bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer and Turbulent Structure in an Annular Channel With an Obstacle
Authors: Kashinsky O. N. , Lobanov P. D. , Kurdyumov A. S. , Pribaturin N. A.
Published: December 2014

Experimental study of liquid flow and heat transfer in an annular channel is performed. The channel consisted of two coaxial tubes with the diameters of 42.2 and 20 mm. An obstacle covering a quarter of the channel section was placed in the channel to produce a strong three-dimensional disturbance of the flow. Measurements of local wall shear stress are performed using an electrochemical technique. Measurements of heat transfer, time-averaged and fluctuational wall shear stress are performed at various points relative to the obstacle, this allowed to study the field of the hydrodynamic parameters of the flow.

The experimental data obtained can be used for validation of existing and developing computer codes accounting for a 3-D structure of turbulent flows.
Suitability Evaluation of Bubble Departure Diameter and Frequency Models for the Simulation of Subcooled Confined Jet Impingement Boiling
Authors: Abishek S. , Narayanaswamy R. , Narayanan V.
Published: December 2014

Accurate estimation of multiphase turbulence, interphase momentum exchange and bubble dynamics parameters such as bubble departure diameter and frequency is critical for a realistic simulation of flow boiling heat transfer. While there are experimental and mechanistic models available for the estimation of these parameters for rather specific geometric configurations, fluids and operating conditions, there is no specific comprehensive model for jet impingement boiling. Nor is there a consensus on a generalized model, particularly for the ebullition parameters, that could be extended to jet impingement boiling. Hence, a problem-based evaluation of the available models to conform to experimental data is often required. In the present work, a rigorous study is carried out to ascertain the suitability of different bubble departure diameter and departure frequency models for the simulation of confined and submerged, subcooled jet impingement boiling. The choice of ebullition models considered encompass both pool boiling as well as flow boiling based models, developed from both experimental as well as mechanistic approaches. The suitability of the models are evaluated by comparison of the predicted local and surface averaged heat transfer characteristics against experimental boiling data from the present research as well as that available in the literature. The computational simulations are carried out using the finite volume computational solver ANSYS FLUENT 14.5, with necessary customized functions for boiling parameters formulated and integrated into the solver.
Aero-Thermal Optimization of a Hybrid Roadster Tricycle Using Multidisciplinary Design Optimization Tools
Authors: Driant Thomas , Moreau Stéphane , Fellouah Hachimi , Desrochers Alain
Published: December 2014

To reach the goal of continuous improvement on automotive vehicles, their overall design strategy needs to be reconsidered. Hence, the future design will have to use global approaches like those developed in the aerospace industry where optimization of all interacting fields is performed jointly. This strategy has been applied to the development and optimization of a hybrid roadster aero-thermal management as part of a major Automotive Partnership Canada (APC) project1. The study presented herein seeks the best compromise between the vehicle aerodynamic drag and the cooling efficiency for the internal combustion engine (ICE) and the electric motor. The optimization of the heat exchanger position is first achieved followed by a multidisciplinary design optimization (MDO) approach with three main steps: first, a design of experiment (DOE) involving parametric CAD model generation, steady state CFD calculations and a heat exchanger optimization loop; secondly, approximations of response surfaces methods; finally, multi-objective optimization on the response surfaces using genetic algorithms and particle swarms. The study is constrained to use the automotive manufacturer’s software and to consider the vehicle environment without bringing significant modifications on non-thermal/aerodynamic parts.
Study of Afterburning in Solid Rocket Booster Jet: Towards a Model for Afterburning in Large Eddy Simulations
Authors: Poubeau Adèle , Paoli Roberto , Cariolle Daniel
Published: December 2014

This paper focuses on two decisive steps towards Large Eddy Simulation of a solid rocket booster jet. First, three-dimensional Large Eddy Simulations of a non-reactive booster jet including the nozzle were obtained at flight conditions of 20 km of altitude. A particularly long computational domain (400 nozzle exit diameters in the jet axial direction) was simulated, thanks to an innovative local time-stepping method via coupling multi instances of a fluid solver. The dynamics of the jet is analysed and comparison of the results with previous knowledge validates the simulations and confirms that this computational setup can be applied for Large Eddy Simulations of a reactive booster jet. The second part of this paper details the implementation of a simple method to study the hot plume chemistry. Despite its limitations, it is accurate enough to observe the various steps of the chemical mechanism and assess the effect of uncertainties of the rate parameters on chlorine reactions. It was also used to reduce the set of chemical reactions into a short scheme involving a minimum of species and having a limited impact on the physical time step of the Large Eddy Simulations.
PIV Investigation of Separated and Reattached Turbulent Flows Over Ribs of Various Aspect Ratio
Authors: Atamanchuk Kathryn M. , Tachie Mark F.
Published: December 2014

