bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalizing Prediction of Bluff Body Aerodynamic Load Maps
Authors: Pirau Sorin , Liberi Brandon , Barbely Natasha , Komerath Narayanan
Published: November 2015

The Continuous Rotation method enables efficient definition of all aerodynamic load components on bodies of arbitrary shape for arbitrary attitudes. This is applied to several bluff body shapes including cylinders, a cuboid, a flat plate and a porous box. Rate effects and unsteadiness are shown to be negligible using a cylinder of aspect ratio 1. The genesis of the side force on the yawed cylinder, and the differences between rough and smooth cylinders, are derived from comparisons between experiments and diagnostic computations with an unsteady Navier-Stokes solver. Interpolating Fourier coefficients of the azimuthal load variation appears to be viable to generalize loads on cylinders of varying aspect ratio. A large variation is seen for aspect ratio 0.5 to 1, with a more gradual transition to ‘high aspect ratio’ features beyond aspect ratio 2.
Improving Student Readiness for Inquiry-Based Learning
Authors: Milanovic Ivana , Eppes Tom
Published: November 2015

We document the four-year long experience aimed at improving student readiness to engage in research. A key ingredient has been the development of a multidisciplinary modeling course that integrates four teaching and learning strategies. Preceded by two sets of scaffolded projects, the course culminates with an inquiry-based learning (IBL) assignment on a topic that is relevant and supported by mentoring. Benefits include the development of modeling skills marketable to external entities, presentations at the University colloquia and symposia, peer-reviewed conference or journal papers, and application software releases. This paper describes the course structure, its evolution over time to meet various challenges, and provides examples of student work.
Spent Flow Effects of Multiple Micro-Jet Impingement Cooling Models
Authors: Husain Afzal , Al-Azri Nasser A. , Samad Abdus , Kim Sun-Min , Kim Kwang-Yong
Published: November 2015

The current study investigated comparative performance of wall-confined and unconfined multiple micro-jet impingement heat sink models for electronic cooling applications. The pressure-drop and thermal characteristics were determined for steady incompressible and laminar flow by solving three-dimensional Navier–Stokes equations. Several parallel and staggered micro-jet configurations consisting of a maximum of 16 jet impingements were tested. The effectiveness of various micro-jet configurations, i.e., inline 2×2, 3×3 and 4×4 jets, and staggered 5-jet and 13-jet arrays with nozzle diameters 50, 76, and 100 μm, were analyzed at various flow rates for the maximum temperature-rise, pressure-drop and heat transfer coefficient characteristics. Two design parameters, the ratio of jet diameter to height of the channel and jet distribution, were chosen for comparative performance analysis.
In-Situ Visualization of Evaporation Induced Self-Assembly Phenomena of Nanofluids Detecting the Interfacial Surface Plasmon Reflectance
Authors: Kim Iltai (Isaac) , Kihm Kenneth David
Published: November 2015

Innovative optical techniques based on nano-biophotonics such as surface plasmon resonance (SPR) imaging and R-G-B natural fringe mapping techniques are developed to characterize the transport and optical properties of nanofluids in situ, real-time, and full field manner. Recent results regarding the characterization of nanofluids are summarized and future research directions are presented.

47 nm Al2O3 nanoparticles are dispersed in water with various concentrations. Al2O3 nanofluids droplets are placed on substrates and evaporated in room temperature. In-situ visualization of evaporation-induced self-assembly is conducted to detect concentration, effective refractive index, and different self-assembled pattern including cavity with various nanofluids concentrations and surface hydrophobbicities with SPR and fringe mapping.

During the evaporation, time-dependent and near-field nanoparticle concentrations are determined by correlating the SPR reflectance intensities with the effective refractive index (ERI) of the nanofluids.

With increasing the concentrations of nanofluids, the existence of hidden complex cavities inside a self-assembled nanocrystalline structure or final dryout pattern is discovered in real-time. R-G-B natural fringe mapping allowed the reconstruction of the 3D cavity formation and crystallization processes quantitatively. The formation of the complex inner structure was found to be attributable to multiple cavity inceptions and their competing growth during the aquatic evaporation.

Furthermore, the effect of surface hydrophobicity is examined in the formation of hidden complex cavities, taking place on three different substrates bearing different levels of hydrophobicity; namely, cover glass (CG), gold thin film (Au), and polystyrene dish (PS).

