bluuebunny/crossref_metadata_2025 huggingface dataset:
A Microturbine Operating With Variable Heat Output
Authors: Ibrahim O. , Zimmermann P. , Hirsch C. , Sattelmayer T. , Gerhard B. , Steinbach C.
Published: November 2008

The concept of variable heat output using a recuperator bypass has been studied on a microturbine. The target of this research is to quantify to which extent variable heat output is possible using an existing microturbine design. In the paper we compare the predicted and measured performance of the system as well as present and discuss the change of NOx emissions resulting from overfiring the microturbine combustor when reducing the air preheating temperature in bypass mode. We clarify which choice of bypass is suitable considering in particular the recuperator thermo-mechanical loading. We show that the performance of the system in variable heat output can be well extrapolated with a thermodynamic model calibrated with the normal operation mode data and how experimental or theoretical data can be used to predict the change of NOx emission. It is shown that the full benefit of variable heat output can only be gained with a modified combustor design. As an example for this a lean-lean staged combutor concept is proposed.
Periodic Unsteadiness of Compressor Tip Clearance Vortex
Authors: Bae Jinwoo , Breuer Kenneth S. , Tan Choon S.
Published: November 2008

Natural and forced responses of the tip clearance vortex are measured in a linear compressor cascade to characterize periodic unsteadiness of the tip clearance vortex. There exists a natural frequency at which the tip clearance vortex is the most receptive to external forcing, thus resulting in mixing enhancement and flow blockage reduction. A physical explanation of the source of the observed periodic unsteadiness is suggested based on the trailing vortex instability theory. Observations of the time scale for the unsteadiness from different compressor geometries and flow conditions are shown to scale with a reduced frequency based on convective time through the blade passage.
Study on the Effect of Asymmetric Vane Spacing on Vibratory Stress of Blade
Authors: Kaneko Y. , Mori K. , Okui H.
Published: November 2008

It is well known that asymmetric vane spacing can result in decreased levels of the excitation at specific frequencies. In this paper, the resonant response reduction of compressor blades due to asymmetric vane spacing is studied both theoretically and experimentally for the most probable asymmetric vane in which the vane count of the upper and lower half is slightly different. First, a method for predicting the vibratory stress of the blade for the asymmetric spacing vane is proposed. Secondly, using a simple model of the asymmetric vane, a parametric study is carried out to clarify the influence of blade damping and vane count on the blade resonant response reduction. Finally, experiments are carried out to verify the validity of the proposed method and the effect of asymmetric vane spacing on resonant stress response using a 3 stage scaled-model compressor.
Fluid Flow and Heat Transfer in Rotating Curved Duct at High Rotation and Density Ratios
Authors: Sleiti A. K. , Kapat J. S.
Published: November 2008

Prediction of flow field and heat transfer of high rotation numbers and density ratio flow in a square internal cooling channels of turbine blades with U-turn as tested by Wagner et. al (1991) is the main focus of this study. Rotation, buoyancy and strong curvature affect the flow within these channels. Due to the fact that RSM turbulence model can respond to the effects of rotation, streamline curvature and anisotropy without the need for explicit modeling, it is employed for this study as it showed improved prediction compared to isotropic two-equation models. The near wall region was modeled using enhanced wall treatment approach. RSM was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotation numbers (as much as 1.29) and high-density ratios (up to 0.4). Particular attention is given to how secondary flow, velocity and temperature profiles, turbulence intensity and Nusselt number area affected by coriolis and buoyancy/centrifugal forces caused by high levels of rotation and buoyancy in the immediate vicinity of the bend. The results showed that 4-side-average Nu, similar to low Ro cases, increases linearly by increasing rotation number and, unlike low Ro cases, decreases slightly by increasing density ratio.
Axial Turbine Tip-Leakage Losses at Off-Design Incidences
Authors: Willinger R. , Haselbacher H.
Published: November 2008

The tip-leakage losses in axial turbines with unshrouded rotor blades can account for as much as one third of the total losses. Various effects are influencing the tip-leakage flow and losses. This paper presents results of an experimental investigation concerning off-design incidences. Off-design incidences occur when the turbine operates at conditions different from the rated load condition. A low speed cascade wind tunnel has been used for the investigation. The geometry of the turbine cascade is an up-scale of the tip section of a low-pressure gas turbine rotor blade row (“Yaras–Sjolander cascade”) with a tip gap width of 2.5% of the chord length. The applied inlet flow angles consist of the design value as well as four off-design incidences in the range ±20°. Total pressures, static pressures and flow angles were obtained by traversing of a pneumatic five-hole probe in a plane about 0.3 axial chord lengths downstream of the turbine cascade. Based on the experimental results, a tip-leakage loss model is presented which can take into account off-design incidences. The model is applied to the present turbine cascade as well as to the turbine cascade of Yamamoto [1]. Due to its underlying concept, the model is able to predict, in addition to the losses, the flow underturning near the endwall caused by the tip-leakage vortex.
Flow Stability of Heat Recovery Steam Generators
Authors: Walter Heimo , Linzer Wladimir
Published: November 2008

