bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of the Laminar Boundary Layer Flow on a Rotating Wavy Disk
Authors: Helcig Christian , Teigeler Christian , aus der Wiesche Stefan
Published: December 2016

Since nearly one century, the flow on a flat rotating disk has provided the paradigm for studying rotating flows. For the laminar flow regime, a self-similar solution was obtained by von Kármán [6] in 1921, and a rather special feature of his exact solution of the Navier-Stokes equation is a constant boundary layer thickness not depending on the radial coordinate. A substantial modification of this canonical configuration is given by a wavy disk with a sinusoidal surface shape. Although axis-symmetric, no exact solution for the laminar flow on a wavy disk is known so far. In this study, detailed measurements of the velocity profiles were performed within the laminar boundary layer flow on a wavy disk. Based upon the experimental data, the potential of a self-similar solution approach for describing the resulting flow field was assessed. It was found that such an approach is useful for approximating the far-field solution but systematic deviations were observed in the vicinity of the disk origin.
Effect of Prandtl Number on Convective Heat Transfer in the Separated and Reattached Flow Region on a Blunt Flat Plate
Authors: Helcig Christian , aus der Wiesche Stefan
Published: December 2016

The understanding of the heat transfer in separated and reattached flows is essential for a wide range of engineering applications. The majority of the literature uses air as a working fluid for experimental and numerical investigations. The blunt flat plate configuration offers a generic starting point for flow and heat transfer investigations in separated and reattached flow regions. The present contribution is dealing with experimental measurements of the flow and convective heat transfer within the separated and reattached flow on a blunt flat plate. The blunt plate was placed inside a closed circuit water tunnel. By this approach, in comparison with reliable literature data for air, it was possible to investigate the effect of the Prandtl number on the convective heat transfer of blunt flat plate.
Boundary Condition Effects on Supersonic Rectangular Cavities
Authors: Schmit Ryan F. , Johnson Rudy , Grove James
Published: December 2016

Traditionally, in rectangular cavity research the fundamental physical understanding of cavity resonance is a handful of empirical equations. The authors have recently derived the cavity acoustic wave equation and the cavity hydrodynamic wave equation from Lighthill’s and Curle’s acoustic analogy wave equations. By changing the cavities boundary conditions with half span doors, in both doors open and one door closed configurations, the resulting pressure spectrum changes are attributable to the boundary condition changes and can capture the large frequency shift differences due to the door configuration changes. These results suggest these derived cavity wave equations are correct.
Coalescence Prevention Algorithm for Level Set Method
Authors: Talley Matthew L. , Zimmer Matthew D. , Bolotnov Igor A.
Published: December 2016

The application of interface tracking methods to bubbly flow modeling has grown in recent years due to improvements in computing performance and development of more efficient solvers. However, the standard formulation of most interface tracking methods is not designed to physically handle the interface interactions at reasonable grid sizes. Regardless of the method used, a high grid resolution is required in the liquid film region in order to properly model drainage process during bubble interaction, which in certain conditions prevents the coalescence. This makes large scale (many bubbles) simulations unaffordable. One of the popular interface tracking approached is the level-set (LS) method. To simulate realistic bubble coalescence behavior in the LS method an algorithm with the capability of delaying or preventing the process of multiple simultaneous coalescence events has been developed.

Bubble interaction plays a significant role in high void fraction flow behavior and affects the transition to other flow regimes (e.g. churn-turbulent or slug flows). The described algorithm allows to improve the accuracy of predicting coalescence events in these relevant cases and has been tested in a variety of conditions and computational meshes.

This novel algorithm uses the LS method field to detect when bubbles are in close proximity, indicating a potential coalescence event, and applies a subgrid scale force to simulate the unresolved liquid drainage force. The subgrid-model is introduced by locally modifying the surface tension force near the liquid film drainage area. The algorithm can also simulate the liquid drainage time of the thin film by controlling the length of time the increased surface tension has been applied. Thus a new method of modeling bubble coalescence has been developed.

Several test cases were designed to demonstrate the capabilities of the algorithm. The simulations, including a mesh study, confirmed the abilities to identify and prevent coalescence as well as implement the time tracking portion, with an additional 10–25% computational cost. Ongoing tests aim to verify the algorithm’s functionality for simulations with different flow conditions, a ranging number of bubbles, and both structured and unstructured computational mesh types. Specifically, a bubble rising towards a free surface provides a test of performance and demonstrates the ability to consistently prevent coalescence. In addition, a two bubble case and a seven bubble case provide a more complex demonstration of how the algorithm performs for larger simulations. These cases are compared to much more expensive simulations capable of resolving the liquid film drainage (through very high local mesh resolution), to investigate how the algorithm replicates the liquid film drainage process.
Progress on Prediction of Bubbly Flows Around Ships
Authors: Li J. , Castro A. M. , Carrica P. M.
Published: December 2016

