bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Boiling of Sub-Cooled Pentane on a Micro-Porous Coating
Authors: Laca Paul J. , Wirtz Richard A.
Published: July 2013

Flow boiling experiments with sub-cooled Isopentane and n-Pentane at 3.0bar pressure assess the utility of compressed copper- and steel-filament screen laminate surface coatings as high performance boiling surfaces. High-speed video show that at high heat flux ebullition is unsteady. Isopentane and n-Pentane are found to produce nearly identical boiling characteristic curves. At the same applied heat flux, the superheat of copper filament coatings are much smaller than the steel filament coating superheats.
Tested Performance of Photovoltaic Array Optimization Technologies
Authors: Paynter Aldrin J. , Aschheim Mark , Gonzalez Jorge E.
Published: July 2013

Growth in the solar industry continues as the cost of photovoltaic power is approaching grid parity. Several technologies have been developed that address reductions in power production associated with partial shading of panels, mismatch at the panel and string levels, and multiple array orientations, conditions that often arise in residential installations. In the absence of existing testing standards, a methodology was developed to evaluate performance of power optimization devices under shading conditions. Technologies investigated include buck-boost, parallel voltage boost, and impedance matching. Performance improvements range from negligible to a 44% increase in energy delivered under partial shading. Comparison data is presented along with guidance for selecting among the different technologies currently available on the market.
Energy Efficiency Design Strategies for Greenhouse in Colorado
Authors: Kwag Byung Chang , Krarti Moncef
Published: July 2013

A basic principle of well designed greenhouse design emphasizes the utilization of solar energy as much as possible to grow the plants indoors during extreme outdoor climate conditions. Greenhouses can use significant amount of energy due to several factors including poor envelope design, inappropriate maintenance practices, and heavy reliance on fuel-based heating systems. In order to reduce energy consumption in the agricultural industry of Colorado, it is important to design energy efficient greenhouses under Colorado climatic conditions.
Deriving Cloud Velocity From an Array of Solar Radiation Measurements
Authors: Bosch Juan L. , Zheng Yuehai , Kleissl Jan
Published: July 2013

Spatio-temporal variability of solar radiation is the main variable affecting the photovoltaic power feed-in to the grid. Clouds are the main source of such variability and their velocity is a principal input to most short-term forecast models. The main goal in this study is to estimate cloud speed using radio-metric data using measurements from 8 sensors located at the UC San Diego Solar Energy test bed.

Two different methods were developed to estimate the cloud speed based on the correlation between the signals from different sensors. Our analysis showed good agreement between both methods. Additional measurements from nearby METAR and radiosonde stations also show comparable results. Both methods require high variability in the input radiation.
Hybrid Distributed Power Generation for Apartment Building Complexes in Korea
Authors: Kim Joowook , Lim Hyunwoo , Krarti Moncef
Published: July 2013

Korea relies significantly on imported fossil fuels to meet its energy needs. Moreover, about 50% of Korean residential buildings are apartment complexes. In this paper, the use of distributed generation (DG) technologies to serve the energy requirements for a typical Korean apartment complex is explored to reduce Korea’s dependence on fossil fuel and CO2 emissions. In particular, a series of sensitivity analyses is conducted using detailed simulation tools to determine the cost-effectiveness of DG systems to meet electrical and thermal loads of an apartment building in Daegu, Korea. The DG systems considered in the analysis include Photovoltaic (PV), Wind turbine, Microturbine, and Fuel Cell. The apartment complex is connected to the utility grid that with electricity typically generated using fossil fuels. It is found that a combination of the grid and Fuel Cell is the most cost effective approach to meet the electrical and thermal loads of the complex residential building with a cost of energy reduction of 12% compared to the grid only option.
Numerical Analysis of a Solar Organic Rankine Cycle (ORC) Unit With R245fa as Working Fluid
Authors: Bamgbopa Musbaudeen O. , Uzgoren Eray
Published: July 2013

This paper presents a solar Organic Rankine Cycle (ORC) for electricity generation; where a regression based approach is used for the working fluid. Models of the unit’s sub-components (pump, evaporator, expander and condenser) are also presented. Heat supplied by the solar field can heat the water up to 80–95 °C at mass flow rates of 2–12 kg/s and deliver energy to the ORC’s heat exchanger unit. Simulation results of steady state operation using the developed model shows a maximum power output of around 40 kWe. Both refrigerant and hot water mass flow rates in the system are identified as critical parameters to optimize the power production and the cycle efficiency.
Bio-Inspired Wind Energy Harvester
Authors: Talarico David , Hynes Kevin
Published: July 2013

