bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of Bounding Pressures Due to Condensation-Induced Water Hammer at the Davis-Besse Nuclear Power Plant in Response to Generic Letter 96-06
Authors: Elicson G. Thomas , Burelbach James P. , Lang Theodore A.
Published: February 2009

The U.S. NRC is currently evaluating nuclear plant responses to Generic Letter (GL) 96-06, “Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions” [1]. GL 96-06 is concerned with potential two-phase flow and water hammer conditions that could be present in the cooling water systems of nuclear power plants during design-basis accidents. Nuclear power plants rely on large capacity service water pumps to supply cooling water flow, via an extensive pipe network, to heat exchangers such as room coolers, pump lube oil coolers, and containment air coolers (CACs), for normal and abnormal plant operation. Following a postulated a loss of offsite power (LOOP) event, the normal electrical power supply to the service water pump would be lost resulting in a 20 to 30 second cooling water flow interruption while a diesel generator is started and the service water pump load is sequenced onto the diesel generator. In power plants, such as the Davis-Besse Nuclear Power Plant with open service water systems that draw from a lake or a river and supply safety-related CAC heat exchangers located 30 to 40 feet above the pump outlet, this could lead to cold water column separation in the heat exchanger supply and return piping. If a loss of coolant accident (LOCA) occurs coincident with the LOOP, then boiling in the CAC heat exchanger tubes could occur, as well. Upon restoration of the cooling water flow, dynamic loading could be expected as steam condenses and water columns rejoin. The TREMOLO computer program [2,3] has been used to calculate dynamic thermal hydraulic response and reaction forces in service water piping systems for several nuclear power plants in response to GL 96-06. A consistent result obtained in each of these GL 96-06 analyses is that the LOOP + LOCA scenario produces the bounding loads rather than the LOOP-only scenario. This result seemingly contradicts current industry thinking which suggests that because the water columns are colder and the void fraction lower during LOOP-only scenarios, the LOOP-only loads should be bounding [4,5,6]. While the physics supports the conclusion that the rejoining of colder water columns will generally yield the largest water hammer pressure rise, when actual plant geometry and credible accident scenarios are analyzed, a different picture emerges. This paper couples insights obtained from the GL 96-06 TREMOLO analysis of the Davis-Besse Nuclear Power Plant with independent hand calculations and experimental evidence to support the conclusion that the LOCA+LOOP scenario will produce the bounding loads in service water piping systems.
Dynamic Pipe Stresses During Water Hammer: IV — Elastoplasticity in Thick Walled Tubes
Authors: Leishear Robert A. , Morehouse Jeffrey H.
Published: February 2009

Closed form equations were used to approximate the elastoplastic stresses in a thick walled pipe subjected to water hammer. The elastoplastic problem was considered for both the stresses during the initial elastic expansion and the ensuing plastic stresses. The stresses in the pipe can be expressed as a function of the static elastic stresses, static plastic stresses, and time dependent vibration equations. Up to the yield stress, existing elastic stress equations govern the pipe response. At the yield stress, plastic deformation is expected during static loading conditions, but the extent of plastic deformation during dynamic loading may be affected by the dynamic yield stress of the material. The effect of the dynamic yield stress was shown to eliminate plastic deformation for time spans shorter than those typically encountered in water hammer events. If the load is sustained after the initial elastic yielding, the pipe will plastically deform. The pipe will also plastically deform if initially loaded to a stress beyond the dynamic yield stress, regardless of the water hammer duration. In either case, a plastic stress zone is formed at the bore of the pipe when a pipe is internally pressurized beyond the dynamic yield stress. As the pressure increases, the plastic zone expands toward the outer pipe wall. Static stress equations are available to fully describe the elastoplastic stresses as the plastic zone slowly expands. These static stress equations were substituted into the appropriate vibration equations to obtain the elastoplastic dynamic stress for sudden pipe wall expansion. The resulting equations were simplified to obtain the maximum plastic stress at a point on the pipe wall.
Water Surface Impact Load Acts on Bulbous Bow of Ships
Authors: Tanizawa Katsuji , Ogawa Yoshitaka , Minami Makiko , Yamada Yasuhira
Published: February 2009

As a part of the project study concerning on ship structural design for oil spill prevention by collision, optimal design of flexible bulbous bow structure is studied to absorb kinetic energy of the colliding ship. Such a flexible bulbous bow is named as buffer bow. To formulate design criteria of the buffer bow, the hydrodynamic impact forces acts on the bulbous bow was studied theoretically and experimentally. For theoretical study, shape of the bulbous bow was approximated by an ellipsoid and von Ka´rman’s momentum theory was applied to estimate the slamming impact loads with given impact velocity of the emerged bow to free surface. Wagner’s impact theory was also applied to study the effect of free surface swell up. Based on the momentum theory, an estimation method of the impact loads was proposed. To validate the estimation method, a experiment was conducted at the 80m square tank of NMRI. A self-propelling container ship model was used for the experiment. The vertical and lateral shearing forces and bending moments at the root of the bulbous bow were measured. In this paper, the results of the study are presented.
Dynamic Response of the Fuel Safety Experimental Capsule Under Pressure Wave and Water Hammer
Authors: Yoshie S. , Nakamura T. , Aizawa T.
Published: February 2009

