bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Analysis of the Acoustic Transfer Behaviour of Pressure Ducts Utilised for Microphone Measurements in Combustion Chambers
Authors: Lourier Jean-Michel , Widenhorn Axel , Noll Berthold , Sto¨hr Michael , Aigner Manfred
Published: January 2011

Acoustic measurements within combustion chambers are expensive due to high thermal loads applied on the measurement devices at operating conditions. As a more feasible substitute, pressure ducts can be used to lead acoustic waves from combustion chambers to externally mounted microphones. Since these pressure ducts are purged by nitrogen at atmospheric temperature, high thermal loads are avoided. However, the acoustic signal measured within the pressure ducts is altered compared to the signal within the combustion chamber. This change in the acoustic signal can be characterised by means of the acoustic transfer function of the pressure duct, which mainly depends on the pressure ducts geometry and the combustion chambers temperature distribution. The main subject of the present paper is to analyse the influence of the combustion chambers temperature distribution on the acoustic transfer function of pressure ducts. For this scope, experiments at standard conditions and transient CFD simulations for different temperature distributions have been carried out. The acoustic signal measured in the pressure duct is found to be amplified with increasing temperatures within the combustion chamber. Moreover this amplification grows with increasing frequency of the acoustic signals.
Heat Transfer Performance of Fan-Shaped Film Cooling Holes: Part I—Experimental Analysis
Authors: Bonanni L. , Facchini B. , Tarchi L. , Maritano M. , Traverso S.
Published: January 2011

Fan-shaped holes are widely used to provide better cooling performance than cylindrical holes over a large range of different operating conditions. Main advantages of such solution include a reduced amount of cooling air for the same performance, increased part lifetime, and fewer required holes. As the overall cooling performance of such holes is strictly related to the adiabatic effectiveness and heat transfer coefficient (HTC) increase due to the coolant injection, both issues should be investigated. In this paper detailed measurements of HTC and adiabatic effectiveness at different blowing ratios, between 0.50 and 2.50, for a single hole on a flat plate surface are presented. Results have been obtained for two laidback fan-shaped holes (called SAA and PAA) with different area ratio. In order to take into account the effects of pressure gradients caused by airfoil curvature, experiments are performed in two different mainstream flow conditions. The former without pressure gradient, the latter with a pressure gradient generated by an inclined opposite wall, with a positive acceleration parameter (K = 2.0·10−6). Both HTC and cooling effectiveness are measured using a steady state technique with wide band Thermo-chromic Liquid Crystals (TLC). A thin Inconel heating foil was used to generate a uniform surface heat flux for the HTC measurements. Results are presented in terms of detailed maps, centerline and spanwise averaged values.
Investigation of Aerodynamic Losses and Film Cooling Effectiveness for a NGV Profile
Authors: Stephan Bruno , Kru¨ckels Jo¨rg , Gritsch Michael
Published: January 2011

Efficiency increase is one of the design targets of a gas turbine. In the highly cooled front stages the air injection out of film cooling holes and the mixing with the hot gases contributes to aerodynamic profile losses. Design parameters for film cooling rows, which the losses influence, are amongst others the blowing rate, the momentum ratio, the shape of the fan and the angle between cooling hole axis and airfoil surface. The film cooling effectiveness is depending on these parameters as well as from the choice of the locations of the film rows. Two series of tests were carried out for a nozzle guide vane at two different linear test facilities. One test series investigated the aerodynamic loss behaviour of the profile under two different cooling schemes, where the locations of cooling air injection on the airfoil suction side varied. Results show a significantly lower aerodynamic loss for the configuration with injection in the front region of the airfoil. In the second test series the film cooling effectiveness of a selected cooling row in the front region on suction side of the airfoil was measured. The analysis of the measurements show that the film is attached to the airfoil over the whole length up to the trailing edge and proved its operability under different flow regimes.
10 Years Later: A Technical and Financial Review of the United States Navy’s High Pressure Turbine Blade Refurbishment Program
Authors: Neff Rob , Driscoll Matthew
Published: January 2011

In 1999, the United States Navy implemented an LM2500 High Pressure Turbine Blade Refurbishment Program. Traditionally, the US Navy had replaced high pressure turbine components each time an engine was removed from a ship during its depot overhaul visit. Following successful testing of several Rainbow rotors built up with refurbished LM2500 blades, as well as experience gained by the Royal Australian Navy, refurbishment of stage 1 and 2 high pressure turbine blades was adopted vice the replace with new part strategy previously utilized. This paper takes a fresh look at the blade refurbishment effort from two perspectives, first, an updated technical assessment is made of Rainbow rotor components as well as parts which were implemented as part of the refurbishment program to evaluate their current (2009) condition and define service life expectations. Secondly, a financial assessment is made of the program itself, defining the cost avoidance of refurbishing customer owned blades versus the cost to procure new components. The financial analysis will also include commentary on risk mitigation based upon the hundreds of thousands of operating hours on these components have acquired while deployed at sea.
Transient Thermodynamic, Thermal and Structure Analysis of a Steam Turbine During Its Start-Up
Authors: Rza˛dkowski Romuald , Lampart Piotr , Kwapisz Leszek , Szymaniak Mariusz , Drewczyn´ski Marcin
Published: January 2011

