bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Schmidt Number on Dynamics of Particle-Driven Gravity Currents
Authors: Chadha Tarun , Kleiser Leonhard
Published: December 2014

Direct numerical simulations (DNS) of particulate gravity currents in a lock-exchange set-up are presented. The effect of the Schmidt number Sc on the current dynamics is analyzed by means of Eulerian-Eulerian simulations. Eulerian-Lagrangian simulations are used as a benchmark for assessing the results of Eulerian-Eulerian simulations. The Schmidt number Sc, the particle properties and the Reynolds number Re are varied. A significant influence of Sc was found, whose magnitude depends on the particle properties (being highest for fine particles) and on Re. For the finest particles used, the deposited particle mass was found to be different by almost 25% when comparing Lagrangian and Eulerian simulations with Sc = 1. The instantaneous flow features like the vorticity field are affected as well. When doubling Re, the effect was still found to be significant for finer particles, though less than that for low Re.
An Experimental Investigation on the Flow Characteristics Over Dimple Arrays Pertinent to Internal Cooling of Turbine Blades
Authors: Zhou Wenwu , Hu Hui , Rao Yu
Published: December 2014

Due to the dimple’s unique characteristics of comparatively low pressure loss penalty and good heat transfer enhancement performance, dimple provides a very desirable alternative internal cooling technique for gas turbine blades. In the present study, an experimental investigation was conducted to quantify the flow characteristics over staggered dimple arrays and to examine the vortex structures inside the dimples. In addition to the surface pressure measurements, a high-resolution digital Particle Image Velocimetry (PIV) system was also utilized to achieve detailed flow field measurements to quantify the characteristics of the turbulent channel flow over the dimple arrays in terms of the ensemble-averaged velocity, Reynolds shear stress and turbulence kinetic energy (TKE) distributions. The experimental measurement results show that the friction factor of the dimpled surface is much higher than that of a flat surface. The measured pressure distribution within a dimple reveals clearly that flow separation and attachment would occur inside each dimple. In comparison with those of a conventional channel flow with flat surface, the channel flow over the dimpled arrays was found to have much stronger Reynolds stress and higher TKE level. Such unique flow characteristics are believed to be the reasons why a dimpled surface would have a better heat transfer enhancement performance for internal cooling of turbine blades as reported in those previous studies.
A Comparative Study of the Dynamic Wind Loads and Wake Flow Characteristics of a Turbine Sited in Onshore and Offshore Wind Farms
Authors: Tian Wei , Ozbay Ahmet , Hu Hui
Published: December 2014

An experimental study was conducted to compare the characteristics of the dynamic wind loads and evolution of the unsteady vortex and turbulent flow structures in the wake of a wind turbine sited in onshore and offshore wind farms. A scaled three-blade Horizontal Axial Wind Turbine (HAWT) model was placed in Atmospheric Boundary Layer (ABL) winds with different mean and turbulence characteristics to simulate the wind conditions in onshore and offshore wind farms. In addition to measuring dynamic wind loads acting on the wind turbine model by using a high-sensitive force-moment sensor unit, a high-resolution digital Particle Image Velocimetry (PIV) system was used to achieve flow field measurements to quantify the characteristics of the turbulent flow in the wake of the wind turbine model. Besides conducting “free-run” PIV measurements to determine the ensemble-averaged statistics of the flow quantities such as mean velocity, Reynolds stress, and Turbulence Kinetic Energy (TKE) distributions in the wake, “phase-locked” PIV measurements were also performed to elucidate further details about evolution of the unsteady vortex structures in the wake flow in relation to the position of the rotating turbine blades. The detailed flow field measurements are correlated with the dynamic wind loads measurements to elucidate underlying physics in order to gain further insight into changes of the dynamic wind loads and wake characteristics behind the wind turbine operating in either onshore or offshore wind farms.
Dynamic Process Modeling on Depressurization by Cooling-Controlled Condensation in a Closed Chamber
Authors: Zhang Bo , He Pengfei , Zhu Chao , Ji Zhiming , Lin Chao-Hsin
Published: December 2014