An experimental study is undertaken to investigate the features of separated and reattached flow over surface mounted traverse ribs of varying aspect ratio (1:1, 1:2, and 1:4) in a recirculating open channel turbulent flow. A particle image velocimetry system was used to conduct the velocity measurements. Upstream conditions were kept consistent among all three test cases. The reattachment length of the separated flow was found to decrease as rib aspect ratio increased, primarily as a result of a secondary separation reattachment formation on the ribs of increased aspect ratio. Contour plots of mean velocities, turbulence intensities, turbulent kinetic energy and Reynolds shear stresses, as well as one-dimensional profiles of streamwise mean velocity, turbulent kinetic energy and Reynolds shear stress in the recirculation and reattachment region are presented and discussed. The results show that maximum wall-normal mean velocities are approximately 40% of the approach freestream velocity. The results also indicate that the turbulence levels downstream of the block tend to decrease as the rib aspect ratio increases.
Impact of Droplet Clustering on Heat Transfer in Spray Processes
Authors: Lampa Aljoscha , Fritsching Udo
Published: December 2014

The transient state and unsteadiness of sprays from twin-fluid atomizers in enclosures is analysed. The investigated flows show differently scaled spray structures. Especially the meso-scale droplet clustering and coherent vortex structures in the gas are quantified. Droplet clustering can be caused by pulsating liquid disintegration procedures or droplet interaction with eddy structures in the gas. The preferential concentration of droplets influences the heat and mass transfer for individual droplets within the spray cone. This effect of droplet clustering is of interest for many spray applications, e.g. in automotive spray combustion. This numerical work focuses on the interaction of droplets with shear layer vortices at the spray edge.
Effects of Gap Ratio on Flow Past a Square Cylinder
Authors: Essel Ebenezer E. , Sharkey Liam , Tachie Mark F.
Published: December 2014

The present study investigates the effect of gap ratio on the turbulent flow characteristics downstream of a square cylinder positioned in an open channel. Detailed velocity measurements were performed using a particle image velocimetry (PIV) system for gap ratios, G/h = 0.5 and 1, where G is the distance from the bottom face of the cylinder to the nearby wall and h is the cylinder height. Each set of experiments was conducted using a water depth of 65 mm and a Reynolds number of 2000 based on the height of the cylinder and the freestream velocity. Mean velocities, Reynolds stresses and Reynolds shear stress producing events of the quadrant decompositions were compared for the different gap ratios investigated. The results showed that as gap ratio decreased from 1 to 0.5 cylinder heights, the length of the separated region increased by 50%. Furthermore, the Reynolds stresses were found to decrease with decreasing gap ratio. Further downstream of the cylinder, the turbulent kinetic energy decreased, while the Reynolds shear stress increased for G/h = 0.5 compared to G/h = 1.
Dynamic Imaging of Multiphase Flows in Rock Using Computed Tomography
Authors: Crandall Dustin , McIntyre Dustin , Jarvis Karl , Lapeer Roger , Tennant Bryan
Published: December 2014

Understanding the mechanisms for multiphase flow within the subsurface is critical to the planning and execution of a multitude of energy related projects including, enhanced oil recovery, geologic carbon sequestration, geothermal energy extraction, and gas production from tight shale reservoirs. This paper provides a brief review of the use of X-ray computed tomography (CT) scanning to visualize multiphase flows within geologically relevant rock cores, and then provides recent examples of multiphase flow at the National Energy Technology Laboratory. With modern CT scanning techniques we show how it is possible to visualize dynamic flooding of cores with fluids, as well as calculate changes in the saturation within the porous matrix from image analysis of the scans.
A Stochastic Galerkin Approach to Uncertainty Quantification in Poroelastic Media
Authors: Delgado Paul , Kumar Vinod
Published: December 2014

Recent concerns over the safety of oil and natural gas extraction, fracking, and carbon sequestration have driven the need to develop methods for uncertainty quantification for coupled subsurface flow & deformation processes. Traditional monte-carlo methods are versatile, but exhibit prohibitively slow convergence. In this work, we develop an intrusive polynomial chaos expansion method for Biot’s Poroelasticity Equations based on galerkin projection with uniform and log-normally distributed material parameters. We analyze accuracy and efficiency of our method and compare it to monte-carlo and anova based probabilistic collocation methods.
Numerical Investigation of the Flow in a Coaxial Piping System
Authors: Farbos de Luzan Charles , Perelstein Yuri , Gutmark Ephraim , Frosell Thomas , Felten Frederic
Published: December 2014

A coaxial piping system (CPS) that involves a transition from a smaller annulus into a larger annulus is investigated to evaluate the generation of vortices and recirculation zones around the transition area. These areas are of interest for industrial applications where erosion within the piping system is a concern. The focus of this work is to evaluate the capabilities of Computational Fluid Dynamics (CFD) using commercial Reynolds-Averaged Navier Stokes (RANS) models to predict the regions and intensity of vortices and recirculation zones. A trusted grid is developed and used to compare turbulence models. The commercial CFD solver Fluent (Ansys Inc., USA) is used to solve the flow governing equations for different CFD numerical formulations, namely the one equation Spalart-Allmaras model, and steady-state RANS with different turbulence models (standard k-epsilon, k-epsilon realizable, k-epsilon RNG, standard k-omega, k-omega SST, and transition SST) [1].