Thermodynamic, thermal and structure calculations of the steam turbine in unsteady states are performed for a turbine heat-up from the cold state. The calculations are made for a given geometry of the turbine outer casing, inner casing, stator blade carriers, rotor and other elements of the turbine heat-up system as well as for given parameters of the steam supplied to turbine inlet/exit pipes and given heat-and-flow balance at crucial turbine flow sections. The objective of these calculations is to determine the maximum unsteady stresses in metal elements as well as temporal expansions (absolute and relative) of the turbine outer casing, inner casing, blade carriers, balance piston glands, outer shaft glands and turbine rotor during the cold start-up. For the first time the heat fluxes at the turbine heat exchange surfaces are calculated using a RANS solver in the code FLUENT. Structure computations are made using a FE model in the code ANSYS (casing) and ABAQUS (shaft), based on the given surface heat fluxes. The investigated 30 MW synchronous (50Hz) turbine was equipped with a measurement system to determine the temperature of the metal at several points and relative displacements of turbine elements at crucial locations during its heat-up. In many cases, the obtained numerical results agree well with available measurement data.
Experimental Investigation of the Aerodynamic Performance of a Linear Axial Compressor Cascade With Water Droplet Loading
Authors: Eisfeld Tjark , Joos Franz
Published: January 2011

Wet compression operation is a commercially attractive way to increase power output and efficiency of a gas turbine cycle. In recent literature the impact of water loading on the aerodynamic performance of the blading has not been entirely clarified yet. The most significant issues of aerodynamics in wet compression are stage rematching and stability. Therefore, these subjects are investigated in a linear compressor rotor cascade. This setup allows an estimation of the aerodynamic performance of the blading from two-dimensional test data at various operating conditions. Moreover, the impact of droplet flow on the two-dimensional flow field of the blade passage is measured in detail in order to understand the deviation of performance parameters. The results indicate that the effect of water injection on compressor aerodynamics is strongly related to the operating condition. It appears that droplet loading has a beneficial effect on the flow at high blade loading.
Numerical Simulation of Combustion Induced Noise Using LES and Computational Aeroacoustics
Authors: Klewer Christian , Kuehne Jens , Janicka Johannes , Kornow Oliver
Published: January 2011

Many technical combustion devices are susceptible to thermoacoustic instabilities. In this work, the noise emission by a turbulent jet flame is analyzed by means of a hybrid LES/CAA (Large Eddy Simulation/Computational Aero Acoustics) approach as a first step towards a numerical investigation of combustion instability. The hybrid LES/CAA approach is based on a LES of the reactive flow utilizing a low Mach number formulation. Within the CAA part of the simulations, linearized Euler equations (LEE) are solved. A simplified formulation to describe the thermoacoustic sound sources is extracted from the reactive LES. For the present study, the CFD code FASTEST is coupled with the aeroacoustic simulation tool PIANO. The two solvers are combined to a single tool for the description of the acoustics of reacting flows. Both codes make use of geometry flexible grids enabling the simulation of complex geometries commonly used within technical combustion systems.
Calculation of Disk Temperatures in Gas Turbine Rotor-Stator Cavities Using Conjugate Heat Transfer
Authors: Vadvadgi Aneesh Sridhar , Yavuzkurt Savas
Published: January 2011

The present study deals with the numerical modeling of the turbulent flow in a rotor-stator cavity with or without imposed through flow with heat transfer. The commercial finite volume based solver, ANSYS/FLUENT is used to numerically simulate the problem. A conjugate heat transfer approach is used. The study specifically deals with the calculation of the heat transfer coefficients and the temperatures at the disk surfaces. Results are compared with data where available. Conventional approaches which use boundary conditions such as constant wall temperature or constant heat flux in order to calculate the heat transfer coefficients which later are used to calculate disk temperatures can introduce significant errors in the results. The conjugate heat transfer approach can resolve this to a good extent. It includes the effect of variable surface temperature on heat transfer coefficients. Further it is easier to specify more realistic boundary conditions in a conjugate approach since solid and the flow heat transfer problems are solved simultaneously. However this approach incurs a higher computational cost. In this study, the configuration chosen is a simple rotor and stator system with a stationary and heated stator and a rotor. The aspect ratio is kept small (around 0.1). The flow and heat transfer characteristics are obtained for a rotational Reynolds number of around 106. The simulation is performed using the Reynolds Stress Model (RSM). The computational model is first validated against experimental data available in the literature. Studies have been carried out to calculate the disk temperatures using conventional non-conjugate and full conjugate approaches. It has been found that the difference between the disk temperatures for conjugate and non-conjugate computations is 5 K for the low temperature and 30 K for the high temperature boundary conditions. These represent differences of 1% and 2% from the respective stator surface temperatures. Even at low temperatures, the Nusselt numbers at the disk surface show a difference of 5% between the conjugate and non-conjugate computations, and far higher at higher temperatures.
Towards a High Order Throughflow: Part I—Investigating the Effectiveness of a Harmonic Reconstruction for 3D Flows
Authors: Thomas J. P. , Le´onard O.
Published: January 2011

