bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards a Numerical Study of Two-Phase Flow Exhaust Plume Jet
Authors: Devals C. , Estivalezes J.-L. , Jourdan G. , Houas L.
Published: March 2009

The aim of the present work is to determine experimental drag coefficients for spherical particles accelerated in shock-tube. Then, validations of two phase flow calculations dealing with solid propulsion rocket in supersonic flight are undertaken. First, experiments in the multi-phase vertical-horizontal shock-tube have been set up at IUSTI in Marseille. The drag coefficient is determinated for particle Reynolds numbers less than 50000 and for particle Mach numbers less than 1.14 and is compared with those found in literature. Second, calculation of two phase flow in solid rocket plume has been performed. The particles are tracked with a stochastic one-way coupling lagrangian method.
Wear in Bends Conveying Air-Solid Mixture
Authors: Chand Prem , Saha Ahindra Chandra
Published: March 2009

This paper aims at establishing a generalized method for predicting wear due to solid-gas flow through a duct. It has been opined that not only does the duct wear out, the particles carried through the duct themselves degrade in the process. The correct evaluation of the fluid-particle, particle-duct and fluid-duct interactions forms the basis of the theoretical equation proposed for the purpose. The method proposed is verified by conducting experiments on a well-designed set-up. The test rig helped to evaluate the essential parameters responsible for the wear such as the material, duct and fluid interaction parameters. As a test case, a 90° bend placed in a vertical plane carrying material from bottom to top has been considered.
Control of the Airflow Close to a Flat Plate With Electrohydrodynamic Actuators
Authors: D’Adamo Juan , Artana Guillermo , Moreau Eric , Touchard Gerard
Published: March 2009

This work analyses the ability of an electrohydrodynamic actuator to modify the characteristics of a flow over a flat plate. The device considered uses flush mounted electrodes and a d.c. power supply to create a plasma sheet on the surface of the plate. We analyze the effect of this plasma sheet on the flow in the region close to the leading edge of the plate. From Particle Image Velocimetry and at incident flow velocities in the range 11.6–18.6 m/s, we estimate the force per unit surface exerted by the discharge. We conclude that it can induce an important acceleration of the flow close to the surface with a relative good efficiency when compared with other actuators.
Experimental Study of Aerodynamic Behavior Downstream of Three Flow Conditioners
Authors: Laribi Boualem , Wauters Pierre , Aichouni Mohamed
Published: March 2009

The present work is concerned a comparative study of the decay of swirling turbulent pipe flow downstream of three flow conditioners, the Etoile, the Tube bundle, and the Laws perforate plate, and its effect on accuracy of orifice plate flow meter. The swirl was generated by a double 90° degrees elbows in perpendicular planes. The discharge coefficients were measured with 3 different orifice meters with β = 0.5, 0.62, 0.70 at different Reynolds number. As a conclusion, the experimental study of the three flow conditioners used separately shows that the flow need longer distance for close to fully developed pipe flow and some errors, by reason of the swirl, on the discharge coefficient were inevitable for distance less 12D.
Investigation of the Rotating Stall in a Centrifugal Compressor
Authors: Horodko Longin , Kryllowicz Wladyslaw
Published: March 2009

Instability of the compressor operation is manifested in two forms: by mild or deep surge. Both of them should be avoided as they lead to reduced performance or serious damage to the machine and its driving system. One of the pre-surge symptoms is rotating stall that appears mainly in the impeller and transfers to other parts of the compressor. This phenomenon can be described as a rotating pressure wave arising and decaying intermittently. Such an irregularly changing object needs an analyzing tool that allows for a spectrum fluctuation study. The authors used the signal time-frequency representation with progressive wavelets to analyze the static pressure signals acquired during a few deep surge cycles. The rotating stall was identified with the cross-correlation of the continuous wavelet transform. The same method allowed for calculation of the time lag between oscillatory pressure signals coming from the diffuser and the inlet of the compressor, which estimates the reverse flow velocity.
Multiscale Calculations Using an Adaptive Wavelet Algorithm
Authors: Rastigejev Yevgenii A. , Paolucci Samuel
Published: March 2009

We present a new wavelet-based adaptive multiresolution representation (WAMR) algorithm for the numerical solution of multiscale evolution problems. Key features of the algorithm are fast procedures for grid rearrangement, computation of derivatives, as well as the ability to minimize the degrees of freedom for a prescribed solution accuracy. To demonstrate the efficiency and accuracy of the algorithm, we use it to solve the two-dimensional benchmark problem of incompressible fluid-flow in a lid-driven cavity at large Reynolds numbers. The numerical experiments demonstrate the great ability of the algorithm to adapt to different scales at different locations and at different times so as to produce accurate solutions at low computational cost. Specifically, we show that solutions of comparable accuracy as the benchmarks are obtained with more than an order of magnitude reduction in degrees of freedom.
Numerical Simulation and Experimental Study of Heat and Mass Transfer Phenomena in Vacuum-Sealed Casting Process
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A.
Published: March 2009

