bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and Analysis of Flame Transfer Function in a Sector Combustor Under High Pressure Conditions
Authors: Cheung W. S. , Sims G. J. M. , Copplestone R. W. , Tilston J. R. , Wilson C. W. , Stow Simon R. , Dowling Ann P.
Published: February 2009

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. A flame transfer function describes the change in the rate of heat release in response to perturbations in the inlet flow as a function of frequency. It is a quantitative assessment of the susceptibility of combustion to disturbances. The resulting fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. Flame transfer functions for LPP combustion are poorly understood at present but are crucial for predicting combustion oscillations. This paper describes an experiment designed to measure the flame transfer function of a simple combustor incorporating realistic components. Tests were conducted initially on this combustor at atmospheric pressure (1.2 bar and 550 K) to make an early demonstration of the combustion system. The test rig consisted of a plenum chamber with an inline siren, followed by a single LPP premixer/duct and a combustion chamber with a silencer to prevent natural instabilities. The siren was used to induce variable frequency pressure/acoustic signals into the air approaching the combustor. Both unsteady pressure and heat release measurements were undertaken. There was good coherence between the pressure and heat release signals. At each test frequency, two unsteady pressure measurements in the plenum were used to calculate the acoustic waves in this chamber and hence estimate the mass-flow perturbation at the fuel injection point inside the LPP duct. The flame transfer function relating the heat release perturbation to this mass flow was found as a function of frequency. The same combustor hardware and associated instrumentation were then used for the high pressure (15 bar and 800 K) tests. Flame transfer function measurements were taken at three combustion conditions that simulated the staging point conditions (Idle, Approach and Take-off) of a large turbofan gas turbine. There was good coherence between pressure and heat release signals at Idle, indicating a close relationship between acoustic and heat release processes. Problems were encountered at high frequencies for the Approach and Take-off conditions, but the flame transfer function for the Idle case had very good qualitative agreement with the atmospheric-pressure tests. The flame transfer functions calculated here could be used directly for predicting combustion oscillations in gas turbine using the same LPP duct at the same operating conditions. More importantly they can guide work to produce a general analytical model.
Design and Off-Design Analysis of a MW Hybrid System Based on Rolls-Royce Integrated Planar SOFC
Authors: Magistri Loredana , Bozzolo Michele , Tarnowski Olivier , Agnew Gerry , Massardo Aristide F.
Published: February 2009

In this paper the design point definition of a pressurised hybrid system based on the Rolls-Royce Integrated Planar-Solid Oxide Fuel Cells (IP-SOFCs) is presented and discussed. The hybrid system size is about 2 MWe and the design point analysis has been carried out using two different IP-SOFC models developed by Thermochemical Power Group (TPG) at the University of Genoa: (i) a generic one, where the transport and balance equations of the mass, energy and electrical charges are solved in a lumped volume at constant temperature; (ii) a detailed model where all the equations are solved in a finite difference approach inside the single cell. The first model has been used to define the hybrid system lay out and the characteristics of the main devices of the plant such as the recuperator, the compressor, the expander, etc. The second model has been used to verify the design point defined in the preview step, taking into account that the stack internal temperature behaviour are now available and must be carefully considered. Apt modifications of the preliminary design point have been suggested using the detailed IP-SOFC system to obtain a feasible solution. In the second part of the paper some off-design performance of the Hybrid System carried out using detailed SOFC model are presented and discussed. In particular the influence of ambient conditions is shown, together with the possible part load operations at fixed and variable gas turbine speed. Some considerations on the compressor surge margin modification are reported.
An Evaluation of the Effects of Water Injection on Compressor Performance
Authors: White A. J. , Meacock A. J.
Published: February 2009

The injection of water droplets into compressor inlet ducting is now commonly used as a means of boosting the output from industrial gas turbines. The chief mechanisms responsible for the increase in power are the reduction in compressor work per unit flow and the increase in mass flow rate, both of which are achieved by evaporative cooling upstream of and within the compressor. This paper examines the impact of such evaporative processes on compressor operation, focussing particular attention on cases with substantial over-spray — i.e., for which significant evaporation takes place within the compressor itself, rather than in the inlet. A simple numerical method is described for the computation of wet compression processes, based on a combination of droplet evaporation and mean-line calculations. The method is applied to a “generic” compressor geometry in order to investigate the nature of the off-design behaviour that results from evaporative cooling. Consideration is also given to the efficiency of the compression process, the implications for choking and stall, and the magnitude of the thermodynamic loss resulting from irreversible phase change.
Development of a 2-D CFD Approach for Computing 3-D Honeycomb Labyrinth Leakage
Authors: Choi Dong-Chun , Rhode David L.
Published: February 2009

