bluuebunny/crossref_metadata_2025 huggingface dataset:
Conventional Probes for the Relative Flow Measurement in a Turbomachinery Rotor Blade Passage
Authors: Sitaram N. , Lakshminarayana B. , Ravindranath A.
Published: November 2009

This paper reports the measurement of the relative flow in the rotor blade passages of an axial-flow compressor and an axial-flow inducer using conventional probes such as five-hole, disk, and spherical pitot-static probes. The five-hole probe provides an inexpensive, yet accurate, method of deriving the three-dimensional flow field in a rotor; the disc probe is suitable for the blade boundary-layer measurement; and the pitot-static probe is useful for obtaining the static and stagnation pressures and the total velocity across the rotor passage. Typical data obtained from each of these probes demonstrate the complex nature of the turbomachinery rotor flow. A detailed discussion of various sources of probe errors and methods of estimating these errors is also included.
Flow Instability at the Inlet of a Centrifugal Compressor
Authors: Flueckiger G. , Melling A.
Published: November 2009

Using laser Doppler anemometry, two components of the gas velocity have been measured at the inlet of a centrifugal compressor impeller, operated at speeds typical of service conditions for a medium-sized turbocharger. The flow was found to be unstable, especially adjacent to the suction side of the blades, such that two predominant conditions existed in the flow. The unstable flow is illustrated in the paper by distributions of relative velocity and relative flow angle, and the effects of different operating conditions on these distributions are examined. The instability is believed to be caused by a pre-stall condition as the compressor operating point approaches a fully stalled condition which occurs during surge.
Flutter Spectral Measurements Using Stationary Pressure Transducers
Authors: Kurkov A. P.
Published: November 2009

Engine-order sampling was used to eliminate the integral harmonics from the flutter spectra corresponding to a case-mounted static pressure transducer. From the optical displacement data it was demonstrated that blade-order sampling of pressure data can yield erroneous results because of the interference caused by blade vibration. Two methods are presented that effectively eliminate this interference and yield the blade-pressure-difference spectra. The phase difference between the differential-pressure and displacement spectra was evaluated.
Experimental Investigation of Morel’s Method for Wind Tunnel Contractions
Authors: Tulapurkara E. G. , Bhalla V. V. K.
Published: November 2009

Based on a numerical study of the potential flow through contractions of chosen geometry, Morel (1975) has given a method to obtain the shape of contraction which gives small adverse pressure gradients and low nonuniformity in the velocity distribution at the exit. Two contractions with area ratios of 12 and 3.464 designed using this method are investigated experimentally. It is found that there is no separation of flow, the thickness of the boundary layer at the exit is small and the nonuniformity in velocity at the exit is smaller than the predicted value.
Experimental and Computational Investigation of the Two-Dimensional Channel Flow Over Two Fences in Tandem
Authors: Durst F. , Founti M. , Obi S.
Published: November 2009

Measurements and computations of the mean streamwise velocity and its fluctuations are reported for an arrangement of two similar fences mounted in tandem in fully developed channel flow. The influence of Reynolds number and blockage ratio, in terms of the size and location of the primary and secondary recirculation zones, were investigated. The flow field around each fence was found to be similar to one another as well as to the corresponding single fence flow, for Reynolds numbers (based on the fence height) of up to 100. For higher Reynolds numbers, the shear layer developing from the first fence was significantly disturbed by the second fence resulting in earlier transition and higher turbulence intensities. This effect was most evident in the measured differences of the recirculation lengths downstream of each fence.
Supercomputing of Supersonic Flows Using Upwind Relaxation and MacCormack Schemes
Authors: Baysal Oktay
Published: November 2009

The impetus of this paper is the comparative applications of two numerical schemes for supersonic flows using computational algorithms tailored for a supercomputer. The mathematical model is the conservation form of Navier-Stokes equations with the effect of turbulence being modeled algebraically. The first scheme is an implicit, unfactored, upwind-biased, line-Gauss-Seidel relaxation scheme based on finite-volume discretization. The second scheme is the explicit-implicit MacCormack scheme based on finite-difference discretization. The best overall efficiences are obtained using the upwind relaxation scheme. The integrity of the solutions obtained for the example cases is shown by comparisons with experimental and other computational results.
Some Observations of Flow Patterns and Statistical Properties of Three Component Flows
Authors: Kyto¨maa H. K. , Brennen C. E.
Published: November 2009

