bluuebunny/crossref_metadata_2025 huggingface dataset:
Reynolds Number Dependence of Laminar Loss Coefficients for a Rectangular-Cross Section Square-Cornered Tee Junction
Authors: Ring Brock P. , Lin Yunhao , Henderson Andrew W. , Hossan Mohammad , Lemley Evan C.
Published: December 2014

Energy losses in junctions are often found by using an assumed loss coefficient for the particular geometry. While this coefficient remains nearly constant under turbulent conditions, this is not true for laminar flow. The loss coefficient through a dividing junction tends to decrease as a function of Reynolds number converging to some value once fully turbulent flow occurs. Research has been done to catalog losses for various geometries under turbulent flow; yet, there has not been the same detailed research for the laminar conditions. This is mostly due to many applications at the macro scale where turbulent flow is prevalent. Flow in microchannels and nanochannels is mostly laminar. Applications at this small scale have created a demand for the study of these loss coefficients under the laminar flow conditions.

This paper focuses on simulations done of flow through a square-cornered tee-junction with a rectangular cross sectional area of 6 by 7 millimeters. The fluid consisted of a glycerin and water mixture that was 30 percent water and 70 percent glycerin by volume. Measurements were made of an actual mixture’s density and viscosity and these parameters were used in the simulations. The mixture was chosen to give sufficient pressure drop to measure in validation experiments. Using these simulations, a detailed account of the energy losses in the junction was observed as a function of Reynolds number. The Reynolds number range in this study was 1–100. Higher Reynolds numbers were simulated where signs of a transition to turbulence were observed.

The stagnation loss coefficient, which includes kinetic energy and pressure changes through the junction, was found to be inversely proportional to Reynolds number. Initial experimental verification has been performed, in which the experimental stagnation loss coefficient followed the same trend as the simulations. Additional experimental validation is underway.
Development of Boiling Heat Transfer Analysis Method
Authors: Fukuta Masato , Yamamoto Yasushi
Published: December 2014

In this study, a numerical analysis method applicable to estimation of the boiling heat transfer has been developed. Currently, the experimental correlations or the empirical laws have been applied to evaluate the boiling heat transfer. Therefore, it is difficult to predict the effects of the change of the heated surface geometry, thermal-hydraulic conditions, the surface activation or modification, because out of the application range of these correlations. The purpose of this work is to construct the boiling two-phase analysis method for thermo-fluid phenomena, and to realize “Design-by-Analysis” independent on the experiments and empirical laws. For this purpose, it is important to predict steam-water interface structure characteristics of the two-phase flow directly. Until now, for evaluating the boiling phenomena, Diffusive Interface Model for the bubble interface tracking was applied. In this model, the steam-water interface is diffuse with a finite width, and values of the thermodynamic properties change between water and steam smoothly within the interface region. For evaluating the wettability of heated surface, the surface energy is estimated by using the phase-field model. The wetting phenomena during boiling are able to be analyzed directly with this model. We present the numerical results of nucleate pool boiling phenomenon by using the developed analysis method. We succeeded in simulating the boiling process, vapor bubbles nucleation, growth, and departure behavior on a heated surface. By present analysis method, it was confirmed that the boiling heat transfer coefficient could be evaluated quantitatively without the experimental correlations.
Research on Critical Stable Sectional Area of Surge Chamber Considering the Fluid Inertia in the Penstock and Characteristics of Governor
Authors: Guo Wen-cheng , Yang Jian-dong , Chen Jie-ping
Published: December 2014

According to the fact that the existing critical stable sectional area of surge chamber does not consider the effect of the fluid inertia in the penstock and characteristics of governor, mathematical model of hydraulic and governor system considering those two factors is established. Critical stable sectional area criterion is equivalent to that the first derivative term of homogeneous differential equation is greater than zero, and the analytical formula of critical stable sectional area is deduced. The analytical formula is composed of diversion tunnel term, penstock term and governor term, diversion tunnel term is Thoma’s formula, penstock term is positive and governor term is negative. Finally, the mathematics essence of the governor parameters’ effect on critical stable sectional area is revealed: the effect of temporary droop bt and damping device time constant Td exist critical values, but the critical value is only meaningful in mathematics and would not appear in actual engineering. Critical stable sectional area is a monotone decreasing function of bt and Td.
Numerical Simulation on Flow Field of Bladeless Fan
Authors: Guoqi Li , Peifeng Lin , Baoling Cui , Yingzi Jin , Yongjun Hu , Zhe Lin
Published: December 2014

