bluuebunny/crossref_metadata_2025 huggingface dataset:
A Flow Model for the Effect of a Slanted Base on Drag
Authors: Sedney R.
Published: October 2009

Experiments by Morel have shown that slanting the base of a bluff body causes large variations in the drag, as the slant angle changes. For a particular, critical slant angle the drag changes discontinuously. This phenomenon was correlated with a drastic change in the type of base flow. A mechanism to explain this change, and therefore, the discontinuity in drag, is proposed. The basis of the mechanism is breakdown of the side edge vortices. An estimate of the swirl angle in these vortices is obtained using a swept-back mixing zone solution. This swirl angle and the other elements of the theory provide an estimate for the critical slant angle that is entirely consistent with the observed value.
Draining of Tanks With Submerged Outlets or Without Vacuum-Relief
Authors: Dodge Franklin T. , Bowles Edgar B.
Published: October 2009

It is shown that the gravity-induced draining of liquid from a tank does not cease when the pressure differential at the outlet is zero if the liquid level is still above the outlet. Instead, either air or exterior liquid is ingested, depending on whether or not the tank outlet is submerged. Analytical models are developed to predict both the onset of ingestion and the subsequent discharge rates; experimental results are used to guide these developments. The models are shown to agree well with tests of draining during air ingestion and during water ingestion when the tank liquid is denser than water. When the tank liquid is less dense than water, however, the predictions of water ingestion are only in qualitative agreement with tests. Some possible reasons for this discrepancy are advanced.
Oil Thickness Variation on Wavy Water in the Presence of Wind
Authors: Kordyban E.
Published: October 2009

The effect of the wind on the distribution of an oil layer on wavy water has been examined analytically and the results are compared with experimental values. It is found that the wind tends to decrease the difference between the oil layer thickness at the wave crest and the wave trough, but for sinusoidal waves this effect is small.
Scaling Laws for Metering the Flow of Gas-Particle Suspensions Through Venturis
Authors: Lee J. , Crowe C. T.
Published: October 2009

An experimental investigation was undertaken to determine those scaling parameters applicable to measuring the mass flow rate of gas-particle suspensions through venturis. It was found that Stokes number and the particle/gas loading ratio are the two most important parameters. The results show that pressure drop increases linearly with loading ratio and decreases monotonically with increasing Stokes number. The results also indicate that β-ratio and orientation of venturi do not significantly affect the pressure drop. Data for irregularly shaped pulverized coal particles show higher pressure drop compared with those for spherical particles. A quasi one-dimensional numerical model overpredicts the pressure drop, but a two-dimensional model demonstrates improved agreement.
Cavitation in an Extremely Limited Flow Through Very Small Orifices
Authors: Oba R. , Ikohagi T. , Kim K. T.
Published: October 2009

In order to clarify the role of cavitation nuclei upon inception, the behavior of inception was carefully investigated in an extremely limited water flow through very small orifices less than 1.0 mm in diameter under a prescribed nuclei condition. The following facts of technical interest were determined: a) The desinent cavitation number (σd) decreased rapidly and exponentially with the orifice diameter d, up to one hundredth in magnitude; and b) the cavitation appearance in such limited flows was quite different from that in fully turbulent flows through larger orifices.
Squish and Swirl-Squish Interaction in Motored Model Engines
Authors: Arcoumanis C. , Bicen A. F. , Whitelaw J. H.
Published: October 2009

Measurements of the three components of velocity and their corresponding fluctuations have been obtained by laser-Doppler anemometry mainly near TDC of compression in a model IC engine motored at 200 rpm with compression ratio of 6.7. The flow configurations comprised an axisymmetric cylinder head with and without upstream induced swirl and each of a flat piston and two centrally located, cylindrical and re-entrant, bowl-in-piston arrangements. In the absence of swirl and squish, the intake-generated mean motion and turbulence decayed considerably by the end of compression. The two piston-bowl configurations, however, resulted in a compression-induced squish motion with consequent formation of a toroidal vortex occupying the whole bowl space. Interacton of swirl, carried from intake and persisting through compression, with squish generated near TDC profoundly altered the axial flow structure. In the case of the cylindrical bowl, the sense of the vortex was reversed by swirl and, in the reentrant bowl, increased the number of vortices to two. The swirling motion inside the cylindrical bowl was close to solid body rotation while the re-entrant bowl gave rise to more complex flow patterns. Squish, in the presence or absence of swirl, did not augment the turbulent energy inside the cylindrical bowl contrary to the reentrant configuration where turbulence generation was observed.
Air Release During Column Separation
Authors: Baasiri Muin , Tullis J. Paul
Published: October 2009

