bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics and Noise Emission of Laser Induced Bubbles in a Vortical Flow Field
Authors: Oweis Ghanem F. , Choi Jaehyug , Ceccio Steven L.
Published: February 2009

The sound produced by the collapse of discreet cavitation bubbles was examined. Laser-generated cavitation bubbles were produced in both a quiescent and a vortical flow. The sound produced by the collapse of the cavitation bubbles was recorded, and its spectral content was determined. It was found that the rise time of the sound pulse produced by the collapse of single, spherical cavitation bubbles in quiescent fluid exceeded that of the slew-rate of the hydrophone, which is consistent with previously published results. It was found that, as the collapsing bubbles were deformed by the vortical flow, the acoustic impulse of the bubbles was reduced. Collapsing non-spherical bubbles often created a sound pulse with a rise time that exceeded that of the hydrophone slew-rate, although the acoustic impulse created by the bubbles was influenced largely by the degree to which the bubbles became non-spherical before collapse. The noise produced by the growth of cavitation bubbles in the vortex core was not measurable. These results have implications for the interpretation of hydrodynamic cavitation noise.
Laboratory Experiments in Fluids and Propulsion Education
Authors: Taghavi Ray
Published: February 2009

The advantages and requirements for propulsion laboratories in engineering schools is discussed. A typical propulsion laboratory set-up suitable for aircraft reciprocating and gas turbine engines is presented. Sample results of engine performance analysis from these laboratories will also be presented.
Energy Loss in Snow-Water Mixture Flow
Authors: Sasaki Mikio , Takeuchi Takahiro , Takahashi Hiroshi
Published: February 2009

Energy losses in the solid-water mixture flow where the density of solid is nearly equal to that of fluid were observed in horizontal pipelines. The observation was carried out to investigate the influence that the specific gravity of the solid particles exerted on the energy loss. A relative friction factor based on the friction factor of the pure water flow becomes larger as the solid concentration increases in the mixture flow of solid particles with the specific gravity 0.86 and 1.04. The relative friction factor is given with the Froude number, the solid concentration and the specific gravity of solid.
An Experimental Study on the Interaction Between Settling Particles and Near-Wall Hairpin Vortices in Turbulent Liquid-Solid Open-Channel Flow
Authors: Fukawa Takumi , Nansaka Kenji , Hagiwara Yoshimichi
Published: February 2009

Simultaneous visualization is carried out for settling fine copper particles and fluorescent tracer particles in turbulent water flow in an open channel. PIV and PTV techniques are applied to the images of the scattered light from the copper particles and those of the fluorescent light of the tracer particles, respectively. In order to mine the hairpin vortices from the images, the motion of tracer particles around the hairpin vortices has been predicted by using the database obtained by direct numerical simulation (DNS) for turbulent channel flow. It is found that the lift-up of hairpin vortices is attenuated by the depositing copper particles. The clusters of copper particles are found to be sustained in convergence-dominant regions of main flow.
Computation of Turbulent Flow Around Blade With Local Surface Roughness
Authors: Chang Yin-han , Toda Kazuyuki , Yamamoto Makoto
Published: February 2009

To improve aerodynamic performance of a blade and to maintain its designed performance, many study have been focused on this point. The factors for aerodynamic performances of a blade are its geometry and operating conditions, which are almost fixed during its lifetime. On the other hand, the factor such as surface roughness generated by impure sand grain or oil droplet is variable one. The surface roughness on the blade affects the flow past it by its aerodynamic nature. The blade design can be improved by revealing this change in aerodynamic performance due to surface roughness. In this study, three-dimensional computations are carried out on the blade root with local surface roughness to investigate how the roughness will change the aerodynamic performance. The locality of the surface roughness distribution is simulated with particle tracks in three-dimensional flow. The model replacing the effect of roughness elements with virtual force is used to simulate turbulent flow around blade with local surface roughness.
The Response of Injection of Vortex Generator Jets to a Backward Facing Step Flow
Authors: Yamagata Koichi , Saito Manabu , Morioka Tadashi , Honami Shinji
Published: February 2009

In this paper, the flow behavior of a reattachment process over a backward facing step flow is reported. The reattachment process is controlled by injection of vortex generator jets. The injection of jets upstream of the step produces the co-rotating longitudinal vortices in a separating shear layer. The experiment of the step response of the injection jet is also conducted in order to investigate the evolution process of the longitudinal vortices. A large scale of primary and counter vortices are observed, when the velocity ratio of the free stream to injected jet is 6. The detailed structure of the longitudinal vortices is clarified. The remarkable effect of the vortices on the separating shear layer downstream of the step is observed.
Flow Field, Turbulent Quantities and Core Stability in Gas-Liquid Two-Phase Swirling Flow: Experiment and Modeling
Authors: Gomez Luis E. , Mohan Ram , Shoham Ovadia
Published: February 2009