With the advent of bladeless fan, technological revolutions begin to hit the industrial design world of fan. However, there is none of the developed methods on bladeless fan. To explore the excellent blowing performance of bladeless fan, numerical simulation on flow field of bladeless fan was carried out in this paper. Based on the simplified model of bladeless fan, the whole process that the airflow passes through the turbine from the inlet to the outlet slit and exit far field at last, were simulated. By comparing the flux of inlet and the flux of far outlet, the causes of flux increasing are analyzed. After analyzing static characteristics of the flow field, it shows that pressure difference is very obvious. The results obtained from velocity distribution and the characteristics of the pathlines near diffuser section and turbine, were described and analyzed. The results show that the internal flow field characteristics of bladeless fans, which we concern. The external flow field characteristics of bladeless fan was studied in the same way. And it is found that the velocity magnitude of the outlet slit and Coanda surface is much larger than other area and different positions play different roles. A general analysis on inside computational domain and outside computational domain, denotes the details about fluid motion. The research could offer reference to improvement of bladeless fan.
Two-Dimensional Computer Simulation of Salinity Gradient Solar Pond Operation
Authors: Mehdizadeh Minoo , Ahmadi Goodarz
Published: December 2014

This study is concerned with computer modeling of flow and thermal analysis of solar ponds with a salinity gradient. Solar ponds have been used as an efficient and environmentally friendly approach for collection of solar energy for low temperature thermal applications. A two-dimensional unsteady computational fluid dynamic (CFD) model was developed and used for numerical study of stability analysis of the pond, as well as heat and mass transfer in the salt gradient solar ponds. Salinity gradient was created in order to stabilize the pond and to restrict convective motions induced by buoyancy driven solar radiation heating during the period of operation.

Fluent® commercial software was enhanced with the implementation of User Defined Functions (UDF) and was used in these simulations. The user defined scalar model was included for analyzing the convection and diffusion of the salt concentration in the solar pond. In addition, user defined functions were developed for relating the water density to temperature and salt concentration, as well as, the amount of solar radiation absorption in the solar pond as functions of thermo-physical properties. In the absence of flow exchange, the natural convection in the pond was simulated and the stability of the pond was verified. Development of salt concentration was also studied, and time evolution of temperature distribution in a small scale salinity gradient solar pond was analyzed. For the case of flow exchange at the bottom of the pond, the energy production was evaluated, and the temperature, concentration and flow field were simulated.
Performance Comparison of Various VRV Systems for a Bank Application
Authors: Karaağaç Mehmet , Celen Ali , Çebi Alican , Dalkılıç Ahmet Selim , Wongwises Somchai
Published: December 2014

In heating and cooling applications, VRV (Variable refrigerant volume) systems can be used instead of air handling units because of their low energy consumption. In this study, a bank which is kept 20°C and 24°C inside temperature heating and cooling seasons respectively was taken into consideration in order to compare different VRV systems such as VRV system for heating only mode and VRV system supported with heat pump mode device. The heat loss from bank was calculated by considering heat loss from walls, air alteration and heat sources such as human, light, devices used in the space. The outdoor integrated heating and cooling capacity calculations were performed by means of commercial software for seven different climate regions in Turkey. R410a was selected as the refrigerant of investigated VRV systems because of its low ODP (Ozone Depletion Potential) and GWP (Global Warming Potential) values and actual common usage. Effect of outside air temperature, evaporation temperature of refrigerant and outdoor unit location (such as high level, same level and lower level) on the performance of VRV systems was considered in calculations. The calculations are performed in order to clarify of effect of outdoor unit level. Payback time is calculated as 4.5 months for usage of VRV system instead of air handling unit.
Adaptive Mesh Simulations of Supersonic Liquid Jets Spreading in Quiescent Gaseous Media
Authors: Majidi Sahand , Afshari Asghar
Published: December 2014

Propagation and evolution of supersonic liquid jets in quiescent gaseous media is studied numerically using a computational fluid dynamics (CFD) tool. A wave propagation method finite-volume solver is employed to discretize and solve the time-dependent two-dimensional Euler equations based on diffuse interface approach. The developed flow solver is implemented in the adaptive mesh refinement code (AMROC) to improve the ability of the solver to capture inherent characteristics of compressible multiphase flow including shocks and contact discontinuities. Several benchmark problems are simulated to evaluate the performance of the numerical tool. Simulations of a supersonic liquid jet flow in gaseous environment are conducted by developed flow solver. The results indicate that our numerical methodology can be considered as a promising approach to study high speed liquid jets.
Experimental Study of Vertical Gas-Liquid Pipe Flow for Annular and Liquid Loading Conditions Using Dual Wire-Mesh Sensors
Authors: Vieira R. E. , Parsi M. , Torres C. F. , Shirazi S. A. , McLaury B. S. , Schleicher E. , Hampel U.
Published: December 2014

