bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation and Analysis of an Early Inducer Design and its Approach to Backflow Control
Authors: Sloteman Donald P. , Redding Jennifer , Cooper Paul
Published: December 2013

The inducer has become an essential component of the modern turbopump. Many investigations have been performed to gain an understanding of the inducer’s adverse operational characteristics that can include fluctuating pressures, unsteady delivery flow and fluctuating loads that compromise reliability. Furthermore, design features have been evaluated that eliminate or attenuate this adverse behavior. This paper describes the first known application of an inducer to a turbopump which fueled a throttleable rocket engine dating from the early 1940’s. The pump is unique in its use of an integral backflow recirculator that corrects the effects of suction recirculation at off-design flow conditions. Modern analysis, including CFD, of this inducer provides insight into its design and operational behavior. The design of this historic inducer offers insight into modern approaches that will correct inducer instabilities.
Experimental Study on Oscillatory Couette-Taylor Flows Behaviour
Authors: Berrich Emna , Aloui Fethi , Legrand Jack
Published: December 2013

In the simplest and original case of study of the Taylor–Couette TC problems, the fluid is contained between a fixed outer cylinder and a concentric inner cylinder which rotates at constant angular velocity. Much of the works done has been concerned on steady rotating cylinder(s) i.e. rotating cylinders with constant velocity and the various transitions that take place as the cylinder(s) velocity (ies) is (are) steadily increased. On this work, we concentrated our attention in the case in which the inner cylinder velocity is not constant, but oscillates harmonically (in time) clockwise and counter-clockwise while the outer cylinder is maintained fixed. Our aim is to attempt to answer the question if the modulation makes the flow more or less stable with respect to the vortices apparition than in the steady case. If the modulation amplitude is large enough to destabilise the circular Couette flow, two classes of axisymmetric Taylor vortex flow are possible: reversing Taylor Vortex Flow (RTVF) and Non-Reversing Taylor Vortex Flow (NRTVF) (Youd et al., 2003; Lopez and Marques, 2002). Our work presents an experimental investigation of the effect of oscillatory Couette-Taylor flow, i.e. both the oscillation frequency and amplitude on the apparition of RTVF and NRTVF by analysing the instantaneous and local mass transfer and wall shear rates evolutions, i.e. the impact of vortices at wall. The vortices may manifest themselves by the presence of time-oscillations of mass transfer and wall shear rates, this generally corresponds to an instability apparition even for steady rotating cylinder. On laminar CT flow, the time-evolution of wall shear rate is linear. It may be presented as a linear function of the angular velocity, i.e. the evolution is steady even if the angular velocity is not steady. At a “critical” frequency and amplitude, the laminar CT flow is disturbed and Taylor vortices appear. Comparing to a steady velocity case, oscillatory flow accelerate the instability apparition, i.e. the critical Taylor number corresponds to the transition is smaller than that of the steady case. For high oscillation amplitudes of the inner cylinder rotation, the mass transfer time-evolution has a sinusoidal evolution with non equal oscillation amplitudes. If the oscillation amplitude is large enough, it can destabilize the laminar Couette flow, Taylor vortices appears. The vortices direction can be deduced from the sign of the instantaneous wall shear rate time evolution.
DBD Plasma Actuator Multi-Objective Design Optimization at Reynolds Number 63,000: Baseline Case
Authors: Sulaiman Taufik , Sekimoto Satoshi , Tatsukawa Tomoaki , Nonomura Taku , Oyama Akira , Fujii Kozo
Published: December 2013

The working parameters of the dielectric barrier discharge (DBD) plasma actuator were optimized to gain an understanding of the flow control mechanism. Experiments were conducted at a Reynolds number of 63,000 using a NACA 0015 airfoil which was fixed to the stall angle of 12 degrees. The two objective functions are: 1) power consumption (P) and 2) lift coefficient (Cl). The goal of the optimization is to decrease P while maximizing Cl. The design variables consist of input power parameters. The algorithm was run for 10 generations with a total population of 260 solutions. Although the number of generations and population size was limited due to experimental constraints, the algorithm was able to converge and the approximate Pareto-front was obtained. From the objective function space, we observe a relatively linear trend where Cl increases with P and after a certain threshold, the value of Cl seems to saturate. We discuss the results obtained in the objective space in addition to scatter plot matrix and color maps. This article, with its experiment-based approach, demonstrates the robustness of a Multi-Objective Design Optimization method and its feasibility for wind tunnel experiments.
Numerical Evaluation of Deformation and Stress in Impellers of Multistage Pumps by Means of Fluid Structure Interaction
Authors: Schneider Andreas , Will Björn-Christian , Böhle Martin
Published: December 2013

The operational reliability of centrifugal pumps strongly depends on an adequate structural design of every single component. Therefore, the design process requires trustworthy information about the expected stresses and deformations.