In this paper the results of a theoretical stability analysis are presented. The investigation was done for two different types of natural circulation Heat Recovery Steam Generators (HRSG) — a two-drum steam generator and a HRSG with a horizontal tube bank. The investigation shows the influence of the boiler geometry on the stability of the steam generators. For the two-drum boiler the static instability, namely the reverse flow is analysed. First results of the investigations for the HRSG with a horizontal tube bank are also presented. In this case the dynamic flow instability of density wave oscillations is analysed.
The Use of Acoustic Emission Technology in Coating Ductility Testing at Various Temperatures
Authors: Li Xin-Hai , Moverare Johan
Published: November 2008

In this study, tests of ductility and ductile to brittle transition temperature DBTT of both PtAl RT22 and MCrAlY Amdry 997 coatings on both single crystal and polycrystalline substrates (CMSX-4, SCB, and In792) have been carried out. An acoustic emission detection technique that makes the detection of coating failures (micro cracking and delamination) possible has been employed during the tensile tests. The acoustic emission AE detection has been calibrated on the uncoated substrates and on some coated specimens at various testing temperatures and at different strain rate, together with metallurgical examination. A correlation between AE signals and failure types is established. It has been found that the substrate materials generate also some AE signals during plastic deformation. The amplitude of the AE signals depends strongly on the type of substrate material and the testing temperature but slightly on the strain rate. The substrate emissions may disturb the detection of coating failure. However, except for the disturbance from the substrate materials, the AE is still a sensitive, reliable, and useful technique to detect coating failures at various temperatures. The ductility results determined in this study have shown that the overlay coating Amdry 997 has a lower DBTT ∼550°C and higher ductilities than the diffusion coating RT22. Both of these differences indicate that Amdry 997 is much more ductile than RT22.
Film Cooling in Unsteady Flow With Separation Bubble
Authors: Deinert M. , Hourmouziadis J.
Published: November 2008

This study gives a detailed experimental evaluation of film cooling characteristics in unsteady flow with a separation bubble. The research project is divided into two phases. In the first phase, which is presented here, only the variation of the velocity caused by upstream blades is simulated in the experiments while the free-stream turbulence intensity is retained at a constant low level. The experiments are carried out on a flat plate with superimposed pressure distribution typical of turbine blading. A contoured wall opposite the flat plate generates this pressure distribution with a strong adverse pressure gradient, which induces a separation bubble in the middle of the plate. The measurements are conducted in an open-circuit, low-speed, suction-type wind tunnel, which can generate periodically pulsating flow. The flat plate is 1000 mm in length and has a width of 400 mm. The cooling air enters the test section through a row of 7 cylindrical film-cooling holes with sharp edges and an inclination angle of 35 degrees. The film cooling holes, which are 8 mm in diameter and have a pitch to diameter ratio of 3:1, are located in the middle of the flat plate. The main objective is to investigate the influence of the separation bubble on the cooling air flow and different film cooling parameters under periodically unsteady flow conditions. Therefore, measurements of the flow velocity and temperature using hot and cold wire anemometry for different boundary conditions were carried out. The results show that the periodic changes of size and shape of the separation bubble in a film cooled flow field under unsteady flow conditions are still dominated by the superimposed periodically changing pressure distribution. The incoming cooling air influences the separation bubble in two ways. On the one hand, the separation bubble is displaced by the film cooling jet, which means that it is only present upstream of the air injection point and on the other hand the separation bubble is thicker directly in front of the incoming film cooling jet because of the superimposed pressure field upstream of the jet. The results of flow temperature measurements show a small low-temperature area upstream of the film cooling jet at the position of the separation bubble.
The Use of CFD for the Thermal Analysis of a High Pressure Compressor Rotor
Authors: Ruedel U. W. , Turner J. R.
Published: November 2008

The prediction of fatigue life of components inside aircraft engines depends on the reliable numerical modelling of the temperature distribution during a mission cycle as this gives rise to life limiting thermal stresses. The transient temperature distribution is usually measured during an engine test and is then used to validate the numerical model, which in turn produces the basis for calculating the thermal stress levels. This paper describes the thermal analysis of a High Pressure Compressor Rotor (HPCR) and how the use of a 3-D Computational Fluid Dynamic (CFD) analysis improved the quantitative agreement between the measured and the predicted temperature profiles. The highly complex three-dimensional flow field within the compressor rotor was modelled by exploiting symmetry conditions and using a standard k-ε turbulence model. Results of the tangential, axial and radial velocity components as well as locations of peaks in turbulence kinetic energy were predicted to help identify the flow field inside the forward cavity of the rotor. Two ways of predicting internal re-circulating rates to the rim area are proposed. Finally, plots of predicted metal temperature profiles before and after the CFD-analysis are presented.
The Combined Effects of Surface Trips and Unsteady Wakes on the Boundary Layer Development of an Ultra-High-Lift LP Turbine Blade
Authors: Zhang Xue Feng , Hodson Howard
Published: November 2008