This paper presents recent progress on prediction of bubbly flows around ships, including bubble entrainment modeling, bubble transport and numerical issues. The bubbly flow is described by a polydisperse two-fluid model that can predict the bubble entrainment locations and rates, bubble dissolution, breakup and coalescence rates, bubble velocities, turbulence quantities and bubble size distribution. To test the performance of the two phase flow model, several simulations are conducted on canonical bubbly flows with wave breaking. These well experimentally studied flows provide important information for the design of the bubble entrainment model, which is the weakest link in the model chain but crucial for prediction of the bubbly wake. The results are compared with experimental data to study the model’s accuracy and to calibrate the entrainment model constants. Full scale simulations for the flat bottom Kann boat and the Athena R/V are performed to evaluate the model under more complex flows of naval relevance that have considerable data available. It is found that the model calibrated with canonical problems predicts good results for Athena R/V, but the current turbulent entrainment model significantly underestimates the entrainment at the bow of Kann boat due to other entrainment mechanisms involved (entrainment due to impact, droplets, etc.). The breakup model, which currently considers turbulent mechanisms, underestimates the population of small bubbles in the boundary layer where strong shear is present. Finally, a grid study is carried on Athena R/V to test grid convergence. Void fraction and size distribution are compared against available experimental data and discussed in detail. Overall, the simulations show encouraging results considering the complexity of two phase flow involved in ship applications, and the model is proven to be grid independent, a very important property for practical applications.
Effects of Blade Inlet Width on Performance of Centrifugal Pump as Turbine With Special Impeller Using in Turbine Mode
Authors: Wang Tao , Liu Xiaobing , Lai Xide , Gou Qiuqin
Published: December 2016

A reverse running centrifugal pump is one of the attractive choices in micro-hydropower development and industrial pressure energy recovery. One of the main problems in utilizing pump as turbine (PAT) is that the performance of PAT is usually not ideal due to the impeller with the routine backward curved blades which do not match well with turbine running condition. A cost effective suitable way for solving this problem is to redesign impeller with forward curved blades from turbine working condition while the other components do not undergo any modifications. Blade inlet width is one of the main factors in impeller design. Therefore, research on the influence of blade inlet width on PAT performance is useful. In this paper, based on the constant velocity moment theory, the velocity moment at impeller inlet is acquired, firstly. Next, a relationship expression between blade inlet angle and the design flow rate is deduced. To perform research on blade inlet width influencing PAT’s performance with special impeller, three impellers which inlet widths are 13 mm, 16 mm and 19 mm, respectively, are designed by using ANSYS Bladegen software. Numerical simulation and analysis of the three PATs are performed using a verified computational fluid dynamics (CFD) technique. Comparison of three PATs’ performance curves obtained by CFD, we can find that the blade inlet width has obvious effect on the performance of PAT. The flow rate, required pressure head, generated shaft power, and efficiency at best efficiency point (BEP) increase with the increase of blade inlet width. The flow rates of three PATs at BEP are about 90 m3/h, 100 m3/h and 105 m3/h, respectively, when impeller inlet width varies from 13 mm to 16 mm and 19 mm. The BEP of three PATs shifts towards higher discharge and its high efficiency range becomes wider with the increase of blade inlet width. At above 100 m3/h discharge, the PAT efficiency increases in accordance with the increase of blade inlet width. And the hydraulic loss and turbulence kinetic energy loss within impeller decrease with the increase of blade inlet width. In order to improve efficiency, it is helpful to choose a relatively larger blade inlet width in the design of special impeller using in turbine mode of PAT.
A Combined Numerical and Experimental Assessment of Air and Dust Flow in a Low-Reynolds Number Valve Including Modifications to Prevent Valve Seal Contamination
Authors: Gill R. S. , Defoe J. J. , Rankin G. W.
Published: December 2016

High concentrations of particulate matter in air lead to deposition at the sealing radius of self-sealing valves involving direct intake from the environment. Dust deposition at and near this radius causes an increase in leakage flow when the valve is closed. In this paper, the mechanism which results in dust deposition in such valves is investigated and a new valve design which reduces leakage flow is developed and experimentally assessed. ANSYS Fluent 15.0 is used to numerically model the laminar flow assuming axisymmetry. Particle paths are predicted using Discrete Phase Modeling (DPM) as a post-processing step. Experimentally, dust deposition, mass flow at the operating pressure differential, and leakage flow rate are measured. The numerical and experimental results are utilized together to gain insight into the particles’ behavior. One of the key outcomes of this work is a post-processing technique which allows the numerical and experimental particle deposition results to be quantitatively compared. This supports the utlity of the numerical approach as locations of high concentrations of particle impacts in the numerical simulations are associated with locations of dense dust deposition in the experiments. High concentrations of particles at and near the sealing radius are observed to lead to increased leakage flow. Therefore, the impact of high concentrations of particles in this region is to be avoided. Utilizing this insight, the valve geometry is modified to reduce the amount of dust deposited in the region of the sealing radius. In the modified design, leakage flow is decreased by up to 93%, with a maximum of 2.1% reduction in flow rate margin relative to valve specifications.
Reynolds Number Effects on the Characteristics of Twin Jets Interacting With a Free Surface
Authors: Rahman M. S. , Nabess E. M. , Tachie M. F.
Published: December 2016