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern three-dimensional Navier-Stokes codes in a design procedure of multi-stage turbomachines. That explains why throughflow simulation is still widely used at industrial scale. The main limitation of throughflow is however the need for empirical models to reproduce blade-flow interactions and major 3D flow features. The purpose of this work is to investigate the degree to which empiricism could be reduced by using the averaged-passage equations of Adamczyk, combined with a harmonic closure strategy. To that aim, results of a computation performed with a steady three-dimensional Navier-Stokes code are used to calculate some of the additional terms of the circumferentially-averaged equations, the so-called circumferential stresses. The importance of the latter to bring back the mean effect of circumferential non-uniformities, linked to 3D phenomena, is illustrated by injecting them into a throughfow simulation. Then the ability of truncated Fourier series to reproduce the level of non-uniformity in the core flow and near the walls is detailed. It is finally shown that the harmonic approximated stresses can lead to a good reproduction of local 3D flow features in throughflow simulation and to a better accuracy.
Towards a High Order Throughflow: Part II—Investigation of the Nonlinear Harmonic Method Coupled With an Immersed Boundary Method for the Modeling of the Circumferential Stresses
Authors: Thomas J. P. , Le´onard O.
Published: January 2011

Capturing a level of modeling of the flow inside a multi-stage turbomachine, such as unsteadiness for example, can be done at different degrees of details, either by capturing all deterministic features of the flow with a pure unsteady method or by settling for an approximated solution at a lower computational cost. The harmonic methods stand in this second category. Amongst them the “Nonlinear Harmonic Method” from He revealed the most efficient. This method consists of solving the fully nonlinear 3D steady problem and a linearized perturbation system in the frequency domain. As it has been shown by the authors that the circumferential variations exhibit a harmonic behavior, it is proposed here to adapt this method to the through-flow model, where the main nonlinear system would be the common throughflow equations and the auxiliary system would give access to the circumferential stresses. As the numerical local explicit impermeability conditions are unsupported by Fourier series, the adaptation of this technique to the throughflow model passes through a reformulation of the blade effect by a smooth force field as in the “Immersed Boundary Method” from Peskin. A simple example of an inviscid flow around a cylinder will illustrate the preceding developments, bringing back the mean effect of the circumferential non uniformities into the meridional flow.
Ignition and Combustion of Heavy Hydrocarbons Using an Aerosol Shock-Tube Approach
Authors: Rotavera Brandon , Polley Nolan , Petersen Eric L. , Scheu Kara , Crofton Mark , Bourque Gilles
Published: January 2011

Results from a heterogeneous shock-tube approach recently demonstrated at Texas A&M University, wherein a hydrocarbon fuel is introduced in liquid phase with gaseous oxidizer, are presented. The shock tube has been designed for controlled measurement of ignition delay times, sooting phenomena, radical species concentrations, time-dependent species profiles, and nanoparticle-aided combustion using heavy hydrocarbons which are difficult to study using the traditional shock tube approach. Aerosol is generated in a high-vacuum manifold positioned 4-m from the endwall where optical and pressure-based diagnostics are stationed. The approach reduces the propensity for fuel-film deposition near the endwall avoiding optical and/or kinetic disturbances that could result. The aerosol enters the shock tube initially as a two-phase flow of liquid fuel and gaseous oxidizer/inert gas. Liquid droplets partially evaporate while resident in the shock tube, prior to shock wave generation, and are then completely vaporized behind the incident shock wave. Behind the reflected shock wave, then, resides a pure gas-phase fuel and oxidizer mixture. The primary benefit of the aerosol shock tube approach is the ability to inject fuels of low vapor pressure at high or low concentrations. The classic shock-tube approach introduces gas-phase constituents only, and has difficulty accommodating low vapor-pressure liquids, except when component partial pressures are much lower than what is usually required. In the present work, n-heptane aerosol (C7H16, Pvap, 20 °C ∼ 35 torr), was generated with O2/Ar carrier gas and dispersed in the shock tube in a uniform manner. Stoichiometric ignition delay times with temperature varied from 1240 K to 1600 K and pressure maintained near 2.0 atm are compared to gas-phase data at similar conditions and a chemical kinetic model for heptane combustion. Excellent agreement was found between the two-phase aerosol approach and the classical method involving vapor-phase n-heptane and pre-mixed gases. The measured activation energy for the stoichiometric mixture at 2.0 atm (EA = 42.3 kcal /mol), obtained with the two-phase technique, compares well with the literature value.
Modeling of Atmospheric Turbulence as Disturbances for Control Design and Evaluation of High Speed Propulsion Systems
Authors: Kopasakis George
Published: January 2011