Compact cyclonic separators are based on swirling flow field, whereby the phases are separated due to the centrifugal forces generated by the flow. This phenomenon is common in several compact separators used by the oil, process and aerospace industries. The objective of this paper is to study experimentally and to develop a model for the hydrodynamics of dispersed two-phase swirling flow, such as present in the lower part of the Gas-Liquid Cylindrical Cyclone (GLCC) or in the Liquid-Liquid Cylindrical Cyclone (LLCC) compact separators. Large amounts of cyclone local measurements of swirling flow data were acquired using an LDV. These data and other published in the literature were used to develop correlations for the swirling flow field and the associated turbulent quantities, based on the swirling intensity concept. The developed correlations can be used to analyze swirling two-phase flow in pipes and cyclonic separators. Finally, an analysis of the gas core stability in the swirling flow field is presented.
A Mechanistic Model for Predicting Subcooled Boiling Flow
Authors: Yeoh G. H. , Tu J. Y.
Published: February 2009

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapor velocity. Work is in progress to circumvent the deficiency of the extended MUSIG model by the consideration of an algebraic slip model to account for bubble separation.
Decaying, Swirling Flow in a Pipe: Axial Velocity Field Development With Reversed Axial Flow
Authors: McClusky Heather L. , Beasley Donald E.
Published: February 2009

Streamwise development of the axial velocity field in a confined, decaying swirling flow is explored in the present study. A tangential injection mechanism produces swirling flow at the inlet of a constant diameter pipe. Particle image velocimetry is employed for axial velocity measurements. Representative axial velocity profiles are presented for axial locations of 3 to 67 pipe diameters. The axial velocity profiles are asymmetric relative to the pipe centerline and the asymmetries persist as the flow develops in the axial direction. The eccentricity of the swirling flow spatially oscillates as the flow develops in the axial direction. The spatial oscillations of the axial velocity suggest that a vortex breakdown may be located near the inlet of the pipe and the entire pipe is the wake region of the vortex breakdown. The centerline axial velocity is also used to document the axial development of the flow. A comprehensive view of the flow field is provided by considering theoretical explanations presented in the literature for decaying, swirling pipe flows and for vortex breakdown.
Experimental and Numerical Investigation of Turbulent High Reynolds Number Flows in a Square Duct With 90-Degree Streamwise Curvature: Part 1 — Experiment
Authors: Ondore Faustin
Published: February 2009

This study was aimed at obtaining a better understanding of turbulent flows in a square duct with a 90° bend, using both experimental and numerical techniques. Turbulent flows that are subjected to streamwise curvature occur in numerical engineering applications. These flows are known to experience extra rates of strain in the plane of mean shear in comparison to plane flows. Hence the gross parameters, such as the mean flow velocities, turbulence intensities and Reynolds stresses are altered dramatically from the plane flow characteristics. The flows examined are specified by the free-stream entry velocities of 12.3 m/s and 20.4 m/s measured at 1.01 duct height upstream of the bend entry plane. These velocities correspond to Reynolds numbers 3.56 × 105 and 6.43 × 105 respectively. The duct has a cross-section of 0.457 × 0.457 m 2 and the mean radius of curvature to duct height ratio is 1:21. Airflow from a wind tunnel passes through an upstream tangent of 1.31 duct height before entering the bend. The flow then exits the bend into a 7.0 duct height downstream tangent before discharging into the atmosphere. The experimental part involved hot-wire measurements. Flow visualisation was performed by smoke in a region close to the convex wall at the bend exit to confirm the numerical prediction of recirculating flow in that area. The numerical part of the investigation was based on the solution of the governing differential equations for turbulent flows in conjunction with a number of turbulence models. The discretisation of the equations was achieved using a finite-volume technique and different discretisation schemes. The main turbulence model used for the study was the Reynolds Stress Model, but the comparisons of the results were also made with those from the standard κ-ε and the RNG-κ-ε turbulence models. The boundary conditions for these simulations were obtained as part of the experimental investigations. Numerical calculations with the Reynolds stress models show a separated flow near the convex wall starting at the bend exit, which was confirmed by experiment using flow visualisation by smoke. The Reynolds stress models are observed to be superior in comparison with the standard κ-ε and the RNG-κ-ε turbulence models in terms of accuracy. Further conclusions from this work can be summarised as: 1. The proper numerical resolution of this type of flow is dependent on the turbulence model formulations as well as numerical procedures. The results highlight the limitations of the generality of turbulence models when used to model more intricate features of complex flows. 2. The need for more accurate experimental techniques in support of improvement of turbulence models is thus underlined.
Evolution of a Non-Invasive Sensor for Fluid Density and Solids Concentration Measurement Using Ultrasound
Authors: Bamberger Judith A. , Greenwood Margaret S.
Published: February 2009

