bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Cold Flow Field of Aero-Engine Combustors for Lean Blow Off Analysis
Authors: Hu Bin , Huang Yong , Wang Fang , Xie Fa
Published: May 2012

Lean blow off (LBO) performance is critical to the operational performance of combustion system in propulsion and power generation. Current predictive tools for LBO are based on decades-old empirical correlations that have limited applicability for modern combustor designs. Recent advances in computational fluids dynamics (CFD) have provided new insight into the fundamental processes that occur in these flows. In this paper, it is envisaged a new methodology for the LBO predictions that is predicting the LBO fuel/air ratio based on the cold flow field of the combustor. Comparing to the traditional tools, this methodology has the lower prediction cost, especially in the designing stage of the combustor. The study presented here is the preliminary study of this method. According to the Lefebvre’s LBO model, a new load parameter (mr·Vf) extracted from the cold flow field is obtained for LBO analysis. Commercial software FLUENT is used to simulate the velocity and concentration field without combustion in different combustors. LBO fuel/air ratios are obtained from the model combustor experiments. Flammable zone volume (Vf) is used instead of Vc (as defined in Lefebvre’s model: combustor volume ahead of the dilution holes) in this LBO analysis. Vf is defined according to the lean/rich limits and increased with the increase of φLBO. In addition, the mass flow rate of back-flow air which enters the flammable zone (mr) is used to account for the combustion air. φLBO is increased in a parabolic way with the increase of mr. The load parameter (mr·Vf) could represent the actual combustion load of the combustor near LBO and relates φLBO to the cold flow field of the combustor. It will be encouraging and beneficial to the study of LBO prediction in the future.
Aero-Thermal Performance of a Cooled Winglet at Engine Representative Mach and Reynolds Numbers
Authors: O’Dowd D. O. , Zhang Q. , He L. , Cheong B. C. Y. , Tibbott I.
Published: May 2012

This paper presents an experimental investigation of the aero-thermal performance of a cooled winglet tip, under transonic conditions (exit Mach number of 1.0, and an exit Reynolds number of 1.27×106, based on axial chord). Spatially-resolved heat transfer data and film cooling effectiveness data are obtained using the transient infrared thermography technique in the Oxford High-Speed Linear Cascade test facility. Aerodynamic loss data are obtained by traversing a specially-made and calibrated three-hole pressure probe and a single-hole probe one axial chord downstream of the blade. Detailed contours of Nusselt number show that for an increase in tip clearance, with and without film cooling, and for coolant injection, for both tip clearances, the Nusselt number increases. Also the smaller tip clearance observes higher film cooling effectiveness overall. Detailed distributions of kinetic energy losses as well as pitch-wise averaged loss coefficients and loss coefficients at a mixed-out plane indicate that the size of the loss core associated with the over-tip leakage vortex decreases with cooling injection.
Impact of Severe Temperature Distortion on Turbine Efficiency
Authors: Beard Paul F. , Smith Andy , Povey Thomas
Published: May 2012

This paper presents an experimental and computational study of the effect of severe inlet temperature distortion (hot streaks) on the efficiency of the MT1 HP turbine, which is a highly-loaded unshrouded transonic design. The experiments were performed in the Oxford Turbine Research Facility (OTRF) (formerly the TTF at QinetiQ Farnborough): an engine scale, short duration, rotating transonic facility, in which M, Re, and Tgas/Twall and N/T01 are matched to engine conditions. The research formed part of the EU Turbine Aero-Thermal External Flows (TATEF II) programme. An advanced second generation temperature distortion simulator was developed for this investigation, which allows both radial and circumferential temperature profiles to be simulated. A pronounced profile was used for this study. The system was novel in that it was designed to be compatible with an efficiency measurement system which was also developed for this study. To achieve low uncertainty (bias and precision errors of approximately 1.5 per cent and 0.2 per cent respectively, to 95 per cent confidence), the mass flow rate of the hot and cold streams used to simulate temperature distortion were independently metered upstream of the turbine nozzle using traceable measurement techniques. Turbine power was measured directly with an accurate torque transducer. The efficiency of the test turbine was evaluated experimentally for a uniform inlet temperature condition, and with pronounced temperature distortion. Mechanisms for observed changes in the turbine exit flow field and efficiency are discussed. The data are compared in terms of flow structure to full stage CFD performed using the Rolls Royce Hydra code.
Thermal Modeling of a Solar Steam Turbine With a Focus on Start-Up Time Reduction
Authors: Spelling James , Jo¨cker Markus , Martin Andrew
Published: May 2012