CFD results are compared to time-averaged particle image velocimetry (PIV) measurements. The PIV provides 3D flow field measurements in the outer annulus of the piping system. Velocities in regions of interest were used to compare each model to the PIV results. An RMS comparison of the numerical results to the measured values is used as a quantitative evaluation of each turbulence model being considered. The results provide a useable CFD model for evaluation of the flow field of this flow field and highlights areas of uncertainty in the CFD results.
Indoor Airflow Simulation Using Lattice Boltzmann Method
Authors: Sajjadi H. , Salmanzadeh M. , Ahmadi G.
Published: December 2014

Indoor air quality (IAQ) is very important to human health and comfort as increasingly people spent most of their time in indoor environment. Numerical simulation of indoor airflows has become a significant tool for investigation of the indoor air quality. Cost effective computational methods with reasonable accuracy have the advantage of being more accessible to designers compared to more precise but expensive DNS methods. Recently developed Lattice-Boltzmann Method (LBM) has proved to be a powerful numerical technique for simulating fluid flows in various applications. In comparison with the conventional CFD methods, the advantages of LBM are: simple calculation procedure, simple and efficient implementation for parallel computation, and easy and robust handling of complex geometries. The indoor airflow is typically in turbulent flow regimes. Due to the high costs of more accurate direct numerical simulation (DNS) and large eddy simulation (LES), in this study the Reynolds Averaged Navier-Stokes (RANS) method was used for analyzing the turbulent flow conditions. The RANS governing equations, and in particular, the k-ε turbulence model was incorporated into the Lattice-Boltzmann computational method. The simulation results showed that the combined LBM-RANS provide a reasonably accurate description of the airflow behavior in the room at modest computational cost.
A Partitioned Strong Coupling Procedure for Simulation of Shock Wave/Flexible Structure Interaction
Authors: Benefice Guillaume , Rozenberg Yannick , Aubert Stéphane , Ferrand Pascal , Thouverez Fabrice
Published: December 2014

The prediction of FSI limit cycles involving transonic separated flows requires efficient and accurate solvers coupling techniques. Explicit partitioned strong coupling is considered in time domain, where careful attention should be paid to energy conservation at the fluid-structure interface. For all the presented results, both meshes are set up such that structural skin points and fluid boundary mesh points are collocated. The presented test case involves a shock tube in which the shock wave impinges on a cross flow flexible panel, initially at rest. Compared to experimental results, the pressure peaks and fluctuations are correctly predicted but the pressure level is over predicted as well as the displacement frequency. Results analysis explains correctly the flow physic which is shown to be weakly modified by structural damping, turbulence modeling and time discretization. This discrepancy between experimental and numerical results could been explained by the structure model, in which the panel root modeling might be questionable.
Turbulence Modulation by Particle Clustering in Dilute and Moderately Dilute Channel Flows
Authors: Capecelatro Jesse , Desjardins Olivier
Published: December 2014

Turbulent wall-bounded particle-laden flows exhibit a variety of interesting phenomena that can greatly impact the underlying carrier-phase turbulence. At sufficiently low particle concentrations and mass loadings, it is well established that inertial particles will accumulate in regions of high strain and avoid regions of high vorticity. At larger concentrations and mass loadings, intimate coupling between the phases may lead to flow instabilities, resulting in the spontaneous generation of dense clusters that can completely reorganize the structure of the underlying fluid turbulence. This work aims at investigating the effect of particle clustering on the carrier-phase turbulence in both dilute and moderately-dilute channel flows with a friction Reynolds number Reτ=630 using highly-resolved Euler-Lagrange simulations. To study the effect of gravity on cluster dynamics, simulations are conducted with gravity aligned in the mean flow direction, as well as gravity opposing the mean flow direction (i.e., a riser configuration). Particle segregation and velocity statistics are compared for each case. It is shown that the fluid turbulence departs significantly from the initially fully-developed turbulent flow when subject to a moderately dilute suspension of particles. In the denser channel flows, the gas velocity retains a viscous sublayer, but displays a strongly reduced boundary layer thickness and a flatter velocity profile compared to the unladen and dilute flows, leading to larger friction velocity. The particle concentration profile along the channel height is not found to be modified greatly by the increased particle loading, but is found to depend strongly on the orientation of gravity.
Deposition Fraction of Ellipsoidal Particles in a Fully Developed Laminar Pipe Flow: Application of New Correlations for Hydrodynamic Forces and Torques
Authors: Tavakol Mohammad Mehdi , Abouali Omid , Yaghoubi Mahmood , Ahmadi Goodarz
Published: December 2014

