bluuebunny/crossref_metadata_2025 huggingface dataset:
CFD Modeling for Optimizing the Fluid Dynamics Patterns of Refractory Lining Drying Process in a Vertical Lime Kiln
Authors: Cristea Eugen-Dan , Sarandrea Luca , Galbiati Massimo
Published: December 2014

This paper presents a 3D Computational Fluid Dynamics (CFD) modeling of flow, combustion and heat transfer processes into an internal enclosure acting as a combustion chamber, confined by the newly patented air cooled “corner ring”, the lower shaft vertical side walls, the vault and the limestone packed bed, located in a vertical twin-shaft regenerative lime kiln. The numerical simulation is restricted only to the kiln first start-up preliminary phase, with the goal to optimize the thermo-fluid dynamics patterns established during the first heat-up of wet gunning refractory concrete lining of the air cooled “corner ring”, to avoid refractory damages.

The present work is performed in the frame of the commercial general-purpose code ANSYS-CFX R14.5. The CFD model is run under transient flow conditions accomplished by the drying burners operated in single-stage “on-off” control mode, to fit at the best the heat-up curve by optimization of the fluid dynamics patterns, with the goal to prevent local hot spots on the refractory lining. The industrial data collected through the supervision system and the local provisional instrumentation on the vertical twin-shaft regenerative lime kiln, model RD15, commissioned in India on September last year, are used to set the test-case and to partially validate the numerical simulation results.

This CFD numerical simulation represents an useful engineering tool, on behalf of refractory designer and commissioning engineer, for the prediction of the refractory lining behavior during the kiln first start-up.
Two-Phase Flow Patterns and Pressure Drop Inside a Vertical Pipe Containing a Short Helical Tape Insert
Authors: Liu Wen , Bai Bofeng
Published: December 2014

Swirling gas-liquid two-phase flow patterns and pressure drop in vertical pipes of a large diameter are widely present in practical applications but not well documented in experimental studies. This paper presented an experimental study on gas-liquid two phase flow patterns and pressure drop inside a vertical pipe of 62mm in inner diameter (ID) containing a helical tape insert. Experimental results were obtained in a vertical visualization test section with a length of 7m, liquid mass velocities ranging from 0.3 to 1000 kg/(m2·s), and gas mass velocities from 3.2 to 900kg/(m2·s). Considering the decay of the swirl flow, the swirling flow regime map at different cross sections (z/D = 16, 32 and 64) were concluded, and their effects on the pressure drop were investigated.
Computational Study of a Low Cost Rope Washer Pump for Brine Pumping Application in Rural Areas
Authors: Bhandari Neelesh , Damodaran Murali
Published: December 2014

The rope washer pump is a hydraulic device in which the rope consisting of equally spaced washers is pulled upward to displace the fluid volume to the desired head before delivering it at the outlet. The straightforward working principle, the ease of manufacture, and the low cost are the main advantages of this pump over a reciprocating pump. The rope washer pump can be either driven by electric motor, by a wind mill, or manually for pumping brine water for salt harvesting in rural areas. In this study computational fluid dynamics (CFD) modeling of the rope washer pump is used to estimate the performance characteristics of the pump. Experimental studies of rope pump can only provide data related to flow rate and head it can achieve, while using CFD it is possible to obtain insight about the flow physics inside the pump. These insights can be used to propose design improvements for more efficient pump operation. Unsteady, incompressible Navier-Stokes equations are solved using a finite volume scheme on unstructured hybrid polyhedral-prismatic overset meshes to obtain flow parameters and the volume of fluid (VOF) interface tracking method is used to capture the free water surface inside the pump by tracking the volume fraction of fluid on each cell. The k-ε turbulence model is used to model turbulence and the motion of the washer is handled by using overset mesh technique for the computation. Leakage between the washer and housing is also considered in this computation. Pump characteristics are calculated for different pump speeds. Thus the flow variables obtained by computation are used to predict the efficiency and flow rate at different washer speed. The pump characteristics define the behavior of the rope washer and are characterized by effective flow rate, volumetric efficiency, power input and the pump torque. These performance characteristics are extracted from the computed flow fields and used for evaluating the optimum range of pump speed, with highest efficiency and flow-rate. This model can serve as a basis for future design optimization studies.
Invariant Forms of Conservation Equations and Some Examples of Their Exact Solutions
Authors: Sohrab Siavash H.
Published: December 2014

A scale-invariant model of statistical mechanics is described leading to invariant Boltzmann equation and the corresponding invariant Enskog equation of change. A modified form of Cauchy stress tensor for fluid is presented such that in the limit of vanishing intermolecular spacing all tangential forces vanish in accordance with perceptions of Cauchy and Poisson. The invariant forms of mass, thermal energy, linear momentum, and angular momentum conservation equations derived from invariant Enskog equation of change are described. Also, some exact solution of the conservation equations for the problems of normal shock, flow over a flat plate, and flow within a spherical droplet located at the stagnation point of opposed cylindrically-symmetric gaseous jets are presented.
Numerical Simulations of Ground Simulation for a Realistic Generic Car Model
Authors: Guilmineau E.
Published: December 2014