These surface plamson resonance imaging and natural fringe mapping techniques are expected to provide a breakthrough in micro-nanoscale thermal fluids phenomena and nano-biochemical sensing when coupled with localized surface Plasmon and metamaterials techniques.
A Combined Numerical and Experimental Study of Air Bubble Dynamics in Converging Section of Effervescent Atomizer
Authors: Law Deify , Shepard Thomas , Wardi Ibrahim
Published: November 2015

Inside of an effervescent atomizer gas is injected into a liquid cross-flow in order to produce a bubbly two-phase mixture. The presence of gas bubbles leads to enhanced liquid break-up as compared to simple pressure atomization of the liquid phase alone [1]. In the present work, the dynamic shapes and sizes of single air bubbles injected in liquid water cross flow of an effervescent atomizer’s mixing chamber are investigated numerically and experimentally. Particular focus is aimed on the convergent channel section just prior to the atomizer exit orifice where the bubble experiences a significant drop in pressure. Volume of fluid (VOF) modeling and simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT and further provide information on the liquid velocities near the air bubble. A high-speed imaging system and digital image processing are used for capturing experimental data on this highly dynamic process. The numerical results are compared with experimental visualizations to better understand the physical interactions between the two phases approaching the atomizer exit.
Study on the Characteristics of Turbulent Flow of Viscoelastic Fluid Through a Planar Sudden Expansion by PIV System
Authors: Wang Lu , Bao Jia-Qi , Wei Tong-Zhou , Cai Wei-Hua , Li Feng-Chen
Published: November 2015

The influences of drag-reducing surfactant additives on the characteristics of a turbulent flow over a planar sudden expansion with expansion ration R = D/d = 3 and aspect ratio A = w/h = 30 were experimentally investigated by a 2D-2C (two dimensional-two component) particle image velocimetry (PIV) system. The 2D-2C velocity fields in the streamwise-wall-normal planes (x-y planes) at three spanwise locations are measured for the flows of water and 50ppm aqueous solution of CTAC/NaSal (CTAC: cetyltrimethyl ammonium chloride; NaSal: sodium salicylate) under the Reynolds number of 1.85 × 104. From the streamline in the x-y plane, it is observed that the reattachment lengths of the vortices in CTAC/NaSal solution are longer. Then the mean streamwise velocity fields and the apparent flow rate at three spanwise locations show that the flow fields in the other two x-y planes are practically symmetrical about the x-y centreplane in CTAC/NaSal solution, as compared with that in water flow. Finally, it is perceived that the Reynolds shear stress for three spanwise locations in CTAC/NaSal solution are obviously decreased.
Computational Fluid Dynamic Analysis of a Blood Pump: An FDA Critical Path Initiative
Authors: Nassau Christopher J. , Wray Timothy J. , Agarwal Ramesh K.
Published: November 2015

Computational Fluid Dynamics (CFD) has become a routine tool in recent times for use in blood-contacting medical device design and analysis, such as prosthetic heart valves and ventricular assist devices (VADs). While CFD can aid in design by decreasing the need for expensive prototyping and iterative laboratory testing, standardizations are not currently available for CFD to be used for medical device safety analysis at the preclinical stage. To address this, the U.S. Food and Drug Administration (FDA)’s Center of Devices and Radiological Health (CDRH) has sponsored CFD “round-robins.” This paper focuses on Computational Round Robin #2 – Model Blood Pump. The exact geometries, flow conditions and fluid characteristics for the CFD analysis have been supplied to the participants. In the CFD analysis presented in this paper, a rotating fluid zone around the pump impeller was used to avoid the complexities of a dynamic mesh. The rotating fluid zone was modeled by including the centrifugal and Coriolis forces in the Navier-Stokes equations. The Shear Stress Transport (SST) k-ω turbulence model was used and the steady-state solutions for the desired flow conditions were calculated. Current experimental data is still being collected by FDA for the flow conditions given in the study. However, some of the pump operating characteristics are available from work of other investigators and are used to validate the CFD results.
Numerical Simulation of the Virtual Maxillary Sinus Surgery Effects on the Heat Transfer in Human Nasal Airway
Authors: Shaghaghian Sana , Naseri Arash , Abouali Omid , Ahmadi Goodarz
Published: November 2015

Uncinectomy and middle meatal antrostomy (MMA) in the maxillary sinus surgery mainly affects the airflow pattern in this sinus. The aim of the present work was to analyze the effect of this surgery on the heating and humidifying function of the nose. A series of CT scan images of a healthy male volunteer was used and a computational model for the human nasal airway including nasal cavity and maxillary sinuses was developed. Then, uncinectomy and MMA was performed virtually on the CT images on a single nasal passage and associated maxillary sinus. The continuity, momentum, energy and moisture transport equations were solved numerically. In particular, a thermal model for evaluating the temperature and moisture distribution on the mucus surface covering the walls of the nasal airway was developed. A steady breathing flow rate related to the rest conditions was investigated, where different relative humidity levels for the ambient air were considered. The airflow pattern, temperature and moisture concentration contours for pre- and post-surgery cases were evaluated and their differences were discussed.
Divergence Speed Prediction for Practical Slung Load Shapes
Authors: Liberi Brandon , Ton Chau , Komerath Narayanan
Published: November 2015

Given the innumerable combinations of flight vehicles, loads and flight conditions, alternatives are sought to flight testing, to certify the safe flight speed with slung loads. With well-resolved airload maps now feasible for arbitrary shapes as analytical functions, dynamic simulation predicts divergence speeds, regardless of the symmetry of the object. Likely modes of amplification are found using wind tunnel experiments with free-swinging objects. A robust control formulation enables safe flight close to divergence speed where the flight control system can prevent disturbance amplification.
Experimental and Measurement Uncertainty Associated With Characterizing Slurry Mixing Performance of Pulsating Jets at Multiple Scales
Authors: Bamberger Judith Ann , Piepel Greg F. , Enderlin Carl W. , Amidan Brett G. , Heredia-Langner Alejandro
Published: November 2015

Understanding how uncertainty manifests itself in complex experiments is important for developing the testing protocol and interpreting the experimental results. This paper describes experimental and measurement uncertainties, and how they can depend on the order of performing experimental tests.