In gas well production, liquid is produced in two forms, droplets entrained in the gas core and liquid film flowing on the tubing wall. For most of the gas well life cycle, the predominant flow pattern is annular flow. As gas wells mature, the produced gas flow rate reduces decreasing the liquid carrying capability initiating the condition where the liquid film is unstable and flow pattern changes from fully co-current annular flow to partially co-current annular flow. The measurement and visualization of annular flow and liquid loading characteristics is of great importance from a technical point of view for process control or from a theoretical point of view for the improvement and validation of current modeling approaches. In this experimental investigation, a Wire-Mesh technique based on conductance measurements was applied to enhance the understanding of the air-water flow in vertical pipes. The flow test section consisting of a 76 mm ID pipe, 18 m long, was employed to generate annular flow and liquid loading at low pressure conditions. A 16×16 wire configuration sensor is used to determine the void fraction within the cross-section of the pipe. Data sets were collected with a sampling frequency of 10,000 Hz. Physical flow parameters were extracted based on processed raw measured data obtained by the sensors using signal processing. In this work, the principle of Wire-Mesh Sensors and the methodology of flow parameter extraction are described. From the obtained raw data, time series of void fraction, mean local void fraction distribution, characteristic frequencies and structure velocities are determined for different liquid and gas superficial velocities that ranged from 0.005 to 0.1 m/s and from 10 to 40 m/s, respectively. In order to investigate dependence of liquid loading phenomenon on viscosity, three different liquid viscosities were used. Results from the Wire-Mesh Sensors are compared with results obtained from previous experimental work using Quick Closing Valves and existing modeling approaches available in the literature.
Thermal Modeling of a Wireline Tool for Ultra-High Temperatures
Authors: Sur Aritra , Kouchmeshky Babak , Satti Rajani
Published: December 2014

The drive to obtain more accurate petrophysical information from deeper wells has led to the demand for operating various downhole tools at higher temperatures for longer time periods. If the borehole temperature reaches values higher than 175°C, it is considered a high temperature (HT) well. In HT wells, reliability of the electronic components of the logging tools is a major concern. One way to address the concern is through using a thermal flask to reduce the heat flow rate from the formation to the tool and evenly distribute the heat generated by the internal electronic components.

Optimizing the design of the aforementioned thermal flask is very important in providing a longer operative time for the tool before the temperature of the sensitive electronic parts reaches a critical threshold. To obtain the sensitive parameters for designing the flask, the thermal transport inside the tool must be accurately modeled.

In this work, high fidelity FEA and CFD-based transient thermal models are developed for thermal transport in a flask for an ultra-high temperature wireline tool. Two models with different levels of complexity are presented. The models are verified by experimental results and the physical insights obtained from them presented. The predictive capability of the models is used to provide recommendations for safe operating time for various environmental conditions which prevail in the formations. The results obtained from the models can also be used for optimizing the performance of the future generation of the tool and reducing the amount of time spent in unnecessary trip outs.
Numerical Investigation on the Coanda Effect Over the S809 Airfoil With Synthetic Jet Actuator at High Angle of Attack
Authors: Moshfeghi Mohammad , Hur Nahmkeon
Published: December 2014

Synthetic jet actuators (SJA) have shown their efficiency in manipulating the aerodynamic forces on airfoils and blades. Generally, the injection angle is assumed to be an important factor for the injection-based flow control techniques, especially in moderate separation. However, it is important to know the level of effectiveness and the aerodynamic mechanism through which a SJA may affect an airfoil at a high angle of attack. The present research studies the effects of angle between the injected flow and the surface’s tangent line (Coanda effect) over the S809 airfoil equipped with a SJA, using detached eddy simulation (DES). The airfoil is assumed to be at an angle of attack of 25°. Three different cases with jet flow angles of 5°, 15° and 25° are simulated at a constant momentum coefficient of 4.5×10−3. The SJA frequency is 125 Hz for all cases and the simulations are conducted at the Reynolds number of one million. The effects of the jet angle on the streamline, pressure distribution and lifts and drag values are investigated.
A Control Strategy to Balance Efficiency and Reliability for Pump System
Authors: Lai Zhounian , Wu Peng , Yang Shuai , Wu Dazhuan
Published: December 2014

In this paper, a model composed of pump and valves used to achieve flow rate regulation is built. A control strategy to improve reliability and efficiency of the pump-valve system is introduced. An optimizer and a controller are developed. The optimizer will calculate the pressure loss across the valve and the head of the pump to limit the operation point of the pump to nearby the design point. The controller manages the control of flow rate and the pressure loss across the valve. The controlled variables of the control system are flow rate and the pressure loss across the valve, the control variables are the speed of pump and the lift of valve. This makes the system a coupled nonlinear Multi-Input Multi-Output (MIMO) system. A differential geometry method is introduced to decouple the MIMO system. The result of the control strategy is shown in simulations. The difference between traditional PID method and the new method is compared. The result shows that the new method sacrifices power consumption for a better reliability. This paper provides an option to improve reliability of pump systems.
Numerical Simulations of Wind Effects on an Array of Ground Mounted Solar Panels
Authors: Jubayer Chowdhury , Hangan Horia
Published: December 2014