A new approach for employing a 2-D CFD model to approximately compute a 3-D flow field such as that in a honeycomb labyrinth seal was developed. The advantage of this approach is that it greatly reduces the computer resource requirement needed to obtain a solution of the leakage for the 3-D flow through a honeycomb labyrinth. After the leakage through the stepped labyrinth seal was measured, it was used in numerically determining the value of one dimension (DTF1) of the simplified geometry 2-D approximate CFD model. Then the capability of the 2-D model approach was demonstrated by using it to compute the 3-D flow that had been measured at different operating conditions, and in some cases different distance to contact values. It was found that very close agreement with measurements was obtained in all cases, except for that of intermediate clearance and distance to contact for two sets of upstream and downstream pressure. The 2-D approach developed here offers interesting benefits relative to conventional algebraic-equation models, particularly for evaluating labyrinth geometries/operating conditions that are different from that of the data employed in developing the algebraic model.
Numerical Investigation of the Influence of the Tip Clearance on Wake Formation Inside a Radial Impeller
Authors: Weiß Carsten , Grates Daniel R. , Thermann Hans , Niehuis Reinhard
Published: February 2009

The objective of the presented work is to investigate the influence of the tip clearance on the wake formation inside a radial impeller. The position and size of the wake region does not only depend on the clearance height, but also on the distribution of the clearance gap along the blade chord. In order to examine this influence, several calculations have been performed with a three dimensional Navier-Stokes flow solver on a centrifugal impeller, which was experimentally investigated in much detail at Aachen University. The original clearance gap was 0.7 mm at the leading edge and 0.48 mm at the trailing edge. These values were independently varied in the computations, such that different distributions of clearance heights could be chosen. The wake position of the smallest clearance height at the leading and trailing edge was closest to the pressure side. The calculations show, that a relatively large clearance height at the leading edge combined with a small height at the trailing edge move the wake further to the suction side, which corresponds very well with the experimental results. Reasons for that behavior are discussed in the paper.
Experimental Study of the Transmission Error for the Detection of Gear Faults
Authors: Mahfoudh Jarir , Remond Didier
Published: February 2009

This study deals with the definition of preventive maintenance procedures for gearboxes. Faults can appear on one or several elements of the studied system. In this work, only gear faults are considered. Faults appear on spur gears, and the transmission error has been measured due to a progressive fault for several operating conditions. The transmission error is the system response that contains the main information about gear health. We intend to study the basic relationship between the presence of gear fault and the modification in the transmission error. We measured the transmission error using low pulse per revolution optical encoders. The operating test conditions were two speeds and three applied loads. Signals were processed in the time domain. Several indicators were examined with respect to the operating conditions. Trends of the system response with respect to fault evolution were established. Basic relationships between gear failure and the change of transmission error have been discussed.
Effects of a Vane-Recessed Tubular-Passage Passive Stall Control Technique on a Multistage, Axial-Flow Compressor: Results of Tests on the First Stage With the Rear Stages Removed
Authors: Akhlaghi M. , Elder R. L. , Ramsden K. W.
Published: February 2009

The objective of the current study was to investigate the effect of casing treatment on a multistage axial flow compressor. The main purpose of the investigation was to extend the range and operability of multistage axial compressors. The study seeks to establish whether a vane-recessed tubular-passage casing-treatment could provide beneficial stall margin improvement, without sacrificing the efficiencies of the compressor with the restricted space available for the treatment. A casing treatment that consisted of three parts: an outer casing ring, with a tubular shaped passage on the inside, a set of 120 evenly spaced curved vanes, and then a shroud or inner ring was developed from two initial designs. The casing treatment, manufactured from high quality acrylic, was positioned upstream and partly covering the tip of the first stage rotor blades. The casing treatment was tested on the first stage of a three-stage low-speed compressor with inlet guide vanes with the rear two stages removed. The rotor blade tip axial chord exposure had a significant impact on the effectiveness of the casing treatment. Seven compressor configuration incorporating casing treatments of 23.2%, 33.3%, 43.4%, 53.5%, 63.6%, 73.7% and 83.8% rotor exposure were tested. The results showed significant improvements in stall margin in all exposures and insignificant efficiency sacrifices in some exposures. Nearly 29% of stall margin improvement in terms of the corrected mass flow rate was achieved with 33.3% rotor blade tip axial chord exposure. The compressor build with 53.5% rotor exposure was the best configuration in terms of maximum efficiency gain. In terms of peak pressure rise coefficients the compressor configuration with a casing treatment of 63.6% exposure was the best design. The results also suggest that the vane-recessed tubular-passage casing treatment designed as part of this research, in most instances enabled the stall conditions in the compressor to become progressive rather than abrupt.
Resonance Effects in the NASA Transonic Flutter Cascade Facility
Authors: Lepicovsky J. , Capece V. R. , Ford C. T.
Published: February 2009