The effects of Reynolds number on the turbulent characteristics of surface attaching twin jet were investigated experimentally. Particle image velocimetry was used as the velocity measuring technique. Twin jets were produced using square orifice nozzle pair. The Reynolds numbers based on the jet exit velocity and the nozzle width were varied from 2620 to 7900. The offset height ratio was fixed at 2 during the experiments. The jet reattached to the free surface and the reattachment length decreased with increase of Reynolds number. Free surface showed significant effect on the maximum velocity decay, jet spread, streamwise mean velocity distribution, Reynolds shear and normal stresses in the upper jet. The decay and spread rate of the lower jet was comparable to free jet due to less confinement effect. The mean and turbulent quantities reported herein were nearly independent of Reynolds number. Proper orthogonal decomposition was performed to reveal the dynamic role of the energetic structures embedded within the flow.
Effects of Reynolds Number on Turbulent Characteristics of Surface Jet
Authors: Rahman M. S. , Tachie M. F.
Published: December 2016

Experimental study was carried out to investigate the Reynolds number effects on surface jet characteristics. The surface jet was produced using orifice nozzle with offset height ratio of 2. Six different Reynolds numbers ranging from 2300 to 11900 were investigated. Potential core region of the jet decreased with Reynolds number up to the Reynolds number of 5500. Reattachment point was sensitive to Reynolds number within the range of the present study. The maximum velocity decay and jet spread were nearly independent of Reynolds number. The streamwise mean velocity, streamwise turbulence intensity and Reynolds shear stress distribution along surface-normal direction were affected by the free surface and showed Reynolds number independency at the Reynolds numbers beyond 5500.
A Study on Heat Transport Phenomena in a Developed Thermal Boundary Layer of Drag Reducing Channel Flow
Authors: Watanabe K. , Kaiho Y. , Hara S. , Tsukahara T. , Kawaguchi Y.
Published: December 2016

The heat transport phenomena in a developed thermal boundary layer of surfactant solution flow were investigated experimentally. The experiment was conducted under different surfactant additive concentrations. The temperature fluctuations in a thermal boundary layer in a smooth channel flow were measured by fine-wire thermocouple probe. Heat transfer reducing rate and temperature fluctuation characteristics including mean temperature distribution, intensity, wave form, spectral density function, and skewness factor were studied. The results showed that the turbulent transport is obstructed by additives, and the temperature field shows dramatic changes. High frequency component of temperature fluctuation of surfactant solution flow was decreased due to suppression of turbulence and viscoelasticity. Large temperature fluctuations occur in the thermal boundary layer because the development of the thermal boundary layer is obstructed, and large temperature fluctuations appear to concentrate the temperature gradient in the near-wall region (10 < y+ < 60). In contrast, viscous sublayer expands due to viscoelasticity, and the temperature gradient and turbulence fluctuation are small in the near-wall region of y+ < 10. As a result, two layers having significantly different characteristics seem to coexist. The heat transfer reduction is constant with variation of additive concentration condition, but heat transport phenomena were microscopically influenced by viscoelasticity.
Interface Tracking Simulation of Phase-Change Phenomena: Boiling and Condensation Verification
Authors: Li Mengnan , Bolotnov Igor A.
Published: December 2016

Interface tracking simulation (ITS) is one of the promising approaches to describe heat transfer of boiling phenomena and their underlying mechanisms. Better understanding and modeling of this process will benefit various engineering systems. In modern nuclear reactors, study on nucleate boiling phenomena is very important for the prediction of the Critical Heat Flux (CHF) phenomena.

The presented research will implement and verify the capability of evaporation process modeling by the massively parallel research code, PHASTA. The comparison of the numerical results and the analytical results demonstrates that the overall behavior of the simulation compares well with the analytical solution. A second simulation of the single bubble growth with non-uniform temperature distribution demonstrates both condensation and evaporation modeling. In the third simulation flow boiling capabilities were preliminary tested with laminar flow demonstration case. These results will be applied to a larger scale, multi-bubble simulations and help modeling of nucleate boiling phenomena.
Parametric Analysis of Erosion in 90 Degree and Long Radius Bends
Authors: Zahedi Peyman , Karimi Soroor , Mahdavi Marzieh , McLaury Brenton S. , Shirazi Siamack A.
Published: December 2016

Solid particle erosion has been recognized as a major concern in the oil and gas production industry. It has been observed that erosion can cause serious and costly damage to equipment and pipelines. Accordingly, different studies have been performed in order to investigate erosion caused by solid particles entrained in the flow. Both experimental and modeling approaches have been used in the past to analyze solid particle erosion under different conditions to be able to mitigate these problems.