Steam turbines in solar thermal power plants experience a much greater number of starts than those operating in base-load plants. In order to preserve the lifetime of the turbine whilst still allowing fast starts, it is of great interest to find ways to maintain the turbine temperature during idle periods. A dynamic model of a solar steam turbine has been elaborated, simulating both the heat conduction within the body and the heat exchange with the gland steam, main steam and the environment, allowing prediction of the temperatures within the turbine during off-design operation and standby. The model has been validated against 96h of measured data from the Andasol 1 power plant, giving an average error of 1.2% for key temperature measurements. The validated model was then used to evaluate a number of modifications that can be made to maintain the turbine temperature during idle periods. Heat blankets were shown to be the most effective measure for keeping the turbine casing warm, whereas increasing the gland steam temperature was most effective in maintaining the temperature of the rotor. By applying a combination of these measures the dispatchability of the turbine can be improved significantly: electrical output can be increased by up to 9.5% after a long cool-down and up to 9.8% after a short cool-down.
Influence of Film Cooling Hole Angles and Geometries on Aerodynamic Loss and Net Heat Flux Reduction
Authors: Lim Chia Hui , Pullan Graham , Ireland Peter
Published: May 2012

Turbine design engineers have to ensure that film cooling can provide sufficient protection to turbine blades from the hot mainstream gas, while keeping the losses low. Film cooling hole design parameters include inclination angle (α), compound angle (β), hole inlet geometry and hole exit geometry. The influence of these parameters on aerodynamic loss and net heat flux reduction is investigated, with loss being the primary focus. Low-speed flat plate experiments have been conducted at momentum flux ratios of IR = 0.16, 0.64 and 1.44. The film cooling aerodynamic mixing loss, generated by the mixing of mainstream and coolant, can be quantified using a three-dimensional analytical model that has been previously reported by the authors. The model suggests that for the same flow conditions, the aerodynamic mixing loss is the same for holes with different α and β but with the same angle between the mainstream and coolant flow directions (angle κ). This relationship is assessed through experiments by testing two sets of cylindrical holes with different α and β: one set with κ = 35°, another set with κ = 60°. The data confirm the stated relationship between α, β, κ and the aerodynamic mixing loss. The results show that the designer should minimise κ to obtain the lowest loss, but maximise β to achieve the best heat transfer performance. A suggestion on improving the loss model is also given. Five different hole geometries (α = 35.0°, β = 0°) were also tested: cylindrical hole, trenched hole, fan-shaped hole, D-Fan and SD-Fan. The D-Fan and the SD-Fan have similar hole exits to the fan-shaped hole but their hole inlets are laterally expanded. The external mixing loss and the loss generated inside the hole are compared. It was found that the D-Fan and the SD-Fan have the lowest loss. This is attributed to their laterally expanded hole inlets, which lead to significant reduction in the loss generated inside the holes. As a result, the loss of these geometries is ≈ 50% of the loss of the fan-shaped hole at IR = 0.64 and 1.44.
Coupled Thermo-Mechanical Fatigue Tests for Simulating Load Conditions in Cooled Turbine Parts
Authors: Mu¨cke Roland , Rau Klaus
Published: May 2012

Modern heavy-duty gas turbines operate under hot gas temperatures that are much higher than the temperature capability of nickel superalloys. For that reason, advanced cooling technology is applied for reducing the metal temperature to an acceptable level. Highly cooled components, however, are characterised by large thermal gradients resulting in inhomogeneous temperature fields and complex thermo-mechanical load conditions. In particular, the different rates of stress relaxation due to the different metal temperatures on hot gas and cooling air exposed surfaces lead to load redistributions in cooled structures, which have to be considered in the lifetime prediction methodology. In this context, the paper describes Coupled Thermo-Mechanical Fatigue (CTMF) tests for simultaneously simulating load conditions on hot and cold surfaces of cooled turbine parts, Refs [1, 2]. In contrary to standard Thermo-Mechanical Fatigue (TMF) testing methods, CTMF tests involve the interaction between hot and cold regions of the parts and thus more closely simulates the material behaviour in cooled gas turbine structures. The paper describes the methodology of CTMF tests and their application to typical load conditions in cooled gas turbine parts. Experimental results are compared with numerical predictions showing the advantages of the proposed testing method.
Repowering of a Rankine Cycle Power Plant by Means of Concentrating Solar Collectors
Authors: Camporeale Sergio M. , Fortunato Bernardo , Saponaro Alessandro
Published: May 2012

Repowering of an existing steam power plant by means of solar concentrating collectors is examined as a viable option to decrease CO2 emissions and increase electric power production during daytime peak load energy demanding hours. In the proposed scheme, the regenerative bleeds from the steam turbine are partially intercepted while boiler feed-water is heated by means of parabolic solar trough concentrating collectors. It is considered that fossil boiler, steam turbine and condenser are the same of the original plant, without modifications. After choosing a steam cycle reproducing an existing power plant, the scheme of solar repowering is examined and the efficiency of conversion of the solar energy is optimized in relation to the characteristics of the solar collector. The paper shows that the modified scheme produces very little effects on the working conditions of the existing components, either at full load or partial load, and does not reduce the conversion efficiency of the fossil fuel. In comparison with solar thermal power plants with heat storage and only solar energy as thermal input, the proposed scheme is expected to have comparable efficiency but lower costs per kWh produced, as a consequence of the fact that there is no need for steam turbine, condenser, cooling tower and auxiliary boiler. Moreover it is expected that personnel and maintenance costs will be lower.
Analytical Forces Parameters Identification of Hybrid Journal Gas Bearing Based on Transfer Function
Authors: Zhang Guang-hui , Liu Zhan-sheng , Wang Gui-long , Yan Jia-jia
Published: May 2012