Investigations of unsteady pressure loadings on the blades of fans operating near the stall flutter boundary are carried out under simulated conditions in the NASA Transonic Flutter Cascade facility (TFC). It has been observed that for inlet Mach numbers of about 0.8, the cascade flowfield exhibits intense low-frequency pressure oscillations. The origins of these oscillations were not clear. It was speculated that this behavior was either caused by instabilities in the blade separated flow zone or that it was a tunnel resonance phenomenon. It has now been determined that the strong low-frequency oscillations, observed in the TFC facility, are not a cascade phenomenon contributing to blade flutter, but that they are solely caused by the tunnel resonance characteristics. Most likely, the self-induced oscillations originate in the system of exit duct resonators. For sure, the self-induced oscillations can be significantly suppressed for a narrow range of inlet Mach numbers by tuning one of the resonators. A considerable amount of flutter simulation data has been acquired in this facility to date, and therefore it is of interest to know how much this tunnel self-induced oscillations influences the experimental data at high subsonic Mach numbers since this facility is being used to simulate flutter in transonic fans. In short, can this body of experimental data still be used reliably to verify computer codes for blade flutter and blade life predictions? To answer this question a study on resonance effects in the NASA TFC facility was carried out. The results, based on spectral and ensemble averaging analysis of the cascade data, showed that the interaction between self-induced oscillations and forced blade motion oscillations is very weak and can generally be neglected. The forced motion data acquired with the mistuned tunnel, when strong self-induced oscillations were present, can be used as reliable forced pressure fluctuations provided that they are extracted from raw data sets by an ensemble averaging procedure.
Computation of Flow and Heat Transfer in Rotating Rectangular Channels (AR = 4) With V-Shaped Ribs by a Reynolds Stress Turbulence Model
Authors: Su Guoguang , Teng Shuye , Chen Hamn-Ching , Han Je-Chin
Published: February 2009

Computations were performed to study three-dimensional turbulent flow and heat transfer in a rotating rectangular channel with 45° V-shaped ribs. The channel aspect ratio (AR) is 4:1, the rib height-to-hydraulic diameter ratio (e/Dh) is 0.078 and the rib-pitch-to-height ratio (P/e) is 10. A total of eight calculations have been performed with various combinations of rotation number, Reynolds number, coolant-to-wall density ratio, and channel orientation. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.40, respectively, while the Reynolds number varied from 10,000 to 500,000. Three channel orientations (90°, −135°, and 135° from the rotation direction) were also investigated. A multi-block Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure for detailed predictions of mean velocity, mean temperature, turbulent Reynolds stresses, and heat fluxes and heat transfer coefficients.
Towards Multi-Component Analysis of Gas Turbines by CFD: Integration of RANS and LES Flow Solvers
Authors: Schlu¨ter Jo¨rg , Pitsch Heinz , Moin Parviz , Shankaran Sriram , Kim Sangho , Alonso Juan
Published: February 2009

The numerical prediction of the entire aero-thermal flow through an entire gas turbine is currently limited by its high computational costs. The approach presented here intends to use several specialized flow solvers based on the Reynolds-averaged Navier-Stokes equations (RANS) as well as Large Eddy Simulations (LES) running simultaneously and exchanging information at the interfaces. This study documents the development of the interface and proves its accuracy and efficiency on simple test-cases.
Conjugate Heat Transfer Analysis for Film Cooling Configurations With Different Hole Geometries
Authors: Bohn Dieter , Ren Jing , Kusterer Karsten
Published: February 2009

Secondary flows in the cooling jets are the main reason for the degradation of the cooling performance of a film-cooled blade. The formation of kidney vortices can significantly be reduced for shaped holes instead of cylindrical holes. For the determination of the film cooling heat transfer, the design of a turbine blade relies on the conventional determination of the adiabatic film cooling effectiveness and heat transfer conditions for test configurations. Thus, additional influences by the interaction of fluid flow and heat transfer and influences by additional convective heat transfer cannot be taken into account with sufficient accuracy. Within this paper, calculations of a film-cooled duct wall with application of the adiabatic and a conjugate heat transfer condition have been performed for different configurations with cylindrical and shaped holes. It can be shown that the application of the conjugate calculation method comprises the influence of heat transfer on the velocity field within the cooling film. In particular, the secondary flow velocities are affected by the local heat transfer, which varies significantly depending on the local position.
Combustion Process Optimization Using Evolutionary Algorithm
Authors: Paschereit Christian Oliver , Schuermans Bruno , Bu¨che Dirk
Published: February 2009

