bluuebunny/crossref_metadata_2025 huggingface dataset:
The Measurement on Micro-Jet Impulse Based on Laser Interferometer
Authors: Ping Zhu , Hou Liya , Zhang Weiyi
Published: July 2010

In the paper the heterodyne laser vibrometer combined with torsion pendulum system is employed to measure contactless the oscillating velocity of the horizontal target struck by pulse hydrone micro-jet in the experimental platform, which has the feature of measuring precisely impulse (measurement error ≤ 0.618%). The oscillating velocities of pulse micro-jet from converging-diverging, converging and cylindrical nozzles striking on horizontal target are measured respectively in normal atmosphere, and the values of the impulses are calculated by employing the dynamic character equation of force acted by pulse micro-jet. The result of experiment show that the impulse of converging nozzle with the ratio of sectional area of exit to that of inlet (Aexit/Ainlet) being 0.1 is 65% of that of cylindrical nozzle, and is 26.8% of that of converging-diverging nozzle with the ratio of sectional area of throat to that of inlet (Athroat/Ainlet) being 0.1145. Converging-diverging nozzle has obvious gaining on the impulse of hydrone propellant.
Infrared Visualization of Automotive Paint Spray Transfer Process
Authors: Akafuah Nelson K. , Salazar Abraham J. , Saito Kozo
Published: July 2010

An Infrared thermography based visualization technique for automotive paint spray is presented. Two common automotive paint applicators were studied using this technique and the results presented. The paint applicators studied were high-speed rotary bell atomizer and low pressure air atomizer. The technique uses a uniformly heated blackbody emitter as a background. The emitted infrared energy from the background passing through the spray is attenuated by the droplets in the spray. The attenuated intensity is captured by an infrared camera, to form a two-Dimensional image of the spray flow field. From the acquired intensity image, the entire spray flow field structure is visualized and the result discussed.
Optimum Meridian Profile With Additional Criteria
Authors: Tsugawa Takuji
Published: July 2010

In the previous paper, the optimum meridian profile of impeller and guidevane was obtained improving efficiency and cavitation performance. But, the meridian profile of impeller and guidevane is necessary to be decided by the consideration of various operative conditions for the practical use. In particularly, it is important that the separation flow in impeller and guidevane is suppressed in partial flow rate. In this paper, the optimum meridian profile of impeller and guidevane is calculated by considering the partial flow rate operative condition. That is, the optimum criteria are the efficiency, the cavitation performance and the partial flow rate operative condition. The partial flow rate operative condition is expressed by the limited condition of diffusion factor (e.g. Deq = 2). In the optimum procedure, the meridian profile is improved considering diffusion factor at partial flow rate in tip, mid-span and hub stream lines of impeller and guidevane become to the objective value (e.g. Deq = 2) in specified partial flow rate (e.g. Qpartial = 0.5Q). The equation of partial flow rate diffusion factor is expressed by partial inlet-outlet flow condition and additional term expressed by increase of attack angle at impeller inlet and at guidevane inlet. As the result, the optimum meridian profile considering partial flow rate operative condition is obtained.
Thermal Chaotic Mixing of Non-Newtonian Fluids in a Two Rod Mixer
Authors: El Omari Kamal , Le Guer Yves
Published: July 2010

We investigate the mixing and heat transfer enhancement in a two rod mixer for highly viscous non-Newtonian fluids. The mixer is composed of two circular rods maintained vertically in a cylindrical tank. Chaotic flows are obtained by imposing temporal modulations of the rotational velocities of the walls. We study the effect of different stirring protocols leading to non-chaotic and chaotic flows on the efficiency of mixing and heat transfer for three different rheological fluid behaviors: shear-thinning, Newtonian and shear thickening. For this purpose we use statistical indicators characterizing the mean value of fluid temperature and its homogenization. We find that chaotic mixing is suitable for shear-thickening fluids for which we observe a manifest enhancement of the thermal mixing (heat extraction and homogenization). This is due to the increase of apparent fluid viscosity in the vicinity of the rotating walls. This aspect confirms the relevance of chaotic mixing for highly viscous fluids.
Autorotation of Two Tandem Triangular Cylinders
Authors: Zhang Xing , Wang Shizhao , He Guowei
Published: July 2010

The autorotation of two tandem triangular cylinders at different gap distances is investigated by numerical simulations. At the Reynolds number of 200, three distinct regimes are observed with the increase of gap distance: namely, angular oscillation, quasi-periodic autorotation and ‘chaotic’ autorotation. For various gap distances, the characteristic of vortex shedding and vortex interaction are discussed. The phase graphs (angular acceleration vs. angular velocity) and the power spectra of moment are analyzed to characterize the motion of the cylinder. The Lyapunov exponent is also calculated to identify the existence of chaos.
Experimental Investigation of the Complete Characteristics of Rotodynamic Pumps
Authors: Ayder Erkan , Ilikan Ayhan N. , S¸en Mete , O¨zgu¨r Cahit , Kavurmacıog˘lu Levent , Kirkkopru Kadir
Published: July 2010