Experiments with pulse-jet mixers in tanks at three scales were conducted to characterize the performance of transient-developing periodic flows in Newtonian slurries. Other test parameters included the simulant, solids concentration, and nozzle exit velocity. Critical suspension velocity and cloud height were the metrics used to characterize Newtonian slurry flow associated with mobilization and mixing. During testing, near-replicate and near-repeat tests were conducted. The experimental results were used to quantify the combined experimental and measurement uncertainties using standard deviations and percent relative standard deviations (%RSD) The uncertainties in critical suspension velocity and cloud height tend to increase with the values of these responses. Hence, the %RSD values are the more appropriate summary measure of near-replicate testing and measurement uncertainty.
OpenFoam Simulations of Flow Over Flapping Wing Using Parallel Computing
Authors: Oler Adam M. , Zhang Ning
Published: November 2015

Numerical simulations of flow over a flapping wing were conducted in this research using OpenFoam. The research aims to understand the aerodynamics of the perching motion of an SD7003 airfoil as well as the parallel performance of OpenFoam package on simulations of moving boundary problems. Multiple levels of nested grid were used, and the moving mesh method was utilized to implement the motion of the airfoil. In order to validate the accuracy of the simulation, a previously published perching motion case was tested and the results were compared to literature data. The results agree reasonably well with the compared data. Different perching motions were then implemented. One perching motion was linear and one was modified by a smoothing function controlled by a sharpness factor. Two Reynolds numbers were used in the study, 500 and 5000, and the Reynolds number effects were also investigated.
Effect of Pipe Inclination on Void Fraction of Two-Phase Gas-Liquid Flow
Authors: aus der Wiesche Stefan , Kapitz Marek
Published: November 2015

Void fraction correlations are widely available in the literature for two-phase gas-liquid flows in pipes, but no general consensus exists with regard to the effect of pipe inclination. By means of an air-water two-phase flow test setup employing quick-closing valves, the pressure drop and the void fraction were systematically measured for various pipe inclinations and volume flow rates. Both mean values and standard deviations were recorded. The experimental data were compared with predictions of representative correlations recommended in the literature. It is found that void fraction predictions of drift-flux models were in excellent agreement with the present measurements.
1-D Modeling of the Denebulization of Fogs by Hygroscopic Seeding
Authors: Reuge Nicolas , Fede Pascal , Berthoumieu Jean-François , Foucoin Florian , Simonin Olivier
Published: November 2015

The purpose of the study is the modeling of the denebulization of fogs by micronic hygroscopic particles from the initial seeding to the fall of the rain droplets on the ground. The microparticles generated by flares are made of hygroscopic salts. Three stages occur: first, the condensation of water vapor on solid particles, this is the deliquescent stage which is very fast and can be ignored by the model, then the stage of condensation of water vapor on liquid salted particles / evaporation of fog droplets and finally the coalescence stage when the liquid salted particles diameter become large enough. Three different salts have been tested: NaCl, CaCl2 and KCl. The 1-D modeling approach studied considers the conservation equations (salt mass, water mass, salted droplets number density, fog droplets number density), the hygroscopicity of the salts through the water activity in the aqueous solution and the coalescence induced by gravity.

The model reveals that NaCl is the most efficient salt because of its stronger hygroscopicity at high dilution rates although CaCl2 is the more hygroscopic at low dilution rates. A cloud of NaCl particles of 9 μm diameter initially generated over a height of about 7 m with a number density of 12 cm−3 allows to completely dissipates a typical fog layer of 40 m within less than 13 mn. This means that 10 kg of NaCl particles could be able to clear such a fog over 13.25 ha. The model shows that a layer of 100 m can be cleared within 29 mn. From the calculations, the contribution of the coalescence to the denebulization process is less than 1%, phenomena of condensation / evaporation are preponderant for these operating conditions.
Investigation of the Effects of Wetland Vegetation on Coastal Flood Reduction Using Hydrodynamic Simulation
Authors: Kumar Yadav Pawan , Thapa Sandesh , Han Xiao , Richmond Cecilia , Zhang Ning
Published: November 2015

Storm surge flood is a major threat to the inhabitants of Southwest Louisiana and to the health of the marshes in the area. Knowledge of potential impacts from a flood allows expedited response and recovery. In order to predict the flooding coverage and damage to the wetlands, hydrodynamic simulation of the flooding event has to be conducted. The target model area is Calcasieu Lake and its surrounding wetlands. The wetlands around Calcasieu Lake are covered by marsh grasses. The presence of these marsh grasses have significant effects on the friction of the flooding water, the size of the total flooded area, the speed, and the distribution of the flooding water. In this study, measured grass information was utilized and incorporated into the hydrodynamic model. A comparison between with and without vegetation models was conducted and the effect of the grasses in the target area was revealed.
Axi-Symmetric Multi-Size Particulate Flow Simulation Model of a Hydrocyclone
Authors: Pagalthivarthi Krishnan , Furlan John , Visintainer Robert
Published: November 2015