A mathematical model for the flow in the hybrid gas journal bearing is depicted by the transfer function in this paper. The average and modified parameters from the pressure distribution of multi-orifices aerostatic journal bearing are acquired to describe the characteristics accurately. The transient gas film forces of multi-orifices hybrid bearing is derived in the generalized form by analytical means, and then the dynamic characteristics coefficients are got by employing the Laplace transform. It indicates that the obtained forces can calculate the dynamic characteristics coefficients simply, quickly and accurately, which provide an efficient means for designing rotor-bearing systems.
Profiled Endwall Design Using Genetic Algorithms With Different Objective Functions
Authors: McIntosh Jamie , MacPherson Richard , Ingram Grant , Hogg Simon
Published: May 2012

Profiled endwalls are a widely researched technology for reducing the secondary loss in turbines. Most designs in the literature have been produced directly by manufacturers and although general performance information is given the detailed design decisions are kept confidential. This paper outlines a simple design system for profiled endwalls that uses genetic algorithms to find an acceptable design. As the design process is produced in an academic environment full details of the design process, geometries produced, objective functions and the various trade-offs involved in the design are available and discussed in the paper. Two designs were produced using the design system: one using secondary kinetic energy as the objective function of the design system and the second using a U-cubed integral. The different designs that are produced with the different objective functions are discussed in detail in the paper. Finally profiled endwalls have traditionally been used in the high pressure stages of gas turbine blades, the paper also discusses the merits and challenges in applying these technologies to the high pressure and intermediate pressure stages of steam turbines.
Novel Concept for an Air-Pressure Driven Micro-Turbine for Power Generation
Authors: Focchi Michele , Persico Giacomo , Guglielmino Emanuele , Caldwell Darwin
Published: May 2012

A novel concept for an air pressure-driven micro-turbine is proposed in this paper. Turbine and generator are embedded in one single component, thus eliminating coupling losses and misalignment issues, and improving compactness, reliability and lifetime. The machine is a single-stage axial impulse turbine with a rotor diameter of 14 mm. Electric and mechanical designs were carried out concurrently. Two prototypes of the micro-turbine were built. The first one was a not fully optimized prototype for concept proofing while the second one was designed to optimize the fluid dynamic efficiency minimizing the air consumption. In the second prototype the air flow can reach speeds up to 100000 rpm (with 2.4 bar of supply absolute pressure) and produces, when coupled to a small generator, a maximum electrical power of 13W. The maximum total efficiency is around 4% in the optimal condition while the maximum turbine efficiency is around 50%.
Assessment of Current Chemiluminescence Kinetics Models at Engine Conditions
Authors: Petersen Eric , Kopp Madeleine , Donato Nicole , Gu¨the Felix
Published: May 2012

Chemiluminescence continues to be of interest as a cost-effective optical diagnostic for gas turbine combustor health monitoring. However, most chemical kinetics mechanisms of the chemiluminescence of target species such as OH*, CH*, and CO2* were developed from atmospheric-pressure data. The present paper presents a study wherein the ability of current kinetics models to predict the chemiluminescence trends at engine pressures was assessed. Shock-tube experiments were performed in highly diluted mixtures of H2/O2/Ar at a wide range of pressures to evaluate the ability of a current kinetics model to predict the measured trends. At elevated pressures up to 15 atm, the currently used reaction rate of H + O + M = OH* + M (i.e., without any pressure dependence) significantly over predicts the amount of OH* formed. Other important chemiluminescence species include CH* and CO2*, and separate experiments were performed to assess the validity of existing chemical kinetics mechanisms for both of these species at elevated pressures. A pressure excursion using methane-oxygen mixtures highly diluted in argon was performed up to about 15 atm, and the time histories of CH* and CO2* were measured over a range of temperatures from about 1700 to 2300 K. It was found that the existing CH* mechanism captured the T and P trends rather well, but the CO2* mechanism did a poor job of capturing both the temperature and pressure behavior. With respect to the modeling of collider species, it was found that the current OH* model performs well for N2, but some improvements can be made for CO2.
Mist/Air Cooling in a Two-Pass Rectangular Rotating Channel With 45-deg Angled Rib Turbulators
Authors: Dhanasekaran T. S. , Wang Ting
Published: May 2012

