bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Sealing in Transient Injector Simulations
Authors: Mohapatra Chinmoy , Jacobsohn Gabriel , Baldwin Eli , Schmidt David
Published: October 2017

The early and late portions of transient fuel injection have proven to be a rich area of research, especially since the end of injection can create a disproportionate amount of emissions in direct injection internal combustion engines. A perennial challenge in simulating the internal flow of fuel injectors is the valve opening and closure event. In a typical adaptive-mesh CFD simulation, the small gap between the needle valve and the seat must be resolved with very small cells, resulting in extremely expensive computations. Capturing complete closure usually involves a topological change in the computational domain. In this work we present a more gradual and easily-implemented model of closure that avoids spurious water-hammer effects. The algorithm is demonstrated with a simulation of a gasoline direct injector operating under cavitating conditions. The results include the the first simulation of a multiple injection event known to the authors. The results show cavitation at low valve lift. Further, they reveal post-closure dynamics that result in dribble, which is expected to contribute to unburned hydrocarbon emissions.
A Compressible Thermohydrodynamic Analysis of Journal Bearings Lubricated With Supercritical CO2
Authors: Chien Ssu-Ying , Cramer Mark , Untaroiu Alexandrina
Published: October 2017

In this study, a compressible thermohydrodynamic (THD) model was developed to examine the flow dynamics of a journal bearing lubricated with supercritical carbon dioxide (sCO2). This model employed a general form of the Reynolds equation governing compressible lubricant flows with a well-known analytical equation of state, and a viscosity model that depends on both pressure and temperature. In order to verify the model, we first compared the results of this compressible Reynolds equation to the full Navier-Stokes solutions. The accuracy of the model was found to be reasonable when the operating condition is sufficiently far from the thermodynamic critical point. Additionally, the numerical solution suggests that different temperature boundary conditions give slight different results due to the small variations of density and temperature across the gap. Finally, the general approach presented in this study introduces a new single parameter — effective bulk modulus that characterize both the frictional and thermodynamic fluid response. The model developed in this study can provide guidance for further studies of CO2-lubricated bearings operating in the full supercritical regime.
Numerical Study of Transient Flow and the Influence of Height and Viscosity in a Cyclonic Chamber in a Distribution System
Authors: Rodrigues Carolina C. , Eidt Henrique K. , Dunaiski Rafael , Ofuchi César Y. , Neves Flávio , Santos Paulo H. D. , Morales Rigoberto E. M.
Published: October 2017

In the petroleum industry, during the production and transportation of oil, multiphase flow occurs, due to the usual mixture of the crude oil, water and gas. This type of flow can be simplified, for study purposes, as a two-phase one, in which the gas is one phase, and a mixture of oil and water is the other. Separation of gaseous and liquid phases at the wellhead level is done by a separator and has innumerous advantages, including avoiding or at least reducing typical problems of multiphase flows such as intermittent flow, severe slugging and hydrates deposition. Another advantage is to increase the efficiency of the submersible centrifugal pumps or other artificial lift process used. A recurrent problem found in exploration and production of oil and gas is the range of the fluid viscosities encountered during exploration and extraction of petroleum, which can greatly vary with the temperature or the composition of the oil being extracted. Thus, it is necessary to understand how this parameter affects the performance of the equipment used. In addition, installation and maintenance of separators are hampered by the large size of this type of equipment. Therefore, a prior distribution system is here proposed, aiming to distribute the flow in more than one branch, in order to decrease the general size of the separation equipment needed, while maintaining the flow rate and separation efficiency. This distribution system has a cyclonic chamber, in which the flow enters through two nozzles tangentially oriented with the wall of the chamber, which performs a pre-separation due to the centrifugal field, and divides the flow into four outlets. This work presents a numerical study on the height influence of the cyclonic chamber in a distribution system. The transient beginning of the flow is analyzed, with the stability of the film being study. This work is focused on the behavior of the liquid phase in this proposed distribution system, so that only single-phase liquid flow at the inlet of the distribution system is considered. A validation was done through comparison with experimental data obtained in a test rig, in which was used one wire mesh sensor with 12 wires in order to evaluate the thickness of the liquid film over time. In addition, different heights and viscosities are studied in order to evaluate their influence on the flow. The parameters investigated are the film thickness, velocity and turbulence kinetic energy fields and flow rates at the outlets, focusing on the stability of the film and the transient effects associated with the beginning of the flow. In order to perform this study, the commercial software ANSYS-CFX 15.0 was used, with a hybrid mesh, for four different heights and two inlet velocities.
Developing an Optimal Helix Angle As a Function of Pressure for Helical Groove Seals
Authors: Watson Cori , Wood Houston G.
Published: October 2017