Vertical air-water flows, solids-water flows and three component air-solids-water flows were investigated in a Three Component Flow Facility. Visual observations of the flow patterns show that three component flows undergo transition and can exhibit strong unsteady vortical motions. Measurements of the fluctuations in cross-sectionally averaged volume fraction measurements were made. The statistical properties of the fluctuations are presented in terms of their amplitude and coherent time scale in the form of the Signal To Noise Ratio (STNR) and the Time Constant (ξ), respectively. Remarkably, the solids-water flows and the dispersed bubbly air-water flows exhibit almost identical values of STNR for the same volume fraction. Equally remarkable in the linear relationship between the Time Constant and the mean bubble or particle velocity; this relationship is found to have the same constant of proportionality for both species in the well behaved disperse regime. In the two-component churn-turbulent and the three-component agitated vortical regimes, the variables ξ and STNR significantly deviate from their dispersed regime values. The onset of large coherent structures characteristic of these regimes is reflected by a rise in the amplitude of the fluctuations and a marked increase in their coherent time scale. The results of this study demonstrate the large information content in the fluctuations of the measured quantity, both as a flow regime indicator and as a measure of flow quantities in two- and three-component flows.
Modelling Collisional Stresses in a Dense Fluid-Solid Mixture
Authors: Shen H. H. , Hopkins M. A. , Ackermann N. L.
Published: November 2009

An idealized dense mixture of fluid and solid is considered. The mixture consists of identical spheres and a Newtonian fluid. Collisional stresses in a simple shear flow of such a mixture are quantified. These stresses are considered to be generated by binary collisions of spheres which result from the mean shear flow. The fluid is considered to act only as a dissipater of the fluctuating motion of the solids. Fluid stresses are neglected. Unlike previous analyses which make similar assumptions about the effect of the fluid, the present work does not require assumptions about the collision kinematics, except that the kinematics be homogeneous in the entire flow field. This is achieved by replacing analytical integrations with a Monte Carlo procedure. The resulting collisional stresses are found to increase and compare better with experimental data than previously obtained analytical results.
Incremental Pressure Drop Number in Parallel-Plate Heat Exchangers
Authors: Nguyen T. V. , Maclaine-cross I. L.
Published: November 2009

Numerical solutions of the Navier-Stokes equations are presented for developing laminar flow in the entrance region of a cascade of parallel horizontal plates with a uniform velocity profile at upstream infinity. Extrapolation to zero mesh size is used. Detailed results on the incremental pressure drop number are presented for Reynolds number ranging from 40 to 2000.
Basic Elements in a Fluid Mechanics Laboratory Experience: An Engineering Science Approach
Authors: Foss J. F.
Published: November 2009

Experiments for a first fluid mechanics course are described. The basic concepts of pressure and velocity as the primitive variables, the control volume equations and the field equations with Reynolds number dependent properties are reinforced in these experiments. The use of such experiments, as the experimental background for future lecture instruction, is emphasized.
An Explicit Non-Real Time Data Reduction Method of Triple Sensors Hot-Wire Anemometer in Three-Dimensional Flow
Authors: Chew Y. T. , Simpson R. L.
Published: November 2009

An explicit non-real time method of reducing triple sensor hot-wire anenometer data to obtain the three mean velocity components and six Reynolds stresses, as well as their turbulence spectra in three-dimensional flow is proposed. Equations which relate explicitly the mean velocity components and Reynolds stresses in laboratory coordinates to the mean and mean square sensors output voltages in three stages are derived. The method was verified satisfactorily by comparison with single sensor hot-wire anemometer measurements in a zero pressure gradient incompressible turbulent boundary layer flow. It is simple and requires much lesser computation time when compared to other implicit non-real time method.
A Simple Model for the Critical Swirl in a Swirling Sudden Expansion Flow
Authors: Hallett W. L. H.
Published: November 2009

A simple momentum integral model for estimating the minimum or “critical” swirl intensity required to produce central recirculation in a swirling sudden expansion flow is presented. An explicit equation is given for the critical swirl as a function of expansion ratio and inlet velocity profile shape, the latter expressed by the radius of the solid body vortex core and a parameter describing an axial velocity maximum or minimum on the axis. The model is tested against experimental data for expansion diameter ratios from 1.25 to 3.0 and a variety of inlet conditions, and found to give good predictions.
Pressure-Driven Ranque-Hilsch Temperature Separation in Liquids
Authors: Balmer R. T.
Published: November 2009

The temperature separation phenomenon of the Ranque-Hilsch (vortex) tube is not limited to compressible gases and vapors. Theoretical analysis using the Second Law of Thermodynamics establishes that a net entropy producing temperature separation effect is possible when incompressible liquids are used in these devices. Experiments with liquid water in a commercial counterflow Ranque-Hilsch tube designed for use with air verify that significant temperature separation does in fact occur when a sufficiently high inlet pressure is used.
An Experimental and Numerical Study of Flow and Convective Heat Transfer in a Freely Falling Curtain of Particles
Authors: Hruby J. , Steeper R. , Evans G. , Crowe C.
Published: November 2009

