bluuebunny/crossref_metadata_2025 huggingface dataset:
Reynolds Averaged and Large Eddy Computations of Flow and Heat Transfer Under Round Jet Impingement
Authors: Natarajan Thangam , Jewkes James , Narayanaswamy Ramesh , Chung Yongmann M. , Lucey Anthony D.
Published: December 2014

The fluid dynamics and heat transfer characteristics of a turbulent round jet are modelled numerically using Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES). Meshes with varying degrees of coarseness, with both radial and axial refinements are investigated. Discretization is carried out using the finite volume method. The jet configurations are chosen to enable validation against well-established experimental jet-impingement heat-transfer studies, particularly that of Cooper et al. [1]. The Reynolds number studied is 23000. The height of discharge from the impingement wall is fixed at twice the jet diameter. The work critically examines the effect of Reynolds number, standoff distance and helps to ascertain the relative merits of various turbulence models, by comparing turbulent statistics and the Nusselt number distributions. The present work is carried out as a preliminary validation, in a wider study intended to determine the thermofluidic behaviour of jets impinging upon an oscillating surface.
Thermo-Economical Optimization of Ground Source Heat Pump With Horizontal Ground Heat Exchangers for a Heating Season in Istanbul: A Case Study
Authors: Demir Hakan , Gönül Alişan , Kayaci Nurullah , Atayılmaz Ş. Özgür , Ağra Özden
Published: December 2014

A ground-source heat pump (GSHP) system has three major components: a heat pump, an earth connection and an interior heating or cooling distribution system. The most important part of a ground source heat pump (GSHP) is the ground heat exchanger (GHE) that consists of pipes buried in the soil and is used for transferring heat between the soil and evaporator of the ground source heat pump. There are plenty of works on ground source heat pumps and ground heat exchangers in the literature. Most of the works on ground heat exchangers are based on the heat transfer in the soil and temperature distribution around the coil. Some of the works for thermo-economic optimization of thermal systems are based on thermodynamic cycles. In this paper, it was carried out that the thermo-economic optimization of a ground source heat pump system with horizontal ground heat exchangers operating in heating mode in Istanbul in Turkey. The monthly heat loads of a villa for every heating months were worked out by using TS825® program. Also, average soil temperature has been calculated according to soil surface temperatures taken from Turkish State Meteorological Service belonging to last ten years. An objective function was defined based on heating capacity, initial investment and operating costs of ground source heat pump (GSHP). Then, the effects of the soil thermal conductivity, burial depth and variation of soil temperature on the objective function were investigated. Also, variation of COP value was carried out for burial depth and different condensation temperatures monthly.
Numerical Simulation of Fluid Flow in the Vicinity of an Oscillating Cavity: Parametric Study
Authors: Ragunathan Srivathsan , Goering Douglas J.
Published: December 2014

In this paper, numerical solutions of fluid flow in the vicinity an oscillating square cavity are presented. OpenFOAM (v 2.2.2), an open-source, Finite Volume CFD code was used to solve the problem. The oscillating cavity problem was studied with respect to the following parameters: (1) peak Reynolds numbers (based on the cavity size, Red) of 50, 100, 200, and 300, and (2) the ratio of the Stokes layer thickness to the cavity size (δ/d) of 0.25, 0.5, and 1. An oscillatory source term was provided to the streamwise momentum equation and the problem was solved with a stationary grid. The resultant fluid velocities were then vectorially corrected for the wall velocity. The patterns and the magnitudes of entrainment and ejection of fluid mass to and from the cavity were studied. Lower Red flows were marked by the absence of a secondary recirculation zone inside the cavity in contrast to higher Red flows. Lower Red flows were observed to have fluid contact with the outside shear layer for a larger portion of the oscillatory cycle, and thus, were observed to result in higher effective fluid transport across the cavity. Higher δ/d ratios resulted in decreased peak mass flow across the cavity aperture plane and only over a smaller portion of the cycle time owing to the thickness of the oscillatory boundary layer in relation to the cavity size. As the δ/d was lowered, effective mass flow was observed to increase and over a larger portion of the cycle time.
Investigating Multiphase Turbulence Statistics of Large-Scale Two-Way Coupled Gravity-Driven Flows
Authors: Capecelatro Jesse , Desjardins Olivier , Fox Rodney O.
Published: December 2014