Flame stabilization in a swirl-stabilized combustor occurs in an aerodynamically generated recirculation region which is a result of vortex breakdown. The characteristics of the recirculating flow are dependent on the swirl number and on axial pressure gradients. Coupling to downstream pressure pulsations is also possible. Flame stability and emission formation depend on flow and mixing properties. The mixing properties of the investigated burner can be influenced by the position and the amount of fuel injection into the burner. The fuel injection is controlled by two different setups using (a) 8 proportional valves to adjust the mass flow for each fuel injector individually or using (b) 16 digital valves to include or exclude fuel injectors along the distribution holes. The objectives are the minimization of NOx emissions and the reduction of pressure pulsations of the flame. These two objectives are conflicting, affecting the environment and the lifetime of the combustion chamber, respectively. A multi-objective evolutionary algorithm is applied to optimize the combustion process. Each optimization run results in an approximation of the Pareto front by a set of solutions of equal quality, each representing a different compromise between the conflicting objectives. One compromise solution is selected with NOx emissions reduced by 30%, while mainaining the pulsation level of the given standard burner design. Chemiluminescence pictures of this solution showed that a more uniform distribution of heat release in the recirculation zone was achieved. The results were confirmed in high pressure single burner tests. The suggested fuel injection pattern has been successfully implemented in engines with sufficient stability margins and good operational flexibility. This paper shows the careful development process from lab scale tests to full scale pressurized tests.
A Multi-Stage Compressor Test Facility: Uncertainty Analysis and Preliminary Test Results
Authors: Bettocchi R. , Pinelli M. , Spina P. R.
Published: February 2009

A multi-stage compressor test-facility, fully instrumented with its dedicated data acquisition and processing system, has been developed to conduct experimental research work at the University of Ferrara. This paper provides a systematic description of the uncertainty analysis procedures required for compressor testing, including preliminary performance test results, in addition to a brief description of the test facility and its capabilities.
Experimental and Computational Study of Hybrid Diffusers for Gas Turbine Combustors
Authors: Walker A. Duncan , Denman Paul A. , McGuirk James J.
Published: February 2009

The increasing radial depth of modern combustors poses a particularly difficult aerodynamic challenge for the prediffuser. Conventional diffuser systems have a finite limit to the diffusion that can be achieved in a given length and it is, therefore, necessary for designers to consider more radical and unconventional diffuser configurations. This paper will report on one such unconventional diffuser; the hybrid diffuser which, under the action of bleed, has been shown to achieve high rates of diffusion in relatively short lengths. However, previous studies have not been conducted under representative conditions and have failed to provide a complete description of the relevant flow mechanisms making optimisation difficult. Utilising an isothermal representation of a modern gas turbine combustor an experimental investigation was undertaken to study the performance of a hybrid diffuser compared to that of a conventional, single passage, dump diffuser system. The hybrid diffuser achieved a 53% increase in area ratio within the same axial length generating a 13% increase in the pre-diffuser static pressure recovery coefficient which, in turn, produced a 25% reduction in the combustor feed annulus total pressure loss coefficient. A computational investigation was also undertaken in order to investigate the governing flow mechanisms. A detailed examination of the flow field, including an analysis of the terms within the momentum equation, demonstrated that the controlling flow mechanisms were not simply a boundary layer bleed but involve a more complex interaction between the accelerating bleed flow and the diffusing mainstream flow. A greater understanding of these mechanisms enabled a more practical design of hybrid diffuser to be developed that not only simplified the geometry but also improved the quality of the bleed air making it more attractive for use in component cooling.
Experimental Investigation of a New LPP Injector Concept for Aero Engines at Elevated Pressures
Authors: Behrendt Thomas , Heinze Johannes , Hassa Christoph
Published: February 2009

A new LPP injector concept for aero engines is presented. The design target was to achieve a fine atomization in order to get a high degree of prevaporization. Inside the injector atomization and mixture homogenization are spatially separated allowing for an individual optimization. The injector was operated in an optical accessible single sector combustor at elevated pressures. The reacting two phase flow was investigated by means of Laser Doppler Anemometry (LDA), Phase Doppler Anemometry (PDA), visualisation of OH* chemiluminescence, kerosene LIF and Mie scattering and OH LIF. The spatially and temporally resolved temperature distribution was calculated from the OH LIF images. The influence of the air preheat temperature on emissions was examined by applying conventional exhaust gas analysis. The results of the optical measurement techniques were used for an analysis of the reacting flow field and for the interpretation of the influence of the preheat temperature.
A Technique for Processing Transient Heat Transfer, Liquid Crystal Experiments in the Presence of Lateral Conduction
Authors: Ling John C. P. W. , Ireland Peter T. , Turner Lynne
Published: February 2009

New techniques for processing transient liquid crystal heat transfer experiment have been developed. The methods are able to measure detailed local heat transfer coefficient and adiabatic wall temperature in a three temperature system from a single transient test using the full intensity history recorded. Transient liquid crystal processing methods invariably assume that lateral conduction is negligible and so the heat conduction process can be considered one dimensional into the substrate. However, in regions with high temperature variation such as immediately downstream of a film-cooling hole, it is found that lateral conduction can become significant. For this reason, a procedure which allows for conduction in three dimensions was developed by the authors. The paper is the first report of a means of correcting data from the transient heat transfer liquid crystal experiments for the effects of significant lateral conduction. The technique was applied to a film cooling system as an example and a detailed uncertainty analysis performed.
Toward Global Modeling Approaches for Dynamic Analyses of Rotating Assemblies of Turbomachines
Authors: Chatelet Eric , D’Ambrosio Flavio , Jacquet-Richardet Georges
Published: February 2009