The physics of transport, deposition, detachment and reentrainment re-entrainment of particles suspended in a fluid are of great interests in many practical fluid engineering problems. For spherical particles, analysis of their translational motions is sufficient for a complete description of their transport processes. Prediction of transport and deposition of non-spherical particles, however, is more complicated due to the coupling of particle translational and rotational motions. Most studies related to dispersion of ellipsoidal particles used the traditional creeping flow formulations for hydrodynamic forces and torques. These formulations are valid for very low Reynolds number flows. In this study, dispersion and deposition of ellipsoidal particles in a fully developed laminar pipe flow are analyzed numerically using new correlations for hydrodynamic forces and torques. The deposition efficiency of the ellipsoidal particles in laminar pipe flow are calculated and the results are compared with other theoretical and numerical studies and good agreement is observed.
Numerical Investigation of Droplet-Droplet Coalescence and Droplet-Interface Coalescence
Authors: Mansouri A. , Arabnejad H. , Mohan R. S.
Published: December 2014

The oil produced from offshore reservoirs normally contains considerable amount of water. The separation of water from oil is very crucial in petroleum industry. Studying the coalescence of two droplets or one droplet and interface can lead to better understanding of oil-water separation process. In this study, the coalescence of two droplets and droplet-interface are simulated using a commercial Computational Fluid Dynamics (CFD) code FLUENT 14. In order to track the interface of two fluids, two approaches, Volume of Fluid (VOF) and Level-Set method were utilized. The results are compared with experimental measurements in literature and good agreement was observed. The effect of different parameters such as droplet velocities, interfacial tension, viscosity of the continuous phase and off-center collision on the coalescence time has been investigated. The results revealed that coalescence time decreases as the droplet velocities increase. Also, continuous phase with higher viscosities and lower water-oil interfacial tension, increase the coalescence time.
Calculation of Turbulent Boundary Layer for a Slot Jet Impingement on a Flat Surface
Authors: Arabnejad H. , Mansouri A. , Shirazi S. A. , McLaury B. S.
Published: December 2014

The objective of this study is to characterize flow parameters for two-dimensional turbulent jets impinging on a flat surface. An integral form of the momentum equation has been used to obtain a hydrodynamic solution. The boundary layer was divided into three regions, stagnation zone, developing zone and fully developed zone for free-surface and free shear, and into two regions, stagnation and wall jet zone for submerged jet configurations. A nonlinear ordinary differential equation has been obtained for frictional velocity at each zone using a logarithmic velocity profile with Coles’s law of the wake and solved numerically to predict wall shear stress as well as boundary layer and momentum thicknesses. The proposed method is more straightforward and computationally less expensive in calculating the main flow parameters as compared to turbulent flow models such as RANS and LES. Predicted wall shear stresses for a submerged jet were compared to experimental data for different cases and showed agreement with experimental data.
Characterizing Slug/Churn Flow Using Wire Mesh Sensor
Authors: Parsi M. , Vieira R. E. , Torres C. F. , Kesana N. R. , McLaury B. S. , Shirazi S. A. , Hampel U. , Schleicher E.
Published: December 2014

A wire mesh sensor (WMS) is a device used to investigate multi-phase flows. The WMS measures the instantaneous local electrical conductivity of multiphase flows at different measuring points. There is a significant difference in the electrical conductivity of the employed fluids (in this work air and water, conductivity of water is much higher than that of air). Using the difference in the electrical conductivity, the WMS provides the local void fraction. The WMS utilized in this work includes two identical planes of parallel 16×16 grid of wires. The separation distance between these two planes is 32 mm. The WMS was installed in a 76.2 mm (3-inch) diameter vertical pipe to extract information such as void fraction distribution, structure velocity, and slug/churn flow structure. The superficial gas (air) velocity (VSG) ranged from 10 to 38.4 m/s. Liquid (water) superficial velocities (VSL) of 0.30, 0.46, 0.61 and 0.76 m/s were employed. To study the effects of viscosity on the slug/churn flow structure, Carboxyl Methyl Cellulose (CMC) was added to water to increase the liquid viscosity without altering its density. Each experiment was performed for 60 seconds. An operation frequency for the WMS of 10 kHz (totaling 600,000 frames of void fraction measurement per experiment) was used for all experiments.
A Two-Fluid Model for Slug Flow Initiation Based on a Lagrangian Scheme
Authors: Conte Marco Germano , Cozin Cristiane , Barbuto Fausto Arinos , Morales Rigoberto E. M.
Published: December 2014