Investigations of the aerodynamic influence of rotating wheels and moving ground on a realistic generic car model are presented. For this study, Computational Fluid Dynamics (CFD) are carried out with the flow solver ISIS-CFD, which is based on a finite-volume method. This paper presents the effects of ground simulation (GS) for the realistic car model DrivAer. Comparisons of the pressure between experimental data and numerical results show a good agreement. A moving ground and rotating wheels reduces the drag and the lift. Though the forces decreases at the front wheel due to the wheel rotation locally, the major change in drag and lift happens directly on the car body itself. The main vortical structures that develop around the wheels are also presented.
Flow Control of a Retreating Airfoil via NS-DBD Actuators Using Large Eddy Simulations
Authors: Shaler Kelsey , Gaitonde Datta V.
Published: December 2014

The capability of Large Eddy Simulations (LES) to accurately model Nano-Second Pulsed Dielectric-Barrier Discharge (NS-DBD) plasma actuators for use as a flow control devise is demonstrated by comparing the newly-developed volumetric heating model to experimental results as well as a previously established surface heating model. The purpose of these models and corresponding experiments is to show that use of NS-DBD actuators can mitigate the presence of stall on a NACA0015 airfoil at a Reynolds number of 100,000 and 15° angle of attack in reversed-flow conditions. Actuators are placed at both the aerodynamic leading and trailing edge — the effects of which are analyzed separately — and forced at several Strouhal numbers StF=fc′U∞. The model validation is carried out by comparing the actuator pulse structure, mean value contours of various parameters, static pressure distribution (Cp) along the airfoil surface, and FFT plots of sound pressure level (SPL). The model results are then compared to the no-control simulations to provide evidence that actuation delays the onset of stall. This process is explored for both unsteady and steady quantities, including FFT plots, intantaneous flow field response, static pressure recovery, and mean quanitites, including a boundary layer analysis. It is concluded that at low Reynolds numbers reattachment occurs through enhanced turbulence of a separated, laminar shear layer; the reattachment processes is shown to take place over approximately 8 characteristic times for both actuator locations, although leading edge actuation only results in reattachment in the mean sense. Under similar situations, the volumetric and surfaec heating models showed similar recovery characteristics; however, since the volumetric model is less empirical than surface heating, it is recommended that volumetric heating be used in the future. Both heating models indicate that actuation at the aerodynamic leading edge has the greatest affect on the flow due to the laminar nature of the corresponding shear layer, as opposed to the turbulent shear layer on the trailing edge. It addition, a change in duty cycle was shown to have little effect on the results whereas an incerase in StF had a large negative effect on reattachment.
Evaluation of the Gamma Stirling Engine Heat Transfers in its Heat Exchangers
Authors: Gheith Ramla , Aloui Fethi , Ben Nasrallah Sassi
Published: December 2014

In this paper, a Gamma type Stirling engine is experimented. A special care was given to the heat exchangers instrumentation. Different set of experimental measurement were made on them. Their corresponding thermal energy and efficiencies are estimated. Three operation parameters are chosen: filling pressure, cooling water flow rate and heating temperature. The influence of these parameters on the performance of each heat exchanger are presented and explained. It can be concluded that all heat exchangers parameters are critical to the performance of the Stirling engine. The regenerator performances are the most significant for the engine. The heating temperature is the parameter that greatly affects performance of heat exchangers. The cooling water flow rate is quite affecting the Cooler efficiency but has a slight influence on other exchangers. The initial filling pressure is significant for the regenerator and for the heater.
Gas-Liquid Foam Through Straight Ducts and Singularities: CFD Simulations and Experiments
Authors: Chovet Rogelio , Aloui Fethi , Keirsbulck Laurent
Published: December 2014

Some industrial processes are associated with the flow of aqueous foams inside horizontal channels. Examples are found in the oil, food and cosmetic industries. This type of flow presents an important pressure loss, originated from the shear stress exerted by the channel walls. Foam flow is one of the most complex fluids. In a macroscopic point of view, the physical-chemical interaction between the bubbles can be related to some non-Newtonian models (Bingham law, power law, etc.) or an apparent viscosity. These last can represent the internal deformations of fluid elements when shear stress is applied. An experimental facility able to create this type of flow is not so easy to design. Many parameters must be taken into consideration. So, Computational Fluid Dynamics (CFD) constitutes an ideal technique for analyzing this kind of problem. The aim of this study is to validate the use of Computational Fluid Dynamics in order to correctly predict the pressure losses and the velocity fields of a foam flowing through a straight channel and singularities (fence and half-sudden expansion). Simulations for a realistic scenario: two-phase flow, change in the surface tension, bubble size, were undertaken. Obtained results showed that simulations are not able to accurately reproduce for such a complex fluid, the important aspects of this study, such as the pressure losses and the velocity fields. Therefore, an approximation to a Bingham fluid was made. For a foam flow quality of 70% and a velocity of 2 cm/s, the numerical results are justified by experimental evidence. Experiments have been done and predictions for the flow behavior are extrapolated. Results show that the software is able to recreate the behavior of foam flow through a straight channel and singularities. However, this approach is extremely sensitive to the choice of several parameters, like the apparent viscosity, the yield stress, the viscosity consistence, etc.
The Wake Behind Two Intersecting Flat Plates
Authors: Dadmarzi Fatemeh Hoseini , Narasimhamurthy Vagesh D. , Andersson Helge I. , Pettersen Bjørnar
Published: December 2014