The V-Process is one of the most exciting metal casting techniques developed recently, and it has many advantages compared to conventional casting methods. In this paper the results of the CFD modeling of mold filling process are presented. A vacuum-sealed step pattern has been used as a molding. Direct numerical simulations were conducted using a commercial CFD code (FLOW-3D software, Flow Simulations, Inc.) for the conventional gravity mold filling technique. Flow velocity, pressure and fluid fraction distributions are obtained for this casting method. The results of the numerical simulations are compared to those obtained experimentally.
Lateral Migration of Single Bubbles Due to the Presence of Wall
Authors: Hosokawa Shigeo , Tomiyama Akio , Misaki Shinji , Hamada Tomoyuki
Published: March 2009

Lateral migration of a single bubble rising in the vicinity of a vertical flat plate was measured to evaluate a wall force acting on the bubble. Experimental results indicated that a wall force coefficient CW3 is a function of the bubble Reynolds number Re and the Eo¨tvo¨s number Eo. Empirical correlations of CW3 were deduced for bubbles and particles. It was confirmed that the wall force model proposed by one of the authors and the proposed correlations of CW3 are applicable not only to high viscousity systems but also for low viscousity systems, provided that a bubble does not collide with the wall.
Simulation of Interface Deformation in Shear Flow Using Binary Fluid Lattice Boltzmann Model
Authors: Takada Naoki , Tomiyama Akio , Hosokawa Shigeo
Published: March 2009

In this paper, we describes the simulations of two- and three-dimensional interfacial motions in shear flow based on the lattice Boltzmann method (LBM), in which a macroscopic fluid flow results from averaging collision and translation of mesoscopic particles and an interface can be reproduced in a self-organizing way by repulsive interaction between particles. A new scheme in the binary fluid model is proposed to simulate motions of immiscible two phases with different mass densities, and examined in numerical analysis of bubble motions under gravity in a circular tube and deformation of bubble under shear stress. For higher Reynolds numbers, a finite difference-based lattice Boltzmann scheme is applied to the kinetic equations of particle to improve numerical stability, which can capture break-up motions of bubble. Parallel computing in LBM is also discussed briefly for efficient speeding up.
Particle Method for Incompressible Flow With Free Surface
Authors: Koshizuka S. , Oka Y.
Published: March 2009

Moving Particle Semi-implicit (MPS) method is a particle method which has been developed to analyze incompressible flows with free surfaces. Fluids are represented by particles which move in fully Lagrangian description. Since grids are not necessary, complex motion of free surfaces can be calculated without grid tangling or numerical diffusion. In the MPS method, a differential equation system is transformed to particle dynamics using the models representing differential operators. Incompressibility is solved by the Poisson equation of pressure to keep the particle number density constant. Solid mechanics is also modeled by particles and fluid-structure interaction can be solved. Calculation examples are provided in this paper: collapse of a water column, melt droplet fragmentation, sloshing with tank deformation, nucleate boiling and droplet breakup. These examples show that the MPS method is a powerful tool to investigate complex behaviors of free surfaces and multiphase flows.
Computing Separated Flows in MEMS Devices
Authors: Baysal Oktay , Aslan Alim Rustem
Published: March 2009

Fluid flows in micro devices span the entire Knudsen (Kn) number regime. Depending on the Kn range, a full continuum or a full free-molecular analysis may be applicable. In the present study, flows in the Kn range of 10−3 to 10−1 are considered and they are modeled using a conventional Navier-Stokes solver. Its boundary conditions, however, have been modified to account for the slip velocity and the temperature jump conditions encountered in these micro-sized geometries. The computations have been performed for straight micro channels, a micro backward facing step, and a micro filter. The present results are then compared with analytical formulae and other computations available in the literature. The results indicate that the rarefaction and compressibility effects present in these micro devices have been accurately predicted. In the case of slip flow, the separation is found to occur at a higher Reynolds number compared to the corresponding no-slip flow case. As the next step of the study, micro synthetic jets will be computed and the optimal cavity actuator geometries will be sought for desired flow deflections.
Study of 3D Mixing Processes by Numerical and Experimental Approaches
Authors: Zhao Y. , Brodkey R. S. , Nakamura S.
Published: March 2009

Mixing vessels are widely used for blending and chemical reactions. Although much has been done on mixing processes, the complex, three-dimensional flow phenomena are still not well understood. The purpose of our first step in this research is the simulation and validation of time-resolved, three-dimensional velocity vector data. Such results are an essential part of the design of mixing systems, but are generally not available to the engineers. The computational work involves direct numerical simulation (DNS) and large eddy simulation (LES) of the Navier-Stokes equations. Later, modeling of the Reynolds averaged Navier-Stokes (RANS) equations will be undertaken as a simplified approach. Simulations and modeling are being validated by experiments. Two flow mixing systems are under investigation. First and most important for validation is an opposed jet flow system that offers some unique characteristics that can be used for validation of DNS/LES simulations. It also has applications in the injection molding of plastics. Second, simulations of impeller driven mixing vessels that are more commonly used in processing are under development. Here the moving mesh system adds complexity. In addition, visualization of both numerical and experimental results, 3-D particle tracking velocimetry (PTV) techniques have been developed. The proposed paper will address the problems in the modeling of chemical mixing and discuss the results of simulation and validation.
Physics of Tip Clearance Flow in Turbomachinery (Keynote Paper)
Authors: Inoue Masahiro , Furukawa Masato
Published: March 2009

