bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Non-Uniform Inlet Conditions on Endwall Secondary Flows
Authors: Hermanson K. S. , Thole K. A.
Published: February 2009

Exit combustor flow and thermal fields entering downstream stator vane passages in a gas turbine engine are highly non-uniform. These flow and thermal fields can significantly affect the development of the secondary flows in the turbine passages contributing to high platform heat transfer and large aerodynamic losses. The flow and thermal fields combine to give non-uniform total pressure profiles entering the turbine passage which, along with the airfoil geometry, dictate the secondary flow field. This paper presents an analysis of the effects of varying total pressure profiles in both the radial and combined radial and circumferential directions on the secondary flow fields in a first stage stator vane. These inlet conditions used for the first vane simulations are based on the exit conditions predicted for a combustor. Prior to using the predictions, these CFD simulations were benchmarked against flow field data measured in a large-scale, linear, turbine vane cascade. Good agreement occurred between the computational predictions and experimentally measured secondary flows. Analyses of the results for several different cases indicate variations in the secondary flow pattern from pitch to pitch, which attributes to the rationale as to why some airfoils quickly degrade while others remain intact over time.
Experimentally Aided Development of a Turbine Heat Transfer Prediction Method
Authors: Forest A. E. , Rawlinson A. J. , Lai C. C. , Guo S. M. , Oldfield M. L. G. , Lock G. D.
Published: February 2009

In the design of cooled turbomachinery blading a central role is played by the computer methods used to optimize the aerodynamic and thermal performance of the turbine aerofoils. It is particularly important that estimates of the heat load on the turbine blading should be as accurate as possible, in order that adequate life may be obtained with the minimum cooling air requirement. Computer methods are required which are able to model transonic flows, which are a mixture of high temperature combustion gases and relatively low temperature cooling air injected through holes in the aerofoil surface. These holes may be of complex geometry, devised after empirical studies of the optimum shape and the most cost effective manufacturing technology. The method used here is a further development of the Heat Transfer Design Code (HTDC), originally written by Rolls-Royce plc under subcontract to Rolls-Royce Inc for the United States Air Force. The physical principles of the modeling employed in the code are explained without extensive mathematical details. The paper describes the calibration and development of the code in conjunction with a series of experimental measurements on a scale model of a high-pressure nozzle guide vane at non-dimensionally correct engine conditions.
Heat Transfer, Fluid Flow, and Pressure Measurements Inside a Rotating Two-Pass Duct With Detached 90° Ribs
Authors: Liou Tong-Miin , Chen Meng-Yu , Wang Yu-Ming
Published: February 2009

Transient thermochromic liquid crystal thermography, a laser-Doppler velocimeter, and pressure transducers have been used to measure the local heat transfer, velocity, and wall static-pressure distributions, respectively, in a rotating two-pass square duct with 90° ribs detached from the leading and trailing walls. The ribs were square in cross-section and their detached-distance/height ratio was 0.38. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number ranged from 0 to 0.2. Results are compared with attached rib cases in terms of regional averaged Nusselt number, transverse mean velocity component, pressure coefficient distributions and variation of friction factor with rotation number. The competition between convection effect of the wall jet and downwash effect of the rib-top separated shear layer on the heat transfer augmentation is addressed in detail. Discussion on local Nusselt number distribution, mean velocity components, and turbulent kinetic energy is included. Simple expressions are obtained to correlate friction factor with rotation number. Rib detachment is found to enhance heat transfer on the leading wall of the first outward pass and on the trailing wall of the second inward pass over as compared to the attached rib case. The trend is reversed on the other two walls. Nevertheless, detached ribs create more uniform heat transfer distributions on the leading and trailing walls than attached ribs.
Heat Transfer in a Complex Trailing Edge Passage for a High Pressure Turbine Blade: Part 2 — Simulation Results
Authors: Rigby David L. , Bunker Ronald S.
Published: February 2009

A combined experimental and numerical study to investigate the heat transfer distribution in a complex blade trailing edge passage was conducted. The geometry consists of a two pass serpentine passage with taper toward the trailing edge, as well as from hub to tip. The upflow channel has an average aspect ratio of roughly 14:1, while the exit passage aspect ratio is about 5:1. The upflow channel is split in an interrupted way and is smooth on the trailing edge side of the split and turbulated on the other side. A turning vane is placed near the tip of the upflow channel. Reynolds numbers in the range of 31,000 to 61,000, based on inlet conditions were simulated numerically. The simulation was performed using the Glenn-HT code, a full three-dimensional Navier-Stokes solver using the Wilcox k-ω turbulence model. A structured multi-block grid is used with approximately 4.5 million cells, and average y+ values on the order of unity. Pressure and heat transfer distributions are presented with comparison to the experimental data. While there are some regions with discrepancies, in general the agreement is very good for both pressure and heat transfer.
Studies on a Blade Leading Edge Separation Bubble Affected by Periodic Wakes: Its Transitional Behavior and Boundary Layer Loss Reduction
Authors: Funazaki K. , Kato Y.
Published: February 2009

