bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual Stresses and Surface Roughness in Turning
Authors: Capello Edoardo , Davoli Piermaria , Bassanini Gianluca , Bisi Alessandro
Published: February 2008

The fatigue resistance of components is greatly influenced by their surface integrity. In particular, residual stresses and surface roughness are held to be the primary factors influencing fatigue resistance. This paper presents an experimental study of the influence of turning parameters on surface roughness and residual stresses. Two steels were machined by turning, the results of variations in four process parameters were measured and analyzed. These results show that in the typical range of industrial machining conditions both surface finish and residual stresses are influenced mainly by the feed rate and the nose radius; the cutting velocity and the primary rake angle play a minor, negligible role. Moreover, two empirical models were identified that can be used to predict residual stresses and roughness as a function of the two major turning parameters. These models can be used to optimize the turning conditions of components when their functionality requires the control of residual stresses and surface roughness.
Strip Yield Analysis on Coalescence of Plastic Zones for Multiple Cracks in a Riveted Stiffened Sheet
Authors: Nishimura Toshihiko
Published: February 2008

The coalescence conditions of plastic zones are calculated for multiple cracks in a riveted stiffened sheet using a strip yield model. The multiple cracks and their plastic zones are treated as a fictitious crack, and algebraic equations are formulated on compatibility of displacements, no stress singularity at the fictitious crack tips, and zero displacement at the coalesced points of plastic zones. These equations are iteratively solved, and critical values of remote stress, fastener forces, plastic zone sizes, and crack tip opening displacements are calculated. Some numerical results are presented for two cracks in a sheet with and without stiffeners.
A Micromechanics-Based Finite Element Model for Compressive Failure of Notched Uniply Composite Laminates Under Remote Biaxial Loads
Authors: Ahn Jung H. , Waas Anthony M.
Published: February 2008

A micromechanics based failure initiation predictive capability for analyzing notched composite laminates loaded remotely in multiaxial compression is reported. The model relies on the results from a previous experimental study that investigated compression failure mechanisms in special “uniply” composite laminates. The finite element method (FEM) was used in the solution process. The experimental results showed that the dominant mode of failure initiation was kink banding near the hole edge. The kink band was confined in extent to a distance within one half of the hole radius. The fibers within the kink band were rotated both in plane and out of the plane of the laminate. The position of the kink band with respect to the center of the notch depended on the remote biaxial load ration. In the FEM, the region in which kink banding takes place is contained within a finite size rectangular area, and is meshed as an alternatingly stacked region of fiber and matrix layers. The values of boundary loads on this rectangular area which correspond to kink banding is related to the remotely applied loads via an available closed form analysis for orthotropic laminates. Good agreement is found between experiment and analysis for a wide range of notch sizes.
Delamination Growth Behavior of a Fabric Reinforced Laminated Composite Under Mode I Fatigue
Authors: Atodaria D. R. , Putatunda S. K. , Mallick P. K.
Published: February 2008

The purpose of this study is to investigate the delamination growth behavior of a glass fabric reinforced laminated composite under Mode I fatigue loading and to examine the applicability of a new fatigue crack growth rate model to this material. In this study, double contilever beam specimens were subjected to tension-tension cyclic loads with three different load ratios and the delamination growth rate was measured using the compliance method. The delamination growth rate was related to the strain energy release rate during fatigue cycling by a power law equation that takes into account not only the effect of the strain energy release rate range, but also the effect of delamination growth at various stages of loading using a weight average strain energy release rate. It was observed that this new model can represent the delamination growth rate of the fabric reinforced laminated composite at three different load ratios in a single unifying curve.
Estimating the Location and Depth of Normal Cracks in Cantilevers From Holographic Fringe Patterns
Authors: Qin S. , Shang H. M. , Leong Q. H. , Tee C. E.
Published: February 2008

Two parameters that are linearly related for a crack-free cantilever but cease to be so when a crack is present, are derived. A simple procedure for detecting the crack and assessing its location and depth is subsequently described.
Single-Edge and Double-Edge Cracks in a Fully Anisotropic Strip
Authors: Huang Haiying , Kardomateas George A.
Published: February 2008

The mode I and II stress intensity factors in a fully anisotropic infinite strip with a single-edge or double-edge crack configuration are obtained from an approach based on the continuous dislocation technique. The elastic solution of a single dislocation in an anisotropic half plane is used in conjunction with an array of dislocations along the boundary of the infinite strip, which is supposed to be traction-free, to provide the solution of a single dislocation in an anisotropic infinite strip. The dislocation densities of the dislocation array are determined in such a way that the traction forces generated by the dislocation array cancel the residual tractions along the boundary due to the single dislocation in the half plane. The stress field of a single dislocation in the infinite strip is thus a superposition of that of the single dislocation and the dislocation array in the half plane. This solution is then applied to calculate the mixed mode I and II stress intensity factors for a single-edge and a double-edge crack in the anisotropic strip, by replacing the cracks with a series of dislocations and satisfying the crack surface traction-free conditions. To illustrate the results, typical material data for graphite/epoxy were used in a unidirectional construction with the fiber orientation, θ, measured from the load direction (perpendicular to the crack direction), varying between 0 and 90 degrees. It is found that the effect of anisotropy on the mode I stress intensity factor is significant between 30 and 60 degrees and depends strongly on the relative crack length, being larger for cracks of relative larger length. The mode mixity, defined such that it is zero for pure mode I and 90 degrees for pure mode II, is significant between 40 and 70 degrees, and is in general between zero and 20 degrees.
A Computational Model for Predicting Damage Evolution in Laminated Composite Plates
Authors: Phillips M. L. , Yoon C. , Allen D. H.
Published: February 2008