Pump failure in a pipeline system can occur for several reasons and this undesirable event causes waterhammer phenomenon. While designing a pipeline system, minimum and maximum pressures caused by waterhammer and the variation of the pressure along the pipeline with respect to time must be determined. In order to calculate the time variation of the pressure, complete characteristics of a pump is used as one of the boundary conditions. In these unsteady conditions, the pump may turn in normal or reverse directions which define eight different working zones called pump, turbine, brake and booster. Specific speed is an essential parameter which affects characteristics of pumps. In the literature, for many years there have been only three complete pump characteristics obtained with the assistance of 1960’s measuring devices and techniques. Each one of those corresponds to pumps having centrifugal (nsq = 35), mixed flow (nsq = 147) or axial impeller (nsq = 261). Recently additional complete pump characteristics that belong to 14 different specific speeds have been published in the literature. By considering improvements in pump design during half a century and innovations in measurement techniques, the present study is performed to repeat experiments of complete characteristics of different specific speeds existing in the literature, and to obtain complete pump characteristics for different specific speeds. The complete characteristics of seven pumps with specific speeds of nsq = 20 – 23 – 33 – 55 – 105 – 209 and 261 are obtained experimentally. The results show that the complete characteristics of a pump is not only function of specific speed but also function of pump design. The number of the complete pump characteristics available in the literature is increased in this study. The obtained results revealed that, unlike the existing approach in the literature, the complete characteristics of pump that is used in the pipeline, must be used in the calculation of waterhammer pressures in the design of pipelines.
CFD Software Applications for Transcritical Free Surface Flow
Authors: Pineda Saira F. , Blanco Armando J. , Rojas-Solo´rzano Luis
Published: July 2010

Open flow channel is very common in engineering applications. Traditional approaches solve shallow-water flow equations, known as Saint-Venant equations, when one or two dimension solutions can be adequate for obtaining most of the important flow characteristics. However, complex situations can require solving Navier-Stokes equations. The arrival of high performance computers and commercial software packages offers new possibilities in the field of numerical hydraulics. However, commercial software packages should be tested on some specific cases; so that these can be used with confidence. In this paper we solve several cases of free surface flow that consider subcritical, supercritical, critical, oscillatory depth profiles and hydraulic jumps using a commercial package, CFX™. Most of these cases are proposed as benchmark solutions for non-prismatic cross section, non-uniform bed slope and transition between subcritical and supercritical flow. Other cases as Hydraulic jump consist of experimental data of hydraulics jumps for incident flow with Froude numbers up to 4.23. Both types of cases allow us to perform the verification and validation of the commercial package used. Results obtained with CFX™ show excellent agreement with analytical solutions, for subcritical, supercritical, transitional and hydraulic jump cases. Special care with grid selection and entrance boundary condition is crucial to simulate with accuracy these types of flows. In particular, when a proper structured mesh is used, quality results are highly improved. Finally, results show to be insensitive to entrance turbulence conditions.
Detachment Criterion for Static Axisymmetric Bubbles on Horizontal Flat Surfaces
Authors: Lee Shong-Leih , Yang Chao-Fu
Published: July 2010

The static Young-Laplace equation is solved with the geometry method to yield the bubble shape on a horizontal flat surface under various contact angles. Multi-solution modes are found. Among the many possible equilibrium shapes of the bubble, however, only the fundamental solution mode could occur naturally. The value of VAR (volume to contact area ratio) could be a good measure for stability of equilibrium bubbles. The bubble becomes less stable when VAR increases. The numerical result reveals that in the course of bubble growth (i.e. volume increases) the VAR of the bubble increases linearly until the maximum contact area is reached. After that, VAR has a sharp increase due to a decreasing contact area. Beyond the maximum volume, equilibrium bubble does not seem possible. Based on the finding, it is postulated that bubble detachment occurs somewhere between the maximum contact area and the maximum volume according to perturbations from environment. However, the postulation seems to underestimate the stability of the bubble significantly for contact angles of larger than 160 degrees. A correction is proposed in the paper. Numerical result of bubble detachment criterion is fitted with polynomial functions of the contact angle.
Experimental and Numerical Investigations of a Turbulent Flow Behaviours in Isolated and Non Isolated Conical Diffusers
Authors: Aloui F. , Berrich E. , Pierrat D.
Published: July 2010

This work presents an experimental and numerical investigation of a confined turbulent flow behavior across a conical diffuser (2α = 16°). The role of a perturbation caused by the presence of an elbow in the test-section, upstream of the progressive enlargement, was studied. The main measurements were the static pressure, and the instantaneous velocity fields using the Particle Image Velocimetry (PIV). Post-processing of these PIV measurements were adopted using the Γ2 criterion for the vortices detection, and the Proper Orthogonal Decomposition (POD) technique to extract the most energetic modes contained in the turbulent flow and to the turbulent flow filtering. A data base has been also constituted, and was used to test the validity of the most models of turbulence, and in particular, a variant of the SST model.
Quadrature Method of Moments for the PDF Modeling of Droplet Coalescence in Turbulent Two-Phase Flows
Authors: Belt Roel , Simonin Olivier
Published: July 2010