The wake flow behind two intersecting flat plates forming a cross is studied by means of direct numerical simulation (DNS) at low Reynolds number. The Reynolds number based on the plate width, d, and the inflow velocity, U0, is 100. The flat plate structure is in one plane. Away from the intersecting center part, vortex streets can be observed similar to the wake flow behind a single normal flat plate. On the other hand, the flow is completely three-dimensional in the vicinity of the intersecting region where the wakes from each of the two normal flat plates interact with each other. The mean pressure distribution on the structure is evaluated in order to study the total drag force as well as the local force distribution.
A Three Dimensional Immersed Boundary Method for Free Convection From Single Spheres and Aggregates
Authors: Feng Zhi-Gang , Musong Samuel G. , Michaelides Efstathios E.
Published: December 2014

A novel numerical technique that utilizes a three-dimensional Immersed Boundary Method (IBM) to solve the thermal interactions between spherical particles in a fluid is developed. At first, the natural convection of an isolated isothermal sphere immersed in a viscous fluid is analyzed and a new correlation for the heat transfer rate from a single sphere is obtained for 0.5≤Pr≤200 and 0 ≤ Gr ≤500. Secondly, the free convection heat transfer rate of a pair of spheres (bi-sphere) and spherical clusters immersed in air (Pr=0.72) were investigated using this numerical technique. The interactions depend on the separation distance between the spheres. It was observed that an increase in the separation of two spheres in tandem or side-by-side within a certain range may enhance the average heat transfer rate, when the interparticle distance is more than five radii. The average heat transfer rate of a cluster of touching, identical spheres with the same Grashof number was found to decrease as the number of spheres increased in the cluster.
Application of Synthetic Wall Jets for Pressure-Less, Counter-Current Conveyance of Thin Liquid Layers
Authors: Sturz Thomas , Sandberg Frieda , Walzel Peter
Published: December 2014

The entrainment by pulsed or rather so-called synthetic wall jets can be used to sustain a pressure-less transport of thin liquid layers along ducts. These jets exhibit zero-net-mass-flow conditions and lead to a break of symmetry in the flow pattern during one oscillation cycle. Therefore, only a net impulse is transferred in jet direction and induces a directed movement of the ambient liquid by entrainment according to the jet direction. The aim is to investigate the applicability of the principle to counter-current contactors as an alternative to pressure drop or gravity as driving forces typically applied e.g. in counter-current liquid-liquid contactors. Experiments are performed with an apparatus containing wall-jet flow drives with a multitude of narrow slit-openings (slit-width s = 190 μm) along a channel for synthetic wall jet generation. Firstly, one single wall-jet flow drive is investigated regarding its conveying performance at different related oscillation amplitudes (eslit/s = 7–25) and frequencies (f = 1–5 Hz). Subsequently, the apparatus is extended by a second identical device, arranged in parallel but above and oriented in the opposite conveying direction. This is to demonstrate the applicability of synthetic wall jets for counter-current operations.
A Study on the Coanda Effect and the Thrust Characteristics of Synthetic Jets
Authors: Iwasaki Takahiro , Nishibe Koichi , Sato Kotaro , Yokota Kazuhiko , Kang Donghyuk
Published: December 2014

Although there have recently been various studies on synthetic jets, many issues remain to be clarified, including details of the structure, Coanda effect and thrust characteristics. The present study clarifies some fundamental flow characteristics of synthetic jets near a rigid boundary by experiments and numerical simulations. In addition, a thruster model using the Coanda effect of synthetic jets is proposed and thrust characteristics are evaluated. As the main results, the flow of a synthetic jet near a rigid boundary is visualized and the trajectory of a vortex pair is demonstrated. It is confirmed that the flow patterns of the synthetic jets near a rigid boundary depend on H/b0 (offset ratio, normalized step height). The behavior of the asymmetric synthetic jets caused by the presence of the rigid wall was observed experimentally and the results were compared with numerical data. Furthermore, typical flow patterns around the proposed synthetic jet thruster and its thrust characteristics curves are shown.
Large-Eddy Simulation of Reactive Pollutant Dispersion Over Street Canyons of Different Aspect Ratios
Authors: Du T. Z. , Liu Chun-Ho , Zhao Y. B.
Published: December 2014

In urban areas, pollutants are emitted from vehicles then disperse from the ground level to the downstream urban canopy layer (UCL) under the effect of the prevailing wind. For a hypothetical urban area in the form of idealized street canyons, the building-height-to-street-width (aspect) ratio (AR) changes the ground roughness which in turn leads to different turbulent airflow features. Turbulence is considered an important factor for the removal of reactive pollutants by means of dispersion/dilution and chemical reactions.