An axi-symmetric multi-size particulate Eulerian-Eulerian flow simulation model of a hydrocyclone is presented in this paper. Finite volume formulation on a collocated grid is implemented. The broad particle size distribution is divided into a specific number of size classes. The air core diameter is estimated using empirical correlations. Pure carrier eddy viscosity field (computed using a mixing length model) is modified to account for the presence of multi-size particles. The computed pressure drop, particle size distribution (PSD) of the overflow and underflow, separation efficiency curve and cutsize diameter obtained from the numerical solution are compared with experimental results.
Physical and Mathematical Modeling of Solid-Liquid Flow at High Bed Shear in Steep Flume
Authors: Matoušek Václav , Zrostlík Štěpán , Krupička Jan , Picek Tomáš , Bareš Vojtěch
Published: November 2015

The paper discusses new results of our experimental- and mathematical modeling of sediment-laden open-channel flows in the upper plane bed regime associated with intense transport of sediment. Our recent studies showed that bed-load transport and bed friction are interrelated and classical formulae for bed friction (Nikuradse formula) and bed-load transport (Meyer-Peter and Muller formula) need to be modified to account for the intense transport of sediment.

The new results of our laboratory experiments in a tilting flume are presented and analyzed for different sediment fractions. The analysis is focused on the effect of solids density and size on the solid-liquid flow characteristics as the solids flow rate, flow depth, and bed slope for certain flow rate of water in a channel of given geometry. The experimental results are compared with outputs of our mathematical model simulating the observed phenomena. The simple 1-D model combines hydrodynamic- and sediment-transport equations and enables to use different transport- and friction formulae to predict the solids transport, flow depth and bed slope under the condition of (pseudo-) uniform flow of solid-water mixture in the open channel.
Simulation of Forward Osmosis Flow in a Two-Dimensional Asymmetric Membrane Channel With Draw Channel Circular Baffle Implementation
Authors: Koch James R. L. , Agarwal Ramesh K.
Published: November 2015

Forward Osmosis (FO) driven asymmetric membrane filtration is a developing technology which shows promise for seawater desalination and wastewater treatment. Due to the fact that asymmetric membranes are widely used in conjunction with this technology, internal concentration polarization (ICP), a flow-entrainment effect occurring within such membranes, is a significant if not dominant source of overall osmotic pressure loss across the membrane. Accurate modeling of ICP effects is therefore very critical for accurate Computational Fluid Dynamic (CFD) modeling of asymmetric membranes. A related, dilutive effect known as external concentration polarization (ECP) also develops on both the rejection and draw sides of the membrane, further contributing to osmotic pressure loss. In order to increase the overall water flux, circular spacers can be implemented within the draw channel of FO cross-flow membrane exchange units to decrease the effects of ICP and draw ECP. The drawback of spacer inclusions is an increased pressure loss across the length of the feed channel. The system efficiency gained by the decrease in ECP must therefore be weighed against the energy cost of hydraulically making up lost channel pressure. To model the geometry of a FO cross-flow channel, the open source CFD package OpenFOAM is used. A compressible flow model with explicit boundary conditions is developed to simulate the flux transfer and ICP effects present within an asymmetric membrane when exposed to a NaCl solution. Results are validated by comparison with the numerical data generated by earlier models of asymmetric membranes implemented by other investigators using similar simulation conditions.
Numerical Study of Vortical Separation From a Three-Dimensional Hill Using Eddy-Viscosity Models
Authors: Chitta Varun , Jamal Tausif , Walters Keith
Published: November 2015

Turbulent flow over an axisymmetric hill is highly three-dimensional (3D) due to the presence of both streamwise and spanwise pressure gradients. Complex vortical separations and reattachments of the turbulent boundary layer are observed on the lee side, accurate prediction of which presents a demanding task for linear eddy-viscosity models (EVMs) when compared to attached boundary layer flows. In this study, an axisymmetric hill is investigated using three Reynolds-averaged Navier-Stokes (RANS) models — fully turbulent model (SST k-ω), transition-sensitive model (k-kL-ω), and a new four-equation model (k-kL-ω-v2). The new model is designed to exhibit physically correct responses to flow transition, streamline curvature, and system rotation effects. The test case includes a hill mounted in a channel with hill height H = 2δ, where δ is the approach turbulent boundary layer thickness. The flow Reynolds number (Re) based on the hill height is ReH = 1.3 × 105. Computational fluid dynamics (CFD) simulation results obtained using the new model are compared with the other two RANS models and with experimental data. Improved mean flow statistics are obtained using the new model that match well with the experiments. The results from this study highlight the need for a model that is able to resolve both flow transition and streamline curvature effects over blunt/curved bodies with reasonable engineering accuracy and computational cost.
A Reduced Order CFD Method for Preliminary Design Analysis of Pumps
Authors: Börjesson Tomas , Burman Jörgen
Published: November 2015