It has long been realized that condensation in a chamber prefilled with condensable vapor leads to chamber depressurization, and the condensation rate can be cooling controlled. While the final state can be reasonably estimated based on the thermodynamic equilibrium, the dynamic process or rate of depressurization has not been satisfactorily modeled, which is due to the complicated coupling mechanisms of heat and mass transfer, the transient nature of non-equilibrium during the process, the complication by the co-existence of non-condensable gas (NCG) within vapor, as well as the complex geometry and material properties of chamber and cooling device involved. In this paper, we have conducted an experimental study on depressurization by steam condensation onto an internal cooling coil in a steam-prefilled closed chamber. To reveal various parametric effects on the depressurization process, a parametric model consisting of a set of coupled ordinary differential equations has been established, with some simplified assumptions including lumped heat capacity sub-models for chamber walls, cooling coils and the gas phase. To further explore the thermal non-equilibrium characteristics during the process, a simplified and transient simulation of computational fluid dynamics (CFD) is also conducted using FLUENT with user-defined function (UDF) on boundary of condensation. Both parametric and CFD models consider the existence of NCG that is pre-mixed with the vapor as impurity. By comparison with the experimental measurements, both models correctly predict the dynamic and asymptotic characteristics of depressurization with time. The CFD simulation indicates an almost instant equilibrium in pressure within the chamber and yet non-equilibrium in temperature with noticeable temperature gradients over the gas phase. The simplified parametric model provides quick and quantitative assessments of some major parametric effects (e.g., vapor purity, coolant flow rate, and vessel volume) on the rate of depressurization. The detailed mechanistic understanding, gained from proposed models, provides insights essential to the optimized design and operation of the depressurization by cooling-controlled condensation.
Numerical Simulations of Particle-Laden Flow Based on Given Friction Reynolds Number and Mean Reynolds Number Respectively
Authors: Li Zhenzhong , Wei Jinjia , Yu Bo
Published: December 2014

Multiphase flow with particles covers a wide spectrum of flow conditions in natural world and industrial applications. The experiments and the direct numerical simulation have become the most popular means to study the dilute particle-laden flow in the last two decades. In the experimental study, the mean Reynolds number is often adjusted to the value of single-phase flow for each set of particle conditions. However, the friction Reynolds number usually keeps invariable in the direct numerical simulation of the particle-laden flows for convenience. In this study the effect of the difference between given mean Reynolds number and friction Reynolds number was investigated. Two simulations were performed for each set of particle parameters, and the mean Reynolds number and friction Reynolds number were kept invariant respectively. From the results it can be found that the turbulence intensity and the dimensionless velocities are larger when keeping the friction Reynolds constant. And the results calculated from the cases of keeping the mean Reynolds number invariable agree with the experiment results better. In addition, the particle distribution along the wall-normal coordinate was found to be unchanged between two simulation conditions. As a suggestion, keeping the same mean Reynolds number in the direct numerical simulation of particle-laden flow is more appropriate.
The Study of Wing-Rock Motions of Wing/Body Model With Chined Forebody and Their Flow Mechanism
Authors: Deng X. Y. , Shi W.
Published: December 2014

An experimental investigation was conducted to obtain behaviors of wing-rock motions over a wing-body model with a chined fuselage and reveal corresponding flow mechanisms. Free-to-roll technique was used to acquire motion behaviors at fixed angles of attack in a wind tunnel at Reynolds number of 1.87×105. Eight dynamic regimes of uncommanded lateral motions can be divided with increasing angle of attack. There is no lateral motion if the angle of attack is low (in A region, α ≤ 20°) or high (in H region, α ≥ 65°) enough. In the other six regions (from B region to G region), wing-rock motions are mainly generated and developed by the wing vortices evolved with angles of attack, which are induced by chined forebody asymmetric vortices. Some new physical concepts are found and proposed in present paper. There are two kind of asymmetric vortices: one is generated by hydrodynamic instability at large enough angle of attack (α > 20°), which can generate the uncommanded lateral motion, the other is created from symmetric vortices over a model with asymmetric boundary condition (ϕ ≠ 0°), which can’t generate any lateral motions. Non-determinacy of asymmetric vortices over the forebody is at ϕ = 0° only, and if ϕ ≠ 0°, the asymmetric vortices are determinant. Based on those concepts the fluid mechanism of the very complicated uncommanded lateral motions can be analyzed and revealed.
Numerical Modeling of Vertical Axis Wind Turbines
Authors: Parra-Santos Teresa , Gallegos-Muñoz Armando , Rodriguez-Beneite Miguel A. , Uzarraga-Rodriguez Cristobal , Castro-Ruiz Francisco
Published: December 2014

This paper aims to predict the performance of Vertical Axis Wind Turbine (VAWT), hence the modeling of kinetic energy extraction from wind and its conversion to mechanical energy at the rotor axis, is carried out. The H-type Darrieus turbine consists of three straight blades with shape of aerofoil attached to a rotating vertical shaft. The criterion on the selection of this kind of turbines, despite its reduced efficiency, is the easy manufacture in workshops.

A parametric study has been carried out to analyze the camber effect on the non dimensional curves of power coefficient so that the self starting features as well as the range of tip speed ratio of operation could be predicted.
Adaptive Finite Elements Simulation Methods and Applications for Monolithic Fluid-Structure Interaction (FSI) Problem
Authors: Ebna Hai Bhuiyan Shameem Mahmood , Bause Markus
Published: December 2014