Starting from the kinetic theory (KT) model for monodisperse granular flow, the exact Reynolds-average (RA) equations were recently derived for the particle phase in a collisional gas-particle flow by Fox [1]. The turbulence model solves for the RA particle volume fraction, the phase-average (PA) particle velocity, the PA granular temperature, and the PA particle turbulent kinetic energy (TKE). A clear distinction is made between the PA granular temperature, which appears in the kinetic theory constitutive relations, and the particle-phase turbulent kinetic energy, which appears in the turbulent transport coefficients. Mesoscale direct numerical simulation (DNS) can be used to assess the validity of the closures proposed for the unclosed terms that arise due to nonlinearities in the hydrodynamic model. In order to extract meaningful statistics from simulation results, a separation of length scales must be established to distinguish between the PA particle TKE and the PA granular temperature. In this work, we introduce an adaptive spatial filter with an averaging volume that varies with the local particle-phase volume fraction. This filtering approach ensures sufficient particle sample sizes in order to obtain meaningful statistics while remaining small enough to avoid capturing variations in the mesoscopic particle field. Two-point spatial correlations are computed to assess the validity of the filter in extracting meaningful statistics. The filtering approach is applied to fully-developed cluster-induced turbulence (CIT), where the production of fluid-phase kinetic energy results entirely from momentum coupling with finite-size inertial particles. Simulation results show a strong correlation between the local volume fraction and granular temperature, with maximum values located just upstream of clusters (i.e., where maximum compressibility of the particle velocity field exists), and negligible particle agitation is observed within clusters.
The Effect of Viscosity Ratio on the Hydrodynamics of Separation From an Oil-Coated Particle
Authors: Mehrabian Sasan , Abbaspour Nima , Bussmann Markus , Acosta Edgar
Published: December 2014

Separating oil from solid particles is of great importance in many industrial processes including the extraction of bitumen from oil sands, and the remediation of oil spills. The usual approach is to separate the oil from the solid by introducing another liquid (e.g. water). Separation is often assisted by fluid mixing, and chemical addition. Yet while oil-water-particle separation has been well studied from a chemical standpoint, little research has taken into account the effect of hydrodynamics on separation. In this work, the separation of oil from a single oil-coated spherical particle falling through an aqueous solution was evaluated as a function of viscosity ratio. Solvents were used to modify the viscosity of the oil. The experiments were recorded using a high-speed camera and post-processed using the MATLAB image-processing toolbox. A CFD model has also been developed to study this phenomenon.

The results indicate that when viscous forces are strong enough, the oil film deforms, flows to the back of the sphere, and forms a tail that eventually breaks up into a series of droplets due to a capillary wave instability. When the viscosity ratio is small (i.e. the oil is less viscous than the solution), a thin tail forms quickly, the growth rate of the instability is high, and hence the tail breaks very quickly into smaller droplets. When the viscosity ratio is high (i.e. the oil is more viscous), more time is required for the deformation/separation to initiate, and the tail is thicker and breaks more slowly into larger droplets. It was observed that when the viscosity ratio is close to 1, the rate of separation is increased and maximum separation is achieved.
A Study of Pulsed Blowing Effect on Flow Separation Over Flap
Authors: Zhou Ping , Wang Yankui , Zhao Dejian
Published: December 2014

A model with main wing and flap which is based on NACA0025 airfoil is used in this paper to study the pulsed blowing effect on flow separation over flap. The effects of average blowing momentum coefficient and Stroul number on flow separation over the flap have been discussed at first. Furthermore, thecontrol effect of this pulsed blowing technique under different deflection angle of flap isdiscussed to make sure whether the control effect of pulsed blowing can meet the needs under different deflection angle of flap. All the research works have been finished by numerical simulation method under conditions of 0deg angle of attack of the main wing.
An Uncertainty Quantification Analysis in a Simplified Problem of Urban Pollutant Dispersion by Means of ANOVA-POD/Kriging-Based Response Surfaces
Authors: Margheri Luca , Sagaut Pierre
Published: December 2014

In the last decade there has been a growing interest in urban flow CFD simulations. As RANS approaches demonstrated to be not enough accurate to predict urban flows, people focus more and more on LES simulations. Though better results could be obtained with fine grid LES, the complexity of the urban physics seems to vanish the increasing computational resources. A different approach is herein considered, proposing a first uncertainty quantification (UQ) analysis on a single building pollutant dispersion case. A hybrid method merging the anchored-ANOVA and the POD/Kriging-based response surface is proposed to reduce the costs of the UQ analysis. Moreover, simulations are performed by the Lattice Boltzman (LBM) code PowerFLOW. Sensitivity results are presented showing the importance of vortex dynamics and the high sensitivity to the wind angle.
Experimental Study of Shallow Open Channel Turbulent Flows Over Rough Walls
Authors: Nyantekyi-Kwakye B. , Essel E. E. , Clark S. , Tachie M. F.
Published: December 2014

An experimental study was undertaken to investigate the effects of bed roughness on the turbulence characteristics of shallow open channel flows. The measurements were performed in a recirculating open channel flow over a reference smooth bed and a three-dimensional rough bed (36-grit sandpaper). The velocity measurements were conducted using a high resolution particle image velocimetry (PIV) system. The Reynolds number based on the depth of flow (h) and freestream velocity (Ue) varied from 21000 to 30000 and the Froude number ranged from 0.46 to 0.65. Two smooth bed experiments were conducted to investigate the effect of Reynolds number on the open channel flow. The mean velocities and Reynolds stresses for the two smooth cases were observed to be weakly dependent on Reynolds number. The effect of bed roughness was observed to penetrate into the outer layer of the boundary layer. The results show that bed roughness significantly increased the skin friction coefficient, wake parameter, boundary layer parameters, as well as the mean velocity, Reynolds stresses and the energy budget terms. A two-point correlation analysis showed that the coherent structures were also significantly modified by bed roughness.
Numerical Simulation and Control of the Flow Over a Backward Facing Ramp
Authors: Bruneau Charles-Henri , Jedouaa Meriem , Khadra Khodor , Mortazavi Iraj
Published: December 2014