Air release caused by column separation in a pipeline was investigated in a test facility where column separation could be generated for any desired length of time. The temperature, pressure, amount of dissolved air, and the other variables affecting the process were carefully controlled. Tests were made for cases where there was no initial free air in the system and for cases where there was some initial free air. The parameters influencing air release were identified and empirical equations developed for predicting the amount of air released during each cycle of column separation.
Supersonic Diffusers With Reverse Flow Injection
Authors: Kuntz D. W. , Dutton J. C. , White S. H. , Addy A. L.
Published: October 2009

In applications such as airborne high energy chemical lasers, diffuser size and weight can be critical parameters. This paper summarizes the authors’ research concerning the effects of flow injection into a supersonic diffuser in a direction opposite to that of the main flow. Experimental studies were conducted concerning the effect of diffuser performance, particularly length and pressure recovery, of this reverse flow, and a quasi-one-dimensional control volume analysis was performed to predict some of the diffuser flow properties. Single-stream, dual-stream, and sudden enlargement configurations were considered. This work has shown that a reverse flow can reduce the length of a diffuser while causing only a small decrease in overall pressure recovery.
Artificially Thickened Turbulent Boundary Layers for Studying Heat Transfer and Skin Friction on Rough Surfaces
Authors: Ligrani P. M. , Moffat R. J. , Kays W. M.
Published: October 2009

Thermal and hydrodynamic characteristics of boundary layers developing over uniform spheres roughness with momentum thicknesses as large as 1.43 cm are presented. To obtain thick hydrodynamic boundary layers, an artificial thickening device is employed. The normalized velocity and turbulence profiles produced using this device are two-dimensional and self-preserving. The turbulent transport and structural characteristics are representative of normal behavior to the level of spectra of the longitudinal velocity fluctuations. In the artificially thickened layers, the effect of the unheated starting length (ξ > 0, Δ < δ) on thermal boundary layer properties is present. Turbulent Prandtl number profiles are generally unaffected by the magnitude of the unheated starting length, whereas measured Stanton numbers, show different behavior as the unheated starting length varies. In thermal boundary layers which would have the same thickness as the augmented hydrodynamic layers (Δ ≃ δ), Stanton numbers are shown to be the same as skin friction coefficients, and are then provided for boundary layers much thicker than those previously studied. As fully rough boundary layers develop downstream and δ/ks increases, Cf/2 is proportional to δ2−b where b = 0.175. In order for such U∞ = constant, thick, rough wall layers to develop far enough downstream to reach smooth behavior where b = 0.250, ks Uτ/ν must become small, and b must increase from 0.175 to become greater than 0.250 in the transitionally rough regime.
Development of Three-Dimensional Turbulent Boundary Layer in an Axially Rotating Pipe
Authors: Kikuyama K. , Murakami M. , Nishibori K.
Published: October 2009

The time-mean velocities and turbulent fluctuations inside the turbulent boundary layers which developed in an axially rotating pipe were measured in the case where an undeveloped flow with a rectangular axial velocity distribution was introduced in the pipe. The pipe rotation gives two counter effects on the flow: one is a destabilizing effect due to a large shear caused by the rotating pipe wall and the other is a stabilizing effect due to the centrifugal force of the swirling velocity component of the flow. The destabilizing effect prevails in the inlet region, but the stabilizing effect becomes dominant in the downstream sections. The intensity of turbulence in the rotating pipe decreases ultimately below that in a stationary state of the pipe. Using the experimental results, the relationship between the mixing length and Richardson number proposed by Bradshaw was examined for the turbulent boundary layer that develops in the rotating pipe.
Pressure Fluctuations on the Surface of Two Circular Cylinders in Tandem Arrangement
Authors: Arie M. , Kiya M. , Moriya M. , Mori H.
Published: October 2009