It is now increasingly necessary to predict accurately, at the design stage and without excessive computer costs, the dynamic behavior of rotating parts of turbomachines, in order to be able to avoid resonant conditions at operating speeds. Classical approaches are based on different uncoupled models. For example, rotordynamics deals with the shaft behavior while bladed assemblies dynamics deals with wheels, and the possibility of interaction between those elements is generally not analyzed. In this study, the global non-rotating mode shapes of flexible bladed disc–shaft assemblies are used in a modal analysis method for calculating the dynamic characteristics (frequencies and mode shapes) of the corresponding rotating system. The non rotating mode shapes are computed using a finite element cyclic symmetry approach. Rotational effects, such as centrifugal stiffening and gyroscopic effects are accounted for. All the possible couplings between the flexible parts and every kind of deformations are allowed. The proposed model is applied to a thin-walled composite shaft and to a turbomolecular pump rotating assembly. The results obtained illustrates clearly some of the limitations of classical approaches.
Advanced High Turning Compressor Airfoils for Low Reynolds Number Condition: Part 2 — Experimental and Numerical Analysis
Authors: Schreiber Heinz-Adolf , Steinert Wolfgang , Sonoda Toyotaka , Arima Toshiyuki
Published: February 2009

Part 1 of this paper describes the design and optimization of two high turning subsonic compressor cascades operating as an outlet guide vane (OGV) behind a single stage low pressure turbine at low Reynolds number condition (Re = 1.3×105). In the numerical optimization algorithm, the design point and off-design performance has been considered in an objective function to achieve a wide low loss incidence range. The objective of the present paper is to examine some of the characteristics describing the new airfoils as well as to prove the reliability of the design process and the applied flow solver. Some aerodynamic characteristics for the two new airfoils and a conventional controlled diffusion airfoil (CDA), have been extensively investigated in the cascade wind tunnel of DLR Cologne. For an inlet Mach number of 0.6 the effect of Reynolds number and incidence angle on each airfoil performance is discussed, based on experimental and numerical results. For an interpretation of the airfoil boundary layer behavior, results of some boundary layer calculations are compared to oil flow visualization pictures. The design goal of an increased low loss incidence range at low Reynolds number condition could be confirmed without having a negative effect on the high Reynolds number region.
A Numerical Investigation of the Flow Mechanisms in a HPC Front Stage With Axial Slots
Authors: Wilke I. , Kau H.-P.
Published: February 2009

This paper describes the impact of axial slots on the flow field in a transonic rotor blade row. The presented results are completely based on time-accurate 3-dimensional numerical simulations of a high pressure compressor front stage with and without casing treatment. Two different axial positions of a casing treatment consisting of axial slots were tested for their impact on flow stability and efficiency. The first tested position (configuration 1) was chosen in a conventional way. The slots extend approximately from the leading up to the trailing edge of the rotor blades. As expected, the simulations of the compressor stage with this configuration showed a significant increase in flow stability near surge compared to the solid wall case. However, a non negligible decrease in efficiency is also observed. Analyses of flow interactions between casing treatment and rotor blade rows under transonic conditions lead to the general conclusion that the stabilizing effect of circumferential grooves or axial slots mainly results from their impact on the tip leakage flow and its resulting vortex. A characteristic vortex inside the slots is observed in the simulations with the conventionally positioned casing treatment. This vortex removes fluid out of downstream parts of the blade passage and feeds it back into the main flow further upstream. The resulting impact on the tip leakage flow is responsible for the increased flow stability. However, the interaction between the configuration 1 casing treatment flow and the blade passage flow results in a significant relocation of the blade passage shock in the downstream direction. This explains the observed decrease in compressor efficiency. A second slot position (configuration 2) was tested with the objective to improve compressor efficiency. The casing treatment was shifted upstream, so that only 25% of the blade chord remained under the slots. The simulations carried out demonstrate that this shift positively effects the resulting efficiency, but maintains the increased level of flow stability. A time-accurate analysis of the flow shows clearly that the modified casing treatment stabilizes the tip leakage vortex and reduces the influence on the flow inside the blade passage.
Conjugate Heat Transfer Effects on a Realistic Film-Cooled Turbine Vane
Authors: Heidmann James D. , Kassab Alain J. , Divo Eduardo A. , Rodriguez Franklin , Steinthorsson Erlendur
Published: February 2009