A two-dimensional backward facing ramp is used to represent a car simplified rear window. Direct numerical simulations are performed to describe the flow behavior over the ramp. Constant blowing jets and synthetic jets are applied on the body to control the flow. The results presented in this work show a significant reduction of the recirculation zone.
Multi-Scale Simulations of Climate-Change Influence on Chicago Heat Island
Authors: Conry Patrick , Fernando H. J. S. , Leo L. S. , Sharma Ashish , Potosnak Mark , Hellmann Jessica
Published: December 2014

Over the past half century, burgeoning urban areas such as Chicago have experienced elevated anthropogenic-induced alteration of local climates within urbanized regions. As a result, urban heat island (UHI) effect in these areas has intensified. Global climate change can further modulate UHI’s negative effects on human welfare and energy conservation. Various numerical models exist to understand, monitor, and predict UHI and its ramifications, but none can resolve all the relevant physical phenomena that span a wide range of scales. To this end, we have applied a comprehensive multi-scale approach to study UHI of Chicago.

The coupling of global, mesoscale, and micro-scale models has allowed for dynamical downscaling from global to regional to city and finally to neighborhood scales. The output of the Community Climate System Model (CCSM5), a general circulation model (GCM), provides future climate scenario, and its coupling with Weather Research and Forecasting (WRF) model enables studies on mesoscale behavior at urban scales. The output from the WRF model at 0.333 km resolution is used to drive a micro-scale model, ENVI-met. Through this coupling the bane of obtaining reliable initial and boundary conditions for the micro-scale model from limited available observational records has been aptly remedied. It was found that the performance of ENVI-met improves when WRF output, rather than observational data, is supplied for initial conditions. The success of the downscaling procedure allowed reasonable application of micro-scale model to future climate scenario provided by CCSM5 and WRF models. The fine (2 m) resolution of ENVI-met enables the study of two key effects of UHI at micro-scale: decreased pedestrian comfort and increased building-scale energy consumption. ENVI-met model’s explicit treatment of key processes that underpin urban microclimate makes it captivating for pedestrian comfort analysis. Building energy, however, is not modeled by ENVI-met so we have developed a simplified building energy model to estimate future cooling needs.
The Structure of Turbulence in a Moving Bed as a Function of Flow and Medium Properties
Authors: de Lemos Marcelo J. S.
Published: December 2014

This article presents simulations for turbulent flows in a moving permeable bed making use of a macroscopic turbulence model. Intra-pore turbulence is considered by means of a two-equation closure. Governing equations for mean and turbulent flows are volume-averaged. The resulting set of transport equations is discretized using the control-volume method and the obtained algebraic equation set is relaxed via the SIMPLE algorithm. Results indicate that for larger values of Reynolds number, a greater amount of available mechanical energy is converted into turbulence. Simulations further indicate that for lower values of Darcy number and bed porosity, higher levels of turbulence kinetic energy are calculated.
Flow Characterization in an ESP Pump Using Conductivity Measurements
Authors: Pirouzpanah Sahand , Gudigopuram Sujan Reddy , Morrison Gerald L.
Published: December 2014

Electrical Submersible Pumps (ESPs) are used in upstream petroleum industry for pumping liquid-gas mixtures. The presence of gas in the flow reduces the efficiency of ESPs. To investigate the effect of gas in the flow medium, Electrical Resistance Tomography (ERT) is performed on the two diffuser stages in a three-stage ESP which was manufactured by Baker Hughes Company. In an ERT system, the relative conductivity of the two-phase fluid mixture in comparison with the conductivity of pure liquid is measured which is used to obtain the Gas Volume Fraction (GVF) and mixture concentration. The measured GVF and concentration is used to characterize the flow for different flow rates of water and air, inlet pressures and rotating speeds.
Numerical and Experimental Study of the Evaporation and Solid Layer Formation of a Bi-Component Droplet Under Various Drying Conditions
Authors: Grosshans Holger , Griesing Matthias , Gopireddy Srikanth R. , Pauer Werner , Moritz Hans-Ulrich , Gutheil Eva
Published: December 2014

This paper presents a combined experimental and numerical study of the evaporation and solid layer formation of a single bi-component mannitol-water droplet in air. For spherically symmetric droplets, the problem is described mathematically by the unsteady, one-dimensional conservation equations of mass and energy. The effect of the formation of a solid layer at the droplet surface on the droplet evaporation and thermal diffusion rate is included in the present approach. The simulations are validated by comparison with experiments using acoustically levitated droplets. The study includes initial droplet diameters varying from 350 to 450 μm, gas temperatures ranging from 80 to 120 °C, and the initial mannitol mass fraction inside the droplet varies from 0.05 to 0.15. The numerical results are analyzed to identify the occurrence of solid layer formation, and the temporal evolutions of both the droplet size and mass are presented. A parameter study of the initial gas temperature, the initial droplet size, and the initial mannitol mass fraction inside the droplet on droplet evaporation and solid layer formation is presented. The present model accurately captures the initial stages of droplet drying under all conditions investigated.
Analytical Model of Post-Impact Droplet Spreading on a Micro-Patterned Superhydrophobic Surface With Surface Slip
Authors: Clavijo Cristian E. , Crockett Julie , Maynes Daniel
Published: December 2014