This study deals with extensive hot-wire probe measurements of wake-affected separation bubble on the leading edge of a test model. The purpose of the study is to investigate time-resolved response of the separation bubble to incoming wake passing. Another focus is placed on the wake effect on aerodynamic loss generated in the separated boundary layer, seeking any relationship between the suppression of the separation bubble on a cascade airfoil and aerodynamic gain due to the clocking in turbomachines. The test model has a semicircular leading edge and two flat-plates. Incoming wakes are generated by circular cylinders which are horizontally fixed in the wake generator. Several types of wake generating cylinders are used in order to change wake properties. The hot-wire measurements have revealed the time-resolved responses of the separated boundary layer to the wake passage. Effects of calmed regions just behind the moving wakes are also identified.
On the Spreading Angle of Turbulent Spots in Non-Isothermal Boundary Layers With Favourable Pressure Gradients
Authors: Zhong S. , Chong T. P. , Hodson H. P.
Published: February 2009

Turbulent spots created artificially in a flat plate boundary layer were visualized using both shear-sensitive and temperature-sensitive liquid crystals for the first time. The experiments were carried out at three different levels of favourable pressure gradients. The purpose of this investigation was to examine the spreading angles of the turbulent spots indicated by their associated surface shear stresses and heat transfer characteristics and hence obtain further insight about the difference in the behaviour of transitional momentum and thermal boundary layers when a streamwise pressure gradient is present. It was shown that under a zero pressure gradient the spreading angles indicated by the two types of liquid crystals are the same, but the difference increases as the level of favourable pressure gradient increases. The result from the present study could have an important implication for the transition modelling of thermal boundary layers over gas turbine blades. Further investigations are to be carried out.
Influence of the Reference State in the SLW Model for Flows With Strong Temperature and Pressure Gradients
Authors: Badinand T. , Fransson T. H.
Published: February 2009

Radiative heat transfer in a real case showing high temperature and pressure gradients is calculated with a global model (SLW) with and without re-scaling of the absorption coefficients to the local conditions. Changes in radiative heat flux to the walls for different reference temperatures and reference pressures are studied. Changes in reference pressure are shown to have a small influence compared to changes in reference temperature, except if the pressure is less than 10 bars for a high-pressure case. The use of the scaling does decrease the dependency on the reference condition. The highest differences obtained with strong reference temperature or pressure changes (800K and 30.105 Pa) are of about 15% and 7% respectively. For smaller changes, an uncertainty of 5% could be assumed.
Calculation of Surface Roughness Effects on Air-Riding Seals
Authors: Guardino C. , Chew J. W. , Hills N. J.
Published: February 2009

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh-pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various 2D or 3D roughness patterns on the stationary wall. A ‘unit-based’ approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.
Design Considerations for Combined Cycle Plants for the Deregulated Market: An EPC Contractor’s Perspective
Authors: Narula Ram G. , Massy Martin , Singh Jyoti
Published: February 2009

Deregulation of the power industry in Europe and the attendant pressures to innovate have led to new approaches to financing and construction of power plants. This paper discusses the salient design, procurement, and project execution considerations of a combined cycle (CC) plant for a deregulated market.
Compressor Fouling Testing on Rolls Royce/Allison 501-K17 and General Electric LM2500 Gas Turbine Engines
Authors: Caguiat Daniel E. , Zipkin David M. , Patterson Jeffrey S.
Published: February 2009

As part of the Gas Turbine Condition Based Maintenance (CBM) Program, Naval Surface Warfare Center, Carderock Division Code 9334 conducted compressor fouling testing on the General Electric LM2500 and Rolls Royce/Allison 501-K Series gas turbines. The objective of these tests was to determine the feasibility of quantifying compressor performance degradation using existing and/or added engine sensors. The end goal of these tests will be to implement an algorithm in the Navy Fleet that will determine the optimum time to detergent crank wash each gas turbine based upon compressor health, fuel economy and other factors which must be determined. Fouling tests were conducted at the Land Based Engineering Site (LBES). For each gas turbine, the test plan that was utilized consisted of injecting a salt solution into the gas turbine inlet, gathering compressor performance and fuel economy data, analyzing the data to verify sensor trends, and assessing the usefulness of each parameter in determining compressor and overall gas turbine health. Based upon data collected during these fouling tests, it seems feasible to accomplish the end goal. Impact Technologies, who analyzed the data sets for both of these fouling tests, has developed a prognostic modeling approach for each of these gas turbines using a combination of the data and probabilistic analysis.
U.S. Navy Development of Air Assist Fuel Nozzle System for the 501K Series Gas Turbine Engines
Authors: Hoffman Matthew G. , DeCorso Richard J. , Russom Dennis M.
Published: February 2009