Helical groove seals are non-contacting annular seals used in pumps between impeller stages and at the balance drum. These seals have helically machined grooves on the surface of the rotor and/or stator. They work to sustain a pressure difference given a mass flow rate of the impeller through two flow phenomena which can be characterized by their flow direction. Fluid flowing axially dissipates kinetic energy through turbulent mixing as fluid is pushed through the jet stream region and mixes in the larger groove region, thus producing a pressure differential. Fluid flowing in the groove direction rotates with the rotor wall and is positively displaced toward the high pressure region, essentially acting as a screw pump. Previous work with optimization of helical groove seals has shown that the ideal helix angle of the seal is steeper for lower pressure applications and shallower for higher pressure applications. This is due to lower pressure applications having higher circumferential velocity in the grooves. In high pressure applications, the groove circumferential velocity has even been shown to be negative, and therefore the fluid leaks out the end of the grooves. The objective of this study is to use computational fluid dynamics simulations to find the optimal helix angle of the seal given the pressure differential. To accomplish this goal, simulations were run in ANSYS CFX for various inlet pressures, given zero gauge outlet pressure, and the helix angle of the grooves are varied. The helical grooves seals in this study have grooves on only the stator surface. The number of grooves is varied with the angle to keep the axial cross section of the seal consistent. By doing this, the study is able to focus in on the pumping mechanism of the helical groove seal without substantially changing the energy dissipation. The mass flow rates from each simulation for a given inlet pressure are plotted and quadratic regression was used to calculate an optimal helix angle as a function of inlet pressure. This study also answers the question of whether is there a limit where circumferentially grooved, i.e. labyrinth, seals outperform helical groove seals for very high pressures. Results comparing the powerloss of helical groove seals versus labyrinth seals and the effect of helix angle on powerloss are also given.
PANS Study of the Flow Around an Oscillating, Simplified Truck Cabin With Flow Control
Authors: Minelli G. , Krajnović S. , Basara B.
Published: October 2017

This work presents an application of the Partially-Averaged Navier-Stokes equations for an external vehicle flow. In particular, the flow around a generic truck cabin is simulated. The PANS method is first validated against experiments and resolved LES on two static cases. As a consequence, PANS is used to study the effect of an active flow control (AFC) on a dynamic oscillating configuration. The oscillation of the model represents a more realistic ground vehicle flow, where gusts (of different nature) define the unsteadiness of the incoming flow. In the numerical study, the model is forced to oscillate with a yaw angle 10° > β > −10° and a non-dimensional frequency St = fW/Uinf = 0.1. The effect of the periodic motion of the model is compared with the quasi-steady flow condition. At a later stage, the dynamic configuration is actuated by means of a synthetic jet boundary condition. Overall, the effect of the actuation is beneficial. The actuation of the AFC decreases drag, stabilises the flow and reduces the size of the side recirculation bubble.
Optimal Leading Edge Vortex Formation of a Flapping Foil in Energy Harvesting Regime
Authors: Siala Firas F. , Totpal Alexander D. , Liburdy James A.
Published: October 2017

An experimental investigation is conducted to study the leading edge vortex (LEV) evolution of a simultaneously heaving and pitching foil operating in the energy harvesting regime. Two dimensional particle image velocimetry measurements are collected in a wind tunnel at reduced frequencies of k = fc/U = 0.05–0.20. Vorticity flux analysis is performed to calculate the constant C in the vortex formation number equation proposed by J. O. Dabiri [1], and it is shown that for a flapping foil operating in the energy harvesting regime, this constant is approximately equal to 1.33. We demonstrate that the optimal LEV formation number (T̂max ≈ 4) is achieved at k = 0.11, which is well within the range of optimal reduced frequency for energy harvesting applications (k = 0.1–0.15). This suggests that the flow energy extraction is closely related to the efficient evolution process of the LEV.
Erosion Modeling in High Concentration Slurry Flow
Authors: Arabnejad Khanouki H. , Zahedi P. , Shirazi S. A. , McLaury B. S.
Published: October 2017

Many industrial processes involve high concentration particulate multiphase flow in which the carrier phase is continuous and the solid particles are dispersed in the carrier phase. Although much research has been directed toward modeling of solid particle erosion, very few have presented a generalized approach for erosion modeling under high concentration slurry impact. Experimental and numerical studies have shown that when particles are transported by liquid or dense gas, the particle impact angles are very low. The impact angles in these cases are sometimes less than the smallest angle that can be obtained in a direct impingement erosion test. Moreover, particle-particle interaction is significant when particle loading is high, and the effect should be accounted for in the numerical simulation. In this work, a mechanistic erosion equation that includes an abrasion term for low angle impacts is implemented in CFD simulation of submerged slurry impinging jet with ANSYS Fluent. The Eulerian-Lagrangian method is used to model the carrier fluid flow and particle tracking, respectively, while the particle-particle interaction is resolved statistically through a two-fluid Eulerian-Granular model. In this approach, particle-particle interaction is modelled through solid stresses acting on the particles in a dense flow by an additional acceleration in the particle force balance for the Lagrangian phase. The CFD erosion predictions are compared with experimental data from a previous work in the literature. It is shown that by including the abrasion term, the total mass loss of the specimen agrees better with experimental data, and the obtained erosion pattern is more comparable to the data collected by 3D profilometry. It was found that the combined two-fluid model is capable of capturing the decrease in the erosion ratio (defined as the ratio of material loss to the particle throughput) with increase in particle loading which can be ascribed to a shielding effect caused by particles moving close to the wall.
An Immersed Boundary Method in OpenFOAM for Arbitrarily Shaped Particles in the Shear Flow Field of Centrifugal Separators
Authors: Buerger Markus , Kumar Chethan Mohan , Janoske Uwe
Published: October 2017