This paper describes the evolution of an ultrasonic sensor to non-invasively measure slurry density and solids concentration. Three generations of probe are discussed: 1) density sensor, 2) densimeter, and 3) fluid and solids monitor. The initial application was to measure slurry density during radioactive waste transport. The probe uses ultrasonic signal reflection at the fluid-pipe wall interface to quantify density in situ in real time and signal attenuation to evaluate solid concentration. In the latest configuration, the transducers are mounted on the wall of the pipe spool piece. This instrument was selected for monitoring radioactive waste transport based on several characteristic features: the sensing surface is non-intrusive and does not disrupt the slurry flow, instrument performance is not affected by slight amounts of entrained air that could be present during waste retrieval and transfer; nor is it affected by electromagnetic noise from nearby pumps and other equipment; and the instrument is compact. The densimeter has been deployed at Hanford tank SY-101 in the prefabricated pump pit process manifold to monitor slurry properties during radioactive waste transfers. To qualify densimeter performance prior to manifold installation in the radioactive pipeline, the probe was installed in the process manifold and performance was evaluated during tests using non-radioactive waste simulants over the density range from 1000 to 1500 kg/m3. The probe predicted density within ± 2%. The sensor is installed in a nominal 5-cm-diameter (2-in.) pipe spool piece; the design pressure is 2.8 MPa (400 psi). To ensure operability during prolonged contact with radioactive waste, the probe wedge in contact with the slurry was selected to operate up to pH 14, and the probe components were radiation tested at exposures of 1×106 R.
Qualification of a Method to Calculate the Irrecoverable Pressure Loss in High Reynolds Number Piping Systems
Authors: Sigg K. C. , Coffield R. D.
Published: February 2009

High Reynolds number test data has recently been reported for both single and multiple piping elbow design configurations at earlier ASME Fluid Engineering Division Conferences. The data of these studies ranged up to a Reynolds number of 42 × 106 which is significantly greater than that used to establish design correlations before the data was available. Many of the accepted design correlations, based on the lower Reynolds number data, date back as much as fifty years. The new data shows that these earlier correlations are extremely conservative for high Reynolds number applications. Based on the recent high Reynolds number information a new recommended method has been developed for calculating irrecoverable pressure losses in piping systems for design considerations such as establishing pump sizing requirements. This paper describes the recommended design approach and additional testing that has been performed as part of the qualification of the method. This qualification testing determined the irrecoverable pressure loss of a piping configuration that would typify a limiting piping section in a complicated piping network, i.e., multiple, tightly coupled, out-of-plane elbows in series under high Reynolds number flow conditions. The overall pressure loss measurements were then compared to predictions, which used the new methodology to assure that conservative estimates for the pressure loss (of the type used for pump sizing) were obtained. The recommended design methodology, the qualification testing and the comparison between the predictions and the test data are presented. A major conclusion of this study is that the recommended method for calculating irrecoverable pressure loss in piping systems is conservative yet significantly lower than predicted by early design correlations that were based on the extrapolation of low Reynolds number test data.
Unstable Regions in Impulsively Started Pipe Entrance Flows Subjected to Infinitesimal Axisymmetric Disturbances
Authors: Moss E. A. , Abbot A. H.
Published: February 2009

This investigation presents computed base flow and stability data (axisymmetric disturbances) for impulsively started pipe entrance flows, and shows that at any given time, the displacement thickness (or any other flow variable) variation with axial distance is given by a varying portion which is accurately described by a steady, spatially developing flow, followed by a constant portion, described by the impulsively started parallel system. At the transition between these two systems is a small portion which is described by neither model. Arising from the inference that the latter region is sufficiently small to be neglected, variations in time and space of unstable regions in impulsively started pipe entrance flows were established, showing that (i) such flows are are unconditionally stable to infinitesimal axisymmetric disturbances for a Reynolds number of less than 23 350; (ii) for 38 770 > Re > 23 350, possible instability is confined to a maximum of 3.7% of the entire steady pipe entrance region; and (iii) for Re > 38 770, unstable regions may occur for finite time durations, over the entire length of the pipe.
LES Analysis of Turbulence Effects on Unsteady Flows Past a Circular Cylinder
Authors: Tamura Tetsuro , Ono Yoshiyuki , Hashida Kohji
Published: February 2009

Recent advancement of LES (Large Eddy Simulation) technique for turbulent wake has made it possible to numerically investigate the turbulence effects on aerodynamic characteristics of a bluff body. Here we carry out LES of wake flows past a circular cylinder in the subcritical Reynolds number regime. For inflow boundary condition, homogeneous turbulence generated statistically is given time-sequentially. We bring into focus the interaction between the oncoming turbulence and the shear layer separated from a circular cylinder. Shear layer instability easily occurs under such a stimulation and details of its behavior are visualized. Turbulence effects on unsteady flows in the cylinder wake are discussed. The resulting aerodynamic characteristics and their physical mechanism are clarified.
Discontinuous Galerkin Methods for Compressible DNS
Authors: Collis S. Scott , Ghayour Kaveh
Published: February 2009