Two-phase slug flow is present in many industrial processes, such as the exploitation and transportation of hydrocarbon mixtures from oil wells. This kind of flow is characterized by two distinct structures which repeat intermittently: a liquid slug with a large amount of momentum followed by a compressible gas bubble. In recent decades, a few models for simulating such complex flows were developed, as the eulerian two-fluid model and drift flux, and the lagrangian slug tracking. The aim of this work is to present a detailed study on the numerical implementation of the hybrid model proposed by Fabien Renault and Nydal which is able to track down waves that arise in the gas-liquid interface and possible slugs generated by them. This model was developed from the two-fluid model equations in which the motion generated by the dynamic pressure of the gas on the slugs is decoupled from the slow movement of the liquid below the gas. The movement of the bubbles in the liquid is then modeled similarly to shallow-water equations. The solution of the equation set is achieved in two steps. The first step provides the pressure field and the gas flow through the numerical solution of the equations for the gas, using the finite difference method. The second step solves the adapted shallow-water equations analytically. The model was coded in object-oriented Intel Visual Fortran95. Simulations to analyze the ability of the code to generate slugs for some pairs of water-air superficial velocities at atmospheric pressure were carried out. The results, as the distribution of the slug length, frequency and average values were compared to experimental results reported in the literature.
Prediction of Typhoon Storm Surge Flood in Tokyo Bay Using Unstructured Model ADCIRC Under Global Warming Scenario
Authors: Hirano Kohin , Murakami Tomokazu , Iizuka Satoshi , Nakatani Tsuyoshi , Shimokawa Shinya , Bunya Shintaro , Kawasaki Koji
Published: December 2014

The possibility of a major typhoon and its likely effects on Tokyo Bay have been estimated using an atmosphere-ocean-wave coupled model for future global climate conditions, based on the Intergovernmental Panel on Climate Change, Special Report on Emissions Scenarios (IPCC SRES) A1B scenario. In addition, the basin- to channel-scale unstructured grid hurricane storm surge model, Advanced CIRCulation (ADCIRC), has been used to determine the risk of storm surge flood in coastal areas, particularly on the Koto Delta, where inundations would most likely reach maximum levels during a strong typhoon. The system uses a high-resolution (down to 45 m) representation of regional geometry, bathymetry, and topography and emphasizes the seamless modeling of processes including those of storm surge, stormtide inundation, and river flow. The numerical experiment is validated by comparing the temporal and spatial distribution of water elevation and inundation with results obtained using a one-way coupling model of storm surge and wave activity. The simulation results show that the maximum tide level may exceed 4 m on the north side of Tokyo Bay, and surge-induced floods may extend throughout most of the Koto Delta region. And the validation results indicate that the sea-land interaction and river flows may significantly affect the depth and increase of extent of inland inundation.
A Study Involving the Flow Pattern Comparison of a PIV Experiment With CFD Simulation, for the Flow Within a Centrifugal Pump
Authors: Rahman Md. Taifur , Siddiqi Mohammed
Published: December 2014

Computational Fluid Dynamics (CFD) modeling software is increasingly being used as the tool of choice for analyzing the flow details and integrated performance of turbo-machinery products. In fact, the use of CFD is rapidly transitioning from a verification tool to an upfront design-enabling & optimization tool. Experimental validation of computational simulation is essential to ensure an acceptable degree of reliability and relevance of the simulated results to real world performance. While CFD has been rigorously validated for numerous simple physics cases like single-phase flow, more complex physics applications, e.g., those involving multi-phase solid-liquid flows, require more elaborate and thoughtful means of validation. In this context, a study was undertaken to review Particle Image Velocimetry (PIV) as a means of validating more complex CFD cases and to contrast the findings with those obtained from CFD simulation. PIV offers a new possibility for flow visualization in turbo-machinery passages, in contrast to traditional methods like flow probing or hot-wire anemometry, which can be a very challenging proposition in the rotating domain of a turbo-machinery blade system. This paper discusses the first phase of this work, which was limited to single-phase flow studies, with the intent to follow up further with multi-phase flow studies. A specially designed fractional horsepower centrifugal pump is used as a test subject to analyze all possible parameters of the flow field using PIV and the result is then compared with the CFD simulations of the same model. The results show a reasonable match in the flow patterns obtained by the two alternate methods, although significant differences are apparent too. In conclusion, each method has its own place in the context of turbo-machinery flow studies.
Numerical Investigation of Low-Reynolds Number Airfoil Flows Using Transition-Sensitive and Fully Turbulent RANS Models
Authors: Chitta Varun , Jamal Tausif , Walters D. Keith
Published: December 2014