The goal of this paper is to use a Computational Fluid Dynamic (CFD) erosion model to predict erosion caused by particles flowing in 90 degree and long radius bends. The fluid flow model is coupled with a Lagrangian particle tracking approach. The CFD-based prediction procedure consists of three main steps: flow modeling, particle tracking and erosion calculation. The Reynolds Stress Model (RSM) is used as the turbulence model for all fluid flow simulations. Solid particles are injected from the inlet of the pipe and tracked throughout the bend. The effect of the number of particles released on the predicted maximum erosion magnitude has been investigated. In order to study the grid independency of the solution, erosion is predicted for 5 different grid spacings to accurately predict the flow and erosion rates. In order to assess the quality of the numerical predictions of the erosion rate, experimental data for single-phase (gas) flow with sand in a 3-inch pipe were used. The effects of particle size, fluid velocity, pipe diameter and radius as well as particle rebound model on erosion pattern and magnitude are also investigated. Comparison of these results with experimental erosion data demonstrates good agreement of the erosion trends.

It is found that the location of highest erosion for single-phase (gas) flow at low pressure containing sand is around 45° in the elbow. It has been also observed that the 300 μm particles cause approximately two times higher metal loss compared to the 150 μm particles. This higher erosion magnitude is not only caused by the increase in particle momentum but also by the significant increase in particle sharpness for the 300 μm sand. Moreover, simulation results indicate that the increase in gas superficial velocity leads to an increase in the erosion magnitude. According to the results, erosion ratios were reduced exponentially with the increase in pipe diameter at constant flow conditions and particle properties. Furthermore, two available rebound models in the literature were investigated, and simulations illustrate that both methods are in reasonable agreement with experimental data.
Experimental Investigation on Influence of Relative Positions Between Diffuser and Volute on Pressure Fluctuation at the Outlet of a Centrifugal Pump
Authors: Wang Wenjie , Yuan Shouqi , Pei Ji , Pavesi Giorgio , Gu Yandong
Published: December 2016

To investigate the influence of relative positions between a radial diffuser and an annular volute on the unsteady pressure at the centrifugal pump outlet, experiment tests were carried out with five positions between the diffuser and volute in an open test rig. Statistical and frequency spectrum analyses were carried out to obtain the pressure fluctuation amplitude range and the frequency domain respectively. The results showed that the relative position has greater influence on the pressure at large flow rate than at part load condition. The dominant frequency and the Power Spectrum Density (PSD) values are affected by diffuser azimuthal position and the harmonic frequencies are determined by number of blades and vanes. The investigation can give a reference to optimize the relative angle between diffuser and volute to reduce the pressure fluctuations.
Particle-Resolved DNS to Study Spatio-Temporal Correlations of Hydrodynamic Forces on Particle-Bed in an Oscillatory Flow Environment
Authors: Ghodke Chaitanya D. , Apte Sourabh V.
Published: December 2016

Particle-resolved direct numerical simulations are performed using fictitious domain approach [1] to investigate the effect of an oscillatory flow field over a rough wall made up of a regular hexagonal pack of fixed spherical particles, in a setup similar to the experimental configuration of [2]. Turbulent flows at Reynolds numbers, Reδ = 200 and 400 (based on the Stokes-layer thickness δ) are studied. The unsteady nature of hydrodynamic forces on particles and their cross-correlations with measurable flow variables are investigated. Temporal correlations showed drag and lift to be positively correlated with a phase difference, which is approximately equal to the Taylor micro-scale related to drag/lift correlations. Spatio-temporal correlations between the flow field and particle-related quantities showed that the lift force is well correlated with the streamwise velocity fluctuations up to distances of the same order as the particle diameter, beyond which the cross correlation decays considerably. On the other hand, the pressure fluctuations are correlated and anti-correlated with the lift force in the front and aft regions of the particle, respectively, as a result of wake effects. Further statistical analyses showed that the near-bed velocity and pressure fluctuations fit poorly with Gaussian distributions. Instead, a fourth order Gram-Charlier distribution model is proposed that may have consequences on the Gaussian descriptions of sediment pick-up functions typically used in quantification of turbulent transport of sediment particles.
Simulation of a 3D Axisymmetric Hill: Comparison of RANS and Hybrid RANS-LES Models
Authors: Jamal Tausif , Walters D. Keith
Published: December 2016

Computational fluid dynamics (CFD) prediction of high Reynolds number flow over a 3D axisymmetric hill presents a unique set of challenges for turbulence models. The flow on the leeward side of the hill is characterized by the presence of complex vortical structures, unsteady wakes, and regions of boundary layer separation. As a result, traditional eddy-viscosity Reynolds-averaged Navier-Stokes (RANS) models have been found to perform poorly. Recent studies have focused on the use of Large Eddy Simulation (LES) and hybrid RANS-LES (HRL) methods to improve accuracy. In this study, the capability of a dynamic hybrid RANS-LES (DHRL) model to resolve the flow over a 3D axisymmetric hill is investigated and compared to numerical results using a traditional RANS model and a conventional hybrid RANS-LES model, and to experimental data. Results show that the RANS model fails to accurately predict the mean flow features in the wake region, which is in agreement with prior studies. The conventional HRL model provides better prediction of the flow characteristics but suffers from grid sensitivity and delayed transition to LES mode. The DHRL method provides the best agreement with experimental data overall and shows least sensitivity to grid resolution. Results also highlight the importance of using a low dissipation flux formulation for flow simulations in which a portion of the turbulence spectrum is resolved, including hybrid RANS-LES.
Validation of an Adaptive Meshing Implementation of the Lattice-Boltzmann Method for Insect Flight
Authors: Feaster Jeffrey , Battaglia Francine , Deiterding Ralf , Bayandor Javid
Published: December 2016