The need for fast and reliable analysis of preliminary pump designs exists. Traditionally this analysis has been performed with streamline-curvature throughflow methods or similar inviscid methods. In this paper a newly developed Reynolds-Averaged Navier-Stokes (RANS) CFD solver for preliminary pump design analysis is described. The solver will serve as a reduced order method, although of a higher order than the streamline-curvature throughflow method, still being fast and reliable and without having to revert to the full 3-D viscous CFD analysis at the early stage of the design process. The new quasi 3D code has two general solver modes, the throughflow (r-z plane) and blade to blade (m’-theta plane), respectively. With the new solver the well known limitation, not allowing for reversal flows, of the traditionally used streamline-curvature throughflow method does not exist due to its formulation. This allows for more realistic off design flow predictions. The RANS solver uses the artificial compressibility method to drive the solution to the incompressible limit and being an implicit unstructured solver allows for fast turnaround time and handles additional compartments, seal cavities and impeller sidewall gaps etc., connected to the blade passage with ease. Both solver modes handle multiple components (rotor and stator). In the blade to blade mode unsteady rotor stator interaction can be performed with the aid of dual-time stepping, moving mesh and non-conformal sliding interfaces. Strengths and shortcomings of the solver are discussed together with validation examples taken from many pump types. These examples show that the solver is an attractive tool for preliminary design analysis.
Efficiency Upgrade of a Double-Case Pump Using CFD-Based Design Optimization and Scaled Model Tests
Authors: van der Schoot Martijn , Visser Frank
Published: November 2015

This paper presents a design optimization study of a low specific-speed, multistage, double-case, volute pump. The goal of this study was to accomplish an increase in overall pump efficiency by at least 3.5 percentage points. To that end, each hydraulic internal component of the pump was analyzed to find opportunities for improvement. This was done by performing a combined classical hydraulic evaluation and in-depth Computational Fluid Dynamics (CFD) analysis. The hydraulic assessment gives a good overview if the component is suitable for the desired operating conditions in a relatively quick manner. It is, however, not suitable for detailed understanding of why a certain component is underperforming.

Pump internals typically have a complex three-dimensional shape, which is not taken into consideration when performing a classical analysis. Therefore, a three-dimensional CFD simulation was performed to identify in detail the potential areas for improvement of each component.

Two different strategies were used for optimizing the internal components. The series impeller geometry was optimized automatically by an objective algorithm to obtain optimum performance; other components, including first-stage impeller, series volutes and short crossovers were redesigned by manual design iterations, which were evaluated using CFD. The results show that the distribution of the cross-sectional area in the crossovers had the greatest influence on the efficiency, and due effort was undertaken to optimize this. To validate the efficiency improvement that was predicted by CFD simulations, scaled model tests were conducted on the series stages. The entire design optimization resulted in better performance in terms of efficiency, power and head for the complete flow range.
CFD-Aided Hydraulic Development of a Steam Generator Feed Pump
Authors: Cooper Paul , Schiavello Bruno , Hosangadi Ashvin , McGuire James T.
Published: November 2015

A rerated single-stage, double-suction nuclear reactor steam generator feed pump, rated at 8,850 hp1 for two-pump operation and 13,300 hp for emergency single-pump operation, underwent fluid dynamic design improvements to achieve satisfactory operability and performance, especially at flow rates below the rated flow of 13,865 gpm2 when running at 4850 rpm. An unsteady-flow CFD solution was conducted at 66% of rated flow via an unstructured RANS code called CRUNCH CFD to provide guidance in a) removing axial shuttling of the rotor; and, b) improving the performance curve of head versus flow rate so as to eliminate hydraulic instabilities at flow rates well below the design value, which could lead to excessive pressure pulsations, vibrations, and also the axial rotor shuttling (a). To aid in this effort, steady-flow solutions via the same CFD code were obtained at this and several other flow rates. The as-built diffuser entry throat area between vanes was found to be nearly 10% larger than intended, and the impeller exit throat areas about 4% oversize. Two new diffusers were designed with 14% less throat area than the as-built original diffuser, the difference being in the vane shape and flow-path area distributions. CFD analysis of these two diffusers showed one to have better performance at low flow, enabling it to be chosen without resorting to building and testing both diffusers. Similarly, CFD solutions of two types of pressure-pulsation-reducing “vee” cuts of the impeller OD enabled a choice of which of these cuts should be implemented in the final design — again without test of both cut types. In addition to these improvements, the radial gap between the impeller and diffuser shrouds — called “Gap A” — was reduced by more than half in an effort to isolate the zones adjacent to the impeller from unsteady backflow emerging from the diffuser. The final design incorporating these features was then analyzed via steady-flow CFD, and then the pump was tested at both its rated speeds and operating flow ranges. The test results agreed very closely with this CFD solution. Moreover, the pump achieved satisfactory performance over the flow range of interest, and has demonstrated the same during operation in the power plant.
Dynamic Response Analysis of Balance Drum Labyrinth Seal Groove Geometries Optimized for Minimum Leakage
Authors: Untaroiu Alexandrina , Morgan Neal , Hayrapetian Vahe , Schiavello Bruno
Published: November 2015