In this study, numerical simulations using unsteady Reynolds-Averaged Navier-Stokes (RANS) approach with Shear Stress Transport (SST) k-ω turbulence closure are employed to investigate the wind loads and wind flow field of a ground mounted solar panel array. Atmospheric boundary layer wind profiles for open terrain roughness with Reynolds number of 2.2×106, based on the wind speed at the lower edge and the chord length of a stand-alone system, are employed. Four different wind directions (0°, 45°, 135° and 180°) are considered. The numerical modeling approach employed in this study is validated for a stand-alone solar panel system by comparing the surface pressures with the study by [1] and the velocity field with a Particle Image Velocimetry (PIV) measurement carried out in the Boundary Layer Wind Tunnel I at the Western University, Canada. Analyzing the wind flow field for the array configuration shows that for 0° and 180° wind directions, all trailing rows are in the complete wake of the first windward row. It is also shown that in terms of maximum drag and lift, 0° and 180° wind directions are the critical wind directions with the first windward row being the critical row. On the other hand, in terms of overturning moment, 45° and 135° are the critical wind directions, with similar overturning moment coefficients for each row.
Analysis of Common Axial-Flow Pump Under Reverse Operation
Authors: Ma Pengfei , Wang Jun
Published: December 2014

A direct reverse changing of the rotation direction can be a reverse operation mode for bi-directional pump station. However, research in this area was rarely conducted due to several reasons. In this paper, an axial-pump was designed by lifting method, of which approximate specific speed was 1250. The external performances, inner flow properties and pressure fluctuation characteristics of the pump were analyzed by numerical method, in both positive and reverse operation. The effectiveness of numerical method was verified by the existing experiment data of bi-directional axial-pump. The results show that the static pressure variation of the inner channel, during positive and reverse operation, is similar. However, the static pressure in the blade surface is obviously different in that the low pressure area in the back moves to the central part of the blade under reverse operation. The maximum value of amplitude occurs near to the inlet edge. Besides, the main frequencies of the pressure fluctuation in each monitoring points are multiple or equal to the blade passing frequency in both positive and reverse operation. This investigation would provide some references to the practical application of the directly reversed axial flow pump station.
A Novel Variant of the K-ω URANS Model for Spectral Element Methods: Implementation, Verification, and Validation in Nek5000
Authors: Tomboulides A. , Aithal S. M. , Fischer P. F. , Merzari E. , Obabko A.
Published: December 2014

Unsteady Reynolds-averaged Navier-Stokes (uRANS) models can provide good engineering estimates of wall shear and heat flux at a significantly lower computational cost compared with LES simulations. In this paper, we discuss the implementation of two novel variants of the k-ω turbulence model, the regularized k-ω standard and the regularized k-ω SST model, in a spectral element code, Nek5000. We present formulation for the specific dissipation rate (ω) in the standard k-ω model, which would obviate the need for ad hoc boundary conditions of ω on the wall. The regularized approach is designed to lead to grid-independent solutions as resolution is increased. We present a detailed comparison of these novel methods for various standard problems including the T-junction benchmark problem. The two approaches presented in this work compare very well with the standard k-ω model and experimental data for all the cases studied.
Numerical Simulation of Cavitating Flow Around a Hydrofoil
Authors: Tran Tan Dung , Nennemann Bernd , Vu Thi Cong , Guibault François
Published: December 2014

The objective of this paper is to evaluate the applicability of different cavitation models and determine appropriate numerical parameters for cavitating flows around a hydrofoil. The simulations are performed for a NACA 66 foil at 6 degrees angle of attack, Reynolds number of 750 000 and for a cavitation number of 1.49 corresponding to the partial sheet cavitating regime. The incompressible, multiphase Reynolds-averaged Navier-Stokes (RANS) equations are solved by the CFD solver CFX with Kubota and Merkle cavitation models. As part of the work, the Merkle model is implemented into CFX by User Fortran code because this model has shown good cavitation prediction capability according to the literature. The effects of the k-ε and SST turbulence models on the cavitating flow dynamics are compared. Also, an investigation on structured and hybrid meshes with different mesh sizes and concentrations is carried out in order to better understand the mesh influence for this cavitation simulation. The local compressibility effect is considered by correcting the turbulent eddy viscosity inside the mixture vapor/liquid zones. The numerical results are validated by experiments conducted in a cavitation tunnel at the French Naval Academy.
LES/FMDF of Mixing in Turbulent Jet in Cross-Flows
Authors: Esmaeili Mostafa , Afshari Asghar
Published: December 2014