The flow characteristics and convective heat transfer in a freely falling curtain of spherical particles with an average diameter of 650 μm has been studied experimentally and numerically. Both heated and unheated particle flows have been considered. This work is part of a larger study to determine the feasibility of using particles to directly absorb the insolation in a solar central receiver for high temperature applications. The particles of interest are Norton Master Beads™ which are primarily aluminum oxide. Measurements have been made of particle velocity in heated and unheated particle flows, and particle temperature and air temperature in heated particle flows. Comparison of the measurements with calculations has been made for two particle mass flow rates at room temperature and at two initial elevated particle temperatures. Excellent agreement between numerical and experimental results is obtained for particle velocity in the unheated flow. For the heated particles, both data and predictions show the same trends with regard to particle velocity, particle temperature, and air temperature. However, the calculations of these quantities overpredict the data. The results suggest that the drag coefficient in flows where the particles are hot compared to the air is larger than predicted using conventional methods to account for nonisothermal effects. The prediction of particle temperature and air temperature attained with a drag coefficient that is larger than the standard drag coefficient agrees well with the data.
A Comparison of Algebraic and Differential Second-Moment Closures for Axisymmetric Turbulent Shear Flows With and Without Swirl
Authors: Fu S. , Huang P. G. , Launder B. E. , Leschziner M. A.
Published: November 2009

Computations are reported for three axisymmetric turbulent jets, two of which are swirling and one containing swirl-induced recirculation, obtained with two models of turbulence: a differential second-moment (DSM) closure and an algebraic derivative thereof (ASM). The models are identical in respect of all turbulent processes except that, in the ASM scheme, stress transport is represented algebraically in terms of the transport of turbulence energy. The comparison of the results thus provides a direct test of how well the model of stress transport adopted in ASM schemes simulates that of the full second-moment closure. The comparison indicates that the ASM hypothesis seriously misrepresents the diffusive transport of the shear stress in nonswirling axisymmetric flows, while in the presence of swirl the defects extend to all stress components and are aggravated by a failure to account for influential (additive) swirl-related stress-transport terms in the algebraic modelling process. The principal conclusion thus drawn is that in free shear flows where transport effects are significant, it is advisable to adopt a full second-moment closure if turbulence modelling needs to proceed beyond the eddy-viscosity level.
The Effect of Inlet Turbulence Intensity on the Reattachment Process Over a Backward-Facing Step
Authors: Isomoto K. , Honami S.
Published: November 2009

Behavior of a separated shear layer over a backward-facing step and its reattachment is presented when a two-dimensional cavity or rod is installed upstream of the step in order to change local turbulence intensity in addition to grid turbulence in the free-stream. The reattachment length has a strong negative correlation with maximum turbulence intensity near the wall at the separation point. Turbulence in the entrainment region immediately downstream of the step plays an important role in determining the reattachment length.
A Modified Van Driest Formula for the Mixing Length of Turbulent Boundary Layers in Pressure Gradients
Authors: Granville P. S.
Published: November 2009

A modified van Driest formula is proposed for the mixing length of turbulent boundary layers in pressure gradients. The slope and intercept of the logarithmic similarity law are satisfied asymptotically unlike existing modified van Driest formulas.
Passive Control of Three-Dimensional Separated Vortical Flow Associated With Swept Rearward-Facing Steps
Authors: Selby G. V.
Published: November 2009

Control of the three-dimensional separated-flow region down-stream of a swept, rearward-facing step has been studied with the purpose of reducing the separated-flow region and attendant drag. Results have indicated that geometric modifications in the region downstream of the step where the spanwise vortex is formed has little effect on the extent of the separated flow, while “conical-lip” and “vortex-trough” base modifications lead to a significant reduction in reattachment distances. The “conical-lip” modification involves a step lip with variable radius and the “vortex troughs” are grooves in the surface upstream of the step which produce longitudinal vortices.
Measurements in Two-Dimensional Plumes in Crossflow
Authors: Ramaprian B. R. , Haniu H.
Published: November 2009

The mean-flow and turbulent properties of two-dimensional buoyant jets discharged vertically upward into a crossflowing ambient have been measured in a hydraulic flume, using laser velocimetry and microresistance thermometry. The trajectory of the resulting inclined plume is found to be nearly straight, beyond a short distance from the source. The flow is essentially characterized by the presence of buoyancy forces along (s-direction) and perpendicular (n-direction) to the trajectory. While the s-component buoyancy tends to destabilize the flow and hence raise the overall level of turbulence in the flow, the n-component buoyancy tends to augment turbulence on the upper part of the flow and inhibit turbulence on the lower part. The experimental data are used to examine these effects quantitatively.
Flow Structure in the Wake of an Oscillating Cylinder
Authors: Lecointe Y. , Piquet J.
Published: November 2009

The numerical solution of the unsteady two-dimensional Navier-Stokes equations is used to investigate the vortex-shedding characteristics behind a circular cylinder immersed in a uniform stream and performing superimposed in-line or transversed oscillations of a given reduced amplitude.
The Law of the Wall for Swirling Flow in Annular Ducts
Authors: Kind R. J. , Yowakim F. M. , Sjolander S. A.
Published: November 2009