The U.S. Navy has experienced problems with liquid fuel nozzles used on the Rolls Royce (formerly Allison) 501K series marine gas turbine engines. The 501K engines used by the U.S. Navy power Ship Service Gas Turbine Generators (SSGTGs) on a number of destroyer and cruiser class ships. Over roughly the last 25 years, 3 different nozzle designs have been employed, the latest and current nozzle being a piloted air blast design. The primary failure modes of these designs were internal fuel passage coking and external carbon deposits. The current piloted air blast design has a hard time replacement requirement of 1500 hours. This life is considered unacceptable. To improve fuel nozzle life, the Navy and Turbine Fuel Technologies (formerly Delavan) teamed in a fast track program to develop a new fuel nozzle with a target life of 5000 hours and 500 starts. As a result, an air assist/air blast nozzle was developed and delivered in approximately 6 months. In addition to the nozzle itself, a system was developed to provide assist air to the fuel nozzles to help atomize the fuel for better ignition. Nozzle sets and air assist systems have been delivered and tested at the NSWC Philadelphia LBES (Land Based Engineering Site). In addition, nozzle sets have been installed aboard operating ships for in-service evaluations. During the Phase one evaluation (July 2000 to June 2001) aboard USS Porter (DDG 78) a set of nozzles accumulated over 3500 hours of trouble free operation, indicating the target of 5000 hours is achievable. As of this writing these nozzles have in excess of 5700 hours. The improvements in nozzle life provided by the new fuel nozzle design will result in cost savings through out the life cycle of the GTGS. In fact, the evaluation nozzles are already improving engine operation and reliability even before the nozzles’ official fleet introduction. This paper describes the fuel nozzle and air assist system development program and results of OEM, LBES and fleet testing.
Ten Years of DLE Industrial Gas Turbine Operating Experiences
Authors: Cowell Luke , Etheridge Colin , Smith Ken
Published: February 2009

Industrial gas turbine manufacturers began offering engines configured with dry low emissions (DLE) control in 1992. In the past ten years the performance and emissions reductions have been well demonstrated by DLE equipment. To date DLE gas turbines have relied on lean premixed combustion technology to achieve emissions reductions of 8 to 10 fold from “conventional” diffusion flame engines. The significant new content incorporated for DLE combustion systems has required industrial gas turbine manufacturers and users to work with greater synergy to overcome significant challenges. As evidence of this ultimately successful integration, DLE gas turbines are now as common in service as conventional diffusion flame engines. With thousands of DLE units sold one would expect that DLE gas turbines are now a mature product. In many aspects, this is true. However, emissions regulations and other market drivers have continued to change, forcing DLE equipment to continually evolve. A Solar history of DLE gas turbine developments, capabilities, and experiences are provided to give operators background and knowledge to reduce field issues and maximize availability of their DLE gas turbines. Design limitations and problems encountered in the field are discussed along with the steps that were taken to resolve them. Recommendations on DLE engine operation to avoid unscheduled downtime are presented. Design improvements to reduce emissions further and improve system flexibility are summarized.
Acceptance Criteria for Gas Compression Systems
Authors: Kurz R. , Fozi A. A.
Published: February 2009

Gas compression systems consist of a number of turbo machinery components: A Gas Turbine consisting of a gas producer turbine, and a power turbine; one or several gas compressors or gas compressor sections; and possibly a gearbox. The end-user usually defines very specific operating conditions. However, the acceptance testing is often performed on the individual components rather than the overall system. Intuitively, one would rather expect criteria that are based on the overall system operation. This paper suggests a different approach of defining the acceptance criteria, such that it is based on the performance of the overall system and thus ties the acceptance criteria to the operational goals of the installation. The review also includes comments on some mechanical aspects of factory and field-testing of turbomachinery. Because the above approach involves the entire system, the verification of the acceptance criteria needs to be addressed. It is therefore described how the overall system performance can be verified, even if the operating conditions during the test are different from the specified acceptance conditions. The advantage of this approach is that it avoids over-specifying equipment due to adding tolerances upon tolerances, while at the same time specifying what really counts for the operational success of the project.
A Study of the Influence of Static Eccentricity and Unbalance on Cavitation Effects in a Squeeze Film Damped Flexible Rotor
Authors: Bonello Philip , Brennan Michael J. , Holmes Roy
Published: February 2009