In this study, an Eulerian-Lagrangian computational methodology is utilized for large eddy simulation (LES) of mixing phenomena in jet in cross-flows. A high-order multi-block algorithm is used to solve Eulerian equations in a generalized coordinate system. The composition is formulated based on the filtered mass density function (FMDF) and its equivalent stochastic Lagrangian equations, which is solved by Lagrangian Monte-Carlo method. Parameters influencing mixing enhancement including jet velocity profile, and jet pulsation are investigated. A good consistency between Eulerian and Lagrangian components of the numerical scheme is established. In jet in cross-flow (JICF) simulations, the vortical structures and flow features are predicted with the current numerical scheme. The results also show that the jet velocity profile affects both trajectory and mixing condition and the jet pulsation can enhance mixing depending on the Strouhal numbers. The obtained results including concentration distributions are in good agreement with available experimental data ensuring the performance and reliability of LES/FMDF methodology to study mixing in relatively complex flow configurations such as JICF.
Computations of Flow Environments in Medium-Scale Stirred-Tank Bioreactors for Stem Cell Expansion
Authors: Liovic Petar , Šutalo Ilija D. , Meagher Laurence , Lovrecz George O.
Published: December 2014

The flow in a New Brunswick Scientific (NBS (now Eppendorf)) 5 L stirred-tank bioreactor (STR) partially filled with 2.2 L of water and agitated at 60 rpm using a pitched-blade impeller is studied in this work, to determine the suitability of the configuration for expanding stem cell lines. Computational Fluid Dynamics (CFD) model development and testing in this work has found Large Eddy Simulation (LES) to be essential for model fidelity and for capturing spatiotemporal stress fluctuations. Stresses were at levels similar to or even higher than those known to damage stem cells or modulate their cellular function to favour differentiation instead of phenotype maintenance. The results raise questions as to the appropriateness of such STRs for stem cell expansion, and motivate better experimental studies to properly quantify the spatiotemporal variability in fluid shear stresses and its effect on stem cell expansion and stem cell fate.
Towards 3D Volume-of-Fluid Methods Featuring Subgrid-Scale Capturing of Interface Curvature
Authors: Liovic Petar
Published: December 2014

A new interface reconstruction method for Volume of Fluid (VOF) interface tracking is presented here, based on subgrid-scale planar interface segment reconstruction (SGS-PISR). In the SGS-PISR method implemented here, the centroid of the initial single-surface interface reconstruction is shifted along that normal to enclose the correct volume. An additional step then moves the SGS plane segments laterally outwards, to ameliorate the SGS curvature by blunting the protrusion of the centroid. The SGS-PISR method results in promising tendency towards second-order accuracy and more importantly reduced interface reconstruction errors across a range of mesh resolutions, and is targeted at improving VOF performance in resolving small grid-scale details of the interface topologies in interfacial flow CFD computations.
A Performance Prediction Model for Low-Speed Centrifugal Fans
Authors: Lee Yu-Tai , Wolfe Tristan , Slipper Michael E.
Published: December 2014

A generalized model for mapping the trend of the performance characteristics of a double-discharge centrifugal fan is developed based on the work by Casey and Robinson (C&R) which formulated compressor performance maps for tip-speed Mach numbers ranging from 0.4 to 2 using test data obtained from turbochargers with vaneless diffusers. The current paper focuses on low-speed applications for Mach number below 0.4. The C&R model uses four non-dimensional parameters at the design condition including the flow coefficient, the work input coefficient, the tip-speed Mach number and the polytropic efficiency, in developing a prediction model that requires limited geometrical knowledge of the centrifugal turbomachine. For the low-speed fan case, the C&R formulas are further extended to a low-speed, incompressible analysis.

The effort described in this paper begins by comparing generalized results using efficiency data obtained from a series of fan measurements to that using the C&R model. For the efficiency map, the C&R model is found to heavily depend on the ratio of the flow coefficient at peak efficiency to that at the choke flow condition. Since choke flow is generally not applicable in the low-speed centrifugal fan operational environment, an alternate, but accurate estimation method based on fan free delivery derived from the fan test data is presented. Using this new estimation procedure, the modified C&R model predicts reasonably well using the double-discharge centrifugal fan data for high flow coefficients, but fails to correlate with the data for low flow coefficients. To address this undesirable characteristic, additional modifications to the C&R model are also presented for the fan application at low flow conditions.