Expressions for the logarithmic portion of the law of the wall are derived for the axial and tangential velocity components of swirling flow in annular ducts. These expressions involve new shear-velocity scales and curvature terms. They are shown to agree well with experiment over a substantial portion of the flow near both walls of an annulus. The resultant velocity data also agree with the law of the wall. The success of the proposed logarithmic expressions implies that the mixing-length model used in deriving them correctly describes flow-velocity behavior. This model indicates that the velocity gradient at any height y in the near-wall region is determined by the wall shear stress, not by the local shear stress. This suggests that the influence of wall shear stress is dominant and that it determines the near-wall wall flow even in flows with curvature and pressure gradient. A physical explanation is suggested for this.
Check Valve Behavior Under Transient Flow Conditions: A State-of-the-Art Review
Authors: Thorley A. R. D.
Published: November 2009

Recent advances in the understanding of check valve behavior are reviewed. It is evident that the basis now exists for providing reliable information on valve dynamics that is in a form that can be easily assimilated and used by pipeline design engineers. The use of nondimensional valve performance curves is discussed and recommended. Manufacturers are encouraged to provide these data. Design engineers are charged with the responsibility of using it and are provided with guidelines for so doing.
Tip Vortex Cavitation Inhibition by Drag-Reducing Polymer Solutions
Authors: Fruman D. H. , Aflalo S. S.
Published: November 2009

This paper presents previous and recent results obtained by the authors concerning the modification of the tip vortex cavitation of a finite span hydrofoil by drag-reducing polymer solutions. Experiments were conducted with homogeneous solutions and with semidilute solutions ejected at the tip of the wing. Measurements of the onset cavitation number for tip vortex cavitation, hydrodynamic forces on the hydrofoil and tangential velocities in the tip vortex have been conducted. The results show that tip vortex cavitation is inhibited in all cases but for different reasons. In homogeneous polymer solutions the lift of the hydrofoil, and hence the circulation, is considerably reduced leading to a less intense vortex as shown by tangential velocity measurements. With semidilute polymer solution ejections there is no noticeable change of the hydrodynamic forces but a significant modification of the tangential velocities in the core region. The mechanism for tip vortex cavitation inhibition is thus completely different in these two situations.
Visualizing the Connectivity of Vortex Systems for Pitching Wings
Authors: Freymuth P.
Published: November 2009

The global visualization of vortex systems of pitching wings is explored. The topological law that vortex strands need to be connected aids in comprehending the visualized vortex systems and in assessing the quality of visualization. Viscous and viscous-turbulent diffusion facilitate the reconnection of vortex strands.
A Useful Approximation to the Error Function: Applications to Mass, Momentum, and Energy Transport in Shear Layers
Authors: Greene P. R.
Published: November 2009

Specific mass, momentum, and energy flux transport integrals are given by the sequence I1 = ∫erfc(x)dx, I2 = ∫erfc2(x)dx, and I3 = ∫erfc3(x)dx for the error function velocity distribution typical of some laminar and turbulent shear layers. In this report, the Gaussian function A exp(−b(x−x0)2) is used to approximate the error function within 0.21 percent, allowing a direct approximate closed-form evaluation of these transport flux integrals. Mass, momentum, and energy flux are accurate to within 0.22, 0.15, and 0.11 percent, respectively, over the entire shear layer. To achieve this same degree of accuracy with a Taylor series requires in excess of 10 terms. Each of the sequence of approximate functions can be inverted to yield the inverse function, i.e., erfc−1(x), etc., also in closed-form. The results presented here are also applicable to the error function as it appears in heat transfer and probability and statistics type problems. A coefficient table is included to allow evaluation of the error function and its various integrals.
The Correction of X-Probe Results for Transverse Contamination
Authors: Clausen P. D. , Wood D. H.
Published: November 2009

This note discusses the interpretation of X-probe measurements obtained in the presence of significant velocities transverse to the plane of the wires. To measure the three mean velocity components, the probe was used in two planes which gave a redundant estimate of the component along the probe axis. A correction of the measured mean velocities for transverse contamination is described and justified. It was found that the corrections reduced the mean component along the probe’s axis by up to 20 percent, while the components orthogonal to that axis were hardly altered.
Unstable Waves of Jet Flows With Density Inhomogeneity
Authors: Fung Y. T.
Published: November 2009

Instability of axisymmetric jet flows of a fluid having a radius-dependent density is investigated. The necessary condition for the existence of unstable waves depends not only on the velocity profile but also on the density gradient as well. Large density gradients, positive or negative, have stabilizing effects. The semicircle theorem for amplified waves is valid in this case. It is shown by considering the top-hat type velocity profile that the velocity-dependent semicircle bound is the best possible.
Extension of the Circle Theorems by Surface Source Distribution
Authors: Rand O.
Published: November 2009

The paper presents a closed-form analytical solution for the source strength distribution along the circumference of a two-dimensional circular cylinder that is required for producing an arbitrary distribution of normal velocity. Being suitable to be used with flows having arbitrary vorticity distribution, the present formulation can be considered as an alternative and extensive form of the circle theorems. Using the conformal transformation technique, the formulation also serves as a closed-form solution of Laplace’s equation in any two-dimensional flow domain that is reducible to the outer or inner region of a circular cylinder having arbitrary prescribed normal velocity over its boundary.
Calculation of Confined Swirling Flows With a Second Moment Closure
Authors: Jones W. P. , Pascau A.
Published: November 2009