Atmospheric turbulence models are necessary for the design of both inlet/engine and flight controls, as well as for studying integrated couplings between the propulsion and the vehicle structural dynamics for supersonic vehicles. Models based on the Kolmogorov spectrum have been previously utilized to model atmospheric turbulence. In this paper, a more accurate model is developed in its representative fractional order form, typical of atmospheric disturbances. This is accomplished by first scaling the Kolmogorov spectral to convert them into finite energy von Karman forms. Then a generalized formulation is developed in frequency domain for these scale models that approximates the fractional order with the products of first order transfer functions. Given the parameters describing the conditions of atmospheric disturbances and utilizing the derived formulations, the objective is to directly compute the transfer functions that describe these disturbances for acoustic velocity, temperature, pressure and density. Utilizing these computed transfer functions and choosing the disturbance frequencies of interest, time domain simulations of these representative atmospheric turbulences can be developed. These disturbance representations are then used to first develop considerations for disturbance rejection specifications for the design of the propulsion control system, and then to evaluate the closed-loop performance.
On the Development of an Oil-Free, High-Speed and High-Temperature Turboalternator
Authors: Heshmat Hooshang , Walton James F.
Published: January 2011

In the paper the authors will present the design and preliminary test results for a distributed electric generating system that uses renewable energy sources for economical load-following and peak-shaving capability in an oil-free, high-speed micro-turboalternator system using compliant foil bearings and a permanent magnet alternator. The high operating temperatures and speeds required to make the Renewable Energy Turbo-Alternator (RETA) an efficient and cost effect system require that oil-free compliant foil bearings be used and that the alternator section be isolated from the turbine. Preliminary simulator testing compares well with design predictions and shows a stable rotordynamic and thermal environment.
Deposition in a Turbine Cascade With Combusting Flow
Authors: Smith C. , Barker B. , Clum C. , Bons J.
Published: January 2011

This report presents the design and operation of an accelerated testing facility for the study of deposition in turbine nozzle guide vanes (NGV). The facility was designed to produce turbine deposits in a 1–2 hour test that simulates thousands of hours of turbine operation. This is accomplished by matching the net foreign particulate throughput of an actual gas turbine. The facility seeds a combusting (natural gas) flow with 10–20 micron diameter coal ash particulate. The particulate-laden combustor exhaust is accelerated through a rectangular-to-annular transition duct and expands to ambient pressure through an NGV annular sector. The cascade contains two NGV doublets (donated from industry) comprising three full passages and two half passages of flow. The inlet Mach number (0.1) and gas temperature (1000 °C) are representative of operating power turbines. The vanes are film cooled from an auxiliary air supply at nominal design operating conditions. Investigations over a range of inlet gas temperatures showed that deposition increased substantially with temperature, with a threshold for deposition occurring between 900 °C and 1000 °C. Qualitative test validation was achieved using direct comparison with deposits from service hardware. Surface topography analysis indicated that the surface structure of the generated deposits were similar to those found on actual turbine blades. Regions of heightened deposition were noted; the leading edge and pressure surface being particularly implicated. Film cooling is shown to provide substantial protection from deposition.
Shell Gasifier-Based Coal IGCC With CO2 Capture: Partial Water Quench vs. Novel Water-Gas Shift
Authors: Kreutz Thomas , Martelli Emanuele , Carbo Michiel , Consonni Stefano , Jansen Daniel
Published: January 2011

We provide a detailed thermodynamic and economic analysis of two novel alternatives to the “standard” Shell coal IGCC with CO2 capture. In the first, the syngas coolers are replaced by a “partial water quench” where the raw syngas stream is cooled and humidified via direct injection of hot water. This design is less costly, but also less efficient. The second approach retains syngas coolers but instead employs a novel WGS configuration, developed at the Energy Research Centre of the Netherlands (ECN), that requires substantially less steam to obtain the same degree of CO conversion to CO2, and thus increases the overall plant efficiency. We investigate how both of these innovations alter the plant’s cost and complexity, and ultimately, the levelized cost of electricity.
A Study on Modeling Program Development of an Environmental Control System Using AMESim S/W
Authors: Yoo Youngjoon , Min Seongki , Lim Jinshik , Kho Seonghee , Ki Jayoung
Published: January 2011

