bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Computational Fluid Dynamic Analysis of Laboratory-Scaled Counter-Rotating Cross-Flow Turbines in Marine Environment
Authors: Doan Minh N. , Alayeto Ivan H. , Padricelli Claudio , Obi Shinnosuke , Totsuka Yoshitaka
Published: October 2018

Power generation of laboratory-scaled marine hydrokinetic (MHK) cross-flow (vertical axis) turbines in counter-rotating configurations was scrutinized both experimentally and numerically. A tabletop experiment, designed around a magnetic hysteresis brake as the speed controller and a Hall-effect sensor as the speed transducer was built to measure the rotor rotational speed and the hydrodynamic torque generated by the turbine blades. A couple of counter-rotating straight-three-bladed vertical-axis turbines were linked through a transmission of spur gears and timing pulleys/belt and coupled to the electronic instrumentation via flexible shaft couplers. A total of 6 experiments in 3 configurations, with various relative distances and phase angles, were conducted in the water channel facility (3.5 m long, 0.30 m wide, and 0.15 m deep) at rotor diameter base Reynolds number of 20,000. The power curve of the counter-rotating turbines (0.068-m rotor diameter) was measured and compared with that of a single turbine of the same size. Experimental results show the tendency of power production enhancement of different counter-rotating configurations. Additionally, the two-dimensional (2D) turbine wakes and blade hydrodynamic interactions were simulated by the shear stress transport k-omega (SST k-omega) model using OpenFOAM. The computational domain included a stationary region and two rotating regions (for the case of counter-rotating turbines) set at constant angular velocities. The interface between the rotating and stationary region was modeled as separated surface boundaries sliding on each other. Velocity, pressure, turbulent kinetic energy, eddy viscosity, and specific dissipation rate field were interpolated between these boundaries.
Experimental Study of Gas-Liquid Flow Through a Multi-Stage, Mixed-Flow Electric Submersible Pump
Authors: Dupoiron Marine
Published: October 2018

Laser Doppler velocimetry (LDV) and high-speed imaging techniques were used in a transparent model of a fourstage, mixed-flow commercial electric submersible pump (ESP) to characterize the flow through a range of inlet gas volume fractions (GVF) from 0 to 30%. Measurements demonstrate the presence high turbulence levels in the wake of the impeller blades, and recirculation cells at low flow rates. In gas-liquid conditions, the bubble size varied within a pump stage, as break-up occurred at the impeller tip, and coalescence was dominant in the diffuser, especially at low flow rates because of recirculation. At moderate-to-high inlet GVF, the first impeller acted as a mixer and the flow patterns at the stage level alternated between bubbly and radially separated flows, as short gas slugs propagated through the stages. The flow patterns at the stage level did not depend on the pump inclination, but the inlet conditions did, with worse performance induced by slugging flows for the horizontal setup.
Flow Structure Formed by a Sweeping Jet Ejected Into a Main Flow
Authors: Fuchiwaki Masaki , Raghu Surya
Published: October 2018

Various methods of controlling flow separation have been proposed and many studies have been performed on active separation control in correspondence with the flow state. However, their efficiency has been hampered by the requirement of electric power for the added stream. Recently, an active flow separation control device based on a fluidic oscillator that does not require electric power has been reported. This device is able to generate a sweeping jet over a wide spatial range as well as fluid oscillations, and its internal structure eliminates the need for a drive unit. The studies of the flow separation control techniques using the fluidic oscillator have been reported. However, most of these results are mainly contribution of the dynamic forces from the viewpoint of the flow control and the study on the flow mechanism for the separation flow control using the fluidic oscillator have not been understood. Especially, it is not known the interaction between the sweeping jet from the fluidic oscillator and the main flow and the flow structure due to the interaction. In order to make a flow separation control devise with high efficiency using the fluidic oscillator, it is require to be understood the complex flow structure by the interaction between the sweeping jet from the fluidic oscillator and the main flow. The purpose of the present study is to investigate the flow structure by the interaction between the sweeping jet from the fluidic oscillator and the main flow quantitatively by the stereo PIV measurement. The sweeping jet ejected from a fluidic oscillator evidently disrupts the main flow at high velocity ratios, leading to a significant change in flow structure. A high-speed jet appears at the center part of the structure, accompanied by low-speed flow at the outside, producing a 3D distribution. The sweeping jet ejected from the fluidic oscillator maintains the spreading angleas a result of the interaction between the two flows at high velocity ratios.
Machine Learning Approach to Predict the Flow Rate for an Immiscible Two-Phase Flow at Pore Scale for Enhanced Oil Recovery Application
Authors: Rodriguez Arturo , Kotteda V. M. Krushnarao , Rodriguez Luis F. , Kumar Vinod , Schiaffino Arturo , Nieto Zackery R.
Published: October 2018