A model is developed herein for predicting the evolution of interface degradation, matrix cracking, and delamination at multiple sites in laminated continuous fiber composite plates subjected to monotonic and/or cyclic mechanical loading. Due to the complicated nature of the many cracks and their interactions, a multi-scale micro-meso-local-global methodology is deployed in order to model all damage modes. Interface degradation is first modeled analytically on the microscale, and the results are homogenized to produce a cohesive zone model that is capable of predicting interface fracture. Subsequently, matrix cracking in the plies is modeled analytically on the meso-scale, and this result is homogenized to produce ply level damage dependent constitutive equations. The evolution of delaminations is considered on the local scale, and this effect is modeled using a three dimensional finite element algorithm. Results of this analysis are homogenized to produce damage dependent laminate equations. Finally, global response of the damaged plate is modeled using a plate finite element algorithm. Evolution of all three modes of damage is predicted via interfacing all four scales into a single multi-scale algorithm that is computationally tenable for use on a desktop computer. Results obtained herein suggest that this model may be capable of accurately predicting complex damage patterns such as that observed at open holes in laminated plates.
Micromechanical Modeling of FRCs Containing Matrix Cracks and Partially Debonded Fibers
Authors: Wang X. D. , Meguid S. A.
Published: February 2008

This study is concerned with the treatment of the dynamic antiplane failure behavior of fiber reinforced composites involving matrix cracks and partially-debonded fibers. The matrix/fiber interphase was modeled as a thin interfacial layer with varying elastic modulus. The steady-state theoretical solution of this class of problems is formulated using a newly developed pseudo-incident wave method, thus reducing the original interaction problem into the solution of coupled single fiber/crack solutions. By using Fourier transform technique and solving the resulting singular integral equations, the dynamic stress intensity factor at the matrix crack was obtained analytically. Numerical examples were provided to show the effect of the location and material property of fibers, the size of debonded layer, and the frequency of the incident wave upon the dynamic stress intensity factors of the matrix crack.
An Investigation of the Effects of Layer Thickness on the Fracture Behavior of Layered NiAl/V Composites
Authors: Li M. , Wang R. , Katsube N. , Soboyejo W. O.
Published: February 2008

The effects of vanadium layer thickness (100, 200 and 400 μm) on the resistance-curve behavior of NiAl/V, microlaminates are examined in this paper. The fracture resistance of the NiAl microlaminates reinforced with 20 vol.% of vanadium layers is shown to increase with increasing vanadium layer thickness. The improved fracture toughness (from an NiAl matrix toughness of 6˜.6MPam to a steady-state toughness of 1˜5MPam obtained from finite element analysis) is associated with crack bridging and the interactions of cracks with vanadium layers. The reinitiation of cracks in adjacent NiAl layers is modeled using finite element methods and the reinitiation is shown to occur as a result of strain concentrations at the interface between the adjacent NiAl layers and vanadium layers. The deviation of the reinitiated cracks from the pure mode I direction is shown to occur in the direction of maximum shear strain. Toughening due to crack bridging is also modeled using large-scale bridging models. The intrinsic toughness levels of the microlaminates are also inferred by extrapolating the large scale bridging models to arbitrarily large specimen widths. The extrapolations also show that the small-scale bridging intrinsic toughness increases with increasing vanadium layer thickness.
The Mechanical Response of Random Swirl-Mat Polymeric Composite
Authors: Elahi M. , Weitsman Y. J.
Published: February 2008

This article concerns the mechanical response of random glass fiber strand swirl-mat/urethane matrix composite under static and cyclic loads as well as under elevated temperatures. The article presents an extensive amount of experimental data as well as predictions based upon a coupled damage/viscoelastic constitutive formulation generated specifically to model the behavior of the material at hand. Damage evolution relations are derived from an empirical relationship. This work extends previously published results.
Manufacture and Testing of a Functionality Graded Material
Authors: Lambros J. , Narayanaswamy A. , Santare M. H. , Anlas G.
Published: February 2008