The numerical evaluation of the deformations and the stresses in the impellers of multistage centrifugal pumps is the topic of this report. The loads acting on the impeller under operating conditions can be subdivided into structural and hydrodynamic components, which are considered by means of one-way coupled fluid-structure interaction (FSI) simulations. For the investigations, an exemplary multistage pump with a specific speed of nq = 30 has been chosen. The hydrodynamic pressure loads on the impeller are derived from the CFD solution for a single stage of the pump. These pressure loads are imposed on the impeller in the structural part of the simulation. In order to determine the resulting deformations and stresses of the impeller, static structural analyses are performed. Different operating conditions, i.e. flow rates and temperatures, are analyzed. Furthermore, the influence of structural impeller design parameters on the resulting deformations and stresses is investigated in detail. The thickness of the impeller shrouds as well as the fillet radii between the blades and the shrouds are considered as design parameters.
Temperature Fluctuations Inside the Infinite Heated Slab Cooled With Turbulent Flow From Both Sides
Authors: Tiselj Iztok
Published: December 2013

Direct Numerical Simulation (DNS) of fully developed velocity and passive scalar temperature fields in two-dimensional turbulent channel flow was coupled with the unsteady conduction in the idealized slab heated with constant volumetric heat source. Similar geometry can be found in some experimental nuclear reactors with fuel in the form of parallel slabs. Beside streamwise and spanwise directions, periodicity of the computational domain was assumed also in the wall-normal direction. Simulations were performed at constant friction Reynolds number 180 and Prandtl number 1, and with various geometrical and material properties of the heated slab. Due to the periodicity, the same Reynolds number and the same flow direction is assumed on both sides of the slab. Results of the simulations predict penetration of the turbulent temperature fluctuations into the solid wall. For thick slab, temperature fluctuations from both sides of the slab do not interfere. As the slab gets thinner, fluctuations from both sides interfere and tend to a finite value as the slab thickness limits toward zero. However, due to the non-coherent turbulent flows on each side of the slab, thermal fluctuations of the zero-thickness slab are actually lower than in the case of the zero-thickness wall heated by the same turbulent flow on one side but cooled by the constant heat flux boundary condition on the other side. Results of the present study can serve as benchmarks for less accurate mathematical models used to predict temperature fluctuations and thermal fatigue in realistic conditions.
Numerical Investigation of an Extended Propeller Viscosimeter by Means of Lattice Boltzmann Methods
Authors: Conrad Daniel , Schneider Andreas , Böhle Martin
Published: December 2013

For the design of mixing and agitation facilities in process engineering it is of central importance to appraise the correct viscosity of fluids. This can be a challenging task when non-Newtonian and/or non-homogeneous fluids need to be processed. Since it is not always possible to analyze them in the classical ways, an propeller viscosimeter approach on the basis of the Rieger-Novak-Method is used. In recent years the Lattice Boltzmann Methods (LBM) are established as an alternative approach to classical computational fluid mechanics methods. The utilization of Cartesian grids avoids the need to discretize with boundary conform meshes. This makes the LBM suitable for complex geometries like a propeller in this case. Numerical simulations were carried out using a 3D in-house Lattice Boltzmann code called SAM-Lattice with our latest extension to non-Newtonian flow. We use a truncated form of the power-law approximation to accommodate the varying flow properties in non-Newtonian simulations, where the effective viscosity is a function of the shear rate. SAM-Lattice comprises the LBM solver and a highly automated grid generator for arbitrarily complex geometries. The code is capable of multi-domain grid refinement as well as multi reference frames and rotational boundaries. The post processing is done using an extension of the open source visualization tool Paraview. We compare results of experiments and LBM simulations for the Newtonian case (Glucose) to validate our Lattice Boltzmann solver. A study of the non-Newtonian, shear thinning case (Xanthan) is conducted to validate the generalized Newtonian model. The propeller viscosimeter is currently under development as a standalone solution for viscosity measurement. For calibration purposes the Metzner-Otto-constant of the propeller device has to be determined. While the constant is valid for the laminar region the numerical results for the agitator characteristics are presented. Different levels of grid refinement are tested to assure independence of the lattice resolutions.
The Growth of Vortices in the Vicinity of a Wall of Elastic Moving Airfoils
Authors: Fuchiwaki Masaki , Kurinami Tomoki , Tanaka Kazuhiro
Published: December 2013

There have been a number of studies on the flow field around a pitching airfoil and a heaving airfoil. Especially, the relationship between the wake structure and the characteristics of dynamic thrust has been clarified. Recently, the flow field around an elastic body has been attracted significant attention and the flow field is treated as a coupled problem between the fluid and structure. The flow field around an elastic body has been investigated primarily by numerical means, and there have been experimental studies. However, the details of the impact of elastic deformation effects on the growth process of vortices generated in the vicinity of the wall have not been clarified. In this study, we investigate the growth process of vortices generated in the vicinity of the wall of elastic moving airfoils experimentally. The elastic NACA0010 generates vortices in a large region of a wall and rolls up vortices, with the vortices growing gradually toward the trailing edge as a result of elastic deformation. The elastic NACA0010 has a characteristic whereby vortices having a rotational component that is stronger than the shear-strain component due to the vorticities in the vicinity of a wall of the elastic NACA0010 change not only spatial change of x- and y-components.
Heat Transfer Enhancement Through Impingement Surface Shape Modification
Authors: Argaw Yacob M. , Kizito John P.
Published: December 2013