Due to global demand for energy, there is a need to maximize oil extraction from wet reservoir sedimentary formations, which implies the efficient extraction of oil at the pore scale. The approach involves pressurizing water into the wetting oil pore of the rock for displacing and extracting the oil. The two-phase flow is complicated because of the behavior of the fluid flow at the pore scale, and capillary quantities such as surface tension, viscosities, pressure drop, radius of the medium, and contact angle become important. In the present work, we use machine learning algorithms in TensorFlow to predict the volumetric flow rate for a given pressure drop, surface tension, viscosity and geometry of the pores. The TensorFlow software library was developed by the Google Brain team and is one of the most powerful tools for developing machine learning workflows. Machine learning models can be trained on data and then these models are used to make predictions. In this paper, the predicted values for a two-phase flow of various pore sizes and liquids are validated against the numerical and experimental results in the literature.
Investigations on Flow Characteristics in Diffuser-Discharge-Channel of Volute Casing
Authors: Gu Yandong , Pei Ji , Yuan Shouqi , Zhang Jinfeng , Nikolajew Ernst , Gan Xingcheng
Published: October 2018

The volute casing used in centrifugal pumps is efficient for the transformation of kinetic energy into pressure energy, however, its asymmetric hydraulic design makes the flow in diffuser-discharge-channel (DDC) inhomogeneous, resulting in unsatisfactory flow patterns. In this study, the unsteady numerical simulations are carried out to investigate the transient flow characteristics in DDC. The accuracy of numerical results is found to agree well with experimental performance and pressure fluctuations. It is observed that the flow in DDC is significantly uneven. At the elbow of DDC, the static pressure on the volute left side (VL) is larger than the volute right side (VR) due to the flow impact and flow separation respectively. Thereby, this high-pressure gradient induces the secondary flow on the cross sections of DDC. Further, there is an obvious dependency of pressure fluctuations in the discharge pipe on the strong interaction between the impeller and tongue, in which four small peaks and four large peaks can be observed. At each moment, the pressure on VL gradually decreases from the inlet of discharge pipe to the pump outlet, while it increases on VR, finally, two sides tend to be the same. The pressure fluctuation intensity gradually becomes equivalent-distributed. In particular, it should be noticed that the energy loss in the diffuser part is larger than the discharge pipe, which requires a redesign concerning hydraulic performance. This study can help to better understand the transient flow characteristics and provide guidance for reducing flow loss in the volute casing.
Mass Flow Performance for Large Aspect Ratio Supersonic Boundary Layer Bleed Holes
Authors: Papadopoulos George , Go Gary , Celentano Frank , Bakos Robert
Published: October 2018

Accurate estimation of the bleed orifice flow coefficient, which relates bleed plenum pressure to mass flow removed, is important to predicting inlet performance, as well as, estimating bleed drag. Much of the flow coefficient data at conditions of interest to inlet designers is based on bleed plates with multiple rows of holes. The flow coefficient for these plates is typically presented as a function of bleed plenum pressure normalized by the freestream total pressure. Numerical simulations of the flowfield at the entrance of the bleed hole show that the flow is complex, especially for supersonic free stream flow, whereby an alternating expansion/compression wave pattern initiates at the porous bleed surface as the flow turns to enter the hole. This implies that a significant portion of the tangential flow total pressure is given up upon entering a 90° hole.

For large aspect ratio (length-to-diameter ratio) bleed holes the effect of the frictional pressure drop is to lower the required plenum pressure to achieve a given mass flow. Conversely, the mass flow will be reduced due to the higher pressure at the start of the duct. Empirical data show that the flow coefficient for supersonic boundary layer bleed holes stops increasing as the plenum pressure to total pressure ratio continues to decrease, indicating that the flow becomes choked. Thus the chocked flow condition helps to make the bleed hole mass flow under these conditions less sensitive or insensitive to the effects of friction caused by the extended hole length. The extent to which this happens is the focus of the current effort, with the paper reporting on experimental and numerical results on flow characteristics and mass flow performance of supersonic bleed holes featuring a range of aspect ratios beyond what has been reported in the past.
Multi-Objective Optimization on Inlet Pipe of a Vertical Inline Pump Based on Genetic Algorithm and Artificial Neural Network
Authors: Gan Xingcheng , Pei Ji , Yuan Shouqi , Wang Wenjie , Tang Yajing
Published: October 2018