An experimental investigation of the combined effects of upstream unsteady wakes and surface trips on the boundary layer development on an ultra-high-lift low-pressure turbine blade, known as T106C, is described. The incoming wakes are not strong enough to periodically suppress the large separation bubble on the smooth suction surface of the T106C blade. Therefore, the profile loss is not reduced as much as might be possible. The first part of this paper concerns the parametric study of the effect of surface trips on the profile losses to optimise the trip parameters. The parametric study included the effects of size, type and location of the surface trips under unsteady flow conditions. The surface trips were straight cylindrical wires, straight rectangular steps, wavy rectangular steps or wavy cylindrical wires. The second part studies the boundary layer development on the suction surface of the T106C linear cascade blade with and without the recommended surface trips to investigate the loss reduction mechanism. It is found that the selected surface trip does not induce transition immediately but hastens the transition process in the separated shear layer underneath the wakes and between them. In this way, the combined effects of the surface trip and unsteady wakes further reduce the profile losses. This passive flow control method can be used over a relatively wide range of Reynolds numbers.
All-Electric Actuator for Mid-Size Gas Turbines
Authors: Fredlund Terry L. , Mares Joe
Published: November 2008

A number of actuators are available for mid-size industrial gas turbine engines in the marketplace today. These designs utilize pneumatic, hydraulic, electro-pneumatic, electro-hydraulic, and all-electric actuation technologies. The electro-hydraulic has been the most common mid-size industrial gas turbine actuation technology over the last 20 years. This paper focuses on a new all-electric actuator technology developed specifically for mid-size gas turbines using an integrally mounted controller. This paper discusses the significant technical challenges to integrally mounting all-electric actuator motor controller.
Measurement and Analysis of an Efficient Turbine Rotor Pump Work Reduction System Incorporating Pre-Swirl Nozzles and a Free Vortex Pressure Augmentation Chamber
Authors: Laurello V. , Yuri M. , Fujii K. , Ishizaka K. , Nakamura T. , Nishimura H.
Published: November 2008

Measurements and analysis of an efficient turbine rotor pump work reduction system is presented. The system features; a “low” radius pre-swirl nozzle comprised of cascade vanes with a radial orientation, equal radius seals downstream of the nozzle, “jumper” tubes across the nozzle, and a free vortex chamber. A scaled experimental rig was utilized to measure and compare with predictions the following; rotor pump work, average tangential velocity exiting the nozzle, tangential velocity variation in the axial and radial direction, free vortex chamber static pressure rise, effect of relative velocity pressure losses, and effect of “pollution” by seal flow. The effort focused on measuring pump work reduction and the efficiency of the pressure augmentation system. In contrast to aero-engines where the main objective of pre-swirl is to reduce cooling air temperature to the blades, the main objective for this industrial gas turbine is to reduce pump work and increase output. An external pre-cooler is utilized to achieve the large cooling air temperature reduction required to maintain disk material limits. The analytical results and rig test data are presented and compared. The results substantiated the following: the level of reduced rotor pump work due to pre-swirl, the static pressure rise in the free vortex chamber, the effect of eliminating “pollution”, and relative velocity pressure losses. CFD analytical results are compared with the rig data.
Transfer Function Measurements on a Swirl Stabilized Premix Burner in an Annular Combustion Chamber
Authors: Kunze Klaas , Hirsch Christoph , Sattelmayer Thomas
Published: November 2008

A generic swirl stabilized premix burner for natural gas is experimentally investigated in both a single burner test rig and in an annular combustion chamber. Flame transfer functions are measured relating the fluctuation of the flame heat release to the axial velocity fluctuation at the burner outlet. The OH-chemiluminescence signal of the flame, captured with a photomultiplier tube, is taken as an estimate for flame heat release, whereas the velocity fluctuation is measured with a hot wire probe. As integral measurements of the entire flame reveal important differences between the single burner and the annular combustor, locally resolved measurements are performed observing slices of the flame that are perpendicular to the main flow direction at a variable distance from the burner outlet. In both the single and the annular combustor a near field and a far field of the dynamic flame behavior can be distinguished. The annular combustor flame has a larger near field than the single combustor flame and a different shape in the presence of circumferential acoustic waves. Variation of swirl, thermal power and mass flow and comparison of the steady state heat release distribution within the flames lead to the result that the effective swirl in the annular combustor is lower than for the identical burner in the single burner combustor. When the difference in swirl is compensated for by modifying the burner configuration in the annular combustion chamber the flame transfer function is still not equal to the single combustor flame. The remaining difference can be attributed to the circumferential acoustic waves in the annular combustor which influence the flame shape.
Application of Multipoint Optimization to the Design of Turbomachinery Blades
Authors: Demeulenaere Alain , Ligout Alban , Hirsch Charles
Published: November 2008