Several analytical models exist to predict droplet impact behavior on superhydrophobic surfaces. However, no previous model has rigorously considered the effect of surface slip on droplet spreading and recoiling that is inherent in many superhydrophobic surfaces. This paper presents an analytical model that takes into account surface slip at the solid-fluid interface during droplet deformation. The effects of slip are captured in terms that model the kinetic energy and viscous dissipation and are compared to a classical energy conservation model given by Attane et al. and experimental data from Pearson et al. A range of slip lengths, Weber numbers, Ohnesorge numbers, and contact angles are investigated to characterize the effects of slip over the entire range of realizable conditions. We find that surface slip does not influence normalized maximum spread diameter for low We but can cause a significant increase for We > 100. Surface slip affects dynamical parameters more profoundly for low Oh numbers (0.002–0.01). Normalized residence time and rebound velocity increase as slip increases for the same range of We and Oh. The influence of slip is more significantly manifested on normalized rebound velocity than normalized maximum spread diameter. Contact angles in the range of 150°–180° do not affect impact dynamics significantly.
Optimisation Methods for Coupled Thermodynamic and 1D Design of Radial-Inflow Turbines
Authors: Persky Rodney , Sauret Emilie , Ma Lin
Published: December 2014

Optimisation is a fundamental step in the turbine design process, especially in the development of non-classical designs of radial-inflow turbines working with high-density fluids in low-temperature Organic Rankine Cycles (ORCs). The present work discusses the simultaneous optimisation of the thermodynamic cycle and the one-dimensional design of radial-inflow turbines. In particular, the work describes the integration between a 1D meanline preliminary design code adapted to real gases and the performance estimation approach for radial-inflow turbines in an established ORC cycle analysis procedure. The optimisation approach is split in two distinct loops; the inner operates on the 1D design based on the parameters received from the outer loop, which optimises the thermodynamic cycle. The method uses parameters including brine flow rate, temperature and working fluid, shifting assumptions such as head and flow coefficients into the optimisation routine. The discussed design and optimisation method is then validated against published benchmark cases. Finally, using the same conditions, the coupled optimisation procedure is extended to the preliminary design of a radial-inflow turbine with R143a as working fluid in realistic geothermal conditions and compared against results from commercially-available software RITAL from Concepts-NREC.
Analysis of Slug Frequency Correlations for Two-Phase Gas-Liquid Horizontal Slug Flow
Authors: Antunes Manoella M. , Cozin Cristiane , Barbuto Fausto A. A. , Morales Rigoberto E. M. , Rodrigues Hendy T.
Published: December 2014

Multiphase flows in pipelines show several flow patterns depending on the industrial applications where they appear. In oil and gas production, typical flow rates, geometries and the physical properties of the phases make slug flow to be the most common of all patterns. This kind of flow is characterized by an intermittent succession of an aerated liquid slug region and a long, turbulent gas bubble surrounded by a liquid film. Due to its complexity, slug flow modelling has been a challenge to many researchers over the last four decades. Presently, steady-state one-dimensional models based on the unit cell concept and more accurate physical representations based on either two-fluid or slug tracking models embedding transient flow capabilities are available. These models require closure relationships for predicting flow parameters. In the present work, a literature review on frequency correlations is presented. An analysis of the performance of those correlations with experimental data for horizontal slug flows was carried out and its results are presented.
Experimental Investigation of Single Roughness Element Effects on Supersonic Boundary Layer Transition
Authors: Bottini Henny , Saracoglu Bayindir H. , Paniagua Guillermo
Published: December 2014

Predicting the characteristics of a transitional boundary layer remains an open challenge in supersonic flow fields. An experimental campaign to understand the effects of a single roughness element on a supersonic laminar boundary layer was designed. Two Mach numbers were tested, 1.6 and 2.3, including two roughness heights, 0.1 mm and 1 mm, over a flat plate. Steady and unsteady wall temperature and pressure levels were recorded to interpret the influence of the wake of the roughness. Heat flux and adiabatic wall temperature trends, temperature and pressure fluctuations RMS trends and time evolution of spectral content were reported. The initial wall temperature was varied during the wall temperature measurements and the resulting steady and unsteady effects on the roughness wake were investigated.
Modeling Dilute Gas-Solid Turbulent Boundary Layers Using Moment Methods
Authors: Dunn D. M. , Squires K. D.
Published: December 2014