In order to save the space for installation, a bent pipe is adopted for inlet of vertical inline pump. In this paper, to improve the performance of inlet pipe, a multi-objective optimization on the inlet pipe is proposed based on Genetic Algorithm (GA) and Artificial Neural Network (ANN) model. A 5th-order Bezier curve is applied to fit the mean line of the inlet pipe and 3rd-order Bezier curves are used for depicting the variation trend of shape of sections. As the outlet of inlet pipe is fixed, 11 design variables are utilized for optimization, and the three optimization objectives are efficiency, head and standard deviation of velocity at the outlet of inlet pipe. To get the surrogate model, 149 different models obtained from Latin hypercube sampling are solved with numerical simulation. The results showed the numerical simulation has a great agreement with the experiment. Artificial neural network can accurately fit the target functions and design variables. The deviation of efficiency, head and standard deviation of velocity between predicted value and actual value were 0.26%, 0.05m and −0.27m/s, respectively. After optimization, an improvement on flow condition and a decrease of standard deviation of velocity before impeller were obtained. The efficiency and head were improved by 1.16% and 0.2m, respectively.
Investigation of Unsteady Flow in a Submersible Tubular Pumping System
Authors: Jin Yan , Chen Hongcheng , Ting David S.-K. , Stagner Jacqueline , Wu Junxin , Liu Chao
Published: October 2018

To better understand the workings of submersible tubular pumping system and to enable future improvements, the pressure fluctuation and unsteady flow characteristics due to the complex rotor-stator interactions need to be properly delineated. High-frequency pressure measurements coupled with CFD simulations have been invoked in this study to elucidate the unsteady flow in different components of a submersible tubular pumping system at different discharges. The focus is on the impeller and guide vane, where the unsteady interaction is the strongest. The pressure pulsation distributions of different characteristic cross sections such as impeller exit, middle of guide vane, and exit of guide vane were quantified. In addition, the flow characteristics and the turbulent kinetic energy inside the impeller, guide vane, and bulb unit were obtained at the different time steps. The results show that the pressure pulsation frequency obtained by simulation was in agreement with the experimental results, including the critical points around the impeller and the guide vanes. The complementary two-prong approach is thus proven to be a powerful duo in researching and advancing a convoluted pumping system.
Experiments and Large Eddy Simulation of Swirling Flow in a Pipe
Authors: Tianxing Zhang , Kharoua Nabil , Khezzar Lyes , Alshehhi Mohamed , Bojanampati Shrinivas
Published: October 2018

Swirling flows in pipes are encountered in several industrial applications for separation or mixing purposes. In this work turbulent swirling flow is generated using a new swirl generator in the form of thick-walled pipe with multi-radial holes which is lodged inside a larger cylindrical housing, called the Swirl Cage. The swirling flow exiting from the Swirl Cage feeds into a long pipe where the Reynolds number based on the pipe diameter and average velocity is equal to 40836.67. Large Eddy Simulation (LES) is used to calculate the swirling flow and explore its characteristics in conjunction with the Dynamic Kinetic Energy Subgrid-Scale model. Experiments were conducted using LDV and the results are used for validation purposes and for the discussion of the flow features.

The results are discussed in relation with the mean fluid velocity and its RMS component. Profiles of the mean tangential velocity reveal a Rankine vortex swirling flow type along the whole axial distance. The core flow was slightly oscillating exhibiting a processing vortex behavior reflected by the radial velocities at the centerline. The profiles of the turbulent kinetic energy were characterized by a peak at the centerline increasing in magnitude with the axial distance. The swirl number decayed from 1.5 right at the outlet of the swirl cage to unity close to the outlet of the pipe.
The Effects of the Inlet Guide Vanes on an Axial Pump Under Off Design Points
Authors: Guo Zhi-Wei , Pan Jing-Ye , Qian Zhong-Dong
Published: October 2018

The performances of an axial pump with and without inlet guide vanes (IGVs) are investigated by both experimental method and computational fluid dynamics (CFD) method. Besides the stall inception, an obvious “positive slope” phenomenon appears under off-design operating points in experiment without IGVs. The experimental data also shows that IGVs can change the performance of axial pumps and remove the “positive slope”. The CFD is mainly used to reveal the mechanism of the “positive slope” phenomenon, where the simulated results are firstly validated in comparison with the experimental data. The results obtained show that the reason for this “positive slope” is due to the backflow vortex in front of the impeller, and the tip clearance is found to take an important role in forming this backflow vortex.
CLOWT: A Multifunctional Test Facility for the Investigation of Organic Vapor Flows
Authors: Reinker Felix , Kenig Eugeny Y. , aus der Wiesche Stefan
Published: October 2018

Organic vapor flows are met in a wide range of technical applications (e.g., energy conversion, chemical processes, and refrigeration). Typically, organic fluids contain complex molecules, and their thermodynamic behavior deviates significantly from the ideal or perfect gas laws. The applicability of scaling laws to organic vapor flows is very limited, and there is a need for detailed experimental investigations under relevant process conditions. Furthermore, such investigations can provide a validation basis for the simulations performed with Computational Fluid Dynamics (CFD) tools. On the other hand, there exists a serious lack in experimental organic vapor flow test facilities. In this contribution, a novel Closed Loop Organic vapor Wind Tunnel (CLOWT) is presented. The concept of CLOWT is based on a closed-loop continuously running wind tunnel cycle. Its main components are a blower, a diffuser, a settling chamber, a contraction zone, a test section module, and a return, including a throttle valve and a mass flow meter. The test facility CLOWT applies the modular design approach which enables analysis of various flow configurations and components like blowers, small axial test turbines, nozzle flows or transonic flows past test objects. Thanks to an auxiliary heating system, organic vapor flows can be investigated at elevated pressure and temperature levels. The operation of CLOWT is based on closed gas turbine cycle control methods (e.g., inventory control). In addition to the general test facility concept, the paper gives a detailed discussion of the CLOWT special design features.
Flow Pattern Prediction in Electrical Submersible Pump (ESP) Under Gassy Flow Conditions Using Transient Multiphase CFD Methods With Visualization Experimental Validation
Authors: Zhu Jianjun , Cuamatzi-Melendez Ruben , Martinez Farfan Jose Alberto , Zhu Haiwen , Zhang Jiecheng , Zhang Hong-Quan
Published: October 2018