This paper presents a new integrated environment FINE™/Design3D developed for the optimization of turbomachinery compressor and turbine blade shapes. The methodology relies on the interaction between a genetic algorithm, an artificial neural network, a database and user generated objective functions and constraints. The optimization is coupled to the FINE™/Turbo environment of NUMECA. The present paper focuses on multipoint optimization. The generality of the formulation of the FINE™/Design3D optimization techniques allows the objective function to be based on the evaluation of the performance at different working conditions. The examples presented in the paper illustrate this new capability, showing the application of multipoint optimization to a turbine rotor and to a re-design of the NASA Rotor 37 transonic compressor rotor.
CFD Simulation of the Flow Within and Downstream of a High-Swirl Lean Premixed Gas Turbine Combustor
Authors: Turrell Mark D. , Stopford Philip J. , Syed Khawar J. , Buchanan Eoghan
Published: November 2008

CFD analysis of the flow within a high-swirl lean premixed gas turbine combustor and over the 1st row nozzle guide vanes is presented. The focus of the investigation is the fluid dynamics at the combustor/turbine interface and its impact on the turbine. For the configuration in question, temperature indicating paint observations of the nozzle guide vanes, acquired during engine development tests, show features consistent with the presence of a highly rotating vortex core emerging from the combustor. The configuration was modelled by a fully compressible reacting CFD analysis, whose domain stretched from the exit of the combustor swirl generator to downstream of the 1st row nozzle guide vanes. The CFD analysis, when using a Reynolds stress turbulence model, predicted a highly rotating vortex core. The predicted interaction between the core and the nozzle guide vanes were consistent with the temperature indicating paint observations. The interaction is dominated by the vortex core being attracted to the locus of lowest static pressure.
Evaluation of an Effective Engine Nozzle Map by Reduction of Data Acquired During Transient Operation
Authors: Lichtsinder M. , Levy Y.
Published: November 2008

This paper discusses low cost and fast evaluation of effective performance maps for engine components such as nozzles, turbines and compressors using data acquired during transient engine operations. The objective of the present study is to re-evaluate effective engine performance maps when not all the engine component maps are known. The work is equally relevant to account for manufacturing tolerances of different engines resulting in small differences in their performance. Disassembly and rebuilding of an engine as well as degradation in performance due to extensive usage can cause small variations in their performance. If the engine maps do not represent particular engine operations with precision, its performance predictions will differ from the actual characteristics. The engine map evaluation is carried out using data acquired during aircraft transient operations at different altitudes, Mach numbers, angles of attack, side slip angles and during post-stall. The method is based on a conventional dynamic engine model. The unknown engine map characteristics are excluded from the model while the corresponding numbers of some measured values are added to the model input. The evaluated map values are calculated using an inverse solution of the equations of the “shortened” mathematical model. Some jet engine maps may be evaluated simultaneously. Two examples for fragments of compressor and compressor/nozzle map evaluations are presented in this paper.
Online Combustor Stability Margin Assessment Using Dynamic Pressure Data
Authors: Lieuwen Tim
Published: November 2008

This paper describes a strategy for determining a combustor’s dynamic stability margin. Currently, when turbines are being commissioned or simply going through day to day operation, the operator has no idea how the dynamic stability of the system is affected by changes to fuel splits/operating conditions unless, of course, pressure oscillations are actually present. We have developed a methodology for ascertaining stability margin from passive monitoring of the acoustic pressure. This method consists of signal processing and analysis that determines a real-time measure of combustor damping. When the calculated damping is positive, the combustor is stable. When the damping goes to zero, the combustor approaches its stability boundary. Changes in the stability margin of each of the combustor’s stable modes due to tuning, aging or environmental changes can then be monitored through online analysis of the pressure signal. This paper outlines the basic approach used to quantify acoustic damping and demonstrates the technique on combustor test data.
Gas Turbine Combustor Heat Shield Impingement Cooling Baffle
Authors: Riahi Ardeshir , Borns Fred G.
Published: November 2008