Fuel behavior under reactivity initiated accident (RIA) conditions in light water reactors are being investigated at the Nuclear Safety Research Reactor (NSRR) in Japan. The capsule containing a fuel rod should be designed so that it could endure the impulsive loads and could be as thin as possible, to avoid losing the neutron economy simultaneously. So the dynamic capsule experiments have been conducted for investigating pressure wave propagation, water hammer and deformation response using explosive as a source. And analytical approach was contrived to reproduce the fluid-structural dynamic response. High tensile tests were carried out for the capsule material and the expression way of dynamic constitution law so as to reproduce the flow stress change due to strain and strain rate. The dynamic plastic deformation behavior of the capsule could be reproduced by this method.
An Application of a Pressure Intensifier Using an Oil Hammer to a Hydraulic Cylinder of a Construction Machine
Authors: Suzuki Katsumasa , Sasaki Daisuke , Yokoyama Kentarou , Suzuki Yukichi
Published: February 2009

The active utilization of the pressure rise phenomenon of an oil hammer and a new type of hydraulic pressure intensifier using an oil hammer were proposed and developed. In this research, an application of this intensifier to a hydraulic cylinder of a construction machine is studied through experimentation and simulation. High pressure is generated when the fluid flow through the pipeline is shut quickly by the solenoid operated valve at the downstream end. If the fluid is taken out through the check valve when the pressure is high, much higher-pressure fluid than the supply is obtained. Therefore the pressure is intensified. The purpose of this research is to help apply this device to industrial machinery. The necessary level of increased pressure is thought to be around 30MPa to apply it to an actual machine. We intend to find a suitable pipeline length and diameter, in order that low pressure supplied by a pump may be increased to the necessary high pressure by an oil hammer.
Beneficial Use of Water Hammer in a Gasoline Direct Injection System
Authors: Bartolini C. M. , Caresana F. , Pelagalli L.
Published: February 2009

This paper reports on the study of an injection system for internal combustion engines that exploits a water hammer oscillating circuit as the high pressure pump. This concept has recently been developed by the authors and successfully used in a direct-injection two-stroke gasoline engine prototype. The fluid dynamic behavior is characterized by unsteady flow in high length/diameter ratio pipes and is dominated by water hammer and cavitation. A numerical code was developed to gain a better understanding of these complex phenomena and as an optimization tool. The flow in the piping was solved by means of a 1D model suitable to describe the cavitation and unsteady friction. An ad hoc experimental analysis was performed to demonstrate model consistency in simple test cases of cavitating and non-cavitating flows. The model was then used in a numerical code for the simulation of the whole water hammer injection plant.
Numerical Simulation for Free Turbulent Reacting Flow by Particle Method
Authors: Uchiyama Tomomi , Otsuki Naohiro
Published: February 2009

This paper presents a particle method for free turbulent reacting flows. The vorticity and concentration fields are discretized into the vortex and concentration elements, respectively, and the behavior of the elements is calculated with the Lagrangian method. The chemical reaction is estimated through the Lagrangian calculation for the strength of concentration element. The particle method is applied to simulate a plane mixing layer with a single-step and irreversible chemical reaction of non-premixed reactants so as to discuss the applicability.
Three-Dimensional Simulation for Diffusion of Matter in Compound Round Jet by Particle Method
Authors: Uchiyama Tomomi , Ichikawa Akihito
Published: February 2009

The diffusion of matter in compound round jet is simulated by three-dimensional particle method. The flow field is calculated with a vortex method, whereas the concentration field is simulated through a particle method analogous to the vortex method. It is shown that the concentration distribution yielded by the three-dimensional vortical flow is in good agreement with the experimental one obtained by the flow visualization. The mean concentration is confirmed to be in the self-preservation state.
Three-Dimensional Numerical Simulation and Performance Study of an Industrial Helical Static Mixer
Authors: Rahmani Ramin K. , Keith Theo G. , Ayasoufi Anahita
Published: February 2009

Viscous liquids have to be homogenized in continuous operations in many branches of processing industries. Consequently, fluid mixing plays a critical role in the success or failure of many industrial processes. The use of static mixers has been utilized over a wide range of applications such as continuous mixing, blending, heat and mass transfer processes, chemical reactions, etc. This paper illustrates how static mixing processes of single-phase viscous liquids can be simulated numerically, and presents the flow pattern of both Newtonian and non-Newtonian single-phase liquids through a helical static mixer, and provides useful information that can be extracted from the simulation results. Three-dimensional finite volume simulations are used to study the performance of the mixer. The CFD code used here solves the Navier-Stokes equations for both laminar and turbulent flow cases. The turbulent flow cases were solved using k–ω and Reynolds Stress models. The flow properties are calculated for both Newtonian and non-Newtonian fluids. The calculated pressure drop is in good agreement with existing experimental data.
Time-Resolved PIV Measurements Within a Triple Impeller Stirred-Tank
Authors: Papadopoulos George , Hammad Khaled J.
Published: February 2009