The fluctuating pressures on the surface of two circular cylinders of the same diameter in tandem arrangement were measured in the upper subcritical regime to obtain the distributions of their rms values and the spanwise and circumferential correlations. These pressures were subsequently integrated to yield the spanwise correlation length and the rms values of fluctuating lift and drag as functions of the spacing between the two cylinders. The rms lift and drag were much larger for the downstream cylinder than for the upstream cylinder up to the spacing of 7.0 diameters. At the spacing of 10.0 diameters, they were different from those for a single cylinder by only a small amount.
Analysis of the Frequency Response of a Fluid Amplifier Using Unsteady Flow Characteristics
Authors: Caen R. , Fonade C.
Published: October 2009

This paper is mainly concerned with the theoretical and experimental study of the frequency response of an analog fluid amplifier. The channels are considered as distributed parameter systems and the frequency effects on the charcteristics of nozzles, vents, and jet interaction are taken into account. The paper considers the dynamic behavior of the flow in vortex vents and the interaction of two jets : a discontinuous profile is used to approximately describe the average velocity distribution in the jet in order that a recursive solution for the eigenvalues resulting from a small perturbation be obtained. The amplifier was tested by means of an electropneumatic signal generator at frequencies up to 3000 Hz. A comparison with experiments performed in the potential core region shows that the linear theory correctly predicts the passband of the jet which is constant provided a local Strouhal number is used.
A Review of Near-Wall Similarity Models in Three-Dimensional Turbulent Boundary Layers
Authors: Pierce F. J. , McAllister J. E. , Tennant M. H.
Published: October 2009

Eleven near-wall similarity models for three-dimensional turbulent boundary layers which have been identified in the literature are reviewed. Each model summary includes a brief review of its derivation, discusses limitations in the derivation, estimates the applicable y+ range, and compares differences among the models. This review of three-dimensional similarity models was developed as part of a larger study which tests the validity of ten of these different models by comparison with experimental data which includes the direct and simultaneous measurement of the local wall shear stress direction and magnitude in a three-dimensional turbulent flow. A direct force measurement of local wall shear stress is necessary to test the local wall shear-shear velocity relationship, τ0 = ρq*2, generally assumed in three-dimensional flows. This review is necessary to acquaint the reader with the similarities and differences among the models tested in companion papers since differences among some of the models are significant, particularly in the coordinate systems of the vector models.
The Effect of Free-Stream Turbulence on Turbulent Boundary Layers
Authors: Hancock P. E. , Bradshaw P.
Published: October 2009

Mean flow measurements, and some turbulence measurements, have been made in a two-dimensional incompressible constant-pressure (“flat plate”) turbulent boundary layer beneath a nearly homogeneous nearly-isotropic (grid-generated) turbulent free stream. An appreciably nonlinear dependence of the skin-friction coefficient and other boundary layer parameters on rms free-stream turbulence intensity has been confirmed. A much wider range of free-stream length scales has been studied than in previous work, and the results (which agree well with previous data where they overlap) clearly indicate the large effect of free-stream length scale on the response of the boundary layer. The decrease of free-stream turbulence effect with increasing length scale is at least partly attributable to simple reduction of normal-component velocity fluctuations by the solid surface; this would not be the case in free shear layers.
The Effect of Transverse Curvature on the Drag and Vortex Shedding of Elongated Bluff Bodies at Low Reynolds Number
Authors: Monson D. R.
Published: October 2009

This paper establishes the drag characteristics of finite cylinders of aspect ratio 1, 4, 10 and 100 for Reynolds numbers less than 1000 including the viscous regime. The effect of the drag and vortex shedding characteristics of curving a finite cylinder into a toroidal shape is investigated. The curvature reduces drag by as much as 13 percent over its linear counterpart in the viscous regime. Vortex shedding characteristics of tori include all the features of cylinders in addition to a solidity range that behaves like solid bodies and an intermediate range where two vortex flow patterns can exist. These patterns can occur either as alternating ring vortices or a less common but more stable counterrotating helical vortex pair.
The Flow States of Liquid Through Two Series-Connected Diffusers Subject to Cavitation
Authors: Tippetts J. R. , Priestman G. H.
Published: October 2009