In this work, Eulerian transport equations are derived for a polydispersed cloud of droplets in a turbulent carrier flow, which take into account the effects of polydispersion and coalescence. The approach is an extension of the Direct Quadrature Method Of Moments (DQMOM) formalism initially proposed by Marchisio and Fox (2005, J. Aerosol Sci., 36, pp. 43–95). In the initial DQMOM approach of Marchisio and Fox, the effects of polydispersion and coalescence can only be accounted for in the mass balance equations. By combining the DQMOM approach and the joint fluid-particle pdf approach of Simonin (1996, Von Karman Lecture Notes), Eulerian transport equations can be written in the frame of the DQMOM formalism for the velocity, agitation and fluid-particle covariance, which quantities are required to predict the behavior of a cloud of droplets in a turbulent flow. It is formally shown that the Eulerian transport equations in the DQMOM framework are the same equations as those in the multi-class Eulerian approach, except that now there is a collision term in the equations. The collision term due to coalescence can be easily expressed due to the assumptions made in the DQMOM framework, and it is shown that it couples the transport equations of the different classes and dispersed phase statistics, according to the change of number, mass and momentum during coalescence.
Thermodynamic Effect on Sub-Synchronous Rotating Cavitation and Surge Mode Oscillation in a Space Inducer
Authors: Yoshida Yoshiki , Nanri Hideaki , Kikuta Kengo , Kazami Yusuke , Iga Yuka , Ikohagi Toshiaki
Published: July 2010

The relationship between the thermodynamic effect and sub-synchronous rotating cavitation was investigated with a focus on cavity fluctuations. Experiments on a three-bladed inducer were conducted with liquid nitrogen at different temperatures (74 K, 78K and 83 K) to confirm the dependence of the thermodynamic effects. Sub-synchronous rotating cavitation appeared at lower cavitation numbers in liquid nitrogen at 74 K, the same as in cold water. In contrast, in liquid nitrogen at 83 K, the occurrence of sub-synchronous rotating cavitation was suppressed because of the increase of the thermodynamic effect due to the rising temperature. Furthermore, unevenness of cavity length under synchronous rotating cavitation at 83 K was also decreased by the thermodynamic effect. However, surge mode oscillation occurred simultaneously under this weakened synchronous rotating cavitation. Cavity lengths on the blades oscillated with the same phase and maintained the uneven cavity pattern. It was inferred that the thermodynamic effect weakened the peripheral cavitation instability, i.e., synchronous rotating cavitation, and thus axial cavitation instability, i.e., surge mode oscillation, was easily induced due to the synchronization of the cavity fluctuation with an acoustic resonance in the present experimental inlet-pipe system.
Flow Structures and Pressure Fluctuations in a Centrifugal Pump at Design and Off-Design Conditions
Authors: Pan Zhongyong , Ni Yongyan , Ho Jinyama , Yuan Shouqi
Published: July 2010

The flow structures and the pressure fluctuations in a centrifugal pump at both design and off-design points are presented in this paper. The flow structures are numerically obtained by solving the viscous incompressible Navier-Stokes equations with a 3D unsteady flow model. A sliding mesh technique is applied to take into account the impeller-volute interaction. The pressure fluctuations are obtained by both numerical simulations and experimental measurements. The former data denote all the flow field characteristics including those in the impeller, the interface, the volute and the diffuser, while the latter ones that acquisitioned by a high-frequency pressure sensor show only one position at the outlet flange. The FFT technology is adopted to process those dynamic pressure data to reveal the frequency features. All the power spectrum results present that the dominant frequencies are the blade passing ones, while the subdominant ones are varied depending on the flow rates and the positions. At design condition, the mean velocity field in both impeller and volute show well behaved flow with no separation, while subtle separation is found along the tongue side in the diffuser. Some unknown high-frequency contents are discovered in the flow field.
Conversion of a Micro-CT Scanned Rock Fracture Into a Useful Model
Authors: Crandall Dustin , Bromhal Grant , Smith Duane H.
Published: July 2010