Time-resolved velocity measurements using particle image velocimetry (PIV) were performed in a triple impeller stirred-tank to evaluate flow structure and flow dynamics. Using a high framing rate digital camera and a high pulse rate laser, the flow field at a planar location along the diameter of the tank was over-sampled to capture the time evolution of vortical structures in the flow. Several tests were performed for rotational speeds ranging from 175 RPM to 1575 RPM. The working fluid was glycerin at ambient conditions. Time averaged results over several blade passage cycles reveal that the vortical toroidal structure and frequency changes significantly over the RPM range investigated. A point of transition exists past which symmetry in the tank is lost, as a result of jet-jet interaction between adjacent Rushton turbines. While the flow in the region near and in between the turbines is unsteady and periodic due to blade passage, further away in the core of the mixing vessel the flow reaches a state of uniformity, as revealed from the reconstructed volumetric velocity field determined from the time-resolved PIV measurements.
Linear Stability Analysis of Bioconvection in Porous Media: The Effect of Fouling
Authors: Kuznetsov A. V. , Avramenko A. A.
Published: February 2009

In this paper, the effect of fouling on the stability of a uniform suspension of gyrotactic motile microorganisms in a fluid saturated porous medium is investigated. Fouling may occur because of the deposition of microorganisms on a porous matrix. This deposition decreases porosity and permeability of the porous medium. Stability analysis carried out in this paper reveals that there is a critical porosity of the porous medium. If the porous medium utilized for this process has a smaller porosity than critical, the uniform suspension of gyrotactic microorganisms is stable and bioconvection does not develop. If the porous medium has lager porosity than critical, the uniform suspension is unstable and bioconvection develops.
A Theoretical Prediction of Laminar Falling Plumes in Bioconvection of Oxytactic Bacteria in Porous Media
Authors: Kuznetsov A. V. , Avramenko A. A. , Geng P.
Published: February 2009

The objective of this paper is to investigate theoretically laminar falling bioconvection plumes in a deep chamber filled with a fluid saturated porous medium. A suspension of motile oxytactic bacteria, such as Bacillus subtilis, which swim up the oxygen gradient, is considered. In a deep chamber, because of the limited diffusivity of oxygen, oxygen concentration is high only in a thin cell-rich upper boundary layer. Since bacteria are heavier than water, the cell-rich upper boundary layer becomes unstable and bioconvection plumes develop. The bioconvection plume carries oxygen and cells from this cell-rich upper boundary layer to the lower region of the chamber.
Gap Flow Field Measurements of Bio-Centrifugal Ventricular Assist Device Using Laser Doppler Anemometer
Authors: Chua Leok Poh , Ong Kang Shiu , Yu Simon Ching Man
Published: February 2009

A flow field study in the gap between the impeller and the stationary casing of a bio-centrifugal pump was conducted using laser Doppler anemometer (LDA). Any stagnation flow and high shear stress flow observed is useful to identify the region of possible blood clotting or blood damage. Blood analog that has the similar characteristics as blood was used in this study. The gap flow was found to be smooth with the absence of any standing vortices. It was also found that the existence of the splitter plate of the double volute design has highly affected the gap flow and created a washout mechanism, which could cause the gap flow tended towards the eye of the impeller and successfully prevent the fluid from being stagnated in the gap.
Flow Separation at 90-Degree Junctions With Opposing Flows
Authors: Frizzell Carl , Werth David
Published: February 2009

Sumps located on the side of cooling tower basins, or any other type of hydraulic structure where opposing flows combine and turn 90-degrees can result in a significant amount of flow separation and energy dissipation at the junction. These separation zones can result in localized regions of higher velocity. If the separation zone is large enough, the flow can approach critical depth. A theoretical method of predicting the size of these separation zones is presented based on the conservation of energy and momentum. To validate the model, the results of an ongoing experimental study are compared to the theoretical predictions. A physical model was constructed and an Acoustic Doppler Velocimeter was used to collect 3-dimensional velocity data within each leg of the junction.
Conceptual Design of the Flow Noise Simulator
Authors: Sato Ryuichi , Mori Takayuki , Yakushiji Ryo , Naganuma Kenji , Nishimura Masaharu , Nakagawa Keizo , Sasajima Takao
Published: February 2009

The Flow Noise Simulator (FNS) of the 1st Research Center of TRDI/JDA (Japan Defense Agency) is a large, variable pressure, recirculating water tunnel with very low background noise level. The tunnel is 20m high and 49m long, containing 2000m3 of water. The test section has a square cross section of 2m × 2m with 10m in length. It will accept large size surface ship models of 6m, submarine models of 4m in length and full scale ship appendix models. The FNS is currently under construction and will be accomplished in 2005. It will be used for a wide variety of hydrodynamic and hydroacoustic testing of surface ships and submarines, such as propeller cavitation noise measurements and propeller-hull interaction observation, with sufficiently large scale models. Conceptual design of the FNS was started in 1996 and evaluated by following scale model studies. This paper discusses some technical issues of the FNS.
Development of a Low Noise Pump by New Design Concept
Authors: Miyagawa Kazuyoshi , Sato Ryuichi
Published: February 2009