In the multiphase simulation of material handling and filtration processes the coupling between the fluid phase, which imposes aero- or hydrodynamic forces onto the particles, and the particulate matter, which in turn impose momentum into the fluid, is of major importance. Conventional simulation methods such as CFD-DEM-coupling are based upon empirical and analytical drag models. Moreover, they have the degradation of particles to point masses in common. Thus empirical modeling neglects the microscopic details that are essential to a profound understanding of micro scale processes and accurate macro scale simulation results.

A new simulation model which is built upon numerical simulation methods like CFD and the immersed boundary method is developed for OpenFOAM®. It is capable of fully discretizing the geometry of arbitrarily shaped bodies.

This work demonstrates the application of our simulation model to the multiphase flow in the near wall shear flow field of centrifugal separators. The validation of the model regarding particle drag and spin of variously shaped particles in the shear flow shows that the particle shape determines essentially the process of settling, separation and resuspension.
Computational Analysis of Benzing Airfoils for Optimization in a Wing Configuration for a Formula SAE Car
Authors: Su Yuling , Basavaraj Akshay
Published: October 2017

Wing selection plays a crucial role for race cars as it generates the most downforce. This is essential to maintain traction which leads to faster lap timings, and maintain efficiency in the performance of the race car. In this paper, the numerical simulation of a Formula SAE (FSAE) Car is performed. The FSAE car is restricted by regulations in terms of the geometry of the front and rear wing configuration. Hence, it becomes necessary to optimize the selection of airfoils in order to get the best out of the wing configuration. It is also essential to observe the tradeoff between the downforce generated and the drag produced in a racecar for optimal performance. This serves as the primary motivation of this research paper. The focus is on Benzing airfoils, which show considerably better performance in terms of downforce production in a race car than conventional airfoils. The wing configuration utilized in this research paper consists of a single mainplane and two flaps.. The freestream velocity of the flow is in the range of 0–60mph (0–26m/s). The 122 series of Benzing airfoils is utilized for the mainplane and the 153 series of Benzing airfoils is utilized for the flaps for manufacturing reasons. Nine different combinations of Benzing airfoils were utilized wherein it was noticed that an appropriate selection of the airfoils for the mainplane and flaps with a fixed angle of attack difference, leads to a 12–15% increase in downforce amongst the Benzing airfoils itself. Similarly, it was also observed that an optimal configuration would lead to a 12–15% decrease in drag in comparison too poor performing airfoil. The Be 153-055 airfoil acts as an excellent flap within the limits of computational error. Data from an on-track test is used in order to verify the approach utilized in this paper in order to validate if the approach used in this paper would be feasible. It is observed that the Benzing airfoil does improve the average cornering speed of the car by around 10% in comparison to the previous configuration of S1223 airfoil as the main plane and the goe 477 airfoil as the flap.
A Conformal Decomposition Finite Element Method for Dynamic Wetting Applications
Authors: Noble David R. , Kucala Alec , Martinez Mario J.
Published: October 2017

An enriched finite element method is described for capillary hydrodynamics including dynamic wetting. The method is enriched via the Conformal Decomposition Finite Element Method (CDFEM). Two formulations are described, one with first-order accuracy and one with second-order accuracy in time. Both formulations utilize a semi-implicit form for the surface tension that is shown to effectively circumvent the explicit capillary time step limit. Sharp interface boundary conditions are developed for capturing the dynamic contact angle as the fluid interface moves along the wall. By virtue of the CDFEM, the contact line is free to move without risk of mesh tangling, but is sharply captured. Multiple problems are used to demonstrate the effectiveness of the methods.
Liquid Film Thickness Prediction in Elbows for Annular Flows
Authors: Zahedi Peyman , Arabnejad Khanouki Hadi , McLaury Brenton S. , Shirazi Siamack A.
Published: October 2017

In many industrial applications such as oil and gas production systems and heat exchangers, annular flow is a frequently observed flow regime. A lot of experiments and analysis have been carried out in the last decades in order to determine the thickness of the liquid film in annular flow and in straight pipes; however, published liquid film thickness models and experimental data in bends are scare. This paper presents a model for predicting average liquid film thickness in bends according to the correlations obtained for calculating dimensionless interfacial friction factor as well as dimensionless liquid film thickness in bends. Correlations were obtained based on analysis carried out using a control volume of gas core and utilizing experimental data available in the literature for liquid film thickness in bends. Furthermore, liquid film thickness distribution at the inner and outer bends of elbows were investigated, and a simple analytical model has been developed for predicting film thickness at the outer and inner radii of a bend. It is shown that, the average film thickness calculations from the current model agree with experimental data and results show that the model can predict the film thickness changes based on the flowrates and properties of liquid and gas phases.
Boundary Layer Formation on Axially Aligned Cylinders
Authors: Jones Nicholas F. , Vaccaro John C. , Rooney David M.
Published: October 2017