This paper presents a numerical study of flow pattern recognition inside the rotating impeller of electrical submersible pump (ESP) using the transient multiphase CFD simulations. Based on the previous experimental facility for visualizing flow patterns in an ESP, the entire flow domain is constructed. The high-quality structured mesh comprising hexahedral grids is generated using multi-block technique in ANSYS ICEM. Mesh independence is confirmed by comparing numerical results with catalog curves. For transient two-phase simulation, the realized RNG k-ε turbulence model with volume of fluid (VOF) and Eulerian multiphase models is successfully implemented in ANSYS Fluent solver. The sliding mesh technique is applied to interfaces where rotating and stationary parts interact. By incorporating the same boundary conditions as experimental study, two different cases with fixed liquid flow rates and varying gas flow rates are selected to conduct CFD simulations. The comparison of numerical results against experimental visualizations shows that the two-fluid Eulerian model is superior to VOF model in simulating gas/liquid flow in a rotating ESP. The single-phase simulation results match catalog curves of ESP, which validates the numerical methodology. For gas-liquid simulations, the simulated flow patterns with Eulerian model agree well with visualization experiments. The distinct flow patterns prevailing inside the rotating ESP impeller are captured by CFD simulations, including dispersed bubble flow, bubbly flow, and intermittent flow.
Numerical Comparison Between Steady and Sweeping Jets for Active Flow Control Applications
Authors: Aram Shawn , DeJong Andrew
Published: October 2018

A computational study is conducted to compare the performance of an array of steady jets and sweeping jets (generated by fluidic oscillator) interacting with an attached turbulent cross flow. Both jets operate at the same supply rate and with the jet-to-freestream velocity ratio of three. Two array spacings are considered in this study; one is chosen based on the minimum possible distance between the adjacent fluidic oscillators, and the other spacing represents an actuator’s configuration with the least interaction between jets. The improved delayed detached eddy simulation model is employed as a high fidelity turbulence modeling approach to resolve accurately the flow structures. Formation of strong vortex pairs is observed in both actuation techniques with the opposite sense of rotation between them. As expected, the sweeping jet affects a wider region of incoming turbulent flow along the spanwise direction compared to the steady jet. Examining the turbulence properties of the flow downstream of the jets indicates that the sweeping jet is a better candidate for enhancing the mixing mechanism used to control separation. Comparing both the instantaneous and time-averaged flow fields generated by the sweeping jets and steady jets reveals that the interaction between the adjacent sweeping jets at the minimum spacing arrangement is significantly stronger than that of the steady jets.
Effect of Cavitation Flow on Energy Conversion Characteristics of Nuclear Main Pump
Authors: Cheng Xiaorui
Published: October 2018

In order to study the relationship between the cavitation flow and energy conversion, based on the continuity equation, Renault N-S equation and RNG k-ε turbulence model, the whole flow field cavitation numerical simulation on unclear main pump model under design condition is carried out. Through the variation of pressure and velocity on the streamlines, combined with the basic equation of the pump, the dynamic and hydrostatic head of the nuclear main pump under different cavitation conditions are studied. The results show that the energy of fluid of nuclear main pump is provided by posterior segment of impeller, and the energy of the fluid decreases gradually from the shroud to the hub. Cavitation interferes with the flow of liquid in the impeller, which leads to the relative velocity increases and the pressure decreases in cavitation region, and the work capacity of blades is almost zero in bubble areas. At the same time, in non-cavitation region along with streamlines the dynamic head increases and the hydrostatic head decreases with the development of cavitation, and the decrease of the hydrostatic head is greater than the increase of the dynamic head, which results in the decrease of pump head and efficiency. In addition, in the cavitation region, with the development of cavitation, the sudden change of the dynamic and hydrostatic head increases, which increase the flow loss in the impeller and results in the decrease of pump head and efficiency moreover.
Validation Study of Compact Planing Hulls at Pre-Planing Speeds
Authors: Wheeler Miles P. , Matveev Konstantin I. , Xing Tao
Published: October 2018