The study of eccentric squeeze film damped rotor dynamic systems has largely concentrated on rigid rotors. In this paper, a newly developed receptance harmonic balance method is used to efficiently analyze a squeeze film damped flexible rotor test rig. The aim of the study is to investigate the influence of damper static eccentricity and unbalance level on cavitation and its resulting effect on the vibration level. By comparing predictions for the rotor vibration levels obtained respectively with, and without, lower pressure limits for the eccentric squeeze film damper model, it is demonstrated that cavitation is promoted by increasing static eccentricity and/or unbalance level. This, in turn, is found to have a profound effect on the predictions for the critical vibration levels, which such dampers are designed to attenuate. The reported findings are backed by experimental evidence from the test rig.
On the Control of Synchronous Vibration in Rotor/Magnetic Bearing Systems Involving Auxiliary Bearing Contact
Authors: Keogh Patrick , Cole Matthew , Sahinkaya Necip , Burrows Clifford
Published: February 2009

During the normal operation of rotor/magnetic bearing systems, contacts with auxiliary bearings or bushes are avoided. However, auxiliary bearings are required under abnormal conditions and in malfunctions situations to prevent contact between the rotor and stator laminations. Studies in the open literature deal largely with rotor drop and the requirements of auxiliary bearing design parameters for safe run-down. Rotor drop occurs when the rotor is de-levitated and no further means of magnetic bearing control is available. This paper considers the case when full control is still available and rotor/auxiliary bearing contact has been induced by an abnormal operating condition or temporary fault. It is demonstrated that events leading to contact from a linearly stable rotor orbit can drive the rotor into a non-linear vibratory motion involving persistent contacts. Furthermore, the phase of the measured vibration response may be changed to such an extent that synchronous controllers designed to minimize rotor vibration amplitudes will worsen the rotor response, resulting in higher contact forces. A modified controller design is proposed and demonstrated to be capable of returning a rotor from a contacting to a non-contacting state.
Analytical Method of Fatigue Damage Estimation for Compressor Stator Blades of Gas Turbines Experiencing Rotating Stall
Authors: Hayasaka Yasushi , Sakurai Shigeo , Kudo Takeshi , Ichikawa Kunihiro
Published: February 2009

To improve the reliability of compressor stator blades of gas turbines, an analytical method for estimating their fatigue damage has been developed. This method is based on blade-vibratory-stress analysis, stress-peak counting, and use of actual environmental data. The blade-vibratory-stress analysis takes the superposition of multi-peaks of the stress spectrum into account. The numerically simulated stress showed better agreement with measured stress than that from a conventional stress analysis, which is based on frequency-response analysis considering a single peak of the lowest single eigen-vibration-mode. A time-domain stress history was synthesized from the blade-vibratory-stress analysis results. Furthermore, the fatigue damage of the blade under rotating stall was estimated by the linear-damage-rule from the stress-peak counting of the stress and from material data. The estimated fatigue-damage agrees well with the measured results. This agreement means that our new fatigue-damage-estimation method is more accurate than the conventional one.
Critical Plane Fatigue Modeling and Characterization of Single Crystal Nickel Superalloys
Authors: Naik Rajiv A. , DeLuca Daniel P. , Shah Dilip M.
Published: February 2009

Single crystal nickel-base superalloys deform by shearing along <111> planes, sometimes referred to as “octahedral” slip planes. Under fatigue loading, cyclic stress produces alternating slip reversals on the critical slip systems which eventually results in fatigue crack initiation along the ‘critical’ octahedral planes. A ‘critical plane’ fatigue modeling approach was developed in the present study to analyze high cycle fatigue (HCF) failures in single crystal materials. This approach accounted for the effects of crystal orientation and the micromechanics of the deformation and slip mechanisms observed in single crystal materials. Three-dimensional (3-D) stress and strain transformation equations were developed to determine stresses and strains along the crystallographic octahedral planes and corresponding slip systems. These stresses and strains were then used to calculate several multiaxial critical plane parameters to determine the amount of fatigue damage and also the ‘critical planes’ along which HCF failures would initiate. The computed fatigue damage parameters were used along with experimentally measured fatigue lives, at 1100° F, to correlate the data for different loading orientations. Microscopic observations of the fracture surfaces were used to determine the actual octahedral plane (or facet) on which fatigue initiation occurred. X-ray diffraction measurements were then used to uniquely identify this damage initiation facet with respect to the crystal orientation in each specimen. These experimentally determined HCF initiation planes were compared with the analytically predicted ‘critical planes’.
Forward Swept Rotor Studies in Multistage Fans With Inlet Distortion
Authors: Wadia A. R. , Szucs P. N. , Crall D. W. , Rabe D. C.
Published: February 2009