Increasing the turbine inlet temperature can increase the gas turbine cycle efficiency. In order to increase the turbine inlet temperature significantly, an advanced cooling system has to be essentially developed. Injection of mist to the coolant fluid is considered a promising technique to protect the hot components such as combustor liners, combustor transition pieces, and turbine vanes and blades. A series of experiments conducted in the past proved the success of mist cooling technology in the laboratory environment. Favorable results from the numerical simulation further encourage continuous exploration of employing mist-cooling technology in the actual gas turbine working environment in various applications. The present study focuses on applying mist cooling to the rotating mist/air internal cooling passage with rib turbulators using numerical simulation. In the first part, the computational fluid dynamics (CFD) models of smooth and ribbed channels without mist and rotation are validated with the experimental results available in literature. The agreement between the predicted and experimental values in the lower Reynolds number (Re) range is within 3% deviation, and, at higher Re range, the deviation is about 10%. For the smooth channel, the agreement with experimental result is good for the entire range of Re values. In the second part, the rotational effect on the smooth and ribbed channels is predicted and analyzed. In the last part, the mist cooling enhancement on the ribbed channel with rotation is simulated. The secondary flows created due to channel bend and rotation are specifically analyzed. The results show that the mist cooling enhancement is about 30% at the trailing surface and about 20% at the leading surface of the first passage with 2% mist injection. In the second passage, 20% enhancement is predicted for both the surfaces.
Fuel-Forced Flame Response of a Lean-Premixed Combustor
Authors: Orawannukul Poravee , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic A.
Published: May 2012

The response of a swirl-stabilized flame to equivalence ratio fluctuations is experimentally investigated in a single-nozzle lean premixed combustor. Equivalence ratio fluctuations are produced using a siren device to modulate the flow rate of fuel to the injector, while the air flow rate is kept constant. The magnitude and phase of the equivalence ratio fluctuations are measured near the exit of the nozzle using an infrared absorption technique. The flame response is characterized by the fluctuation in the flame’s overall rate of heat release, which is determined from the total CH* chemiluminescence emission from the flame. The relationship between total CH* chemiluminescence intensity and the flame’s overall rate of heat release is determined from a separate calibration experiment which accounts for the nonlinear relationship between chemiluminescence intensity and equivalence ratio. Measurements of the normalized equivalence ratio fluctuation and the normalized rate of heat release fluctuation are made over a range of modulation frequencies from 200 Hz to 440 Hz, which corresponds to Strouhal numbers from 0.4 to 2.8. These measurements are used to determine the fuel-forced flame transfer function which expresses the relationship between the equivalence ratio and rate of heat release fluctuations in terms of a gain and phase as a function of frequency. In addition, phase-synchronized CH* chemiluminescence images are captured to study the dynamics of the flame response over the modulation period. These measurements are made over a range of operating conditions and the results are analyzed to identify and better understand the mechanisms whereby equivalence ratio fluctuations result in fluctuations in the flame’s overall rate of heat release. Such information is essential to guide the formulation and validation of analytical fuel-forced flame response models and hence to predict combustion dynamics in gas turbine combustors.
HP Vane Aerodynamics and Heat Transfer in the Presence of Aggressive Inlet Swirl
Authors: Qureshi Imran , Smith Andy D. , Povey Thomas
Published: May 2012

Modern lean burn combustors now employ aggressive swirlers to enhance fuel-air mixing and improve flame stability. The flow at combustor exit can therefore have high residual swirl. A good deal of research concerning the flow within the combustor is available in open literature. The impact of swirl on the aerodynamic and heat transfer characteristics of a HP turbine stage is not well understood, however. A combustor swirl simulator has been designed and commissioned in the Oxford Turbine Research Facility (OTRF), previously located at QinetiQ, Farnborough UK. The swirl simulator is capable of generating an engine-representative combustor exit swirl pattern. At the turbine inlet plane, yaw and pitch angles of over +/-40 degrees have been simulated. The turbine research facility used for the study is an engine scale, short duration, rotating transonic turbine, in which the non-dimensional parameters for aerodynamics and heat transfer are matched to engine conditions. The research turbine was the unshrouded MT1 design. By design, the centre of the vortex from the swirl simulator can be clocked to any circumferential position with respect to HP vane, and the vortex-to-vane count ratio is 1:2. For the current investigation, the clocking position was such that the vortex centre was aligned with the vane leading edge (every second vane). Both the aligned vane and the adjacent vane were characterised. This paper presents measurements of HP vane surface and endwall heat transfer for the two vane positions. The results are compared with measurements conducted without swirl. The vane surface pressure distributions are also presented. The experimental measurements are compared with full-stage three-dimensional unsteady numerical predictions obtained using the Rolls Royce in-house code Hydra. The aerodynamic and heat transfer characterisation presented in this paper is the first of its kind, and it is hoped to give some insight into the significant changes in the vane flow and heat transfer that occur in the current generation of low NOx combustors. The findings not only have implications for the vane aerodynamic design, but also for the cooling system design.
Experimental Studies of Bifurcations Leading to Chaos in a Laboratory Scale Thermoacoustic System
Authors: Kabiraj Lipika , Sujith R. I. , Wahi Pankaj
Published: May 2012