Within geologic reservoirs the flow of fluids through fractures is often orders of magnitude greater than through the surrounding, low-permeability rock. Because of the number and size of fractures in geological fields, reservoir-scale discrete-fracture simulators often model fluid motion through fractures as flow through narrow, parallel plates. In reality fractures within rock are narrow openings between two rough rock surfaces. In order to model the geometry of an actual fracture in rock, a ∼9 cm by 2.5 cm fracture within Berea sandstone was created and the aperture distribution was obtained with micro-Computed Tomography (CT) scans by Karpyn et al. [1]. The original scans had a volume-pixel (voxel) resolution of 27 by 27 by 32 microns. This data was up-scaled to voxels with 120 microns to a side to facilitate data transfer and for practicality of use. Using three separate reconstruction techniques, six different fracture meshes were created from this up-scaled data set, each with slightly different final geometries. Flow through each of these fracture meshes was evaluated using the finite-volume simulator FLUENT. While certain features of the fracture meshes, such as the shape of the fracture aperture distributions and overall volume of the void, remained similar between the different geometric reconstructions, the flow in different models was observed to vary dramatically. Rough fracture walls induced more tortuous flow paths and a higher resistance to flow. Natural fractures do vary in-situ, due to sidewall dissolution and mineral precipitation, smoothing and coarsening fracture walls respectively. Thus for our study the range of fracture properties was actually beneficial, allowing us to describe the flow through a range of fracture types. A compromise between capturing the geometric details within a domain of interest and a tractable computational mesh must always be addressed when flow through a physical geometry is modeled. The fine level of detail that is currently available from micro-CT scanning equipment can compound this problem. This study evaluates several methods of obtaining rational CFD meshes from a complex physical geometry, and discusses the benefits and disadvantages of the different procedures as they pertain to flow through a natural fracture in rock.
Three Dimensional Simulation of Rayleigh-Be´nard Convection for Rapid Microscale Polymerase Chain Reaction
Authors: Muddu Radha , Ugaz Victor M. , Hassan Yassin A.
Published: July 2010

A variety of biochemical reactions involve cycling reagents through different temperature regimes in a specific order as dictated by chemical kinetics. One such reaction is the polymerase chain reaction (PCR), a fundamental process used to selectively amplify specific regions of interest within a larger DNA strand to very high concentration levels. Natural convection has recently been explored as a novel way to perform PCR by providing a passive approach to circulate reactants through the correct temperature zones. Optimal reactor design requires the spatial velocity and temperature distributions to be precisely controlled to ensure that the reactants sequentially occupy the correct temperature zones for a sufficient period of time. Rayleigh-Be´nard convection in vertical cylindrical reaction chambers maintained at fixed upper and lower surface temperatures provides a convenient model system to study these phenomena. In this work, we present results of three dimensional numerical simulations of the flow and temperature distributions in cylindrical reactors of different aspect ratios (height (h) / diameter (d)). These results helped identify different flow profiles that are possible in each of the geometries and led to an optimized redesign of the Rayleigh-Be´nard PCR convection system for rapid DNA replication.
Effect of Carbon Nanotube Additives on Drag Reduction in Pipe Flows
Authors: Steele Adam , Bayer Ilker , Allen Kenneth , Loth Eric
Published: July 2010

The drag reduction effects of dispersing carbon nanotube (CNT) additives into water-glycerin pipe flow were investigated experimentally. While nanofluid (i.e. fluids with nano-scale additives) drag reduction from the addition of long and flexible polymers into turbulent flows has been long identified, the mechanism that causes this effect is not yet fully understood. Other additives such as rigid polymers, surfactants, and bubbles have also been shown to be effective drag reducing agents. In the current work, high molecular weight polymers such as polyethylene oxide (PEO) as well as CNT additives produced significant drag reduction in both the transitional and turbulent regimes. CNTs were shown, for the first time, to enhance the drag reducing characteristics of polymer additives. CNTs were chosen in place of traditional nano-scale fibers in order to take advantage of their high strength properties in an attempt to reduce degradation and scission effects. The results were quantified by measuring the pressure drop across a downstream test section after the flow was fully developed. Reynolds numbers between about 500 and 5000 were studied in order to provide sufficient detail from laminar to transitional and turbulent flow regimes. The additive dispersion quality was also investigated over multiple dispersion techniques.
Self-Organization of Fibers in a Suspension Between Two Counter-Rotating Discs
Authors: Ahlberg Charlotte , Lundell Fredrik , So¨derberg L. Daniel
Published: July 2010

The behavior of fibers suspended in a flow between two flat counter-rotating discs has been studied experimentally. Captured images of the fibers in the flow were analyzed by steerable filters, to extract positions and orientations of the fibers. Experiments were performed for gaps between the discs of less than one fiber length, and for equal absolute values of the angular velocities for the discs. The length-to-diameter ratio of the fibers was approximately 14. During certain conditions, the fibers organized themselves in a distinct manner, which we will denote as fiber trains, in which three or more fibers are aligned next to each other, at the same radial position, with a short fiber-to-fiber distance. The direction of the individual fibers is radial and the direction of the whole train is tangential. Trains containing more than 60 fibers have been observed and are quite impressing.
Modeling of Immiscible, Two-Phase Flows in a Natural Rock Fracture
Authors: Crandall Dustin , Ahmadi Goodarz , Smith Duane H.
Published: July 2010