Three values of aspect ratio, covering most flow scenarios of urban street canyons, are employed in this study. The pollutant dispersion and reaction are calculated using large-eddy simulation (LES) with chemical reactions. Turbulence timescale and reaction timescale at every single point of the UCL domain are calculated to examine the pollutant removal. The characteristic mechanism of reactive pollutant dispersion over street canyons will be reported in the conference.
Study of Two Phase Flow Breakup Behavior for Application to Solid Rocket Motor Nozzle
Authors: Amano Ryo S. , Yen Yi-Hsin , Hamman Michael
Published: December 2014

This paper presents a method of characterizing liquid breakup phenomena using a probability distribution flow pattern and compares CFD results of a straight channel two-phase flow using k-ε, SST k-ω and Reynolds Stress Model (RSM). Examination of liquid breakup level is essential for solving erosion phenomenon of solid fuel rocket motor (SRM), due to their use aluminum based solid propellants. During the propellant combustion, the aluminum oxidizes into alumina (Al2O3), which tends to agglomerate into molten droplets under a certain flow conditions. The molten droplets can then impinge on the combustion chamber walls, and flow along the nozzle wall. Such agglomerated aluminum leads to erosive damages to the geometry of de Laval nozzle and reduces the SRM propulsion performance. The volume fraction (VF) contour of the liquid can be used as the raw data for time average flow VF contour of straight channel. The flow shows the probability distribution of two-phase boundary which is mostly controlled by the features of different turbulence models. Those results will be used for future comparison to two-phase flow experiment as model selection reference of SRM two-phase supersonic flow simulation.
Numerical Investigation on Droplet Wetting Effect With the MPS Method
Authors: Chen Xiao , Sun Zhongguo , Xi Guang
Published: December 2014

The wetting effect of droplets is widely encountered in various industrial processes, such as mist cooling, dropwise condensation and electro wetting. Since these complicated processes are mostly free surface flow with large deformation, the moving particle semi-implicit (MPS) method is used for simulation in this study. The MPS method is a kind of Lagrangian meshless method and has advantages in simulating incompressible flows with large deformation. In order to simulate the surface tensions and interface tensions of different substances, the interparticle potential method was used in this paper. However, under the conventional surface tension model, the stable and well-formed droplets are hard to simulate due to the particle clustering and the shape distortion. In this paper, the parameters of interparticle potential model were studied and optimized to resolve these problems. Additionally, with the improved surface tension model, the oscillation and deformation process of a square droplet was simulated, and the result of which agreed well with the theoretical results. A circular relative error was defined to assess the final stable, well-formed droplet. Besides, the shrinkage and wetting effect, due to the surface tension, between multi-substances (gas-liquid, solid-liquid or liquid-liquid) were examined and analyzed. The calculated wetting angle and wetting area were extracted and agreed with the analytical ones. The wetting relationships under different interface tensions agreed with the lowest energy principle. The droplets with different substances would wet each other in a certain order due to the differences between their interface tensions. The self-assembly processing in Micro-Electro-Mechanical Systems (MEMS) was simulated and the component finally moved to directly above the adhesive area.
PIV Investigation of Reynolds Number Effects on a Closed Channel Flow Over a Smooth Forward Facing Step
Authors: Essel Ebenezer E. , Thacher Eric W. , Tachie Mark F.
Published: December 2014

This paper presents an experimental investigation of Reynolds number effects on the characteristics of separated and reattached flow over a smooth forward facing step. Particle image velocimetry technique was used to conduct detailed velocity measurement for a wide range of Reynolds numbers based on the step height and freestream velocity, 2040≤Reh≤8750. For each test case, the aspect ratio, AR = 21, ratio of boundary layer to step height, δ/h = 2.6 ± 0.2 and freestream turbulence level of 4% were kept constant. The results showed that the reattachment length increased monotonically with increasing Reynolds number for Reh < 6000, beyond which the reattachment length was independent of Reynolds number. In the recirculation region on top of the step, the Reynolds normal stresses were independent of Reynolds number but a higher Reynolds number increased the Reynolds shear stress in the region adjacent to the top of the step.
Flow Characteristics and Structure of 3D Turbulent Offset Jets
Authors: Nyantekyi-Kwakye B. , Clark S. , Tachie M. F. , Malenchak J. , Muluye G.
Published: December 2014

Three-dimensional turbulent offset jets were investigated with a particle image velocimetry (PIV) technique. Detailed velocity measurements for the flow were performed at an exit Reynolds number ranging from 8080–12080 for three offset height ratios of 0, 2 and 4. Profiles of the maximum mean velocity decay and wall-normal spread rates were observed to be sensitive to offset height ratio. Contour plots of mean velocity and turbulence kinetic energy exhibited dependence on offset height ratio. The reattachment lengths of the turbulent three-dimensional offset jets were observed to increase with offset height ratio. The results within the symmetry plane revealed that the production of Reynolds shear stress was not significantly enhanced by offset height ratio further downstream.
Roughness Effect Downstream of Flow Over a Forward Facing Step
Authors: Afriyie Yaw Y. , Essel Ebenezer E. , Thacher Eric W. , Tachie Mark F.
Published: December 2014