Will an aircraft wing have the structural integrity to withstand the forces or fail when it’s racing at a full speed? Fluid-structure interaction (FSI) analysis can help you to answer this question without the need to create costly prototypes. However, combining fluid dynamics with structural analysis traditionally poses a formidable challenge for even the most advanced numerical techniques due to the disconnected, domain-specific nature of analysis tools. In this paper, we present the state-of-the-art in computational FSI methods and techniques that go beyond the fundamentals of computational fluid and solid mechanics. In fact, the fundamental rule require transferring results from the computational fluid dynamics (CFD) analysis as input into the structural analysis and thus can be time-consuming, tedious and error-prone. This work consists of the investigation of different time stepping scheme formulations for a nonlinear fluid-structure interaction problem coupling the incompressible Navier-Stokes equations with a hyperelastic solid based on the well established Arbitrary Lagrangian Eulerian (ALE) framework. Temporal discretization is based on finite differences and a formulation as one step-θ scheme, from which we can extract the implicit euler, crank-nicolson, shifted crank-nicolson and the fractional-step-θ schemes. The ALE approach provides a simple, but powerful procedure to couple fluid flows with solid deformations by a monolithic solution algorithm. In such a setting, the fluid equations are transformed to a fixed reference configuration via the ALE mapping. The goal of this work is the development of concepts for the efficient numerical solution of FSI problem and the analysis of various fluid-mesh motion techniques, a comparison of different second-order time-stepping schemes. The time discretization is based on finite difference schemes whereas the spatial discretization is done with a Galerkin finite element scheme. The nonlinear problem is solved with Newton’s method. To control computational costs, we apply a simplified version of a posteriori error estimation using the dual weighted residual (DWR) method. This method is used for the mesh adaption during the computation. The implementation using the software library package DOpElib and deal.II serves for the computation of different fluid-structure configurations.
Detached Eddy Simulation of High Pressure Diesel Injectors
Authors: Prater Russell , Lian Yongsheng
Published: December 2014

The internal flows of high pressure diesel injectors are simulated numerically in order to investigate the complex transient flow structures and the unsteady forces imparted to the injector needle that result. The gas-liquid two phase flow is modeled using a mixture schematic with the cavitation numerically modeled using the Zwart-Gerber-Belamri model. Both the k-ε model and the detached eddy simulation (DES) model are used and the numerical results are compared. Our study shows that the DES model is able to capture the important unsteady flow features missed by the k-ε model. Our simulation also shows that the injector geometry, specifically the gain orifice, plays an important role in the forces developed on the injector needle.
Effect of Active Control on Under-Expanded Jets
Authors: Goparaju Kalyan , Gaitonde Datta V.
Published: December 2014

In an effort to reduce the aircraft jet noise, control of jets has become one of the highly explored areas. In this work, we examine an underexpanded jet subjected to control with Localized Arc Filament Plasma Actuators (LAFPA) to complement prior results on perfectly expanded flow. High fidelity, Large Eddy Simulations (LES) are employed with a simple model for the actuators, eight of which are placed along the periphery of a Mach 1.2 converging nozzle exit. The axisymmetric mode (m=0) is excited at two different Strouhal numbers of 0.3 (corresponding to the most amplified jet-column mode) and 0.9, based on the exit diameter of the nozzle. Baseline (no control) simulations at two different Reynolds numbers (100,000 and 1.2 million) are also performed. Results indicate a good correlation between the numerical and the experimental results. Undulations are observed in the mean flow, which correspond to the increase and decrease of the flow velocity as the jet traverses the complex shock cell structures generated as a result of the under-expansion of the jet. Baseline simulations at the two chosen Reynolds numbers reveal no significant difference between the two cases indicating that the effect of Reynolds number is negligible. Phase-averaged results, for St=0.3, indicate the presence of large vortical structures generated as a result of amplification of the natural structures due to actuation. Two different kinds of structures are generated corresponding to the switching on and switching off of the plasma actuators. These structures are absent when the flow is actuated at St=0.9. Quantitative near field acoustic analysis is conducted using two-point correlation technique. The qualitative effect of forcing on far-field noise propagation is also investigated.
Development of High Efficiency and Low Noise Cross-Flow Fans for Room Air Conditioner Indoor Unit
Authors: Yamakawa Hironobu
Published: December 2014

Cross flow fans are used for fan systems in a household room air conditioner indoor unit. In recently, in the view of environmental problem and cost saving, energy saving performance is important specification for users. Reducing fan motor electric power consumption is effective for this purpose. And also low noise fans are needed for comfortable circumferences. To meet these user needs, we developed a high efficiency and silent cross flow fan using CFD (Computational Fluid Dynamics) and experiments. In CFD, numerical model is calculated by commercial software using steady state, Reynolds-averaged Navier-Stokes (RANS) and k-ε turbulent flow model. The developed cross flow fan is geometrically characterized by the solidity (the ratio of the blade pitch and blade cord length) distribution, and the blade edge shape. The solidity average of developed fan was larger than the conventional fan and the solidity distribution was smooth. And the developed fan has the sinusoidal shape of the outer diameter edge. This sinusoidal shape edge makes pressure distribution on the tongue to be more dispersed compare to that of conventional straight edge so that tonal noise was restrained.
Droplet Size Characterization for Mist Flow in a Single-Side Heated Vertical Square Duct
Authors: Liu Yao-Hsien , Lin Chia-Cheng , Chen Chiao-Hsin
Published: December 2014