An experimental study was undertaken to investigate the influence of leading edge geometry and of relative curvature on the formation of a boundary layer on the surface of a cylinder aligned axially in a uniform flow. Hot wire anemometry was used to measure mean and fluctuating velocity components at a number of axial locations from the leading edge of cylinders of three different relative curvatures and two different leading edge shapes. In all cases a minimum relative axial length of greater than ten radii was examined, hence allowing adequate inspection of the formation region. Six cylinders were employed in the study, three with a blunt leading edge, and three with an ellipsoid of 3:1 ratio leading to the constant radius length. The Reynolds number based on cylinder radius (Rea = Uoa/v) varied from 3000 ≤ Rea ≤ 9000. The elliptical leading edge cylinders experienced laminar boundary layers, and the blunt cylinders created a separated bubble region followed by the development of a turbulent boundary layer. The laminar boundary layer was smaller than what a flat plate would produce at a corresponding length, and its experimental data generated profiles could be universalized with previously developed similarity variables. The turbulent boundary layer assumed a nearly constant velocity profile in the region 10 ≤ x/a ≤ 40, and its height grew proportionally to x1/3 rather than to x4/5 as for a flat plate. Streamwise turbulence intensities diminished rapidly with vertical distance from the surface of the cylinder, and also assumed a constant profile as relative axial distance increased. Over the limited range examined, changes in curvature were of secondary importance on relative boundary layer growth.
Study on Vortex Generators for Control of Attached Cavitation
Authors: Che Bangxiang , Wu Dazhuan
Published: October 2017

Attached cavitation is a type of common cavitation phenomenon in fluid machinery. It is important to develop methods to control its generation. From the view of cavitation inception, the generation of attached cavitation is greatly influenced by the separated boundary layer upstream of cavitation detachment. In this research, a row of microscopic delta-shaped counter-rotating vortex generators (VGs) was applied on the leading edge of the NACA0015 hydrofoil in order to suppress the boundary layer separation and then suppress the generation of attached cavitation.

The application of VGs fixed the position of cavitation inception on hydrofoil thus the sheet cavitation became more stable and the cloud cavity shed from hydrofoil with trim trailing edge more regularly. It was found that cavitation inception always appeared adjacent to VGs due to the low pressure in the corner of streamwise vortices induced by VGs. Hydrofoil with VGs showed an entirely different cavitation morphology on the leading edge. A row of separate microscopic vortex cavitation was induced by the counter-rotating vortices firstly. With the lower the height of VGs, the longer the length of these vortex cavitation due to the weaker interaction between vortices and main flow. Following the vortex cavitation, the attached cavitation was developing, but without typical “finger” structure anymore.
Cryo-Adsorbent Hydrogen Storage Systems for Fuel Cell Vehicles
Authors: Tamburello David , Hardy Bruce , Corgnale Claudio , Sulic Martin , Anton Donald
Published: October 2017

Numerical models for the evaluation of cryo-adsorbent based hydrogen (H2) storage systems for fuel cell vehicles were developed and validated against experimental data. These models simultaneously solve the equations for the adsorbent thermodynamics together with the conservation equations for heat, mass, and momentum. The models also use real gas thermodynamic properties for hydrogen. Model predictions were compared to data for charging and discharging both activated carbon and MOF-5™ systems. Applications of the model include detailed finite element analysis simulations and full vehicle-level system analyses. The full system models were used to compare prospective system design performance given specific options, such as the adsorbent materials, pressure vessel types, internal heat exchangers, and operating conditions. The full vehicle model, which also allows the user to compare adsorbent systems with compressed gas, metal hydride, and chemical hydrogen storage systems, is based on an 80 kW fuel cell with a 20 kW battery evaluated using standard drive cycles.

This work is part of the Hydrogen Storage Engineering Center of Excellence (HSECoE), which brings materials development and hydrogen storage technology efforts together to address onboard hydrogen storage in light duty vehicle applications. The HSECoE spans the design space of the vehicle requirements, balance of plant requirements, storage system components, and materials engineering. Theoretical, computational, and experimental efforts are combined to evaluate, design, analyze, and scale potential hydrogen storage systems and their supporting components against the Department of Energy (DOE) 2020 and Ultimate Technical Targets for Hydrogen Storage Systems for Light Duty Vehicles.
Computational Fluid Dynamics Study on the Effect of Inlet Modifications of Gas-Liquid Cylindrical Cyclone (GLCC©) Compact Separators
Authors: Kolla Srinivas Swaroop , Mohan Ram S. , Shoham Ovadia
Published: October 2017