The Japan Defense Agency is conducting a project to develop a cavitation tunnel, called the FNS (Flow Noise Simulator project) (1). The FNS was designed as a large cavitation tunnel with low background noise level to measure the noise of an object. In order to satisfy the low noise level for the FNS, it is important to develop a low noise pump. In the present study, several new design concepts were developed using CFD (Computational Fluid Dynamics) and these concepts and the pump performance were verified by model test. In developing low noise pump, it is important to avoid cavitation generation in all operating conditions. It is also important to reduce blade-passing influence due to blade row interaction between impeller and diffuser. To control unsteadiness by interaction, the axial gap between two blade rows was widened and viscous wake from the impeller was decreased. Many extensive parametric studies (e.g. blade sweep, number of blades) were conducted using three-dimensional CFD computations. The impeller developed for the FNS pump has seven blades, 4.3 m diameter and the stator downstream has nine blades. Several model tests were carried out to verify the design concept of the pump. It was confirmed that the noise level of the new design pump was decreased compared to a conventional industrial pump and efficiency was also improved.
Development of a Near Real-Time Instrument for Nuclei Measurement: The ABS Acoustic Bubble Spectrometer®
Authors: Chahine Georges L. , Kalumuck Kenneth M.
Published: February 2009

The ABS Acoustic Bubble Spectrometer® (ABS) is an acoustics based device that measures bubble size distributions and void fractions in liquids using the properties of acoustic wave propagation through a two-phase medium. The ABS is PC-based and uses software that controls signal generation, detection and signal processing through data boards and two hydrophones. The data is processed and analyzed utilizing inverse problem solution algorithms to obtain the bubble size distribution. All physical, experimental, and analytical parameters are input by the user via a series of dialog boxes. The results are displayed graphically by the interface in real time and can also be stored or printed. In this paper we describe the method and present validation experiments that compare bubble distributions and void fraction results of ABS measurements with optical measurements in the laboratory. The two methods give very close results with the ABS possessing the significant advantage of enabling near real-time measurements with the potential to become an on-line measuring device.
Numerical Simulation of Leading Edge Cavitation
Authors: Ait Bouziad Youcef , Guennoun Faic¸al , Farhat Mohamed , Avellan Franc¸ois
Published: February 2009

In the present paper, we compare two different computation methods for the simulation of leading edge cavitation. In the first one, known as interface tracking method, the cavity interface is taken as a free surface boundary and the calculation is performed in a single phase flow. The cavity shape is then determined apart from the flow calculation using an iterative procedure. The second method is based on the socalled interface-capturing law state model, assuming a constant enthalpy during the vaporization and condensation processes. Both methods are tested in the case of an isolated Naca 0009, 2-D hydrofoil. Both models gave good prediction of the cavity length and pressure distribution. Moreover, results obtained with the Interface-tracking one predict well the pressure distribution near the cavity detachment. Either methods do not allow a good prediction of the drag coefficient nor the drop of the lift due to cavitation. We have also performed an insight experimental investigation of the onset and detachment of a leading edge cavitation. We have demonstrated how the water may withstand negative pressure upstream to the cavity while the pressure measured in the cavity is almost equal to the vapor pressure. Furthermore, flow visualization clearly shows that a well developed leading edge cavitation turns into bubble cavitation in a continuous way when specific flow parameters are gradually changed and we suppose that the cavity aspect depends highly of the vapor generation rate at its detachment location. The negative pressure measured upstream to the cavity detachment may thus be explained by the dynamic delay of vaporization due to inertia. Owing to those results, we have summarize the actual cavitation modelisation need and made a perspective of future research.
Tip Vortex Cavitation Inception Scaling for High Reynolds Number Application
Authors: Shen Young T. , Jessup Stuart , Gowing Scott
Published: February 2009

Tip vortices that are generated by marine lifting surfaces such as propeller blades, ship rudders, hydrofoil wings, and anti-roll fins can lead to cavitation. Prediction of the onset of this cavitation depends on model tests at Reynolds numbers much lower than those for the corresponding full-scale flows. The effect of Reynolds number variations on the scaling of tip vortex cavitation inception is investigated using a theoretical flow similarity approach. The ratio of the circulations in the full-scale and model-scale trailing vortices is obtained by assuming that the spanwise section lift coefficient distributions are the same between model and full-scale. The vortex pressure distributions and core sizes are derived using the Rankine vortex model and McCormick’s assumption about the dependence of the vortex core size on the boundary layer thickness at the tip region. Using a logarithmic law to describe the velocity profile in the boundary layer over a large range of Reynolds number, the boundary layer thickness becomes dependent on the Reynolds number to a varying power. In deriving the cavitation inception scaling in the traditional scaling format of σif / σim = (Ref/Rem)n, the values of n are not constant and depend on the values of Ref and Rem themselves. This contrasts traditional scaling for which n is treated as a fixed value that is independent of Reynolds numbers. At very high Reynolds numbers, the present theory predicts the value of n to approach zero, consistent with the trend of these flows to become inviscid. Comparison of the present theory with available experimental data shows promising results, especially with recent results from high Reynolds number tests. Numerical examples are given of the values of n for different model to full-scale sizes and Reynolds numbers.
Specification of Acceptable Blade Porosity for Cavitation Performance of Marine Propellers
Authors: Stinebring David R. , Straka William A. , Hall W. R.
Published: February 2009