Engineers and designers often mimic mechanisms found in nature to accomplish a specific task. This concept was applied to wind power generation to simplify and reduce cost of the HAWT design. The advantage of the flapping wing design lies in the additional power generated by leading edge vortices. It has previously been demonstrated by others that a flapping wing section undergoing simultaneous, coordinated heaving and pitching is capable of extracting energy from an oncoming flow using the CFD code FLUENT. The encouraging results suggest that efficiencies as high as 36.3% are achievable with such a system with the strongest influence on efficiency being reduced heaving amplitude, H/c, pitching amplitude, θ, and reduced frequency, f*. The suggested values of these motion parameters for optimal performance was found to be H/c≈1, θ≈73°, and f*≈0.15. Hence, an adjustable flapping wing energy extraction device was designed in accordance with these parameters. Preliminary testing has demonstrated the effective operation of the device over a range of Reynolds numbers in a wind tunnel.
Development of a Concentrator With a Rectangular Flat Focus Used for Hydrogen Production via Photocatalytic Water Splitting Employing Solar Radiation
Authors: Wullenkord Michael , Jung Christian , Sattler Christian
Published: July 2013

Hydrogen is a promising energy carrier. A carbon-free option to produce hydrogen is the photocatalytic splitting of water, when solar radiation provides the photons needed for the reaction. The DLR develops a test bed to assess the activity of potential catalysts either in suspensions or in fixed-bed electrochemical cells under practical sun-light conditions, concentrated by a factor up to 20. A rectangular flat focus is required in order to guarantee a homogeneous distribution of concentrated radiation on the planar receiver plate, where the light enters the receiver. A low deviation of irradiation on the receiver plate promotes a reliable evaluation of the catalysts’ efficiency and quantum yields. This paper is focused on the development of a suitable concentrator concept. A concentrator/receiver-concept featuring a homogeneous distribution of radiation on the reactor surface was chosen after analyzing different options by means of a ray tracing tool. The favorite concept employs a 2-axis modified linear Fresnel collector. The overall dimensions were determined taking the optical properties of the irradiated surface of the reactor into account. A limitation of the angle of incidence ensures that only a marginal fraction of the radiation is lost due to reflection on the irradiated surface of the reactor.
Performance Comparisons of Solar Desalination Devices and Processes
Authors: Modaresifar Masoud , Zenouzi Mansour , Kowalski Gregory J.
Published: July 2013

Numerical analysis of two passive solar desalination designs, the traditional pool evaporation design and the proposed tray design are performed. The significance of common assumption for the pool evaporation design that neglect the mass balance and psychrometric relationships for the air-water vapor volume were investigated and found that neglecting this component results in over predicting the freshwater production by 32.6% and 19.5% for the summer and winter design day, respectively. It was also found that the tray design produced 31.3 % and 7% more freshwater per summer and winter design day, respectively. These results support the need to include all physical components in the numerical simulation. The results also support the tray design as producing significantly more freshwater for the same input.
Measurements of Gas Bubble Size Distributions in Flowing Liquid Mercury
Authors: Wendel Mark , Riemer Bernard , Abdou Ashraf
Published: July 2013

Pressure waves created in liquid mercury pulsed spallation targets have been shown to induce cavitation damage on the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, measuring such a population in mercury is difficult since it is opaque and the mercury is involved in a turbulent flow. Ultrasonic measurements have been attempted on these types of flows, but the flow noise can interfere with the measurement, and the results are unverifiable and often unrealistic.

Recently, a flow loop was built and operated at Oak Ridge National Labarotory to assess the capability of various bubbler designs to deliver an adequate population of bubbles to mitigate cavitation damage. The invented diagnostic technique involves flowing the mercury with entrained gas bubbles in a steady state through a horizontal piping section with a glass-window observation port located on the top. The mercury flow is then suddenly stopped and the bubbles are allowed to settle on the glass due to buoyancy. Using a bright-field illumination and a high-speed camera, the arriving bubbles are detected and counted, and then the images can be processed to determine the bubble populations.

After using this technique to collect data on each bubbler, bubble size distributions were built for the purpose of quantifying bubbler performance, allowing the selection of the best bubbler options. This paper presents the novel procedure, photographic technique, sample visual results and some example bubble size distributions.

The best bubbler options were subsequently used in proton beam irradiation tests performed at the Los Alamos National Laboratory. The cavitation damage results from the irradiated test plates in contact with the mercury are available for correlation with the bubble populations. The most effective mitigating population can now be designed into prototypical geometries for implementation into an actual SNS target.
Use of CFD Tools in Internal Deflector Design for Cross Flow Turbine Efficiency Improvement
Authors: Croquer Sergio D. , de Andrade Jesus , Clarembaux Jorge , Jeanty Freddy , Asuaje Miguel
Published: July 2013