The specific focus of the current effort is on modeling dilute particle-laden turbulent boundary layers in which the gas-phase carrier flow is populated with a second phase of small, dispersed solid particles possessing material densities much larger than that of the carrier flow. A novel approach known as the conditional quadrature method of moments (CQMOM) developed by Yuan and Fox [1], derived from the quadrature-based method of moments (QMOM) developed originally by McGraw [2], is being implemented to model the dispersed particles as an Eulerian phase. Both enabled and disabled inter-particle collision treatments are included in the model for a dispersed phase coupled to the fluid via a drag force acting on the particles. Simulations are conducted with a Reynolds number of 2800 based on the boundary layer thickness at the inlet to the domain. The full 3-D mesh contains 800×128×98 structured cells with overall dimensions in terms of the inlet boundary layer thickness of 80×6 ×4 in the streamwise, spanwise, and wall-normal directions, respectively. The gas-phase carrier flow is computed using Direct Numerical Simulation of the incompressible Navier-Stokes equations. The boundary layer develops spatially from a turbulent inflow condition and drives the particulate phase via drag and collisions. Comparisons are made against simulations performed using Lagrangian-based discrete particle simulation (DPS) of the dispersed phase and demonstrate the utility of the Eulerian moment method approach. Both instantaneous and time-averaged quantities are presented.
Performance of Bi-Directional Blades for Tidal Current Turbines
Authors: Nedyalkov Ivaylo , Wosnik Martin
Published: December 2014

Horizontal-Axis Tidal Current Turbines can utilize bi-directional blades which operate well in both directions in a reversing flow, avoiding the use of yaw or pitch mechanisms, thus reducing initial and maintenance costs. A “class” of bi-directional hydrofoil shapes was designed, and studied numerically using OpenFOAM, and one foil with favorable characteristics, named B3-351045, was tested experimentally in the University of New Hampshire High-Speed Cavitation Tunnel - HiCaT. The foils were designed with considerations for lift, drag, and cavitation inception. Simplified 2D simulations for a range of angles of attack for foils with different foil-geometry parameters were used to select a favorable hydrofoil. The selected hydrofoil was fabricated and tested in the HiCaT. Lift and drag were measured using a custom-designed force balance and cavitation inception was observed visually. Experimental and numerical data were compared. Bi-directional blades may be an economically-feasible option when addressing the reversing direction of tidal flows, since the decreased performance of the blades can be offset by the lower costs compared to unidirectional blades.
Dynamic Learning Framework: Adaptive Assessment Development for the Undergraduate Fluid Mechanics
Authors: Kumar V. , Castellanos A. , Ortega J. , Tandon V. , Agarwal N. , Udoewa V. , Kumar A. , Prasad S.
Published: December 2014

This paper presents a dynamic learning framework (DLF) for engineering courses with rich mathematical and geometrical contents. The word “dynamic” implies that there are several moving components in the course contents and assessments. Moving contents are enabled by random-number generators to select text/paragraph from a database or chose a number between two ranges within engineering bounds. Dynamic contents are usually missing in traditional form of instructions such a fixed format book-type problem or static online material. The framework leverages on the computing resources from the recent advancement in touchpad computing devices (such as IPAD and Android based tablets) and web-based technologies (such as WebGL/SVG for virtual-reality and web-based graphics and PHP based server level programming language). All assessments are developed at four increasing levels of difficulty. The levels one through three are designed to assess the lower level learning skills as discussed in the “Bloom’s taxonomy of cognitive skills” whereas level four contents are designed to test the higher level skills. The level-one assessments are designed to be easiest and include guiding materials and solved examples. To lessen the impact of disinterests caused by mathematical abstractions, the assessment and content presentations are strengthened by integrating the mathematical concepts with visual engineering materials from real-world and local important applications. All problems designed to assess the lower level skills are computerized and tested using the Computer Adaptive Testing (CAT) algorithm which enabled the instructor to focus on the higher level skills and offer the course in partially flipped classroom setting.
Direct Numerical Simulation of Compressible Flow Past a Low Pressure Turbine Blade at High Incidence
Authors: Ranjan Rajesh , Deshpande S. M. , Narasimha Roddam
Published: December 2014

A direct numerical simulation (DNS) code has been developed to solve the compressible Navier-Stokes equations. This code is capable of handling unstructured grids, often a requirement for simulating flow past complex geometrical shapes like turbine and compressor blade passages. The code is validated for a compressible turbulent channel flow.

Flow past a low pressure (LP) turbine blade passage is computed at Re = 51,831 based on axial chord length and incoming velocity, and angle of incidence = 45.5° with respect to axial chord. Several interesting fluid-dynamical phenomena including multiple separation bubbles and laminar-turbulent-laminar transition cycles are noticed on the suction side of the blade. Also a strong curvature effect is seen in the boundary layer near the leading edge on the suction side, where use of higher order boundary layer theory will be needed.
A Consistent Mass and Momentum Flux Computation Method Using Rudman-Type Technique With a CLSVOF Solver
Authors: Vaudor Geoffroy , Berlemont Alain , Ménard Thibaut , Doring Mathieu
Published: December 2014

In this paper, a computational method is presented that addresses the problem of multiphase flow characterized by phases with significant density ratio accompanied by strong shearing. The Coupled Level-Set Volume-of-Fluid (CLSVOF) technique is used for interface tracking, while the momentum transfer is coupled to that of mass by means of momentum fluxes computed using a sub-grid. This is an extended adaptation of Rudman’s volume tracking technique [1]. The new method is shown to conserve kinetic energy when applied to cases otherwise unfeasible, such as shear layer with high density ratio.
Numerical Investigation of Positive Displacement Rotary Lobe Pump With Twisted Rotors
Authors: Jiang Xiaojun , Li Yi , He Zhaohui , Baoling Cui , Dong Wenlong
Published: December 2014