A “diffuser” is a venturi-like element with a well-formed contraction followed by a small-angle diffuser. When liquid flows through two diffusers connected in series various flow states are possible depending on whether or not cavitation occurs in the diffusers. It is shown that, in the absence of strong “Reynolds-number effects,” one of just two possible sequences of flow states can occur for a particular pair of diffusers. Denoting the diffusers by “upstream” and “downstream,” cavitation can occur as follows with increasing flow: 1. Neither; upstream only; both. 2. Neither; downstream only (and upstream never). Once this classification is known it is easy to predict the characteristics of the circuit which can then be used to define an “equivalent single diffuser” to represent the pair of diffusers. Experimental data verifying the theory are included.
Measurements of the Spray Angle of Atomizing Jets
Authors: Wu K.-J. , Su C.-C. , Steinberger R. L. , Santavicca D. A. , Bracco F. V.
Published: October 2009

Liquid jets are considered issuing from single-hole, round nozzles into quiescent gases under conditions such that they break up into a well defined conical spray immediately at the nozzle exit plane. The initial angles of such sprays were measured at room temperature by a spark photography technique. Water, n-hexane, and n-tetradecane at pressures from 11.1 MPa to 107.6 MPa were injected into gaseous N2 at pressures from 0.1 MPa to 4.2 MPa through sixteen nozzles of different geometry. Under the test conditions, the spray angle is found to be a strong function of the nozzle geometry and the gas-liquid density ratio and a weak function of the injection velocity. The measured trends are then discussed in the light of possible mechanisms of the breakup process and shown to be compatible with the aerodynamic theory of surface breakup if modified to account for nozzle geometry effects.
Influence of Base Slant on the Wake Structure and Drag of Road Vehicles
Authors: Ahmed S. R.
Published: October 2009

The time averaged wake structure of a realistically dimensioned quarter scale automobile model was studied in a wind tunnel on the basis of flow visualization, wake surveys, force and pressure measurements. Through a systematic variation of base slant angle in the range of 0 to 40 deg, the ensuing changes in the wake structure were observed and the wake structure present at lowest value of aerodynamic drag is shown. Experimental data were obtained at a model length based Reynolds number of 4.29 million. Correlation of wake structure with drag, pressure distribution, and kinetic energy content of vortex motion in wake is addressed.
Similar Solutions of Brinkman Equations for a Two-Dimensional Plane Jet in a Porous Medium
Authors: Friedrich R. , Rudraiah N.
Published: October 2009

The similar solution of the Brinkman equations for flow of a plane jet issuing into a fluid saturated porous medium is studied. The velocity field is determined in the plane of physical as well as transformed coordinates. It is shown that the jet in a porous medium is of finite length in contrast to the infinite length in the case of pure viscous flow. The difference in the volume rate of discharge and the width of the jet between the Brinkman model and the pure viscous case is brought out clearly and it is shown that the Darcy resistance tends to make the jet broader. Near the origin, the streamlines show an entrainment of fluid from infinity which results in negative transverse velocity.
Cavitation Inception Observations on Six Axisymmetric Headforms
Authors: Huang T. T.
Published: October 2009

Cavitation inception observations on a series of axisymmetric headforms were made in the DTNSRDC 36-in. water tunnel. Cavitation inception observed on headforms with natural flow transition is characterized by the growth and collapse of the individual undissolved air bubbles in the water when traveling through the low pressure regions of flow transition. Cavitation inception observed on headforms with laminar separation is characterized by an attached band or bubble-ring cavitation starting at the separation point. The traveling bubble type cavitation inception is significantly affected by the microbubble population. However, the effect of total air content and size distribution of the bubbles on attached cavitation inception is less pronounced. Attached spot or ring/band cavitation never occur at the location of minimum static pressure but are observed first in the regions of natural flow transition or laminar separation.
Forces on Staggered Airfoil Cascades in Unsteady In-Phase Motion
Authors: Shoji H. , Ohashi H. , Kemp N. H.
Published: October 2009