One potential method of geologically sequestering carbon dioxide (CO2) is to inject the gas into brine-filled, subsurface formations. Within these low-permeability rocks, fractures exist that can act as natural fluid conduits. Understanding how a less viscous fluid moves when injected into an initially saturated rock fracture is important for the prediction of CO2 transport within fractured rocks. Our study examined experimentally and numerically the motion of immiscible fluids as they were transported through models of a fracture in Berea sandstone. The natural fracture geometry was initially scanned using micro-computerized tomography (CT) at a fine volume-pixel (voxel) resolution by Karpyn et al. [1]. This CT scanned fracture was converted into a numerical mesh for two-phase flow calculations using the finite-volume solver FLUENT® and the volume-of-fluid method. Additionally, a translucent experimental model was constructed using stereolithography. The numerical model was shown to agree well with experiments for the case of a constant rate injection of air into the initially water-saturated fracture. The invading air moved intermittently, quickly invading large-aperture regions of the fracture. Relative permeability curves were developed to describe the fluid motion. These permeability curves can be used in reservoir-scale discrete fracture models for predictions of fluid motion within fractured geological formations. The numerical model was then changed to better mimic the subsurface conditions at which CO2 will move into brine saturated fractures. The different fluid properties of the modeled subsurface fluids were shown to increase the amount of volume the less-viscous invading gas would occupy while traversing the fracture.
V&V Application on Private and U. S. Government Projects
Authors: Knight Kelly J. , Peltier Joel , Berkoe Jon M.
Published: July 2010

This paper will discuss the application of verification and validation (V&V) on both private and US government sponsored projects. Application of V&V for business and legal purposes is very tightly defined when executing a project compared to the open ended research of V&V performed in national laboratories and academia. Major purchases on the order of millions to hundreds of millions of dollars depend upon an accurate V&V if the calculation supporting the purchase involves a simulated solution or design. Examples of application will be given to illustrate the use of V&V within projects. The examples will motivate a discussion on the future needs and directions of the business industry from the larger V&V community. It is hoped that this discussion will promote greater interaction between the national labs, academia and business to help develop methodologies, consistencies and directions of effort that will support execution of the V&V process in the business sector.
CFD Prediction of Pressure Drop and Flow Field in Standard Gas Cyclone Models
Authors: Kharoua Nabil , Khezzar Lyes , Nemouchi Zoubir
Published: July 2010

Pressure drop is an important performance parameter for cyclone separators. A computational fluid dynamics (CFD) study of the pressure drop in cyclones using the Reynolds stress (RSM) and the granular mixture models is presented in this paper. The study includes three different cases; pure gas at ambient temperature, pure gas at different temperatures, and particle-laden flow. The first two cases were reasonably well predicted while the presence of particles with a relatively high loading (up to 1 kg/m3 of fluid) caused some discrepancies in the predicted results. The concept of entropy generation, used in this work, has permitted to detect regions of high frictional effect in the vortex finder, the bottom of the conical part, and at the interface separating the outer and the core streams. The simplifying assumptions employed in the CFD models and some numerical details are discussed.
X-Ray Particle Tracking Velocimetry in Fluidized Beds
Authors: Drake Joshua B. , Tang Lie , Heindel Theodore J.
Published: July 2010

Fluidized beds are commonly found in the chemical and energy processing industries because of their low pressure drop, uniform temperature distribution, and high heat transfer rates. For example, in biomass gasification, biomass particles are injected into a heated bubbling bed of inert material (typically refractory sand) that volatilizes to form a flammable gas. However, the movement of the biomass particle through the bubbling bed is difficult to quantify because the systems are opaque. This paper describes X-ray particle tracking velocimetry (XPTV) applied to fluidized beds, where X-ray flow visualization is used to track the location of a single fabricated tracer particle as a function of time in a fluidized bed to study the bed/particle hydrodynamics. Using stereoscopic X-ray imaging, the 3D position of the tracer particle as a function of time is determined, from which tracer particle velocity can be calculated. Details and challenges of the XPTV process are also summarized.
Predictive-Computational Fluid Dynamics Validation Assessment for an Impinging Diffuser Flow
Authors: Lorentz D. G. , Buchanan J. R. , Bauer R. C.
Published: July 2010

As part of a Predictive-Computational Fluid Dynamics (P-CFD) verification and validation (V&V) program, post-processed CFD analysis results are being compared to high-quality, high-resolution validation-level flow field data obtained from fundamental experiments. This paper provides initial results and findings from the CFD validation assessment of an impinging diffuser flow (IDF) using validation-level flow field data obtained from experiments. The paper describes the CFD models, meshing, solutions, and error assessments for comparison to experimental results from the experimental data. To date, quantitative comparisons have been performed for velocity profiles and turbulent statistics taken from laser Doppler and particle image velocimetry measurements as well as surface static pressure measurements. Methods for quantifying the computational uncertainty through the Grid Convergence Index (GCI) and experimental uncertainties including both instrumentation as well as flow condition uncertainty are discussed. This paper also identifies tasks and issues that will improve modeling and experimental methods for future Predictive CFD V&V assessments.
Pump Sump CFD for Vertical Pump Design
Authors: Kru¨ger Susanne , Ait Bouziad Youcef , Maurer Wolfgang
Published: July 2010