Free stream flow past a heated wedge can be modeled and solved using Falkner-Skan equation when the wedge angle is within a limit. These types of flows at times, depending on the wedge angle or impingement direction, are referred to as Blasius and/or Hiemenz flows. When the impingement surface is constrained between walls from the side to create a cavity, these methods are no longer valid where the side walls significantly affect the flow field. We have used a numerical simulation to determine the effect of impingement shape described by wedge angle. The cooling process described by maximum heat flux with minimum surface temperature is the overall goal of the present study. The results show that the presence of side walls does affect the boundary layer of flow across the impingement surface. The results computed using similarity solution method in Matlab and a commercial CFD code simulation validates shape modification enhances the heat transfer process and the side wall’s effect is significant.
Quantification of Hydrodynamic Forces due to Torsional and Axial Vibrations in Ship Propellers
Authors: van Esch B. P. M. , van Hooijdonk J. J. A. , Bulten N. W. H.
Published: December 2013

CFD is used to compute the hydrodynamic coefficients for torsional and axial vibrations, for one type of the Wageningen B-series of ship propellers in open-water condition. It is shown that the wakes shed from the blades have an influence on the magnitude and the phase of the damping forces. The dependency on reduced frequency of the vibratory motion is explained. This phenomenon can be related to the lift deficiency of trailing vortices in the wake of an oscillating plate, as derived by Theodorsen and Von Kármán and Sears, and is frequently overlooked by more recent investigations. Results of the calculations are compared with theoretical and experimental data from literature.
Intermittently Operated Oil Hydraulic Pump Unit With Accumulator to Save Energy and Hydraulic Assist for Restart
Authors: Suzuki Katsumasa , Ota Shinpei , Kasuya Shuji , Sugimura Ken
Published: December 2013

Efforts to conserve energy have been made in a number of fields due to a shortage of energy resources, such as oil, and the need to protect the Earth’s environment. In the field of hydraulics, energy-saving pump units are very important because they consume less energy.

At present, variable displacement type hydraulic pump units (VD pump units) and inverter control type pump units (INV pump units) are widely used. The authors propose using an intermittently operated pump unit coupled with an accumulator (ACC pump unit). It is verified that the ACC pump unit is superior to the others in terms of efficiency, especially when the flow rate to the load is small or the duty ratio for the intermittent work is low.

However, the stop/restart operation of the electric motor for the pump drive is repeated frequently, and the instantaneous electric power consumed by the electric motor is more than six times the rated electricity when the pump is restarted. Therefore, we decreased the excess electricity consumption at pump restart using a method called “hydraulic assist”.

Before the electric motor is turned on, high-pressure fluid is supplied to the pump inlet from the accumulator. The pressure at the pump outlet is made to be zero by opening the valve to the tank. The pump essentially works as a hydraulic motor. Then, the electric motor is turned on. In this method, the instantaneous electric power consumption is reduced.

This method is also applied to a hydraulic pump unit driven by an internal combustion engine. The intermittent operation of the engine-driven hydraulic pump unit was accomplished using hydraulic assist to restart the pump. In this report, the energy-saving characteristics are shown.
Numerical Modeling of High-Speed Flows Over a Microsphere in the Slip and Early Transition Flow Regimes
Authors: Cheng Chi-Yang , Dai Yi , Li Genong , Richter Horst J. , Lai Ming-Chia
Published: December 2013

The focus of this paper is on using computational fluid dynamics to investigate the drag and convection heat transfer of high-speed flows over a microsphere. The flow under investigation is steady-state, subsonic, transonic or supersonic laminar flow over a sphere. Due to the small size of the particle (< 80 microns), the flow is in the slip and early transition regimes. Typical Reynolds number based on sphere’s diameter is between 10 and 6000, and the Knudsen number is between 0.001 and 0.75.

For the slip flow as well as the early transition regimes, instead of using the Direct Simulation Monte Carlo methods (DSMC) or lattice Boltzmann methods, we use ANSYS FLUENT, a Navier-Stokes-Fourier solver with the first-order velocity-slip and temperature-jump boundary conditions. In order to capture the non-equilibrium effects in the Knudsen layer, a constitutive scaling model for gas viscosity and conductivity is also implemented in the CFD model.

CFD simulations were performed at the free-stream Mach number from 0.6 to 3.0, with particle diameter from 1 to 80 microns and the Knudsen number from 1.4 × 10−3 to 0.14. The CFD results are in good agreement with experimental data. The deviations from the data are within 10%.