A discontinuous Galerkin (DG) method is formulated, implemented, and tested for simulation of compressible turbulent flows. The method is applied to a range of test problems including steady and unsteady flow over a circular cylinder, inviscid flow over an inclined ellipse, and fully developed turbulent flow in a planar channel. In all cases, local hp-refinement is utilized to obtain high quality solutions with fewer degrees of freedom than traditional numerical methods. The formulation and validation cases presented here lay the foundation for future applications of DG for simulation of compressible turbulent flows in complex geometries.
A High Order Theory for an Isothermal Rarefied Gas Flow in Micro Channels
Authors: Stevanovic Nevena D.
Published: February 2009

Gas flows take place in a number of micro-electro-mechanical systems (MEMS). Since the dimensions of the MEMS are within μm range, it is necessary to take into account the gas rarefaction effects in investigations of these flows. This paper presents the solution and analysis of isothermal compressible gas flow through micro channels with slow varying cross section under low Mach number conditions. The problem is solved by the introduction of the small parameter ε that presents the square of the Mach and Reynolds numbers ratio. Small parameter ε is used in a regular perturbation analysis of the problem. The exact dependence among Mach, Reynolds and Knudsen number is utilized, which leads to accurate prediction of the influence of the inertia forces and the slip boundary conditions.
Two Fluid Modeling of Microbubble Turbulent Drag Reduction
Authors: Kunz Robert F. , Deutsch Steven , Lindau Jules W.
Published: February 2009

An unstructured 3D multiphase CFD method has been adapted and applied for the modeling of high Reynolds number external flows with microbubble drag reduction (MDR). An ensemble averaged multi-field two-fluid baseline differential model is employed. Interfacial dynamics models are incorporated to account for drag, lift, virtual mass and dispersion. Wall kinematic constraints, porous-wall shear apportionment, coalescence, breakup and attendant turbulence attenuation are also accounted for. The results of several high Reynolds number applications are presented, including quasi-1D analysis of an equilibrium bubbly boundary layer, 2D analysis of flat plate flow across a range of gas injection flow rates, and 3D analysis of a notional high lift hydrofoil with MDR. For the flat plate analyses, quantitative comparisons are made with available experimental skin friction measurements, and qualitative comparisons are made with available volume fraction profile measurements. Though some accuracy shortcomings remain, the generally good agreement observed serves to validate the appropriateness of two-fluid modeling in these flows, while elucidating areas where modeling improvements can be made. It is observed that the extraction of turbulent kinetic energy from the liquid phase by the action of bubble breakup can be a significant source of skin friction reduction. Also, the role of mixture density in the boundary layer on wall shear stress is discussed in the context of the homogenous mixture and two-fluid simulations presented.
Reynolds Stress Modeling for Drag Reducing Viscoelastic Flows
Authors: Leighton Richard , Walker David T. , Stephens Todd , Garwood Gordon
Published: February 2009

A Reynolds-stress transport equation model for turbulent drag-reducing viscoelastic flows, such as that which occurs for dilute polymer solutions, is presented. The approach relies on an extended set of Reynolds-Averaged Navier-Stokes equations which incorporate additional polymer stresses. The polymer stresses are specified in terms of the mean polymer conformation tensor using the FENE-P dumbbell model. The mean conformation tensor equation is solved in a coupled manner along with the Navier-Stokes equations. The presence of the polymer stresses in the equations of motion results in additional explicit polymer terms in the Reynolds-stress transport equations, as well as implicit polymer effects in the pressure-strain redistribution term. Models for both the explicit and implicit effects have been developed and implemented in a code suitable for boundary layer, rectangular channel and pipe-flow geometries. Calibration and validation is has been carried out using results from recent direct numerical simulation of viscoelastic turbulent flow.
Recent Progress in the Studies of Gas-Liquid Two-Phase Flows at Microgravity Conditions
Authors: Takamasa Tomoji , Hibiki Takashi
Published: February 2009

In a thermal system of spacecraft, two-phase flow system now is an excellent alternative to the conventional single-phase system in transporting large amount of thermal energy at a uniform temperature regardless of variations in the heat loads. In addition, two-phase flows exist in a wide range of applications and enabling technologies in space. This report outlines recent progress in the studies of gas-liquid two-phase flows at microgravity conditions, especially for which regarding to interfacial area transport and drift flux.
Conservative CIP Method and Application to Splashing Phenomena
Authors: Yabe Takashi
Published: February 2009

We present a review of the CIP method [1–3] that is known as a general numerical solver for solid, liquid, gas and plasmas. This method is a kind of semi-Lagrangian scheme and has been extended to treat incompressible flow in the framework of compressible fluid. Since it uses primitive Euler representation, it is suitable for multi-phase analysis. The recent version of this method guarantees the exact mass conservation [4] even in the framework of semi-Lagrangian scheme. Comprehensive review is given for the strategy of the CIP method that has a compact support and subcell resolution including front capturing algorithm with functional transformation, pressure-based algorithm. In this paper, particular attention is placed on splashing phenomena in which water surface breaks up and disintegrated into many pieces.
Water Hammer Analysis/Prevention/Mitigation in Fire Protection Systems at Power Plants
Authors: Arastu Asif H. , Tom Eugene
Published: February 2009