A Reynolds stress transport equation model and the k–ε turbulence model have been applied to the calculation of a confined, strongly swirling flow. A comparison of the results with measurement shows clearly the superiority of the transport equation model. It reproduces the major features of the flow including the strong stabilizing effects of the swirl on the shear stresses and the calculated axial and circumferential components of mean velocity are in reasonable agreement with measured profiles. The corresponding normal stresses are, however, overpredicted but previously suggested modifications to the ε-equation to account for rotation did not bring any improvement. The k–ε model does not contain any mechanism to describe the stabilizing effects of swirling motion and as a consequence it performs poorly; large discrepancies exist between the measured and calculated mean velocity field.
The Effect of Pitch Location on Dynamic Stall
Authors: Jumper E. J. , Dimmick R. L. , Allaire A. J. S.
Published: November 2009

This paper reports the results of theoretical and wind-tunnel studies of the effect of pitch location on dynamic stall for an airfoil pitching at constant rate. A modified momentum-integral method was used to predict the effect of pitch location and rate on the delay in quarter-chord separation. The wind-tunnel study involved the collection of time-varying pressure readings from 16 locations on an NACA 0015 airfoil that were subsequently used to determine lift, pressure-drag, and moment coefficients as functions of angle of attack for 140 test cases, covering 28 dynamic airspeed/pitch-rate/pitch-location combinations. Dynamic-stall effects of change (from steady flow) in the angle of attack at which separation occurs at the quarter chord (for comparison with the momentum-integral results), and change in the angle of attack at which stall occurs were extracted from these data and found to collapse best onto a non-dimensional pitch rate given by the chord times the pitch rate divided by two times the free-stream velocity. An adjusted non-dimensional rate formed by replacing one half the chord with the fraction of the chord corresponding to the pitch location was also examined and found not to be the proper non-dimensional variable for collapsing the data. The quarter-chord separation data compared favorably with the theoretical predictions.
Noise Generated by Cavitation in Orifice Plates
Authors: Bistafa S. R. , Lauchle G. C. , Reethof G.
Published: November 2009

An experimental investigation of the noise generated by cavitation in turbulent shear flows produced by confined sharp-edged orifice plates is reported. The acoustic source strength of cavitation was determined by means of reciprocity type measurements. Two experimental checks of the reciprocity method were performed. Proposed scaling relations, derived from dimensional analysis, were empirically adjusted and used to predict prototype acoustic performance based on the results of model tests. The dependence of the acoustic source strength on flow velocity and cavitation number was determined experimentally and compared with similar results reported in the literature.
Pipe Flow Measurements of a Transparent Non-Newtonian Slurry
Authors: Park J. T. , Mannheimer R. J. , Grimley T. A. , Morrow T. B.
Published: November 2009

An experimental description of the flow structure of non-Newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is the primary objective of this research. Experiments were conducted in a large-scale pipe slurry flow facility with an inside pipe diameter of 51 mm. The transparent slurry formulated for these experiments from silica, mineral oil, and Stoddard solvent exhibited a yield-power-law behavior from concentric-cylinder viscometer measurements. The velocity profile for laminar flow from laser Doppler velocimeter (LDV) measurements had a central plug flow region, and it was in agreement with theory. The range of the transition region was narrower than that for a Newtonian fluid. The mean velocity profile for turbulent flow was close to a 1/7 power-law velocity profile. The rms longitudinal velocity profile was also similar to a classical turbulent pipe flow experiment for a Newtonian fluid; however, the rms tangential velocity profile was significantly different.
Mean Drop Sizes From Fan Spray Atomizers
Authors: Snyder H. E. , Senser D. W. , Lefebvre A. H.
Published: November 2009

The drop size distributions produced by two geometrically similar fan spray nozzles were measured over an injection pressure range from 1.38 to 10.34 MPa (200 to 1500 psi). The fluids employed were water, water/glycerine mixtures, silicone oils, paint, and paint solvent. These liquids were selected to provide wide ranges in liquid viscosity and surface tension. A nonintrusive Malvern 2600 particle sizer, based on the forward scattering of a 5 mW He-Ne laser beam, was used to yield line-of-sight and cross-sectional drop size distributions. The atomizer was traversed across the laser beam and drop size profiles as a function of distance from the centerline were developed. Analysis of the experimental data showed that the effects of injection pressure and liquid properties on atomization quality are described with good accuracy by the following dimensionally-correct equation. SMDdh=2.83σμL2ρAdh3ΔPL20.25+0.26σρLρAdhΔPL0.25
Experiments on Transition to Turbulence in a Constant-Acceleration Pipe Flow
Authors: Lefebvre P. J. , White F. M.
Published: November 2009