Planing hard-chine hulls are often employed on fast boats to ensure high lift and moderate drag in high-speed regimes. Although such boats are usually designed for relatively light loadings, occasionally they may need to operate in overloaded conditions with reduced speed. The focus of this study is on planing hull hydrodynamics in such pre-planing, high-lift regimes. A numerical tool based on a finite-volume viscous solver is applied to simulate a compact planing hull in a speed range from the displacement to planing modes. Numerical results for the model-scale hull resistance, trim and sinkage are compared with experimental data. Additionally, an overloaded condition of this hull is simulated. The resulting variations of hydrodynamic parameters are discussed.
Simulations of an Air-Ventilated Strut Crossing Water Surface at Variable Yaw Angles
Authors: Matveev Konstantin I. , Wheeler Miles P. , Xing Tao
Published: October 2018

Hydrodynamic devices intended to produce lift, control actions, or propulsion can be prone to air ventilation when operating near the free water surface. The atmospheric air may propagate to the low-pressure zones around these devices located under the nominal water level. This often leads to performance degradation of hydrodynamic systems. Modeling of air-ventilated flows is challenging due to complex flow nature and many factors in play. In this study, the computational fluid dynamics simulations are carried out for a surface-piercing strut at different yaw angles. At small yaw angles, the strut underwater surfaces remain wetted, whereas at large yaw and sufficiently high Froude numbers the suction side becomes air ventilated. At the intermediate yaw angles, both wetted and ventilated flow regimes are possible, and the existence of a specific state depends on the history of the process. The present computational results demonstrate good agreement with available experimental data.
Optimization and Investigation on the Impact of Centrifugal Impeller Blade Thickness Distribution on Hydro-Induced Vibration
Authors: Qian B. , Wu D. Z.
Published: October 2018

The vibration performance of centrifugal impellers is of great importance for pumps in some application areas such as automobiles and ships. Apart from mechanical excitations for instance, unbalanced rotor and misalignment, attentions should be concentrated on the hydraulic excitations. The complex internal secondary flow in the centrifugal impeller brings degradation on both hydraulic and vibration performances. On the purpose of repressing the internal secondary flow and alleviating vibration, an attempt of optimization by controlling the thickness distribution of centrifugal impeller blade is given. The vibration performances of the impellers are investigated numerically and experimentally. Meanwhile, further study on the mechanism of the influence of the thickness distribution optimization on vibration is conducted. There is a relative velocity gradient from suction side (SS) to pressure side (PS) due to the Coriolis force, which causes non-uniformity of energy distribution. By means of thickness distribution optimization, the impeller blade angle on the PS and SS along the blade-aligned (BA) streamwise location is respectively modified and therefore the flow field can be improved.
Governing Parameters of Adverse Pressure Gradient Turbulent Boundary Layers
Authors: Maciel Yvan , Wei Tie , Gungor Ayse G. , Simens Mark P.
Published: October 2018

We perform a careful nondimensional analysis of the turbulent boundary layer equations in order to bring out, without assuming any self-similar behaviour, a consistent set of nondimensional parameters characterizing the outer region of turbulent boundary layers with arbitrary pressure gradients. These nondimensional parameters are a pressure gradient parameter, a Reynolds number (different from commonly used ones) and an inertial parameter. They are obtained without assuming a priori the outer length and velocity scales. They represent the ratio of the magnitudes of two types of forces in the outer region, using the Reynolds shear stress gradient (apparent turbulent force) as the reference force: inertia to apparent turbulent forces for the inertial parameter, pressure to apparent turbulent forces for the pressure gradient parameter and apparent turbulent to viscous forces for the Reynolds number. We determine under what conditions they retain their meaning, depending on the outer velocity scale that is considered, with the help of seven boundary layer databases. We find the impressive result that if the Zagarola-Smits velocity is used as the outer velocity scale, the streamwise evolution of the three ratios of forces in the outer region can be accurately followed with these non-dimensional parameters in all these flows — not just the order of magnitude of these ratios. This cannot be achieved with three other outer velocity scales commonly used for pressure gradient turbulent boundary layers. Consequently, the three new nondimensional parameters, when expressed with the Zagarola-Smits velocity, can be used to follow — in a global sense — the streamwise evolution of the stream-wise mean momentum balance in the outer region. This study provides a clear and consistent framework for the analysis of the outer region of adverse-pressure-gradient turbulent boundary layers.
Force Production Mechanisms of a Heaving and Pitching Foil Operating in the Energy Harvesting Regime
Authors: Siala Firas F. , Prier Michael W. , Liburdy James A.
Published: October 2018