A conjugate heat transfer solver has been developed and applied to a realistic film-cooled turbine vane for a variety of blade materials. The solver used for the fluid convection part of the problem is the Glenn-HT general multiblock heat transfer code. The solid conduction module is based on the Boundary Element Method (BEM), and is coupled directly to the flow solver. A chief advantage of the BEM method is that no volumetric grid is required inside the solid — only the surface grid is needed. Since a surface grid is readily available from the fluid side of the problem, no additional gridding is required. This eliminates one of the most time consuming elements of the computation for complex geometries. Two conjugate solution examples are presented — a high thermal conductivity Inconel nickel-based alloy vane case and a low thermal conductivity silicon nitride ceramic vane case. The solutions from the conjugate analyses are compared with an adiabatic wall convection solution. It is found that the conjugate heat transfer cases generally have a lower outer wall temperature due to thermal conduction from the outer wall to the plenum. However, some locations of increased temperature are seen in the higher thermal conductivity Inconel vane case. This is a result of the fact that film cooling is a two-temperature problem, which causes the direction of heat flux at the wall to change over the outer surface. Three-dimensional heat conduction in the solid allows for conduction heat transfer along the vane wall in addition to conduction from outer to inner wall. These effects indicate that the conjugate heat transfer in a complicated geometry such as a film-cooled vane is not governed by simple one-dimensional conduction from the vane surface to the plenum surface, especially when the effects of coolant injection are included.
Computational Fluid Dynamic Modeling for Engine Diagnosis
Authors: Parthasarathy Girija , Mylaraswamy Dinkar
Published: February 2009

This paper presents the results of a demonstration problem where computational fluid dynamics modeling (CFD) is used for engine diagnosis. As computational resources become faster and cheaper and detailed numerical models of heat transfer, fluid dynamics and chemical kinetics become more accurate, these numerical models can become viable alternatives for seeded fault tests. The work done here is one of the ways this could be done; that is, by using the results of a CFD model to map the effects of certain faults to a model parameter computed by a less detailed lumped parameter model.
An Evaluation of the Effect of Ambient Conditions on the Integration of Inlet Conditioning Systems With Industrial Gas Turbine Engines
Authors: Nixon Janel N. , Waters Mark , Mavris Dimitri
Published: February 2009

All industrial power systems are influenced by ambient parameters, and power plant output fluctuates significantly with changes in ambient conditions such as pressure, temperature, and humidity. The use of an inlet conditioning system is frequently proposed to lower the temperatures at the inlet of an industrial gas turbine engine, particularly in hot and arid regions. To evaluate such a system, a robust design methodology has been developed whereby ambient operating conditions and their impacts can be modeled easily and accurately. Ambient models are developed that are specific to a given locale and consider daily and annual variations in temperature and humidity. A robust design is one that has a high probability of meeting design goals, and at the same time, is insensitive to operational uncertainty. This paper addresses the possibility of enhancing the robustness of gas turbine engines by means of technology additions. The results of this study have been developed in part using the probabilistic analysis techniques developed at the Aerospace System Design Laboratory at Georgia Tech, and they demonstrate how differing ambient conditions can affect the decision to install an inlet conditioning system with the engine [1]. An industrial gas turbine power plant is modeled, and the ambient models are integrated with the engine model and used to predict the overall impact on power plant net revenue over a year-long period of operation. This is done at four specified locales each with widely different ambient characteristics.
Field Methods for Identification of Bearing Support Parameters: Part I — Identification From Transient Rotor Dynamic Response Due to Impacts
Authors: De Santiago Oscar C. , San Andre´s Luis
Published: February 2009

A simple procedure, with potential as a field resource, for identification of bearing support parameter from recorded transient rotor responses due to impact loads follows. The method is applied to a test rotor supported on a pair of mechanically complex bearing supports, each comprising a tilting pad bearing in series with an integral squeeze film damper. Identification of frequency dependent bearing force coefficients is good at a rotor speed of 2,000 rpm. Stiffness coefficients are best identified in the low frequency range (below 25 Hz) while damping coefficients are best identified in the vicinity of the first natural frequency (48 Hz) of the rotor bearing system. The procedure shows that using multiple-impact frequency averaged rotor responses reduces the variability in the identified parameters. The identification of frequency-dependent force coefficients at a constant rotor speed is useful to assess rotor-bearing system stability.
Steady Thermochromic Liquid Crystal Technique for Study of Conjugate Heat Transfer Problems
Authors: Douglass C. J. , Kapat J. S. , Divo E. , Kassab A. J. , Tapley J. , Durham M.
Published: February 2009