Insects, sustaining flight at low Reynolds numbers (500<Re<10,000), fly utilizing mechanically simple kinematics (3 degrees of freedom) at an extremely high flap frequency (150–200 Hz), resulting in a complicated vortical fluid field. These flight characteristics result in some of the most agile and maneuverable flight capabilities in the animal kingdom and are considered to be far superior to fixed wing flight, such as aircraft. Bees are of particular interest because of the utilization of humuli to attach their front and hind wings together during flight. A Cartesian-based adaptive meshing implementation of the Lattice-Boltzmann Method is utilized to resolve the complex flow field generated during insect flight and is verified against experimental and computational results present in the literature in two dimensions. The Lattice-Boltzmann Method was found to agree well in both qualitative and quantitative comparisons with both two-dimensional computational and three-dimensional experimental results.
A Numerical Approach for Modeling Roughness for Marine Applications
Authors: Vargas Abel , Shan Hua
Published: December 2016

A roughness wall model based on the equivalent sandgrain roughness approach that accounts for the log-law solution for turbulent boundary layer over fully rough surfaces is implemented into a viscous flow solver called NavyFOAM. The rough wall model is implemented as a wall function and is used in conjunction with the k-ω turbulence model. The roughness model is validated against experiments conducted on rough plates in a water tunnel and towed in a channel. Two sets of simulations, single-phase Reynolds-Averaged Navier-Stokes (RANS) and two-phase unsteady RANS were conducted to validate the current roughness model. Current results show good agreement with the roughness functions (ΔU+) and is within 1.5% of the experimental results. The overall frictional resistance predicted for the rough plates towed in a water channel is within 2% of the experimentally obtained results. With these promising results, the aim is to develop a computational capability for predicting added hull resistance due to biofouling.
Development of an Efficient Phase Separator for Space and Ground Applications
Authors: Wu Xiongjun , Loraine Greg , Hsiao Chao-Tsung , Chahine Georges L.
Published: December 2016

The limited amount of liquids and gases that can be carried to space makes it imperative to recycle and reuse these fluids for extended human operations. During recycling processes gas and liquid phases are often intermixed. In the absence of gravity, separating gases from liquids is challenging due to the absence of buoyancy. This paper discusses a phase separator that is capable of efficiently and reliably separating gas-liquid mixtures of both high and low void fractions in a wide range of flow rates that is applicable to reduced and zero gravity environments.

The phase separator consists of two concentric cylindrical chambers. The fluid introduced in the space between the two cylinders enters the inner cylinder through tangential slots and generates a high intensity swirling flow. The geometric configuration is selected to make the vortex swirl intense enough to lead to early cavitation which forms a cylindrical vaporous core at the axis even at low flow rates. Taking advantage of swirl and cavitation, the phase separator can force gas out of the liquid into the central core of the vortex even at low void fraction. Gas is extracted from one end of the cylinder axial region and liquid is extracted from the other end. The phase separator has successfully demonstrated its capability to reduce mixture void fractions down to 10−8 and to accommodate incoming mixture gas volume fractions as high as 35% in both earth and reduced gravity flight tests. The phase separator is on track to be tested by NASA on the International Space Station (ISS). Additionally, the phase separator design exhibits excellent scalability. Phase separators of different dimensions, with inlet liquid flow rates that range from a couple of GPMs to a few tens of GPMs, have been built and tested successfully in the presence and absence of the gravity.

Extensive ground experiments have been conducted to study the effects of main design parameters on the performance of the phase separator, such as the length and diameter of the inner cylinder; the size, location, and layout of injection slots and exit orifices, etc., on the swirling flow behavior, and on the gas extraction performance. In parallel, numerical simulations, utilizing a two-phase Navier-Stokes flow solver coupled with bubble dynamics, have been conducted extensively to facilitate the development of the phase separator. These simulations have enabled us to better understand the physics behind the phase separation and provided guideline for system parts optimization.

This paper describes our efforts in developing the passive phase separator for both space and ground applications.
The Effect of Advance Ratio, Solidity, and Wake Interactions on a 2D Vertical Axis Turbine
Authors: Norman Adam E. , Tafti Danesh K.
Published: December 2016