Recently, modeling and simulation (M&S) has been used to predict the performance of a system in its operating conditions in order to reduce the cost and period of a development. Due to this reason, the necessity of modeling and simulation has been rapidly increased in system developments. A modeling and simulation program for an environmental control system (ECS) of a pod installed under wings of an aircraft was developed in order to estimate the system’s performance during the vehicle flight. First, through the system configuration analysis in the main operational condition of the aircraft system, an ECS configuration adopting an air cycle machine (ACM) was selected. Therefore the modeling program was developed to simulate the ECS with an ACM. Second, the sensitivity analyses on performance variation of main components were conducted to complete the conceptual design of the ECS. A design point for the system and its components was obtained through the analysis with the modeling and simulation program. Third, in order to study the feasibility of the ECS configuration, off-design performances of the ECS on various flight conditions, such as take off, manoeuvre, cruise and landing etc were estimated. Dynamic characteristics were analyzed by transient performance evaluations. From results of this study, overall performances of the ECS were able to be estimated and predicted prior to manufacturing an actual ECS with the modeling and simulation program so that development costs and oversights could be minimized. Moreover an optimum design process has been established for the ECS in this study.
Design and Engine Performance Simulation of a Turbo-Cooling System
Authors: Shi Xin , Ma Chaochen , Qi Mingxu , Chen Wei , Li Wenxiang
Published: January 2011

With the purpose of further lowering the intake temperature of diesel engine, a turbo-cooling system was developed, which was matched with a diesel engine. The system consists of two turbochargers and an intercooler: one turbocharger is the traditional exhaust driven turbo, and the other is an air turbocharger, which consists of a low expansion ratio radial air turbine coupled with a low pressure ratio centrifugal compressor. The 1-D preliminary design and the 3-D simulation of the air turbine and the low pressure ratio compressor were carried out. The new designed air turbine and compressor were manufactured and tested to get the performance maps. Further, the computational model of the diesel engine matched with this turbo-cooling system was set up. The simulated result shows that the turbo-cooling system can lower the intake temperature effectively and potential of reducing NOx exhaust. It is also can be expected that exhaust gas recirculation could be realized more easily.
Effects of Clearances on the Leakage Flow Characteristics of Two Kinds of Brush Seals and Referenced Labyrinth Seal
Authors: Li Jun , Huang Yangzi , Li Zhigang , Feng Zhenping , Yang Hong , Yang Jiandao , Shi Liqun
Published: January 2011

Numerical investigations of leakage flow fields of two kinds of brush seals with four sealing clearances were conducted in this paper. The Reynolds-Averaged Navier-Stokes (RANS) and non-Darcian porous medium model solutions were applied as the numerical approach to analyze the flow characteristics of brush seal. The reliability and accuracy of the RANS and non-Darcian porous medium model for leakage flow in brush seals were established by comparison with the experimental data. The referenced labyrinth seal was changed into a multi-stage brush seal which has two configurations. One configuration had a traditional geometrical structure. The other had a shim structure installed between the front plate and brush bristle pack. The leakage flow rates of the brush seal with two different configurations were calculated for four bristle pack tip clearances (0mm, 0.1mm, 0.3mm, 0.5mm) which were compared with the results for the referenced labyrinth seal. The numerical results show that the leakage flow rate increases rapidly with the increasing of clearance between the bristle pack tip and the rotor surface for two kinds of brush seals. The sealing performance of the brush seal with shim structure is similar to that of the traditional design with the same sealing clearance and flow conditions. In addition, as compared with the traditional brush seal, the brush seal with shim structure can reduce the pressure difference between the bristle free and fence height at 0.3mm and 0.5mm sealing clearance. The leakage flow patterns in brush seals with two different configurations were also illustrated.
Integration of Combined Cycle Power Plants and Parabolic Solar Troughs Using CO2 as Heat Transfer Fluid
Authors: Cau Giorgio , Cocco Daniele , Concas Pamela , Tola Vittorio
Published: January 2011

In this paper, a performance assessment of integrated solar combined cycle systems (ISCCS) is reported on. The main aim of the study was to evaluate the solar conversion efficiency of ISCCS plants based on parabolic troughs using CO2 as heat transfer fluid. The use of CO2 instead of the more conventional thermal oil as heat transfer fluid can allow an increase in the trough outlet temperature and thus in solar energy conversion efficiency. In particular, the ISCCS plant considered here was developed on the basis of a triple-pressure, reheated combined cycle power plant rated at 252 MW. Two different solutions for the solar steam generator are considered and compared. Moreover, the performance of the ISCCS system was evaluated with reference to different values of CO2 maximum temperature, solar radiation and solar share of the power output. The results of the performance assessment show that the solar energy conversion efficiency ranges from 23% to 25% for a CO2 maximum temperature of 550°C. The use of a CO2 temperature of 450°C reduces the solar efficiency by about 1.5–2.0 percentage points. The use of a solar steam generator including only the evaporation section instead of the preheating, evaporation and superheating sections allows the achievement of slightly better conversion efficiencies. However, the adoption of this solution leads to a maximum value of the solar share around 10% on the ISCCS power output. The solar conversion efficiencies of the ISCCS systems considered here are better than those of the more conventional Concentrating Solar Power (CSP) systems based on steam cycles (14–18%) and are very similar to the predicted conversion efficiencies of the more advanced direct steam generation plants (22–27%).
Sensitivity of Numerical Simulations of Low-Reynolds Number Flow Over the T106 Turbine Blade
Authors: de Saint Victor X.
Published: January 2011