In a recent advanced aerodynamic design of turbomachinery, the physical interpretation of three-dimensional flow field obtained by a numerical simulation is important for iterative modifications of the blade or impeller geometry. This paper describes an approach to the physical interpretation of the tip clearance flow in turbomachinery. First, typical flow phenomena of the tip clearance flow are outlined for axial and radial compressors, pumps and turbines to help comprehensive understanding of the tip clearance flow. Then, a vortex-core identification method which enables to extract the vortical structure from the complicated flow field is introduced, since elucidation of the vortical structure is essential to the physical interpretation of the tip clearance flow. By use of the vortex-core identification, some interesting phenomena of the tip clearance flows are interpreted, especially focussing on axial flow compressors.
Numerical Prediction of the Aerodynamic Tonal Noise in a Centrifugal Fan
Authors: Velarde-Sua´rez Sandra , Ballesteros-Tajadura Rafael , Santolaria-Morros Carlos , Ferna´ndez-Francos Joaqui´n
Published: March 2009

In this work, a numerical study about the aerodynamic tonal noise generation in an industrial centrifugal fan with backward curved blades has been carried out. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been performed. Special attention has been focused on the impeller-volute interaction phenomena, analysing the influence of the distance between the impeller and the volute tongue. The numerical results have been contrasted using previous experimental investigations carried out in the same machine.
Numerical Investigation of the Influence of the Particle/Pipe Diameter Ratio in a Non-Isothermal Gas-Solid Flow
Authors: Chagras V. , Moissette S. , Boulet P. , Oesterle B.
Published: March 2009

Heat transfer in a gas-solid suspension flowing upwards in a heated pipe has been addressed numerically using an Eulerian-Lagrangian approach. Following the basic idea of available experimental studies, several configurations have been simulated and compared, varying the relative size of the particles, i.e. the ratio dp/D. Numerical results show that this ratio has a significant influence upon the fluid and particle velocities and temperatures. However, the resulting suspension Nusselt number is found to be only weakly modified by the parameter dp/D at moderate loading ratio m. This is in accordance with available measurements (e.g. Farbar and Depew, 1963) which do not show a clear dependence of the Nusselt number upon dp/D in the range 0 < m < 3. Associating the influence of this relative size parameter with effects related to inter-phase exchange area, other dimensionless parameters like the flow and particle Reynolds numbers, some Froude number, as well as the heat capacity ratio, density- and loading ratios, would of course be required in order to achieve full similarity of the suspension flow.
Full Lagrangian Approach to the Calculation of Dilute Dispersed Phase Flows: Advantages and Applications
Authors: Tsirkunov Yury M. , Volkov Aleksei N. , Tarasova Natalia V.
Published: March 2009

An efficient numerical method developed recently in Russia for calculations of dilute particle phase flow fields in two-phase gas-particle flows is presented in this paper. The method is based on the full Lagrangian approach (FLA) to the description of the regular motion of the particle phase. The collisionless “gas” of particles is treated as a continuum for which all basic equations, namely, the continuity equation, the momentum equation and the energy equation are written in the Lagrangian coordinates. The traditional Lagrangian approach (LA) widely used in the West does not deal with the explicit form of the continuity equation for the particle phase, and this is the key difference between FLA and LA. The FLA-method has some advantages over the traditional Lagrangian technique. Examples of numerical calculations of two-phase flows with a complex particle phase flow structure illustrate this method.
The Effect of Electrostatic Forces on the Distribution of Drops in a Channel
Authors: Ferna´ndez Arturo , Lu Jiacai , Esmaeeli Asghar , Tryggvason Gre´tar
Published: March 2009

Direct numerical simulations are used to examine the effect of electric fields on the behavior of suspension of drops in dielectric fluids. The effect of electric field is modeled using the “leaky dielectric” model, coupled with the full Navier-Stokes equations. The governing equations are solved using a front-tracking/finite volume technique. The interaction of the drops is strongly dependant on the conductivity and the permittivity ratio, but fibration, where drops line up into long columns, takes place over a wide range of these parameters. The hydrodynamic interaction due to fluid circulation induced by the electric field has a strong influence on the drop distribution and the rate of fibration.
Wall Heat Flux Under Persistent Vortices
Authors: Breidenthal R. E.
Published: March 2009

It is commonly perceived that turbulent flows yield turbulent wall fluxes, while laminar flows yield correspondingly laminar wall fluxes. Experiments support a recent theory that turbulent flows can yield laminar wall fluxes if the flow is “persistent.” Adding strong, stationary vortices to a turbulent boundary layer lowers the wall heat flux to a laminar value.
Compressor Volute Design System: Part II — New Volute Design System Approach
Authors: Phuong Guy , Abanteriba Sylvester , Haley Paul
Published: March 2009