The numerical model also provides additional insight to the concept of the thermal recovery temperature in high-speed convection. Due to the nature of the temperature-jump boundary condition, the thermal recovery temperature in the slip flow regime can be obtained numerically only by solving the conjugate heat transfer problem. A “thin-wall” model is introduced in this paper in order to determine the thermal recovery temperature (or recovery factor) for the given Mach and Reynolds numbers.

Although a number of publications have been devoted to particle drag correlations as functions of particle Reynolds and Mach numbers, the dependence of drag on particle temperature has not been investigated. By using the rarefied gas flow model in this study, we have not only confirmed that the drag increases as particle temperature goes higher, but also found that rate of drag increase is higher for the transonic than for the supersonic flows.
An Approach on Fluid-Structure Interaction for the Prediction of Blood Flow in Aneurysms With Various Shapes
Authors: Lee Sang Hyuk , Hur Nahmkeon , Kang Seongwon
Published: December 2013

Recently, the rapid evolution of numerical methodologies for CFD and structural analyses has made it possible to predict the arterial hemodynamics closely related to vascular disease. In the present study, a framework for fluid-structure interaction (FSI) analysis was developed to accurately predict the arterial hemodynamics. The numerical results from the FSI analysis of the hemodynamics inside aneurysms of various shapes were compared to the results without FSI analysis. The results showed that FSI analysis needs to be performed in order to accurately predict the blood flow affected by the wall motion of compliant arteries. FSI analysis is essential to predict the hemodynamics in a saccular aneurysm because the arterial wall’s movement, which is a result of the variation of blood pressure in the aneurysmal sac, mainly produces the blood flow to a saccular aneurysm.
A Numerical Simulation on the Fluid Flow and Heat Transfer Around a Vehicle in a Paint Drying Process
Authors: Choi Jongrak , Hur Nahmkeon , Kim Hee-Soo
Published: December 2013

In the automotive manufacturing process, the paint drying process is very important to improve the appearance of the vehicle. In the present study, the fluid flow and heat transfer around a vehicle were numerically investigated for the purpose of predicting the drying performance of the paint drying process. In order to simulate the operating conditions of the paint drying process, the following techniques were used: relative moving boundary conditions, multiple reference frames, and conjugated heat transfer. The present numerical method was verified by comparing the numerical results of the temperature at several monitoring points on a vehicle, while using the experimental data. To evaluate the drying performance quantitatively, the absorbed heat energy that is closely related to the drying of paint was obtained from the numerical simulation. It was found that the drying performance is greatly affected by operating conditions such as the temperature and flow rate of blowing air. To improve the drying performance, the operating conditions of the paint drying process were optimized using the numerical results of various operating conditions.
Experimental Study of Aerodynamic Noise From the Trailing Edge and Leading Edge of Blades in a Coaxial-Double Shaft Fan
Authors: Madadnia Jafar , Shekeb Mustafa , Ulluwishewa Thimantha
Published: December 2013

Proactive acoustic noise control technologies in wind turbines and blowers have in recent years been the focus of intensive research to integrate wind turbines in residential building and to address public concerns on noise pollution. However efforts to understand the mechanics has been inconclusive, mainly due to the complexity and commercial confidentiality of the topic.

The paper reports on the experimental investigation on two methods in controlling aerodynamic noise. A counter-rotating-double-row-turbine with variable gap/spacing (s) was designed, built and tested. Serrations were designed and attached on the leading edge and the trailing edge of the blades to proactively control aerodynamic noise. The model was operated in fan-mode and air velocity, shaft-revolution; electric-fan-power, acoustic noise amplitude (dB) and Centre frequency (CF in Hz) were measured for a number of spacing and serrations. Coefficients of Performance (COP), dB, CF were plotted against tip speed (TS).

It was noticed that:

• The double-shaft-fan has operated quieter than the single shaft fan especially as TS decreases. Acoustic noise (dB) dropped 20% at TS = 4m/s to less than 2% at TS = 10m/s. Efficiency and CF increased in the double-shaft fan as TS increased. Spacing variation between blade-rows had insignificant effect on the dB, Cf, and efficiency.

• Serrations on single-shaft fan have also reduced dB (up to 10%), increased efficiency and CF with more positive effects with the serrations on the leading edge than the trailing edge. Serrations are more effective at higher TS range.

• Serrations on a double-shaft fan with an optimum spacing, reduced acoustic noise (dB) only allow speeds [at TS <4m/s]. However minor improvement was noticed in efficiency or noise frequency.
Effect of Rotor-Stator Configuration in the Generation of Vortical Scales and Wake Mixing in Single Stage Axial Fans: Part II — Assessment of Vortex Sound Sources
Authors: Galdo Vega Mónica , Fernandez Oro Jesus Manuel , Argüelles Díaz Katia María , Santolaria Morros Carlos
Published: December 2013

This second part is devoted to the identification of vortex sound sources in low-speed turbomachinery. As a starting point, the time-resolved evolution of the vortical motions associated to the wake shear layers (reported in the first part of the present study) is employed to obtain vorticity distributions in both blade-to-blade and traverse locations throughout the axial fan stage.