This paper presents results of an experimental research conducted to study roughness effects downstream of a forward facing step (FFS). A rough surface and a hydraulically smooth surface were used as a rough-FFS and a smooth-FFS, respectively. The upstream condition was kept smooth. Particle image velocimetry (PIV) technique was used for the velocity measurements. The Reynolds number based on the step height (h) and freestream velocity of the approach flow was kept constant at 8685. The results show that the mean reattachment length for the smooth-FFS (SM-SM) is 1.9h. Roughness reduced the peak values of the streamwise mean velocity, Reynolds shear stress and turbulent kinetic energy by 3%, 45% and 16.7% respectively in the recirculation region. In the early redevelopment region, roughness also reduced the peak values of turbulent kinetic energy and the Reynolds shear stress by 41% and 22% respectively.
Numerical and Experimental Investigation on Unsteady Inflow Conditions of a Pump-Turbine at Low Load
Authors: Erne S. , Edinger G. , Doujak E. , Bauer C.
Published: December 2014

This paper examines the occurrence of prerotation and reversal flow in the conical draft tube of a pump-turbine by using different turbulence models and compares the results to experiments. The computational domain consists of the entire geometry of a reduced scale pump-turbine. The results based on time-dependent computational fluid dynamics (CFD) are compared to laser doppler velocimetry (LDV) and wall-pressure-measurements in the conical part of the draft tube. Beside the LDV measurements, pressure fluctuations induced by complex flow patterns are also recorded and analyzed. The capability of simulations is assessed by an evaluation of the global integral values of the pump-turbine. The velocity profiles in axial and circumferential directions are compared at two measurement planes for two part-load operating points. The increased wall pressure distribution caused by swirling inflow is compared to the time averaged wall static-pressure from experiments. When operating at unstable pump conditions, an unsteady flow behavior arises in form of co-rotating vortices upstream of the impeller inlet. Analysis of the inlet flow shows continuously appearing and decaying vortex ropes in the conical draft tube. On the basis of these observations, discrete fourier transformation (DFT) analysis provides the power spectrum of the simulated time dependent pressure signal in the draft tube cone, where significant peaks below the runner rotational frequency are observed. The spectral analysis applied to transient pressure measurements at the draft tube wall shows dominant peaks in the low frequency region, which may indicate weak vortex structures rotating at low frequency.
An Experimental Study of the Wind-Driven Water Droplet/Rivulet Flows Over an Airfoil Pertinent to Wind Turbine Icing Phenomena
Authors: Zhang Kai , Hu Hui
Published: December 2014

Wind turbine icing represents the most significant threat to the integrity of wind turbines in cold weather. Advancing the technology for safe and efficient wind turbine operation in atmospheric icing conditions requires the development of innovative, effective anti-/de-icing strategies tailored for wind turbine icing mitigation and protection. Doing so requires a keen understanding of the underlying physics of complicated thermal flow phenomena pertinent to wind turbine icing phenomena, both for the icing itself as well as for the water runback along contaminated surfaces of wind turbine blades. In the present study, an experimental investigation was conducted to characterize the surface wind-driven water film/rivulet flows over a NACA 0012 airfoil in order to elucidate the underlying physics of the transient surface water transport behavior pertinent to wind turbine icing phenomena. The experimental study was conducted in an icing research wind tunnel available at Aerospace Engineering Department of Iowa State University. A novel digital image projection (DIP) measurement system was developed and applied to achieve quantitative measurements of the thickness distributions of the surface water film/rivulet flow at different test conditions. The measurement results reveal clearly that, after impinged on the leading edge of the NACA0012 airfoil, the micro-sized water droplets would coalesce to form a thin water film in the region near the leading edge of the airfoil. The formation of rivulets was found to be time-dependent process and relies on the initial water runback flow structure. The width and the spacing of the water rivulets were found to decrease monotonically with the increasing wind speed. The film thickness icing scaling law is evaluated by the time-average measurement film thickness. The measurement results show good consistent with the analytical scaling predictions.
A High-Order Immersed-Boundary Method for Complex/Moving Boundaries
Authors: Zhu Chi , Li Guibo , Luo Haoxiang
Published: December 2014

In this study, we intend to develop a high-order numerical approach using the immersed-boundary method to solve problems with complex and moving boundaries such as biological locomotion (animal swimming and flying) and biomedical flow systems. The basic idea is to use the compact finite-difference scheme to resolve the flow field and a higher-order forcing scheme to treat the immersed boundaries. In this work, the one-dimensional formulation of the numerical approach is presented and is tested extensively for its convergence. Such tests are necessary before more complicated tests in 2D/3D. An overall third-order accuracy is achieved as desired. Extension to higher dimensions is ongoing.
Sensitivity of WRF Model to Urban Parameterizations, With Applications to Chicago Metropolitan Urban Heat Island
Authors: Sharma Ashish , Fernando Harindra J. S. , Hellmann Jessica , Chen Fei
Published: December 2014