Volutes are widely used in industrial process, refrigeration system, small gas turbines and gas pipeline centrifugal compressors as the transition from the impeller-diffuser to the pipings, because of their simple structure, ease of production and wide operating range. This paper illustrates a new design tool that incorporates a new volute design system that integrates and automates geometry generation, grid generation and aerodynamic analysis. In optimizing the available technology in terms of grid generation, CFD, and computer graphics, the program will utilize existing technology used by industry to generate a powerful volute design tool. The design tool is programmed in a way that integrates the features and methods a designer would use for volute design. This is fundamentally by means of geometrical constraints and/or functional relationships. Grids can be generated in minutes accommodating geometrical changes thus reducing the bottlenecks associated with geometry/grid generation for CFD applications. Prior to most CFD analysis work, a structured grid must be produced ensuring high quality such that convergence is assured and the time to convergence of the solution is minimized. However, there are usually only a few people that have the required skills to produce the geometry and generate a high quality structured grid. In essence, the tool provides a sidestep around both the geometry generation and the grid generation process. It automates the process such that anybody can produce a high quality grid from the geometry and move straight to the CFD component of the work and hence can incorporate CFD as part of the design process. The volute design tool will enable the user to generate a family of volutes and display 2D volute cross sections and 3D solid models of the scroll, diffuser inlet, discharge conic, and connecting channel. Separate interfaces will be written to accommodate the different operating systems. The geometry generation will be written in windows however, a separate interface will be written to produce the grid being compatible in NT, Unix, and Linux platforms.
Improvements in the Power Output of a Horizontal Axis Wind Turbine Due to the Introduction of a Curved Blade
Authors: Clarke Erin K. , Abanteriba Sylvester
Published: March 2009

This paper examines the impact on the power generation capacity of a wind turbine as a result of the modification of the shape of the blades of an existing wind turbine. The modification involves curving the blades in the direction of rotation resulting in an increase in generated lift and therefore an increase in the power output of the wind turbine. Two three-bladed models were tested in a wind tunnel, one original straight-bladed model and one modified model both of which were 0.84 m in diameter. A study of the methods of flow visualization for a wind turbine in a wind tunnel was investigated. The corresponding results are presented. It was discovered that the china clay method of flow visualization in conjunction with a strobe light gave a good indication of the direction of the airflow over the turbine blades as did condensed oil droplets from a smoke wand which presented a very clear indication of the span-wise flow. It was concluded from the investigation that curving the blade into the direction of rotation on a wind turbine produced a greater power output at the same wind speed as an unmodified wind turbine.
Large Eddy Simulations of a Hydrocyclone
Authors: de Souza Francisco Jose´ , Silveira Neto Aristeu
Published: March 2009

Subgrid-scale modeling, which characterizes Large Eddy Simulation (LES), has been used to predict the behavior of a water-fed hydrocyclone operating without an air core. The governing equations were solved by a fractional step method on a staggered grid. The Smagorinsky subgrid-scale model was employed to account for turbulent effects. Numerical results actually capture the main features of the flow pattern and agree reasonably well with experiments, suggesting that LES represents an interesting alternative to classical turbulence models when applied to the numerical solution of fluid flows within hydrocyclones.
Erosion in Swirl-Inducing Pipes
Authors: Wood R. J. K. , Jones T. F. , Ganeshalingam J.
Published: March 2009

Swirl inducing pipes are proposed for the alleviation of problems of poor particle distribution and sliding wear, particularly at downstream bends and elbows. In a well-designed conventional pipeline, the mean axial velocity to assure good dispersion of particles is much greater than the velocity required to merely transport the slurry. This gives the impetus to design swirl-inducing pipes which allow for reduced pumping power, and reduced erosion, while efficiently maintaining suspension at strategic points. This paper covers research that has been aimed at producing good distribution of particles at relatively low velocities, by applying swirl induction. Computational models for the impact velocity and impact angle in a bend have been successfully applied to the flow field and validated by experiments in a perspex flow loop including electrical resistance tomography (ERT) to confirm the placement of particle burdens. Particle impact parameters from this work have been used as inputs to erosion models to predict wall wastage rates in bends and the location of damage from well distributed and swirling particulate flows.
Lifetime of a Control Valve Plug Related With Cavitation Erosion at Differential Pressure of 20 MPA
Authors: Yuzawa Satoshi , Hashizume Takumi , Okutsu Ryoji , Outa Eisuke
Published: March 2009