Cross Flow Turbines (CFT), also known as Banki or Ossberger turbines are broadly used in small scale hydropower generation. Easy construction and operation, low CAPEX and OPEX and fairly independent efficiency from flow rate are the main characteristics of the CFT. However, they also tend to have a modest efficiency (80%), hence they are not considered for large scale power plants. Previous work have focused on use of Internal Deflectors (ID) for CFT efficiency improvement. However experimental flow observation and characterization inside CFT is hard to achieve. This work proposes use of Computational Fluid Dynamic (CFD) tools as an aid in ID design. A transient regime, two-dimensional, numerical model of a CFT without any internal deflectors was carried out. Deviation from experimental results at BEP was close to 5%. CFT w/o ID results were used as ID design starting point. Parameters: Upper Blade Position and ID Length were defined and varied obtaining six different ID versions. Numerical models were carried out for evaluation of ID effect on CFT. CFT hydraulic efficiency improvement was achieved for all ID versions studied (range 0.5%–3%, average:1.9%). Output power was also augmented (range 0.3%–4%, average:2.5%)for all cases.
A Preliminary Analysis of a Turgo Type Turbine CFD Simulation Designed With an Integrated Dimensional Methodology
Authors: Clarembaux Correa Jorge Luis , De Andrade Jesús , Asuaje Miguel
Published: July 2013

A useful methodology in the design of a Turgo Type Turbine (TTT) has been accomplished through the theoretical calculation of the runner performance and efficiency, using 1D, 2D and 3D theory with certain simpliflying assumptions. The adaptation of several geometric and hydrodynamic parameters into the solution of the Rankine ovoids streamlines function, a three-dimensional potential flow, resulted in the design of a three dimensional TTT runner. A significant CFD simulation of this turbine was achieved, showing its hydrodynamic performance and the behaviour of the streamlines path through the buckets hit by the jet. The distribution of the water volumetric fraction was reported from the nozzle to the buckets In the same way, this numerical approach described the evolution of the velocity vectors from the water crossing the buckets. Furthermore, a comparison between the relative velocity angles from the three dimensional potential theory and the CFD simulation results was done, in order to find potential similarities from the water that actually passes into the buckets.
An Empirical Investigation on Seal-Interface Leakage of an Elastomer Face Seal
Authors: Garafolo Nicholas G. , Daniels Christopher C.
Published: July 2013

For the application of seals used in space, a common assumption is that all leakage is attributed to permeation, that is the gas flows through the porous seal material. In this case, leakage across any seal interfaces are assumed negligible. In fact, state-of-the-art gas leak rate prediction methods rely heavily on this assumption. A recent study into the quantification of the seal-interface leakage of elastomer face seals, however, has revealed that this is not the case. As the preliminary study previously presented, with moderate contact pressure the interface leakage components were found to be significant and distinct from zero. The objective of the research presented herein was to further quantify both the elastomer-metal and elastomer-elastomer interface leakages for various contact pressures. To this end, a series of leak rate experiments is presented on a square-ring seal, manufactured from silicone elastomer S0383-70. The unique experimental design affords the ability to quantify both the elastomer-metal interface, as well as an elastomer-elastomer interface. The experiments utilized matched sets of test specimens, each with a common width but different height. The test apparatus contained both a flow fixture capable of quantifying ultra-low leak rates and an electro-mechanical actuated load frame for precision contact pressure control. The leak rate apparatus consisted of stainless steel platens, near-hermetic plumbing, and the required instrumentation. The initial data reduction was accomplished by the mass point leak rate technique; whereas mass was calculated through measurements of gas pressure, temperature, and volume and a regression analysis yielded the leak rate of the seal. A secondary reduction of the leak rates in the unique experimental configuration further distinguished the total leakage into permeation and interface leak components, accomplished through the algebraic solution of the design of experiments guided matrix. Foremost, results confirmed that the interface leakage is non-negligible and distinct from zero, as with previous studies. Furthermore, results suggested that the interface leakage was drastically decreased with modest seal contact pressure.
Surface Tension Model for Particle Method Using Inter-Particle Force Derived From Potential Energy
Authors: Ishii Eiji , Sugii Taisuke
Published: July 2013

Fluid-flow simulation within micro/nano spaces is essential for designing micro/nano devices, such as those in micro-electro-mechanical systems and nanoimprint processes. Surface tension is a dominant force in the fluid flow within micro/nano spaces. Surface-tension models can be classified into two groups: models based on continuous surface force in immiscible phases, and models based on inter-particle force in miscible phases. The surface-tension model based on inter-particle force for modeling interactions between materials would fit fluid-flow simulation within micro/nano spaces better than the surface-tension model based on continuous surface force.