Chicago is one of the most populated cites of US. It is located next to a freshwater source, Lake Michigan, and surrounded by productive agricultural land and diverse natural habitats. This study explores the sensitivity of mesoscale urban heat island (UHI) simulations to urban parameterizations, focusing on the Chicago metropolitan area (CMA) and its environs. For this purpose, a series of climate downscaling experiments using the Weather Research and Forecasting (WRF) model at 1 km horizontal resolution. A typical summer hot day in Chicago was considered, which is imitative of a summer day in the late 21st century. This study utilizes National Land Cover Database (NLCD) 2006 classifications to test UHI sensitivity for CMA. Among different urban parameterization schemes, BEP+BEM best reproduces the urban surface temperatures in comparison to other urban schemes. Results show that UHI is more pronounced with BEP and BEP+BEM schemes due to explicit accounting of anthropogenic heat (AH). The study also investigates the effects of urbanization on regional climate by replacing Chicago metropolitan area by agricultural landscape, which yielded increased surface wind speeds due to reduced mechanical and thermal resistance.
Numerical Research of the Effect of the Outlet Diameter of Diffuser on the Performance and the Radial Force in a Single-Stage Centrifugal Pump
Authors: Wei Jiang , Guojun Li , Pengfei Liu , Lisheng Zhang , Hongyang Qing
Published: December 2014

In this paper, a single-stage pump with diffuser vanes of different outlet diameters has been investigated both numerically and experimentally. The influence of the diffuser vane outlet diameter on pump hydraulic performance and on the radial force of the impeller is explored. Pumps equipped with three different diffusers but with impellers and volutes of the same parameters were simulated by 3D Navier-Stokes solver ANSYS-FLUENT in order to study the effect of the outlet diameter of vaned diffuser on performance of the centrifugal pump. Structured grids of high quality were applied on the whole computational domain. Experimental results were acquired by prototype experiments and were then compared with the numerical results. Both experimental and numerical results show that the performance of a pump with a diffuser of smaller outlet diameter is better than of bigger outlet diameter under all operating conditions. The radial force imposed on the impeller obtained by unsteady numerical simulation was analyzed. The results also indicated that an appropriate decrease in the outlet diameter of the diffuser vane could increase the radial force.
Numerical Study of Turbulent Convective in Upward Flows of Supercritical Water in the Triangular Lattice Fuel Rod Bundle
Authors: Modirshanechi Mohsen , Hooman Kamel , Abdi Iman Ashtiani , Forooghi Pourya
Published: December 2014

Convection heat transfer in upward flows of supercritical water in triangular tight fuel rod bundles is numerically investigated by using the commercial CFD code, ANSYS Fluent© 14.5.

The fuel rod with an inner diameter of 7.6 mm and the pitch-to-diameter ratio (P/D) of 1.14 is studied for mass flux ranging between 550 and 1050 kg/m2s and heat flux of 560 kW/m2 at pressures of 25 MPa.

V2F eddy viscosity turbulence model is used and, to isolate the effect of buoyancy, constant values are used for thermo-physical properties with Boussinesq approximation for the density variation with temperature in the momentum equations. The computed Nusselt number normalized by that of the same Reynolds number with no buoyancy against the buoyancy parameter proposed by Jackson and Hall’s criterion. Mentioned results are compared with V2F turbulence model whereas strong nonmonotonic variation of the thermo-physical properties as function of temperature have been applied to the commercial CFD code using user defined function (UDF) technique.

A significant decrease in Nusselt number was observed in the range of 10-6<Grq/Reb3.425Prb0.8<5×10-6 before entering a serious heat transfer deterioration regime. Based on an analysis of the shear-stress distribution in the turbulent boundary layer and the significant variation of the specific heat across the turbulent boundary layer, it is found that the same mechanism that leads to impairment of turbulence production in concentric annular pipes is present in triangular lattice fuel rod bundles at supercritical pressure.
Dynamic Forces Acting on Elastic Heaving Airfoils Based on the Bending Stiffness Considerations
Authors: Fuchiwaki Masaki , Nagata Tetsushi , Tanaka Kazuhiro
Published: December 2014

In recent years the flow field in the vicinity of moving airfoils capable of flexible elastic deformation has become a focus of attention, and its effects are beginning to be understood. Flow in the vicinity of an elastically deforming airfoil may be understood as a fluid-structure interaction (FSI) problem, and the motion and deformation of elastic airfoils, as well as the associated vortex flow phenomena in their vicinity, are complicated. Especially, the shape and hardness of the elastic regions of an airfoil may affect its rigidity and its bending characteristics and for this reason the influence of such airfoils on the flow fields around them require more detailed consideration. In this study, we fix the bending stiffness, which uniquely determines the nature of the elastic deformation of an elastic airfoil, and study the impact of changes in this quantity on the flow field, as well as the parameters that govern the fluid forces acting on the airfoil. In particular, our goal is to clarify the relationship between three key parameters, Strouhal number St, Reynolds number Re and bending stiffness K and is to elucidate the nature of the dynamic forces acting on an elastic airfoil as a function of these three dimensionless parameters. The bending stiffness K of the elastic airfoil is an important parameter that determines the bending characteristics and the moving boundary conditions at the wall surfaces in the fluid. By defining the new quantity St2/K, we showed that the characteristic of dynamic forces depends on the ratio St2/K.
Suppression of Unsteady Vortex Shedding From a Circular Cylinder by Using a Passive Jet Flow Control Method
Authors: Chen Wenli , Li Hui , Hu Hui
Published: December 2014