A contoured plug of stainless steel #316 inserted in a low CV valve has been subjected to erosion tests at a pressure reduction of 20MPa. The test duration on a single plug has extended over 300 hours until the shut-off function becomes incomplete. The fundamental flow pattern inside the valve is almost unchanged at the inlet pressure up to 20MPa in a sense that the pressure reduction has been almost completed at the throat formed by the seat-ring and the characteristic surface of the plug head. The kinetic energy of the flow at the throat describes the energy that is dissipated in the valve. Simulated pressure distribution and cavitation pictures obtained at a low inlet pressure condition indicate that the plug seat-joint-taper is the part that suffers impact of the high kinetic energy flow and collapse of the cavitation bubbles. Then this part is specified as the part of the most heavy erosion. In the erosion test, the process of the erosion development shifts from a phase of pit formation to a phase of rooting out the inside at a stage that the mass loss has reached a certain critical level. In the initial phase, the time averaged loss rate is proportional to a power of the dissipated flow energy. In the second stage of rapid growth, the cumulative mass loss increases with fourth power of the working duration. By using values of the exponent and factor obtained at the full opening test, that provides the shortest test periods, mass loss at an arbitrary condition of CV-value and cavitation number is estimated. Then, a procedure to estimate the valve lifetime is suggested based on a criterion that the seat-leakage flow must not exceed the controllable minimum flow of the valve.
A Computational Fluid Dynamics Comparison of Wells Turbine Blades in 2D and 3D Cascade Flow
Authors: Daly John , Frawley Patrick , Thakker Ajit
Published: March 2009

This paper deals with the application of Computational Fluid Dynamics (CFD) to the analysis of the aerodynamic characteristics of symmetrical airfoil blades in 2-Dimensional cascade flow. Theoretical two dimensional cascade analyses of Wells Turbines blade profiles have been used in the past to predict the performance of three-dimensional turbines. The use of two-dimensional cascade models is beneficial as it allows the analysis and optimisation of the blade profile with approximately one tenth the computational requirements of a three-dimensional model. The primary objective of this work was to provide further validation of the use of two dimensional cascade models by comparing the computational predictions with traditional theoretical calculation results and also with three-dimensional turbine results. A secondary objective was to use the two dimensional cascade models to better understand the blade interaction effects that occur in the Wells Turbine. The model was used to analyse and compare three different blade profiles at different cascade settings. This paper presents the results of the numerical investigation, the validation of the results and the subsequent analysis.
Gas Distribution in Air/Water and Air/Oil Bubble-Column Flows
Authors: Shollenberger K. A. , Torczynski J. R. , George D. L.
Published: March 2009

The effect of liquid properties on axial development of gas-volume-fraction profiles in bubble-column flows is investigated. Experiments are conducted in a cylindrical vessel with an inner diameter of 0.48 m and a height of 3 m. The liquids examined include water and two lightweight mineral oils. A cross sparger with 96 holes is used to inject air into the column with all the holes facing either upwards or downwards. The superficial gas velocity ranges from 5 to 30 cm/s, and the absolute column pressure ranges from 0.1 to 0.5 MPa. Gamma-densitometry tomography (GDT) is used to measure radial distributions of gas volume fraction at eight axial locations. The development length of the gas-volume-fraction profile is shown to increase with gas velocity and column pressure for all three liquids. The development of the cross-sectionally averaged gas-volume fraction for the air/water flow is remarkably different from that for the air/oil flows.
Unsteady Energy and Entropy Transfer in Suspensions: A Few Suggestions for an Improved Modelling
Authors: Lhuillier Daniel
Published: March 2009

The thermo-mechanical description of two-phase mixtures, as it is presented in Ishii’s text-book for example, is quite general but not particularly suited for mixtures in which one phase is dispersed into the second one : in fact, the introduction of two stress tensors and two heat fluxes (related to the velocity gradients and temperature gradients of the respective phases) is in conflict with the hydrodynamic description of suspensions in which there is a single stress tensor and a single heat flux, related to the gradients of the volume-weighted average velocity and of the volume-weighted average temperature respectively. The problem of a two-phase description suitable for suspensions of particles was initiated among others by Buyevich, Nigmatulin and Prosperetti who focused mainly on the two momentum equations but did not consider in so much detail the two energy equations. In this forum on multiphase flows we will suggest the way these energy (and entropy) equations are to be written. We will start from a “mean-field” type of approach, in which the energy exchange between a particle and the surrounding fluid is related in part to the mean energy exchanges and to the mean energy dissipation that occur in the medium surrounding the particle. In fact we extend to energy the reasoning applied to momentum when one says that a large part of the force exerted by the fluid on a particle is due to the mean stress that exists around that particle, leading to the concept of a generalized Archimede’s force. That mean-field approach results in evolution equations (for momentum, energy and entropy) that are common to all types of particles but which can be simplified when the particles are supposed to be rigid or to have a constant volume. Phase transitions between the particles and the fluid will be taken into account, and the role of collisions between particles will be considered briefly. It must be clear at the outset that we are not so much interested in the constitutive relations as in the structure of (and the links between) the various evolution equations. But the proposed description has the merit of requiring a minimum number of constitutive relations for the system of equations to be closed.
How Has the Study of Coherent Structures Contributed to Our Understanding of Turbulent Free Shear Flows? (Keynote Paper)
Authors: George William K. , Johansson Peter B. V. , Gamard Stephan
Published: March 2009