We developed a surface tension model using inter-particle force for use with a particle method in a past study. However, workings of inter-particle forces in miscible phases were not verified. Furthermore, accuracy in three-dimensional simulation needed to be verified. These subjects were verified in this study using simple benchmark tests. First, cohesion based on potential energy was validated to qualitatively check the workings of inter-particle force. The phase separation from the mixed two-phase flow due to inter-particle force was simulated. Next, the inter-particle force at the gas-liquid interface was quantitatively verified using the theory of the Young-Laplace equation; the pressure in a droplet was compared in two- and three-dimensional simulations, and the predicted pressures in a droplet agreed well with this theory. The inter-particle force at the gas-liquid-solid interface for the wall adhesion of a droplet was also verified; the results for wall adhesion in three-dimensional space agreed much better than that in two-dimensional space. We found that our surface tension model was useful for simulating the fluid flow within micro/nano spaces.
Roles of Neutrally Buoyant Particles in Gas-Liquid-Solid Flows
Authors: Zhang Xinyu , Ahmadi Goodarz
Published: July 2013

A CFD study is carried out to investigate the roles of neutrally buoyant particles in gas-liquid-solid flows in bubble columns. An Eulerian-Lagrangian model is used and the liquid flow is modeled using a volume-averaged system of governing equations, while motions of bubbles and particles are evaluated using Lagrangian trajectory analysis. Bubbles are assumed to remain spherical. Bubble-liquid interaction and particle-liquid interaction are included in the study. The drag, lift, buoyancy, and virtual mass forces are included in the discrete phase equations. Particle-particle interactions and bubble-bubble interactions are accounted for by a hard sphere model. The bubble coalescence is also included in the analysis. Neutrally buoyant particles are used in the study. The predicted results were compared with the experimental data in a previous work, and good agreement was obtained. The transient flow characteristics of a gas-liquid-solid three-phase flow and a gas-liquid two-phase flow are studied and the roles of neutrally buoyant particles are discussed. The simulations show that the transient characteristics of the flows in a bubble column are dominated by time-dependent vortices. The presence of particles can affect the characteristics of the flows and flows with particles evolve faster.
Numerical Simulation of a Micro Pelton Turbine Working in the Two-Phase Flow Regime
Authors: Schuster Sebastian , Benra Friedrich-Karl , Dohmen Hans Josef
Published: July 2013

This paper deals with the numerical calculation of an energy-recovering unit for air-conditioning and heat pump systems. Currently, working fluids are expanded in expansion valves in air-conditionings or, in general, refrigeration systems. The aim of this work is to increase the efficiency of the air-conditioning systems by replacing the irreversible nozzle with an energy recovering working machine. An air-conditioning system with a high enthalpy difference between inlet and outlet combined with a small volume flow is in the focus of the investigation in the presented study. According to the well-known Cordier diagram, a Pelton turbine with one nozzle is the most efficient machine for this purpose. One part of the investigation is the nozzle and the other is the Pelton wheel. The inlet conditions for the nozzle are supercritical and the pressure ratio is 2.3; the working fluid is CO2. During the expansion, the phase changes from supercritical to liquid and finally at the outlet two-phase flow is expected. The numerical calculations were executed with Ansys CFX 12. Two different numerical approaches — the homogeneous binary mixture and the Eulerian-Eulerian inhomogeneous multiphase model — are used. For the Eulerian-Eulerian calculation, the flow morphology is assumed to be polydispersed. Different bubble diameters are simulated with the MUSIG model. A comparison between the calculation with homogeneous binary mixture and Eulerian-Eulerian is presented as well. A parameter study about the nozzle, impeller and casing is performed which leads to the design point geometry. It will be shown that the optimal nozzle contour at design point conditions is converging - diverging although the flow is subsonic.
An Accurate and Simple Approach to Allow for the Transient Temperature Gradient in a Vaporizing Droplet
Authors: Snegirev Alexander , Talalov Victor
Published: July 2013

The purpose of this work is to analyze the importance of considering internal temperature gradient in modeling droplet evaporation, and to demonstrate performance of simplified methods in which the temperature gradient is approximately taken into account. Based on three characteristic time scales, two dimensionless criteria have been identified which determine magnitude of the internal temperature gradient and its effect on the evaporation dynamics. Numerical values of these criteria in a wide range of ambient temperatures show that the effect of the internal temperature gradient is more pronounced in more volatile liquid at higher ambient temperatures. Although droplet life time predictions are not sensitive to the internal temperature gradient, its effect might be strong at the initial stages of droplet evaporation, and this substantiates the need in robust and computationally inexpensive methods to take it into account. Two simple and yet accurate approaches (quasi-steady higher order polynomial approximation and the integral balance method) have been favourably tested and recommended for use in CFD spray modeling.
Recent Achievements and Challenges in Modelling and Simulation of Complex Multi-Scale MHD Phenomena
Authors: Kenjeres Sasa
Published: July 2013

The paper reviews some of the most important challenges and recent progress in modeling and simulations of flow, turbulence and heat transfer of the electrically conductive fluids interacting with electromagnetic fields (EMF). Despite the differences in flow geometries and huge disparity of the length- and time-scales, ranging from astrophysical and geophysical to laboratory-scale applications, it is demonstrated that magneto-fluid-dynamics (MFD) phenomena, in their essence, are characterized by two fundamental features — a time-dependent spiraling flow patterns and non-homogeneous distributions of the magnetic fields. Some representative examples of both two- and one-way coupled MFD phenomena are considered: the turbulent magnetic dynamo under realistic experimental conditions (the Riga-dynamo experimental setup), and the turbulent Rayleigh-Bénard convection in a differentially heated enclosure subjected to the localized Lorentz force originating from combining electrodes and array of permanent magnets located beneath the lower thermally active enclosure wall. In both considered cases, a good agreement between available experimental results and numerical simulations is obtained, proving accuracy and potentials of the multi-scale modeling approach in simulating complex MFD phenomena.
CFD Simulation of Particle Transport and Dispersion in Indoor Environment by Human Walking
Authors: Goldasteh Iman , Ahmadi Goodarz , Ferro Andrea
Published: July 2013