Bifurcation analysis is conducted on experimental data obtained from a simple setup comprising of ducted, laminar pre-mixed conical flames to investigate the features of nonlinear thermoacoustic oscillations. It is observed that as the bifurcation parameter is varied, the system undergoes series of bifurcations leading to characteristically different nonlinear oscillations. Through the application of nonlinear time series analysis on pressure and flame (CH* chemiluminescence) intensity time traces, these oscillations are characterised as periodic, aperiodic or chaotic oscillations and subsequently the nature of the obtained bifurcations is explained based on dynamical systems theory. Nonlinear interaction between the flames and the acoustic modes of the duct is clearly reflected in the high speed flame images acquired simultaneously with pressure and flame intensity measurements.
Analysis of Flutter-Induced Limit Cycle Oscillations in Gas-Turbine Structures With Friction, Gap and Other Nonlinear Contact Interfaces
Authors: Petrov E. P.
Published: May 2012

A frequency-domain method has been developed to predict and comprehensively analyse the limit-cycle flutter-induced vibrations in bladed discs and other structures with nonlinear contact interfaces. The method allows, for the first time, direct calculation of the limit-cycle amplitudes and frequencies as functions of contact interface parameters and aerodynamic characteristics using realistic large-scale finite element models of structures. The effects of the parameters of nonlinear contact interfaces on limit-cycle amplitudes and frequencies have been explored for major types of nonlinearities occurring in gasturbine structures. New mechanisms of limiting the flutter-induced vibrations have been revealed and explained.
Determination of Crack Initiation on L-1 LP Steam Turbine Blades: Part 1—Measurements on Rotor Train, Material Specimens and Blades
Authors: Kubin Zdenek , Cerny Vaclav , Panek Pavel , Misek Tomas , Hlous Jan , Prchlik Lubos
Published: May 2012

After 10 years of operation of a steam turbine with large output power there was an accident during the turbine run-up. One of rotating blade fell off. All 6 LP rotors (two machines) were checked and many cracks on the L-1 blades were found. Due to economic reasons, blades with an identical geometry were manufactured quickly and a new material was used. A better material was chosen in terms of yield limit. The egalization of rotor grooves was performed because of manufacturing accuracy. Tip-timing measurement was installed on two L-1 stages to monitor and protect the blades. After one year of smooth operation new inspections were made. Surprisingly, it was found that the blades made of the new material had comparatively more cracks than the original blades. A new investigation has been started. This article describes measurements including rotor torsional excitation, blade tip-timing measurements, modal analysis and material tests. A computational analysis is presented in Part 2. Application of both approaches revealed what hypotheses should be rejected and, on the other hand, which of them should be analyzed in a deeper way. Consequently, the unstalled flutter has been identified as the most probable cause of blade cracks.
Experimental and Numerical Investigation of an Aerodynamically Loaded Guide Vane in a Turbine Duct
Authors: Johansson Martin , Chernoray Valery , Stro¨m Linda , Larsson Jonas , Abrahamsson Hans
Published: May 2012

To obtain validation for an aerodynamically loaded guide vane in a turbine duct, a new configuration was implemented in the large-scale low-speed turbine rig facility at Chalmers University of Technology. The new configuration represents a modern counter rotating turbine design, with a flow turning structural vane. The flow in a turbine duct is very complex, due to the influence of the upstream turbine stage flow structures, and becomes even more complex if the turbine duct is equipped with an aerodynamically loaded structural vane. The flow has large secondary motions and is sensitive to flow separation, which is difficult to predict with numerical CFD methods. Very limited information is found in the open literature that can be used for validation of numerical methods. This paper presents the new experimental configuration and validation of its aerodynamic performance. Measurements including surface pressure, mapping of pressure losses and flow structures are presented and discussed. Comparison to initial CFD analyses enhance the understanding of the flow structures and gives a preliminary validation of used methods.
Effect of Wake Flow Non-Uniformity on Wind Turbine Performance and Aerodynamics
Authors: Barber S. , Chokani N. , Abhari R. S.
Published: May 2012

Dynamically scaled experiments and numerical analyses are performed to study the effects of the wake from an upstream wind turbine on the aerodynamics and performance of a downstream wind turbine. The experiments are carried out in the dynamically-scaled wind turbine test facility at ETH Zurich. A 5-hole steady-state probe is used to characterize the cross-sectional distribution of velocity at different locations downstream of the wake-generating turbine. The performance of the downstream wind turbine is measured with an in-line torquemeter. The velocity field in the wind turbine wake is found to differ significantly from the velocity field assumed in numerical wake models. The velocity at hub-height does not increase monotonically up to the freestream velocity with downstream distance in the wake. Furthermore, the flowfield is found to vary significantly radially and azimuthally. The application of wake models that assume a constant axial velocity profile in the wake based on the measured hub-height velocity can lead to errors in Annual Energy Production predictions of the order of 5% for typical wind farms. The application of wake models that assume an axisymmetric Gaussian velocity profile could lead to prediction errors of the order of 20%. Thus modeling wind turbine wakes more accurately, in particular by accounting for radial variations correctly, could increase the accuracy of Annual Energy Production predictions by 5–20%.
Impeller–Vaned Diffuser Interaction in a Centrifugal Compressor at Off Design Conditions
Authors: Gaetani P. , Persico G. , Mora A. , Dossena V. , Osnaghi C.
Published: May 2012