This paper presents a steady measurement technique based on thermochromic liquid crystals (TLC) that can be used for study of conjugate heat transfer. In contrast to the more commonly used transient thermochromic liquid crystal technique, this technique requires steady-state experiments, and eliminates some of the limitations of the transient version at the cost of measurements or knowledge of thermal conditions all surfaces and increased computations for data reduction. This technique requires that thermal boundary conditions be known or measured on all internal or external surfaces of the test block. All surfaces that are exposed to external air flow are coated with a broad-bandwidth TLC. The thermal boundary conditions are then sent to a steady conduction solver that involves the boundary element method (BEM) and an inverse problem approach (BEM/IP). This combined BEM/IP approach minimizes the effects of random experimental error in measured data and calculates surface heat flux, from which the intended convective heat flux coefficients can then be calculated. The technique is applied to a prismatic stainless steel block exposed to warm air flows on three sides — an arrangement that has been used often to simulate flow through a blade tip gap. It is found that an in-situ pixel-by-pixel calibration of TLC hue vs temperature is needed in order to obtain reasonable accuracy. A calibration-curve-fit uncertainty of better than 0.4°C (at 95% confidence level) was obtained in this process. In the actual experiments, conjugate heat transfer was set up by passing cold water through three cooling channels that span the test block. Once the experiments are completed and the TLC colors are converted to surface temperature distributions, the BEM/IP approach is used to obtain surface heat flux distributions, and then distribution of heat transfer coefficients.
Effects of Freestream Turbulence on the Losses of a Highly-Loaded Compressor Stator Blade
Authors: Douglas J. W. , Li S.-M. , Song B. , Ng W. F. , Sonoda Toyotaka , Arima Toshiyuki
Published: February 2009

Very little published literature documents the effects of different freestream turbulence intensities on compressor flows at realistically high Reynolds numbers. This paper presents a study of these effects on a transonic, linear, compressor stator cascade. The cascade consisted of high turning stator airfoils that had the camber of 55 degrees. The effects of freestream turbulence intensities of approximately 0.1% (baseline) and 1.6% were examined. Inlet Mach numbers to the cascade were tested from 0.55 to 0.89. Reynolds numbers, based on the inlet conditions and blade chord, varied between 1.0–2.0×106. Inlet flow angles to the cascade ranged from a choking to a stall condition. For the baseline cases, at most positive incidence angles to the cascade, surface oil flow visualization and Schlieren pictures showed a significant flow separation on the suction surface of the blade. Under these conditions, the increase in freestream turbulence from 0.1% to 1.6% significantly reduced the flow losses of the cascade (by as much as 57% in some cases). In other test conditions where no evidence depicted flow separation on the blade, there were no measurable effects on the losses due to the increase in freestream turbulence intensity. In addition, the increase of freestream turbulence intensity also improved the effective operating range of the cascade significantly (e.g., by 46% or higher).
Effects of Rib Arrangements and Rotation Speed on Heat Transfer in a Two-Pass Duct
Authors: Cho Hyung Hee , Kim Yun Young , Kim Kyung Min , Rhee Dong Ho
Published: February 2009

The present study investigates heat/mass transfer characteristics in a rotating two-pass duct for smooth and ribbed surfaces. The duct has an aspect ratio (W/H of 1:2) of 0.5 and a hydraulic diameter (Dh) of 26.67 mm. 70°-angled rib turbulators are attached on the leading and trailing sides of the duct in parallel and cross arrangements. The pitch-to-rib height ratio (p/e) is 7.5 and the rib height-to-hydraulic diameter ratio (e/Dh) is 0.075. The Reynolds number based on the hydraulic diameter is constant at 10,000 and the rotation number ranges from 0.0 to 0.2. Detailed local heat/mass transfer coefficients are measured using a naphthalene sublimation technique, which is analogous to the two-side heating condition of heat transfer experiment. The results show that the secondary flows generated by the 180°-turn, rib turbulators, and duct rotation affect the wall heat/mass transfer distribution significantly. The curvature of the 180°-turn produces Dean vortices causing high heat/mass transfer in the turning region and in the upstream region of the second-pass. When the duct is roughened with ribs, the disturbed main flow produces recirculation and secondary flows near the ribbed surfaces. Consequently, the heat/mass transfer is enhanced two to three times more. As the duct rotates, the rotation-induced Coriolis force deflects the main flow and results in differences on the heat/mass transfer distribution between the leading and trailing surfaces. Its effects become more dominant as the rotation number increases. Discussions are presented describing how the rib configuration and the rotation speed affect the flow patterns and local heat/mass transfer in the duct.
Numerical Study of Flow and Heat Transfer on a Blade Tip With Different Leakage Reduction Strategies
Authors: Acharya Sumanta , Yang Huitao , Prakash Chander , Bunker Ron
Published: February 2009

Numerical calculations are performed to explore different strategies for reducing tip leakage flow and heat transfer on the GE-E3 High-Pressure-Turbine (HPT) rotor blade. The calculations are performed for a single blade with periodic conditions imposed along the two boundaries in the circumferential-pitch direction. Several leakage reduction strategies are considered, all for a tip-clearance of 1.5% of the blade span, a pressure ratio (ratio of inlet total pressure to exit static pressure) of 1.2, and an inlet turbulence level of 6.1%. The first set of leakage reduction strategies explored include different squealer tip configurations: pressure-side squealer, suction-side squealer, mean-camber line squealer, and pressure plus suction side squealers located either along the edges of the blade or moved inwards. The suction-side squealer is shown to have the lowest heat transfer coefficient distribution and the lowest leakage flow rates. Two tip-desensitization strategies are explored. The first strategy involves a pressure-side winglet shaped to be thickest at the location with the largest pressure difference across the blade. The second strategy involves adding inclined ribs on the blade tip with the ribs normal to the local flow direction. While both strategies lead to reduction in the leakage flow and tip heat transfer rates, the ribbed tip exhibits considerably lower heat transfer coefficients. In comparing the two desensitization schemes with the various squealer tip configurations, the suction side squealer still exhibits the lowest heat transfer coefficient and leakage flow rates.
Linearised Theory for LPP Combustion Dynamics
Authors: Armitage C. A. , Cant R. S. , Dowling A. P. , Hynes T. P.
Published: February 2009