The three-dimensional flow field characteristics are obtained by performing numerical simulation of flow in a lobe pump with twisted rotors. The relationship between the dynamic flow structure and the flow fluctuation is explored. Actually, the viscous incompressible Navier-Stokes equations are solved within an unsteady flow model. The dynamic mesh technique is applied to obtain the dynamic flow structure. By comparing the simulated results of straight rotor with those of twisted rotor, the effect of rotor shape on the flow fluctuation was revealed. Finally, the impact of the lobes number of rotors on flow pulsations is discussed. The results show that there is an intrinsic relationship between the flow fluctuation and the vortex in the lobe pump. The use of twisted rotors can effectively improve the internal flow characteristics of lobe pump and reduce flow fluctuation. With the increase of the number of lobes, the lobe pump output is more stable and capacity has been improved.
The Effect of Surfactants on the Flow Patterns in Vertical Air-Water Pipe-Flow
Authors: van Nimwegen A. T. , Portela L. M. , Henkes R. A. W. M.
Published: December 2014

In this work, we consider the influence of surfactants on the flow pattern transitions of air-water flow in vertical pipes. Surfactants cause the formation of foam, which suppresses the irregularities in the flow. Thereby, the foam significantly decreases the gas flow rate associated with the transition between annular and churn flow. Furthermore, this transition is no longer independent of the liquid flow rate, as the foam can more easily suppress the churning at low liquid flow rates. At sufficiently large surfactant concentrations, the foam suppresses all churning, leading to a direct transition between annular and slug flow. Using results from flow visualisation, the effect of the surfactants on the morphology of the different flow patterns is analysed. The results provide important subsidies for a mechanistic model of air-water-foam flow.
Direct Numerical Simulation and Linear Stability Analysis of the Flow in a Pebble Bed
Authors: Ward P. , Hassan Y. , Merzari E. , Fischer P.
Published: December 2014

The flow in a tightly packed array of spheres is important to various engineering fields. In nuclear engineering applications, for instance, researchers have proposed core geometries of the pebble bed reactor (PBR) type cooled by gas or molten salt. Proper core cooling, both at operation and during accident conditions, is a key issue that must be addressed in any reactor design; and the limited amount of data available for the complicated geometry of PBR cores makes this task even more complex. A detailed understanding of coolant flow patterns and properties must be developed in order to meet safety requirements and ensure core longevity.

We address this issue by using the spectral-element computational fluid dynamics code Nek5000, developed at Argonne National Laboratory, to conduct both large eddy simulation (LES) and direct numerical simulation (DNS) of fluid flow through a single face-centered cubic sphere lattice with periodic boundary conditions. Moreover, a statistical analysis of the flow field and a global linear stability analysis of the laminar flow were performed in order to investigate the mechanism of laminar-turbulent transition in this geometry. One of the main objectives of the present study is, in fact, to determine how the Reynolds number affects the development of asymmetries within the flow patterns.
Experimental Study of Mixing and Entrainment in a Horizontal Turbulent Stratified Jet
Authors: Xu Duo , Chen Jun
Published: December 2014

The mixing efficiency, flux Richardson number Rif, is investigated in a horizontally injected turbulent stratified jet with a co-existence of stable and unstable stratifications. The high resolution experimental data from a developed laser-based technique show the statistical relationship between Rif and the gradient Richardson number Rig. In addition, the data are used to study the development of entrainment by two approaches, and compared with theoretical predictions.
Study on Pressure Fluctuation and Fluctuation Reduction of a Micro Vortex Pump
Authors: Zhang Feixi , Wu Peng , Wu Dazhuan
Published: December 2014

With the increasing demand of small-flow and high-head pumps, vortex pump, which can be used in industry, agriculture, medical and aerospace etc., has become more and more popular as low specific pump. However, the pressure fluctuation of fluid in the vortex pump would cause flow noise and vibration which may result in damage to the equipment. Clearly, it is important to reduce the fluctuation causing by fluid flow as much as possible.

This study examined and discussed the law of pressure fluctuation in a micro vortex pump by the method of numerical simulation. In addition, a random distribution method was applied to design two new impellers with different blade spacing. Moreover, the influence on pressure fluctuation of different blade positions was predicted by theoretical analysis and CFD analysis.

The results show that the blade passing frequency is dominative in the pressure fluctuation. Although the average static pressure distribution on the circumference of the micro vortex pump increased gradually along inlet to outlet, the pressure pulse amplitudes were fluctuant and the maximum amplitude area was close to the stripper. Affected by the vortex motion in the pump, there were clutters in the spectrum from inlet to outlet even for the vortex pump with uniform circumferential blade spacing. The study also indicated that uneven circumferential spacing would yield additional frequency in the spectrum compared with even one and reduce the magnitude of the dominant frequency without decreasing the performance of the pump sharply.