Numerical calculations are performed to examine the merits of a novel cooling scheme proposed to improve the durability of heat shields in a gas turbine combustor. The novel scheme is comprised of a combination of convective and impingement heat transfer. The impingement scheme incorporates three rows of holes two of which target the bore of the heat-shield while the third row targets the OD of the heat-shield and are all staggered with respect to each other. The convective heat transfer is provided through annular collection of the spent impingement flow from the two rows targeting the bore. The impingement height-to-hole diameter spacing is in the range of 1.4 ≤ Z/d ≤ 2.3, with the jet Reynolds number 12050 ≤ Red ≤ 13770. The spent impingement flow from the inner-diameter holes however, acts as a cross-flow on the impingement jets targeting the outer diameter of the heat-shield which reduces the impingement heat transfer rate of these outer-diameter holes. U-shaped ribs are introduced on the surface of heat-shield with the objective of first reducing the detrimental effects of cross-flow on impingement heat transfer and secondly, to increase the convective heat transfer area due to annular collection of the spent flow. It is shown that, provided the U-ribs are clocked with respect to the 3rd (outer-diameter) impingement row, the maximum heat-shield metal temperature is reduced by as much as 80 °C. The thermal gradients in both radial and “through-the-wall” directions are also reduced which in turn reduce the hoop (tangential) stresses. The combination of heat-shield temperature and stress reduction, due to the introduction of U-ribs, increase the heat-shield life.
Investigation of a High Aspect Ratio Rectangular Channel With High Blockage Ratio Round-Corner Ribs
Authors: Diette Christophe , Arts Tony , Sgarzi Olivier , Laroche Emmanuel
Published: November 2008

The flow behavior and heat transfer were measured in a large scale, high aspect ratio, turbine blade rib-roughened internal cooling channel. The ribs, installed on one wall, were inclined at 90 deg with respect to the main flow direction and generated a blockage of 20%. The rib corners were rounded to take into account manufacturing aspects. The bulk flow Reynolds number was 20,000. Pressure drop and velocity measurements were first conducted. Liquid crystal thermography was applied to quantify the heat transfer, not only along the ribbed and the smooth opposite walls but also on the rib itself. Numerical simulations were conducted with two flow solvers, IGG/FINE (Numeca) and MSD (ONERA) and compared with measurements. They also supported the analysis of the flow behavior. The influence of round-corner versus sharp edge ribs was numerically evaluated with IGG/FINE.
Numerical Simulation of 3D Bristle Bending in Brush Seals
Authors: Guardino Cesare , Chew John W.
Published: November 2008

This paper presents a new method for predicting the 3D bending behaviour of bristles in brush seals. The model builds upon and addresses shortcomings in an earlier 2D bending model. The work was motivated by the need to develop a general 3D solid mechanical model which can ultimately be incorporated into CFD models of flow and heat transfer through brush seals. The iterative method considered here, which is based upon linear beam-bending theory, allows relatively large numbers of bristles to be considered with arbitrary imposed aerodynamic forces. Bristle-to-bristle contacts and deflections are considered, as well as shaft and backing ring contacts. The method also allows arbitrary initial bristle packs and lay-angles to be considered, as well as periodic conditions so that the model represents a sector of a brush seal. Other physically important features such as the so-called ‘3D-splay’ and ‘inclined prop’ effects are also taken into account. The method described here has been incorporated into a new computer code called ‘SUBSIS’ (Surrey University Brush Seal Iterative Simulator). Example results from this code are presented which show the bending behaviour of initially hexagonally packed brush seals under model imposed pressure loads acting on the bristle tips. The effects of rotor incursions into the bristle pack, increase of the pressure load, and changes in the lay-angle and Young’s modulus are also shown. The results illustrate the expected bending behaviour observed in real brush seals. Procedures for coupling SUBSIS with CFD models are also currently under investigation.
Three-Dimensional Finite Element Analysis of Dovetail Attachments With and Without Crowning
Authors: Beisheim J. R. , Sinclair G. B.
Published: November 2008

The stress analysis of dovetail attachments presents some challenges. These stem from the high stress gradients present, the contact inequalities attending conforming contact, and the nonlinearities inherent in Coulomb friction laws. Obtaining converged contact stresses in the presence of these phenomena is demanding, especially in three dimensions. In [1], a submodeling approach with finite elements is employed to meet these challenges when friction is not present. Here we extend this approach to treat contact when friction is present. Converged stresses are obtained by using two successive submodels. Comparing these stresses with two-dimensional analysis elucidates some of the truly three-dimensional aspects of the stress analysis of dovetail attachments. Further comparisons of contact stresses when crowning is added indicate the possible alleviation of fretting fatigue that may be afforded by this means.
Linear and Non-Linear Simulations of the Wake-Bubble Interaction and the Generated Surface Pressure Fluctuations on High Lift Turbine Profiles
Authors: Antoranz Antonio , de la Calzada Pedro
Published: November 2008