Cooling with mist flow can achieve higher heat transfer rates to meet the cooling requirements in recent industry applications. The mist flow was produced by introducing the dispersed water droplets in the air stream, and was used for cooling a heated surface in a vertical square duct with the hydraulic diameter of 4 cm. Digital image analysis method was developed to obtain the size of the droplets ranging from 20 to 110μm. The digital images were segmented using the optimal threshold gray level for droplets sizing. Droplet size variation subjected to a single-side heated wall with constant heat flux was investigated. Infrared thermography was applied to obtain the surface temperature distribution during the cooling test. The air-water mist flow gave much lower surface temperature compared to the air cooling, and the mean droplet diameter decreased as it flowed over the heated surface.
Thermodynamic Effect on Cavitation in High Temperature Water
Authors: Yamaguchi Yuki , Iga Yuka
Published: December 2014

Thermodynamic effect on cavitation appears in cryogenic fluids, refrigerant and high temperature water. The thermodynamic effect is considered to suppress the development of cavitation and improve the performance of hydraulic machinery. However, the actual appearance degree of thermodynamic effect depends on not only thermal property of each fluid but also each hydraulic machinery and its operating condition. So, the clarification of the influence of the flow field with unsteady cavitation on the degree of thermodynamic effect is necessary. In order to investigate thermodynamic effect, many experiments had been conducted with using cryogenic fluids or refrigerant as working fluids. However, there are some difficulties to visualize cryogenic fluids and the experimental results cannot be directly correlated to the condition without thermodynamic effect in same fluid.

In the present study, in order to conduct cavitation experiments with and without thermodynamic effect in same fluid, high temperature and high pressure cavitation tunnel had been constructed. The working fluid of this tunnel is water and the free-stream temperature can be varied from room temperature to 140 °C. In the present study, NACA 0015 hydrofoil had been chosen as a cavitator.

The extent of thermodynamic effect was estimated through the measurement of temperature in the cavity. The temperature was measured by a thermistor probe which has high accuracy. When the thermodynamic effect appears, temperature depression in the cavity is observed. The maximum temperature depression of cavity about 0.3 K had been measured in water of 80 °C.
Hydrodynamic Forces and DPIV on a Towed Pitching Foil
Authors: Fernandez-Prats R. , Huera-Huarte F. J.
Published: December 2014

More than 90% of the thrust generated by thunniform swimmers is known to be produced by the oscillation of their caudal fin, and the rest by their caudal peduncle. We have designed an experiment in which we can mimic, in a simplified manner, the kinematics of swimmers that mainly use their caudal fin for propulsion. The set-up consists of a rectangular foil attached to a shaft that is controlled by a stepper motor, and the whole assembly can be towed in still water at different controllable speeds. With this system we can study the effect of different types of pitching on the hydrodynamic loads and the performance of the propulsion system. By changing the type of foil, the effects of the flexibility in the propulsion can also be analysed. Hydrodynamic loads were measured with a 6-axes balance, and the flow structures were investigated using a Digital Particle Image Velocimetry (DPIV). Loads and DPIV velocity fields were acquired synchronously.
Effect of Hole Pitch Ratio and Compound Angle on the Thermal Flow Fields of Double-Jet Film Cooling Hole
Authors: Cho Moon-Young , Seo Hyeon-Seok , Kim Youn-Jea
Published: December 2014

In this study, the effect of a row of double-jet film-cooling hole configurations on the thermal-flow characteristics of gas turbine blades was examined. To investigate the effect of the interference of anti-kidney vortices, the ratios of the pitch distance and hole diameter (P/d=5, 6.25, 8.333) were considered with two different compound angles (λ=0°, 4°). The film cooling performance and the generated losses were studied. Then, the relevant mechanisms were identified and explained. A numerical study was performed using ANSYS CFX 14.5 with the shear stress transport (SST) turbulent model. The blowing ratio was kept at a constant value of M=1.5. The film cooling effectiveness and temperature distribution are graphically depicted with various geometrical configurations.
Turbulent Kinetic Energy Budget and Dissipation in the Wake of 2D Obstacle: Analysis of the K-ε Closure Model
Authors: Gamel H. , Salizzoni P. , Soulhac L. , Méjean P. , Marro M. , Grosjean N. , Carissimo B.
Published: December 2014

The prediction of the flow dynamics produced by the interaction between a sheared turbulent flow and a bluff body has important implications in the domain of the wind engineering and for what concerns the simulation of atmospheric dispersion of air-born pollutants.

In this study we present the results of the experimental investigation on the wake of a 2D obstacle, immersed in a neutrally stratified boundary layer flow. Measurements are performed by means of two different techniques, namely Laser Doppler Anemometry and Stereo-Particle Image Velocimetry. These allow us to map the spatial evolution of the velocity statistics up to their third order moments.