Following, the Powell analogy for generation of vortex sound is revisited to obtain the noise sources in the nearfield region of the fan. Both numerical and experimental databases presented previously are now post-processed to achieve a deep understanding of the aeroacoustic behavior of the vortical scales present in the flow.

A LES simulation at midspan, using a 2.5D scheme, allows an accurate description of the turn-out time of the shedding vortices, within high-density meshes in the blades and vanes passages, and a correct modeling of the dynamics of turbulence. Besides, thermal anemometry has been employed with a two-wire probe to measure the planar flow in the midspan sections of the fan. Statistical procedures and signal conditioning of velocity traces have confirmed experimentally the unsteady flow patterns devised in the numerical model.

The comparison of the rotor-stator and the stator-rotor configurations provides the influence of the wake mixing and the nucleation of turbulent spots in the distribution of the Powell source terms. Moreover, the relation between the turbomachine configuration and the generation of vortex sound can be established, including the impact of the operating conditions and the contributions of the interaction mechanisms.
Physical Attributes of Pulse Jet Mixer Operation
Authors: Kuhn William L. , Rector David R. , Bamberger Judith A. , Minette Michael J.
Published: December 2013

Vessels mixed using pulse jet mixers that produce a periodic, rather than steady, flow present challenges with respect to modeling slurry mixing. A PJM is a cylindrical tank within the mixed tank that has a conical bottom with an orifice through which process fluid cyclically enters and is expelled forcefully by pressurizing the air space above the liquid in the PJM. Between pulses, some of the solids settle from the slurry, which nominally is a failure in mixing, but during the pulses (if operated to attain bottom clearing conditions), all of the solids are resuspended and made available for processing or transfer. Overall, mixing is successful if the solids are processed and removed from the vessel as needed when averaged over repeated PJM cycles. This paper describes the physics of pulse jet mixing process based on physical observation during experiments and analysis of experimental concentration profile data obtained during the mixing cycle.
Dispersion due to Electroosmotic Flow Through a Circular Tube With Axial Step Changes of Zeta Potential and Hydrodynamic Slippage
Authors: Zhou Qi , Ng Chiu-On
Published: December 2013

The hydrodynamic dispersion of a neutral non-reacting solute due to steady electro-osmotic flow in a circular channel with longitudinal step changes of zeta potential and hydrodynamic slippage is analyzed in this study. The channel wall is periodically micro-patterned along the axial position with alternating slip-stick stripes of distinct zeta potentials. Existing studies on electrically driven hydrodynamic dispersion are based on flow subject to either the no-slip boundary condition on the capillary surface or the simplification of lubrication approximation. Taking wall slippage into account, a homogenization analysis is performed in this study to derive the hydrodynamic dispersion coefficient without subject to the long-wave constraint of the lubrication approximation, but for a general case where the length of one periodic unit of wall pattern is comparable with the channel radius. The flow and the hydrodynamic dispersion coefficient are calculated numerically, using the packages MATLAB and COMSOL, as functions of controlling parameters including the period length of the wall pattern, the area fraction of the slipping region (EOF-suppressing) in a periodic unit, the ratio of the two zeta potentials, the intrinsic hydrodynamic slip length, the Debye parameter, and the Péclet number. The dispersion coefficient is found to show notable, non-monotonic in certain situations, dependence on these controlling parameters. It is noteworthy that the introduction of hydrodynamic slippage will generate much richer behaviors of the hydrodynamic dispersion than the situation with no-slip boundary condition, as slippage interacts with zeta potentials in the EOF-suppressing and EOF-supporting regions (either likewise or oppositely charged).
Sharp Interface Cavitation Modeling Using Volume-of-Fluid and Level Set Methods
Authors: Michael Thad , Yang Jianming , Stern Frederick
Published: December 2013

A sharp interface cavitation modeling methodology is presented. A simplified Rayleigh-Plesset equation is used to obtain the phase change rate from the local pressure. The phase change rate is expressed as mass flux jump conditions. The phase interface is tracked using a second-order volume-of-fluid method with a constructed level set function. The interface normal velocity jump is extended into the flow field using a fast marching method. A ghost fluid method is used to prevent difficulties computing high-order derivatives near the interface. Two separate intermediate velocity fields from the momentum equation are solved considering the velocity jump conditions. Some preliminary results will be demonstrated to show the promise of the present approach.
Toward Wall Modeling in Cartesian Grid Solver Using Overset Grid Technique for Ship Hydrodynamics
Authors: Hanaoka Akira , Yang Jianming , Stern Frederick
Published: December 2013