Results of a numerical investigation on the non-linear effects on the unsteady pressure fluctuations due to interaction between vorticity wakes and suction surface separation bubbles of high lift LPT profiles are presented. A comparison of the obtained predictions with both the non-linearised and linearised versions of an in-house CFD code (known as Mu2s2T and Mu2s2TL, respectively) for three different representative LPT profiles of Low Lift, High Lift and Ultra High Lift design are shown. Analysis of the unsteady pressure fluctuations resulting from the simulation shows that the interaction of a vorticity wake with an attached boundary layer may be considered linear and, hence, can be correctly predicted with a linearised CFD code. Nevertheless, the interaction between a vorticity wake and a closed suction surface bubble presents non-linear effects, and therefore, needs to be resolved with a non-linearised CFD code.
The Influence of Incidence Angle on the Discharge Coefficient for Rotating Radial Orifices
Authors: Idris A. , Pullen K. R. , Read R.
Published: November 2008

This paper describes an extensive experimental and computational investigation of the fluid flow in radial and radially inclined oriented rotating orifices. Such geometries frequently occur as part of the internal cooling system within gas turbine engines and can also be found in many classes of high speed machinery such as industrial compressors and high speed electrical machinery. The objective of the work was to enhance the understanding of the flows in such geometries and reliably establish discharge coefficients which can be used for air system design purposes. Publications in the area of rotating orifices are still sparse in comparison with other subjects although some important work has very recently been published for rotating orifices with axial orientation [1]. However, for radially or radially inclined orifices, there is close to nothing in the public domain. Although much of the understanding derived from the study of axially orientated orifices is relevant, the effect of change in radius is much more substantial, as significant Euler work transfer occurs. In many cases, there is a rise in static pressure as opposed to a reduction, normally associated with the flow through orifices. A rig was designed and built to perform the experiments and the results were compared with the numerical analysis performed using the proprietary software STAR-CD. The results indicate that the discharge coefficient is affected by the presence of the pumping effect from rotation of the orifice. This effect is more visible when the orifices are inclined towards the direction of rotation of the disc since the flow enters the orifice with reduced entry losses. To describe this phenomenon, the usual approach used in orifice flow theory is merged with the turbomachinery concepts, particularly through the Euler Turbomachine equation. A new theory for maximizing discharge coefficient based on the evaluation of the incidence angle has been developed and found to be successful. Most of the studies in the past used the ratio of tangential velocity and axial velocity as a parameter to represent the discharge coefficient, but it has been observed that using the incidence angle is more helpful in formulating discharge coefficient in rotating systems, especially when orifices with angle of inclination are to be treated. The results show that by having incidence angle at around zero degrees, the discharge coefficient for any combinations of flow and geometric parameters can be optimized.
Shop Testing of the W501FD Gas Turbine at the Berlin Test Facility
Authors: Veerappan Selvam , Chehab Abdullatif , Gravett Phillip , Bland Robert , Lechner Christof
Published: November 2008

This paper describes the successful full load shop testing of the W501FD 190 MW-class 60 Hz gas turbine engine at the Berlin Test Facility in Germany. A three phase test program aimed at verifying and optimizing new design concepts for improving fleet reliability, performance and operational flexibility is presented. The Berlin test facility set-up, capabilities for continuous full load testing and extensive test instrumentation used to monitor critical engine parameters are described. Some of the verification testing includes speed variation with load, performance and emissions testing to cover a wide range of operating conditions. Engine operation includes inlet guide vane changes, alternate loading rates, shutdown, spin cooling and restarts to verify transient clearance effects and their effects on performance. Vital instrumentation includes compressor and turbine tip clearances, fluid and metal temperature measurements for rotating and stationary components at key locations.
Experimental Study of the Flow and Thermal Development of a Row of Cooling Jets Impinging on a Rotating Concave Surface
Authors: Iacovides Hector , Kounadis Diamantis , Launder Brian E. , Li Jiankang , Xu Zeyuan
Published: November 2008

The paper reports an experimental study of impingement cooling in a rotating passage of semi-cylindrical cross-section. Cooling fluid is injected from a row of five jet holes along the centerline of the flat surface of the passage and strikes the concave surface. The cooling passage rotates orthogonally about an axis parallel to that of the jets. Tests have been carried out, using water, both within the passage and as the jet fluid, at a fixed Reynolds number of 15,000, for clockwise and anti-clockwise rotation. Local Nusselt number measurements, using the liquid-crystal technique, show that under stationary conditions a high Nusselt number region develops around each impingement point, with secondary peaks half-way between impingement points. Rotation reduces heat transfer, leads to the disappearance of all secondary peaks and also, surprisingly, of some of the primary peaks. Flow visualization tests suggest that these changes in thermal behavior are caused because rotation increase the spreading rate of the jets. LDA and PIV measurements are also presented. They show that under stationary conditions the five jets exhibit a similar behavior, with their cores remaining intact up to the point of impingement at the top dead center. The LDA and PIV studies help explain the rather surprising thermal behavior under rotating conditions.
Cooling the Tip of a Turbine Blade Using Pressure Side Holes: Part 2 — Heat Transfer Measurements
Authors: Christophel J. R. , Thole K. A. , Cunha F. J.
Published: November 2008