Pump sump designs play an important role for vertical pumps since they are responsible for the flow conditions at the impeller inlet. To first foresee and then prevent possible damages resulting from uneven flow conditions, computational fluid dynamics (CFD) can support model tests to reduce at least costs, but, with increasing computer power, also time. This paper compares different approaches to model the flow in pump sumps: The conventional single phase fixed water surface method and the multiphase (air+water) free water surface method. Both methods are compared with unsteady state computations and two different geometries (original and modified geometry) regarding differences in water surface, flow distribution in the pump wells, measurements, and computational time. All CFD results compare well with the experiments and are in good agreement with the vortex formation, type, and location as well as flow pre-rotation. Most of the time, the main interest lies in flow, vortices, forces, and frequencies in the attached pump, and additional computations need to be undertaken. Due to different timescales between the flow in the pump sump and in the pump itself, a decoupled technique is conventionally used in which firstly the flow field of the sump and secondly in the vertical pump is computed. We compare this decoupled method with a fully coupled one regarding computational time needed and time discretisation required as well as resulting flow structures and radial forces. Results of both methods are mainly in a good agreement, show slight differences in the velocity profile at the impeller inlet, and larger ones in magnitude of radial forces and force modulus. Decoupled and coupled method show practically the same computational effort, which recommends the application of the fully coupled approach not only in special cases where the vortices in the sump are triggered by the impeller rotations, especially at low flow rate operating points and existence of pre-swirl vortices.
Study of Planform-Shape Influence on MAV Wings
Authors: Esmaeili Monir Hessan , Tadjfar Mehran
Published: July 2010

We study the influence of wing geometry on the aerodynamic performance of micro aerial vehicles (MAVs). Four different wing planforms: rectangular, Zimmerman, inverse Zimmerman, and elliptical are considered. The inverse-Zimmerman planform have a slightly better performance. The peak of aerodynamic performance moves to lower angles of attacks as the aspect ratio of the wing is increased. The influence of the edge-shape of the wing on the aerodynamic coefficients is also studied. We find that moderate edge-ratio of 2 or 3 produces the lowest drag coefficients. Changing the side-edge geometry influences the lift coefficients but not the drag coefficients.
A CFD-Based Investigation of Boundary Layer Skew in the Hub Region of a Low Speed Axial Compressor and its Influence on Performance and Losses
Authors: Hilgert M. , Bo¨hle M.
Published: July 2010

The flow in the hub end-wall region has a substantial influence on the aerodynamic performance of axial-flow compressors. A numerical investigation of this three-dimensional flow phenomenon, often referred to as boundary layer skew, that contributes to the interaction between the end-wall and blade suction surface flow, thus determining the losses in this area, is the topic of this report. A single-staged model compressor (flow coefficient: 0.5, work coefficient: 0.34) with a 7-blade rotor row and a highly loaded 11-blade stator row was designed for the simulation. To account for the complex time-dependent flow patterns in the end-wall area, a transient calculation with the rotor and stator rows fully modeled (360°) is carried out. The flow is assumed to be incompressible as the velocities of the low-speed axial compressor do not exceed a Mach-number value of 0.3. The calculations show that the boundary layer in the end-wall region is highly skewed and transient. There is a direct connection to local flow phenomena such as separation as well as to global pressure loss coefficient distributions in pitchwise and streamwise direction. Different levels of flow overturning in the end-wall area are observed, depending on the boundary layer skewness varying by simulating the compressor at different operational points.
Centrifugal Pump Pressure Pulsation Prediction Accuracy Dependence Upon CFD Models and Boundary Conditions
Authors: Park Sang Hyun , Morrison Gerald L.
Published: July 2010

Unsteady CFD simulations for a low specific speed open faced impeller centrifugal pump operating with and without balancing holes and having cut-away sections of the impeller are performed and compared to experimental data obtained using the actual pump simulated. For this simulation, the entire pump from suction inlet to exit flange is modeled. General pump performance characteristics are compared between the actual pump and the simulation. Pressure pulsation data are recorded at various locations in the pump using flush mounted pressure transducers and directly compared to the simulation results. Pressure spectrum data are used to evaluate the effects of three different boundary conditions upon the accuracy of the pressure pulsation simulations as well as the overall pump performance. These boundary conditions are a) fixed inlet and exit pressure, b) mass flow rate inlet condition with outflow exit, and c) target mass flow rate inlet with outflow exit which lets the inlet pressure fluctuate. All of these are available in the commercial CFD package utilized. Based upon comparisons between CFD simulations and experimental data for both the steady and unsteady conditions, the mass inlet condition is found to produce the best overall results for the installed pump.
Analysis of the Flow Between the Impeller and Pump Casing Back Face for a Centrifugal Pump
Authors: Park Sang Hyun , Morrison Gerald L.
Published: July 2010