A numerical analysis is performed to study the pre-stall and post-stall aerodynamic characteristics over a group of six airfoils using commercially available transition-sensitive and fully turbulent eddy-viscosity models. The study is focused on a range of Reynolds numbers from 6 × 104 to 2 × 106, wherein the flow around the airfoil is characterized by complex phenomena such as boundary layer transition, flow separation and reattachment, and formation of laminar separation bubbles on either the suction, pressure or both surfaces of airfoil. The predictive capability of the transition-sensitive k-kL-ω model versus the fully turbulent SST k-ω model is investigated for all airfoils. The transition-sensitive k-kL-ω model used in this study is capable of predicting both attached and separated turbulent flows over the surface of an airfoil without the need for an external linear stability solver to predict transition. The comparison between experimental data and results obtained from the numerical simulations is presented, which shows that the boundary layer transition and laminar separation bubbles that appear on the suction and pressure surfaces of the airfoil can be captured accurately by the use of a transition-sensitive model. The fully turbulent SST k-ω model predicts a turbulent boundary layer on both surfaces of the airfoil for all angles of attack and fails to predict boundary layer transition or separation bubbles. Discrepancies are observed in the predictions of airfoil stall by both the models. Reasons for the discrepancies between computational and experimental results, and also possible improvements in eddy-viscosity models, are discussed.
Domain Partitioned Transformation of Pump-Turbine Characteristic Curves in 3-D Space
Authors: Zeng Wei , Yang Jiandong , Cheng Yongguang
Published: December 2014

Pump-turbine characteristic curves are the most important boundary condition in the hydraulic transient simulation of a pumped-storage hydropower station. Conventional representation of them, however, has serious defects, For instance, the “S” and “hump” shapes, composed of multiple values and steep twists, lead to the difficulty in interpolation between known guide-vane opening curves, which is necessary in hydraulic transient simulations. Here, a new transformation method was figured out to settle this problem thoroughly and to improve the accuracy of interpolation between the constant opening curves. Prior to the transformation, the characteristic curves are partitioned into eight domains. Curves of each domain were transformed through different formulae that fit the curves well. Eight characteristic surfaces in the 3-D space can be obtained by adding the guide vane opening as the coordinate axis. The theoretical method has been validated by the excellent agreements achieved by comparing the curves interpolated on the characteristic surfaces with the measured data.
Dynamic of Water Droplet Impacting on a Hydrophilic Surface Accompanied With Stagnation Flow
Authors: Mohammadi Morteza , Attarzadeh Mohammadreza , Tembely Moussa , Dolatabadi Ali
Published: December 2014

Droplet impact on solid surfaces has been extensively reported in the literature, however the effect of accompanying air flow on the outcome of impacting droplet has yet to be addressed and analyzed which is similar to real scenario of impacting water droplet on aircraft’s leading edge at in-flight icing conditions. This study addresses the net effect of airflow (i.e. stagnation and the resultant shear flow) on the impacting water droplet with the same droplet impact velocity which is exposed to different airspeeds. In order to provide stagnation flow, a droplet accelerator was built which can generate different airspeeds up to 20 m/s. Droplet impact behavior accompanied with stagnation flow on a polished aluminum surface with a contact angle of 70° was investigated by high speed photography. 2.5 mm water droplet size with impact velocities of 2, 2.5 and 3 m/s which correspond to non-splashing regime of impacts are exposed to three different regimes of air speeds namely 0 (i.e. still air case), 10, and 20 m/s. It was observed that when droplet reaches to its maximum spreading diameter, some fingered shape at the end of spreading lamella (i.e. Rayleigh-Taylor instability) is appeared. When stagnation flow is present these fingered shape droplets are exposed to the generated shear flow close to the substrate (i.e. Homann flow approach) causes a droplet break up while complete non-splashing regime is observed in still air case. In spite of the fact that maximum spreading diameter is not largely affected by air flow compare to still air case, droplet height variation is significantly reduced by about 70 percent for strong stagnation flow (i.e. 20 m/s) which generates non-recoiling condition resulting in the thin film formation.
Bubble Entrapment in Sprayed Films
Authors: Dalili A. , Chandra S. , Mostaghimi J. , Fan H. T. Charles , Simmer J. C.
Published: December 2014

A compressed air sprayer was used to spray model paint onto two glass substrates at the same time. Afterwards, one glass substrate was placed on a LED light source and still photographs were taken from the top using a DSLR camera with a timer system. The other substrate was put on a balance to record weight. Pictures and weight measurements were taken at 5 second intervals for 15 minutes. The sprayed film thickness was varied. The pictures were analyzed using ImageJ software. Bubble Count vs. Time, Sauter Mean Diameter (SMD) of Bubbles vs. Time as well as Weight vs. Time was plotted. It was seen that the pace of weight loss was faster for thinner films. The rate of bubble escape also depended on film thickness. It took a longer time for thicker films to lose the bubbles entrapped in them. In the first 30 seconds, large bubbles escaped due to buoyancy forces and afterwards surface-tension driven flows became dominant. There was also a lot of bubble movement in thicker films. The effect of gravity was studied as well. Gravity did not affect the bubble escape rate since a downward facing film had the same bubble count as an upward facing film confirming that bubble motion was not due to buoyancy forces alone. However, the SMD of bubbles in a downward facing film was larger than an upward facing film. Buoyancy is not a factor in bubble escape from the downward facing film and only surface-tension driven flows play a role.
Eulerian Two-Phase Flow Modeling of Steam Direct Contact Condensation for the Fukushima Accident Investigation
Authors: Pellegrini Marco , Agostinelli Giulia , Okada Hidetoshi , Naitoh Masanori
Published: December 2014