The influence of vortex dynamics on the force production of a heaving and pitching foil operating in the energy harvesting regime is studied experimentally using 2C-PIV. Results are obtained for reduced frequencies in the range of k = fc/U = 0.06 to 0.14. The flow induced vertical force-time history during cyclic operation is evaluated from PIV data by using the impulse-based derivative moment transformation method. The contribution of each term in the equation is investigated. The results show that the leading edge vortex has the largest contribution to the total force, whereas the trailing edge vortex is shown to contribute negatively. In addition, the dynamics of the leading edge vortex are further analyzed by measuring the circulation and trajectory relative to the foil. It is shown that the force is not only dependent on the circulation magnitude, but also on the LEV foil-normal and chord-wise trajectories. The force-time history for all reduced frequencies exhibit two main distinct peaks. The primary peak is generated when the leading edge vortex forms. The secondary peak, on the other hand, is formed when the chord-wise convection of the leading edge vortex increases, as well as when the LEV is closer to the foil surface during the reversal of pitching motion.
The Effects of Wakes on Aerodynamic Characteristics of Flapping Wings in Clap-and-Fling Motion at Re of ~104
Authors: Han Jong-Seob , Han Jae-Hung
Published: October 2018

In this paper, aerodynamic characteristics of two flapping wings in clap-and-fling motion at Re of ∼104, which corresponds to the flight regime of flapping-wing micro air vehicles, was investigated. The test employing dynamically scaled-up robotic arms installed on a water tank revealed that the wingbeat motion at such high Re in1duced the fully developed wake within two wingbeat cycles. This wake widely influenced the lift production covering the entire wingbeat period; the wings earned the additional lift during the entire downstroke, and lost the lift during the upstroke. Chordwise cross-sectional DPIV showed the massive downwash with enlarged tip vortices, when the wake was fully developed. The wake blew down the headwind and reduced the effective angles of attack. In the case of the clap-and-fling motion, the wake was leaned toward the dorsal part, in which the wings created the clap-and-fling motion, causing the global fluctuation of the aerodynamic force production.
Interactional Effects of Inlet Guide Vane and Blade Angle on Hydraulic Performance Characteristics of a Submersible Axial-Flow Pump
Authors: Kim Youn-Sung , Shim Hyeon-Seok , Kim Kwang-Yong
Published: October 2018

This study aims to evaluate effects of blade pitch and inlet guide vane (IGV) angle on the performance characteristics of a submersible axial-flow pump. According to the results of the previous study, the efficiency at the design and over-load conditions were significantly affected by the angle of IGV due to change in the incidence angle. To investigate the interactional effects of IGV and blade angle are analyzed using three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model. The hexahedral grids are used in the computational domain and a grid-dependency test is performed to obtain an optimal number of the grids. In this study, combinations of three different blade angles and two different IGV angles are tested. Adjusting angle of IGV increases the total pressure of the pump with a blade pitch increase, which can increase the efficiency of the pump in operating range.
Effect of Green Wall Modules on Air Temperature and Humidity
Authors: Abdo Peter , Huynh B. P. , Avakian Vahik
Published: October 2018

Green or living walls are active bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. They can be classified as passive or active systems. The active systems are designed with ventilators which force air through the substrate and plant rooting system, therefore the air is purified and filtered through a bio-filtration process which also acts as a natural cooling system. Their benefits include temperature reduction, improvement of air quality and reduction of air pollution, oxygen production as well as the social and psychological wellbeing. They can produce changes in the ambient conditions (temperature and humidity) of the air layers around them which create an interesting insulation effect. The effect of green wall modules on the air temperature and on humidity is investigated in this work. A closed chamber made of acrylic sheets is used to monitor the temperature and humidity variation caused by a green wall module placed at its center. A fan positioned at the back center of the module drives air at ambient conditions and direct it into the module. Temperature and humidity are measured at different locations inside the chamber during operation for different modules with different plant species. The effect of changing the surrounding ambient conditions is also investigated.
Effect of Windcatcher’s Inlet Shape on Ventilation Flow Through a Two Dimensional Room
Authors: Abdo Peter , Taghipour Rahil , Huynh B. P.
Published: October 2018

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment by decreasing moisture content in the air and reducing pollutants concentration. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Generally, it is difficult for wind to change its direction, and enter a room through usual openings, the windcatcher is designed to overcome such problems since they have vertical columns aimed at helping wind to channel down to the inside of a building. The efficiency of a windcatcher is maximized by applying special forms of opening and exit. The openings depend on the windcatcher’s location and on its cross sectional area and shape such as square, rectangular, hexagonal or circular. In this study the effect of the inlet design is investigated to achieve better air flow and increase the efficiency of windcatchers. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a two dimensional room fitted with a windcatcher based on different inlet designs such as a uniform inlet, a divergent inlet and a bulging-convergent inlet.
Analysis of Transient Two-Phase Flow in Pressure Safety Valve Outlet Headers
Authors: Taghva Maral , Damkilde Lars
Published: October 2018