Previous experimental investigations of an open faced impeller, low specific speed, centrifugal pump showed that increasing the clearance between the impeller and the pump casing back face decreased the axial thrust generated on the impeller. This is contrary to normal convention. It was also found that if the front clearance of the pump was maintained at a constant value, the efficiency of the pump was not affected by the changing back clearance when no balance holes were present. The pump performance did vary with back clearance when balance holes were present. These results were obtained by measuring pump casing pressure distributions by Hossain (2000). In order to determine the reasons for this axial thrust dependence upon back clearance, it is necessary to determine the flow field within this small region. It is very difficult to measure the fluid flow in the small back clearance so the entire pump was simulated with varying back clearances and with and without balance holes using CFD. The CFD results are compared to the pump housing pressure distributions and to analytical analyses of flow between simple rotating disks. The dependence of the flow inside the back clearance region of the centrifugal pump has been analyzed in terms of the gap size and balance hole size. The impeller used in the analyses and experiments includes a cutaway section on the impeller. The flow inside the gap was severely affected by the gap size and, as a consequence, the pressure distribution and the axial thrust.
Comparison of Measurements on Axial Fans and Performance Prediction Using Common Scale-Up Methods at Part- and Overload
Authors: Hess Michael , Pelz Peter F.
Published: July 2010

There is a need to reliably predict the performance (efficiency and total pressure rise) of axial fans from model tests not only at the design point but also at part- and overload. The commonly used scale-up formulae give satisfactorily results only near the design point where inertia losses are small in comparison with frictional losses. At part- and overload the inertia losses are dominant and the scale-up formulae so far used fail. This is shown by applying several common scale-up methods in comparison to measured values of two axial model fans with a diameter of 1000 mm respectively 250 mm at different rotational speeds, hence Reynolds-numbers. In addition efficiency split-up for axial fans is shown and compared to former measurements on pumps.
Fibrous and Spherical Particle Transport and Deposition in the Human Nasal Airway: A Computational Fluid Dynamics Model
Authors: Shanley Kevin T. , Ahmadi Goodarz , Hopke Philip K. , Cheng Yung-Sung
Published: July 2010

As the interface between the human respiratory system and the environment, the nose plays many vital roles. Not the least of which is filter. Resulting from numerous natural and anthropogenic processes, particulate matter becomes airborne. Should particulate matter reach the lower portions of the respiratory tract, a host of maladies may occur. In an attempt to further understand the physics behind particulate matter transitioning from the environment into humans a computational model has been developed to predict the efficiency with which human noses can remove particles before they reach the lungs. To this end computational fluid dynamics and Lagrangian particle tracking simulations have been run to gather information on the deposition behavior of both fibrous and spherical particles. MRI data was collected from the left and right passages of a 181.6 cm, 120.2 kg, human male. The two passages were constructed into separate computational volumes consisting of approximately 950,000 unstructured tetrahedral cells each. A steady laminar flow model was used to simulate the inhalation portion of a human breathing cycle. Volumetric flow rates were varied to represent the full range of human nasal breathing. General agreement was shared quantitatively and qualitatively with previously published in vitro studies on other nasal models. Lagrangian particle tracking was performed for varying sizes of fibrous and spherical particles. Deposition efficiency was shown to increase with fiber aspect ratio, particle size, and flow rate. Anatomy was also identified as effecting deposition.
Numerical Simulation of Optimized Forebay of Pumping Station
Authors: Cheng Li , Zhou Jiren
Published: July 2010

The incompressible N-S equations are solved by the finite volume method. Based on the standard k-e model, the SIMPLEC algorithm is applied for the solution of the discretization governing equation. Using CFD, the flow pattern in the forebay of pumping station is revealed. The calculation results showed that there were large scale recirculation in the forebay of original scheme and the flow patterns of optimized forebay with bottom sills were improved. The calculated results were in good agreement with experiment data, which show that the calculated model was reliable and practical.
Dynamic Characteristics of the Radial Clearance Flow Between Axially Oscillating Rotational Disk and Stationary Disk
Authors: Horiguchi Hironori , Ueno Yoshinori , Takahashi Koutaro , Miyagawa Kazuyoshi , Tsujimoto Yoshinobu
Published: July 2010

Dynamic characteristics of the clearance flow between an axially oscillating rotational disk and a stationary disk were examined by experiments and computations based on a bulk flow model. In the case without pressure fluctuations at the inlet and outlet of the clearance, parallel and contracting flow paths had an effect to stabilize the axial oscillation of the rotating disk. The enlarged flow path had an effect to destabilize the axial oscillation due to the negative damping and stiffness for outward and inward flows, respectively. It was shown that the fluid force can be decomposed into the component caused by the inlet or outlet pressure fluctuation without the axial oscillation and that due to the axial oscillation without the inlet or outlet pressure fluctuation. A method to predict the stiffness and damping coefficients is proposed for general cases when the device is combined with an arbitrary flow system.
Subsonic Venturi Interaction With Free-Stream Flow
Authors: Rahai Hamid R. , Hoang Huy T. , Bonifacio Jeremy , Horstman Raymond H.
Published: July 2010