Annular labyrinth seals often have a destabilizing effect on pump rotordynamics due to the large cross-coupled forces generated when the fluid is squeezed by an oscillating rotor. In this study several novel groove geometries are investigated for their effect on the rotordynamic coefficients of the labyrinth seal. The groove cavity geometry of a baseline 267 mm balance drum labyrinth seal with a clearance of 0.305 mm and 20 equally spaced groove cavities were optimized for minimum leakage. From the pool of possible groove designs analyzed, nine test cases were selected for maximum or minimum leakage and for a variety of groove cavity shapes. The rotordynamic coefficients were calculated for these cases using a hybrid CFD-bulk flow method. The rotordynamic coefficients obtained by this method were then used with a rotordynamic model of the entire pump to determine the overall stability. Results show that labyrinth seal’s groove shape can be optimized to generate lower leakage rates, while the effects on dynamic properties are only minimally changed. If the seal dynamic response needs to be modified in addition to targeting a lower leakage rate, for instance to exhibit increased damping values, then the leakage rate and the damping coefficient need to be set as objective functions in the optimization loop.
Numerical and Experimental Investigation on the Radial Force Characteristic of a Large Double Suction Centrifugal Pump in a Real Pumping Station
Authors: Yao Zhifeng , Wang Fujun , Zhang Zichao , Xiao Ruofu , He Chenglian
Published: November 2015

The pump operation stability is one of the most important indicators for large discharge pumping stations. Impeller seal rings wear is a key problematic issue. A large double suction centrifugal pump in a real water supply pumping station is numerically and experimentally investigated, of which the seal rings are seriously wore on a fixed location. The pump shaft throws in two orthorhombic directions are measured at flow rates ranging from 0 to 110% of nominal flow rate, as well as the startup and shut down periods. And careful analysis of radial forces under various steady and unsteady conditions is carried out combining with the experimental results. The results show that the value of the shaft displacement obviously increases as the flow rate decreases, especially on the operating conditions with the flow rates below 87% of the design flow rate for the drive end side. The absolute value of the shaft displacement is 0.37mm, which is more than 3 times as large as that at nominal operating condition. There exit a lasting time of large shaft displacements during pump startup and shutdown periods, and the largest value of shaft displacement at the drive end side happens during the pump startup process, which can be increase to 0.95mm. There exists relative large radial force, and the direction of which is exactly the same with the pump shaft displacement at the flow rate from 0.73Qn to 0.32Qn, and also meet the wear locations of the impeller seal rings.
Numerical Study of Pump-Turbine Instabilities Under Pumping Mode Off-Design Conditions
Authors: Ješe Uroš , Fortes-Patella Regiane , Dular Matevž
Published: November 2015

Pumped storage power plants, using reversible pump-turbines, are a great solution to maintain the stability of an electrical network. The continuous operating area of reversible pump-turbines machines is usually delimited by cavitation or a hydraulic instability called hump phenomena at part load. If the machine operates under these off-design conditions, it might be exposed to vibrations and performance losses.

The paper focuses on the numerical analysis of the pumping mode regime and pays special attention to the prediction of the hump shaped characteristic curve and associated rotating stall. The investigations were made on a high head pump-turbine design (nq=27) at model scale for four different guide vane opening angles and a wide range of flow rates. Numerical simulations were performed and analyzed in LEGI and were compared to the global experimental data, provided by Alstom Hydro.
Numerical Simulation and Performance Prediction of Reversible Submersible Tubular Pumping System
Authors: Jin Yan , Liu Chao , Zhou Jiren , Yang Hua , Cheng Li
Published: November 2015

Submersible tubular pump is a kind of horizontal pump with low head and large discharge, which uses the structure of postpositive tubular type with motor and pump coaxial. Nowadays, more and more urban pumping stations need to have the function of irrigation and drainage. In the plain areas, the head of many pumping stations are very low, even only about one meter. Considering the efficiency and practicability, the reversible submersible tubular pump is chosen to realize the function of irrigation and drainage.

Research on three-dimensional flow field in a submersible tubular pumping system using numerical simulation based on the Reynolds time-averaged Navier-Stokes equations and the RNG k-ε turbulent model. By using this method, the performance of pumping system such as head, shaft power and efficiency are predicted based on the calculation of different operating conditions. For verifying the accuracy and reliability of the calculation results, a model test was conducted. The comparison of simulation results and the experiment data shown that the calculation performances close agreement with the experiment results in the high efficiency area, but in the condition of large discharge and small discharge, deviations were existed between the two results. Combining with the numerical simulation and experimental, which can provide more evidences for the hydraulic performance prediction and optimization design of pumping system.
Shut-Off Head Prediction in Single Stage Centrifugal Pumps
Authors: Berten Stefan , Tomasini Filippo , Maurer Wolfgang , Dupont Philippe
Published: November 2015

The prediction of the performance characteristic in centrifugal pumps at flow rates other than the design flow is of high relevance but relatively uncertain.