The issues of cavitation inception for porosity for cast propeller blades are addressed. Desinent cavitation measurements were made in the ARL Penn State 48-inch diameter water tunnel for a series of holes machined into inserts mounted in the tunnel test section. The data were compared to previous measurements with slots and isolated roughnesses. A design exercise is presented for a generic propeller blade to specify “acceptable” blade porosity for a given cavitation inception goal. The application to the blade accounts for the spanwise velocity distribution, local blade surface pressure distribution, local boundary layer thickness, and porosity size. The final result is a mapping of ranges in acceptable porosity for locations on the blade.
Experimental Investigations Concerning Influences on Cavitation Inception at an Axial Test Pump
Authors: Bachert Bernd , Brunn Bernhard , Stoffel Bernd
Published: February 2009

The aim of this work is to demonstrate the significant influence of liquid property on cavitation inception. The experimental results were obtained on two different test rigs, one with an axial test pump (nS = 180 min−1 in European Units or 9000 min−1 in US Units) and another one with a single hydrofoil configuration. To realize a variation of the gas content (nuclei content and distribution of nuclei) of the test water a special device, a so-called “micro bubble generator”, was developed and installed in the test rigs. The measuring of the tensile strength of the test water was also one point of the investigations of this work.
Tip-Vortex Induced Cavitation on a Ducted Propulsor
Authors: Chesnakas Christopher J. , Jessup Stuart D.
Published: February 2009

An extensive experimental investigation was carried out to examine tip-vortex induced cavitation on a ducted propulsor. The flowfield about a 3-bladed, ducted rotor operating in uniform inflow was measured in detail with three-dimensional LDV; cavitation inception was measured; and a correlated hydrophone/high-speed video system was used to identify and characterize the early, sub-visual cavitation events. Two geometrically-similar, ducted rotors were tested over a Reynolds number range from 1.4×106 to 9×106 in order to determine how the tip-vortex cavitation scales with Reynolds number. Analysis of the data shows that exponent for scaling tip-vortex cavitation with Reynolds number is smaller than for open rotors. It is shown that the parameters which are commonly accepted to control tip-vortex cavitation, vortex circulation and vortex core size, do not directly control cavitation inception on this ducted rotor. Rather it appears that cavitation is initiated by the stretching and deformation of secondary vortical structures resulting from the merger of the leakage and tip vortices.
Cavitation in Ice-Milling With a Podded Propulsor
Authors: Atlar Mehmet , Prasetyawan Ika , Aryawan Wasis Dwi , Wang Dazheng , Sasaki Noriyuki
Published: February 2009

Some experimental evidence of cavitation and effect of other parameters, which influence the performance of an ice-class podded propulsor in blockage and milling condition, are presented for the first time. Conducting ice-milling tests in cavitation tunnels is extremely rare due to complexity of the tests as well as the neglected effect of cavitation. The paper describes the details of a novel test set up and preliminary results to demonstrate the importance of the cavitation and presents a proposal how to consider this effect in the design of an ice-class propeller.
Can Shapes With Negative Pressure Gradients Prevent Cavitation?
Authors: Nesteruk Ihor
Published: February 2009

Axisymmetric and plane shapes with negative pressure gradients at a surface are calculated. It is shown that the length of the pressure increase zone may be very short. The axisymmetric bodies tested in a wind tunnel with a small obstacle placed on the surface provide unseparated flow patterns. The discussed shapes may probably be used for the prevention of cavitation.
Turbulence Modeling: A Brief Overview of Charles G. Speziale’s Contributions
Authors: Bushnell Dennis M. , Thangam Siva
Published: February 2009

Charles Speziale was, throughout his career, associated almost exclusively with the academic community. His affiliations included Princeton, Stevens, Georgia Tech, ICASE, CTR, and Boston University. His collaborators during his career constitute a sizable portion of the “Movers and Shakers” in the Turbulence Modeling and Turbulence Computation Arenas. However and perhaps atypically for the era of the late 70’s to early 90’s he was interested in and focused on the exigencies/requirements arising from “Practical Applications”. The Research areas to which he contributed throughout his career are exceedingly broad in scope — allowing him to bring to the Turbulence Modeling problem a rich/continually-enriched background in continuum mechanics. These areas included non-Newtonian fluid dynamics, kinetic theory of gases, vortex dynamics and non-linear transition flow dynamics. This intellectual experience base enabled him to make serious and lasting contributions to the turbulence modeling areas of streamline curvature, rotational influences, renormalization group theory, large eddy simulation, dissipation rate equation development, wall region modeling, direct numerical simulation, compressibility influence, second order closure and a plethora of canonical criteria for modeling, calibration and validation.
Scaling Properties in Rotating Homogeneous Turbulence
Authors: Yeung P. K. , Xu Jia , Sreenivasan K. R.
Published: February 2009