Steam condensation is characterized by a relatively large interfacial region between gas and liquid which, in computational fluid dynamic (CFD) analyses, allows the creation of a discretized domain whose average cell size is larger than the interface itself. For this reason generally one fluid model with interface tracking (e.g. volume of fluid method, VOF) is employed for its solution in CFD, since the solution of the interface requires a reasonable amount of cells, reducing the modeling efforts. However, for some particular condensation applications, requiring the computation of long transients or the steam ejected through a large number of holes, one-fluid model becomes computationally too expensive for providing engineering information, and a two-fluid model (i.e. Eulerian two-phase flow) is preferable. Eulerian two-phase flow requires the introduction of closure terms representing the interactions between the two fluids in particular, in the condensation case, drag and heat transfer. Both terms involve the description of the interaction area whose definition is different from the typical one adopted in the boiling analyses. In the present work a simple but effective formulation for the interaction area is given based on the volume fraction gradient and then applied to a validation test case of steam bubbling in various subcooling conditions. It has been shown that this method gives realistic values of bubble detachment time, bubble penetration for the cases of interest in the nuclear application and in the particular application to the Fukushima Daiichi accident.
Effects of Blade With Perforation on Aerodynamic Performance of Dual-Rotor Small Axial Flow Fans
Authors: Yongjun Hu , Yingzi Jin , Yi Li , Yanping Wang , Guoqi Li , Zhe Lin
Published: December 2014

The static characteristics of dual-rotor small axial flow fans are better than that of single rotor small axial flow fans. While, compared with single rotor small axial flow fans, the noise of dual-rotor small axial flow fans highly increases. Regarding to this reason, the perforation blade are designed for dual-rotor small axial flow fans in this paper. Pre-stage blades, post-stage blades, and both pre-stage and post-stage blades were perforated respectively. The k–ε turbulence model and the FW-H noise model were used to simulate. Then, the static characteristics and aerodynamic performance of the prototype fan and the fans with perforation blade were contrasted and analyzed. The results show that: In general, the pressure rising and efficiency of the fans with perforation blade declines slightly. Compared to another two perforation blade, and the pressure rising and efficiency of the fans of pre-stage perforating fan shows the smallest reduction, but increases slightly at the optimum operating condition; With the difference of perforation way, the variation of the noise level are different, while, in the outlet zones, the noise are all reduced;. The centralized region of vorticity in the trailing edge of the blades are reduced, and the noise of the fans are all reduced. All the results show that, using perforation blade can improve the aerodynamic performance of dual-rotor small axial flow fans.
Numerical Simulation of a Fluid Flow Inside a Novel Ducted Wind Turbine
Authors: Goudarzi N. , Zhu W. D. , Bahari H.
Published: December 2014

A novel ducted wind turbine, referred to as the Wind Tower technology, for capturing wind power in either residential or commercial scale applications is developed. A mathematical model of the fluid flow inside the tower is derived and the experimental tests have been conducted on a 1/8th prototype. Proposing an optimum design under the consideration of a maximum output power generation and a minimum cost of energy, which leads to a maximum return on investment, is a big challenge in developing the Wind Tower technology. Numerical simulation of the fluid flow inside the tower helps to make a more precise and accurate estimation of the flow characteristics at different sections of the tower. Hence, a two-dimensional single-nozzle Wind Tower is modeled to perform the computational fluid dynamics calculation. This provides the effect of major components of the Wind Tower, including the inlet and the outlet dimensions, and the Wind Tower structure configurations on the flow characteristics going through the tower at laminar steady-state condition. The average velocity values at the outlet due to changing the Wind Tower component configurations are measured. The results provide the optimum dimension ranges of the major Wind Tower components; these values would be further refined at a specific site with its certain wind characteristics.
An Assessment on the Wind Energy Potential and Possible Solutions for Power Generation in Baltimore County in Maryland, USA
Authors: Goudarzi N. , Zhu W. D. , Delgado R. , St. Pé A.
Published: December 2014

The statistical data of five years wind speed measurements at University of Maryland, Baltimore County are used to find out the availability of wind energy resource for power generation. Wind speeds are measured at an approximately 30 meters above the ground; the monthly and yearly mean wind speeds are calculated and evaluated by using the Weibull distribution function. The annual values of k (dimensionless Weibull shape parameter) ranged from 1.78 to 1.99 with a five-year mean value of 1.87. The annual values of c (Weibull scale parameter) ranged from 3.15 to 3.60 with a five-year mean value of 3.28. The results show the highest and lowest wind power potential occurs in February and July, respectively. While this site is not appropriate for large-scale power generation, this study shows the availability of enough wind potential for non-grid connected electrical and mechanical applications. Different residential wind harvesting technologies in urban areas have been studied and more promising ones are introduced as solutions to provide larger-scale power generation at this site with a low annual mean wind speed.
Direct Numerical Simulations (DNS) of Particles in Spatially Varying Electric Fields
Authors: Amah Edison C. , Singh Pushpendra , Janjua Mohammad
Published: December 2014