A Reynolds number correction is implemented in the work input prediction of the C&R model to account for low-speed test conditions. The new model provides reasonable prediction with the current fan data in both work input and pressure rise coefficients. Along with the developments for the efficiency and work input coefficient maps, the use of fan shut-off and free delivery conditions are also discussed for low-speed applications.
On the Collision Detection for Ellipsoidal Particles in Turbulence
Authors: Siewert Christoph , Kunnen Rudie P. J. , Meinke Matthias , Schröder Wolfgang
Published: December 2014

Collisions of small and heavy non-spherical particles settling in a turbulent environment are very important to various fields of physics and engineering. However, in contrast to spherical particles the collision probabilities are virtually unknown. In this study we focus on a very important condition for the numerical determination of collision probabilities: the collision detection. We discuss the need for efficient strategies to narrow down the number of possible collision pairs and compare three collision detection methods for ellipsoidal particles. We derive an analytical formula for the collision probability in the case of gravitational settling and validate the collision detection methods with this. Finally, we present statistics of the accuracy and efficiency of the methods. For the case of ellipsoidal particles in turbulence we find that the continuous collision detection with neglected rotation within a time step is the optimal trade-off between accuracy and efficiency.
Flow Measurements in a Matched-Index-of-Refraction Aortic Arch Model for Endothelial Cell Culture
Authors: Alloush M. M. , Oweis G. F. , Nasr R. , Zeidan A.
Published: December 2014

Flow details such as wall shear stress, hemodynamic pressure, and separation can play an important role in the development and progression of inflammation and cardiovascular disease, such as atherosclerosis. Clinical evidence correlating blood vessel locations exhibiting atherosclerosis and plaque buildup to flow disturbances and separation is significant. Prevalence of atherosclerosis in cardiovascular patients is noticed in vessels exhibiting geometric features such as bifurcation, arching, and stenosis. The bending vessel geometry is interesting for the wealth and variety of flow physics that it incorporates. An in vitro flow loop system for the study of cardiovascular disease is described. The system incorporates an aortic arch vessel model that permits endothelial cell culturing, sampling, and imaging on the aortic lumen. The model was designed to allow imaging of the internal flow by choice of the clear model material and the optically compatible working fluid. Particle image velocimetry measurements were acquired at different locations on the arch, for time-averaged inlet Reynolds number range of 2000 to 4400. It was found that the peristaltic pump introduced significant pulsatility to the flow particularly at the low rpm. The flow behavior in the arch is discussed with emphasis on separation and recirculation zones.
Research on the Effect of Impeller Reflux Balance Holes on Pressure and Axial Force of Centrifugal Pump
Authors: Weidong Cao , Xun Dai , Qixiang Hu
Published: December 2014

The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5m3/h, H=60m, n=2950r/min was selected to be designed with eight axial reflux balance holes 4.5mm in diameter. The simulated Q-H curve and NPSH were in good agreement with experimental data, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic to that with traditional reflux balance holes; however, it appeared little difference in head and efficiency. Compared with experiment results, the error of pressure at monitoring points in rear pump chamber was within permission. The pressure in rear pump chamber at 0.6 times rated flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rated flow and 28.33% at 1.4 times rated flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreased as flow rate increased. Radical reflux balance holes chosen to be 5.2mm and 5.9mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics of reflux holes with different diameters was conducted based on momentum equations and standard turbulence model (κ-ε). It is found that axial force of pump with radical reflux balance holes 5.2mm and 5.9mm in diameter is significantly less than that with radical reflux balance holes 4.5mm in diameter, so are the head and efficiency. Better effect of axial force balance can be obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.
A New Approach to Mesh Adaptation Procedure Using Linear Elasticity for Geometries Undergoing Large Displacements
Authors: Hasbestan Jaber J. , Newman James C. , Arabshahi Abdollah
Published: December 2014

The equations of linear elasticity have been extensively used in computational fluid dynamics to deform meshes for moving boundary simulations, shape design optimization, solution adaptive refinement, and for the construction of higher-order discetizations in finite-element schemes. Inherently this method does not have any mechanism to control the quality of the mesh, since it represents the structural response to prescribed surface deflections. Unfortunately, this method does not prevent the possibility of generating negative volumes in the mesh when large deformations take place. In the current work, two approaches are examined in an attempt to mitigate this shortcoming. In the first approach, a source term is added to each node in the mesh. These source terms are chosen as design variables, and an optimization strategy is utilized to improve mesh quality. The second approach represents a modification to an existing method whereby each element in the mesh may be considered as a different material. Entries in the constitutive relations are then selected as the design variables. In this approach the number of design variables is extremely large and, thus, very computationally expense. To alleviate some of this computational burden, the design variables are selected from a subset of the elements in the mesh. In both approaches presented, the cost function is defined as a function of the mesh quality, and a limited memory BFGS optimization scheme used to minimize this function. Results for two dimensional test cases are presented; however, the concept can be easily applied to three dimensional meshes and practical problems.
Large Eddy Simulation of the Flow and Heat Transfer in a Matrix of Cubes
Authors: Lampitella Paolo , Mereu Riccardo , Colombo Emanuela , Inzoli Fabio
Published: December 2014