The study focuses in particular on the budget of the turbulent kinetic energy (t.k.e.) and the estimate of its mean dissipation rate. The experimental data-set is the basis for a detailed analysis of the reliability and the main limitations of a classical k-ϵ closure model. This has major implication for the numerical simulation of pollutant dispersion in the built environment.
A Comparison of Adjoint-Based Optimizations for Industrial Pipe Flow
Authors: Helgason Eysteinn , Krajnović Siniša
Published: December 2014

This paper presents results from adjoint-based optimization processes applied to an inlet pipe of an exhaust gas recirculation cooler in a diesel engine. The boundary conditions applied resemble those of a truck at cruising speed. Three implementations are considered for the gradient calculations with the objective of minimizing the total pressure drop through the pipe. In the first implementation the gradients are evaluated with respect to the motion of the center of the cell using a newly presented implementation based on the ALE formulation of the Navier-Stokes equations. The results are compared to the surface sensitivities, where the gradient of the cost function is evaluated with respect to the normal motion of the surface of the pipe. In the last approach a topological optimization is performed where the gradients are evaluated with respect to a momentum loss in each cell. This gives information that is used when blocking the cells.
Low Reynolds Number Effect on Open Channel Flow Over a Rib
Authors: Essel Ebenezer E. , Atamanchuk Kathryn , d’Auteuil Samuel , Tachie Mark F.
Published: December 2014

An experimental study was conducted to investigate low Reynolds number effects on open channel flow over a transverse square rib. Particle image velocimetry technique was used to perform detailed velocity measurement in the upstream and recirculation region of a square rib of height, h = 12 mm. The Reynolds number based on the freestream velocity and rib height, Reh = 1510, 2650 and 3950 and the ratio of the boundary layer thickness to step height, δ/h = 2.5 ± 0.2. The results showed that the reattachment length of Reh = 2650 and 3950 increased by 5.7% compared with corresponding value of Reh = 1510. The mean velocities were independent of Reynolds number in the recirculation region but at the reattachment point, Reh = 3650 reduced the streamwise mean velocity and enhanced the wall-normal mean velocity in the region adjacent to the wall. The turbulent kinetic energy beyond the center of the recirculation region increased with increasing Reynolds number.
Wake Analysis and Drag Reduction for a Square Back Ahmed Body Using LES Computations
Authors: Eulalie Yoann , Gilotte Philippe , Mortazavi Iraj , Bobillier Pierre
Published: December 2014

The trend of automotive design induces vertical shape in the region of the rear tailgate, which leads to important aerodynamic losses in the rear back of vehicles. Experimental wake analysis performed behind a square back bluff body shows influence of the vortex transport in the mixing layers backward the detachment region. It is therefore important to carry on studies on turbulent wake understanding in order to find solutions for drag reduction with the current vehicle design. This paper presents LES simulation results computed in order to describe transport of large vortices produced in the 3D wake structure behind a square back bluff body. Prior to this result analysis, we will show comparison with experimental results, helpful to validate these transient computations, performed with different pulsed jets implemented at the top end of the square back, close to the separation zone. Analysis of these computations results will also focus on the relation between amplitude of the flow structure and Cd results.
Reactive Geochemical Flow Modeling With CT Scanned Rock Fractures
Authors: Crandall Dustin , Wen Hang , Li Li , Hakala Alexandra
Published: December 2014

Obtaining quality three-dimensional geometries of fractures in a natural medium, such as rock, is a non-trivial task. This paper describes how several geothermal fractured rocks were scanned using computed tomography (CT), the reconstruction procedure to generate the three-dimensional (3D) geometry of the fractured rock, and the methodology for isolating the fracture from the CT scan. A conversion process to capture the relevant geometric features of the fracture is then discussed. The scanned aperture distribution was then used to simulate the reactive flow and transport processes using a reactive transport code CrunchFlow. The accurate use of CT images in fluid flow models within complex structures allows detailed understanding on how the aperture distribution affects mineral dissolution and fracture property evolution during the EGS process. Our preliminary simulation results show the formation of the preferential flow in zones with larger apertures, which led to higher calcite dissolution rates and even larger aperture size over time in these zones. Because calcite only occupied 10% of the solid phase, its dissolution did not completely open up the aperture because other relatively non-reactive minerals (clay and quartz) remained. The traditional measure of mechanical aperture could not take into account the partial increase in void space in the rock matrix and underestimated the increase in average aperture. The chemical and hydraulic apertures, which explicitly take into account changes in mineral volumes in the rock matrix, relate better to the overall change in the effective permeability of the sample.
Experimental Investigation of Engine Bypass Flow Behavior in the Presence of Surface Heat Exchangers
Authors: Villafañe Laura , Paniagua Guillermo
Published: December 2014