A novel technique is presented for the fabrication and fracture testing of large-scale polymeric based Functionality Graded Materials (FGMs). The technique generates a continuously inhomogeneous property variation by taking advantage of the susceptibility of a polyethylene carbon monoxide copolymer (ECO) to ultraviolet irradiation. The resulting FGMs exhibit a varying Young’s modulus, usually in a linear fashion, from approximately 160 MPa to 250 MPa over 150 mm wide specimens. The fracture behaviour of the FGM is experimentally investigated through the use of single edge notch fracture tests on both homogeneously irradiated and functionally graded ECO. Two approaches are used to evaluate fracture parameters: The first, a hybrid numerical-experimental method, is based on far field measurements only. The second uses digital image correlation to obtain near tip measurements. The energy release rates of uniformly irradiated ECO and of several FGMs are measured and compared. It was seen that the FGM showed a built-in fracture resistance behavior implying that it requires increased driving force to sustain crack growth.
Investigation of Failure Processes in Porous Battery Substrates: Part I—Experimental Findings
Authors: Wang C. , Cheng X. , Sastry A. M. , Choi S. B.
Published: February 2008

Experimental findings are presented which demonstrate the coupled transport, mechanical and morphological changes in porous battery materials when they are cycled electrochemically. These materials, comprised of a mixture of powdered nickel and nickel fiber, act as substrates in nickel-metal hydride (NiMH) cells, and function as porous, conductive containment for positive-plate active material. They can offer substantial weight and cost savings over more traditional sintered or foam materials, provided they can be designed to produce good conductivity over many (>500) electrochemical cycles. This study represents an expansion of previous work by the authors, which had established some key differences in the behavior of substrate materials for a small number of cells. Here, these difference are validated with a greater variety and number of electrochemical/material experiments, along with a parallel study on morphological changes. In the second paper in this series (Cheng et al., 1999b), transport and mechanics models are presented to explain the observed differences, using microstructural models based on observations in this study.
Investigation of Failure Processes in Porous Battery Substrates: Part II—Simulation Results and Comparisons
Authors: Cheng X. , Wang C. , Sastry A. M. , Choi S. B.
Published: February 2008

Models are presented for the evolution of transport and mechanical properties of nickel-metal hydride (NiMH) battery substrates. In the first paper in this series (Wang et al., 1999), conductive losses and enhancement of mechanical properties in these materials were quantified experimentally. These were qualitatively shown to be related to observed morphological changes in the substrate materials. Here, an evolution hypothesis for changes in these structures is presented, along with a simplified approximation of the real material microstructure (porous fiber/powder nickel network) with a tractable simulation geometry (porous fiber networks). Transport and mechanics models are then compared with experimental results, with stochastically-arranged fibers approximated as conductive beams connected by elastic torsion springs. Both quantitative and qualitative agreement are found with the models. Limitations of the approaches proposed are also discussed, along with the consequences of the simplifications of geometry for analysis.
Modeling of Martensite Accommodation Effect on Mechanical Behavior of Shape Memory Alloys
Authors: Evard M. E. , Volkov A. E.
Published: February 2008

An approach has been presented to account for micro-plastic deformation and stress produced by accommodation of martensite. This has made it possible to describe such phenomena as incomplete recovery of strain, strain accumulation at thermocycling, and repeated two-way shape memory effect. Results of modeling are in good qualitative agreement with experimental data.
The Electrical Transport Properties of Shape Memory Alloys Under a Stress State
Authors: Airoldi G. , Pozzi M.
Published: February 2008

The electrical resistance of shape memory alloys under an increasing stress state is here examined: the relevance of the transformation strain connected with the stress induced transformation and the concomitant electronic resistivity change at the transformation are examined for the best alloys now in use.
The Influence of Aging on Critical Transformation Stress Levels and Martensite Start Temperatures in NiTi: Part I—Aged Microstructure and Micro-Mechanical Modeling
Authors: Gall Ken , Sehitoglu Huseyin , Chumlyakov Yuriy I. , Kireeva Irina V. , Maier Hans J.
Published: February 2008

Transmission electron microscopy is used to determine the microstructures of a Ti-50.8 at% Ni alloy given different aging treatments. Two different peak-aging treatments are shown to result in disk shaped semi-coherent Ti3Ni4 precipitates with a diameter ranging from 50 nm to 200 nm depending on the aging temperature. In the peak-aged materials, strong strain fields are clearly visible on TEM micrographs. An Eshelby based model is used to predict the local stress fields due to the differences in the lattice parameters of the precipitates and surrounding matrix. The position dependent local stress fields are then resolved onto the 24 different martensite correspondence variant pairs (CVP’s). It is further demonstrated that due to the unique orientation relationship that exists between the precipitate variants and the martensite CVP’s, the local resolved shear stresses are extremely large on some CVP’s and negligible on others. When the Ni rich NiTi is over-aged, it is found that the precipitates coarsen to approximately 1000nm, they become in-coherent, and the local stress fields disappear. It is also determined that after over-aging the average composition of the matrix drops from 50.8 at% Ni to approximately 50.4 at% Ni. In a subsequent paper (part II) the results here are used to explain the dependence of the critical transformation stress levels and martensite start temperatures on the aging treatment.
The Influence of Aging on Critical Transformation Stress Levels and Martensite Start Temperatures in NiTi: Part II—Discussion of Experimental Results
Authors: Gall Ken , Sehitoglu Huseyin , Chumlyakov Yuriy I. , Kireeva Irina V. , Maier Hans J.
Published: February 2008