A passive jet flow control method was employed to suppress the unsteady vortex shedding from a circular cylinder at the Reynolds number level of Re = (0.18∼1.1)×105. The passive jet flow control was achieved by blowing jets from the holes near the rear stagnation point of the cylinder, which are connected to the in-take holes located near the front stagnation point through channels embedded inside the cylinder. Since a part of the oncoming flow would inhale into the in-take holes, flow through the embedded channels, and blow out from the holes near the rear stagnation point to suppress/manipulate the alternating vortex shedding in the wake flow behind the circular cylinder, the present passive jet flow control method does not require any additional energy inputs for the flow control. In the present study, the aerodynamic force (i.e., both lift and drag) acting the circular cylinder model with and without the passive jet flow control were compared quantitatively at different Reynolds numbers (i.e., different inlet mean speed). It was found that, in addition to almost eliminating the fluctuations of the lift forces acting on the cylinder, the passive jet flow control method was also found to reduce the mean drag acting on the cylinder model greatly. The instantaneous vorticity distributions and corresponding streamline patterns were used to reveal the underlying physics about why and how the passive jet flow control method can be used to suppress the alternating vortex shedding and induce a symmetrical wake pattern behind the cylinder model.
Direct Numerical Simulation of Particle Heat and Mass Transfer in a Fluidized Bed
Authors: Feng Zhi-Gang , Roig Adam
Published: December 2014

We have developed a Direct Numerical Simulation combined with the Immersed Boundary method (DNS-IB) to study heat transfer in particulate flows. In this method, fluid velocity and temperature fields are obtained by solving the modified momentum and heat transfer equations, which result from the presence of heated particles in the fluid; particles are tracked individually and their velocities and positions are solved based on the equations of linear and angular motions; particle temperature is assumed to be a constant. The momentum and heat exchanges between a particle and the surrounding fluid at its surface are resolved using the immersed boundary method with the direct forcing scheme. The DNS-IB method has been used to study heat transfer of 1024 of heated spheres in a fluidized bed. By exploring the rich data generated from the DNS-IB simulations, we are able to obtain statistically averaged fluid and particle velocity as well as overall heat transfer rate in a fluidized bed.
Development of an Ultra-Quiet Fan for Computer Cooling Applications
Authors: Wang Zhenyu , Hu Hui
Published: December 2014

We report the progress made in our recent study to develop an ultra-quiet axial fan for computer cooling applications. By using a commercially-available cooling fan as the baseline, a number of acoustically tailored modifications are implemented in order to reduce the noise level of the cooling fan, which includes optimizing the rotator blades and guide vanes according to axial fan design theory, adding an intake cone in the front of the hub to guide the airflow into the axial fan smoothly, and reducing the tip clearance to lower the noise generation due to tip vortex structures. A comparison study is conducted to measure the sound pressure level (SPL) of the reformed axial fan in an anechoic chamber, in comparison to that of the prototype fan, in order to assess the effects of the modifications on the fan noise reduction. The measurement results of our preliminary study reveal that, at the same flow rate, the SPL of the reformed fan would be up to 5 dB lower than that of the prototype fan. In addition to measuring the sound pressure levels (SPLs) of the fans, a digital particle image velocimetry (PIV) system is also used to conduct detailed flow field measurements to reveal the changes of the flow characteristics and unsteady vortex structures associated with the modifications. Besides conducting “free-run” PIV measurements to determine the ensemble-averaged statistics of the flow quantities such as mean velocity, Reynolds stress, and turbulence kinetic energy (TKE) distributions at the exit of the axial fan, “phase-locked” PIV measurements are also performed to elucidate further details about evolution of the unsteady vortex structures in fan exhaust in relation to the position of the rotating fan blades. The detailed flow field measurements are correlated with the SPL measurements in order to elucidate underlying physics associated with the fan noise reduction.
Numerical Study on Hydraulic Performances of Pump as Turbine With Forward-Curved Blades
Authors: Wang Tao , Kong Fanyu , Yang Sunsheng , Fu Yanxia
Published: December 2014

A reserved running centrifugal pump can work as a hydraulic turbine with its wide application in industrial energy recovery and the development of micro-hydraulic power. In order to improve the efficiency from the point of turbine working condition, the impeller with forward-curved blades was designed and the hydraulic performances were further analyzed based on the commercial software ANSYS CFX 12.0 in this study. Moreover, to improve the computational accuracy of numerical simulations on turbines, the grid number, the turbulence model, the circumferential flow distribution in the clearance between the volute and the impeller as well as the grid distribution in the boundary layer were considered.

According grid independency analysis, the 1.2 million grids’ number was assumed for numerical simulations. Considering the consuming time and computational stability, as well as the accuracy of the CFD calculation, the k–ε turbulence model was chosen for further calculations. The shaft power and the efficiency of the turbine were more close to the experimental data as the whole computational flow domain in the clearance between the volute and the impeller was connected on the impeller domain. Compared with the performance curves with or without grids in the boundary layer, the boundary layer with grids used in the PAT during numerical simulations was more close to the experimental one.