Particle resuspension is an important source of particulate matter in indoor environments that significantly affects the indoor air quality and could potentially have adverse effect on human health. Earlier efforts to investigate indoor particle resuspension hypothesized that high speed airflow generated at the floor level during the gate cycle is the main cause of particle resuspension. The resuspended particles are then assumed to be dispersed by the airflow in the room, which is impacted by both the ventilation and the occupant movement, leading to increased PM concentration.

In this study, a three dimensional model of a room was developed using FLUENT™ CFD package. A RANS approach with the RNG k-ε turbulence model was used for simulating the airflow field in the room for different ventilation conditions. The trajectories of resuspended particulate matter were computed with a Lagrangian method by solving the equations of particle motion. The effect of turbulent dispersion was included with the use of the eddy lifetime model. The resuspension of particles due to gait cycle was estimated and included in the computational model. The dispersion and transport of particles resuspended from flooring as well as particle re-deposition on flooring and walls were simulated. Particle concentrations in the room generated by the resuspension process were evaluated and the results were compared with experimental chamber study data as well as simplified model predictions, and good agreement was found.
A Study of Cavitation Flow in a Centrifugal Pump at Part Load Conditions Based on Numerical Analysis
Authors: Yuan Jianping , Fu Yanxia , Yuan Shouqi
Published: July 2013

In order to predict cavitation performance of the centrifugal pump, including cavitating structures and vapour volume at the blade suction side, as well as its relationship with the backflow in the impeller eye, a 3D numerical simulation of detailed steady and unsteady cavitating flow was applied to reproduce its inner flow fields at part load conditions (0.5Qd and 0.4Qd). The comparisons of cavitation characteristics of the current centrifugal pump at an on-design point (1.0Qd) and a high flow rate (1.2Qd) were achieved as well. In addition, Frequency analysis of pressure fluctuations at the blade passages and the inlet pipe were also obtained during cavitation for a flow coefficient of 50%. The results further show that successive blade cavitation patterns and the creeping cavitation number dropping appear for a wide range of flow rates when the inlet total pressure decreases from cavitation inception to the breakdown of the centrifugal pump, as is quite different from that when cavitation occurs at 1.0Qd or 1.2Qd. Unbalanced attached cavities on the blade suction side were also observed at 0.5Qd. Meanwhile, the unsteady behaviour of cavities attached to the blade suction side and cavitation number dropping depend on the flow rate and cavitation number. Another significant characteristic of the phenomenon is that all the domain frequencies in blade passages and inlet pipe at part load conditions are 0.048Hz∼48.285Hz, which is typically lower than the shaft rotational frequency of the model centrifugal pump.
Using Graphics Processing Units to Accelerate Numerical Simulations of Interfacial Incompressible Flows
Authors: Codyer Stephen R. , Raessi Mehdi , Khanna Gaurav
Published: July 2013

We present a GPU accelerated numerical solver for incompressible, immiscible, two-phase fluid flows. This leads to a significant simulation speed-up and thus, the capability to have finer grid sizes and/or more accurate convergence criteria. We solve the Navier-Stokes equations, which include the surface tension force, by using a two-step projection method requiring the iterative solution to a pressure Poisson problem at each time step. However, running a serial linear algebra solver on a CPU to solve the pressure Poisson problem can take 50–99.9% of the total simulation time. To remove this bottleneck, we employ the large parallelization capabilities of GPUs by developing a double-precision parallel linear algebra solver, SCGPU, using NVIDIA’s CUDA v.4.0 libraries. The performance of SCGPU in serial simulations is presented, in addition to an evaluation of two pre-packaged GPU linear algebra solvers CUSP and CULA-sparse. We also present preliminary results of a GPU-accelerated MPI CPU flow solver.
Stability of an Axial-Thrust Self-Balancing System
Authors: Shimura Takashi , Kawasaki Satoshi , Uchiumi Masaharu , Kimura Toshiya , Hayashi Mitsuaki , Matsui Jun
Published: July 2013