The effects of uniform solid-body rotation on the scaling properties of turbulent flow (considered in a rotating frame) are studied by direct numerical simulation at two rotation rates, with a focus on the statistics of the velocity field including velocity gradients, enstrophy and energy dissipation rate. Especially at the high rotation rate, there is substantial evidence for anisotropy at the small scales, for reduced likelihood of extreme events in both enstrophy and dissipation (whose statistics become some-what alike), and for the failure of classical Kolmogorov scaling in this flow.
Development and Application of an Anisotropic Two-Equation Model for Flows With Swirl and Curvature
Authors: Wang Xiaohua , Thangam Siva
Published: February 2009

An anisotropic two-equation Reynolds-stress model is developed by modeling the energy spectrum and through invariance based scaling. In this approach the effect of rotation is used to modify the energy spectrum, while the influence of swirl is modeled based on scaling laws. The resulting generalized model is validated for benchmark turbulent flows with swirl and curvature.
Stokes’ Mechanism of Drag Reduction
Authors: Bandyopadhyay Promode R.
Published: February 2009

The mechanism of drag reduction due to spanwise wall oscillation in a turbulent boundary layer is considered. Published measurements and simulation data are analyzed in light of Stokes’ second problem. A kinematic vorticity reorientation hypothesis of drag reduction is first developed. It is shown that spanwise oscillation seeds the near-wall region with oblique and skewed Stokes vorticity waves. They are attached to the wall and gradually align to the freestream direction away from it. The resulting Stokes’ layer has an attenuated nature compared to its laminar counterpart. The attenuation factor increases in the buffer and viscous sublayer as the wall is approached. The mean velocity profile at the condition of maximum drag reduction is similar to that due to polymer. The final mean state of maximum drag reduction due to turbulence suppression appears to be universal in nature. Finally, it is shown that the proposed kinematic drag reduction hypothesis describes the measurements significantly better than what current Direct Numerical Simulation does.
An Explicit Algebraic Model for Turbulent Buoyant Flows
Authors: So R. M. C. , Jin L. H. , Gatski T. B.
Published: February 2009

This paper presents a derivation of an explicit algebraic stress model (EASM) and an explicit algebraic heat flux model (EAHFM) for buoyant shear flows. The models are derived using a projection methodology. The derived EASM has a four-term representation and is applicable to 2-D and 3-D flows. It is an extension of the three-term EASM for incompressible flow and the fourth term is added to account for the effect of buoyancy. The projection methodology is further extended to treat the heat flux transport equation in the derivation of an EAHFM. Again, the weak equilibrium assumption is invoked for the scaled heat flux equation. The basis vector used to represent the scaled heat flux vector is formed with the mean temperature gradient vector and 3×3 tensors, not necessarily symmetric or traceless, deduced from the shear and rotation rate tensors and the stress anisotropy tensor. An explicit algebraic model for buoyant shear flows is then formed with the derived EASM and EAHFM. From the derived EAHFM, an expression for the thermal diffusivity tensor in buoyant shear flows can be deduced. Thus, a turbulent Prandtl number for each of the three heat flux directions can be determined. These Prandtl numbers are functions of the gradient Richardson number. Alternatively, a scalar turbulent Prandtl number can be derived; its value is compared with the directional turbulent Prandtl numbers. The EASM and EAHFM are specialized to calculate 2-D homogeneous buoyant shear flows and the results are compared with direct numerical simulation (DNS) data and other model predictions. Good agreement with DNS data and other model predictions is obtained.
Proposal of a RANS Model to Predict Both K- and D-Type Roughness
Authors: Yamamoto Makoto
Published: February 2009

The effect of surface roughness on the aerodynamic performance of a blade and an airfoil is one of very important issues in aeronautic and mechanical engineering. Since existing turbulence models were developed for uniformly distributed roughness, the availability would be limited under a certain flow and roughness conditions. Considering a blade surface with ice accretion, foreign object damage and erosion, the roughness is not uniformly distributed, but isolated or local. Therefore, in such a multi-physics simulation, it is needed to develop a more universal turbulence model to predict the flow fields around a blade with various types of surface roughness. In the present study, employing the virtual force that represents the effect of each roughness element on the mean flow field, I develop and verify a new k–ε turbulence model that can be successfully applied to both k- and d-type roughness.
Applicability of the Dynamic Two-Parameter Clark Model to the LES of Incompressible Turbulent Channel Flows
Authors: Shimomura Yutaka , Kobayashi Hiromichi
Published: February 2009

It is analytically shown that the dynamic two-parameter Clark model (DTCM) overcomes the inapplicability of the dynamic one-parameter Clark model to the large eddy simulation (LES) of incompressible turbulent channel flows by diminishing the negative effective viscosity in the viscous sublayer for the tensor diffusivity term that models the sum of the Leonard and the cross terms. The actual LES shows that the prediction of DTCM for the turbulent channel flows at Reτ = 590 is similar to that of the dynamic Smagorinsky model.
Subgrid Scale Modeling of Turbulence for the Dynamic Procedure Using FDM and Its Assessment on the Thermally Stratified Turbulent Channel Flow
Authors: Tsubokura Makoto
Published: February 2009