The Gas-Liquid Cylindrical Cyclone (GLCC©1) is a simple, compact and low-cost separator, which provides an economically attractive alternative to conventional gravity based separators over a wide range of applications. More than 6,500 GLCC©’s have been installed in the field to date around the world over the past 2 decades. The GLCC© inlet section design is a key parameter, which is crucial for its performance and proper operation. The flow behavior in the GLCC© body is highly dependent on the fluid velocities generated at the reduced area nozzle inlet. An earlier study (Kolla et al. [4]) recommended design modifications to the inlet section, based on safety and structural robustness. It is important to ensure that these proposed configuration modifications do not adversely affect the flow behavior at the inlet and the overall performance of the GLCC©. This study is carried out for a specific GLCC© field application, separating light oil, steam flooded wells in Minas, Indonesia. Computational Fluid Dynamics (CFD) software is used to analyze the hydrodynamics of flow with the proposed modifications of the inlet section for GLCC© field applications.
Numerical Modeling of Spores Dispersal of Sphagnum Moss Using ANSYS FLUENT
Authors: Whitaker Dwight L. , Simsiman Robert , Chang Emily S. , Whitehead Samuel , Sarvghad-Moghaddam Hesam
Published: October 2017

The common peat moss, Sphagnum, is able to explosively disperse its spores by producing a vortex ring from a pressurized sporophyte to carry a cloud of spores to heights over 15 cm where the turbulent boundary layer can lift and carry them indefinitely. While vortex ring production is fairly common in the animal kingdom (e.g. squid, jellyfish, and the human heart), this is the first report of vortex rings generated by a plant. In other cases of biologically created vortex rings, it has been observed that vortices are produced with a maximum formation number of L/D = 4, where L is the length of the piston stroke and D is the diameter of the outlet. At this optimal formation number, the circulation and thus impulse of the vortex ring is maximized just as the ring is pinched off. In the current study, we modeled this dispersal phenomenon for the first time using ANSYS FLUENT 17.2. The spore capsule at the time of burst was approximated as a cylinder with a thin cylindrical cap attached to it. They were then placed inside a very large domain representing the air in which the expulsion was modeled. Due to the symmetry of our model about the central axis, we performed a 2D axisymmetric simulation. Also, due the complexity of the fluid domain as a result of the capsule-cap interface, as well as the need for a dynamic mesh for simulating the motion of the cap, first a mesh study was performed to generate an efficient mesh in order to make simulations computationally cost-effective. The domain was discretized using triangular elements and the mesh was refined at the capsule-cap interface to accurately capture the ring vortices formed by the expulsed cap. The dispersal was modeled using a transient simulation by setting a pressure difference between inside of the capsule and the surrounding atmospheric air. Pressure and vorticity contours were recorded at different time instances. Our simulation results were interpreted and compared to high-speed video data of sporophyte expulsions to deduce the pressure within the capsule upon dispersal, as well as the formation number of resulting vortex rings. Vorticity contours predicted by our model were in agreement with the experimental results. We hypothesized that the vortex rings from Sphagnum are sub-optimal since a slower vortex bubble would carry spores more effectively than a faster one.
Understanding the Mechanics of Blast Pressure Waves Inside a Shock-Tube: Effects of Geometry Optimization on the Blast Profile
Authors: Eslaminejad Ashkan , Sarvghad-Moghaddam Hesam , Ziejewski Mariusz , Karami Ghodrat
Published: October 2017

While many theoretical and numerical studies have been carried out to study blast induced traumatic brain injury (bTBI), validation of simulation results is still a concern due to moral issues and experimental constraints. Shock-tubes are one of the major means for replicating blast waves in a controlled medium. North Dakota State University Shock-tube (NDSUST) has been designed to simulate the blast shockwaves in an attempt to study and investigate bTBI. However, accurate replication of a blast profile in terms of the impulse and overpressure is highly dependent on the geometrical features of the shock-tube. To this end, numerical methods such as computational fluid dynamic (CFD) analysis can help to evaluate and increase the efficiency of the current shock-tubes. The NDSUST contains three major parts, namely, driver (the high pressure container), driven cone, and the chamber to setup the head model. The driver and driven cone are separated by layers of Mylar membrane. Shockwaves are defined by three pressure-time characteristics; positive phase (positive impulse), negative phase (negative impulse), and maximum pressure (overpressure). While the current NDSUST simulated most shockwave characteristics accurately, the negative impulse was observed to be considerably long. The diameter of Mylar membrane interface, the volume of the deriver, and the chamber room cross-section connected to the driven cone, were considered as possible parameters affecting the efficiency of the shock-tube. Accordingly, NDSUST was modeled in ANSYS CFX using its actual dimensions. A transient CFD analysis was carried out using ANSYS CFX to simulate the turbulent, supersonic, and compressible flow upon rupture of the Mylar membrane in order to study the pressure wave propagation inside the shock-tube. No-slip boundary conditions were chosen for the shock-tube walls. Driver and driven sections were considered as two separate domains connected using an interface. The shockwave was generated by setting the driver and driven sections at high and low pressures, respectively and running the simulation for a total time of 1 second. The primary results revealed that the current cross-section at the interface of the driven cone and the square chamber caused the pressure disruption (pressure oscillation) upon entrance of the pressure waves into the chamber room. In addition, it was concluded that the driver volume would affect the negative impulse’s duration and the negative peak pressure.
Study on the Transient Characteristics of Pump During the Starting Process With Assisted Valve
Authors: Li Qiao , Wu Peng , Wu Dazhuan
Published: October 2017