Fire Protection water systems are typically piping networks where water is pumped from a low elevation reservoir at atmospheric pressure to higher elevations in the buildings served by the system. Because of this nature of their design, they are prone to water hammers due to water column separation & rejoining. A loss of pressure can lead to void formation at high elevations whose collapse can result in severe water hammer. A damaging water hammer event that occurred at a nuclear power plant (Arastu, et al, 1999) causing a catastrophic valve failure pointed to the need to prevent and mitigate such potential events at other plants. One important aspect of that event is that prior to it, several events of similar magnitude had occurred that did not apparently cause physical damage but degraded the system sufficiently to make it susceptible to damage. This paper discusses the causes of water hammer in Fire Protection Systems at power plants and identifies analysis, prevention, and mitigation strategies. Using a Method Of Characteristics based program, computer simulation results of the application of the mitigative measures are given for three large plant systems to demonstrate the effectiveness of the measures proposed at these plants.
Centrifugal Compressor Volute Design Software
Authors: Phuong Guy , Abanteriba Sylvester , Haley Paul , Guillerot Philippe
Published: February 2009

Volutes are widely used in centrifugal compressors for industrial processes, refrigeration systems, small gas turbines and gas pipelines. However, large costs associated with the volute design and analysis process can be reduced with the introduction of a software design system that ties together both geometry creation and mesh generation having the ultimate intent of improving stage efficiency. Computational Fluid Dynamics (CFD) has become an integral part of engineering design. High quality grids need to be produced as part of the analysis process. Engineers of different expertise may be required to determine volute design constraints and parameters, produce the geometry, and generate a high quality grid. The current research aims to develop and demonstrate a volute design tool that allows design engineers the ability to easily and efficiently generate volute geometry and automate grid generation by means of geometrical constraints using functional relationships. The approach was outlined in [1]. Visualization of volute geometry can be in two-dimensional (2D) or three-dimensional (3D) modes. Control of the diffuser upstream of the scroll, the scroll itself and the conic are totally integrated in the design system. The user can position the conic anywhere in space and control the shape of the conic centroid curve, therefore having complete control over the development of the tongue region. The program will output data for automated grid generation where user can control resulting grid properties. Once the desired design configuration has been determined, the users can output the geometry surfaces and wireframes to a Computer Aided Design (CAD) package for production. Every little detail is also incorporated into the software from volute draft angle, discharge conic centroid shape, to cross section fillet radii. Upon entering all the required constraints and parameters of the volute, the geometry is created in seconds. Grids can be generated in minutes accommodating geometrical changes thus reducing the bottlenecks associated with geometry/grid generation for CFD applications.
Minor Losses Due to Flow Through a Rounded Sudden Expansion
Authors: Smith Barton L.
Published: February 2009

Experiments on steady flow through a nominally 2-D exit geometry with rounded edges are presented. The minor loss coefficient, K, can be greater than unity for sudden expansions with non-uniform velocity profiles. Pressure recovery due to deceleration of the exiting flow before it detaches results in conversion of kinetic energy to flow energy and a reduced the value of K. It is shown that K is a function of the dimensionless edge radius and the Reynolds number. Substantial pressure recovery is reported at large Re for r/h < 1.
High-Resolution Schemes for Dense Gas-Particle Two-Phase Flow Computation
Authors: Zhang Sijun , Zhao Xiang
Published: February 2009

This work concerns the effects of differencing schemes on the simulation of dense gas-particle two-phase flows. The first-order upwind difference, the central difference, the second-order upwind difference, the central difference plus artificial dissipation, the deferred correction, the quadratic upstream interpolation (for convective kinematics) and the monotone upstream-centered schemes for conservation laws with different forms of flux limiters were all accomplished to simulate the multi-phase flows. It was found that differencing schemes might significantly affect the solution accuracy and numerical convergence. The monotone upstream-centered schemes for conservation laws are the best choice of all, because they can effectively suppress the nonphysical oscillations with the introduction of adaptive numerical dissipation into numerical solutions.
Simulation Flows Over Hemisphere at the Bed of an Open Channel by DNS and Immersed Boundary Method
Authors: Dinh T. X.
Published: February 2009

The immediate aim of this study is to check the accuracy of Kajishima’s method (one kind of immersed boundary method) for the direct numerical simulation (DNS) of turbulent channel flow over a complicated bed. In this paper, the simulation of three dimensional, time -dependent turbulent flows over a fixed hemisphere at the bed of an open channel is carried out. A finite different method (FDM) is applied with a staggered Cartesian mesh. The forces, the moments about the center of the hemisphere, and the distribution of pressure on the hemisphere in the plane of symmetry are calculated.
Empirical Modeling of Unsteady Flows
Authors: Haupt Sue Ellen
Published: February 2009