As centrifugal compressors find a huge number of applications in industry and in aero-engine, the detailed analysis and comprehension of the impeller–vaned diffuser interaction is of interest to improve the efficiency and the operating range. The paper presents the results of a wide experimental campaign devoted to the understanding of the impeller–diffuser interaction; in particular the paper focuses on the features occurring when the compressor works in off design conditions. Data were taken at 3 operating points (near surge, best efficiency and maximum flow rate point) in the impeller–vaned diffuser gap by a fast response probe; the single stage compressor runs at 12500 RPM giving peripheral Mach number of 0.77. At first, data are reduced to evidence the main impeller flow features which are compared at different flow rates. Furthermore time mean diffuser effects on the impeller are commented and finally the impeller–diffuser interaction is discussed. Results evidence the effect of the diffuser on the impeller, mainly in terms of static pressure and flow velocity, which have a strong dependence on the flow rate.
Thermal Validation of a Heat Shield Surface for a High Lift Blade Profile
Authors: Cochet M. , Colban W. , Gritsch M. , Naik S. , Schnieder M.
Published: May 2012

Low emission requirements for heavy-duty gas turbines can be achieved with flat combustor temperature profiles, reducing the combustor peak temperature. As a result, the heat load on the first stage heat shield above the first stage blade increases. High lift airfoils cause increased thermal loading on the heat shield above the blade tip and impact the unavoidable secondary flows, including complex vortex flows. Cascade tests have been performed on a blade with a generic high lift profile and the results on the heat shield are presented. A transient thermochromic liquid crystal measurement technique was used to obtain heat transfer coefficients on the heat shield surface. Several variations of blade tip clearance were investigated, and the impact on heat transfer coefficients is shown. Computational fluid dynamics predictions are compared to the experimental data to interpret the data and validate the CFD.
Heat Transfer Investigation of the Channels With Rib Turbulators and Double-Row Bleed Holes
Authors: Guo Tao , Zhu Huiren , Xu Dunchun
Published: May 2012

The detailed heat transfer distributions are measured for the wall of a channel with rib turbulators and double-row bleed holes by transient liquid crystal technique. The effects of the relative positions of rib turbulators and bleed holes, rib angles, channel Reynolds numbers and bleed ratios on heat transfer character are studied. The bleed holes are located near the upstream ribs, equidistant between ribs and near the downstream ribs. Three different rib angles of 60°, 90° and 120° are selected with the holes equidistant between ribs. The channel Reynolds numbers are changed from 30000 to 120000. The bleed ratios are between 0.09 and 0.22. The results show that angled ribs produces higher heat transfer enhancement in conjunction with the effect of bleed holes. The heat transfer characters are best when the bleed holes are located near the upstream ribs in the channels with 90° ribs. The change of bleed holes locations does not change the position of the flow reattachment, but affect the heat transfer distribution and intensity in the region. The average heat transfer enhancement decreases with the increasing of Reynolds number, and slight increases as the bleed ratio increases.
Direct Simulations of Wake-Perturbed Separated Boundary Layers
Authors: Gungor Ayse G. , Simens Mark P. , Jime´nez Javier
Published: May 2012

A wake-perturbed flat plate boundary layer with a stream-wise pressure distribution similar to those encountered on the suction side of typical low-pressure turbine blades is investigated by direct numerical simulation. The laminar boundary layer separates due to a strong adverse pressure gradient induced by suction along the upper simulation boundary, transitions and reattaches while still subject to the adverse pressure gradient. Various simulations are performed with different wake passing frequencies, corresponding to the Strouhal number 0.0043 < fθb/ΔU < 0.0496 and wake profiles. The wake profile is changed by varying its maximum velocity defect and its symmetry. Results indicate that the separation and reattachment points, as well as the subsequent boundary layer development, are mainly affected by the frequency, but that the wake shape and intensity have little effect. Moreover, the effect of the different frequencies can be predicted from a single experiment in which the separation bubble is allowed to reform after having been reduced by wake perturbations. The stability characteristics of the mean flows resulting from the forcing at different frequencies are evaluated in terms of local linear stability analysis based on the Orr-Sommerfeld equation.
LES and RANS of Premixed Combustion in a Gas-Turbine Like Combustor Using the Flamelet Generated Manifold Approach
Authors: Cardoso de Souza T. , Bastiaans R. J. M. , Geurts B. J. , De Goey L. P. H.
Published: May 2012