Recent applications of the ‘slice POD’ to the axisymmetric turbulent wake and jet are reviewed, and the results used to provide a critique of commonly held views about these flows. It is argued that the so-called ‘coherent structures’ are simply artifacts of the source conditions, and have little to do with the far down-stream development of these flows. Also, experimental evidence is presented for the possible presence of Townsend’s large eddies, eddies whose primary role is to warp the mean motion. Finally, classical linear stability analysis which ‘predicted’ that only azimuthal mode-1 could be unstable for these flows is shown to be deficient, with the result that at very least modes-0, 1 and 2 could be important, consistent with the experiments.
Towards Practical Flow Sensing and Control via POD and LSE Based Low-Dimensional Tools (Keynote Paper)
Authors: Taylor Jeffrey , Glauser M. N.
Published: March 2009

We present the application of Proper Orthogonal Decomposition (POD) and Linear Stochastic Estimation (LSE) based low-dimensional methods to the flow over a backward facing ramp with an adjustable flap above the ramp which allows for dynamic variation of the adverse pressure gradient. There is a range of flap angles where the flow is incipiently separated so that this relatively simple experiment can be used to flush out ideas for active feedback separation control strategies. The study utilized a combination of PIV and multi-point wall pressure measurements to estimate the full velocity field (mean plus fluctuating) from a modified complementary technique. Specifically we want to identify a low-dimensional mean flow to observe when the profiles are inflectionary, i.e., the incipient condition, just from wall pressure. We demonstrate via this method, that a reasonable estimate of the low dimensional full velocity field can be obtained. This is important for practical active feedback flow control strategies since from wall pressure we can estimate the state of the flow without resorting to probes in the flow.
A Comparison of the Numerical Simulation and Experimental Investigation of the Flow Around a High Speed Train
Authors: Paradot N. , Talotte C. , Garem H. , Delville J. , Bonnet J.-P.
Published: March 2009

Numerical simulations of the turbulent flow surrounding a high speed train are carried out at SNCF (French Railways) using the commercial code Star CD. The numerical methodology developed consists in building the complete detailed topology of a train with basic blocks. The validation of the method is done through a comparison with wind tunnel experiments. A globally good agreement is found concerning the drag estimation of a short trainset. Predictions of mean streamwise velocity and turbulent kinetic energy show the quite satisfactory capabilities of the methodology.
Structure of Flows in Viscoplastic Fluids Mixing
Authors: Savreux Fre´de´ric , Jay Pascal , Magnin Albert , Piau Jean-Michel
Published: March 2009

The laminar isothermal mixing of a viscoplastic fluid is considered in the absence of any free surface and when the material can be modelled using a Bingham constitutive equation. The material is mixed by a rotating cylindrical tank and a fixed anchor impeller. A two-dimensional numerical simulation is performed with a finite elements method. The effects of viscoplasticity and inertia are related to an Oldroyd (Od) and to a Reynolds (Re) number. Stream lines, vortices, yield surfaces and power consumption are shown and analysed depending on the value of Od and Re parameters.
An Example Evaluation of IGCC Performance Test Code ASME PTC47
Authors: Anand Ashok K. , Parmar Jeff , Breton David L. , Le Patrick
Published: March 2009

Integrated Gasification Combined Cycle (IGCC) utilizing solid and unconventional liquid fuels has now reached commercial stage as evidenced by their world wide construction and successful operation. The proposed ASME Performance Test Code 47 (PTC47) provides the users and owners of these new power plants, the guidance and procedures on conducting a performance test and evaluate the deviation from the performance guarantees. This paper reports the use of PTC47 codes in evaluating the test correction factors for the Wabash River IGCC Power Plant.
Engineering Aspects of a Novel High Efficiency Reciprocating Internal Combustion Engine
Authors: Coney Mike W. , Cross Andrew M. , Linnemann Claus , Morgan Robert E. , Wilson Bruce
Published: March 2009

A new type of high efficiency reciprocating internal combustion engine, which is predicted to achieve an electrical efficiency of up to 60% on diesel fuel or 58% on natural gas, is described with particular focus on the engineering of its novel components. The so-called isoengine, which is being developed by Innogy plc, involves quasi-isothermal compression of combustion air. In commercial applications it is envisaged that the engine will run at 600 rpm and produce 7 MW of electric power. The engine will also be capable of producing up to 3 MW of heat in the form of hot water, with the electrical efficiency reduced by two percentage points. The engine is intended for distributed and on-site power generation with the option of switchable co-generation of hot water for industrial use or for space heating. A 3 MWe engineering demonstrator is currently under construction.
Integrated Diagnostic System for the Equipment of Power Plants: Part I — Formulation and Algorithms
Authors: Kubiak J. , Garci´a-Gutie´rrez A. , Urquiza G. , Gonza´lez G.
Published: March 2009