We consider incompressible potential flow through a cascade of staggered thin airfoils in general, unsteady, in-phase motion. With the assumptions of the Kutta condition and linearized wakes, exact analytical expressions are derived for pressure distribution, lift, and moment, using conformal mapping applied to the velocity field. The results are then specialized to harmonic motion, and applied to plunging, pitching, and sinusoidal gusts. All the results are expressed in closed-form as quadratures, and reduce to the well-known relations for thin airfoil theory, as the solidity decreases to zero. They agree with the unstaggered results of Kemp and Ohashi when the stagger angle is zero. Typical numerical results are given in the figures. They should serve as a measure of the accuracy of numerical or approximate solutions, as well as representing in a simple way the effects of stagger and solidity on unsteady cascade aerodynamics.
A Prediction Method for Planar Diffuser Flows
Authors: Bardina J. , Lyrio A. , Kline S. J. , Ferziger J. H. , Johnston J. P.
Published: October 2009

A method is presented for computation of performance of two-dimensional (planar) diffusers with steady turbulent inflow of an incompressible fluid. Previous methods can predict one regime of flow. The present method gives accurate predictions covering three flow regimes: unstalled flow, transitory stall, and fully developed stall. The method is a considerable extension of the procedure given by Ghose and Kline [5]; it also uses some ideas from the method for fully stalled flows given by Woolley and Kline [4]. The flow model is zonal and steady. It uses a one-dimensional flow model for the potential core. A momentum integral equation and an entrainment equation are employed for the boundary layer zone. Simultaneous solution is employed to model the different zones where the flow is separating or separated. Improved correlations of flow detachment and of the boundary layer flow state approaching detachment are presented as part of the work and employed in the computations. These will be reported more fully in a separate paper. This model is too simple for the full representation of the physics of transitory stall, which is not symmetric, steady, or one-dimensional in the core. Despite this, the main features of the mean flow, including wall pressure as a function of streamwise location, are accurately represented with very modest computation times, typically tenths of a second on an IBM 3033. The results again indicate that the key features in modeling separated flows are: • correct representation of blockage of shear layers and stalled zones, • adequate modeling of the interaction of potential and viscous zones.
Initial Region of Subsonic Coaxial Jets of High Mean-Velocity Ratio
Authors: Ko N. W. M. , Au H.
Published: October 2009

This paper describes an experimental investigation of the initial region of subsonic coaxial jets of three different mean-velocity ratios λ higher than unity. Detailed measurements have found similarity of the mean velocity and turbulence intensity profiles within the three zones: initial merging, intermediate, and fully merged zone. Similarity with single jet results has been found. In the inner mixing region, however, only the similarity of the mean velocity profiles has been found.
Calculation of Annular and Twin Parallel Jets Using Various Discretization Schemes and Turbulence-Model Variations
Authors: Leschziner M. A. , Rodi W.
Published: October 2009

The paper examines the performance of three discretization schemes for convection and three turbulence-model variations when used to simulate the recirculating flow in an annular and a plane twin-parallel jet in still air. The discretization schemes considered are: (i) the hybrid central/upwind differencing scheme (CUDS), (ii) the hybrid central/skew-upwind differencing scheme (CSUDS) and (iii) the quadratic, upstream-weighted differencing scheme (QUDS). Of these, the second and third were proposed recently as superior alternatives to the first in respect of numerical diffusion. The turbulence models examined are the standard k-ε model and two variants of this. The first accounts for effects of streamline curvature on turbulence and the second for the preferential influence of normal stresses on the dissipation of turbulence energy. It is shown that numerical scheme (i) results, particularly in conjunction with the turbulence-model modifications, in severe solution errors and in a generally anomalous response to changes in the modelled viscosity field. In contrast, schemes (ii) and (iii) yield, in all cases, similar results and respond in an expected manner to the modifications. The modifications, particularly that accounting for streamline curvature, reduce, in some cases drastically, the discrepancies between computed and experimental data and yield for both jets examined generally satisfactory results.
Prediction of Gaseous Cavitation Occurrence in Various Liquids Based on Two-Phase Flow Analogy
Authors: Kamiyama S. , Yamasaki T.
Published: October 2009

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.
Cavitation Inception in Spool Valves
Authors: Martin C. Samuel , Medlarz H. , Wiggert D. C. , Brennen C.
Published: October 2009

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.
A Possible Criterion for Cavitation Inception on Hemispherical Headforms
Authors: Parkin B. R.
Published: October 2009

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.
Velocity Field and Entrainment of a Pulsed Core Jet
Authors: Bremhorst K. , Watson R. D.
Published: October 2009