Among the various transient operations, the startup process of a centrifugal pump brings attention to a number of practical issues. A representative application of the startup process is the underwater launch, which requires transient high pressure and high flowrate during a very short time.

Due to the rotational inertia of the pump and motor, the dynamic response of the pump is slow, so the rotational speed cannot reach the design point rapidly. To get a high response of the starting process, a throttle valve is installed in the downstream of the pump. The valve keeps closed before the rotational speed of the pump reaches a certain point. It is important to investigate the transient behavior of pump during such transient operations.

In this paper, experiment and numerical simulation are implemented to study the external transient hydrodynamic performance and the internal flow of the pump during the transient process. Different operating schemes of the pump and valve are designed to find the best coordinated modes.

The contents and conclusions of the current work can provide references for the performance prediction, design optimization and fluid control of the pump and valve during the transient process.
A Preliminary Investigation of Caudal Fin Shape Effects on Thrust and Power of a Newly Designed Robotic Tuna
Authors: Matta Alexander , Pendar Hodjat , Bayandor Javid
Published: October 2017

Thunniform swimmers are known to travel at high speeds for long periods of time and at high hydrodynamic efficiency. Thus, there is a great deal of interest in their swimming physics. In order to better understand these physics, a newly designed robotic tuna was constructed that allows for interchangeable caudal fins. This robot was put in a water tunnel and tested at tail beat frequencies ranging from 0.5 to 1.0 Hz and at freestreams of 0, 0.2, and 0.4 m/s. A lever assembly was used to transmit thrust force to a load cell, and power was calculated using data from current sensors. Preliminary results suggest that swept caudal fins produce more thrust and are more efficient than trapezoidal fins at higher freestreams while the opposite is true at lower freestreams. However, several induction factors need to be resolved before more confident assertions can be made.
Study on the Effects of Active Flow Control on Aerodynamic Performance of Two Airfoils in Tandem Configuration
Authors: Asgari Ehsan , Sheidani Armin , Tadjfar Mehran
Published: October 2017

Aerodynamic investigation of tandem airfoil configuration has so many applications in different industries that has become a topic of scientific interest since many years ago. One can name a lot of applications in this field such as the aerodynamic interaction between a wing and a tail or a wing and a flap of an aircraft, blades of a rotor and a stator in a compressor or turbine, the tandem blades in the rotor of a compressor, wings of an MAV, to name but a few. The primary objective of this research is to investigate the effect of active flow control (AFC) on two airfoils in tandem configuration, in which the upstream airfoil undergo pitching motion and the downstream airfoil is stationary. In the first place, the aerodynamic characteristics of airfoils in tandem configuration such as lift and drag coefficient is obtained when there is no flow control on the airfoils (clean case). Following this, the mentioned quantities are calculated for the airfoils when AFC has been applied on the forefoil. In order to analyze the effect of AFC and tandem configuration aerodynamic characteristics, the lift and drag coefficient of clean case is compared to those of the controlled case. The result suggests that AFC has caused the amount of CL to grow significantly. It was also observed that the tandem configuration had little influence on the forefoil. On the other hand, the vortices coming from the upstream airfoil generated thrust on the hindfoil. In case of AFC, our results suggest that fluctuations of both lift and drag forces decrease in the hindfoil. It is worth mentioning that this research is among the firsts studying the effect of AFC on tandem airfoils and will pave the way for those who are interested in this field.
Design of a Dual Propeller Micro-Pump in Conjunction With Flared TCPC for Cavopulmonary Assist in Fontan Patients
Authors: Jagani Jakin , Untaroiu Alexandrina
Published: October 2017

A single ventricular physiology of the human heart caused by a dysfunctional right ventricle is usually treated with the three-stage Fontan operation. The outcome of this operation is an extra-cardiac total cavopulmonary connection (TCPC) which supplies the deoxygenated blood from the body to the lungs by directly connecting the inferior and superior vena cava (IVC and SVC) to the left and right pulmonary arteries (LPA and RPA). However, the situation is worsened due to non-physiologic flow conditions and pressure loss inside the cavopulmonary track, which ultimately calls for a heart transplantation. A modest pressure rise of 5–6 mm Hg will help to regain the normal physiology of the patient. In order to achieve this, a conceptual design of a dual propeller pump inside a flared TCPC is developed and studied.