Ongoing engine developments require advanced thermal management technologies to handle the increasing demand of refrigeration and lubrication. As the thermal capacity of the oil lubricant and coolant circuits becomes saturated, cooling sources in addition to the conventional fuel based oil cooling systems are essential for the engine operation. This research is focused in the experimental investigation of the turbofan bypass flow behavior in the presence of finned heat exchangers oriented with the mean flow direction. Engine testing methods alternative to flight testing were developed for this purpose. A new test facility reproducing the engine bypass flow at cruise velocities and take off atmospheric conditions was built to study the flow phenomena. Different measurement techniques were adapted to the requirements of the flow and wind tunnel characteristics. Particular attention was dedicated to the development of a multi-hole probe and a data reduction methodology providing accurate results in a wide angular range at transonic conditions. The flow development along the bypass channel flow was characterized in the presence of different heat exchanger geometries, and compared to the flow development in the absence of heat exchangers.
Foamed Cement Analysis With Computed Tomography
Authors: Crandall Dustin , Gill Magdalena , Moore Johnathan , Kutchko Barbara
Published: December 2014

Foamed cements are widely used for cementing oil or gas wells that require lightweight slurries, gas migration prevention, or wells in high-stress environments. When this manufactured slurry solidifies in the sub-surface environment the distribution of gas voids can affect the resultant strength, permeability, and stability of the wellbore casing. Researchers at the National Energy Technology Laboratory have produced the first high-resolution X-ray computed tomography (CT) three-dimensional images of atmospheric and field generated foamed cement across a range of foam qualities. CT imaging enabled the assessment and quantification of the foamed cement structure, quality, and bubble size distribution in order to provide a better understanding of this cement. Ultimately, this research will provide industry the knowledge to ensure long-term well integrity and safe operation of wells in which foamed cements are used. Initial results show that a systematic technique for isolating air voids can give consistent results from the image data, laboratory generated foamed cements tend to be uniform, and that high-gas fraction foamed cements have large interconnected void spaces.
New Approach for Multi-Rotor Mixed-Flow Pump Design and Optimization
Authors: Tosin Stefano , Friedrichs Jens , Farooqi Rehan , Dreiss Andreas
Published: December 2014

Counter-rotating blade rows in single stage machines have been widely investigated in several applications like naval propulsion [1], axial fan [2] and axial pump design [3]. Previous publications have presented this design philosophy as a promising way to improve efficiency and cavitation performance [4]. Differently the goal of the presented design is to achieve lower required rotational speeds and at the same time a higher power density ratio, indirectly improving also the cavitation’s performance, aspiring actually to a compact design. However, a literature survey did not produce any evidence of significant advantage in axial-flow machines from this design philosophy in terms of machine power density. This paper presents a preliminary analysis of the applicability of the counter-rotating impeller concept on mixed-flow and radial-flow pumps. The design example presented in this paper constitutes a mixed-flow first rotor with a radial second rotor that rotates in opposite direction. A 1-D design model demonstrates that power density coefficient has a maximum for optimum speeds of the rotors range. The design example parameters were selected based on the highest power density coefficient and efficiency. Unlike most published literature where the rotor speed ratios are not fixed, instead the speeds can be independently varied through two separate electric drives. Both the front and rear rotor were developed using multi-streamline curvature analysis which combines fluid dynamic loss model [5] with a slip model at the rotor exit [6]. Several hypotheses were considered to determine the most significant and independent parameters that run through a response surface optimizer tool, scripted in MATLAB®. It detects optimum specific speed for the rotors which maximizes the benefits of counter-rotating impeller design compared to rotor-stator machine with same design point. Assuming steady numerical approximation error, the fitness function of the optimizer tool is based on steady state CFD results. The fitness function depends on total head and hydraulic efficiency, which show a maximum as a result. Optimum geometries were identified and one was chosen for manufacturing and testing in a test rig. Transient CFD analysis was also done to determine volute losses and incidence losses between first and second rotor and pressure pulsations generated. At this stage, manufacturing of hydraulic components of test model is in progress, while the mechanical design of the machine is close to completion.
Turbulent Flow in a Conical Diffuser With a Small Divergence Angle at Reynolds Numbers Less Than 2000
Authors: Reshmin Alexander I. , Trifonov Vladimir V. , Teplovodskii Sergei Kh.
Published: December 2014

Experimental and numerical investigations of a flow in a unseparated conical diffuser with a small tilt angle of the generatrix are carried out. A steady turbulent air flow was delivered at the diffuser inlet through a tube with a diameter ∼0.3 of the diffuser inlet diameter. The velocity and turbulent stresses were measured at the outlet of the diffuser, at 600 < Reout < 3000. A strong influence of the channel expansion on the flow pattern was discovered. In contrast to a tube, where for Re < ∼2000 only laminar flow is observed as steady, at the outlet of the diffuser a turbulent flow is formed for Reout > ∼1000. The formation of a turbulent flow is confirmed by both the results of Reynolds stresses measurements and calculations. While decreasing Reout below ∼1000, flow becomes laminar and turbulent perturbations disappear. For 600 < Reout < 3000 the velocity and the turbulent stresses measured in the diffuser outlet are well described by the three-parameter model of shear turbulence. The same calculations showed, that for Reout > ∼1300 the turbulent flow can be considered as steady, that means that its outlet parameters are almost independent of the conditions at the inlet of the diffuser, if these conditions are sufficient for the formation of a turbulent flow.
Computational Aeroacoustic Analysis of a Heating Coil Within a Ventilation Duct
Authors: Herther Joseph C. , Gent Stephen P.
Published: December 2014