The clearance gap between a turbine blade tip and its associated shroud allows leakage flow across the tip gap from the pressure side to the suction side of the blade. Understanding how this leakage flow affects heat transfer is critical in extending blade tip durability in terms of oxidation, erosion, clearance, and overall turbine performance. This paper is the second of a two part series that discusses the augmentation of tip heat transfer as a result of blowing from the pressure side of the tip as well as dirt purge holes placed on the tip. For the experimental investigation, three scaled-up blades were used to form a two-passage linear cascade in a low speed wind tunnel. The rig was designed to simulate different tip gap sizes and coolant flow rates. Heat transfer coefficients were quantified by measuring the total power supplied to a constant heat flux surface placed on the tip of the blade and measuring the tip temperatures. Results indicate that increased blowing leads to increased augmentations in tip heat transfer, particularly at the entrance region to the gap. When combined with adiabatic effectiveness measurements, the coolant from the pressure side holes provides an overall net heat flux reduction to the blade tip but is nearly independent of coolant flow levels.
Experimental Measurements and Modeling of the Effects of Large-Scale Freestream Turbulence on Heat Transfer
Authors: Nix A. C. , Diller T. E. , Ng W. F.
Published: November 2008

The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. High intensity, large length-scale freestream turbulence was generated using a passive turbulence-generating grid to simulate the turbulence generated in modern combustors after passing through the first stage vane row. The grid produced freestream turbulence with intensity of approximately 10–12% and an integral length scale of 2 cm (Λx/c = 0.15) near the entrance of the cascade passages. Mean heat transfer results with high turbulence showed an increase in heat transfer coefficient over the baseline low turbulence case of approximately 8% on the suction surface of the blade, with increases on the pressure surface of approximately 17%. Time-resolved surface heat transfer and passage velocity measurements demonstrate strong coherence in velocity and heat flux at a frequency correlating with the most energetic eddies in the turbulence flow field (the integral length-scale). An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations and length-scale. The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane and turbine blade) and boundary layer conditions.
Development of Actual TBC Exposure Temperature Prediction Method
Authors: Morinaga Masahiko , Fujii Tomoharu , Takahashi Takeshi
Published: November 2008

Gas turbines are being operated at ever-higher temperatures in order to increase their efficiency. As a result, thermal barrier technology to protect the gas turbine hot gas path parts from high-temperature combustion gas is becoming increasingly important, making it necessary to evaluate the thermal barrier performance of the thermal barrier coating (TBC) coated on these gas turbine hot gas path parts. Thermal barrier performance of the TBC deteriorates with the number of operating hours of the gas turbine. The degradation of TBC thermal barrier performance raises substrate temperature, and this rise in substrate temperature reduces the remaining life of the substrate. We proposed an effective nondestructive inspection (NDI) method to evaluate the thermal barrier performance of the TBC by infrared transient heating of the TBC surface. The temperature behavior closely correlated with the thermal barrier performance of the TBC. The results of numerical analysis and laboratory tests showed that the proposed NDI method was effective for evaluating the thermal barrier performance of TBC. So we developed NDI apparatus to inspect the thermal barrier performance of actual combustion liner TBC. In this NDI apparatus, the surface of the TBC was heated using a CO2 laser, and the temperature of the heated surface measured using an infrared camera. The CO2 laser and infrared camera were fixed, while the measured combustion liner was traversed continuously. The NDI apparatus developed enabled us to inspect the whole inner surface of an actual gas turbine combustion liner. We also showed the correlation with thermal conductivity of a virgin TBC, thermal conductivity of an inspected TBC, operating hours and TBC exposure temperature in our TBC thermophysical property study. The combination of this method and the NDI apparatus developed proved an effective way of clarifying the operating temperature of the hot gas path parts of the gas turbine. In this paper, we show a method for predicting actual gas turbine TBC exposure temperature, important when evaluating the remaining life of gas turbine substrate by the NDI apparatus developed and method of predicting TBC exposure temperature.
Biomass Gasification Combined Cycle Thermodynamic Optimisation Using Integrated Drying
Authors: Boha`r-Nordenkampf Markus , Hofbauer Hermann
Published: November 2008