A Cartesian grid solver is coupled with an orthogonal curvilinear grid solver using overset grid interpolation and a coupled pressure Poisson solver. It aims at resolving the boundary layer on the body surface effectively. SUGGAR code, an overset grid assembly program, provides overset grid information of a Cartesian background grid and a thin orthogonal body-fitted grid to resolve the boundary layer on the surface. The overset grid information is used to interpolate velocity, pressure, turbulence quantities, and level set function. A coupled pressure Poisson equation is solved using PETSc. The coupled curvilinear/Cartesian grid solver has been applied to two-phase turbulent flows past a circular cylinder and has shown good agreement with the experimental data and the LES results in the literature. The solver is being applied to a free surface flow around Wigley’s parabolic hull form at Re = 3.4×106 and Fr = 0.25. The numerical results are promising compared to an experimental result of wave elevations at the same Fr.
CFD Solution for Low Tube-to-Particle Diameter Ratio Packed Beds
Authors: Li Genong , Cheng Chi-Yang , Mukhopadhyay Aniruddha , Dai Yi
Published: December 2013

Packed beds are the dominant reactor type for industrial heterogeneous catalytic reactions. Packing pattern affects the flow, heat and mass transfer characteristics within the beds. With the development of high performance computing and advances in CFD, it becomes possible to resolve flow/reactions in detail in packed beds, especially for beds with low tube-to-particle diameter ratio. In this paper a whole set of CFD solutions in dealing with such packed beds from packing, meshing, solving and post-processing is discussed. The solution process is illustrated by considering cylindrical beds packed with spherical balls. As an example, a plant-scale bed packed with about 1000 balls is simulated in the paper.
Particle Transport in a Turbulent Square Duct Flow With an Imposed Magnetic Field
Authors: Liu Rui , Vanka Surya P. , Thomas Brian G.
Published: December 2013

In this paper we study the particle transport and deposition in a turbulent square duct flow with an imposed magnetic field using Direct Numerical Simulations (DNS) of the continuous flow. A magnetic field induces a current and the interaction of this current with the magnetic field generates a Lorentz force which brakes the flow and modifies the flow structure. A second-order accurate finite volume method in time and space is used and implemented on a GPU. Particles are injected at the entrance to the duct continuously and their rates of deposition on the duct walls are computed for different magnetic field strengths. Because of the changes to the flow due to the magnetic field, the deposition rates are different on the top and bottom walls compared to the side walls. This is different than in a non-MHD square duct flow, where quadrant (and octant) symmetry is obtained.
Isothermal Efficiency of Liquid Piston Compressors Employed in Compressed Air Energy Storage Systems
Authors: Dolatabadi Amirali , Fabris Drazen , Samara-Rubio Dean
Published: December 2013

This paper models the compressor work for a prototype small-scale compressed air energy storage system to predict the heat transfer to the walls and the system pressure, temperature, and work required. The modeled system uses a hydraulically driven compressor to enable variable frequencies of compression and to improve heat transfer. Since the compression is hydraulically driven, speed of compression can be controlled through adjusting hydraulic pump’s speed in order to enhance the efficiency and also being able to couple the system with different sources of power. The energy conservation model considers gas under non-ideal conditions and properties of the gas are predicted using Redlich-Kwong equation of state. For heat transfer calculations, correlations for thermal entry length for turbulent flows are employed. Material properties of air including specific heat capacity, thermal conductivity and viscosity are corrected at different operating temperatures and pressures. The differential equation form of the first law of thermodynamics is then integrated numerically in the time domain in order to find the instantaneous properties of the bulk gas. Isothermal efficiency is then predicted based on the temperature rise in the working fluid during compression. It is determined that at low frequencies of compression, at a compression ratio of 5:1, isothermal efficiencies as high as 93% can be achieved.
Toward Direct Numerical Simulation of Aeroacoustic Field Around Airfoil Using Multi-Scale Lattice Boltzmann Method
Authors: Kusano K. , Yamada K. , Furukawa M.
Published: December 2013

Lattice Boltzmann method (LBM) has a potential to simulate airfoil self-noise with low Mach number flow including turbulent flow and aerodynamic feedback loops. In this study, the computational techniques concerning LBM were developed toward direct numerical simulation of aeroacoustic fields with low Mach number. For applications of multi-scale phenomena such as flow and acoustic fields, multi-scale model was introduced, which enables to use locally refined grids. The grids were efficiently arranged using the Building-Cube Method (BCM) by dividing the computational domain into multiple blocks with various grid sizes. Furthermore, the zonal DNS and LES approach was adopted to suppress the numerical instability in the region of coarse grids.