To protect a pressurized system from overpressure, one of the most established strategies is to install a Pressure Safety Valve (PSV). Therefore, the excess pressure of the system is relieved through a vent pipe when PSV opens. The vent pipe is also called “PSV Outlet Header”. After the process starts, a transient two-phase flow is formed inside the outlet header consisting of high speed pressurized gas interacting with existing static air. The high-speed jet compresses the static air towards the end tail of the pipe until it is discharged to the ambiance and eventually, the steady state is achieved. Here, this transient process is investigated both analytically and numerically using the method of characteristics. Riemann’s solvers and Godunov’s method are utilized to establish the solution. Propagation of shock waves and flow property alterations are clearly demonstrated throughout the simulations. The results show strong shock waves as well as high transient pressure take place inside the outlet header. This is particularly important since it indicates the significance of accounting for shock waves and transient pressure, in contrast to commonly accepted steady state calculations. More precisely, shock waves and transient pressure could lead to failure, if the pipe thickness is chosen only based on conventional steady state calculations.
Numerical Analysis of the Turbulent Flow Characteristics Around Submerged Permeable Breakwaters
Authors: Foltz William , Zhang Ning
Published: October 2018

A breakwater is a structure used to reduce the energy of waves. When used properly, they can protect coasts from being affected by waves. One such application is to lessen erosion along Louisiana’s coastlines, where wave action is strong and is the main source of the erosion. Additionally, the breakwater can change how sediments are transported, and allow for the deposition and accumulation of sediment at target areas. This research aims to give a numerical comparison of the effectiveness of three different breakwater designs, and reveal the turbulence characteristics downstream of the breakwaters. Three breakwaters are examined: a solid panel without any holes, another panel with one hole, and a third panel with three holes. These breakwaters are expected to be placed on the banks of various water bodies in coastal Louisiana, to protect the surrounding wetlands from coastal erosion and land losses. The designs aim to reduce the wave action from the water bodies, while the holes on them allow the sediments to pass through and deposit on the wetlands downstream. To run the simulations, the CFD software ANSYS FLUENT was used. The numerical results were compared to experimental data, and the good agreement proves the accuracy of the results. The effects of different wave patterns on the downstream turbulence were also analyzed and discussed in this study.
Fluid Properties of Microencapsulated Phase Change Material Slurries
Authors: Young Jonathan , Benner Jingru , Santamaria Anthony D.
Published: October 2018

Electrochemical energy conversion and storage devices are becoming a large part of the renewable energy market. For these systems to operate optimally over a wide range of operating and environmental conditions, advanced strategies for thermal management must be developed. Incorporating microencapsulated phase change materials (MEPCM), which utilize latent heat storage, into coolant fluids has been shown to increase the fluid’s thermal capacity. This mitigates the temperature gradient between the coolant loop inlet and outlet which is important in systems such as fuel cells and batteries where sensitivity to temperature directly impacts the electrochemical reaction, transport processes, and component lifetimes. The use of MEPCMs may allow for lower coolant flow rates which may reduce parasitic pumping power, further increasing overall system efficiency. In this work MEPCM material is added to liquid water at several mass concentration ratios, and an analytical study was conducted to determine pressure drop and channel power requirements. The viscosity of the slurry is measured along with its density, conductivity, and heat capacity as a function of temperature. Inlet and outlet channel slurry temperatures are monitored, flow rate is controlled, and the heat flux can be varied to simulate waste heat outputs of various devices. From this data the optimal conditions for the slurry flow can be assessed and thermal management strategies can be designed for specific devices.
Development of an Advanced Wind Turbine Actuator Line Model
Authors: O’Dea Murphy Leo , Guessous Laila
Published: October 2018

Large-scale wind turbine installations are sited using layouts based on site topology, real estate costs and restrictions, and turbine power output. Existing optimization programs have limited capabilities to site multiple turbines and are based on simple geometric turbine wake models, which typically overestimate individual turbine output. Alternatively, complete CFD modeling of entire wind turbine fields requires enormous computational resources, which has led to the development of blade modeling techniques which are combined with CFD field computations. The most promising method, using the actuator line model, typically uses an exponential function to spread blade forces over CFD grid points. In addition, little development work has been performed to determine the optimal grid point density and force spreading radius for these methods.

In this paper, we report on our ongoing efforts to develop an advanced actuator line formulation which uses an alternate geometric method for distributing blade forces to the CFD field. Domain and blade force application parameters are currently being developed to determine optimum run time conditions for the new actuator line model. The Actuator line method is implemented using the parallel CFD program, NEK5000. NEK5000 is an advanced Navier Stokes code which uses spectral methods for the spatial discretization, and has been proven to provide high-resolution results with significantly reduced compute resources. A Large Eddy Simulation turbulence model is used. In this paper, we report on our current work using large scale supercomputer resources at the Extreme Science and Engineering Discovery Environment (XSEDE) to perform computational experiments to validate our codes, and perform parametric studies to develop optimum run time parameters. Development and verification work is centered around domain size, grid spacing and clustering, and development of steady state conditions. The parametric studies are underway and are based on investigating various selection volume and force application point settings. Continuing work will compare the new actuator line method with a traditional exponential force distribution model.
Effects of an Underbody Device on the Characteristics of a Trailer Truck Wake Region
Authors: Ibrahim M. , Agelin-Chaab M.
Published: October 2018

The aerodynamics of bluff bodies and flow separation are encountered in many industrial applications. Flow separation causes significant pressure fluctuations that can yield undesirable effects such as vibration, noise, and drag. It is well-known that at highway speeds, over 50% of the fuel is used by a road vehicle to overcome aerodynamic drag. Due to these reasons, bluff body aerodynamics has been the subject of intensive research interests for many decades. In this paper, a new concept of an underbody aerodynamic device is used to modify the turbulent wake region of a bluff body.