This study computationally investigates the sound generation of air flow through a heating coil within a ventilation duct. Noise sources originating from unsteady flow through the centrifugal fan, heating coil, and ducting are identified with steady RANS techniques using a commercially available CFD solver. Built-in aeroacoustic modules are used to refine the mesh to resolve acoustic frequencies in the computational model. Sound spectral analysis is performed in the near field. With the continued exponential progression of technology, computational numerical models become increasingly more applicable and practical to a larger variety of engineering problems. Traditionally, aeroacoustic analysis has been performed on noise sources such as aircraft. However, more interest into acoustic source modeling in other fields has expanded. For example, wind turbines, automotive sources such as rear view mirrors, HVAC systems, and other noise generating devices. As the population continues to grow it is of interest to characterize the acoustics of HVAC equipment, in the future, to prevent unwanted noise within buildings. Furthermore, the inquiry is to question the practicality of computational aeroacoustic methods, which are known to be computationally intensive, for industrial use in HVAC design.
Code Verification for Multiphase Flows Using the Method of Manufactured Solutions
Authors: Choudhary Aniruddha , Roy Christopher J. , Dietiker Jean-François , Shahnam Mehrdad , Garg Rahul
Published: December 2014

Code verification is the process of ensuring, to the degree possible, that there are no algorithm deficiencies and coding mistakes (bugs) in a computational fluid dynamics (CFD) code. In order to perform code verification, the Method of Manufactured Solutions (MMS) is a rigorous technique that can be used in the absence of exact solution to the problem. This work addresses major aspects of performing code verification for multiphase flow codes using the open-source, multiphase flow code MFIX which employs a staggered-grid and a modified SIMPLE-based algorithm. Code verification is performed on 2D and 3D, uniform and stretched meshes for incompressible, steady and unsteady, single-phase and two-phase flows using the two-fluid model of MFIX. Currently, the algebraic gas-solid exchange terms are neglected as these can be tested via unit-testing. The no-slip wall, free-slip wall, and pressure outflow boundary conditions are verified for 2D and 3D flows. A newly-developed curl-based manufactured solution for 3D divergence free flows is introduced. Temporal order of accuracy during unsteady calculations is also assessed. Techniques are introduced to generate manufactured solutions that satisfy the divergence-free constraint during the verification of the incompressible governing equations. Manufactured solutions with constraints due to boundary conditions as well as due to divergence-free flow are derived in order to verify the boundary conditions. Use of staggered grid and SIMPLE-based algorithm for numerical computations in MFIX requires specific issues to be addressed while performing MMS-based code verification. Lessons learned during this code verification exercise are discussed.
Modelling the Wall Collision of Regular Non-Spherical Particles and Experimental Validation
Authors: Arboleda Brian Quintero , Qadir Zeeshan , Sommerfeld Martin , Beatove Santiago Lain
Published: December 2014

The importance of numerical calculations (CFD) for supporting the optimization and lay-out of industrial processes involving multiphase flows is continuously increasing. Numerous processes in powder technology involve wall-bounded gas-solid flows where wall collisions essentially affect the process performance. In modelling the particle wall-collision process in the frame of numerical computations the general assumption is that the particles are spherical. However, in most practical situations one is dealing with irregular non-spherical particles or particles with a certain shape, such as granulates or fibers. In the case of non-spherical particle-wall collisions in confined flows, additional parameters such as roughness, particle shape and orientation play an important role and may strongly affect the transport behavior. The change of linear and angular velocity of the particle depends on these parameters, specifically the orientation and the radius of impact of the particles. In order to improve the non-spherical particle-wall understanding and modeling, in this work regular non-spherical particle-wall collisions in three dimensions are studied experimentally and computationally. For that purpose, cylindrical particles impacting a smooth wall at different angles are used. Single particle motion is tracked in space solving for both the translational and the rotational motion whereby the orientation of the non-spherical particle is obtained through the Euler angles and the Euler parameters. Once the particle touches the wall, the change of translational and angular velocity is determined by the non-spherical particle wall collision model. Experiments are made by shooting cylindrical non-spherical particles against a smooth plane wall at various impact angles and velocities. The collision event is recorded by two perpendicular arranged high-speed cameras. The experimental velocities obtained are used for validating the model.
Exposure Assessment Analysis of a Heated Breathing Manikin With Rotation in a Displacement Ventilated Room by Numerical Methods
Authors: Keshavarz S. A. , Salmanzadeh M. , Ahmadi G.
Published: December 2014