Gas turbines which are operated under lean, premixed, pre–vaporised (LPP) conditions are notoriously susceptible to self–excited oscillations. In the combustion chamber the unsteady heat released by combustion processes interacts with pressure fluctuations. The challenge is to develop a tool which can determine the frequency and stability characteristics of self–excited oscillations in realistic gas–turbine geometries. To this end, the flow through the gas turbine is described as far as possible by taking advantage of linearised theory and analytical models of the behaviour in the combustion chamber. First, a steady, mean flow solution for an idealised axi–symmetric combustor geometry is calculated using the inviscid Euler equations for continuity, momentum and energy with a specified distributed mean heat release. Superimposed on this is a linearised, three–dimensional perturbed flow in which the time and circumferential variation are described by a complex frequency and mode number respectively. Within this numerical model of the combustor a ‘flame model’ is used to describe the change in the rate of combustion due to inlet flow perturbations. The flame model may be given by an analytical expression—for example using a simple time lag with an expression proportional to the mean heat release in order to describe the unsteady heat release. An alternative approach would be to use a localised and detailed unsteady CFD calculation to determine the flow downstream of a generic premix duct geometry. If the flow is perturbed at the inlet a relationship between these fluctuations and the unsteady heat release may be obtained. In order to capture the response of the system to a wide frequency range an appropriately chosen broad–band forcing function may be used to perturb the flow. System identification techniques allow the transfer function to be extracted and a suitable flame model for the linearised Euler calculations may be constructed. Sample calculations of each aspect of the research will be presented to demonstrate the capabilities of each technique and the viability of combining the approaches towards the goal of aiding the design of gas–turbine combustors. Calculations using the linearised Euler methodology with analytical expressions for the flame model will demonstrate the capability of the approach to identify the frequencies of oscillation, mode shapes and zones of stability of particular combustor geometries.
Experimental and Computational Investigation of the Tip Clearance Flow for an Axial Ventilation Fan
Authors: Zhu Xiaocheng , Lin Wanlai , Du Zhaohui
Published: February 2009

The tip leakage flow in an axial ventilation fan with various tip clearances is investigated by experimental measurement and numerical simulation. The characteristic of a ventilation fan is an extreme low-pressure difference, a large tip clearance with a low rotating speed. A three dimensional PDA (Particle Dynamics Analysis) system is used for the measurement of the velocity field in the tip clearance region. The flow field is surveyed across the whole passage at fifteen axial locations (from 100% axial chord in front of the leading edge to 100% axial chord behind the trailing edge), mainly focusing on areas close to the blade tip (from 90% of the blade span to the casing wall). Both experimental measurement and numerical simulation indicate that the leakage flow originating from the tip clearance along the chord rolls up into a three-dimensional spiral structure to form a leakage flow vortex. A low axial velocity zone shows up in the tip region, which leads to blockage of the main flow. There are under-turning zones near and in the blade tip region, and an overturning zone in a lower span region with a critical span-wise position of about 94%. A reverse flow appears at the suction side near the trailing edge. As the tip clearance increases, the tip leakage flow and the reverse flow become stronger and fully developed. In addition, the position of the first appearance of the tip leakage vortex moves further downstream in a direction parallel to the mid chord line.
Factors Affecting Corrosion Resistance of Recuperator Alloys
Authors: Pint Bruce A. , Peraldi Raphae¨lle
Published: February 2009

As microturbine recuperators are needed to operate at higher temperatures in order to achieve higher engine operating efficiencies, a recurring problem encountered is a severe degradation in environmental resistance of type 347 stainless steel. Above 600°C, stainless steels can experience accelerated attack caused by water vapor, which is often present as a combustion product. Nickel-base alloys are less susceptible to this accelerated attack but their cost is prohibitive. In order to provide a clear, fundamental understanding of alloy composition effects on corrosion resistance of stainless steel components used in recuperators, the oxidation behavior of model alloys is being studied. A composition range of Cr and Ni contents has been identified with better corrosion resistance than type 347 stainless steel. Finer-grained alloys showed improved corrosion resistance compared to coarse-grained alloys with the same composition. It also has been demonstrated that minor alloy additions of Mn and Si are beneficial to corrosion resistance in these environments. This type of information will aid in the development of a corrosion-resistant and cost-effective recuperator material for operation at 650°–700°C.