In recent years there has been an increased effort to utilize hydrokinetic devices to harvest energy from both wind and tidal flows. Vertical axis turbines utilization is of particular interest in tidal flows. A major disadvantage in vertical axis turbines is that they are less efficient than horizontal axis turbines. To increase the efficiency of the vertical axis turbines, 2D CFD simulations are completed in an effort to better understand the physics behind the operation of these turbines. Specifically, the effect of advance ratio, solidity, and wake interactions were investigated. Simulations were completed in OpenFOAM using the k-ω SST turbulence model at a nominal Reynolds number of 500,000 using a NACA 0015 airfoil. To simulate the motion of the turbine, Arbitrary Mesh Interfacing (AMI) was used. For all of the parameters tested, it was found that the geometric effective angle of attack seen by the turbine blades had a significant impact on the power extracted from the flow. The range of effective angles of attack was found to decrease as the advance ratio increased. In spite of this, a severe loss in the power coefficient occurred at an advance ratio of 2.5 during which the blade experienced dynamic stall. This effect was also seen when the number of turbine blades was changed to four, at a solidity of 1.08. Results indicate that wake interactions between subsequent blades have a large impact on performance especially when the wake interaction alters the flow direction sufficiently to create conditions for dynamic stall.
Quantifying the Fluid Modeling Capability of SPH and CLE Through the Study of the Lid-Driven Cavity Problem
Authors: Horton Brandon , Bayandor Javid
Published: December 2016

Despite recent interest in complex fluid-structure interaction problems, the baseline fluid modeling capability for commercially available numerical methodologies used for multidisciplinary analysis is yet to be established. The current work is among those to first underline such a reference for coupled Lagrangian-Eulerian (CLE) and smooth particle hydrodynamics (SPH). These methodologies are quantitatively assessed using the classical 2-D lid-driven cavity and compared against an implicit Navier-Stokes solution in addition to other benchmarks from the literature. Qualitative comparison is made through the use of velocity magnitude contour plots with accompanying streamlines, whereas quantitative analysis is made using centerline velocity profiles for both U and V flows. Throughout the investigated Reynolds numbers (1000–20,000), SPH provides inaccurate results and is unable to represent vorticity in the cavity corners. Alternatively, CLE retains a high level of accuracy up to Re = 10,000, before deviating from published literature at Re = 20,000. In addition to being qualitatively similar, the centerline profiles consistently display ≤ 10% error when compared to the Navier-Stokes solutions. By establishing the limits of closed-system fluid modeling capability for SPH and CLE, this work can be extended to full fluid-scenarios.
Stability and Transition Over a Low-Reynolds Number Airfoil
Authors: Ziadé Paul , Sullivan Pierre E.
Published: December 2016

Large-eddy simulation and linear stability analysis were performed on a NACA 0025 airfoil at a chord Reynolds number of 105 and four angles of attack. The computations showed that the initial vortex roll-up quickly breaks down to three-dimensional turbulence. Flow separation was observed at all angles, whereas only the lowest angle of attack formed a laminar separation bubble due to flow transition occuring close to the airfoil surface. A Chebyshev collocation method was employed to solve the viscous and inviscid stability equations. Linear stability analysis demonstrated that high-frequency disturbances occur in the laminar separation bubble case, whereas lower frequencies are present for the fully separated angles of attack. The maximum disturbance growth rates were dampened with the addition of viscosity but negligible change in peak frequency was noted.
Performance Improvement of Capacitive Deionization for Water Desalination Using a Multi-Step Buffered Approach
Authors: Salamat Yasamin , Rios Perez Carlos A. , Hidrovo Carlos
Published: December 2016

Due to the increasing demand for clean and potable water stemming from population growth and exacerbated by the scarcity of fresh water resources, more attention has been drawn to different and innovative methods for water desalination. Capacitive deionization (CDI) is a relatively new, low maintenance, and energy efficient technique for desalinating brackish water. In this technique, an electrical field is employed to adsorb ions into a high-porous media. After the saturation of the porous electrodes, their adsorption capacity can be restored through a regeneration process. Various parameters affect the overall performance of CDI. The flow rate at which water is purified in CDI plays an essential role in its ultimate performance. Many studies have shown that desalination percentage decreases as flow rate increases in CDI, since the advection of ions in the flow becomes more dominant than their diffusion toward the electrodes. However, herein, based on a physical model previously developed, we conjecture that for a given amount of time and volume of water, multiple desalination cycles in a high flow rate regime will outperform desalinating in a single cycle at a low flow rate. Moreover, splitting a CDI unit into two sub-units, with the same total length, will lead to higher desalination. Based on these premises, we introduce a new approach aimed at enhancing the overall performance of CDI. An array of CDI cells are sequentially connected to each other with intermediate solutions placed in between them. These intermediate solutions act as buffers to homogenize the outlet concentration of the preceding cell and maintain a constant inlet concentration for the following cell. Desalination tests were conducted to compare the performance of the proposed system, consisting of two CDI units and one intermediate solution buffer, with a two-cascaded-CDI unit system with no intermediate solution. Desalination tests were performed in a high flow rate regime with a low salinity initial solution of NaCl in water. In the buffered arrangement, the concentration of the solution buffer was set at the minimum average outlet concentration of the first CDI test. Experimental data demonstrated the improved performance of the buffered system over the non-buffered system, in terms of desalination percentage and energy consumption. Increasing the number of CDI units and solution buffers in a buffered system, the new proposed method will lead to lower amount of energy consumed per unit volume of the desalinated water.
Characterization of a Pulsating Drill Bit Blaster
Authors: Thorp Nicholas J. , Hareland Geir , Elbing Brian R. , Nygaard Runar
Published: December 2016