Numerical simulations with a Navier-Stokes solver have been performed in case of weak chord Reynolds numbers varying from 80000 to 160000 over the T106 turbine blade. Results are compared to experiments in the literature. The sensitivity of these computations to different parameters has been examined. Six different transition criteria are tested and results exhibit significant differences as they do not predict the transition starting at the same location. Some of them predicting a too early transition do not allow the separation bubble existence. The sensitivity of the separation bubble to the transition start is studied imposing the location of the transition point. So, a change of 1% chord in the transition location leads to drastically different physical behaviours. Different turbulence models have been tested. It is shown that the bubble appearance is submitted to the turbulent production level of the used model. The sensitivity to the grid refinement has been tested doubling the initial number of grid points in each spatial direction. This study is followed by an error estimate using a Richardson extrapolation technique. From its results, the initial mesh is adapted and a real improvement is noted.
Static and Dynamic Pressure Measurements With Temperature Correction Using High Temperature Optical Pressure Sensors
Authors: Harpin A. P. R.
Published: January 2011

We describe our range of high temperature (1100°C) pressure sensors capable of measuring both static pressures of several Bar as required by gas turbine and jet engines, and measuring dynamic pressure fluctuations with a total dynamic range of in excess of 100000. This is achieved by a combination of rugged sensor design and our proprietary optical interrogator. This allows operation in harsh environments, EMI immunity, and simultaneous interrogation of not only static and dynamic pressure, but also the temperature of the sensor. This allows the sensor to maintain high accuracy over a wide range of operating temperatures. To date sensors have not been able to offer operation temperatures this high whilst enabling accurate dynamic pressure readings at the locations required. Also the static pressure cannot be retrieved simultaneously in real time from the same sensor. Also the temperature coefficient of the sensor has to be taken into account by measuring the temperature the sensor is operating at. Oxsensis has addressed these issues and we will present results showing dynamic pressure and temperature and explain how we can measure the temperature of the sensor with our interrogation schemes. We will describe the form of the sensor and the test data confirming its suitability for harsh environments. We will also explain the optical interrogator performance and present simulated results. The interrogator may be realised by a slave cavity or preferably on an integrated optical platform. As these sensors are intended for hostile gas turbine and aerospace environments, we will also present data from real life engine trials that we have performed, and compare the data we obtained with existing measurement techniques. Tests on a combustor rig have tested the sensor up to 1000°C, demonstrating that using our sensors in an engine at these temperatures is a realistic prospect. We believe that the ruggedness and performance of these sensors together with our complimentary interrogators mean that they are of significant interest to instrumentation of gas turbine engines and in the future the development of sophisticated engine feedback and emission control schemes, both in land based and aerospace environments.
Train Torsional Vibrations: Monitoring System Based on Model Result
Authors: Golebiowski Mateusz , Naldi Lorenzo , Rossi Valerio , Ponticelli Stefano
Published: January 2011

Development of a novel train torsional vibration monitoring approach utilizing system modal analysis has been reported in this paper. Common use of high power electric helper machines especially in large turbocompressor strings together with LCI speed control system characteristics dramatically increase the risk of machinery torsional vibration problems. Contemporary, industry-wide accepted measurement technologies (strain gage with telemetry, optical probes, laser) fit well the test needs but their lack of ruggedness and durability as well as problematic installation impacting machine operation don’t allow to consider them for the long-term monitoring applications. The authors present a methodology which allows to evaluate alternating torque amplitudes in different string sections based on standard instrumentation installed on a train. The approach adopted in this paper relies heavily on modal representation of dynamic system, being analyzed. Described calculation method utilizes results of such analysis along with gas turbine speed pick-up signal spectrum. Robustness and accuracy of the proposed technique was benchmarked against test data coming from several LNG production train measurement campaigns, where the alternating torque was measured by means of standard measurement systems. Authors present the results of such verification together with prospective system applications.
CFD Modeling of the Influence of Fuel Staging on the Mixing Quality and Flame Characteristics in a Lean Premixed Combustor
Authors: Schro¨dinger Christina , Oevermann Michael , Kru¨ger Oliver , Lacarelle Arnaud , Paschereit Christian O.
Published: January 2011