Numerical and experimental investigations of a venturi flow into a cross flow have been performed. The numerical analyses were performed using the CD-Adapco CCM+ commercial software with non-uniform mesh and the standard k-ε turbulence model. The analyses were performed for the venturi outlet directly connected to the bottom surface of the wind tunnel and for the venturi connected to the wind tunnel bottom surface with a 15.24 cm long tube extension of the same diameter. The experimental investigations were carried out in a subsonic open-circuit wind tunnel facility of the Center for Energy and Environmental Research and Services (CEERS) in conjunction with a single hot wire sensor and a LabView-National Instrument data acquisition system. For the experimental investigations, the venturi was connected to the bottom surface of the wind tunnel without the extension tube. For the numerical investigations, the ratios of the venturi flow momentum to the cross flow momentum, r, were 0.25, 0.5, 0.75, and 1.0. For the experimental investigations, the momentum ratios were 0.5, 0.85, and 1.0. For all analyses, isothermal condition is assumed. Results indicate when r = 0.25 and 0.5, the venturi flow is confined to an area near the wind tunnel surface with high static pressure within the venturi and the extension tube. However, for momentum ratios higher than 0.5, the venturi flow penetrates into the cross flow, before being tilted into the cross flow. For high r values, there is a counter-rotating vortex pair which grows in downstream direction. The adverse pressure gradient upstream of the venturi flow affects the flow characteristics inside the venturi at low momentum ratios. However, there were no indications of flow separation or flow recirculation within the venturi or the extension tube.
Prediction of Transition Region in Flow Over the Flat Plates
Authors: Zahedi Gh. , Mansouri S. H. , Salmanzadeh M.
Published: July 2010

A new model has been developed to predict the onset of transition from laminar to turbulent regime and also calculate the transition flow field. In developing the model, we have used the V2F turbulence model to predict the Reθ and velocity fluctuations, u′, at the onset of transition point, extracted from the same available experimental cases over a flat plate for several experimental cases. Then, we have correlated Reθ as a function of u′ at the transition point. This correlation has been used in conjunction with the V2F model to find the onset of transition point. The intermittency model has also been modified to calculate the probability of turbulence regime all over the flow field to improve the eddy viscosity calculated by V2F model. The model has been tested for different flat plate flows and the results compared with experimental data insuring the accuracy of the model. Comparison showed that the model is a powerful tool for prediction of transition onset and also transition region.
Update on Progress in Creating Stabilized Gas Layers in Flowing Liquid Mercury
Authors: Wendel Mark , Felde David , Abdou Ashraf , Reimer Bernard
Published: July 2010

The Spallation Neutron Source (SNS) facility in Oak Ridge, Tennessee uses a liquid mercury target that is bombarded with protons to produce a pulsed neutron beam for materials research and development. In order to mitigate expected cavitation damage erosion (CDE) of the containment vessel, a two-phase flow arrangement of the target has been proposed and was earlier proven to be effective in significantly reducing CDE in non-prototypical target bodies. This arrangement involves covering vulnerable surfaces with a protective layer of gas. The difficulty lies in establishing a persistent gas layer that is oriented vertically and holds up to the strong buoyancy force and the turbulent mercury flow. Several new multiphase experiments have been completed at the Oak Ridge National Laboratory toward developing such layers. The gas hold-up is accomplished by machining regular features (grooves or pits) into the wall with dimensions on the order of 1 mm. The thickness of the gas layer varies, and it is currently unknown how thick a layer must be in order to successfully mitigate the damage, although this aspect is also under investigation. The paper includes a description of the various tests, a presentation of high-speed video images of the gas/mercury interaction viewed through a transparent window, and a discussion of how the results can be used to design a new SNS target that might be resistant to cavitation damage erosion.
The Study of Guide Vanes on Submersible Pump
Authors: Chen Bin , Zhang Lanjin , Zhang Kewei , Peng Guangjie
Published: July 2010

Because the structure of submersible pump is special, and common guide vane is a factor effecting low efficiency, those guide vanes design method is different from ones of common axial flow pump and mixed flow pump. This paper introduces the design methods of guide vane on submersible pump. To improve the total performance, submersible pump structure, hydraulic performance, diffusion and friction loss are considered comprehensively when the meridian plane of guide vane is designed. The coefficient of diffusion on meridian plane should be larger than the recommended value and limited to avoid heavy flow separation. The guide vane number is bigger and meridian length of guide vane is shortened. For example, the number of guide vane can be nine or eleven, even thirteen when impeller blade number is four. Bigger number of guide vane makes the short guide vane placed on smaller diameter and avoids flow passage diffused more. On the other hand, smaller diameter will decrease pump dimension, weight, and production cost. To Balance the recycled energy and loss energy, outlet angle of guide vane should be reduced suitable. The angle should be 90 degree if completely recycling the rotating flow energy, but outlet angle should be larger than 90 degree if considering finite cascade. Those two angles will bring large diffusion of flow passage, large diffusion loss and flow friction force. Since the diffusion loss counts heavier percent of hydraulic loss, the angle should be reduced, such as 70 degree. That smaller angle doesn’t recycle completely the rotating energy, but hydraulic loss is decreased, and the efficiency of pump is higher instead. The test testifies that the efficiency of submersible pump designed by those above measures can reach 88%.