In this work we demonstrate the utility of stochastic empirical models. Linear stochastic models have been successful at reproducing responses to forcing of large-scale atmospheric flow. However, the linear forms of the models reach their limit on highly nonlinear problems. It is shown here that for simple low dimensional problems, a quadratically nonlinear empirical model is successful at reproducing a chaotic attractor. In addition, empirical models can be used to diagnose the important dynamics of a flow system and identify the essential terms to include in a forward dynamical model. Once the empirical model has been built, it can then be used to diagnose the underlying dynamics.
Complex Rheology in Particle-Laden Composite Materials
Authors: Rao Rekha R. , Adolf Douglas B. , Mondy Lisa A.
Published: February 2009

The rheology of curing composite materials is important to many manufacturing processes. At Sandia, we work with particle-filled epoxy systems for a variety of applications. One particular system, designated as “459,” exhibits complex, counter-intuitive rheological dependence on temperature, flow history and particle-concentration. Despite the particles being relatively large (10 μm), 459 exhibits shear-thinning hysteretic behavior reminiscent of colloidal systems. It is hypothesized that the thixotropy arises from reaction of the 459 curative with the surface of the particulates. Under certain conditions, the addition of filler offsets the effect of epoxy polymerization on the viscosity, resulting in a viscosity that is constant with time. For this reason, we have developed an experimental model system that can be used to separate the effects of particle aggregation from the effects of cure on the viscosity. We have done experiments with this model suspension to determine its time-dependent response in step shear. In addition, we are working on a computational model that can be used to predict the behavior of the aggregating suspension. Preliminary modeling efforts focus on using a generalized Newtonian constitutive equation that relates the viscosity to the local aggregate concentration, defined by a dimensionless structure factor, to capture the time-dependence. Results from this constitutive equation are presented and compared to the experimental data from step-shear experiments in a Couette viscometer. Modeling results are also presented for a transient fiber spinning problem where the free surface evolves as the viscosity develops over time.
Swirling Flow of Viscoelastic Fluid in a Cylindrical Casing
Authors: Itoh Motoyuki , Suzuki Masahiro , Moroi Takahiro
Published: February 2009

The swirling flow of viscoelastic fluid in a cylindrical casing is investigated experimentally, using aqueous solutions of 0.05–1.0 wt% polyacrylamide as the working fluid. The velocity measurements are made using laser Doppler anemometer. The aspect ratios H/R (H: axial length of cylindrical casing, R: radius of rotating disc) investigated are 2.0, 1.0 and 0.3. The Reynolds numbers Re0 based on the zero shear viscosity and the disc tip velocity are between 0.36 and 50. The velocity measurements are mainly conducted for the circumferential velocity component. The experimental velocity data are compared with the velocity profiles obtained by numerical simulations using Giesekus model and power-law model. It is revealed that at any aspect ratios tested the dimensionless circumferential velocity component Vθ’ decreases with increasing Weissenberg number We. The Giesekus model could predict this retardation of circumferential velocity fairly well at small We, but the power-law model could not. The extent of the inverse flow region where the fluid rotates in the direction opposite to the rotating disc is clarified in detail.
Operating Experience of Ansaldo V94.2 K Gas Turbine Fed by Steelworks Gas
Authors: Bonzani Federico , Pollarolo Giacomo , Rocca Franco
Published: February 2009

ANSALDO ENERGIA S.p.A. has been commissioned by ELETTRA GLT S.p.A, a company located in Trieste, Italy for the realisation of a combined cycle plant where all the main components (gas turbine, steam turbine, generator and heat recovery steam generator) are provided by ANSALDO ENERGIA. The total power output of the plant is 180 MW. The gas turbine is a V94.2 K model gas turbine dual fuel (natural gas and steelworks process gas), where the fuel used as main fuel is composed by a mixture of natural gas, blast furnace gas and coke oven gas in variable proportions according to the different working conditions of the steel work plant. The main features adopted to burn such a kind of variability of fuels are reported below: • fuel as by product of steel making factory gas (coke oven gas “COG”, blast furnace gas “BFG”) with natural gas integration; • modified compressor from standard V94.2, since no air extraction is foreseen; • dual fuel burner realised based on Siemens design. This paper describes the operating experience achieved on the gas turbine, focusing on the main critical aspect to be overcome and on to the test results during the commissioning and the early operating phase. The successful performances carried out have been showing a high flexibility in burning with stable combustion a very different fuel compositions with low emissions measured all operating conditions.
Fault Diagnostics Using Genetic Algorithm for Advanced Cycle Gas Turbine
Authors: Sampath Suresh , Gulati Ankush , Singh Riti
Published: February 2009