The grid dependency of the results provided by the present numerical method was investigated by two-dimensional simulations of flow fields around a NACA0012 airfoil using four different grids. Furthermore, a three-dimensional simulation of flow around a NACA0018 airfoil with moderate Reynolds number was conducted. The computational results were compared and have a good agreement with the experimental ones. The present method can simulate flow around airfoil with moderate Reynolds number involving the laminar-to-turbulent transition.
Effects of Kinematics on Low Reynolds Number Wing
Authors: Mojgani Rambod , Tadjfar Mehran
Published: December 2013

Insects’ aerodynamic performance has been an area of interest for years, for both biologists and engineers. Micro-air vehicles developments require more research in this area to determine best flight performance. Their flapping wings’ effectiveness in producing both lift and thrust has been enabled them to hover and fly forward. Recent studies have proved that with capabilities of CFD calculations, parametric investigation of the associated parameters is possible. The purpose of present investigation is to numerically study the effects and phenomena caused by different kinematics of flapping wing, so different flapping kinematics has been simulated and investigated to better understand fluid characteristics in such cases. Effect of wing’s vertical displacement as well as the effects of wing rotation (pitch angle) is studied. Dynamic mesh with laminar finite volume flow solver is used and the method is validated. Results show that how wing-vortex interaction and angle between flapping direction and wing inclination can control hovering (vertical) force.
Implicit LES Simulations of a Flapping Wing in Forward Flight
Authors: Gordnier Raymond E. , Demasi Luciano
Published: December 2013

Computations of an aspect ratio 3.5 flat plate wing in flapping forward flight are performed. A high-order implicit LES approach is employed to compute the mixed laminar/transitional/turbulent flowfields present for the low Reynolds number flows associated with micro air vehicles. The ILES approach is implemented by exploiting the properties of a well validated, robust, sixth-order Navier-Stokes solver. The analyzed kinematics are a flapping motion described by an anti-clockwise 8 cycle. A Reynolds number based on the freestream velocity of 1250 is prescribed. A detailed description of the dynamic vortex system engendered by the unsteady flapping motion is given and related to the development of lift and thrust during the flapping cycle. Effective angle of attack, which results from the wing motion, and its interplay with the aerodynamic angle of attack play a key role in determining the flow structure and forces produced.
Hybrid RANS-LES Modeling of a Normal Jet in Crossflow for Film Cooling Applications
Authors: Dhakal Tej P. , Walters D. Keith
Published: December 2013

Numerical simulation of a normal jet in crossflow has been performed using a recently developed hybrid RANS-LES model. The model form utilizes a solution based parameter that dynamically determines the RANS and LES regions. Numerical simulations using commercially available DDES model and a RANS model have also been performed for comparison purposes. Three jet to crossflow velocity ratios (R = 2, 1, 0.5) have been investigated. Computational results obtained are compared with the experiment of Andreopoulos and Rodi (1984). The results highlight the predictive capabilities of hybrid RANS-LES model to reproduce the important vortical structures of a jet in crossflow case, which play a crucial role in the film cooling. The hybrid RANS-LES model results from the velocity ratio R = 2 case fare well with the experiment in comparison to RANS predictions. For lower velocity ratios, discrepancies in mean flow statistics have been observed at some measurement stations. The near wall statistics from the hybrid model resembles RANS predictions for the case with jet to crossflow velocity ratio R = 0.5. This observation can be attributed to the requirement of higher grid resolution necessary to capture the near wall structures for low velocity ratio cases.
Reynolds Averaged Navier Stokes Models Compared to Direct Numerical Simulations in an Adverse Pressure Gradient Boundary Layer Over a Flat Plate
Authors: Routson Daniel , Ferguson James , Crepeau John , McEligot Donald , Budwig Ralph
Published: December 2013

In Reynolds-Averaged Navier Stokes (RANS) models simplifying assumptions breakdown in near wall regions. Wall functions/treatments become inaccurate and the homogeneity and isotropy models may not hold. To see the effect that these assumptions have on the validity of boundary layer results in a commercially available RANS code, key boundary layer parameters are compared from laminar, transitional, and fully turbulent RANS results to an existing direct numerical simulation (DNS) simulation for flow over a flat plate with an adverse pressure gradient (APG). Parameters compared include velocity profiles in the free stream, boundary layer thicknesses, skin friction coefficient and the pressure gradient parameter. Results show comparable momentum thickness and pressure gradient parameters between the transition RANS model and the DNS simulation. Differences in the onset of transition between the RANS transition model and DNS are compared as well. These simulations help evaluate the models used in the RANS code. Of most interest is the transition model, a transition shear-stress transport (SST) k–omega model. The RANS code is being used in conjunction with an APG boundary layer experiment being undertaken at the Idaho National Laboratory (INL).
Cavitation Investigation of Hydrofoils for Marine Hydrokinetic Turbines
Authors: Nedyalkov Ivaylo , Wosnik Martin
Published: December 2013

Three different hydrofoil sections were investigated in the recently renovated High-Speed Cavitation Tunnel (HiCaT) at the University of New Hampshire: a NACA 0015 (reference foil), a NACA 63-424, and a bidirectional version of the NACA 63-424 hydrofoil. Bi-directional hydrofoils are of interest for marine renewable energy conversion, since they allow the elimination of pitch control mechanisms on marine hydrokinetic turbines. Hydrofoil lift and drag were measured for different velocities, pressures, and angles of attack. For some experimental conditions, comparative PIV measurements were performed in the near-wake region. A cavitation inception model for marine hydrokinetic turbines was derived. Cavitation numbers for inception were obtained for the two NACA 63-424 foils by varying pressure at constant speed as well as by varying speed at constant pressure. The performance of the NACA 63-424 and the bidirectional NACA 63-424 was compared.
Optimization Design and Inner Flow Analysis on a Medium-High Specific Speed Centrifugal Pump
Authors: Zhang Fan , Yuan Shouqi , Fu Qiang , Hu Bo , Tao Yi , Wang Wenjie
Published: December 2013