This work presents Large Eddy Simulations of the flow and heat transfer characteristics in a matrix of surface mounted cubes, studying the effect of the grid resolution and the sub-grid scale modeling. Three sub-grid scale models, implemented in an unstructured, finite volume, commercial solver, are compared on four different grids in terms of first and second order statistical quantities. A classical Dynamic Smagorinsky model is compared with a no-model, Implicit Large Eddy Simulation, approach and a recently developed, two parameters, dynamic-mixed model. A general lack of sensitivity to the sub-grid scale model is evidenced for the flow quantities at all the resolutions, but the grid design emerges as the most determining factor for this kind of flows, showing that accurate results are possible with very coarse resolutions. In contrast, heat transfer characteristics show a strong dependence on both the grid and the sub-grid scale model with a lack of clear convergence in the investigated range of scales. The dynamic-mixed model, which for the first time is tested in a heat-transfer application, is found stable on strongly stretched grids and cheaper than the classical Dynamic Smagorinsky model due to its specific finite volume formulation, showing its suitability for more complex applications.
Modeling and Simulation of Tropospheric Ozone Depletion in the Polar Spring
Authors: Cao Le , Gutheil Eva
Published: December 2014

In polar spring, tropospheric ozone depletion is related to the presence of halogen oxide concentrations in the atmospheric boundary layer. Halogen oxides such as BrO participate in an autocatalytic chemical reaction cycle, leading to the release of Br2 and BrCl from the fresh sea ice. The paper presents the identification of a detailed chemical reaction mechanism for the ozone depletion event, where bromine plays the major role. The heterogeneous reactions in the chemical reaction mechanism are studied in detail, and a sensitivity analysis is performed to identify the importance of each reaction in the mechanism. A skeletal reaction scheme is identified on the basis of the sensitivity analysis,. This skeletal chemical reaction mechanism then is used in a 3-D large eddy simulation (LES) with the Smagorinsky sub-grid model. The configuration studied includes a mountain located at the ground above which the ozone depletion is studied. In this situation, the height of the boundary layer varies, which greatly affects the ozone depletion event.
Numerical Modelling of Bubble Columns for High Temperature Glass Melting Applications
Authors: Ravinuthala Sharad Chand , Celik Ismail B.
Published: December 2014

Bottom heating approach for glass melting offers potential benefits of higher efficiency and lower emissions compared to the conventional surface fired melters with burners above the bath surface. Recent advances in the enabling technologies such as burners, controls, heat recovery and refractive materials have led to successful demonstration of bottom heating Submerged Combustion Melting (SCM) of glass. In the proposed reactor, combustion products of natural gas oxy combustion are bubbled through the three phase re-circulating tank reactor. The turbulence generated by the rising bubble column would result in rapid heating and mixing of the charge resulting in fast melting and homogeneous composition of the product. Detailed understanding of such two-phase gas liquid flows is imperative for developing efficient multi-phase reactors through precise control of mixing and reaction kinetics. The bubble column, without any phase change and heating, is a good apparatus for an elementary experimental study and numerical modeling of such flows. In this study, the hydrodynamics of the bubble column are investigated using two different numerical approaches i) Using ANSYS FLUENT with an Eulerian-Eulerian approach to model the bubble and continuous phases and ii) Using a Navier-Stokes solver with the Eulerian-Lagrangian method with the Particle-in-Ball approach. The results thus obtained are discussed in detail in comparison with the experimental data available. Experiments have been conducted to gain a deeper understanding of the behaviour of the bubbles in very viscous media.
Implementation and Validation of a Hybrid RANS/LES Model in the Spectral Element Solver Nek5000
Authors: Bhushan S. , Walters D. K. , Merzari E. , Obabko A.
Published: December 2014

A dynamic hybrid RANS/LES (DHRL) model has been implemented in the spectral-element solver Nek5000 to reduce computational expense for high Reynolds number applications. The model couples a k-ε URANS model and the dynamic Smagorinsky model for LES. The model is validated for plane channel flow at Reτ = 590 using DNS data, and compared with LES predictions. The model is then applied for the ANL-MAX case, which is a test case relevant to nuclear reactor cooling flow simulations. For the channel flow case, DHRL predictions were similar to LES on finer grids, but on coarser grids, the former predicted velocity profiles closer to DNS than the latter in the log-layer region. The improved prediction by the DHRL model was identified to be due to a 30% additional contribution of RANS stresses. For the ANL-MAX case, the URANS simulation predicts quasi-steady flow, with dominant large-scale turbulent structures, whereas LES predicts small-scale turbulent structures comparable with results in rapid mixing of cool and warm flow jets. DHRL simulations predict LES mode in the inlet jet region, and URANS mode elsewhere, as expected.
Shared-Memory Parallelization for Two-Way Coupled Euler-Lagrange Modeling of Bubbly Flows
Authors: Ma Jingsen , Hsiao Chao-Tsung , Chahine Georges L.
Published: December 2014