Previous experimental and analytical studies conducted to compare the performance of transonic swept rotors in single stage fans have demonstrated the potential of significant improvements in both efficiency and stall margin with forward swept blading. This paper extends the assessment of the payoff derived from forward sweep with respect to aerodynamic performance and stability to multistage configurations. The experimental investigation compares, on a back-to-back test basis, two builds of an advanced good efficiency, high pressure ratio, two-stage fan configuration tested alternately with a radial and a forward swept stage 1 blade. In the two-stage evaluations, the testing was extended to include the effect on inlet flow distortion. While the common second stage among the two builds prevented the overall fan from showing clean inlet performance and stability benefits with the forward swept rotor 1, this configuration did demonstrate superior front stage efficiency and tolerance to inlet distortion. Having obtained an already low distortion sensitivity with the radial rotor 1 configuration relative to current production military fan standards, the sensitivity to inlet distortion was halved with the forward swept rotor 1 configuration. In the case of the 180-degree one-per-rev distortion pattern, the two-stage configuration was evaluated both with and without inlet guide vanes (IGVs). The presence of the inlet guide vanes had a profound impact in lowering the two stage fan’s sensitivity with inlet distortion.
Experimental Investigation of an Innovative Cooling System (ICS) for High Temperature Transonic Turbine Stages
Authors: Go¨ttlich E. , Lang H. , Sanz W. , Woisetschla¨ger J.
Published: February 2009

Gas turbine design technology requires the development of transonic turbine stages capable of carrying high stage load and of handling hot gas temperatures at turbine inlet. A reliable cooling system is necessary to cope with the shock system in the main flow field especially in the leading edge region of the rotor blades. These requirements are fulfilled by the Innovative Cooling System (ICS) developed at the Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology. The ICS is also able to cover large areas of the blade surface with an effective cooling film and to reduce the metal temperature. In this paper the authors present results on the flow measurements giving the aerodynamic behavior of these cooling films and on the investigation of their cooling effectiveness. The measurements were done on an industrial turbine blade in a linear cascade arrangement. In addition to conventional measurement methods optical methods (Schlieren visualization, Laser Doppler Velocimetry) were employed to investigate and visualize the transonic flow through the linear blade cascade. An infrared (IR) camera system was used to determine the effectiveness of this newly designed cooling system by measuring the temperature distribution on the blade surface. Experimental results concerning aerodynamic flow behavior and cooling effectiveness are presented.
Unsteady Interaction Between a Transonic Turbine Stage and Downstream Components
Authors: Davis Roger L. , Yao Jixian , Clark John P. , Stetson Gary , Alonso Juan J. , Jameson Antony , Haldeman Charles W. , Dunn Michael G.
Published: February 2009

Results from a numerical simulation of the unsteady flow through one quarter of the circumference of a transonic high-pressure turbine stage, transition duct, and low-pressure turbine first vane are presented and compared with experimental data. Analysis of the unsteady pressure field resulting from the simulation shows the effects of not only the rotor/stator interaction of the high-pressure turbine stage but also new details of the interaction between the blade and the downstream transition duct and low-pressure turbine vane. Blade trailing edge shocks propagate downstream, strike, and reflect off of the transition duct hub and/or downstream vane leading to high unsteady pressure on these downstream components. The reflection of these shocks from the downstream components back into the blade itself has also been found to increase the level of unsteady pressure fluctuations on the uncovered portion of the blade suction surface. In addition, the blade tip vortex has been found to have a moderately strong interaction with the downstream vane even with the considerable axial spacing between the two blade-rows. Fourier decomposition of the unsteady surface pressure of the blade and downstream low-pressure turbine vane shows the magnitude of the various frequencies contributing to the unsteady loads. Detailed comparisons between the computed unsteady surface pressure spectrum and the experimental data are shown along with a discussion of the various interaction mechanisms between the blade, transition duct, and downstream vane. These comparisons show overall good agreement between the simulation and experimental data and identify areas where further improvements in modeling are needed.
Experimental Investigation and Characterization of the Rotating Stall in a High Pressure Centrifugal Compressor: Part I — Influence of Diffuser Geometry on Stall Inception
Authors: Ferrara G. , Ferrari L. , Mengoni C. P. , De Lucia M. , Baldassarre L.
Published: February 2009

Extensive research on centrifugal compressors has been planned to define diffuser stall limits for a group of stages characterized by low blade-outlet-width-to-impeller-radius-ratio. Very little data is available on this centrifugal compressor family, especially for the last stage configuration. In addition, the most important stall diffuser prediction criteria barely cover this machine type. Many experimental tests have been planned to investigate several geometry variations. A simulated stage with a backward channel upstream, a 2D impeller with a vaneless diffuser and a constant cross section volute downstream constitute the basic geometry. Several diffuser geometries with different widths, pinch shapes, diffusion ratios were tested. Test results and conclusions are shown in the paper in terms of critical diffuser inlet flow angles, flow coefficients at stall inception and stage working ranges. The main task of the present work is to increase the knowledge and the amount of available data to characterize rotating stall phenomena, in particular for very narrow stages.
Experimental Investigation and Characterization of the Rotating Stall in a High Pressure Centrifugal Compressor: Part II — Influence of Diffuser Geometry on Stage Performance
Authors: Ferrara G. , Ferrari L. , Mengoni C. P. , De Lucia M. , Baldassarre L.
Published: February 2009