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.
An Improvement in the Calculation of Turbulent Friction in Smooth Concentric Annuli
Authors: Jones O. C. , Leung J. C. M.
Published: October 2009

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.
Low-Reynolds-Number Turbulent Boundary Layers
Authors: White B. R.
Published: October 2009

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 Ka´rma´n 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.
Aerodynamic Effects of Shape, Camber, Pitch, and Ground Proximity on Idealized Ground-Vehicle Bodies
Authors: George A. R.
Published: October 2009

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.
On the Scaling of Impulsively Started Incompressible Turbulent Round Jets
Authors: Kuo T.-W. , Bracco F. V.
Published: October 2009

A scaling law for transient, turbulent, incompressible, round jets is reported. Numerical solutions of the Navier-Stokes equations were obtained using a k-ε model for turbulence. The constants of the k-ε model were optimized by comparing computed centerline velocity, mean radial velocity distribution, longitudinal kinetic energy distributions with those measured by other authors in steady round jets. The resulting constants are those also used in computations of steady planar jets except for the one that multiplies the source term in the ε-equation. After optimization, the agreement is satisfactory for all mean quantities but is still rather poor for the kinetic energy distribution. Parameteric studies of the transient were performed for 9•103 ≤ ReD ≤ 105. Then the definition was adopted that a jet reaches steady state between the nozzle and an axial location when, at that location, the centerline velocity achieves 70 percent of its steady state value, and characteristic steadying length and time scales (D•ReD0.053 and D•ReD0.053/u cL,0 respectively) were determined as well as a unique function that relates dimensionless steadying time to dimensionless steadying length. This function changes in a predictable way if a percent other than 70 is selected but the characteristic length and time scales do not. It is found that the 70 percent threshold is reached within the head vortex of the transient jet. Thus a transient jet, practically, is a steady jet except within its head vortex. This, in part, justifies our use of steady state k-ε constants in our transient computations. The computed jet tip arrival times are shown to compare favorably with measured ones.
Impulsively-Started Flow About Four Types of Bluff Body
Authors: Sarpkaya T. , Kline H. K.
Published: October 2009

Measurement of the forces acting on a circular cylinder and those on three other noncircular cylinders is reported. The results confirm and quantify the profound effects of the shedding of the first two or three vortices on all the characteristics of resistance and demonstrate that the evolution of the flow, and hence the forces, significantly depend on whether the separation points are fixed or mobile, or a combination thereof. The data are expected to form the basis of future numerical analysis based on refined discrete vortex models.
Numerical Solution for Laminar Two Dimensional Flow About a Cylinder Oscillating in a Uniform Stream
Authors: Hurlbut S. E. , Spaulding M. L. , White F. M.
Published: October 2009

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.
Review—Numerical Models for Dilute Gas-Particle Flows
Authors: Crowe C. T.
Published: October 2009

The rapidly increasing capability of computers has led to the development of numerical models for gaseous flows and, in turn, gas-particle and gas-droplet flows. This paper reviews the essential features of gas-particle flows from the point of view of model development. Various models that have appeared for one-dimensional and two-dimensional flows are discussed. The advantages and disadvantages of the trajectory and two-fluid models are noted.
Fluid Structure Interaction in Piping by Component Synthesis
Authors: Hatfield F. J. , Wiggert D. C. , Otwell R. S.
Published: October 2009

Pipe vibrations can be induced by internal liquid pulsations which propagate throughout the piping system and create unbalanced oscillatory pressure forces at locations where either flow area or direction changes. The fluid motion is set up by a source of mechanical excitation or flow instability. Dynamic interaction of the liquid and piping may be modelled by separate analyses of liquid and solid components followed by synthesis of the component solutions. In contrast to other formulations that correctly represent interaction, the technique presented herein has the computational advantage of decomposing the anaysis into steps. The most time-consuming step is structural analysis, which may be delegated to existing, efficient computer algorithms. The synthesis method is outlined, the advantages discussed and application illustrated with numerical examples.
The Viscous-Gravity Jet in Stagnation Flow
Authors: Cruickshank J. O. , Munson B. R.
Published: October 2009

Simple solutions are presented for the equation governing one-dimensional flow of very viscous jets that issue from a round orifice and fall against a flat plate. Due to the viscous axial stresses developed, the jet may be either in tension or compression, depending on the values of various dimensionless parameters involved. The comparison of the theoretical and experimental results is good.
Fluid Dynamics of Inducers—A Review
Authors: Lakshminarayana B.
Published: October 2009