Dry-low NOx gas turbine technology relies on lean premixed combustion of fuel. Additionally the accurate prediction of turbulent premixed combustion is still very difficult. In the present paper the calculation of reduced chemistry is assessed efficiently through the use of the flamelet generated manifold (FGM), which is used in conjunction with a CFD code in a RANS as well as in an LES context. In order to predict the combustion phenomena in a high swirl and high Reynolds number flow (the SimVal setup, at atmospheric pressure with elevated temperature), the present model is used concomitantly with a pre-assumed PDF for which fluctuations are completely determined in terms of an algebraic model. The mixing model for the variance has an arbitrary model constant, and the results show that the flame stabilization is not very sensitive to the model parameter present in the model. Stabilization of the combustion occurs at a location comparable to that found in experiments. In order to investigate the effects of this parameter on the numerical solutions, first RANS simulations were addressed considering arbitrary values for this parameter, defined within a certain range, and in a next step the grid resolution was changed. LES calculations were also performed showing similar features predicted in RANS. It is found that with the use of FGM combustion features in gas turbine conditions can be reproduced in a robust way.
Experimental Investigation on Leakage Losses and Heat Transfer in a Non Conventional Labyrinth Seal
Authors: Bozzi Luca , D’Angelo Enrico , Facchini Bruno , Micio Mirko , Da Soghe Riccardo
Published: May 2012

Different labyrinth seal configurations are used in modern heavy-duty gas turbine such as see-through stepped or honeycomb seals. The characterization of leakage flow through the seals is one of the main tasks for secondary air system designers as well as the evaluation of increase in temperature due to heat transfer and windage effects. In high temperature turbomachinery applications, knowledge of the heat transfer characteristics of flow leaking through the seals is needed in order to accurately predict seal dimensions and performance as affected by thermal expansion. This paper deals with the influence of clearance on the leakage flow and heat transfer coefficient of a contactless labyrinth seal. A scaled-up planar model of the seal mounted in the inner shrouded vane of the Ansaldo AE94.3A gas turbine has been experimentally investigated. Five clearances were tested using a stationary test rig. The experiments covered a range of Reynolds numbers between 5000 and 40000 and pressure ratios between 1 and 3.3. Local heat transfer coefficients were calculated using a transient technique. It is shown that the clearance/pitch ratio has a significant effect upon both leakage loss and heat transfer coefficient. Hodkinson’s and Vermes’ models are used to fit experimental mass flow rate and pressure drop data. This approach shows a good agreement with experimental data.
Effects of Endwall Motion on the Aero-Thermal Performance of a Winglet Tip in a HP Turbine
Authors: Zhou Chao , Hodson Howard , Tibbott Ian , Stokes Mark
Published: May 2012

In a gas turbine, the casing endwall moves relative to the blades. In this paper, numerical methods are first validated using experimental results for a stationary endwall. They are then used to study the effects of endwall motion on the aero-thermal performance of both winglet tips with and without tip film cooling at a tip gap of 1.9%C. The endwall motion imposes a tangential force on the flow. A scraping vortex is formed and the flow pattern within the tip gap, changes significantly. The tip leakage mass flow rate that exits the tip gap from the suction side edge reduces by about 42% with endwall motion. Overall, the endwall motion reduces the tip leakage loss by 15%. The flow field downstream of the cascade also changes with endwall motion. With endwall motion, the changed flow pattern within the tip gap significantly changes the distribution of the Nusselt number on the winglet tip. For the winglet tip without tip film cooling, the Nusselt number and the heat load decrease with endwall motion. This is mainly due to the reduction in the tip leakage mass flow ratio, which reduces the leakage velocity over the tip. On the winglet tip with tip film cooling, the cooling effectiveness increases by 9% with endwall motion. Combined with the reduced Nusselt number, the heat flux on the winglet tip with tip film cooling reduces by 31% with endwall motion. The cooling effectiveness on the near tip region of the pressure side remains almost unchanged, but the heat flux rate in this area reduces. This is because the reduced tip leakage mass flow ratio reduces the Nusselt number. With the moving endwall, the thermal performance of the suction side surface of the blade is affected by the scraping vortex. The effects of endwall motion should be considered during the design of the blade tip.
Experiments on Lean Blowout and NOx Emissions of a Premixed Trapped Vortex Combustor With High G-Loading
Authors: Lee Jong Guen , Armstrong Jeffrey P. , Santavicca Domenic A.
Published: May 2012

The feasibility of a novel combustor concept (‘g-load’ combustion with trapped-vortex chamber) to extend the premixed lean-blowout (LBO) limit and to decrease NOx emissions was experimentally determined in a scaled-modular rig that simulated a commercial 250 kilowatt microturbine combustor. The effect of a wide range of g-load’s (770–5050) on the flame regime was identified. The natural gas flame was found to be stabilized in the trapped-vortex cavity (TVC) when the equivalence ratio was within a certain range near the lean blowout limits. The TVC extended the LBO limits to marginally lower mass-based equivalence ratio levels (5%). The LBO limits were found to decrease as the g-loads decrease and the residence time increases, indicating the increase of flame mixing and reaction rates with respect to g-load is not the reason for the extension of LBO limits. The increase of residence time of mixture in the TVC was the reason for the improvement of LBO limits. The new combustor concept would enable operation at lower equivalence ratios, reducing the NOx emissions as much as much as 30%. It also showed that when the flame is contained in the trapped vortex cavity, NOx is reduced compared to baseline combustion concept without TVC.
Effect of Pressure and Oil Mist on Windage Power Loss of a Shrouded Spiral Bevel Gear
Authors: Simmons Kathy , Johnson Graham , Wiedemann Nikolas
Published: May 2012