Extensive research on centrifugal compressors has been planned. The main task of the research is to improve present prediction criteria coming from the literature with particular attention to low flow coefficient impellers (low width to radius ratios) where they are no more valid. Very little data has been published for this kind of stages, especially for the last stage configuration (with discharge volute). Many experimental tests have been planned to investigate different configurations. A simulated stage with a backward channel upstream, a 2D impeller with a vaneless diffuser and a constant cross section volute downstream constitute the basic configuration. Several diffuser types with different widths, pinch shapes and diffusion ratios were tested. The effect of geometric parameters on stage stability has been discussed inside part I of the present work; the purpose of this part of the work is to illustrate the effect of the same geometric parameters on stage performance and to quantify the impact of stability improvements on stage losses.
High Performance and Cost Effective Recuperator for Micro-Gas Turbines
Authors: Lagerstro¨m Gunnar , Xie Max
Published: February 2009

Rekuperator Svenska AB owned by VOLVO Technology Transfer Corporation and Avesta Polarit, has successfully developed a completely laser welded recuperator for micro-gas turbine applications. Tests have shown that the thermal performance is very competitive. The recuperator was installed in a 100 kW(e) micro-gas turbine power plant for combined electricity and heat generation by a customer. The recuperator is a primary surface counter flow heat exchanger with cross corrugated duct configuration. The primary heat transfer surface plate patterns are stamped and a pair of the plates are laser welded to form an air cell. The air cells are then stacked and laser welded together to form the recuperator core which is tied between two end beams. Manifolds for air inlet and outlet as well as piping system are welded to the core. Through varying the number of air cells the recuperator core can easily be adapted for micro-gas turbine applications with different output rates of electrical power. The key manufacturing technologies are stamping of the air cell plates and laser welding of the air cells. These processes can be fully automated for mass production at low costs.
Some Unconventional Aero Gas Turbines Using Hydrogen Fuel
Authors: Boggia Stefano , Jackson Anthony
Published: February 2009

The use of hydrogen as an aviation fuel can be beneficial for the reduction of CO2 emissions, if renewable energy sources are used for hydrogen production. Pure hydrogen fuel produces no CO2 in flight. NOx emissions can be significantly lower for hydrogen fuelled combustors than for current kerosene fuelled combustors. Other advantages derive from the high energy content, which reduces the necessary fuel mass, and from the availability of a valuable heat sink, useful to improve cycle performance. The present paper (based on the EU Cryoplane Project) focuses on the use of hydrogen in aero gas turbine engines. It studies the differences in performance produced by of its cryogenic properties in unconventional cycles. Three novel concepts are applied to a turbofan aero engine; for each cycle the improvement in performance at take-off and cruise is presented. An estimation of the weight and size of the engine is then made.
A Numerical Investigation on the Influence of Lateral Boundaries in Linear Vibrating Cascades
Authors: Corral Roque , Gisbert Fernando
Published: February 2009

The effect of the finite extent of linear cascades on the unsteady pressure distribution of vibrating blades is assessed by means of a numerical study. The span of a reference cascade made up of flat plates has been changed to investigate its influence on the computed influence coefficients. It is concluded that the number of passages required to match a solution obtained with a traveling-wave mode strongly depends on the inter-blade phase angle under consideration and that existing linear vibrating cascade facilities have a marginal resolution to accurately match CFD analysis that assume that the blade is vibrating in a traveling-wave mode.
Characterization of Ceramic Matrix Composite Fasteners Exposed in a Combustor Liner Rig Test
Authors: Verrilli Michael , Brewer David
Published: February 2009

Combustion tests on SiC/SiC CMC components were performed in an aircraft combustion environment using the Rich-burn, Quick-quench, Lean-burn (RQL) sector rig. SiC/SiC fasteners were used to attach several of these components to the metallic rig structure. The effect of combustion exposure on the fastener material was characterized via microstructural examination. Fasteners were also destructively tested, after combustion exposure, and the failure loads of fasteners exposed in the sector rig were compared to those of as-manufactured fasteners. Combustion exposure reduced the average fastener failure load by 50% relative to the as-manufactured fasteners for exposure times ranging from 50 to 260 hours. The fasteners exposed in the combustion environment demonstrated failure loads that varied with failure mode. Fasteners that had the highest average failure load, failed in the same manner as the unexposed fasteners.
Multi-Swirler Aerodynamics: Comparison of Different Configurations
Authors: Cai J. , Jeng S.-M. , Tacina R.
Published: February 2009