An experimental study was performed to determine the effect of aging on martensitic transformations in NiTi, Polycrystalline and single crystal NiTi ([100], [110], and [111] orientations) were both considered, Stress-induced transformations in polycrystalline NiTi were found to closely resemble transformations in single crystals of the [110] and [111] orientations. Solutionized and over-aged single crystals exhibited a strong orientation dependence of the critical stress required to trigger the transformation, σcr The Schmid law was able to accurately predict the orientation dependence of σcr in the solutionized and over-aged single crystals. Peak-aged single crystals demonstrated a much weaker orientation dependence of σcr and in general, the Schmid law was not obeyed. By considering the local stress fields outside of the semi-coherent precipitates, the decrease in the orientation dependence of σcr was accounted for. The martensite start temperatures, Ms, in aged single crystal and polycrystalline NiTi were much higher than in solutionized samples In peak-aged NiTi the increase was primarily attribited to the local stress fields outside the coherent precipitates which create preferential nucleation sites for the martensite. In the over-aged NiTi the increase in Ms was primarily attributed to the decrease in the average Ni concentration of the matrix surrounding the coarsened precipitates.
Microstructure and Mechanical Properties of Sputter-Deposited Ti-Ni Alloy Thin Films
Authors: Ishida A. , Miyazaki S.
Published: February 2008

The shape memory effect, superelasticity and two-way shape memory effect of Ni-rich Ti-Ni sputter-deposited thin films were evaluated quantitatively. The results indicated that they are almost comparable to those of bulk specimens. On the other hand, Ti-rich Ti-Ni thin films were found to exhibit a good shape memory behavior owing to a peculiar fine microstructure unlike bulk specimens. Addition of Cu or Pd to a Ti-50at.%Ni thin film was also confirmed to improve the shape memory behavior. These results suggest that shape memory thin films are a promising material for microactuators.
In-Situ Investigations of the Martensitic Transformation in TiNi by Synchrotron Radiation
Authors: Kulkov S. N. , Mironov Yu. P.
Published: February 2008

By means of synchrotron X-ray diffraction method the stress-induced martensite transformation in TiNi (with two different phase compositions) at room temperature was investigated in situ. It has been shown that in the alloys with temperature-induced martensite in the initial state a nonperiodic fluctuation of intensity of the X-ray reflexes appeared due to anomalous transformation B2 + B19′T → B2 → B19′Si.
Material Characterization of SMA Actuators Under Nonproportional Thermomechanical Loading
Authors: Bo Zhonghe , Lagoudas Dimitris C. , Miller David
Published: February 2008

The application of SMA actuators in smart structures usually involves thermally induced phase transformation with a variable applied stress in SMA actuators, resulting in thermomechanical nonproportional loading of SMAs in stress-temperature space. To investigate the constitutive response of SMAs under thermomechanical nonproportional loading, experiments for thermally induced phase transformation of binary NiTi SMA wires loaded by an elastic linear spring are performed in the Active Materials Laboratory at Texas A&M University. A constitutive model developed by Bo and Lagoudas (1998a, b, c) and Lagoudas and Bo (1998) is used as the basis for the theoretical prediction of the response of SMA line actuators loaded by springs with different elastic constants. Model predictions are compared with experimental results.
Role of Microstructure in the Thermomechanical Behavior of SMA Composites
Authors: Song Gu Quan , Sun Qing Ping , Cherkaoui M.
Published: February 2008

A numerical study on the role of microstructure in the thermomechanical behavior of shape memory alloy (SMA) composites under uniaxial tension is performed. The simulation is based on the micromechanics model established recently by the authors. The influence of the shape and volume fraction of SMA on the overall behavior of the composite as well as on the internal stress and strain evolution is investigated. The strengthening effect of SMA on ductile matrix is illustrated. The obtained results demonstrate several interesting features of the new composite and may serve as a quantitative basis for the microstructure design of this composite in the future.
Crystallographic Attributes of a Shape-Memory Alloy
Authors: Bhattacharya Kaushik
Published: February 2008

Shape-memory Alloys are attractive for many potential applications. In an attempt to provide ideas and guidelines for the development of new shape-memory alloys, this paper reports on a series of investigations that examine the reasons in the crystallography that make (i) shape-memory alloys special amongst martensites and (ii) Nickel-Titanium special among shape-memory alloys.
Mechanical Behavior of an Ni-Ti Shape Memory Alloy Under Axial-Torsional Proportional and Nonproportional Loading
Authors: Lim T. Jesse , McDowell David L.
Published: February 2008