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.
Scale Effects in the Dynamic Transfer Functions for Cavitating Inducers
Authors: Brennen C. E. , Meissner C. , Lo E. Y. , Hoffman G. S.
Published: October 2009

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) are evaluated and recommended for use in applications.
New Method for Monitoring and Correlating Cavitation Noise to Erosion Capability
Authors: De M. K. , Hammitt F. G.
Published: October 2009

For the purpose of obtaining a correlation between cavitation noise and damage, the source of damage, and its variance with flow parameters, was investigated. The individual cavitation pressure pulses were monitored by measuring the peak pulse amplitudes in a cavitating venturi. A pressure-bar probe and an acquisition system has been designed, constructed and used along with a commercial Kistler 601A probe for this purpose. The acoustic power derived from the pulse height spectra (PHS) was found to vary with the nth power of venturi throat velocity, where 6.8 < n < 10.5. The major component in this variation was the number of bubbles collapsing. This is a key factor in cavitation noise intensity variation, in this and other cavitating geometries. The acoustic power has been found to correlate linearly, with a small threshold, with the cavitation damage rate (MDPR) of 1100-0 aluminum. The feasibility of using cavitation erosion efficiency (ratio between erosion power and acoustic power) in predicting eventual cavitaion erosion rates in various geometries has been investigated.
Non-Newtonian Liquid Blade Coating Process
Authors: Hwang S. S.
Published: October 2009

A blade coating process for non-Newtonian liquids is presented using different air pressure applied at the inlet and the exit of the coating gap. The system consists of a coating blade to form a gap and a vacuum box to create different air pressures to permit coating a thin liquid film on an advancing plastic web. The solution consists of matching the boundary conditions of each subregion of the coating process. The calculated liquid film thickness as a function of the coating gap and applied air pressure difference agrees closely with experimental data obtained on a laboratory coating device.
Resonant Entrainment of a Confined Pulsed Jet
Authors: Parikh P. G. , Moffat R. J.
Published: October 2009

This paper reports the discovery of a new resonant entrainment phenomenon associated with a confined, pulsed jet flow. It was found that a confined jet, when pulsed at an organ-pipe resonant frequency of the confinement tube, experiences greatly enhanced entrainment and mixing near the exit end of the confinement tube compared to a steady confined jet. The mixing and entrainment rates for the resonantly pulsed confined jet approach, and in some cases slightly exceed, those for an unconfined pulsed jet. Both visual and quantitative evidence of this phenomenon is presented. The new effect should be of considerable interest in ejector and combustor design, both of which benefit from any enhancement in mixing between a primary and a secondary flow.
Measurements in a Jet-Pipe Flow Issuing Perpendicularly Into a Cross Stream
Authors: Andreopoulos J.
Published: October 2009

Measurements are presented of velocity fluctuation statistics in the jet-pipe of a jet in a cross-flow situation for various values of the jet-pipe to cross-flow velocity ratio. The nonuniformities of the velocity profiles inside the pipe extend as far as 3 pipe-diameters upstream of the exit plane for small velocity ratios and to 2.5 diameters for higher velocity ratios. Longitudinal flow acceleration and strong streamline curvature affect turbulence activities at the exit plane for small velocity ratios. The horseshoe vortex which is formed in front of the exit plane results in a streamline curvature with a stabilizing effect on turbulence in the nearby flow field while the streamlines are unstably curved everywhere else. At high velocity ratios the pipe flow is very weakly affected by the cross-flow.
Viscous Flow in an Annulus With a Sector Cavity
Authors: O’Brien V.
Published: October 2009

The two-dimensional interaction of a circular shear flow and a sector cavity flow is predicted by finite-difference solution of the governing biharmonic equation for steady Stokes planar flow. The location of the dividing streamline is a function of geometry, lying perhaps wholly within the cavity or bulging up into the circular annulus. Also pressure-driven axial flow through the annular configuration is predicted by numerical solution of the governing Poisson equation. The results can be combined with the planar solution to describe a steady three-dimensional flow field which will enhance laminar mixing.
Investigation of Wall Induced Modifications to Vortex Shedding From a Circular Cylinder
Authors: Angrilli F. , Bergamaschi S. , Cossalter V.
Published: October 2009