The objective of this study is to develop the SGS stress and heat-flux models that are suitable for the dynamic procedure using FDM. The models are derived with taking the consistency of the numerical error in the procedure under consideration [1]. They are assessed a priori using the DNS data of the stably stratified turbulent channel flow. It was found that for the SGS heat-flux modeling, effect of the GS velocity gradient plays an important role for the estimation of especially the streamwise heat-flux. Therefore for the SGS heat-flux model, isotropic eddy diffusivity together with the effect of the GS velocity was finally proposed. The proposed models were also found to be insensitive to the discretized test filtering operation.
Turbulence Structures of Flow Over a Two-Dimensional Hill-Shaped Model
Authors: Tamura Tetsuro , Cao Shuyang , Shindou Takako
Published: February 2009

This study brings into focus the turbulent boundary layer flow over a two-dimensional hill with sinusoidally curved slope, which has both of convex and concave surfaces. In the regions over these two types of surfaces, it is well known that turbulence is deformed and much influenced due to velocity acceleration and deceleration. DNS has been applied to simulate the development, deformation and downstream recovery of the turbulent boundary layer flow. The momentum thickness Reynolds number of is equal to 973. Detailed information regarding streamwise changes of turbulence intensity, turbulent shear stress and kinetic energy, etc. are provided in data base manner. We hope to shed some lights on turbulence modeling for complex flows with the DNS data base of turbulence structures over the hill model.
On the Role of Correlation Between Instantaneous Velocity and Pressure-Gradient in Large-Scale Turbulence
Authors: Obi Shinnosuke
Published: February 2009

Turbulent transport of Reynolds stress by triple moment of fluctuating velocity and pressure-velocity correlation are evaluated from a DNS for wake of a rectangular cylinder located in a uniform flow. The turbulent diffusion transport of turbulent kinetic energy hardly correlates with its gradient vector, indicating that the generally accepted gradient diffusion model is inadequate. It is inferred that the separate modeling of the individual Reynolds stress component provides a better possibility for modeling the turbulent transport in this flow, because of the strong departure from the equilibrium state of turbulence. The possibility of the direct modeling of the pressure gradient-velocity correlation is discussed.
Current Status and Future Needs in Turbulence Modeling: An Aeronautical Perspective
Authors: Bushnell Dennis M. , Thangam Siva
Published: February 2009

An overview of current issues in turbulence modeling is presented along with a brief description of the current and future needs of NASA, especially from the point of advancing the state-of-the-art in aircraft design and air transportation.
Dynamic Behavior of Stand-Alone Parallel Operation System Using Two Wind Turbine-Generators
Authors: Wakui Tetsuya , Hashizume Takumi , Nagao Toshio , Saito Hisao
Published: February 2009

This paper discusses the dynamic behavior of the stand-alone parallel operation system using two wind turbine-generators by our dynamic simulation model. The stand-alone parallel operation system is composed of two Darrieus-Savonius hybrid turbines, two load induction generators, one inverter, batteries, and one controller. This system is mainly operated at the maximum power coefficient points of two parallel turbines by the inverter frequency control for a simple system composition and high power extraction. The computed results of the dynamic behavior of the system to various wind speed changes shows that our control scheme of the parallel operation system is effective.
Computation of Aerodynamic Performance Deterioration of Wind Turbine Blade Due to Ice Accretion
Authors: Nushi Kousuke , Kasai Shingo , Toda Kazuyuki , Yamamoto Makoto , Iida Makoto , Arakawa Chuichi
Published: February 2009

The attention for a wind power-generator has been attracted as one of the solutions for the environmental problems. When a wind turbine is operated in winter, supercooled water droplets impinge on the blade surface, and as the result ice accretes around the leading edge. It is well known that the occurrence of ice accretion on the wind turbine blade can lead to the severe deterioration of aerodynamic performance. However, the experiment is difficult, because it is not easy to create repeatedly the accretion conditions in a laboratory. Therefore, CFD is expected as a useful tool to predict and investigate the phenomena. In the present study, we develop the ice accretion code, and apply it to the MEL wind turbine blade. From the computational results, the shape of the ice-accreted blade and the deterioration of aerodynamic performance are numerically investigated.
Blade Three-Dimensional Dynamic Stall Response to Wind Turbine Operating Condition
Authors: Schreck S. , Robinson M.
Published: February 2009

To further reduce the cost of wind energy, future turbine designs will continue to migrate toward lighter and more flexible structures. Thus, the accuracy and reliability of aerodynamic load prediction has become a primary consideration in turbine design codes. Dynamically stalled flows routinely generated during yawed operation are powerful and potentially destructive, as well as complex and difficult to model. As a prerequisite to aerodynamics model improvements, wind turbine dynamic stall must be characterized in detail and thoroughly understood. In the current study, turbine blade surface pressure data and local inflow data acquired by the NREL Unsteady Aerodynamics Experiment during the NASA Ames wind tunnel experiment were analyzed. The dynamically stalled, vortex dominated flow field responded in systematic fashion to variations in wind speed, turbine yaw angle, and radial location, forming the basis for more thorough comprehension of wind turbine dynamic stall and improved modeling.
Analysis of Unsteady Flow Around Airfoil of a HAWT by Vortex Method
Authors: Imamura Hiroshi , Takezaki Daisuke , Kawai Masahiro , Hasegawa Yutaka , Kikuyama Koji
Published: February 2009