A numerical scheme is developed to simulate the motion of dielectric particles in uniform and nonuniform electric fields of a micro fluidic device. The particles are moved using a direct simulation scheme in which the fundamental equations of motion of fluid and solid particles are solved without the use of models. The motion of particles is tracked using a distributed Lagrange multiplier method (DLM) and the electric force acting on the particles is calculated by integrating the Maxwell stress tensor (MST) over the particle surfaces. One of the key features of the DLM method is that the fluid-particle system is treated implicitly by using a combined weak formulation where the forces and moments between the particles and fluid cancel, as they are internal to the combined system. The MST is obtained from the electric potential, which, in turn, is obtained by solving the electrostatic problem. In our numerical scheme the Marchuk-Yanenko operator-splitting technique is used to decouple the difficulties associated with the incompressibility constraint, the nonlinear convection term, the rigid-body motion constraint and the electric force term. A comparison of the DNS results with those from the point-dipole approximation shows that the accuracy of the latter diminishes when the distance between the particles becomes comparable to the particle diameter; the domain size is comparable to the diameter; and also when the dielectric mismatch between the fluid and particles is relatively large.
Details Study of Ambient Wind Effect on Heat Dissipation Capacity of Thermal-Powerplant Dry Cooling-Towers
Authors: Darbandi Masoud , Behrouzifar Ali , Mirhashemi Ahmad , Salemkar Hossein , Schneider Gerry E.
Published: December 2014

Thermal powerplants report a reduction in their dry cooling tower performances due to surrounding wind drafts. Therefore, it is very important to consider the influence of wind velocity in cooling tower design; especially in geographical points with high wind conditions. In this regard, we use the computational fluid dynamics (CFD) tool and simulate a dry cooling tower in different wind velocities of 0, 5 and 10 m/s. To extend our calculations; we also consider the temperature variation of circulating water through the tower heat exchanger or deltas one-by-one. We show that some heat exchangers around the tower cannot reduce the circulating water temperature sufficiently. This causes an increase in the mean temperature of those heat exchangers. The worst performances can be attributed to heat exchanger located on side wind places. We will discuss the detail performance of each delta and their assembly in draft wind conditions. This study suggests some effective ways to overcome thermal-performance of cooling tower in wind conditions.
Methods for Reducing Aerodynamic Drag on Cargo Carrying Railcars
Authors: Condie Robert , Maynes Daniel
Published: December 2014

In recent years the cost of diesel fuel has increased sharply and this has led to an interest in reducing shipping costs by train. Current manufacturing practices of railcars provide an opportunity for research in methods that reduce the aerodynamic drag. This paper reports on a study which involved collecting experimental data from wind tunnel tests using 1/29 scale train models. Two cargo carrying railcar types were studied. The first were coal carrying railcars and the second were auto carrying railcars. Different features of the railcars were investigated. The largest contributor to drag on the coal cars is the large void space of an empty car. The research investigates several roof structures that cover this space and act to reduce drag. From these structures it is determined that the drag can potentially be reduced by nominally 46%. Similarly, profile features of the auto carrying railcars are also investigated. This research reviewed the roof structure, side panels and chassis structure. From the data, it was determined that drag could be reduced by modifying or covering the roof, side panels and chassis structure by nominally 20%, 5% and 15% respectively.
Spray-Quenching for Process-Integrated Heat Treatment of Construction Components
Authors: Bucquet Thibaud , Fritsching Udo
Published: December 2014

Spray quenching processes in heat treatment processes of specimen and components demonstrated its efficiency and potential of direct in-process integration in applications as forging or sheet metal forming. Ensuring local quenching homogeneity and offering a range of quenching intensities, spray-quenching provides optimal solutions to carry out energy-efficient, homogeneous and intensive heat treatment processes. In this contribution, spray quenching of specimen using twin-fluid, flat-spray nozzles is evaluated in order to integrate the heat treatment process within an automated production line of forging or forming components. The quenching strategies firstly aim at providing appropriate microstructures (homogeneous and bainitic) to forged metallic parts of various geometries. Experiments and simulations are carried out to derive optimal cooling strategies. Temperature-dependent heat transfer coefficient (HTC) distributions based on a parameter study of the spray nozzle involving thermography have been evaluated. Transient heat transport simulations where the components are quenched according to local and dynamic HTC distribution using various arrangements of the nozzle field were performed. It is shown that the a priori simulated process parameters provided homogeneous microstructures in the components. The characteristic specimen geometries under investigation range from flat plates to cylindrical parts as e.g. stepped shafts. The possibility to extend spray quenching to more complex-shaped specimen geometries is outlined.