The drill bit blaster (DBB) studied in this paper aims to maximize the drilling rate of penetration (ROP) by using a flow interrupting mechanism to create drilling fluid pulsation. The fluctuating fluid pressure gradient generated during operation of the DBB could lead to more efficient bit cutting efficiency due to substrate depressurization and increased cutting removal efficiency and the vibrations created could reduce the drill string friction allowing a greater weight on bit (WOB) to be achieved. In order to maximize these mechanisms the effect of several different DBB design changes and operating conditions was studied in above ground testing. An analytical model was created to predict the influence of various aspects of the drill bit blaster design, operating conditions and fluid properties on the bit pressure characteristics and compared against experimental results. The results indicate that internal tool design has a significant effect on the pulsation frequency and amplitude, which can be accurately modeled as a function of flowrate and internal geometry. Using this model an optimization study was conducted to determine the sensitivity of the fluid pulsation power on various design and operating conditions. Application of this technology in future designs could allow the bit pressure oscillation frequency and amplitude to be optimized with regard to the lithology of the formations being drilled which could lead to faster, more efficient drilling potentially cutting drilling costs and leading to a larger number of oil and natural gas plays being profitable.
Modeling of Multiphase Flows in Porous Media With Applications to Reservoir and Well Performance Analysis
Authors: Li Huiying , Vasquez Sergio A. , Azhar Mohammed
Published: December 2016

The present work concerns the development of a comprehensive model capability in ANSYS CFD software FLUENT towards modeling of multiphase flows in porous media with targeted applications in reservoir/well analyses. The modeling approach is based on the Eulerian multifluid model. Porous media are modeled by both Superficial and Physical Velocity formulation with embedded sub-models to account for the resistance sink, relative-permeability and capillary pressure effect. An advanced numerical algorithm has been developed to achieve time-step and mesh independent solutions as well as to satisfy the physical constraints/limits. In particular, the resistance sinks are rearranged and linearized to ensure numerical stability and to handle mathematically infinite resistance caused by possible zero relative permeability. The capillary pressure and body forces are implicitly treated to enhance solver robustness. The multiphase porous medium model is compatible with all the numerical schemes and solvers (iterative and non-iterative) available in FLUENT. The present model has been applied to simulate 1D, 2D and 3D transient oil-water two-phase flows mimicking the conditions in reservoirs and wells. The solutions are time-step and grid independent, and successfully reproduce the flow characteristics and physical limits. The solvers are fast and robust, allowing the time step to be as large as 2 hours for a reservoir setting with the flow physical time in 2–20 years. The model capability shows great promises for reservoir and well performance analysis.
Impacts of Industrial Fresh Water Withdrawals on Calcaiseu Lake Hydrodynamics and Salinity Concentration
Authors: Han Xiao , Zhang Ning
Published: December 2016

In the authors’ previous study, vegetation information was utilized into a hydrodynamic model to predict the flooding coverage and damage to the wetlands in a major water system in southwest Louisiana, the Calcasieu Lake water system. In this study, the target area is extended, ranging from the city of Lake Charles as the north end to the Gulf of Mexico as the south end, including Lake Charles, Calcasieu Lake, Prien Lake, Gulf Intracoastal Waterway (GIWW) and the entire Calcasieu Ship Channel. Measured vegetation data is utilized in the vegetated areas and appropriate friction values are assigned to different types of non-vegetated areas. Salinity is important to aquatic life. It can impact agricultural production, water quality and streams, biodiversity and infrastructure. In this study, both hydrodynamic and salinity transport simulations are conducted. Measurement data from NOAA and USGS are used as boundary conditions. Simulation results were compared with NOAA and USGS data in several other locations. Lake Charles is one of the largest petrochemical industry centers in the country. Numerous plants use tremendous amount of fresh surface water in the area. Recent expansions of several companies increase the fresh water withdraws from the system significantly. One of the purposes of the study is to investigate the effects of increased water withdraw on the hydrodynamics and salinity in the system. The industrial water withdrawals could be from the Calcasieu River in the north of Lake Charles, which is the north boundary of the simulation domain. Cases of different reduced flow rates at Lake Charles were tested, and the effects on hydrodynamics and salinity concentrations and distributions were analyzed. The results can be used as a guideline for industrial and city development in the areas.
Experimental Investigations of Couette-Taylor-Poiseuille Flows Using the Electro-Diffusional Technique
Authors: Berrich Emna , Aloui Fethi , Legrand Jack
Published: December 2016