Rocket pump is characterized by high speed and high delivery pressure. Therefore, balancing of axial thrust acting on the rotor assembly is one of the most important factors. To realize complete axial thrust balancing, a balance piston-type axial-thrust self-balancing system is often used in rocket pumps. Such a system is comprised of an inlet orifice (#1) located at the outlet part of the impeller, outlet orifice (#2) located at the small-radius position of the back shroud and a chamber between these two orifices. Those orifices made by edges of the casing and the impeller shroud look like rings. The rotor assembly is allowed to move axially less than 1 mm to control the clearances of the orifices. The rotor assembly moves toward the turbine part when unbalanced axial thrust is imposed on the rotor assembly in the direction from the inlet of the pump toward the turbine part. As a result, the clearance of the inlet orifice increases and that of the outlet orifice decreases. This results in an increase in the pressure in the chamber between the orifices and makes the axial thrust generated by the balance piston in the direction from the turbine part toward the inlet of the pump increase. In this way, unbalance axial thrust imposed on the rotor assembly can be compensated automatically. This axial thrust balance system acts dynamically as if it is a mass and spring system although there is no mechanical spring. Too much vibration in the axial direction causes metal to metal rubbing, resulting in the explosion of rocket turbopumps. Although large amplitude axial vibration has been observed in rocket engine turbopumps, the cause of the vibration has not yet been clarified. In the present study, the self-balancing system was modeled by combining the mechanical structure and the fluid system in a calculation program. Stability of the system was investigated using this program. Effects of geometry, fluids, etc., were examined and methods to stabilize the system in order to suppress the axial vibration were developed.
Improvement of Axial-Flow Pump Part Load Behavior by a Double Inlet Nozzle
Authors: Dohmen Hans Josef , Benra Friedrich-Karl , Brinkhorst Sven
Published: July 2013

In highly loaded axial flow pumps considerable changes of the flow structures are known when lowering the flow rate from design point operation to part load operation. After the stall inception the backward tip flow increases in axial and radial direction upstream of the impeller forming the part load “vortex B”.

The backflow has a strong co-swirl, which is transmitted to the inlet flow. This leads to less Euler work and often to a drop of pump head. To overcome these negative effects of the stall, a so called double inlet nozzle can be used. At the University of Braunschweig this device is investigated experimentally. In this contribution the time dependent three dimensional flow fields have been numerically investigated by unsteady Reynolds averaged Navier-Stokes simulations.

The geometry of the test stand, the geometry of the numerical model and the used meshes are described. The experimental results and the numerical obtained results are compared to each other. First the measured overall performance characteristic is compared to the numerical results obtained by averaging the head and the efficiency over the last computed impeller revolution. In addition the numerical obtained flow field upstream of the inlet nozzle is compared to flow fields measured in Braunschweig by PIV method. Also the flow field is shown in regions of the pump which are not accessible by experimental methods.

Based on these results the shape of the double inlet nozzle is varied in different ways. The influence of the modifications on the flow field and the part load behavior of the pump is displayed and discussed.
Flow Regime Characteristics in Porous Media Flows at High Reynolds Numbers
Authors: Patil Vishal A. , Liburdy James A.
Published: July 2013

An experimental study on the turbulent flow characteristics in a randomly packed porous bed is presented and discussed. Time resolved PIV measurements, taken in specific pore spaces are used to evaluate transitional and developed turbulent flow statistics for pore Reynolds numbers from 54 to 3964. Three different regimes of steady laminar, transitional and turbulent flow are presented. Small scale coherent vortical structures are examined, using large eddy scale (LES) decomposition, for pore Reynolds number of greater than 1000. Integral length scales were found to reach asymptotic values of approximately 0.1 times the hydraulic diameter of the bed. The integral Eulerian time scales are found to reach an asymptotic value of approximately 0.3 times the convective time scale in the bed. Mean velocity vector maps show flattening of the velocity distribution due to increased momentum mixing. Turbulent stresses show increasing level of homogeneity at higher pore Reynolds numbers.
Numerical Simulation of Breakup of Elliptical Liquid Jet in Still Air
Authors: Farvardin Ehsan , Dolatabadi Ali
Published: July 2013

Numerical simulation of liquid jets ejecting from a set of elliptical jets with different aspect ratios between 1 (circular) to 3.85 is performed for several Weber numbers ranging 15 to 330. The axis-switching phenomenon and breakup length of the jets are characterized by means of a Volume of Fluid (VOF) method together with a dynamic mesh refinement model. This three dimensional simulation is compared with a recent experimental work and the results agree well. It is concluded that at Weber numbers less than 100, the breakup length of the liquid jet increases, reaches a peak and then decreases suddenly.
Parallel Implementation and Performance of an Immersed Boundary Method
Authors: Wei Z. , Zheng Z. C.
Published: July 2013

An implementation for parallelization of an immersed boundary method is presented using the standard MPI communication. The immersed boundary method in the present work follows that in Zhang & Zheng [1]. The Poisson problem is solved with assistance of a scientific parallel computational library PETSc. A staggered grid mesh is employed to reduce the discretization error. The 2nd order accuracy is obtained eventually. This method is validated by a case with a 2D uniform flow over a stationary or oscillating circular cylinder and a 3D uniform flow over a stationary sphere. Comparisons with previous studies are presented. Also, performances of parallelization, including parallelism and scalability, are tested.
Experimental Investigation of Falling Liquid Film in Vertical Downward Two-Phase Pipe Flow
Authors: Lopez Jose M. , Mohan Ram , Shoham Ovadia , Wang Shoubo , Kouba Gene
Published: July 2013

In this research the hydrodynamics of falling liquid film in a vertical downward two-phase flow (liquid-gas) is experimentally studied.