The non-reacting fluid flow fields generated by multi-swirler arrays with two different port configurations were investigated experimentally. These two cases include a co-swirling array, where all swirlers act in the same direction, and a counter-swirling array, where all swirlers alternate between clockwise and counter-clockwise rotations. Each configuration consists of a three by three arrangement of swirlers, which use analogous geometries to generate the swirling flows, i.e. eight discrete jets. For each array, the mean and turbulence velocities were measured at approximately 25,000 discrete spatial locations by a two-component LDV system. Furthermore, the third velocity component was derived based on the symmetric geometry of the arrays. In both cases, the coalescence distance, distance for eight discrete jet streams to form uniform swirling flows, is very short; and each swirler within the arrangement possesses a central recirculation zone. These nine zones have varying strengths depending on the individual swirler location, and some rotate with the swirler direction. In comparison, the co-swirler configuration provides a large unified rotational flow in the same direction as the individual swirlers, while a counter-rotating flow pattern is formed by the other case. Lastly, interactions between the unified flow with that of each swirler in the array are discussed and further comparisons are made between the two cases.
Film Cooling on a Modern HP Turbine Blade: Part I — Experimental and Computational Methodology and Validation
Authors: Buck Frederick A. , Walters D. Keith , Ferguson Jeffrey D. , McGrath E. Lee , Leylek James H.
Published: February 2009

State-of-the-art experimental and computational techniques are used to study film cooling on the suction and pressure surfaces of a modern turbine blade under realistic engine conditions. Measured data and predicted results are compared for coolant jets injected through a row of three fundamentally different configurations: (1) Compound-angle round (CAR) holes; (2) Axial shaped holes (ASH); and (3) Compound-angle shaped holes (CASH). Experiments employ a single-passage cascade for validation-quality adiabatic film effectiveness measurements using a gas analysis technique. Computations use a novel combination of geometry and grid generation techniques, discretization scheme, turbulence modeling, and numerical solvers to evaluate a “best practice” standard for use in the gas turbine industry. The gridding procedure uses a super-block, multi-topology, unstructured/adaptive, non-conformal, near-wall resolved mesh to accurately capture all of the mean flow features of the 3-D jet-in-crossflow interaction. The effects of blowing ratio (M) are examined, with M = 1.0, 1.5, and 2.0 on the suction surface and M = 1.5, 3.0, and 4.5 on the pressure surface. All simulations are run with a density ratio of 1.52. The simulations model the three-way coupling between a transonic blade passage flow, subsonic film-hole flow, and creeping plenum flow; high pressure gradients; high rates of curvature; and large strain-rates found in actual engines. Computed results are compared to experimental data in terms of aerodynamic loading and spanwise-averaged adiabatic effectiveness on the blade surfaces in order to validate the computational methodology for this class of problems and to explain the mechanisms responsible for the performance of CAR, ASH, and CASH configurations.
Mist/Steam Heat Transfer With Jet Impingement Onto a Concave Surface
Authors: Li Xianchang , Gaddis J. Leo , Wang Ting
Published: February 2009

Internal mist/steam blade cooling technology has been considered for the future generation of Advanced Turbine Systems (ATS). Fine water droplets about 5 μm were carried by steam through a single slot jet onto a concave heated target surface in a confined channel to simulate inner surface cooling at the leading edge of a turbine blade. Experiments covered Reynolds numbers from 7,500 to 22,000 and heat fluxes from 3 to 21 kW/m2. The general level of heat transfer coefficient is, within experimental uncertainty, the same as the flat surface at comparable conditions. The experimental results indicate that the cooling is enhanced significantly near the stagnation point by the mist, decreasing downstream. Unlike impingement onto a flat plate the enhancement continues at all points downstream. Similar to the results of the flat surface, the heat transfer enhancement declines at higher heat fluxes. Up to 200% heat transfer enhancement at the stagnation point was achieved by injecting approximately 0.5% of mist.
Experimental Racetrack Shaped Jet Impingement on a Roughened Leading-Edge Wall With Film Holes
Authors: Taslim M. E. , Pan Y. , Bakhtari K.
Published: February 2009

Compatible with the external contour of the turbine airfoils at their leading edge, the leading-edge cooling cavities have a complex cross-sectional shape. To enhance the heat transfer coefficient on the leading-edge wall of these cavities, the cooling flow in some designs enters the leading-edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. The crossover jets then impinge on the concave leading-edge wall and exit through the showerhead film holes, gill film holes on the pressure and suction sides, and, in some cases, form a crossflow in the leading-edge cavity and move toward the airfoil tip. The main objective of this investigation was to study the effects that racetrack crossover jets, in the presence of film holes on the target surface, have on the impingement heat transfer coefficient. Available data in open literature are mostly for impingement on a flat smooth surface with no representation of the film holes. This investigation covered new features in airfoil leading-edge cooling concept such as impingement with racetrack shaped holes on a roughened target surface with a row of holes representing the leading-edge showerhead film holes. Results of the circular crossover jets impinging on these leading-edge surface geometries with and without showerhead holes were reported by these authors previously. In this paper, however, the experimental results are presented for the impingement of racetrack-shaped crossover jets on a concave surface with showerhead film holes. The investigated target surface geometries were : (1) a smooth wall, (2) a wall roughened with big conical bumps, (3) a wall roughened with smaller conical bumps and (4) a wall roughened with tapered radial ribs. The tests were run for a range of flow arrangements and jet Reynolds numbers and the results were compared with those of round crossover jets. The major conclusions of this study are: (a) for a given jet Reynolds number, the racetrack crossover jets produce a higher impingement heat transfer coefficient than the circular jets, (b) the overall heat transfer performance of 0° racetrack crossover jets is superior to that of 45° racetrack crossover jets and (c) there is a heat transfer enhancement benefit in roughening the target surface. With the presence of showerhead holes, the enhancement is due to both the impingement heat transfer coefficient and the heat transfer area increase.
Swirl and Tip Leakage Flow Interaction With Struts in Axial Diffusers
Authors: Fleige H.-U. , Riess W. , Seume J.
Published: February 2009