The conversion of solid fuels such as biomass into a combustible gas provides the opportunity to enhance the efficiency of biomass based power systems. It allows solid fuels to be used in high efficiency power generation processes such as Integrated Gasification Combined Cycle (IGCC). Using woody biomass with high water content without drying has negative effects on the overall efficiency of the process. The option of using dryer biomass is limited by the higher fuel costs. Drying with low temperature heat is the link between the usage of wet low price fuel and optimum process conditions. In this paper, the possibilities of integrating fuel drying into a pressurized IGCC process and the effects on the efficiencies are discussed. For this purpose, an equation oriented process simulation environment with a modular structure is used. Different dryer types are integrated into this tool. Several solutions for the implementation of a drying into an IGCC process are investigated using steam and exhaust gas as heat sources. The obtained results are analyzed by the means of an exergetic analysis. Finally an optimum concept with a high electrical efficiency was obtained which will also meet the environmental regulations. Integrating drying into a biomass based IGGC concept can be an essential step for the economic operation of a plant.
Characterization of Turbine Blade Friction Dampers
Authors: Koh K.-H. , Griffin J. H. , Filippi S. , Akay A.
Published: November 2008

This paper discusses approach for characterizing the dynamic behavior of a friction damper. To accomplish this, the deflection of the damper is measured as a function of an applied force for a range of amplitudes, normal loads, and excitation frequencies. The resulting hysteresis curves are used to generate curves of nonlinear stiffness and damping as a function of the amplitude of motion. A method of presenting this information in a dimensionless format is demonstrated. This format allows direct comparisons of the nonlinear stiffness and damping of actual dampers with that often used in analytical models to compute the dynamic response of frictionally damped turbine blades. It is shown that for the case of a damper with a spherical head significant differences exist between the actual behavior of the damper and that often assumed in simple analytical models. In addition, Mindlin’s analysis of a sphere on a half space is used to estimate the damper’s stiffness as well as its theoretical hysteresis curves. The hysteresis curves are then used to determine dimensionless stiffness and damping curves. The results compare favorably with those found experimentally.
Sensitivity of Tuned Bladed Disk Response to Frequency Veering
Authors: Kenyon J. A. , Griffin J. H. , Kim N. E.
Published: November 2008

A continuous method is presented for representing the mode interaction that occurs in frequency veering in terms of the nominal sector modes of a cyclic symmetric bladed disk model constrained at a fixed reference interblade phase angle. Using this method, the effect of frequency veering on the mode shapes can be considered in the context of the generalized forces exciting the system and the modal response of the bladed disk. It is shown that in a blade-dominated family of modes, the transfer of modal energy to the disk in the veering results in a lower generalized force exciting the mode as well as reduced response amplitude in the blade. For the disk-dominated modes, the sharing of modal energy with the blades can lead to the disk being excited by aerodynamic loading. These effects can have important implications for predicting and interpreting forced response in bladed disks. Numerical examples are provided to illustrate these concepts.
Comparison of CFD and PIV Data for the Airflow in an Aero-Engine Bearing Chamber
Authors: Lee C. W. , Palma P. C. , Simmons K. , Pickering S. J.
Published: November 2008

Investigations into the single-phase velocity field of a model aero-engine bearing chamber are presented. Adequately resolving the airflow field is important to subsequent computational modelling of two-phase fluid transport and heat transfer characteristics. A specially designed test rig, representing the features of a Rolls-Royce Trent series aero-engine bearing chamber, was constructed. Experimental data for the airflow field was obtained using particle image velocimetry (PIV). The results show a strong influence of shaft rotation and chamber geometry on the flow features within the bearing chamber. A computational fluid dynamics (CFD) simulation was carried out using the commercial CFD code FLUENT 6. Flow features were adequately modelled, showing the features of secondary velocities. Turbulence modelling using the differential Reynolds stress (RSM) model shows good agreement with the experimental data.
Early Stall Warning Technique for Axial Flow Compressors
Authors: Tahara Nobuyuki , Kurosaki Masahiro , Ohta Yutaka , Outa Eisuke , Nakakita Tomofumi , Tsurumi Yuki
Published: November 2008

This paper proposes a unique stall warning index based on pressure signals by high response transducers on the casing wall at the rotor leading edge location. The aim of the research is to explore the possibility of reducing current excessive stall margin requirement for compressor design based on the worst case scenario. The index is generated by computing correlation degradation of pressure time histories of current and one revolution before over each blade pitch. Tests conducted on a research compressor exhibits that the correlation diminishes significantly with proximity to stall and the proposed technique might have the capability of generating a stall warning signal sufficiently in advance of spike inception. Extensive experiments on a research compressor show that the degree of the index degradation depends on various factors such as flow coefficient, tip clearance and rotor blade incidence. In order to obtain a reliable stall warning signal in practical use, these effects must be carefully examined.