Aiming at the problems of low efficiency, easily overload and having humps of the TS100–200 centrifugal pumps, four impellers are designed with different blade curves to improve the performances of the pumps. Non-overload design method is adopted for parameters selection of impellers. The 3-D models and the 1.61 million structure grids were generated by Pro/E and ICEM respectively. After the boundary conditions of velocity inlet, outflow in the outlet and no-slip wall were specified, and the flow model was complemented with the standard k-ε model by using the commercial software CFX 12.1. The distributions of pressure, turbulence kinetic energy and streamlines in four impellers are obtained during simulation, as well as their hydraulic performances. The wrap angle φ is a critical parameter to the blade shape. Impeller-2 with appropriate wrap angle φ shows good hydraulic characteristics and excellent inner flow patterns, and it is produced for experiments by prototyping rapidly. The test results are in accordance with the simulating results. The head of impeller-2 is 5% higher than the design parameter at most and the efficiencies are nearly 6% higher than the efficiencies of the prototype pump at the design flow rate QR. The test results also show a good non-overload performances. The results prove that it is an effective and reliable method to the optimal design of centrifugal pumps with medium-high specific speed.
Numerical Optimal Design of Impeller Back Pump-Out Vanes on Axial Thrust in Centrifugal Pumps
Authors: Hong Feng , Yuan Jianping , Heng Yanguang , Fu Yanxia , Zhou Banglun , Zong Weiwei
Published: December 2013

Axial thrust in centrifugal pumps attracts extensive attention in order to improve the operating reliability of pumps. High axial thrust can cause rapid thrust bearing wear and subsequent pump failure or frequent overhauls. A centrifugal pump (XA65/20) was selected in this study, based on L16 (43) orthogonal array and CFD methods. The time-averaged Navier-Stokes equation was calculated for a 3D steady flow in the model pump in ANSYS CFX with the standard k-ω turbulence model and standard wall function applied. The structured meshes with different numbers were used for comparison in order to confirm that the computational results were not influenced by the mesh. Meanwhile, the effects of impeller back pump-out vane geometrical parameters, including its thickness Sk, its outlet diameter De and axial clearance δ, on the axial thrust and performances of the model centrifugal pump were analyzed. The different orthogonal schemes were obtained on the different values of Sk, De, and δ.

Finally, when the parameters of the impeller Sk, De, and δ are 5mm, 100mm, 1.5mm, respectively. The Best Efficiency Point (BEF) of 69.9% was achieved with 60.12m for the designed head and −952.133N for the minimum total axial force. The corresponding impeller with minimum total axial force was considered as the optimal scheme and manufactured for experimental test. The external characteristics by CFD have a good agreement with their experimental data, which also better verified the accuracy of the numerical method of axial thrust applied in this research.
Experimental Results on Air Release and Absorption in Hydraulic Oil
Authors: Manhartsgruber Bernhard
Published: December 2013

Mineral-oil based hydraulic fluids are used for power transmission in a number of wide-spread technologies such as hydraulic drives in heavy industrial equipment and construction vehicles as well as automotive systems like power steering and fuel injection. The mathematical modeling of these systems traditionally focuses on the medium to high pressure range where the effects of increased compressiblity due to free air are assumed to be negligible. The goal of the present paper is the precise measurement of the behaviour of a sample of a standard mineral oil based hydraulic fluid under controlled periodic volume change. The fluid is contained in a sealed test chamber equipped with sensors for pressure and temperature as well as a servo-hydraulic actuation system for the controlled volume change. Preliminary results show the expected hysteresis behavior according to the different time scales of the processes of air release and dissolution. Fifty consecutive cycles of compression and decompression are measured in steady state. This collection of measurement data is used for the identification of a dynamic model for the prediction of the amount of free air from the history of pressure change in the system. The fluid used in the tests is an HLP type hydraulic oil with a nominal viscosity of 32 cSt (32· 10−6 m2/s). Absolute pressure values between 0.3 bar and 32 bar (3 · 104 Pa to 3.2 · 106 Pa) are covered by the published experimental results.
Unlocking the Physics of Hypervelocity Impact
Authors: Thurber Andrew , Bayandor Javid
Published: December 2013

Satellites and spacecraft in orbit can impact micrometeorites and other debris at velocities exceeding thousands of meters per second. The shock pressures and temperatures created by these hypervelocity impacts greatly surpass standard material strengths, and deform structures in unconventional failure modes. Under these extreme conditions and strain rates, plastic deformation of a solid can resemble viscous fluidic motion. Using meshless finite element analysis methods, the present research attempts to quantify this fluidic structural response and identify analogous interactions in fluid dynamics.