Several biaxial proportional and nonproportional loading experiments are reported for thin-wall tubes of a pseudoelastic Ni-Ti shape memory alloy (SMA). In addition to the mechanical behavior, temperature was measured during the experiments. It is shown that the phase transformation exhibits asymmetrical behavior in the case of tension-compression cycling. The transformation strain rate is determined for selected histories by numerical differentiation of data. Under nonproportional loading, the rate of phase transformation does not follow a generalized J2-J3 criteria based on results of micromechanical simulations for proportional loading. The role of simultaneous forward and reverse transformations on the nonproportional transformation response is examined using a simple micromechanical model, and the direction of the inelastic strain rate is adequately predicted. Load- and strain-controlled experiments at different strain rates, with and without hold times, are reported and coupled thermomechanical effects are studied.
The Influence of Swirl Brakes on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Centrifugal Pumps
Authors: Sivo J. M. , Acosta A. J. , Brennen C. E. , Caughey T. K.
Published: February 2008

Increasing interest has been given to swirl brakes as a means of reducing destabilizing rotordynamic forces due to leakage flows in new high speed rocket turbo-pumps. Although swirl brakes have been used successfully in practice (such as with the Space Shuttle HPOTP), no experimental tests until now have been performed to demonstrate their beneficial effect over a range of leakage flow rates. The present study investigates the effect of swirl brakes on rotordynamic forces generated by discharge-to-suction leakage flows in the annulus of shrouded centrifugal pumps over a range of subsynchronous whirl ratios and various leakage flow rates. In addition, the effectiveness of swirl brakes in the presence of leakage inlet (pump discharge) swirl is also demonstrated. The experimental data demonstrates that with the addition of swirl brakes a significant reduction in the destabilizing tangential force for lower flow rates is achieved. At higher flow rates, the brakes are detrimental. In the presence of leakage inlet swirl, brakes were effective over all leakage flow rates tested in reducing the range of whirl frequency ratio for which the tangential force is destabilizing.
Measurement and Analysis of Static Pressure Field in a Torque Converter Pump
Authors: By R. R. , Lakshminarayana B.
Published: February 2008

In this paper, the static pressure field and performance parameters of a torque converter pump are measured, analyzed, and interpreted under three turbine/pump speed ratio conditions (0, 0.6, and 0.8). A potential flow code is used to predict the static pressure distribution. Results show that: 1) centrifugal force has a dominant effect on the static pressure rise in the pump; 2) the static pressure field is generally poor at the core section; and 3) the potential flow code can fairly well predict the static pressure distribution at the blade mid-span, but not at the core and shell sections.
Numerical Investigation of Unsteady Transitional Flow Over Oscillating Airfoil
Authors: Kim S.-W. , Zaman K. B. M. Q. , Panda J.
Published: February 2008

A numerical investigation of unsteady transitional flow over an oscillating NACA 0012 airfoil at a Reynolds number of 44,000 and reduced frequency of 0.2 is carried out and the results are compared with experimental data. The Navier-Stokes equations defined on arbitrary Lagrangian-Eulerian coordinates are solved by a time-accurate finite volume method that incorporates an incremental pressure equation for the conservation of mass. The transitional turbulence field is described by multiple-time-scale turbulence equations. The numerical method successfully predicts the large dynamic stall vortex (DSV) and the trailing edge vortex (TEV) that are periodically generated by the oscillating airfoil. The numerical results show that the transition from laminar to turbulent state and relaminarization occur widely in time and in space. The calculated streaklines and the ensemble-averaged velocity profiles are in good agreement with the measured data.
Centrifugal Pump Performance During Transient Operation
Authors: Lefebvre P. J. , Barker W. P.
Published: February 2008

The effect of transient operation on the hydrodynamic performance of a centrifugal pump impeller was investigated experimentally. All experiments were conducted in the Naval Undersea Warfare Center’s Impeller Test Facility (ITF), which was designed and built for transient and steady-state operation impeller research. The ITF provides transient operation through simultaneous control of both impeller rotational speed and flow rate over time. The impeller was accelerated from rest with peak angular accelerations up to 720 radians/s2 and inlet flow mean accelerations up to 1.7 g, reaching a peak rotational speed of 2400 rpm and a flow rate of 416 l/s. The impeller was then decelerated to rest. Results showed substantial transient effects in overall impeller performance and demonstrated that the quasisteady assumptions commonly used for the design of impellers that operate under high transient (accelerating or decelerating) conditions are not valid.
An Investigation of Nucleating Flows of Steam in a Cascade of Turbine Blading-Theoretical Treatment
Authors: Bakhtar F. , Mahpeykar M. R. , Abbas K. K.
Published: February 2008

This paper describes the theoretical part of an investigation into nucleating flows of steam in a cascade turbine nozzle blading. The main flow field is regarded as inviscid and treated by the time-marching technique. The viscous effects are assumed to be concentrated in boundary layers which are treated by the integral method. The agreement obtained with the observed surface pressure distributions and overall efficiency measurements is very good.
A Numerical Investigation of Laminar Flow Past Nonspherical Solids and Droplets
Authors: Comer J. K. , Kleinstreuer C.
Published: February 2008