In particular, the underbody device was designed in order to allow for the recirculating flow to reattach and exit the underside of the bluff body while increasing the average speed of the flow and preventing side winds from disturbing the flow. This significantly reduces the underbody recirculation zone, which is a major source of drag. In addition, this ensures that the flow exits with minimum turbulence to reduce the size of the bluff body’s wake. The studies were conducted using the RANS based turbulence model, k-ω SST in ANSYS Fluent. A width-based Reynolds number of 1.1 × 106 was used to conduct the simulations in order to validate the baseline model with NASA’s wind tunnel data; which include the surface pressure coefficients and a drag coefficient. The paper focuses on the changes in the model’s wake that were introduced due to the device and their influence on the underside flow. The results showed that the device significantly reduced the recirculation at the underside of the bluff body. This was found to increase the coefficient of pressure at the base of the model, which reduced the size of the wake. These changes in the flow field resulted in an overall drag coefficient reduction of 4.1%.
Comparison of Experimental, Thermoelastohydrodynamic (TEHD) and Isothermal, Non-Deforming Computational Fluid Dynamics (CFD) Results for Thrust Bearings
Authors: Deng Xin , Watson Cori , He Minhui , Wood Houston , Fittro Roger
Published: October 2018

Bearings are machine elements that allow components to move with respect to each other. A thrust bearing is a particular type of rotary bearing permitting rotation between parts but designed to support a predominately axial load. Oil-lubricated bearings are widely used in high speed rotating machines such as those found in the aerospace and automotive industries. With the increase of velocity, the lubrication regime will go through boundary lubrication, mixed lubrication, and hydrodynamic lubrication (full film). In this paper, the analysis was in the hydrodynamic lubrication region.

THRUST is used to predict the steady-state operating characteristics of oil-lubricated thrust bearings. As a thermoelastohydrodynamic prediction tool, THRUST assumes a 3D turbulence model, 3D energy equation, and 2D Reynolds equation. Turbulence is included by obtaining average values of eddy momentum flux (Reynolds stress) and averaging the influence down to a 2D Reynolds equation. Convergence is achieved by iterating on the pad tilt angles and pivot film thickness until the integrated pressure matches the load applied to the pad. Despite the multiple experimental, CFD, and TEHD studies of thrust bearings that have been performed to date, no validation has yet been performed to confirm the accuracy of TEHD methods in modeling the performance of thrust bearings by both experimental and advanced computational means simultaneously. This study addresses this need by comparing TEHD and CFD simulation results of film thickness, temperature, power loss, and pressure in thrust bearings taken from the literature at multiple speeds and loads with results from experimental data.

Starting from the case of the lowest speed and load, it was verified that this case is indeed laminar and with negligible thermal and elastic effects. Four cases were run in THRUST, a TEHD solver, combining thermal and deformation in each rotational speed and load combination. Additionally, a CFD study was performed in ANSYS CFX with the assumptions of isothermal, non-deforming. The average viscosity from THRUST was used in CFD to follow the effects of the isoviscous assumption. Then, the experimental, TEHD and CFD results were compared at each case. Experimental, TEHD, and CFD results show acceptable agreement when turbulence is negligible.
Study of the Similarity Laws for Supercritical CO2 Turbine Performance Testing Using High Pressurized Air
Authors: Ying Qiyu , Zhuge Weilin , Zhang Yangjun , Song Panpan , Zhang Lei
Published: October 2018

Closed regenerative Brayton cycle utilizing supercritical CO2 as working fluid has attracted more concern recently as it offers high cycle thermal efficiency and decreases size of turbomachinery. The performance testing of the CO2 turbine is very important for the supercritical CO2 cycle development. However, testing the turbine performance in a closed supercritical CO2 cycle is of difficulty and complication. This paper proposes a novel experimental method on CO2 turbine testing using high pressurized air as surrogate fluid. The performance similarity laws for the experimental method are studied, because traditional similarity criteria are not applicable since supercritical CO2 and high pressurized air are both non-ideal gases. A CO2 turbine is simulated by the CFD method under similar operating conditions with CO2 and high pressurized air, and turbine performance and flow field is analyzed. CFD analysis results show that turbine’s overall performance matches up well, and difference of parameter in flow field is small. The proposed experimental method can be used for CO2 turbine performance testing without setting up the complex closed supercritical CO2 cycle test bench.