Based on the consequence, this paper proves the feasibility of applying uneven blade spacing to reduce pressure fluctuation in a vortex pump. And it could be meaningful for the noise and vibration reduction as well as development of vortex pumps.
Volume-of-Fluid Interface Reconstruction Algorithms on Next-Generation Computer Architectures
Authors: Francois Marianne M. , Lo Li-Ta , Sewell Christopher
Published: December 2014

With the increasing heterogeneity and on-node parallelism of high-performance computing hardware, a major challenge to computational physicists is to work in close collaboration with computer scientists to develop portable and efficient algorithms and software. The objective of our work is to implement a portable code to perform interface reconstruction using NVIDIA’s Thrust library. Interface reconstruction is a technique commonly used in volume tracking methods for simulations of interfacial flows. For that, we have designed a two-dimensional mesh data structure that is easily mapped to the 1D vectors used by Thrust and at the same time is simple to work with using familiar data structures terminology (such as cell, vertices and edges). With this new data structure in place, we have implemented a recursive volume-of-fluid initialization algorithm and a standard piecewise interface reconstruction algorithm. Our interface reconstruction algorithm makes use of a table look-up to easily identify all intersection cases, as this design is efficient on parallel architectures such as GPUs. Finally, we report performance results which show that a single implementation of these algorithms can be compiled to multiple backends (specifically, multi-core CPUs, NVIDIA GPUs, and Intel Xeon Phi coprocessors), making efficient use of the available parallelism on each.
Proper Orthogonal Decomposition Based Reduced Order Modeling of the Very High Temperature Reactor Lower Plenum Hydrodynamics
Authors: Banyay Gregory A. , Ahmadpoor Mohammad , Brigham John C.
Published: December 2014

The feasibility of reduced order modeling for turbulent flows using Proper Orthogonal Decomposition (POD) based Surrogate modeling and Galerkin Projection is demonstrated for use in the hydrodynamic modeling of the Very High Temperature Reactor (VHTR) lower plenum. The lower plenum of the Helium-cooled VHTR consists of vertical cylinder arrays subjected to turbulent jetting and cross-flow. Unsteady Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) simulations are used to acquire an ensemble of possible solution fields for flow around a circular cylinder in an open domain. Numerical results are validated to prior published literature. From the resultant data ensemble are extracted the coherent structures to create an optimal basis. POD is used to extract the coherent structures as this technique has been demonstrated to provide a basis of a chosen dimension such that the average L2-error is minimized for the best approximation of the basis to the data ensemble. The resultant optimal basis is used to construct accurate reduced order models. The computational effectiveness and insights revealed by this reduced order modeling approach are discussed for both the Surrogate modeling approach and Galerkin Projection.
Review of Expander Selection for Small-Scale Organic Rankine Cycle
Authors: Saghlatoun Saeedeh , Zhuge Weilin , Zhang Yangjun
Published: December 2014

After more than twenty years working on the selection of an appropriate expander for Organic Rankine cycles and wide research and attentions about its influence on the performance and total cost of waste heat recovery systems, now there is a good-enough background studies and achievement for large scale applications. But small-scale industries is like a art space to modify and revise the previous results.

As it is clearly known, in small-scale applications and industries especially in internal combustion engines, besides the investigation of performance, physical properties and final efficiency of expander, other parameters should be analyzed accurately like manufacturing cost, availability, reliability, sensitivity to operating condition fluctuations.

Due to a significant role of expander equipment to enhance the efficiency of ORC system in the first step expanders is investigated.

In this paper, as per related operating characteristics, a complete comparison of small-scale expanders will be debated to guide designers to select more appropriate and the best efficient expansion machine as per their requirements. According to available literatures there is more need to do research about different types of expanders with various operating conditions in small-scale industries.
Investigation of Two-Phase Flow in an Effervescent Atomizer
Authors: Jobehdar Mona Hassanzadeh , Gadallah Aly H. , Siddiqui Kamran , Chishty Wajid A.
Published: December 2014

Aerated-liquid atomization, also called “effervescent atomization”, is a technique that has a wide range of applications such as gas turbine combustors, internal combustion engines, furnaces and burners, and pharmaceutical sprays. We report on an experimental study conducted to investigate the two-phase flow in an Effervescent atomizer. A novel aerator tube base was implemented and tested. It is observed that the novel configuration suppresses the separation bubble at the trailing edge and results in more uniform and smaller bubbles compared to the standard flat base aerator. It has been found that the more uniform and smaller bubbles are generated as the mixing chamber length is reduced. It is concluded that by using a conical base aerator and by reducing the mixing chamber length, the spray steadiness and the atomization process can be significantly improved.
Study of Factors Influencing Non-Uniform Gas-Liquid Distribution in the Refrigerant Distributor in an Air Conditioner
Authors: Ishii Eiji , Yoshimura Kazuki
Published: December 2014

