvilinear co-ordinates. The general features of the flows are adequately predicted although discrepancies in detail seem to indicate deficiencies in the turbulence model.
Added Mass and Damping for Cylinder Vibrations Within a Confined Fluid Using Deforming Finite Elements
Authors: Chilukuri R.
Published: October 2009

Added mass and fluid damping coefficients for vibrations of an inner cylinder that is enclosed by a concentric outer cylinder are determined by finite element analysis of the unsteady, laminar, incompressible flow in the annulus. Continuously deforming space-time finite elements are used to track the moving cylinder and the changing shape of the space domain. For small cylinder vibration amplitudes, the present results agree well with the work of earlier investigators who solved the linearized Navier-Stokes equations on a fixed mesh. Fluid damping coefficients are shown to increase with vibration amplitude. Added mass coefficients may either increase or decrease with increasing vibration amplitude.
Friction and Heat Transfer Measurements for Clay Suspensions With Polymer Additives
Authors: Matthys E. F. , Ahn H. , Sabersky R. H.
Published: October 2009

Local heat transfer and friction coefficients were measured in a circular tube for suspensions of bentonite and for a combination of bentonite and polyacrylamide in water. Both the entrance and fully-developed regions were examined in laminar and turbulent regimes. A viscosity model based on rheological measurements makes it possible to represent the results obtained for the pure suspensions with newtonian relationships. The fluid combining clay and polymer, however, exhibited characteristics typical of viscoelastic solutions and was observed to display an unexpectedly high sensitivity to mechanical degradation.