Experiments were conducted to study transition to turbulence in pipe flows started from rest with a linear increase in mean velocity. The data were taken at the Unsteady Flow Loop Facility at the Naval Underwater System Center, using a 5-cm diameter pipe 30 meters long. Instrumentation included static pressure, wall pressure, and wall shear stress sensors, as well as a laser Doppler velocimeter and a transient flowmeter. A downstream control valve was programmed to produce nearly constant mean flow accelerations, a, from 2 to 12 m/s2. In each of 37 runs, the time of transition to turbulence was the same throughout the pipe to within ± 30 ms, indicating a global instability. As acceleration increased, the transition Reynolds number ReD increased monotonically from 2 × 105 to 5 × 105. Other dimensionless transition parameters are also presented, the simplest and most effective of which is T* ≈ 400 ± 10 percent for the present experiments, where T* = ttr(a2/ν)1/3 and ν is kinematic viscosity.
Transient Free Surface Shape in an Abruptly Rotating, Partially Filled Cylinder
Authors: Choi Sangmin , Kim Jae Won , Hyun Jae Min
Published: November 2009

An experimental investigation has been made to depict the transient free surface shape in spin-up from rest of a liquid in a partially filled cylinder. The rotational Reynolds number is large and the cylinder aspect ratio is 0(1). The experiments have been designed to validate the analytical model due to Homicz and Gerber, which is an extension of the model of Wedemeyer, Goller, and Ranov. An outline of this analytical model is given. The experimental setup and techniques are briefly described. The main emphasis is placed on presenting the experimental data of the free surface shape when the steady-state free surface intersects one or both of the endwall disks. The analytical predictions of the free surface shape are found to be in satisfactory agreement with the experimental measurements for all the possible free surface configurations. These explicit comparisons establish the practical usefulness of the analytical model; the model is capable of predicting the transient free surface shape during the spin-up phase of a liquid.
Experimental Investigation of the Flow Through Axisymmetric Expansions
Authors: Stieglmeier M. , Tropea C. , Weiser N. , Nitsche W.
Published: November 2009

This study examines the flow field in three axisymmetric expansions having diffuser half-angles of 14, 18, and 90 deg, respectively. Velocity measurements were performed at a Reynolds number of Re = 1.56 × 104 using a single component LDA operated in forward scatter. The test facility was refractive index matched, allowing measurement of the velocities U, V, W, u2, v2, w2, uv and uw upstream of, and throughout the entire recirculation region. The results indicate that the diffuser geometry influences the separated shear layer appreciably over the entire length of the diffuser section. The production of turbulence immediately after separation is much higher in the case of the 14 and 18 deg diffuser compared to the 90 deg expansion, leading to higher diffusion rates in the separated shear layer, and hence earlier reattachment of the shear layer.
Turbulent Boundary Layer Development in the Presence of Small Isolated Two-Dimensional Surface Discontinuities
Authors: Cockrell D. J. , Nigim H. H. , Alhusein M. A.
Published: November 2009

Discontinuities in surfaces over which fluids flow can occur in a variety of situations. One of contemporary engineering significance is that which arises on aircraft wings, where the wing forms a junction with an auxiliary lifting surface. Such discontinuities are often two-dimensional and may well be small, lying within the logarithmic regions of the turbulent boundary layers in which they are immersed. In this paper such surface discontinuities are idealized into shapes whose drag coefficients, when they have been isolated from their surrounding surfaces, have been previously determined and tabulated. By making appropriate assumptions about the boundary layer characteristics in the vicinity of the discontinuities and then adopting appropriate integral boundary layer prediction techniques, methods are developed for continuing the boundary layer prediction process across them and then downstream of them. These computations compare well with experimental results, even for comparatively large discontinuities and the technique is recommended for use in a predictive role.
A Trajectory-Simulation Model for Heavy Particle Motion in Turbulent Flow
Authors: Zhuang Y. , Wilson J. D. , Lozowski E. P.
Published: November 2009

For many purposes it is useful to be able to mimic the paths of heavy particles in a turbulent flow. This paper gives a simple procedure by which this may be achieved, provided particle spin is not important and under the restriction that the ratio of particle to fluid density exceeds about 1000. The procedure is related to the models of Faeth (1986) and Hunt and Nalpanis (1985). Simulation of the experiments of Snyder and Lumley (1971) yielded acceptable agreement with the observed rate of heavy particle dispersion.
The Damage Capacity of Cavitating Flow From Pulse Height Analysis
Authors: Fry S. A.
Published: November 2009

Digital pulse amplitude acquisition systems are reviewed and an analogue pulse height analyser (PHA) is described. Cavitation experiments are reported in which pressure pulses in the liquid (water) are picked up by a flush mounted pressure transducer and measured using the PHA. Tests were carried out on two cavitation sources: a 60 deg symmetric wedge and a circular cylinder. Despite generating similar r.m.s. noise levels the wedge is 21 times as damaging as the circular cylinder at peak noise flow conditions (at V = 16 m/s). By imposing thresholds on the spectra parameters it had been possible to find a linear calibration beween noise and erosion applicable to both cavitation sources over a range of flow velocities. A good correlation between cavitation noise and erosion was found by simply measuring the number of pulses above a suitable threshold.
Dynamic Analysis for Transportation of Barge-Jacket Assembly in Time-Frequency Domain
Authors: Sun F. , Gao C.
Published: November 2009