In many aeroengines the accessory power offtake is achieved using a spiral bevel gear set running off one of the main shafts. The crown and bevel gears are housed in an internal gearbox and there is significant heat generation within this chamber, some of which is attributed to windage power loss (WPL) generated by the gear. Over the past few years the University of Nottingham Technology Centre (UTC) in Gas Turbine Transmissions has been researching spiral bevel gear windage power loss both computationally and experimentally using a purpose-built test rig at the UTC. In this study the test rig has been adapted such that chamber pressures up to 8 bar can be generated. Test data has been obtained that shows the effect on WPL of chamber pressure, advancing understanding of the relationship between data obtained at ambient and pressurised conditions. Three configurations have been studied: unshrouded gear, gear with 360° shroud and shrouded, crown and pinion meshing pair. Further, the effect of oil mist within the chamber on WPL has been studied. An oil mist generation system was developed for introducing a fine mist into the chamber and results are presented for varying mist flowrates. A mist measurement system was developed to sample mist mass fraction within the chamber and the data obtained is used to calculate an effective (oil/gas mixture) chamber density. Increasing chamber pressure increases Reynolds number, moving the system behavior further along the Moment coefficient-Reynolds number correlation. The Cm-Re correlation is similar in form to that for a shrouded cone, showing transitional behavior around Re = 2×106. Beyond transition Cm decreases with increasing Re. Introducing an oil spray has two effects: reduction in chamber temperature and increase in effective density of chamber fluid. Both effects can be accounted for by calculating Re and Cm based on mixture properties but it seems highly likely that the properties of the fluid under the shroud differ from those of the fluid in the external chamber.
Application of an Efficient Pressure-Temperature Coupled Solver to Industrial Hydrodynamic Bearings in Conjunction With Multi-Objective Evolutionary Optimization
Authors: Indriolo V. , Melina G. , Ottino G. , Romanelli G. , Minniti S. , Rindone F.
Published: May 2012

Hydrodynamic bearings have a key role in the functioning of heavy duty gas turbines: they join a great vibration absorption with an efficient power dissipation by means of a film oil inserted between the turbo machine axes and the bearing case. A classical approach for studying the functioning and the performance of this kind of bearings is to solve the so called Reynolds’ equation, which is obtained from the Navier-Stokes equations under simplifying assumptions. As a result the pressure field is derived, the fluid film being considered isothermal: dissipation effects have to be estimated a posteriori in a postprocessing procedure. On the other hand a fluid environment having to be taken into account, a direct approach is carried out by the time consuming CFD analysis. After defining an appropriate mesh and choosing the appropriate solver, an almost exact solution of the entire flow field is obtained, that is pressure, velocity and temperature distributions. The main drawback is that the required time is several order greater than that required for the solution of the Reynolds’ equation. In the present work an alternative strategy is proposed, which consists of an iterative procedure: at each step the Reynolds’ equation is solved in order to obtain the pressure field; a 1D energy balance is then applied along the length of the bearing for computing the temperature field. In this way the close relationship between pressure and temperature is modelled, the former depending on the oil viscosity locally changing with temperature, and the latter depending on the local oil mass flow and on dissipated power strictly correlated to the pressure distribution. The upgrading of both the entities ends when the convergence is reached. Comparisons with literature test cases reveal the efficiency of the proposed technique: treating the interaction between pressure and temperature gives a solution which is very close to industrial configurations investigated, and at the same time the computational load is as light as that needed for the solution of the only Reynolds’ equation. The performance of the above coupled solver can be greatly emphasised applying it to the bearing design. An integration with a multi-objective genetic optimization process is proposed, taking as objects to be optimized both geometrical and environmental variables. Application examples are shown about an industrial Ansaldo Energia lemon bore hydrodynamic bearing: given a currently applied configuration, possible improvements are suggested. Results are presented.
Selection of Climatic Design Points for Gas Turbine Power Augmentation
Authors: Chaker Mustapha , Meher-Homji Cyrus B.
Published: May 2012

There is a widespread interest in the application of gas turbine power augmentation technologies such as evaporative cooling or mechanical chilling in the mechanical drive and power generation markets. Very often, the selection of the design point is based on the use of ASHRAE data or a design point that is in the basis of design for the project. This approach can be detrimental and can result in a non optimal solution. In order to evaluate the benefits of power augmentation, users can use locally collected weather data, or recorded hourly bin data set from databases such as TMY, EWD, and IWS. This paper will cover a suggested approach for the analysis of climatic data for power augmentation applications and show how the selection of the design point can impact performance and economics of the installation. The final selection of the design point depends on the specific application, the revenues generated and installation costs. To the authors’ knowledge, this is the first attempt to treat this topic in a structured analytical manner by comparing available database information with actual climatic conditions.