The output capacity of combined cycle power plants is reduced in many cases, and sometimes forced to outages, when its main components are affected by faults, i.e., when the rotating equipment such as turbines, generators, compressors, pumps and fans suffer a failure. Normally, the overall reduction of the efficiency, and sometimes the component efficiencies, is monitored but it is difficult to identify the primary causes of the fault of the specific equipment that causes the reduction of plant efficiency. Therefore, to reduce the time of faulty operation, a precise diagnostic tool is needed. One such tool is an expert system approach, which is presented in this work. It consists of several expert systems for the identification of the faults caused by deterioration of the inner parts of the equipment, Fig. 1. Such faults not only reduce the plant efficiency but in many cases also increase the vibrations of the rotor-bearing system. Based on knowledge, the various expert systems have been constructed and their algorithms (efficiency reduction) developed for the following equipment: steam turbines, gas turbines and compressors, condenser, pumps and water cooling system. An expert system for detecting faults that increase the vibration of the rotor–bearing system is also presented. As far as the turbo compressor expert system is concerned the fault hybrid patterns previously developed were implemented and described elsewhere [1].
Corrosion Fatigue Life Evaluation Method for the Bladed Disk Attachments of Low-Pressure Steam Turbine
Authors: Asai Kunio , Saito Eiji , Namura Kiyoshi , Sakurai Shigeo , Nomura Kenichiro
Published: March 2009

The mechanism of disk cracking was investigated and an evaluation method for its failure occurrence rate was developed. It was found that the disk cracking was caused by the corrosion pit growth, the superposition of the multiple vibration modes, and the increase in the scatter of the natural frequency due to the interface condition change after long-term operation. The effects of several uncertainties on the failure occurrence rate were examined and the values of the uncertainties were obtained by solving the inverse problem according to the failure analysis; the examined uncertainties were the standard deviation of the natural frequency and the stimulus ratio. It is recommended to perform the replica inspection by removing the blades and to take the proper maintenance actions based on the remaining life evaluations because relatively small corrosion pits can cause crack initiation. It was found that a continuous cover blade is superior to the conventional tenon-shroud-type grouped blade because the former reduces resonance points in the interference diagram and eliminates any tangential modes which are main contributors for the disk cracking.
Cost Optimization for Steam Turbine Control Upgrades
Authors: Weiss Gerhard J. , Kopczynski Jerry A.
Published: March 2009

The basic principles of generating electricity from steam have not changed during the last 100 years. Consequently, current steam turbine design is similar to the one introduced to the market by BBC, ALSTOM, ASEA or GE about a century ago. Of course modern blade and valve design dramatically improves heat rate; new materials increase effective longevity of the turbine. Similarly, the basic principles of how to control a turbine are the same as many years ago. However, equipment being used now to operate and control a turbine is quite different than that of the time when the first steam turbine was put into commercial operation. It is common knowledge that the control system is technically aging much faster than the turbine itself. Steam turbines achieve an average service life of 40 years. There are many steam turbines still operating with originally installed control systems. These aging control systems installed 20–30 years ago are becoming unreliable and costly to maintain. For most power plant owners/operators it has become a necessity to modernize their originally installed mechanical/hydraulic control systems. This is particulary important now, due to the very competitive, deregulated power production business. Control system upgrades together with improvement of the steam path components will result in efficient operation of the power plant for an extended number of years for a fraction of the cost necessary to build a new power generation station. Several control upgrade solutions and options are available at substantial cost saving, without compromising safety requirements, flexibility and reliability of the power plant. Step by step modular upgrades, utilizing the majority of pre-existing equipment, using proven standard software modules and inexpensive PLCs (programmable logic controllers), applying 2 out-of-three 3 analog signal acquisitions for 2 out of 3, or 1 out of 2 protection — these are some ways of reducing the cost of plant modernization. This paper will discuss and document particular cases where the cost optimization concept was successfully implemented with positive results in the following areas: • High availability and reliability achieved; • Safety and flexibility of operation improved; • Maintenance cost reduced.
Troubleshooting Turbine Steam Path Damage
Authors: McCloskey Thomas
Published: March 2009

Steam path damage, particularly of rotating and stationary blading, has long been recognized as a leading cause of steam turbine unavailability for large fossil fuel plants worldwide. Turbine problems cost the utility industry as much as one billion dollars per year. Failures of blades, discs, and rotors in both fossil and nuclear steam turbines, represent a serious economic loss of availability and reliability for electric power generation suppliers and other energy supplies worldwide. Turbine problems such as deposition and erosion of blades can result in severe efficiency losses, resulting in significant economic penalties. The primary objective of this paper is to provide a methodology to identify the underlying damage or failure mechanisms, determine the root cause, and choosing immediate and long-term actions to lessen or prevent recurence of the problem.
40 Years of Combined Cycle Power Plants
Authors: Balling Lothar , Termuehlen Heinz , Baumgartner Ray
Published: March 2009