Cavitating bubbly flows are encountered in many engineering problems involving propellers, pumps, valves, ultrasonic biomedical applications, … etc. In this contribution an OpenMP parallelized Euler-Lagrange model of two-phase flow problems and cavitation is presented. The two-phase medium is treated as a continuum and solved on an Eulerian grid, while the discrete bubbles are tracked in a Lagrangian fashion with their dynamics computed. The intimate coupling between the two description levels is realized through the local void fraction, which is computed from the instantaneous bubble volumes and locations, and provides the continuum properties. Since, in practice, any such flows will involve large numbers of bubbles, schemes for significant speedup are needed to reduce computation times. We present here a shared-memory parallelization scheme combining domain decomposition for the continuum domain and number decomposition for the bubbles; both selected to realize maximum speed up and good load balance. The Eulerian computational domain is subdivided based on geometry into several subdomains, while for the Lagrangian computations, the bubbles are subdivided based on their indices into several subsets. The number of fluid subdomains and bubble subsets are matched with the number of CPU cores available in a share-memory system. Computation of the continuum solution and the bubble dynamics proceeds sequentially. During each computation time step, all selected OpenMP threads are first used to evolve the fluid solution, with each handling one subdomain. Upon completion, the OpenMP threads selected for the Lagrangian solution are then used to execute the bubble computations. All data exchanges are executed through the shared memory. Extra steps are taken to localize the memory access pattern to minimize non-local data fetch latency, since severe performance penalty may occur on a Non-Uniform Memory Architecture multiprocessing system where thread access to non-local memory is much slower than to local memory.

This parallelization scheme is illustrated on a typical non-uniform bubbly flow problem, cloud bubble dynamics near a rigid wall driven by an imposed pressure function.
Theoretical-Experimental Investigation of CO Emission From an Oil Refinery Incinerator
Authors: Darbandi Masoud , Abrar Bagher , Yazdi Mohsen Khodadadi , Zeinali Mazdak , Schneider Gerry E.
Published: December 2014

In this paper, we investigate the CO emission from an oil refinery gas incinerator both theoretically and experimentally. At the beginning of this research, our collected data from this incinerator showed that the CO contamination would be far exceeding the permissible environmental standards at the stack exhaust. Therefore, we decided to perform a combined theoretical-experimental study to find a reasonable solution to reduce the CO pollution suitably. Our theoretical study showed that a reliable solution would be to increase the incinerator operating temperature. However, we needed to collect some data from this incinerator to examine if our achieved analytical solution would work correctly. In data collection procedure, we were faced with one major difficulty due to the limits of automatic system of incinerator control, which did not let us increase the incinerator temperature readily in real work conditions. As a general remedy, our suggestion was to interfere in this automatic control system and to increase its maximum possible limit of temperature. Evidently, this needed a number of considerations, which could not be performed in a short length period. As a short length remedy, we designed a number of manual control procedures, which let us examine different temporary working conditions for the incinerator. Trying different operating condition, we eventually found a suitable one with minimum CO emission from the incinerator. Although this choice resulted in an increase in the incinerator temperature and a remedy to reduce the high CO emission, it was inversely increased the incinerator fuel consumption, which is rather a negative point. Our further data collection indicated that the excess air of primary incinerator was relatively high. Therefore, we designed an automatic system of inlet air damper to adjust the inlet air, which resulted in avoiding high excess air and consequently suitable saving in the fuel consumption. The details are provided in the rest of paper.
Numerical Simulation of Flame Spray Pyrolysis Process for Nanoparticle Productions: Effects of 2D and 3D Approaches
Authors: Noriler Dirceu , Hodapp Maximilian J. , Decker Rodrigo K. , Meier Henry F. , Meierhofer Florian , Fritsching Udo
Published: December 2014

Nanoparticle production in flames was modeled in an Eulerian-Lagrangean framework, considering droplet evaporation and fuel combustion to predict the flame chemical species concentration and the flame temperature fields by means of Computational Fluid Dynamics (CFD). A mathematical model was carried out considering two-way coupling between the gas phase and the droplets. For the combustion model, the eddy dissipation concept model was applied, taking into account the droplets vaporization, the chemical reaction mechanisms, and the chemistry-turbulence interaction. 2D axisymmetric and 3D approaches were investigated in standard operations conditions. The initial conditions for the droplet sizes and droplet velocities were taken in experiment test facility by means of Laser-Diffraction. The grid independence study was made according to the Grid Convergence Index (GCI) methodology for both approaches. The droplets mass evaporated, temperature and velocities profiles were used to compare the 2D and 3D results. The results show similar behavior for both approaches, however, with some quantitative difference. The 2D approach showed lower temperature resulted by a larger mass fuel not evaporated and unburned.