In the present study, an evaluation of the existing shut-off head prediction methods and an assessment of both, the empirical approach and the numerical simulation are performed. For this purpose, after a review of existing methodologies, the empirical predictions are compared against available statistical data for single stage volute pumps. The CFD study, performed for 3 different single stage volute pumps with specific speeds between nq = 12 and nq = 54 is quantitatively compared against available model test data, which were obtained using precision manufactured hydraulic components.

Several empirical methods from open literature have been reviewed for the shut-off head prediction. An overview of different prediction methods has been presented by Dyson [1], these and an empirical correlation proposed by Guelich have been compared against available data.

The numerical study at shut-off condition requires a full-pump geometry, which also includes long suction and pressure pipes. Unlike several analyses present in the literature (Dyson & Texeira [2], Benigni et al. [3], Liu et al. [4]), which consider the internal leakage flow in the outlet boundary, the shut-off condition is obtained by imposing walls at inlet and outlet boundaries, but leakage flow through the gap between casing and impeller which is essential for the recirculation of the flow is numerically modeled. Because of the unsteady nature of the pressure in the pump volute, a transient simulation is performed and the predicted shut-off head is the average of the whole range of results for a minimum of 10 impeller revolutions.
Effects of Tip Gap Size on the Flow Structure in the Tip Region of an Axial Turbomachine
Authors: Li Yuanchao , Tan David , Chen Huang , Katz Joseph
Published: November 2015

This experimental study examines the effect of tip gap size on the flow structure and turbulence in the tip region of an axial turbomachine. The experiments have been performed in the Johns Hopkins University (JHU) optically index-matched facility using an axial compressor settings designed based on the geometry of the inlet guide vanes (IGV) and the first stage of the Low Speed Axial Compressor (LSAC) facility at NASA Glenn. Two sets of rotor blades with similar cross sections, but with tip gap sizes of 0.49% and 2.3% of the blade chord (or 1.1% and 5.4% of the blade span) have been installed and tested. The measurements include performance tests, visualization of the tip leakage vortex (TLV) using cavitation, and stereo PIV (SPIV) measurements in several meridional planes. Increasing the tip gap size causes a substantial reduction in pressure rise across the machine for the same flow rate. The cavitation images, whose trends agree with the velocity and vorticity distributions obtained by the SPIV measurements, show that TLV rollup in the less loaded blade occurs at later chordwise location, and that the vortex remains located closer to the suction side (SS) corner of the originating blade. The delayed detachment from the blade with increasing gap is attributed to the increase of distance of the ‘image vortex’ (wall interaction) from the TLV. The wider gap also reduces the entrainment by the TLV of the endwall boundary layer after it separates at the point where the backward leakage flow meets the main passage flow. The previously observed TLV breakup, which is evident for the narrow gap in the aft part of the rotor passage, is delayed significantly for the wider gap. Consistent changes also appear in the distributions of turbulent kinetic energy, which peaks in the vicinity of the TLV core, the endwall boundary layer separation, and in the shear layer connecting the TLV center to the SS corner of the blade tip.
Direct Numerical Simulation of the Flow Through a Structured Pebble Bed Near a Wall Boundary
Authors: Fick Lambert , Merzari Elia , Hassan Yassin
Published: November 2015

Packed pebble beds occur in many industrial applications, including the very high temperature and molten salt nuclear reactor design concepts. These designs are currently being researched as possible fourth-generation nuclear power system designs. In order to ensure proper cooling of the reactor cores in these systems during normal operation, as well as under accident conditions, a detailed understanding of the coolant flow behavior is required. Direct numerical simulation (DNS) can be used to simulate specific pebble bed flow and geometry conditions in order to develop high-fidelity fluid flow data and hence improve scientists’ understanding and enhance lower-fidelity modeling.

We have used Nek5000, a spectral-element computational fluid dynamics code, to develop DNS fluid flow data for pebble bed flow, including budgets for the Reynolds stresses. The geometry is a structured pebble bed with a face-centered cubic packing arrangement. The flow domain features periodic boundaries in both streamwise and spanwise directions except for a single bounding wall parallel to the flow direction. In a fully periodic domain, the flow was found to be asymmetric. In this work we focus on turbulence properties in the near-wall region and their effect on the overall flow behavior. A set of preliminary Reynolds-averaged Navier-Stokes calculations was also performed to investigate the effect of geometric parameters such as the distance of the wall from the first row of pebbles.
Multiphase Computation of Cavitation Breakdown in Model and Prototype Scale Francis Turbines
Authors: Leonard Daniel J. , Lindau Jules W.
Published: November 2015