Steady laminar flow past solitary spheroids and nonspherical droplets has been numerically analyzed. Specifically, interfacial transport properties such as surface pressures, interfacial velocities, shear stresses and separation angles as well as the resulting drag coefficients are evaluated for specified aspect ratios (0.2 ≤ E = b/a ≤ 1.0) and intermediate gas stream Reynolds numbers (40 ≤ Re ≤ 120). For one case, it was determined that the use of the traditional spherical-droplet assumption would result in a 30 percent underprediction of the total drag coefficient.
A Two-Temperature Model for Turbulent Flow and Heat Transfer in a Porous Layer
Authors: Travkin V. , Catton I.
Published: February 2008

A new model of turbulent flow and of two-temperature heat transfer in a highly porous medium is evaluated numerically for a layer of regular packed particles. The layer can have heat exchange from the defining surfaces. The commonly used models of variable morphology functions for porosity and specific surface were used to obtain comparisons with other works in a relatively high Reynolds number range. A few outstanding features of the closure models for additional integral terms in equations of flow and heat transfer are advanced. Closures were developed for capillary and globular medium morphology models. It is shown that the approach taken to close the integral resistance terms in the momentum equation for a regular structure can be obtained in a way that allows the second order terms for laminar and turbulent regimes to naturally occur. These terms are taken to be close to the Darcy term or Forchheimer terms for different flow velocities. The two-temperature model was compared with a one-temperature model using thermal diffusivity coefficients and effective coefficients from various authors. Calculated pressure drop along a layer showed very good agreement with experiment for a porous structure of spherical beads. A simplified model with constant coefficients was compared with analytical solutions.
The Axisymmetric Motion of a Liquid Film on an Unsteady Stretching Surface
Authors: Usha R. , Sridharan Rukmani
Published: February 2008

The axisymmetric motion of a fluid caused by an unsteady stretching surface that has relevance in extrusion process and bioengineering has been investigated. It has been shown that if the unsteady stretching velocity is prescribed by rb/(1−αt), then the problem admits a similarity solution which gives much insight to the character of solutions. The asymptotic and numerical solutions are obtained and they could be used in the testing of computer codes or analytical models of more realistic engineering systems. The results are governed by a nondimensional unsteady parameter S and it has been observed that no similarity solutions exist for S > 4.
Molecular Dynamics Simulations on Internal Structures of Normal Shock Waves in Lennard-Jones Liquids
Authors: Satoh Akira
Published: February 2008

The present paper describes a highly efficient method for simulating the generation of shock waves in liquids by using the periodic-shell boundary condition, which is an outer boundary condition for molecular dynamics simulations. This method is used to simulate normal shock waves in Lennard-Jones liquids, clarifying the internal structures of shock fronts and the dependence of shock thicknesses on the shock Mach number. The present method significantly decreases computation times because it enables us to simulate only the shock fronts. Some of the main results derived by these simulations of molecular dynamics are that an overshoot in the profile of longitudinal temperature arises in liquid shock waves as well as in gas shock waves, that the thickness of shock front decreases with increasing Mach number, and that this thickness is about two times the diameter of molecules when the Mach number is 4.
Perspective: Selected Benchmarks From Commercial CFD Codes
Authors: Freitas C. J.
Published: February 2008

This paper summarizes the results of a series of five benchmark simulations which were completed using commercial Computational Fluid Dynamics (CFD) codes. These simulations were performed by the vendors themselves, and then reported by them in ASME’s CFD Triathlon Forum and CFD Biathlon Forum. The first group of benchmarks consisted of three laminar flow problems. These were the steady, two-dimensional flow over a backward-facing step, the low Reynolds number flow around a circular cylinder, and the unsteady three-dimensional flow in a shear-driven cubical cavity. The second group of benchmarks consisted of two turbulent flow problems. These were the two-dimensional flow around a square cylinder with periodic separated flow phenomena, and the steady, three-dimensional flow in a 180-degree square bend. All simulation results were evaluated against existing experimental data and thereby satisfied item 10 of the Journal’s policy statement for numerical accuracy. The objective of this exercise was to provide the engineering and scientific community with a common reference point for the evaluation of commercial CFD codes.
Finite Aspect Ratio Effects on Vortex Shedding Behind Two Cylinders at Angles of Incidence
Authors: Rooney D. M. , Rodichok J. , Dolan K.
Published: February 2008

Wind tunnel tests were undertaken at subcritical Reynolds numbers to determine the vortex shedding characteristics behind a pair of finite circular cylinders at distances from one to six diameters apart and at all angles to one another. In addition, individual finite cylinders with aspect ratios 0.67 ≤ L/D ≤ 11.33 were examined to determine the effect of aspect ratio on shedding frequency, and to measure the frequency of the tip vortex when it is present. Aspect ratio was found to be a significant factor in the difference between shedding frequencies of the two cylinders at oblique angles. It was also found that “lock-on” of the two frequencies occurred when longer aspect ratio cylinders were upstream of shorter ones, but not in the reverse case.
The Effect of Torsion on the Bifurcation Structure of Laminar Flow in a Helical Square Duct
Authors: Bolinder C. J.
Published: February 2008