In order to provide a modest pressure rise, a blood pumping device was inserted inside the flared TCPC connection which consisted of two propellers, each placed in the SVC and the IVC and connected by a single shaft. The IVC and the SVC propellers were designed to rotate at the same rotational speed, having the same pressure rise but different blood inflow rate. The equal pressure rise across both the propellers was necessary at the design speed and flow rate to prevent any blood flow into the opposite vena cava. The TCPC-dual propeller conjunction was examined for the hydraulic performance and the flow pattern inside the TCPC using the 3D-CFD simulations on Ansys-CFX. The effect of axial distance between the two propellers on the blood flow interference and energy loss was also studied to select an optimal separation distance between them.

The introduction of dual propeller pump inside the flared TCPC led to a pressure rise of 2–15 mm Hg at a total flow rate of 4.5 lpm (63% from IVC and 37% from SVC) with the rotational speed ranging from 6000–12000 rpm. It was seen that an axial separation of 70 mm between the two propellers provided the best performance in terms of flow interference and energy loss.

A dual propeller pump assembled with an optimized TCPC could provide the required pressure rise for a particular age group of patients with univentricular Fontan physiology. The ability of dual micro-propeller pump to provide the required pressure rise will help to augment the cavopulmonary flow and hence help to regain the normal flow physiology as that witnessed by a human with biventricular circulation.
Use Multiphysics Simulations and Resistive Pulse Sensing to Study the Effect of Metal and Non-Metal Nanoparticles in Different Salt Concentration
Authors: Chiang Chun-Lin , Lee Che-Yen , Yeh Yu-shan
Published: October 2017

Wafer fabrication is a critical part of the semiconductor process when the finest linewidth with the improvement of technology continues to decline. The nanoparticles contained in the slurry or ultrapure water used for cleaning have a large influence on the manufacturing process. Therefore, semiconductor industry is hoping to find a viable method for on-line detection of the nanoparticles size and concentration. Resistive pulse sensing technology is one of the methods that may cover this question. There were a lot of reports showing that nanoparticles properties of materials differ significantly from their properties at nano length scales. So, we want to clear the translocation dynamic and ion current changes in measurement of metal nanoparticles or non-metal nanoparticles in different concentration electrolytes through the nanopore when resistive pulse sensing technology has been used. In this study, we try to use a finite element method that contains three governing equations to do multiphysics coupling simulations. The Navier-Stokes equation describes the laminar motion, the Nernst-Planck equation describes the ion transport, and the Poisson equation describes the potential distribution in the flow channel. Then, the reliability of the simulation results was verified by resistive pulse sensing test. The existing results showed that the lower the ion concentration the greater the effect of resistive pulse sensing was. We investigated the effect of resistive pulse sensing on different materials by both simulations and experiments. The results are discussed in this article.
Effects of Medium Containing Free Gas on Hydraulic Performance of Certain Single Stage Centrifugal Pump in 3rd Generation Reactor
Authors: Zhang Tiejian , Cong Guohui , Yan Yan , Zhang Wei , Wang Xueling
Published: October 2017

Pumping medium containing gas has a negative impact on the centrifugal pump on mechanical properties (such as vibration, noise) and hydraulic performance, but also affect the accuracy of hydraulic test. in the GL2008-01 open letter, the United States Nuclear Regulatory (NRC) requires that some safety systems shall take into account the adverse effects of gas and the American Institute for Nuclear Research (NEI) and the Electric Power Research Institute (EPRI) pointed out the American Institute for Nuclear Research (NEI) and the Electric Power Research Institute (EPRI) pointed out that the gas in suction side shall not exceed the limit of 2% (volume ratio). In HPR1000, the 3rd generation reactor, it is the first time proposed that some systems are with long-term gas entrainment condition, and there is up to 3% (volume ratio) free gas in the horizontal centrifugal Spray Pump suction side water. In order to study the 3% gas entrainment condition effects on the hydraulic performance of Spray pump, a way is found to calculate the head drop by some equations and carried out a containing free gas hydraulic test. The results show that under the 3% gas condition, Spray pump head is 0.60% dropped by equation calculation and 0.66% dropped by test, comparing with no gas condition. The 3% gas effects on the Spray pump performance are very small. The reasons is that the structure of the Spray pump is well for vent during operation and the gas is not accumulate in the pump, so the performance of the pump has no effect.
Fluid Flow, Heat and Contaminant Transport in a Ventilated Enclosure due to the Presence of Thermosolutal Body
Authors: Gupta Neha , Nayak Ameeya
Published: October 2017