The 4 inch clear PVC test section is 6.1 meters long, with a length to diameter ratio (L/D) of 64. The fluids utilized are compressed air, water, Conosol mineral oil (light oil) and Drake mineral oil (heavy oil). The superficial liquid velocities tested range from 12 to 72 cm/s while the superficial gas velocities range from 0.2 to 29 cm/s. The vertical facility is equipped with the state-of-the-art instrumentation for two-phase flow measurements, the capacitance Wire-Mesh Sensor (WMS), allowing two-phase flow measurements with conducting and non conducting fluids.

Experimental results show that the liquid film thickness has a quasi-linear relationship with the superficial liquid velocity for the air-water case. For the air-oil cases, at superficial liquid velocities higher than 50 cm/s, the liquid film thickness trend is affected by the liquid droplet entrainment. Furthermore, it was found that the liquid droplet entrainment increases as the superficial liquid velocity increases or the surface tension decreases. Details of the liquid droplets traveling in the gas core, wave formation, wave breakup and film thickness evolution are observed in the WMS phase reconstruction.
Micro/Nano-Particle Deposition in the Airway of a 6-Year-Old Child From Nostril to the Third Generation
Authors: Keshavarzian Erfan , Ghalati Pejman Farhadi , Abouali Omid , Ahmadi Goodarz , Bagheri Mohammad Hadi
Published: July 2013

In the present study the transport and deposition of micro/nano-particles in the airway model of a 6 year-old girl was investigated. The realistic airway model includes the nasal cavity, larynx, pharynx, trachea and also bronchial airways up to third generations. This model was developed from a series of high resolution CT scan images. For low to moderate activities, the steady airflows through the entire model of the child’s upper airway passages were simulated. Micro particle trajectories and deposition in the range of 1–30 μm were evaluated using a Lagrangian tracking approach and Eulerian method was used to assess the deposition rate of the nano-particles in the range of 1–150 nm. The deposition of micro and nano-particles in the airway of a child was evaluated and the results were with those for the adults and the differences were discussed. As was expected, a higher breathing resistance was observed for the 6-year-old child compared to adults, which leads to a higher particle deposition rate. The results of this study for the flow field and micro/nano-particle deposition showed the important differences between children and adults. Therefore care should be given to reduce the risk of airborne toxicants on infants and children.
The Interior Design of a 40% Scaled DrivAer Body and First Experimental Results
Authors: Mack Steffen , Indinger Thomas , Adams Nikolaus A. , Blume Stefan , Unterlechner Peter
Published: July 2013

This report addresses the interior design of a 40% scaled wind tunnel model of a generic medium-sized car geometry — the so-called DrivAer body. The model was designed for being investigated inside the wind tunnel facility at the Technische Universität München, which was recently upgraded by a single-belt ground simulation system. The wind tunnel model is very modular: it features several exchangeable parts, such as three exchangeable rear ends, three different underbody configurations, and different wheel rim geometries. In addition to this, the engine compartment is equipped with a model heat exchanger to adjust the mass flow rate through the underhood area. Apart from the model itself, we would also like to introduce some of the measurement equipment that we used during our wind tunnel tests, for example a set of five independent force balances. Furthermore, a method to account for the falsifying rolling resistance of the wheels is shown. Finally, results of experiments to determine the aerodynamic drag generated at the front and the rear axes of the vehicle will be discussed and a small data base of drag values for various vehicle configurations will be provided.
Modeling and Simulation of Multiple Bubble Entrainment and Interactions With a Traveling Vortex Ring
Authors: Cihonski Andrew J. , Finn Justin R. , Apte Sourabh V.
Published: July 2013

Bubble interactions with vortical structures are important to better understand the mechanisms of bubble induced boundary layer drag reduction and chemical mixing. Traditionally, many studies of disperse bubble or particle-laden flows have utilized an Euler-Lagrange two-way coupling approach, wherein the dispersed phase is assumed subgrid and its dynamics is modeled. In this work, results on full three-dimensional simulation of traveling vortex ring together with a few microbubbles are presented utilizing a volumetric coupling approach, wherein the displaced mass due to the presence of the bubbles is accounted for by using mixture theory based conservation laws in an Euler-Lagrange formulation. It is shown that the volumetric coupling approach is necessary to reproduce the experimental observations of Sridhar & Katz, JFM (1999). Experimental work by S&K on bubble entrainment into a traveling vortex ring has shown that the settling location of the bubble relative to the vortex core can be well predicted based on the ratio of the buoyancy force to the hydrodynamic pressure gradient. Additionally, the experimental results find that even at low volume fractions, bubble injection can significantly affect the structure of the vortex core. The two-way coupling model, wherein the fluid displacement due to bubble motion is neglected, of bubble-laden flows is unable to capture these effects on the vortical structure.
Numerical Simulation and Control of the Flow Around One or Two Ahmed Bodies
Authors: Bruneau Charles-Henri , Creusé Emmanuel , Depeyras Delphine , Gilliéron Patrick , Mortazavi Iraj
Published: July 2013