Factors that influence the non-uniform gas-liquid distribution in refrigerant distributors in air conditioners were studied. Gas-liquid flows in two-pass and multi-pass distributors were numerically simulated with a particle/grid hybrid method; droplets and liquid films were mainly simulated using a particle method, and gas flows were simulated using a grid method. Complex behaviors of multi-scale gas-liquid interfaces in the multi-pass distributor were simulated because droplets that were smaller than the grid size could be simulated without numerical diffusion through the gas-liquid interfaces. The effect of the connecting angle of the bend pipe was studied in the two-pass distributor, whereas the effects of the tube’s position relative the distributor inflow and the effect of gravity were investigated in the multi-pass distributor. The model was validated against multiple experimental data taken from an at-scale physical model. We found that keeping the liquid at the inlets of the multi-pass tubes was important for ensuring a uniform distribution.
Investigation of Turbulent Mixing in a Macro-Scale Multi-Inlet Vortex Nanoprecipitation Reactor by Stereoscopic-PIV
Authors: Liu Zhenping , Hill James C. , Fox Rodney O. , Olsen Michael G.
Published: December 2014

Flash Nanoprecipitation (FNP) is a technique to produce monodisperse functional nanoparticles through rapidly mixing a saturated solution and a non-solvent. Multi-inlet vortex reactors (MIVR) have been effectively applied to FNP due to their ability to provide both rapid mixing and the flexibility of inlet flow conditions. Until recently, only micro-scale MIVRs have been demonstrated to be effective in FNP. A scaled-up MIVR could potentially generate large quantities of functional nanoparticles, giving FNP wider applicability in the industry. In the present research, turbulent mixing inside a scaled-up, macro-scale MIVR was measured by stereoscopic particle image velocimetry (SPIV). Reynolds number of this reactor is defined based on the bulk inlet velocity, ranging from 3290 to 8225. It is the first time that the three-dimensional velocity field of a MIVR was experimentally measured. The influence of Reynolds number on mean velocity becomes more linear as Reynolds number increases. An analytical vortex model was proposed to well describe the mean velocity profile. The turbulent characteristics such as turbulent kinematic energy and Reynolds stress are also presented. The wandering motion of vortex center was found to have a significant contribution to the turbulent kinetic energy of flow near the center area.
Modelling Cavitation and Flash Atomization
Authors: Lu Nai-Xian , Reveillon Julien , Meslem Yann , Demoulin François-Xavier
Published: December 2014

Cavitation occurs in many engineering configurations such as marine propellers, liquid turbines, injectors and even flash atomization can be considered related to cavitation. Cavitation occurs when the pressure of liquid falls below the vapour pressure. As the vapour pressure depends on temperature, boiling can happen on superheated liquid. Indeed, homogeneous boiling and cavitation are similar phenomena that can be viewed either based on heat transfer or based on pressure changes, which is more linked to dynamics of the flow. Depending on the amount of produced vapour thermal effect can be considered to be negligible or preponderant to characterize the final two-phase flow. To be applicable for atomization, models of cavitation have to be considered both from pressure and thermal point of view. This is because vapour volume fraction can range from few percent to nearly hundred percent in case of phase inversion. For high level of vapour concentration the structure of two-phase flow changes drastically. Models based on isolated spherical bubbles do not represent the interaction that appears around the surface when a phase inversion occurs. The topic of this paper is therefore to discuss a model based on dense liquid-gas turbulent flows where cavitation modelling has been included in an attempt to capture both thermal and pressure effects. This model is derived from ELSA (Eulerian Lagrangian Spray Atomization) model for atomization. The whole mixture is considered globally with two species: the liquid and the gas. An equation of the amount of surface per unit volume helps to represent momentum transfer at the surface in the ELSA model. Based on this approach, modelling proposals will be presented to represent heat and mass transfer in a wide range of conditions to allow a complete description of cavitation in the context of atomization.
Particle-Induced Flow Reattachment in a Diffuser
Authors: de Souza Francisco José , de Souza Ana Marta , Utzig Jonathan
Published: December 2014

In this work, a numerical investigation on the gas-particle flow in a vertical diffuser is carried out. This study was motivated by the experimental work of Kale and Eaton [1], who noticed that the fully attached flow in a diffuser in the freeboard region of a particle bed would become detached if no particles were present. It was concluded at the time that this effect was not caused by the high inlet turbulence levels, but rather by the particles. With the goal to better understand the interactions between the particles and the fluid in a diffuser, simulations of a dilute particle-laden gas flow in a vertical diffuser are run using the Euler/Lagrange approach. The model, which includes interparticle collisions, the particle influence on the gas phase and wall roughness effects, is first validated based on experimental results from a horizontal channel and a vertical diffuser for both the continuous and dispersed phases at different mass loadings. Investigations on the effects of particles at different mass loadings and wall roughness on the diffuser flow are then carried out. It has been found that, even at moderate mass loadings, particles can significantly affect the diffuser flow pattern, and actually reattach the otherwise separated flow under some conditions. It has also been found that wall roughness plays a very important role in homogenizing the particle distribution at the diffuser section. The resulting more uniform concentration and velocity profiles can then reenergize the otherwise separated boundary layer and reattach it to the wall. The mechanism for the flow reattachment owing to the particle flow and the high wall roughness is investigated and an explanation is proposed.