This paper describes a new approach to the development of a fault diagnostics and prognostic capability for an advanced cycle gas turbine. It is based on techniques using sensor based and model based information. Sensor based information is the actual information obtained from the real engine and the model based information comes from the data obtained from engine performance model simulation with a permutation of implanted faults taking into account sensor noise and bias. The approach adopted here is to minimize an objective function which represents the difference between the actual and simulated data and the minimized objective function allows us identify the nature of fault. After the initial success with simple cycle engines, it was decided to extend this technique to advanced cycle engines. The technique is being tested on an in-house model of an intercooled recuperated engine with variable geometry similar to the ICR-WR21cycle. A detailed analysis of the technique applied to simple cycle and advanced cycle will be presented.
Interpretation of Weighted-Least-Squares Gas Path Analysis Results
Authors: Doel David L.
Published: February 2009

Gas turbine performance analysis programs convert raw measurements (thrust, fuel flow, gas path temperatures and pressures) into engine and component figures of merit (e.g., specific fuel consumption, component efficiencies). The derived parameters allow a diagnostician to recognize a poorly performing engine and help to identify the root cause for the problem. These goals can be foiled by measurement problems or by analysis assumptions embedded in the programs. A gifted analyst learns to recognize measurement or assumption problems via characteristic “fingerprints” in the program output. The latest data analysis tools tackle the same issues using a weighted-least-squares algorithm which estimates sensor errors at the same time component health is being determined. The weighted-least-squares algorithm modifies the “fingerprint” of a measurement problem and also that of a problem-free solution. To develop intuition for these new programs, the analyst must understand how weighted-least-squares works and how normal and problem situations are reflected in the output. This paper describes the weighted-least-squares algorithm, as implemented in GE’s TEMPER program, with the goal of stimulating a new intuition for interpreting gas path analysis results.
Application of Preprocessed Classifier Type Neural Network for Searching of Faulty Components of Power Cycles in Case of Incomplete Measurement Data
Authors: Głuch Jerzy , Krzyz˙anowski Jerzy
Published: February 2009

Thermal and flow diagnostics of power units makes use of diagnostic relations i.e. relations between fault signatures (sets of symptoms) and geometry degradation of its components. Determining symptoms may base on thorough thermal measurements of the cycle. However, numerous apparatuses in the cycle are not or cannot be properly equipped for necessary measurements. Examples of such apparatuses in a steam turbine are external glands and nozzle box sealings. The paper studies the applicability of a selected type of Artificial Neural Network, ANN, as a diagnostic relation for locating faulty apparatuses in HP and IP turbine casings, including their sealing systems. The obtained results can be assessed as good for single faults, and satisfactory for multiple faults of the cycle components. The examined type of ANN can be used e.g. in a modular hierarchical diagnostic system proposed by Gluch & Krzyzanowski, 1998, 1999.
Setting Up of a Probabilistic Neural Network for Sensor Fault Detection Including Operation With Component Faults
Authors: Romessis C. , Mathioudakis K.
Published: February 2009

The diagnostic ability of Probabilistic Neural Networks (PNN) for detecting sensor faults on gas turbines is examined. The structure and the features of a PNN, for sensor fault detection, are presented. It is shown that with the proposed formulation, a powerful tool for sensor fault identification is produced. A particular feature of the PNN produced is the ability to detect sensor faults even in the presence of engine component malfunction, as well as on deteriorated engines. In such situations, the size of bias that can be identified increases. The way to establish the limits of sensor bias that can be detected is presented along with results from application to test cases with realistic noise magnitudes. The diagnostic procedure proposed here is also supported by an engine performance model. The data used for setting up and testing the PNN are generated by such a model.
Modern Telemetry Systems and Rotating Instrumentation
Authors: Zeisberger Andreas , Matziol Lutz , Deubert Frank
Published: February 2009

The knowledge of component stresses and operating conditions (pressure, temperature, vibration) within the rotating parts of aircraft engines and other turbomachines is essential to evaluate performance and load conditions. The rotating data acquisition is accomplished using telemetry systems that have to fulfill extremely high mechanical and thermal requirements. Despite these restrictions, an increasing number of measurement positions have to be recorded simultaneously with a very high bandwidth to resolve oscillations up to 50 kHz or even more. In the following, the requirements on a modern telemetry system will be presented in detail. In addition to the analogue systems used today MTU Aero Engines and Manner Sensortelemetrie have developed a new digital system that enables the simultaneous measurement of 48 dynamic channels with a bandwidth of 50 kHz and improved signal quality. The data is transmitted from the rotating to the stationary side using a high frequency carrier while the electric power is supplied inductively.
Computational Comparison of the RB199 and GE90 Pyrometer Purging Systems
Authors: Kerr Clive , Ivey Paul , Oxley Neil
Published: February 2009