The laminar fully developed flow problem in a helical square duct with a finite pitch is solved numerically using the finite-volume method with the SIMPLEC algorithm. h2-extrapolation is used to locate the limit points of the stable solution branches. Results for the friction factor are presented. For helical ducts of small pitch, or torsion, it is verified that all investigated flow properties are very similar to those for a toroidal duct with the same dimensionless curvature. A new correlation is proposed for the friction factor ratio.
The Effect of Rotary Arms on Corotating Disk Flow
Authors: Girard John , Abrahamson Scott , Uznanski Kevin
Published: February 2008

This investigation studied the impact of rotary style arms on the flow between corotating disks contained by a stationary cylindrical enclosure. Both ventilated and nonventilated hub configurations were considered. The particular geometry used represents a simplified model for common disk drives. Flow visualizations were performed over the Reynolds number range of 3.4 × 104 to 3.4 × 105. The arms were observed to dramatically alter the flow field and to produce an azimuthal pressure gradient throughout the flow field. The dominant feature of the flow between two disks was the arm wake. Moreover, an exchange of fluid across the shroud opening, which provided arm access, was observed. Arm effects became stronger as the arm tips were positioned closer to the hub. The combination of arms and radial through flow was studied over a similar Reynolds number range. In this case, the flow field remained dominated by arm effects, although some effects arising from the radial flow were observed.
Reinvestigation of Hot-Wire Anemometry Applicable to Subsonic Compressible Flows Using Fluctuation Diagrams
Authors: Stainback P. C. , Nagabushana K. A.
Published: February 2008

Much has been written about the improbability and impossibility of obtaining solutions to the mean square equation for constant current anemometry in subsonic slip and transonic flows. For these flow conditions, the voltage across a heated wire mounted normal to the flow is a function of velocity, density, and total temperature. In principal, the fluctuations of these quantities can be measured; however, to date there are no known acceptable solutions to the mean square equation in these flow regimes. In this study, data presented in the 1950’s by Spangenberg were used to compute the sensitivities of a heated wire to changes in velocity, density, and total temperature. These results indicated that there was a large region in the Nusselt number-Reynolds number or Nusselt number-Knudsen number regimes where the velocity and density sensitivities were different, a condition required for solutions to the mean square equation. A second necessary condition for a solution was also noted. The possible existence of a solution to the mean square equation was based on the evaluation of the condition number of the sensitivity matrix. The condition numbers obtained from Spangenberg’s data were very large and near perfect data would be required to obtain accurate measurements of the fluctuations.
Dense Gas Flow in Minimum Length Nozzles
Authors: Aldo A. C. , Argrow B. M.
Published: February 2008

Recently, dense gases have been investigated for many engineering applications such as for turbomachinery and wind tunnels. Supersonic nozzle design can be complicated by nonclassical dense-gas behavior in the transonic flow regime. In this paper, a method of characteristics (MOC) is developed for two-dimensional (planar) and axisymmetric flow of a van der Waals gas. A minimum length nozzle design code is developed that employs the MOC procedure to generate an inviscid wall contour. The van der Waals results are compared to perfect gas results to show the real-gas effects on the flow properties and inviscid wall contours.
A Fast, Accurate Real Gas Equation of State for Fluid Dynamic Analysis Applications
Authors: Aungier R. H.
Published: February 2008

A modified form of the Redlich-Kwong two-parameter equation of state is presented. The modified equation employs the acentric factor and the critical point compressibility factor as additional parameters to improve its accuracy and to extend its application range to include the critical point. This modified equation is as simple as the original form, yet achieves substantially better prediction accuracy, including thermodynamic parameters such as enthalpy and entropy. Results from this equation, the original equation, and three other popular modified forms are compared with gas property data for several compounds to demonstrate its improved accuracy and increased application range. Practical application limits to the other modified forms are identified to guide current users of those methods.
Mathematical Modeling of Swirling Flames of Pulverized Coal: What Can Combustion Engineers Expect From Modeling?
Authors: Weber R. , Peters A. A. F. , Breithaupt P. P. , Visser B. M.
Published: February 2008

The present study is concerned with mathematical modeling of swirling pulverized coal flames. The attention is focused on the near burner zone properties of high-and low-NOx flames issued from an Aerodynamically Air Staged Burner of 3.4 MW thermal input. The swirling combusting flows are calculated using the k–ε model and second-order models of turbulence. The Eulerian balance equations for enthalpy and mass fractions of oxygen, volatiles, carbon monoxide and final combustion products (CO2 + H2O) are solved. The Lagrangian particle tracking is accompanied by appropriate models of coal devolatilization and char combustion. Nitric oxide emissions are calculated using a NOx post-processor for thermal-, prompt- and fuel-NO. The objective of this paper is to examine whether the engineering information required for designing industrial burners is obtainable through the mathematical modeling. To this end, the flame computations, including NO emissions, are compared with the measured in-flame data. The guidelines as to the combination of physical submodels and model parameters needed for quality predictions of different flame types are given. The paper is a shorter version of our recent ASME publication (Weber et al., 1993).
Sizing of an Aircraft Fuel Pump
Authors: Rohatgi U. S.
Published: February 2008