In this paper, we investigate the feasibility and limitation of modeling non reacting and reacting flows of a premixed burner with steady RANS. The burner investigated here is a standard industrial swirl-inducing burner equipped with a staging of fuel injection. The simulation results on mixing quality, flame shape and position and convective time delays are compared to measurements which are performed in a water test rig and in a combustion chamber. The RANS simulations can qualitatively capture the trends observed from experimental data. The simulated mixing quality evolves in a similar way as the experimental data when the fuel distribution is changed. Using a turbulent Schmidt number of 0.2, the absolute values are in good agreement with the measured ones. Variations of the fuel injection distribution lead to changes in the flame shape and its stabilization location. The simulated reacting flow optimized with respect to the turbulent Schmidt/Prandtl number (Sct /Prt = 0.55) is able to predict the changes in flame shape and flame position. However, the shifting of the flame is not as distinct as observed in the experiments. This explains that variations in simulated convective time delays are also smaller than in reality. Nevertheless, the qualitative characteristics of the time delays depending on the fuel distribution parameter can be reproduced and absolute values are generally similar to those of the measurements.
Steady and Transient Computations of Interaction Effects in a Centrifugal Compressor With Different Types of Diffusers
Authors: Anish S. , Sitaram N.
Published: January 2011

A computational study has been conducted to analyze the performance of a centrifugal compressor under various levels of impeller-diffuser interactions. The study has been conducted using a low solidity vaned diffuser (LSVD), a conventional vaned diffuser (VD) and a vaneless diffuser (VLD). The study is carried out using Reynolds-Averaged Navier-Stokes simulations. A commercial software ANSYS CFX is used for this purpose. The intensity of interaction is varied by keeping the diffuser vane leading edge at three different radial locations. Frozen rotor and transient simulations are carried out at four different flow coefficients. At design flow coefficient maximum efficiency occurs when the leading edge is at R3 (ratio of radius of the diffuser leading edge to the impeller tip radius) = 1.10. At lower flow coefficient higher stage efficiency occurs when the diffuser vanes are kept at R3 = 1.15 and at higher flow coefficient R3 = 1.05 gives better efficiency. It is observed that at lower flow coefficients positive incidence causes separation of flow at the suction side of the diffuser vane. When the flow rate is above design point there is a negative incidence at the leading edge of the diffuser vane which causes separation of flow from the pressure side of the diffuser vane. Compressor stage performance as well as performance of individual components is calculated at different time steps. Large variations in the stage performances at off-design flow coefficients are observed. The static pressure recovery coefficient (Cp) value is found to be varying with the relative position of impeller and diffuser. It is observed that maximum Cp value occurred at time step where Ψloss value is lowest. From the transient simulations it has been found that the strength and location of impeller exit wake affect the diffuser vane loading which in turn influences the diffuser static pressure recovery.
A Study of Fan-Distortion Interaction Within the NASA Rotor 67 Transonic Stage
Authors: Jerez Fidalgo V. , Hall C. A. , Colin Y.
Published: January 2011

The performance of a transonic fan operating within non-uniform inlet flow remains a key concern for the design and operability of a turbofan engine. This paper applies computational methods to improve the understanding of the interaction between a transonic fan and an inlet total pressure distortion. The test case studied is the NASA rotor 67 stage operating with a total pressure distortion covering a 120-degree sector of the inlet flow-field. Full-annulus, unsteady, three-dimensional CFD has been used to simulate the test rig installation and the full fan assembly operating with inlet distortion. Novel post-processing methods have been applied to extract the fan performance and features of the interaction between the fan and the non-uniform inflow. The results of the unsteady computations agree well with the measurement data. The local operating condition of the fan at different positions around the annulus has been tracked and analysed, and this is shown to be highly dependent on the swirl and mass flow redistribution that the rotor induces ahead of it due to the incoming distortion. The upstream flow effects lead to a variation in work input that determines the distortion pattern seen downstream of the fan stage. In addition, the unsteady computations also reveal more complex flow-features downstream of the fan stage, which arise due to the three-dimensionality of the flow and unsteadiness.
A Novel Technique for Measuring Stagnation Quantities and Gas Composition in High Temperature Flows
Authors: Massini Michela , Miller Robert J. , Hodson Howard P. , Collings Nick
Published: January 2011

A new probe has been developed to measure the time averaged stagnation temperature, stagnation pressure and gas composition. This probe can be used in the high temperature regions of gas turbines, including downstream of the combustor and in the first stages of the high pressure turbines, as well as in other environments. The principal benefits of the new probe are that it overcomes the limitations of the standard methods that are used to measure temperature in high temperature environments and that it replaces three separate probes, for the three quantities mentioned above, with one single probe. A novel method of measuring temperature is used, which improves upon the accuracy of thermocouples and increases the temperature operating range. The probe consists of a choked nozzle placed in the hot flow at the point of interest. The working principle is based on the theory that for a choked nozzle, there is a fixed relationship between the stagnation quantities, the gas characteristics and the mass flow rate through the nozzle. The probe has an aspirated phase, where the gas composition and the mass flow rate are measured and a stagnated phase, where the stagnation pressure is measured. The stagnation temperature is determined from the above quantities. The operating principle has been proven valid through laboratory and rig tests. The probe has been successfully tested in a Rolls-Royce Viper engine up to 1000K and 2 bar and in a combustor rig up to 1800K and 4 bars. Measurements of stagnation temperature, stagnation pressure and gas compositions for these tests are presented in the paper and are compared with reference measurements. The accuracy of stagnation pressure and gas composition measurements is equal to the accuracy achievable with techniques that are commonly used in gas turbines. The estimated achievable accuracy of the aspirated probe in terms of temperature measurements is ±0.6%, i.e. ±10K at 1800K, which improves upon the accuracy of temperature measurements performed with standard thermocouples at the same temperatures, the uncertainty of which could be as high as ±2%.
Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics
Authors: Persico G. , Mora A. , Gaetani P. , Savini M.
Published: January 2011