It is well known that the airflow is instrumental in the transmission of airborne infectious diseases in indoor environments. The airflow pattern in indoor environment is affected by the ventilation airflow, thermal plume around human bodies, human respiration, human motion and other activities. In this study, the CFD approach was used to simulate airflow field and particle transport in a room to provide exposure assessment for a heated breathing manikin with and without rotational motion. The simulation results indicated that the rotation of the manikin significantly impacts the thermal plume of the body and the associated transport of particulates.
Simultaneous Measurements of 3D Flow and Wall Deformation in a Compliant Wall Turbulent Channel Flow
Authors: Zhang Cao , Miorini Rinaldo L. , Katz Joseph
Published: December 2014

This study focuses on the interaction of a turbulent channel flow at Reτ=2310 over a flat, compliant boundary made of PDMS (Polydimethylsiloxane). Two noninvasive optical techniques, namely tomographic PIV (TPIV) and Mach-Zehnder Interferometry (MZI), are integrated to perform simultaneous measurements of the 3D flow field and the corresponding surface deformation. The measurements are performed in a refractive index-matched facility, where the working fluid is aqueous solution of sodium iodide (NaI). The TPIV measurement volume is 30×10×10 mm3 in the streamwise, wall-normal and spanwise directions, respectively. The MZI phase evaluation and unwrapping algorithms have been developed, calibrated and implemented. Preliminary results show qualitative correlation between wall deformation and flow structures near the wall.
Acoustic Sound Source Identification in a Gasoline DI Pump for High Pressure Fuel Flows
Authors: Avireddi Prashanth , Seera Nikhil , Badarinarayan Harsha
Published: December 2014

The passenger class automobiles operating with gasoline direct injection (DI) pump have a better fuel economy than the automobiles operating with gasoline port fuel injection (PFI) pump. The fuel economy is higher because DI pump injects fuel directly into combustion chamber at pressures over 150 bar compared to a PFI pump which injects fuel into combustion chamber through inlet port at pressures over 50 bar. By injecting fuel directly into the combustion chamber, DI system prevents condensation of fuel, pressure leakage and improves atomization of fuel for internal combustion process. However, the disadvantage of high pressure operation is that the DI pump is noisier than a PFI pump. The loud sound in a DI pump is generated due to phenomenon such as high pressure pulsations, liquid jet impact and high velocity flows. To investigate the sound production in a DI pump, High fidelity hybrid numerical simulations were developed using CFD and Acoustic tools to simulate the operational effects and identify the behavior of internal components of DI pump. The fidelity of the numerical simulations depends on the transient boundary conditions and the fluid structure interactions in the DI pump. The CFD simulation model of DI pump has 8 million mesh elements and the simulation model is computed using 256 cores of super computer operating at a rate of 2 TFLOPS. The results derived from the CFD simulations were processed using a commercial acoustics tool for computing sound pressure level in liquid domain. Sound pressure level in liquid domain is used as a relative parameter for distinguishing the behavior of liquid-acoustic sources. The results from the numerical simulations provide a good account of the behavior of internal components in DI pump and the simulation results are in good agreement with the experiments performed on DI pump.
LES of Turbulent Airflow Field and Microparticle Deposition in a Realistic Model of Human Upper Airways
Authors: Ghahramani Ebrahim , Abouali Omid , Emdad Homayoon , Ahmadi Goodarz
Published: December 2014

The Large Eddy Simulation (LES) technique was used to study the turbulent airflow field in a realistic model of human upper airways. The geometric model includes nasal cavity, pharynx, larynx and trachea. The Lagrangian approach was used to calculate the trajectories and deposition of micro-particles for the breathing rate of 60 l/min. The results are compared with those obtained from the RANS model from an earlier study. For the latter model the effect of airflow turbulent velocity fluctuations on particle trajectories was modeled using a Continuum Random Walk (CRW) stochastic model.

A qualitative comparison of the results obtained by the LES method with the earlier RANS model reveals that the total depositions of micro-particles evaluated be these two methods are similar. The LES and RANS predictions for regional depositions, however, differ significantly.
Impact of Micro-Droplets on Superhydrophobic and Hydrophilic Surfaces
Authors: Gomaa Hany , Tembely Moussa , Esmail Nabil , Dolatabadi Ali
Published: December 2014

Ice accretion is a major threat to all exposed structures such as wind turbines, overhead power cables, offshore structures and aircrafts. Such deposition starts by an impact of water droplets of different sizes on the surface of the exposed structure. This work aims to shed more light on the difference in the dynamics occurring upon the impact of microdroplets on substrates with various wettabilities, hydrophilic (aluminum) and Superhydrophobic (Aluminum + WX2100) surfaces. Experiments are conducted on a wide range of diameters, between cloud sized droplets with diameters ranging down to 20μm, and 10 times larger droplets with a diameter of 250 μm. A comparison in the impact (through deformation) results is made all through the wide range and explained using the two extremes. This is done experimentally by analyzing the maximum spread diameter on the hydrophillic surface and superhydrophobic surface and maximum height as a function of time on the hydrophillic surface. Both parameters are visualized experimentally, simulated numerically for the same impact velocities and then results are compared for verification.