Even though the first installations of combined cycle power plants with heat recovery steam generators (HRSG’s) are only about forty years old, the first attempt to build gas turbines for power generation was made more than 100 years ago. It took however about 40 years before gas turbines were installed to supply peaking power.
Knock Prevention of Gas SI Engine by Adjunction of Inert Gases to the Fuel
Authors: Brecq Guillaume , Bellettre Je´roˆme , Tazerout Mohand , Muller Thomas
Published: March 2009

This work focuses on the prevention from knock in the case of SI engines supplied by natural gas network. The effect of two inert gases (N2 and CO2) adjunction is experimentally studied. The added quantities are between 0% and 25% in volume for N2 and between 0% and 15% for CO2. A significant increase of the Knock Limited Spark Timing (KLST) is measured in all the cases. A twice-higher augmentation is noted when CO2 is added compared to N2 for an equivalent volumetric concentration. The overall augmentation varies between +1 to +6 °CA depending on the operation. Finally, a law for predicting the KLST augmentation implied by the adjunction of inert gases is deduced from all the measurements.
Steam System Design Considerations for Three Pressure Reheat Cycles With Cascade Bypass System
Authors: Greer Brandon , Schnaithmann Kurt , Klatt Stefan
Published: March 2009

This paper discusses various issues that should be considered when designing the steam system for a typical three pressure reheat cycle, which is used at many of today’s combined cycled plants. A cascade bypass arrangement in the steam system is commonly used to ensure steam flow is available to the reheat section of the HRSG during startup. For the purposes of this paper, a cascade bypass system will be defined as high pressure steam being bypassed to the cold reheat steam and hot reheat steam being bypassed to the condenser. This arrangement can lead to conflicts between plant operation needs and the steam turbine desire to reduce the HP turbine backpressure as much as possible during startup. Plant operation needs that may dictate keeping the reheat system pressure high include export steam minimum pressure guarantees to customers, cycling operation which forces the plant to restart when equipment is still hot, and hot reheat steam bypass or condenser limitations. The HP turbine and cold reheat steam piping can have temperature limitations which may necessitate keeping the HP turbine exhaust pressure as low as possible during startup.
NOx Reduction of a 165 MW Wall-Fired Boiler Utilizing Air and Fuel Flow Measurement and Control
Authors: Cherry Marion , Earley Dave , Silzle David
Published: March 2009

As a result of increasingly stringent emissions limitations being imposed on coal-fired power plants today, electric utilities are faced with having to make major compliance related modifications to their existing power plants. While many utilities have elected to implement expensive post-combustion NOx reduction programs on their largest generating units, infurnace NOx reduction offers a less expensive alternative suitable to any size boiler, to reduce NOx while also improving overall combustion. In-furnace NOx reduction strategies have proven that, when used with other less expensive approaches (Overfire air, fuel switching, and/or SNCR), levels less than 0.15 lb./MMBtu can be economically achieved. Furthermore, when implemented in conjunction with an expensive post-combustion SCR program, initial capital requirements and ongoing operating costs can be cut to save utilities millions of dollars. For the purpose of developing a system-wide NOx reduction strategy, Santee Cooper, a southeastern U.S. utility applied pulverized coal flow and individual burner airflow measurement systems to Unit 3 at its Jefferies Station, a 165MW, 16-burner front wall-fired boiler. The airflow measurement system, in service for many years, applied a well-proven averaging Pitot tube technology to measure individual burner secondary airflow. The coal flow measurement system utilized low energy microwaves to accurately measure coal density and coal velocity in individual coal pipes. The combination of these two systems provided the accurate measurements necessary for controlled manipulation of individual burner stoichiometries, giving the plant the ability to improve burner combustion, yielding a reduction in NOx levels approaching 20%. Optimized burner combustion also resulted in a leveling of the excess O2 profile, which will enable the plant to pursue further reductions in excess air as well as staged combustion, thus allowing for further NOx reductions in the future. How this program produced a significant NOx reduction will be presented in detail in this paper. The paper will also discuss the effects on excess O2, opacity, and unburned carbon. In addition, this program will allow for future system-wide planning with regard to possible SCR implementation.
Cofiring Tire-Derived Fuel With Coal
Authors: Harding N. Stanley
Published: March 2009

Tires provide a resource of significant interest to many utilities. Tires—and tire-derived fuel (TDF)—have a high calorific value along with other favorable fuel characteristics. At the same time they present material preparation and handling issues for fuel users. For environmental reasons, they are more difficult and costly to dispose of in landfills. In 1990, only 25 million tires or 11% of the annually generated scrap tires in the U.S. were utilized (recycled, retreaded, and burned for energy). In 1994, this number increased to 138 million tires or 55% of the annually generated scrap tires with the largest increase due to tires used for energy (101 million tires). With an estimated number between 1–3 billion tires in stockpiles throughout the United States, this potential energy source is enormous. This paper will review several commercial demonstrations of tire-derived fuel cofired with coal in industrial and utility furnaces. Included will be discussions on fuel characteristics, preparation and handling of the tire-derived fuel, methods of utilization of the cofired fuel including appropriate combustion systems (e.g., cyclone boilers, stokers, fluidized bed boilers) and environmental results of the cofiring demonstrations.