Couette-Taylor-Poiseuille flow CTPF consists on the superposition of Couette-Taylor flow to an axial flow. The CTPF flow hydrodynamics studies remain rather qualitative or numerical or are restricted to relatively low Taylor and/or axial Reynolds numbers. For more comprehensive and control of CTPF, especially for relatively high Taylor numbers and high axial Reynolds numbers, we investigated experimentally CTF with and without an axial flow, using the electro-diffusion ED method. This technique requires the use of Electro-Diffusion ED probe which allows the determination of the local mass transfer rate from the Limiting Diffusion current measurement delivered by the ED probe while it is polarized by a polarization voltage. From the local mass transfer (the Sherwood number), we determined the wall shear rate using different approaches. The results illustrate that low axial flow can generate a stabilizing effect on the CT flow. The time-evolutions of the local mass transfer and the wall shear rate are periodic. These evolutions characterize the waviness or the stretching of the vortices. However, Taylor Wavy Vortex Flow TWVF is destabilized under the effect of relatively important axial flow. The time-evolutions of wall shear rate are no longer periodic. Indeed, Taylor vortices are overlapped or completely destructed.
Predicting the orientation of protein G B1 on hydrophobic surfaces using Monte Carlo simulations
Authors: Harrison Elisa T. , Weidner Tobias , Castner David G. , Interlandi Gianluca
Published: December 2016

A Monte Carlo algorithm was developed to predict the most likely orientations of protein G B1, an immunoglobulin G (IgG) antibody-binding domain of protein G, adsorbed onto a hydrophobic surface. At each Monte Carlo step, the protein was rotated and translated as a rigid body. The assumption about rigidity was supported by quartz crystal microbalance with dissipation monitoring experiments, which indicated that protein G B1 adsorbed on a polystyrene surface with its native structure conserved and showed that its IgG antibody-binding activity was retained. The Monte Carlo simulations predicted that protein G B1 is likely adsorbed onto a hydrophobic surface in two different orientations, characterized as two mutually exclusive sets of amino acids contacting the surface. This was consistent with sum frequency generation (SFG) vibrational spectroscopy results. In fact, theoretical SFG spectra calculated from an equal combination of the two predicted orientations exhibited reasonable agreement with measured spectra of protein G B1 on polystyrene surfaces. Also, in explicit solvent molecular dynamics simulations, protein G B1 maintained its predicted orientation in three out of four runs. This work shows that using a Monte Carlo approach can provide an accurate estimate of a protein orientation on a hydrophobic surface, which complements experimental surface analysis techniques and provides an initial system to study the interaction between a protein and a surface in molecular dynamics simulations.
Efficient approximation of the Struve functions H
n occurring in the calculation of sound radiation quantities
Authors: Aarts Ronald M. , Janssen Augustus J. E. M.
Published: December 2016

The Struve functions Hn(z), n=0, 1, ...  are approximated in a simple, accurate form that is valid for all z≥0. The authors previously treated the case n = 1 that arises in impedance calculations for the rigid-piston circular radiator mounted in an infinite planar baffle [Aarts and Janssen, J. Acoust. Soc. Am. 113, 2635–2637 (2003)]. The more general Struve functions occur when other acoustical quantities and/or non-rigid pistons are considered. The key step in the paper just cited is to express H1(z) as (2/π)−J0(z)+(2/π) I(z), where J0 is the Bessel function of order zero and the first kind and I(z) is the Fourier cosine transform of [(1−t)/(1+t)]1/2, 0≤t≤1. The square-root function is optimally approximated by a linear function ĉt+d̂, 0≤t≤1, and the resulting approximated Fourier integral is readily computed explicitly in terms of sin z/z and (1−cos z)/z2. The same approach has been used by Maurel, Pagneux, Barra, and Lund [Phys. Rev. B 75, 224112 (2007)] to approximate H0(z) for all z≥0. In the present paper, the square-root function is optimally approximated by a piecewise linear function consisting of two linear functions supported by [0,t̂0] and [t̂0,1] with t̂0 the optimal take-over point. It is shown that the optimal two-piece linear function is actually continuous at the take-over point, causing a reduction of the additional complexity in the resulting approximations of H0 and H1. Furthermore, this allows analytic computation of the optimal two-piece linear function. By using the two-piece instead of the one-piece linear approximation, the root mean square approximation error is reduced by roughly a factor of 3 while the maximum approximation error is reduced by a factor of 4.5 for H0 and of 2.6 for H1. Recursion relations satisfied by Struve functions, initialized with the approximations of H0 and H1, yield approximations for higher order Struve functions.
Robotic vertical jumping agility via series-elastic power modulation
Authors: Haldane Duncan W. , Plecnik M. M. , Yim J. K. , Fearing R. S.
Published: December 2016

Animal agility studies inspired a leg mechanism that improves power modulation and a high-jumping and wall-jumping robot.
Hybrid EEG/EOG-based brain/neural hand exoskeleton restores fully independent daily living activities after quadriplegia
Authors: Soekadar S. R. , Witkowski M. , Gómez C. , Opisso E. , Medina J. , Cortese M. , Cempini M. , Carrozza M. C. , Cohen L. G. , Birbaumer N. , Vitiello N.
Published: December 2016

A noninvasive, hybrid brain/neural hand exoskeleton restored intuitive control of grasping motion, restoring independent activities to quadriplegics.
Science for robotics and robotics for science
Authors: Yang Guang-Zhong , Bellingham James , Choset Howie , Dario Paolo , Fischer Peer , Fukuda Toshio , Jacobstein Neil , Nelson Bradley , Veloso Manuela , Berg Jeremy
Published: December 2016

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