Vortex methods have features such as relatively simple algorithm, no grid-generation in flow field and lagrangian scheme which traces each vortex element concentrated in a tiny region. It is considered that the vortex methods are effective tools for the analysis of three-dimensional, incompressible and unsteady outer flow such as flow around wind turbines. Recently, vortex methods are employed as engineering tools for three-dimensional unsteady flow. In a flow simulation by vortex methods, accuracy of simulation depends chiefly on the vortex creation model on the wall and the viscous diffusion effects. However, it seems that the deterministic model to introduce the vortex element created on the wall into flow field has not yet been accomplished. In this paper, an introduction model of vortex elements from the wall into flow field is proposed. This model is based on the analogy of the consideration of boundary-layer. In this model, intensity of vortex elements created on the wall is determined by applying both no-through and no-slip boundary conditions and the diffusion height of each element created on the wall is determined dynamically. To investigate the applicability of the model, proposed method is applied to flow around impulsively started airfoil section.
Detailed Flow Analysis Around Blade Tip With a Mie Vane in Case of Different Blade Aspect Ratios and Different Reynolds Numbers
Authors: Shimizu Yukimaru , Ismaili Edmond , Kamada Yasunari , Maeda Takao
Published: February 2009

The results of an extensive experimental research work related to the performance of a HAWT with a tip-mounted Mie type vane are presented in this paper. From performance experiments carried out on four sets of blades with varying aspect ratios and for different Reynolds number, it was found that the application of a tip-mounted Mie vane resulted in a larger increase in maximum power coefficient for rotors with smaller aspect ratio and for lower Reynolds number. To investigate further the phenomenon and to explain the relationships found between power increase due to a Mie vane and blade aspect ratios and Reynolds number, detailed flow visualization around blade tip and the Mie vane were performed. It was found that the tendency of the power increase due to a Mie vane was dependent on the size of a corner vortex between blade tip and the downstream extension of the Mie vane.
Aeroacoustics Simulation Around a Wind Turbine Blade Using Compressible LES and Linearized Euler Equations
Authors: Fleig Oliver , Arakawa Chuichi
Published: February 2009

There is a strong need to investigate aerodynamic noise caused by large and fast rotating wind turbines, especially trailing edge and tip noise. This work constitutes the first part of a project which aims to simulate the broadband tip noise emitted when the wind turbine is in operation. Several aeroacoustics methods are analyzed and their suitability for a typical wind turbine blade is assessed. A stationary wind turbine blade in an incident flow with a large region of separated flow is studied. The surface pressure fluctuations are calculated using compressible Large-Eddy simulation (LES). The aerodynamic noise perceived in the far-field is predicted by simulating the propagation of the pressure perturbations using LES and Linearized Euler equations (LEE) in the near field and Kirchhoff’s integral method in the far-field. It was found that for the present wind turbine blade with a large region of separated flow and thus relatively large fluctuations, LES with a fine enough mesh and a third-order upwind scheme is able to compute the propagation of acoustic waves as accurately as LEE with higher order schemes and separate treatment of acoustic perturbations. The method described in this paper will be used in the future to analyze a full wind turbine blade with the aim of optimizing the tip shape for reduced noise emission.
A Stochastic Representation of Particle Behavior in Gas-Liquid Horizontal Annular Flow
Authors: Mito Yoichi , Hanratty Thomas J.
Published: February 2009

A stochastic method which uses a modified Langevin equation to represent the velocities of the fluid seen by a particle in a turbulent field is explored. Calculations of the dispersion of particles from a source on a wall agree with calculations at Reτ = 150 which use a DNS to represent the fluid velocity field. The paper demonstrates how wall source calculations can be used to analyze problems involving atomization and deposition, which are of interest in horizontal gas-liquid annular flows.
Experimental Study on the Effect of Surface Tension on Void Fraction and Frictional Pressure Drop of an Air-Liquid Two-Phase Flow in a Horizontal Flat Narrow Rectangular Channel
Authors: Ide Hideo , Fukano Tohru
Published: February 2009

Air-liquid two-phase flow in a horizontal flat capillary rectangular channel has been studied to clarify the effects of surface tension on the flow phenomena, such as flow patterns, holdup and frictional pressure drop and so on. The concentrations of surfactant solution were 0, 10, 50 and 100 ppm and the surface tension of each solution was reduced to about 34mN/m from that of pure water of about 72mN/m. The dimension of the channel used was 10.0 mm×1.0 mm. The drag reduction by mixing the surfactant was examined in both the single phase flow and the two-phase flow. The experimental data of void fraction and two-phase frictional pressure drop were compared with the respective correlations which were previously proposed by the other researchers. Finally, we proposed new correlations of two-phase frictional pressure drop in which the effect of surface tension and the aspect ratio of cross section of channel were taken into account.