A combined time-frequency domain method is proposed to analyze the stresses of barge-jacket assembly during transportation. Starting with the motion of analysis in frequency domain, the time history of waves and motions in random seas are simulated, then the stresses are determined in time domain. The stress autocorrelation functions are calculated and the stress spectra and statistical characteristics are obtained through Fourier transformation. A computer program has been developed. The effects of barge flexibility and the forces caused by the immersion of jacket have been discussed.
Boundary Element Analysis of Three-Dimensional Water Wave-Structure Dynamic Interaction Problems
Authors: Tosaka N. , Kakuda K.
Published: November 2009

Water wave-structure dynamic interaction problems are treated as eigenvalue problems of the coupled system by means of the boundary element method. The coupled system for a large-sized ocean structure is modelized generally with the three-dimensional continuum mechanics. The boundary integral equations of the coupled system are derived by the weighted residual method and related fundamental solutions. The solving scheme for the discretized equations is discussed in detail. Numerical examples of the three-dimensional problem are given to show the validity of the present method through the comparison with other results.
Laboratory Compression Tests of Sea Ice at Slow Strain Rates From a Field Test Program
Authors: Wang Y. S. , Poplin J. P.
Published: November 2009

In the winter of 1979/80, five petroleum companies participated in a field test program conducted by Exxon Production Research Company in Prudhoe Bay, Alaska, to measure the unconfined compressive strength of the sea ice sheet in its full thickness at various strain rates between 10−7 and 8 × 10−5 s−1. As part of this program, ice sample blocks at four different levels in the ice sheet were collected from seven field test sites and shipped to Exxon’s Cold Laboratory in Houston. A total of 221 cylindrical ice samples were made from the ice blocks and tested for their compressive strengths on a closed loop test machine. The sample size was 2.725 in. (6.92 cm) in diameter and 5.75 in. (14.60 cm) long. The strain rate and temperature under which each sample was tested were selected to match actual field test conditions. In addition, 76 thin sections were prepared from tested samples and were studied for the crystallographic structure. Results indicate that local variations of the crystalline structure of the ice sheet could be significant and could cause large variations in the strength of individual samples. The results of the laboratory tests were used to estimate the strength of the full-thickness ice sheet by taking the average value of the through-thickness strength profile. Comparison with field tests shows that this procedure gives very accurate strength estimation for the strain rate range used in the field tests.
Variations of the Local Failure Pressure With Depth Through First-Year and Multi-Year Ice
Authors: Blanchet D.
Published: November 2009

Typical vertical distributions of the failure pressure in an ice sheet are presented. The distributions, derived for intermediate strain rates, are a function of many parameters, namely, the salinity, the temperature, the type of ice, the location of the ice pressure area through the ice thickness, the thickness of ice, the density, and the crack and flaw distributions. Two combinations of these parameters lead to “representative” summer and winter vertical ice pressure profiles for 8 and 2-m thick ice floes. The importance of the vertical distribution of the failure pressure inside an ice cover is fundamental for two reasons. The change in the eccentricity of the resultant of the load induces changes in failure mode and load transmission to the structure. This nonuniform distribution will create nonsimultaneous failure and the ice pressure on the structure will not be hydrostatically distributed over a given area.
The Strength and Ductility of Ice Under Tension
Authors: Lee R. W. , Schulson E. M.
Published: November 2009

Tensile experiments have been performed on aggregates of equiaxed and randomly oriented ice Ih of varying grain size (1.4 to 7.9 mm) at −10°C at two strain rates, 10−3 s−1 and 10−7 s−1. At both rates, which were held constant using “feed-back” control, the tensile strength decreased with increasing grain size. This result confirms earlier work on grain size effects in which the rate randomly varied (from 0.6 × 10−6 s−1 to 3 × 10−6 s−1) from test to test. At the higher rate the ice is brittle over the complete range of grain size and its strength is given by the relationship σf = σo + kd−1/2 where σo = 0.51 MPa and k = 0.03 MPa m1/2. At the lower rate the ice is ductile over the same range of grain size and its strength is given by the relationship σf = Kd−1/2 where K = 0.050 MPa m1/2. These effects are explained quantitatively in terms of the nucleation and propagation of cracks.
The Fracture Toughness of Ice Over a Range of Grain Sizes
Authors: Nixon W. A. , Schulson E. M.
Published: November 2009

Tests have been performed at −10°C on circumferentially notched right circular cylinders of randomly oriented granular polycrystalline freshwater ice, to determine whether grain size affects fracture toughness (KIc). Grain sizes, as measured by the linear intercept method, varied from 1.6 mm to 9.3 mm in diameter. The circumferentially notched specimen was used because of the ease with which it can be manufactured from right circular cylinders, made regularly and with considerable accuracy of alignment for some years now by workers of the Thayer School Ice Research Laboratory. A slight (25 percent) decrease in values of KIc is observed as grain size increases over the range investigated. Consideration is given to the cause of this effect and to its possible contribution to the scatter in KIc values observed by earlier workers. Other possible causes of this scatter are indicated.
Inferring Ice/Ocean Surface Roughness from Horizontal Current
Measurements
Authors: McPhee M. G.
Published: November 2009