Compared with the experimental data, the H-Q curves of the hydraulic performances of the turbine with forward-curved blades predicted by CFD were positioned under the experimental one. With respect to the efficiency of the turbine, the various ranges of the efficiency is less than 5%, even there is some deviations between the CFD and experimental results. Therefore, the good agreement of the hydraulic performances between CFD and experimental results in present study indicates that the proposed numerical methods can adequately capture the internal flow in a hydraulic turbine with forward-curved blades, and can also provide a reliable reference for the design of hydraulic turbines.
Hydrodynamic Model of Gas-Solids Risers Flow With Continuous Axial and Radial Flow Structure
Authors: He Pengfei , Patel Rajesh , Wang Dawei , Zhu Chao , Zhang Bo
Published: December 2014

The dynamic transport of gas-solids in a riser leads to highly non-uniform and complex flow distributions in both axial and radial directions. This study presents a continuous modeling approach that simultaneously computes the axial and radial non-uniform distribution of gas and solid phase transport properties in the risers. The radial non-uniform distributions of transport properties of gas and solids are approximated by the 3rd order polynomials, which have been validated by available experimental data from literatures. The radial heterogeneity is due to a combined effect of riser wall boundary, the radial transport by the collision-induced diffusion, and the turbulent convection of solids. Some important transport properties, such as core-wall boundary and back-mixing ratio, are flow-coupled and solved by the proposed model. The model predictions have been validated against some published experiment data, including the distributions of solid concentration, velocity and pressure gradient along the risers.
Molecular Dynamics Simulations of Thermo-Mechanical Effects in Nanodrop Impact
Authors: Finkbeiner John , Watkins Charles , Koplik Joel
Published: December 2014

Nanodrop impact onto a solid substrate is of interest for nano-scale liquid-impingement, phase-change cooling and for material deposition processes. In the present study, classical molecular dynamics (MD) simulation techniques were implemented to study the thermo-mechanical properties of the impact of nanometer scale liquid droplets upon an atomistic substrate at a temperature higher than that of the droplet. The droplets were comprised of approximately 50,000 Lennard-Jones atoms arranged in tetramer finitely extensible non-linear elastic (FENE) chain molecules forming a sphere of 8 nm radius. They were equilibrated and then projected towards a wall, where we observed the response upon collision by changes in shape, temperature, and density gradients, across a variety of impingement velocities, substrate temperatures, and wetting conditions. The baseline cases of equal substrate and nano-drop temperature were validated by comparison with previously reported results. A reaction spectrum ranging from full thermal vaporization of the drop, with respective substrate cooling, to complete kinetic disintegration upon impact and surface heating are analyzed. The variation of thermal and kinetic effects across the parametric environment is used to identify those regimes that optimize heat transfer from the surface, as well as those that best facilitate material deposition processes.
DNS and LES of the Compressible Flow Over a Delta Wing With the Symmetry-Preserving Discretization
Authors: Rozema Wybe , Kok Johan C. , Verstappen Roel W. C. P. , Veldman Arthur E. P.
Published: December 2014

A fourth-order accurate symmetry-preserving discretization for compressible flow is used to perform simulations of the turbulent flow over a delta wing. A symmetry-preserving discretization eliminates the non-linear convective instability by preserving conservation of kinetic energy at the discrete level. This enhances the stability of a simulation method, so that little artificial dissipation is needed for numerical stability. It is shown that simulations of the flow over a sharp-edge delta wing at Re = 50,000 with the symmetry-preserving discretization are stable without artificial dissipation in a region of interest around the delta wing. To assess the accuracy of the simulation method, results obtained on a fine computational grid are compared with results obtained on a coarser grid. Also results obtained with large-eddy simulation models and with sixth-order artificial dissipation are presented.
Numerical Investigation of the Effect of Balancing-Hole on the Axial Force of a Partial Emission Pump
Authors: Lisheng Zhang , Jin Jiang , Zhihuai Xiao , Yanhui Li
Published: December 2014

In this paper numerical simulations were conducted to analyze the effects of design parameters and distribution of balancing-hole on the axial-force of a partial emission pump. The studied pump is a single stage pump with a Barske style impeller. Based on the original impeller, we designed 7 pumps with different balancing-hole diameters and the partial emission pump equipped with different impellers were simulated employing the commercial computational fluid dynamics (CFD) software Fluent 12.1 to solve the Navier-Stokes equations for three-dimensional steady flow. A sensitivity analysis of the numerical model was performed with the purpose of balancing the contradiction of numerical accuracy and the cost of calculation. The results showed that, with increasing of the capacity, the axial force varies little. The diameter of the inner balancing-hole plays a dominant role of reducing axial-force of partial emission pump, the axial-force decreases with increasing of inner balancing-hole diameter on the whole range of operation, the axial-force of impeller without inner balancing-hole is approximately 3 times larger than that of impeller with inner balancing-hole. While the diameter of outer balancing-hole has a reverse effects compared with that of inner balancing-hole. With increasing of outer balancing-hole, the axial force increases accordingly.