A scale model of a typical gas turbine exhaust diffuser (annular followed by conical) is investigated experimentally and numerically. The turbine exhaust flow is modelled using a radial type swirl generator and a simulated tip leakage flow. Static pressure measurements are carried out on the walls and on the center line of the conical part. Four swirl angles and three strut configurations are investigated. Pressure recovery coefficients are depicted as a function of diffuser length. Velocity and turbulence profiles are measured using ID-LDA in two directions. A CFD analysis of the model is carried out using a commercial Navier-Stokes code and the standard as well as the Chen k-ε turbulence model. Even without struts, inlet swirl higher than 8° is found to adversely influence the pressure recovery of the diffuser. The profiled struts showed not to be able to redirect the flow and for swirl angles higher than 10°, cylindrical struts were found to yield better diffuser performance than profiled struts.
Simulating the Failure Behaviour of Ceramic Components Under Gas Turbine Conditions
Authors: Bru¨ckner-Foit A. , Hu¨lsmeier P. , Diegele E. , Rettig U. , Hohmann C.
Published: February 2009

Advanced monolithic ceramics have a good potential to survive under the severe thermal and mechanical loading conditions which are present in stationary gas turbines. Long term volume stability and high creep resistance are hard to achieve from a materials point of view but comparatively easy to verify. Resistance against thermal shock loading, on the other, has to be tested in a test rig, and test results obtained in the lab have to be scaled up to provide a database for a reliable design. This implies that advanced methods of fracture statistics have to be used. In this paper, failure probabilities under thermal shock loading are calculated using a modified version of the Weibull theory which takes the pronounced stress gradients into account. The basic idea is to determine the stress intensity factors of the natural flaws using weight functions. The new approach is used to estimate the failure probability in a thermal shock experiment which is designed to simulate critical gas turbine conditions. The predicted value of the failure probability is lowered by a factor of about 5 if the stress gradients are taken into considerations. The agreement between theory and experiments is very good.
ACACIA: A Small Scale Nuclear Power Plant With Cogeneration Capabilities
Authors: van Heek A. I.
Published: February 2009

Nuclear power currently only serves the market segment of large scale base load electricity generation. Other energy markets, like cogeneration and heat production or market segments like the smaller scale (but still industrial) electricity production are entirely served with fossil fuels (and hydropower). When these fuels at acceptable prices are being depleted and if actively marketed, and if an inherently safe small-scale nuclear plant could be developed and marketed, a huge market could emerge for this new form of nuclear power. Pebble Bed High Temperature Reactor technology is most suitable for designing small inherently safe nuclear reactors. The oldest small designs were meant for application as district heating plants, making full use of the self-controlling features of nuclear reactors. The ACACIA concept (AdvanCed Atomic Cogenerator for Industrial Applications) is a design for industrial cogeneration, producing 13.6 MW of electricity and 17 tons of industrial quality steam per hour, with a total efficiency of 63%. In case the electricity production would be maximized at the expense of the steam quality, an electrical output of 16.5 MW could be achieved, and the plant efficiency would rise to 86% (electric efficiency 41%). The heat source is a pebble bed reactor with 40 MW of thermal power. The energy conversion system is a direct recuperated helium cycle with a radial compressor and an axial helium turbine. A number of operational and safety related transients have been calculated with two different simulation codes. The safety related transient analyses show the reactor power and the fuel temperature bebaviour after a full loss of coolant accident, and illustrate the inhrently safe nature of the plant. The operational transient simulations show the suitability of the system for an industrial user. Furthermore, the transport of radioactive fission products within the primary circuit has been analyzed. A cost study shows high kWh-costs compared to large scale generating plants, but the treatment of scaling factors for this particular case needs continued attention. However, for those areas in the world without fossil fuel supply networks and with only small-scale demand, ACACIA will still be an economic option. To improve matching with non-utility market needs, the current ACACIA design will be adapted from a direct cycle system to an indirect cycle system, where primary cycle will be strictly separated from the remainder of the plant. A conceptual comparison with the direct cycle system will be discussed.