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage is studied. Fully unsteady, three-dimensional numerical simulations are performed using the commercial code ANSYS-CFX The numerical model is critically evaluated against experimental data. Measurements were performed with a three-dimensional fast-response aerodynamic pressure probe in the closed-loop test rig operating in the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy). An analysis is first reported about the strategy to reduce the CPU and memory requirements while performing three-dimensional simulations of stator-rotor interaction in actual turbomachinery. What emerges as the best choice, at least for subsonic stages, is to simulate the unsteady behaviour of the rotor blade row alone by applying the stator outlet flow field as rotating inlet boundary condition. When measurements are available upstream of the rotor the best representation of the experimental results downstream of the stage is achieved. The agreement with the experiments achieved at the rotor exit makes the CFD simulation a key-tool for the comprehension and the interpretation of the physical mechanisms acting inside the rotor channel (often difficult to achieve using experiments only). Numerical investigations have been carried out by varying the incidence at the vane entrance. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator. The configuration is chosen is such a way to isolate the effects of the vortex-blade interaction. Results show that some general trends can be recognized in the vortex-blade interaction. The sense of rotation and the spanwise position of the incoming vortices play a crucial role on their interaction with the rotor vortices, thus determining both the time-mean and the time-resolved characteristics of the stage-exit secondary field.
Combined Effect of Slot Injection, Effusion Array and Dilution Hole on the Heat Transfer Coefficient of a Real Combustor Liner: Part 2—Numerical Analysis
Authors: Andreini Antonio , Ceccherini Alberto , Facchini Bruno , Coutandin Daniele
Published: January 2011

Due to the higher cooling requirements of novel combustor liners a comprehensive understanding of the phenomena concerning the interaction of hot gases with different coolant flows plays a major role in the definition of a well performing liner. A numerical study of a real engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. Geometry consists of a rectangular cross-section duct with a flat plate comprised 272 holes arranged in 29 staggered rows (d = 1.65 mm, Sx/d = 7.6, Sy/d = 6, L/d = 5.5, α = 30 deg); a dilution hole (D = 18.75 mm) is located at the 14th row. A detailed experimental survey has been performed on this test article making possible to compare both predicted adiabatic effectiveness and heat transfer coefficient. The study has a twofold objective. On one hand it aims to assess the accuracy of standard industrial CFD analysis in the prediction of heat transfer on the hot side of realistic effusion cooled plates, and, on the other hand, it allows to better understand the structure of flow field, not investigated with experiments. Steady state RANS calculations have been performed on 3D computational domain with a full explicit discretization of effusion holes, with a sensitivity to standard two-equation turbulence models. Numerical results have pointed out a large dependence on effusion velocity ratio and, despite the well known deficiency of eddy viscosity models in the prediction of film effectiveness, CFD results have shown an excellent agreement with experiments in the prediction of hot side heat transfer coefficient. The entity of local heat transfer augmentation due to gas-jets interaction and its dependence on jets velocity ratio were predicted with very satisfactory agreement. The increase of heat transfer is usually located very close to jet exits and it is mainly due to local flow acceleration and vortices whose calculation is not affected by the inaccurate jet mixing prediction of first order turbulence models. Besides the comparison with experimental data of the companion paper, an additional numerical investigation was performed to assess the effect of a variable density ratio. Obtained results point out the opportunity to scale the increase in heat transfer coefficient with effusion jets velocity ratio.
Torsional Vibrations Caused by Geared Coupling in a Shaft Train Driven by a Steam Turbine
Authors: Pennacchi Paolo , Vania Andrea , Frattaroli Franco
Published: January 2011

Rotating machines that include geared shaft-trains can be affected by a dynamic behaviour that is influenced by coupling effects between lateral and torsional vibrations. These latter vibrations are rarely measured by means of permanent probes in industrial machines; therefore these phenomena can be often pointed out only by detecting abnormal harmonic components in the frequency spectrum of the lateral vibrations measured during common monitoring activities. Then, the diagnosis of the occurrence of coupling effects between torsional and lateral vibrations can be supported by the results provided by model-based techniques. In this paper the results of the analysis of the dynamic behaviour of a small power unit that was affected by abnormal lateral vibrations caused by the excitation of torsional normal modes of the geared shaft-train are shown and discussed.