A need to pump a mixture of two-phase fluid appears naturally in many situations. One example of this situation is aircraft fuel systems, where the pump inlet may have two-phase mixture due to the desorption of the dissolved gases at low pressures at higher altitudes. A simple procedure of selecting proper design conditions for the inlet inducer and a method of sizing the inducer, impeller and volute to meet all the design requirements has been described. This procedure has also been applied to a typical fighter plane boost pump design.
Macroscopic Wetting Behavior of a Two-Dimensional Meniscus Under a Horizontal Plate
Authors: Katoh Kenji , Fujita Hideomi , Sasaki Hideharu
Published: February 2008

The purpose of this study is to investigate macroscopic wetting behavior and to verify the validity of the assumption made in the analysis of the preceding report that the complicated effects of the microscopic structures of the solid surface such as roughness or heterogeneity on the macroscopic wetting behavior are simply represented by the values of the apparent contact angles. The unstable phenomenon of a two-dimensional meniscus under a horizontal plate, in which the meniscus falls spontaneously at a certain height of the plate, is considered theoretically from a thermodynamic viewpoint. The results of the analysis based on the above assumption agree with those by an analysis in which the effect of microscopic structures of the solid surface, such as roughness and heterogeneity, are taken into consideration. Therefore, the validity of the assumption made in the preceding report is verified.
Liquid Jet Pumps for Two-Phase Flows
Authors: Cunningham R. G.
Published: February 2008

Isothermal compression of a bubbly secondary fluid in a mixing-throat and diffuser is described by a one-dimensional flow model of a liquid-jet pump. Friction-loss coefficients used in the four equations may be determined experimentally, or taken from the literature. The model reduces to the liquid-jet gas compressor case if the secondary liquid is zero. Conversely, a zero secondary-gas flow reduces the liquid-jet gas and liquid (LJGL) model to that of the familiar liquid-jet liquid pump. A “jet loss” occurs in liquid-jet pumps if the nozzle tip is withdrawn from the entrance plane of the throat, and jet loss is included in the efficiency equations. Comparisons are made with published test data for liquid-jet liquid pumps and for liquid-jet gas compressors. The LJGL model is used to explore jet pump responses to two-phase secondary flows, nozzle-to-throat area ratio, and primary-jet velocity. The results are shown in terms of performance curves versus flow ratios. Predicted peak efficiencies are approximately 50 percent. Under severe operating conditions, LJGL pump performance curves exhibit maximum-flow ratios or cut-offs. Cut-off occurs when two-phase secondary-flow streams attain sonic values at the entry of the mixing throat. A dimensionless number correlates flow-ratio cut-offs with pump geometry and operating conditions. Throat-entry choking of the secondary flow can be predicted, hence avoided, in designing jet pumps to handle two-phase fluids.
Experimental Study of a Laminar Jet in a Double-Diffusion Environment
Authors: Priven M. , Bemporad G. A. , Atkinson J. , Rubin H.
Published: February 2008

An experimental analysis of the flow development caused by the simultaneous injection and withdrawal of a buoyant fluid layer with low Reynolds number in a double-diffusion environment is presented. The injection of positively, neutrally, and negatively buoyant fluid layers was simulated in the experimental setup. Innovative procedures were developed to efficiently create the desired density distributions in the laboratory flume. Results presented in this paper concern the injection of fluid into environments stratified by temperature, salinity or both. Basic features of the flow patterns are described, in particular, intrusion rate, effect on ambient stratification and vertical displacement. The experimental data on the fluid vertical displacement were compared with results from a numerical model and good agreement was found.
The Vortical Structure of Parasitic Capillary Waves
Authors: Mui R. C. Y. , Dommermuth D. G.
Published: February 2008

A two-dimensional numerical simulation of the parasitic capillary waves that form on a 5 cm gravity-capillary wave is performed. A robust numerical algorithm is developed to simulate flows with complex boundary conditions and topologies. The free-surface boundary layer is resolved at the full-scale Reynolds, Froude, and Weber numbers. Seventeen million grid points are used to resolve the flow to within 6 × 10–4 cm. The numerical method is used to investigate the formation of parasitic capillary waves on the front face of a gravity-capillary wave. The parasitic capillary waves shed vorticity that induces surface currents that exceed twenty-five percent of the phase velocity of the gravity-capillary wave when the steepness of the parasitic capillary waves is approximately 0.8 and the total wave steepness is 1.1. A mean surface current develops in the direction of the wave’s propagation and is concentrated on the front face of the gravity-capillary wave. This current enhances mixing, and remnants of this surface current are probably present in post-breaking waves. Regions of high vorticity occur on the back sides of the troughs of the parasitic capillary waves. The vorticity separates from the free surface in regions where the wave-induced velocities exceed the vorticity-induced velocities. The rate of energy dissipation of the gravity-capillary wave with parasitic capillaries riding on top is twenty-two times greater than that of the gravity-capillary wave alone.