The aim of this work is to show that the drag coefficient of a bluff body is mainly linked to the circulation and the distance of the vortices in the close wake of the body. Thus an active control can be used to push away the vortices to decrease the pressure forces at the back. For the size of the vortices a passive control by means of porous layers is used taking benefit of the Kelvin-Helmholtz instability to change the vortex shedding. For two bodies with a short distance between them, the presence of strong vortices in the wake of the first body changes significantly the pressure force in front that governs the drag of the second body. The results of the control processes are illustrated on a single Ahmed body and on two Ahmed bodies following each other on top of a road.
Flow Structure Above Stationary and Oscillating Low-Aspect-Ratio Wing
Authors: Visbal Miguel R. , Garmann Daniel J.
Published: July 2013

Computations have been carried out in order to describe the complex unsteady flow structure over a stationary and plunging aspect-ratio-two wing under low Reynolds number conditions (Rec = 104). The flow fields are computed employing a high-fidelity implicit large-eddy simulation (ILES) approach found to be effective for moderate Reynolds number flows exhibiting mixed laminar, transitional and turbulent regions. The evolution of the flow structure and aerodynamic loading as a function of increasing angle of attack is presented. Lift and pressure fluctuations are found to be primarily dominated by the large scale circulatory pattern established above the wing due to separation from the leading edge, and by the inherent three dimensionality of the flow induced by the finite aspect ratio. The spanwise distribution of the sectional lift coefficient revealed only a minor direct contribution to the loading exherted by the tip vortex. High-frequency, small-amplitude oscillations are shown to have a significant effect on the separation process and accompanying loads suggesting potential flow control through either suitable actuation or aero-elastic tailoring.
A Methodology for Geometry Generation of the Lower Conductive Zone of the Lung Airways and Simulation by Intermediate Boundary Conditions
Authors: Tena Ana F. , Casan Pere , Barrio Raúl , Marcos Alberto , Parrondo Jorge
Published: July 2013

This paper presents a general methodology for the development and simulation of a human lung between scales 0–16. The methodology is based on the simulation of only one of the two possible branches at each bronchiole. The operation of the truncated branches is included by means of a user-defined function. This function prescribes the velocity profile calculated for the active branches in the truncated ones in order to make the hydraulic losses equal between them. This procedure was tested between 0 and 7th generation by imposing the time profile of a real forced spirometry test in the trachea as boundary condition. The test showed a very good agreement between the numerical predictions and the spirometry data.
Statistical Procedure to Obtain Accurate Time-Resolved Measurements in Turbomachinery Environments Using Fast-Response Probes
Authors: Fernández Oro Jesús Manuel , Argüelles Díaz Katia María , Rodríguez Lastra María , Galdo Vega Mónica
Published: July 2013

Fast-response probes in multistage turbomachinery are typically used to measure unsteady flows and turbulence in a number of traverse locations throughout the machine (rotor-stator inter-regions, inlet and outlet sections, tip clearance gaps…). When used intensively, they provide complete information of time-resolved flow structures, including wake patterns, wake mixing, wake-wake and rotor-wake interactions or turbulence transport in 2D planes and even 3D pictures if the raw signals are post-processed accurately.

The segregation between deterministic, unsteady features and turbulent scales is essential to understand the unsteady mechanisms responsible for the energy transfer and requires an accurate selection of the sampling frequencies and the total length of the measured traces to assure a valid statistical reduction. Similar considerations must be made if they are filtered in a frequency basis (for example, filtering low-scale turbulence or extracting only BPF components), employing well-designed periodograms or power spectra with minimum scatter and large periods of time integration.

This work presents the general guidelines that any statistical procedure must follow to assure that phase-locked averaging results are consistent when applied to velocity signals in multistage turbomachinery. The procedure is established in terms of convergence (residuals) and coherence (error) between time-resolved traces retrieved using different sampling frequencies and number of total samples. The possible effects of three-dimensionality, the measured regions (hub, tip, midspan) or the sensibility to turbulence levels is also explored.

The proposed methodology is applied to a low-speed axial fan, so a concise survey of usual practices employed by other authors in the literature is firstly reviewed, in order to identify fundamental parameters and values typically adopted to guarantee convergence. Finally, recommendations are made as a function of the variable analysed, the wake pattern to be described or the global disorder of the flow structures inside axial flow fans.