Turbulence measurements in the underice boundary layer from two Arctic drift stations are used to develop a method for estimating the small-scale roughness, zo, of the ice underside from horizontal current and current variance, sampled at one level. Horizontal variance is shown to be well correlated with turbulent kinetic energy (TKE). Measurements also indicate that at depths where turbulence is fully developed to the surface roughness, shear production of TKE is approximately in balance with viscous dissipation, so that the magnitude of local horizontal stress is proportional to flow variance. A similarity model is used to extrapolate local stress to the interface, and zo is estimated from the logarithmic profile for current speed. The method has application for using remote data buoys, equipped with “smart” current meters, for mapping the underice roughness.
Application of a General Technique for Prediction of Riser
Vortex-Induced Response in Waves and Current
Authors: Lyons G. J. , Patel M. H.
Published: November 2009

This paper describes applications of an extension to a recently developed calculation method for vortex-induced response of risers and tethers. The vortex-induced vibration response for the excited modes is generated using a semi-empirical formulation which is applied within a time domain calculation. This makes it possible to take account of the variation of flow properties along the riser length, as well as in time. The calculation method has been verified by comparison with model test data for vortex-induced response to surface vessel motions in still water. This paper presents applications of the technique for vortex shedding due to the combined action of current, surface vessel motions and waves. The mathematics of the extended prediction technique is described and results are illustrated by presenting typical vortex-induced responses for single-tube risers. The results of the prediction method are used to highlight the relative magnitudes and nature of vortex-induced response excited by currents, surface vessel motions and waves.
Shear Modulus of Soft Marine Clays
Authors: Pamukcu S.
Published: November 2009

Instabilities occur frequently in ocean-bottom sediments where the deposition is faster than the consolidation of the material. Cyclic loading of waves contribute to the existing pore pressures within the sediment reducing the effective stresses. The sediment can lose strength and stability and flow in gullies of depth up to 30 m, on slopes less than 0.5 deg. One theory and some related experiments indicate that, depending on the depositional conditions and state of stress, the failure mechanism for such soft saturated marine clays may not necessarily require large straining of the material. Laboratory determination of low-strain shear behavior or shear modulus of soft marine clays can be complicated if high-frequency dynamic testing methods are utilized. Cyclic loading can promote fast degradation of moduli for these soils even at low strain amplitudes. A monotonic torsional shear device, namely a triaxial vane device, was equipped with a computer-aided data acquisition system to detect low-strain shear deformations under quasi-static loading conditions. The average range of electronically measured strain range was 10−4 to 1 percent, which was compatible with that of a high-frequency, low-strain dynamic testing method, namely, resonant column. Comparison of the dynamic and static moduli reduction curves of artificially prepared soft kaolinite specimens demonstrated the cyclic degradation effects on such clays. The relatively continuous, high-resolution low-strain static data indicated further gain in understanding of low-strain nonlinearity and yielding behavior of soft marine clays.
Mathematical Modeling and NDT: A State of the Art
Authors: Georgiou G. A. , Blakemore M.
Published: November 2009

During the past decade or so there have been significant advances in the mathematical modeling of nondestructive testing (NDT) techniques. The current state of modeling is reviewed, with the aim of demonstrating the important role that it can play in improving and validating NDT techniques and procedures. This paper was presented at the 6th International Offshore Mechanics and Arctic Engineering Symposium, (1987). Since that time, a number of advances have been made in mathematical modeling. A more recent review of mathematical modeling techniques, with additional references, is currently in preparation by the authors.
The Behavior of a Poroelastic Seabed Under Normal and Shear
Loads
Authors: Sabin G. C. W.
Published: November 2009

One of the effects of ice and water forces on large offshore structures which rest on the seabed is to transmit surface tractions to the region of contact. A recent paper by Sabin and Raman-Nair [1] has examined the effect of a normal axisymmetric load P(r, t) on a poroelastic seabed under several different conditions of boundary permeabilities. That study provided a number of general formulas for an arbitrary normal load. The present paper extends the results found in [1] to include shear tractions. While reference [1] was primarily a theoretical discussion, the present paper examines several specific forms of loading and presents graphs showing the normal stress and pore pressure response for various values of the parameters of interest. These results are compared with the limiting case of an extended period of time.
Structural Modeling of Undersea Cables
Authors: Knapp R. H.
Published: November 2009

A structural model for undersea cables is described. This model has been implemented in a computer-aided design program with the capability to determine cable deformations and internal stresses in response to applied loads including tension, twist, bending, pressure and enforced displacements. Complex geometries and nonlinearly elastic material properties can also be treated. Results of a comprehensive series of physical cable tests to validate the computer code are reported.