Steady-periodic multiphase Computational Fluid Dynamics (CFD) simulations were conducted to capture cavitation breakdown in a Francis hydroturbine due to large-scale vaporous structures. A reduced-scale model and a full-scale prototype were investigated to display differences in vapor content and machine performance caused by lack of Reynolds and Froude similarity. The model scale efficiencies compared favorably (within 3%) to the experimental cavitation tests. The CFD model and prototype displayed distinct qualitative and quantitative differences as σ was reduced. A stage-by-stage analysis was conducted to assess the effect of cavitation on loss distribution throughout the machine. Furthermore, a formal mesh refinement study was conducted on efficiency and volume of vapor, with three mesh levels and Richardson extrapolation, to ensure convergence.
Cavitation in Submerged Water Jet at High Jet Pressure
Authors: Kang Can , Liu Haixia , Li Xiuge , Cheng Xiaonong
Published: November 2015

Recent industrial applications have unfolded a promising prospect for submerged water jet. Apart from widely acknowledged water jet properties, submerged water jet is characterized by the formation and complex evolution of cavitation bubbles. These bubbles not just alter the flow behavior of submerged water jet but also pose a profound effect upon impinged solid surface. At low jet pressures, some conclusions associated with submerged water jet have been acquired, while studies at high jet pressures have rarely been reported. From today’s view, both numerical and experimental approaches manifest apparent limitations in the presence of high-pressure submerged water jet. Consequently, validation of numerical results cannot be implemented conveniently due to lack of relevant experimental results.

The major purpose of the present study is to explore cavitation features in submerged water jets with jet pressures of 120 and 150 MPa. Numerical techniques are utilized to locate cavitation zone in submerged water jet stream and to delineate cavities as well. Meanwhile, velocity distribution in the jet stream is obtained to calculate jet kinetic energy. Under submerged conditions, bubbles disperse rapidly in ambient water and therefore impede the penetration of incident light. Thus submerged water jet stream cannot be distinguished accurately. Such a difficulty encountered in optical flow measurement and flow visualization for submerged water jet seems insurmountable. Thus experimental efforts are devoted to an interpretation of cavitation effect through examining surface morphology features of the solid sample impinged by submerged water jet. And these features are obtained quantitatively using an optical profiling system.

The results show that the occurrence of cavitation depends largely on the shear effect between fluid layers with different velocity magnitudes. Annular cavity shape is typical for submerged water jets. The existence of cavitation can be maintained within a limited streamwise distance from the nozzle. Furthermore, different jet pressures result in considerably different cavitation severity and effective streamwise lengths of cavity. According to the footprints on the impinged sample surface, it can be concluded that the impingement effect is ascribed to both cavitation effect and jet kinetic energy. The footprint produced on the target surface is in accordance with that predicted with numerical techniques in terms of size and shape. Several important aspects associated with the cavitation phenomenon in the submerged water jet are clarified in the present study.
Optimization of the Rear Propeller Profile of a Counter-Rotating Type Tidal Stream Power Unit Based on CFD Simulation
Authors: Huang Bin , Kanemoto Toshiaki , Kawashima Ryunosuke , Kim Jin-Hyuk
Published: November 2015

In order to convert the kinetic energy of tidal stream, the authors have invented a novel counter-rotating type tidal-stream power unit, which is composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. The commercial code (GH-Tidal Bladed) and academic in-house code (SERG-Tidal) based on blade element momentum theory have been proven well applied to performance prediction for the traditional wind turbine and tidal turbine. However, for the counter-rotating type tidal turbine, it is very difficult to simulate the mutual effect between the tandem propellers using blade element momentum. This paper sets up a CFD model for the counter-rotating type tidal turbine and optimizes the chord and pitch distribution of the rear propeller. The predicted results are compared between the original turbine and optimized turbine, which show great improvement in power efficient after optimization.
Research on Fluid Transmission Performance of Propellant Acquisition Vane Under Microgravity Environment
Authors: Hu Qi , Luo Xianwu
Published: November 2015

Propellant acquisition vane (PAV) is a key part of vane type surface tension tank (STT) and is mostly used to transmit fluid under microgravity environment, its transmission performance will determine fluid management of STT. In present paper, a ribbon type PAV with hems on both sides is conceptually designed, and its transmission performance has been analyzed based on four configuration parameters of its section form, which are flat part breadth, hems’ height, hems’ angle and separation distance between PAV and inner wall of STT. The laws of the effects of four configuration parameters on PAV’s transmission performance have been obtained and a set of most optimized configuration parameters has been given. Then transmission performance of the PAV whose configuration parameters of section form are the set of optimized parameters has been studied in-depth. Our results revealed that the optimized PAV is able to meet orbital demand of gas-free propellant completely during the end of STT’s life under harsh microgravity environment. On the basis of analyzed laws, microgravity environment has been conducted by the hundred meters drop tower tests, so the model test system with PAV is established and the campaigns have as objective to test the PAV’s fluid transmission performance under axial and lateral acceleration conditions. All these analyses and tests have been successfully conducted to demonstrate fluid transmission performance of such a PAV. According to present research, PAV with different section forms influences fluid transmission performance of STT remarkably. Thus, it is an effective way to control liquid transmission velocity by reasonably design of section form of PAV. Present research can not only provide a guideline for optimized design of new-style vane type fluid management assembly, but also present a new way for liquid control in space environment.