A numerical study is performed for the fluid flow, heat and mass transfer in a ventilated enclosure where a thermally and solutally activated square block is placed for heat and solute exchanges. The block is maintained with higher temperature and concentration than that of inlet flow and the walls are impermeable and adiabatic to heat and solute. Cold fluid is entered through a slot of left vertical wall and flushes out at the different slots of opposite wall to study the mixed air distribution due to the thermosolutal source present in the core of the enclosure. The dynamic, thermal and solutal transport phenomena are computationally visualized through the streamlines, isotherms and iso-concentration lines. The efficient cooling activities are studied by changing the locations of inlet and outlet ports with the variation of Richardson number (Ri) and Reynolds number (Re) for a fixed Prandtl number (Pr = 0.71).
Modeling of Cavitation Induced Fuel Atomization and Breakup Processes
Authors: Zhao Bolin , Chen C. P.
Published: October 2017

Recent experimental and modeling studies have indicated that turbulence and cavitation behaviors within a realistic fuel injector have significant effects on the liquid atomization and spray processes. In addition to the breakup process induced by aerodynamic force at the liquid/gas interface, the effects of flow characteristics including turbulence and cavitation inside the injector nozzle on atomization have been shown to be important. The cavitation within the injector is complicated by the turbulent flow under large pressure gradient and geometry of the injector orifice. We have previously developed the “T-blob” and “T-TAB” model, for liquid fuel primary and secondary breakup predictions respectively, to account for liquid turbulence effects within the injector. The objective of this study is to further account for the cavitation effect in the atomization process of a cylindrical liquid jet. In the primary breakup model, the level of the turbulence effect on the liquid breakup depends on the characteristic scales and the initial flow conditions. These scales are further modified to include the cavitation effect. The drop size formed is estimated based on the energy distribution among wave, turbulence and cavitation modes. This paper describes theoretical development of the current model. Both non-evaporating and evaporating spray cases will be investigated to validate the newly developed cavitation-induced atomization model.
Dispersion of Shock Wave Transmitted Into Non-Uniform Materials
Authors: Kobayashi Susumu , Henmi Hiroki
Published: October 2017

When a shock wave is incident on an obstacle, it is not only reflected back but also transmitted into the obstacle itself. The transmitted shock wave has not been fully investigated so far, compared with the reflected shock wave. In actual situations, the behavior and the characteristics of the transmitted shock wave are also of importance. In battlefields, human bodies are often subject to explosions and resulting shock waves. In particular, severe damage can be caused when a shock wave is transmitted into the human brain.

In the present study, we conducted experiments to investigate the behavior and intensity of a shock wave, after it is transmitted into various materials. The materials used were sintered metal, silicone, and polyethylene foam. They were fixed on a specially devised model with a cavity, by which the resulting wave after a shock wave is transmitted could be observed. In order to understand what is happening in sintered metal, a 2-D model made of straws was devised and used.
Evaluation of an Integrated Micro-Cooling Chip Architecture for Managing Thermal Concerns of a Power Electronics Module
Authors: Papadopoulos George , Kearney Daniel , Torresin Daniele
Published: October 2017

The field of consumer and power electronics is surging ahead with more sophisticated and powerful devices that are smaller and more capable than before. Proper and efficient thermal management of such devices is increasingly challenging when addressing requirements to reduce size, weight and cost (both manufacturing and operational) while enabling the overall system to operate at higher power densities. The current effort considers a typical power electronic module most often used to address DC to AC voltage conversion in larger distributed energy systems. Significant heat generation results from switching and conduction losses inherent in such a circuit, which can then cause a drop in the power processing capabilities or worse, the destruction of the device itself if not properly cooled. A nominal architecture for the circuit module is selected and a combined experimental and analytical study is performed to implement an integrated micro-cooling chip architecture that leverages single phase jet-impingement and vortex flow approaches. The micro-cooling chip array is a multi-laminate design that features localized fluidic cells ducted to bring coolant in and out of a heat exchanger section. The paper reports on the design of the multi-laminate micro-cooling chip module in terms of manufacturability and fluid dynamics of the coolant in combination with the power electronics module. Results from bench-scale testing done on a monolithic part fabricated using additive manufacturing process are reported and compared with analysis. The results provide an initial basis for further miniaturization of the power electronic module and insights to manufacturability using standard 3D printing approaches.
Assessment and Prediction of EOF Mixing in Binary Electrolytes
Authors: Banerjee Abhishek , Nayak Ameeya Kumar
Published: October 2017

A two dimensional simulation is made to analyse the mixing enhancement due to surface roughness and geometric modulation in a sufficiently long rectangular nano-channel filled with electrolyte solutions of different concentrations. Geometric modulation is made by mounting non-conducting rectangular blocks on the bottom wall of the channel. An overpotential patch is placed on the upper wall of each block to create surface heterogeneity. Based on a finite volume staggered grid approach, the flow characteristics and mixing efficiency are discussed by a complete numerical solution of coupled nonlinear set of PDEs involving Nernst-Planck equation for ion distribution, Navier-Stokes equation for velocity components and Maxwells equation for potential distribution. A linear pressure drop is observed above the overpotential region which creates a recirculating zone. Mixing efficiency is improved with increasing vortex strength which is enhanced by decreasing EDL (electric double layer) thickness and increasing overpotential patch strength.