At present, one of the most problematic topics associated with the application of optical pyrometry to in-service use on gas turbine aeroengines is the fouling of the system optics. Even though only one optical surface is, in general, exposed to the turbine environment the resulting deposition of particulates, from the combustion process or atmospheric ingestion, can greatly inhibit the benefits of utilising such an instrument for direct temperature measurement. The particulates that deposit on the pyrometer lens act as an interference filter by absorbing a portion of the thermal radiation from the target, for example the turbine blades. As a control function input, this will then bias the indicated temperature low and thus permit higher turbine temperature operation resulting in blade temperatures in excess of their intended limits. In practice, a purge air system is therefore incorporated into turbine pyrometer designs in order to minimise the number of particulates that can potentially deposit and build-up on the exposed system optics. This paper examines and compares the flow fields in two purge air designs that have already gained acceptance in-service, namely the military RB199 and civil GE90 pyrometer purging systems. This study of the airflow within actual purge designs will allow gas turbine engineers develop an understanding of the fluid flow structures and how they presently impede the achievement of sufficient lens cleanliness.
Spray Test of Fuel Nozzle for Lean Pre-Mixed Pre-Vaporized Combustor
Authors: Nakae Tomoyoshi , Saigo Masao , Santo Akihiro , Tanaka Atsushi
Published: February 2009

An LPP (Lean Pre-mixed Pre-vaporized) combustor is one of the most promising systems to make it possible to reduce NOx emission drastically. To realize low NOx combustors using liquid fuel, uniformity and fine atomization of fuel droplets are essential requirements. Droplet diameters of a fuel nozzle designed for LPP combustor as determined by PDPA measurement system are presented in this paper. An annulus pre-mixing duct was employed for the LPP fuel nozzle test model. Spray tests were conducted at pressures from 0.18MPa to 0.53MPa. Pre-mixing air velocity was also varied. Data show that the test nozzle produces a fine spray. In this paper, fuel droplet size distribution and velocity are presented and effects of air pressure and velocity on atomization are discussed. SMD of fuel droplets increases with the increases of ambient pressure. This is inconsistent with the trend determined by other works. But when the effect of fuel flow rate (or fuel film thickness) is considered, these inconsistencies can be resolved.
Flashback Limits for Combustion Induced Vortex Breakdown in a Swirl Burner
Authors: Kro¨ner Martin , Fritz Jassin , Sattelmayer Thomas
Published: February 2009

Flame flashback from the combustion chamber into the mixing zone limits the reliability of swirl stabilized lean premixed combustion in gas turbines. In a former study, the combustion induced vortex breakdown (CIVB) has been identified as a prevailing flashback mechanism of swirl burners. The present study has been performed to determine the flash-back limits of a swirl burner with cylindrical premixing tube without centerbody at atmospheric conditions. The flashback limits, herein defined as the upstream flame propagation through the entire mixing tube, have been detected by a special optical flame sensor with a high temporal resolution. In order to study the effect of the relevant parameters on the flashback limits, the burning velocity of the fuel has been varied using four different natural gas-hydrogen-mixtures with a volume fraction of up to 60% hydrogen. A simple approach for the calculation of the laminar flame speeds of these mixtures is proposed which is used in the next step to correlate the experimental results. In the study, the preheat temperature of the fuel mixture was varied from 100 °C to 450 °C in order to investigate influence of the burning velocity as well as the density ratio over the flame front. Moreover, the mass flow rate has been modified in a wide range as an additional parameter of technical importance. It was found that the quenching of the chemical reaction is the governing factor for the flashback limit. A Peclet number model was successfully applied to correlate the flashback limits as a function of the mixing tube diameter, the flow rate and the laminar burning velocity. Using this model, a quench factor can be determined for the burner, which is a criterion for the flashback resistance of the swirler and which allows to calculate the flashback limit for all operating conditions on the basis of a limited number of flashback tests.
Integrating the Staged Prevaporizer-Premixer Into Gas Turbine Cycles
Authors: Campbell J. S. , Malte P. C. , de Bruyn Kops S. , Novosselov I. , Lee John C. Y. , Benjamin M. A.
Published: February 2009

This paper describes a cycle analysis study on the use of the staged prevaporizer-premixer injector (SPP) in high-pressure gas turbine systems fired with liquid fuel. A review of the SPP is given, including discussions of its operational concepts and previous research. The main portions of the paper consist of analyzing the use of the SPP in three different gas turbine systems: a steam-injected gas turbine (STIG) engine, a Frame H gas turbine in combined cycle, and a reheat gas turbine in combined cycle. Focus is placed on determining the effect of the SPP on cycle efficiency. In addition, SPP use in an engine conventionally recuperated by heat exchange from the exhaust gas stream to the compressor discharge air is examined. The SPP offers the potential of low NOx emissions for liquid-fired gas turbines. Because water injection is a method currently practiced for the reduction of NOx, simulations of engines without the SPP but with water injection into the combustor are also performed and comparisons are made. The simulation process is described, as are methods of how the SPP is implemented into the various engines. Results of the study are given, showing the effect of SPP use on cycle efficiency. In general, except for application to the conventionally recuperated engine, use of the SPP causes a decrease in cycle efficiency of around 1–3 percent (relative). The impact of water injection is somewhat greater, causing a 2.5–4 percent (relative) decrease in cycle efficiency. Further, the water injection does not provide as much NOx control as the lean prevaporized-premixed combustion.