In this paper the influence of a wall on vortex shedding frequency, geometrical pattern, and velocity field are investigated. Frequency measurements were carried out with three circular cylinders at Reynolds numbers of 2860, 3820, and 7640. Mean and fluctuating velocities at several traverses were also measured at Re = 3820 both for an isolated cylinder and for an arrangement with a gap from the wall equal to one cylinder diameter. The modifications of the wake pattern are shown in several figures. It is also shown that the proximity of the wall induces a slight increase of vortex shedding frequency.
An Experimental Evaluation of Drag Coefficient for Rectangular Cylinders Exposed to Grid Turbulence
Authors: Courchesne J. , Laneville A.
Published: October 2009

This paper describes an experimental evaluation of the effects of the intensity and scale of turbulence on the drag coefficient of two-dimensional rectangular cylinders exposed to grid turbulence. It is observed that the mean drag coefficient is principally influenced, for a given cylinder, by the intensity of turbulence and that the scale of turbulence plays a secondary role.
Velocity Coefficients For Free Jets From Sharp-Edged Orifices
Authors: Lienhard J. H. , Lienhard J. H.
Published: October 2009

The viscosity-dependence of the velocity coefficient for a free liquid jet, issuing from a sharp-edged orifice, is predicted by computing the dissipation of energy in the boundary layer on the back of the orifice plate. The prediction is upheld by the only known direct measurements of velocity coefficients. The resulting coefficients are much closer to unity for large orifices than they are generally assumed to be. The influence of surface tension on small jets is also explained.
Flow and Temperature Profile Independence of Flow Measurements Using Long Acoustic Waves
Authors: Robertson Baldwin
Published: October 2009

An expansion in powers of V/c is derived for the wave number of the fundamental sound mode in a flow conduit, where V is the velocity of fluid in the conduit and c is the local sound speed. Both V and c are assumed to be independent of the longitudinal coordinates and of the time, but may have arbitrary profiles. The calculation applies to frequencies well below the cutoff frequency of the conduit, which may have an arbitrary cross-sectional shape. To lowest order, the wave number depends only on the average of the longitudinal component of V and is independent of its profile.
A Similarity Between Plane and Axisymmetric Viscous-Gravity Jets
Authors: Cruickshank J. O.
Published: October 2009

The equations governing the flow of plane and axisymmetic viscous-gravity jets are shown to have solutions which can be derived from one generalized equation. Solutions for the plane jet for various boundary and flow conditions are given here. Similar solutions for the axisymmetric jet are already in the literature.
Potential Flow From a Tapering Nozzle Impinging on a Flat Plate
Authors: Jones J. E.
Published: October 2009

A perfect flow from a two-dimensional nozzle is considered discharging against a normally placed flat plate. Particular attention is given to the effect of the angle of the nozzle, and results for angles of 15, 30, 45, and 60 deg are compared with those for a parallel-sided orifice. This model can be regarded as a two-dimensional representation of a plate valve or flapper valve in which the flow does not reattach to the land of the nozzle. The variations of the back pressure and the contraction coefficient with valve aperture have been plotted, and the shape of the free streamlines and the pressure distribution on the plate have been found. By considering the effect of fluctuations far upstream, the flow in a tapering orifice is shown to be inherently more unstable than that in a parallel-sided orifice. It is also shown that the control of the valve aperture over the back pressure is better in parallel-sided orifices than in angled ones.
An Experimental Verification of Laser-Velocimeter Sampling Bias and Its Correction
Authors: Johnson D. A. , Modarress D. , Owen F. K.
Published: October 2009

The existence of “sampling bias” in individual-realization laser velocimeter measurements is experimentally verified and shown to be independent of sample rate. The experiments were performed in a simple two-stream mixing shear flow with the standard for comparison being laser-velocimeter results obtained under continuous-wave conditions. It is also demonstrated that the errors resulting from sampling bias can be removed by a proper interpretation of the sampling statistics. In addition, data obtained in a shock-induced separated flow and in the near-wake of airfoils are presented, both bias-corrected and uncorrected, to illustrate the effects of sampling bias in the extreme.