bluuebunny/crossref_metadata_2025 huggingface dataset:
Forced Response Assessment Using Modal Force Based Indicator Functions
Authors: Vahdati M. , Breard C. , Simpson G. , Imregun M.
Published: August 2009

This paper will focus on core-compressor forced response with the aim to develop two design criteria, the so-called chordwise cumulative modal force and heightwise cumulative force, to assess the potential severity of the vibration levels from the correlation between the unsteady pressure distribution on the blade’s surface and the structural modeshape. It is also possible to rank various blade designs since the proposed criterion is sensitive to changes in both unsteady aerodynamic loads and the vibration modeshapes. The proposed methodology was applied to a typical core-compressor forced response case for which measured data were available. The Reynolds-averaged Navier-Stokes equations were used to represent the flow in a non-linear time-accurate fashion on unstructured meshes of mixed elements. The structural model was based on a standard finite element representation from which the vibration modes were extracted. The blade flexibility was included in the model by coupling the finite element model to the unsteady flow model in a time-accurate fashion. A series of numerical experiments were conducted by altering the stator wake and using the proposed indicator functions to minimize the rotor response levels. It was shown that a fourfold response reduction was possible for a certain mode with only a minor modification of the blade.
Gas Turbine Accessory Health Management Evaluation Using a Hybrid Prognostic Approach
Authors: Byington Carl S. , Watson Matthew J. , Bharadwaj Sudarshan P.
Published: August 2009

The authors have developed model-based and data-driven techniques aimed at providing a more reliable health assessment of gas turbine engine accessory components, which have contributed to a significant number of events that compromise mission success and equipment availability in military aircraft. As part of this approach, a physical model is used to derive parameters indicative of component-specific faults. Statistical fault classifiers and evolutionary prognostics methods are then used to track these parameters and identify the most likely health state and time to failure for each component. This assessment is fused with the results of independent data-driven routines, which are also used to analyze dynamic signal response and detect faults that would be difficult to incorporate into physical models. The developed approach was demonstrated using an experimental setup representative of aircraft fuel and lubrication systems. Pump leakage, pump gear damage, and valve blockage were seeded on the setup, and the developed routines were trained with high-bandwidth experimental data. The approach produced wide separation between baseline and faulted cases, yielding negligible missed detection rates for moderate faults and reasonable missed detection rates for an incipient valve blockage fault. The demonstration produced a quantifiable estimate of achievable performance using the hybrid techniques.
The Effect of Turbulence Intensity on Film Cooling of Gas Turbine Blade From Trenched Shaped Holes
Authors: Baheri S. , Jubran B. A. , Alavi Tabrizi S. P.
Published: August 2009

This paper reports a computational investigation on the effects of mainstream turbulence intensity on film cooling effectiveness from trenched holes over a symmetrical blade. Computational solutions of the steady, Reynolds-Averaged Navier-Stokes equations are obtained using a finite volume method with k – ε Turbulence model. Whenever possible, computational results are compared with experimental ones from data found in the open literature. Computational results are presented for a row of 25 deg forward-diffused film hole within transverse slot injected at 35 deg to AGTB symmetrical blade. Four blowing ratios, M = 0.3, 0.5, 0.9 and 1.3 are studied together with four mainstream turbulence intensities of Tu = 0.5%, 2%, 4% and 10%. Results indicate that the trenched shaped holes tend to give better film cooling effectiveness than that obtained from discrete shaped holes for all blowing ratios and all turbulence intensities. The trenching of shaped holes has changed the optimum blowing ratio and also the location of re-attachment of separated jet at high blowing ratios. Moreover, it has been found that the effect of mainstream turbulence intensity for trenched shaped holes is similar to that obtained for discrete shaped holes with the exception that the sensitivity of film cooling effectiveness to turbulence intensity has decreased for trenched shaped holes.
The Impact of the Vortex Design Method on the Stall Behavior of Axial Flow Fan and Compressor Rotors
Authors: Vad Ja´nos , Horva´th Csaba
Published: August 2009

The paper presents comparative studies on low-speed isolated rotors of free vortex design and controlled vortex design (CVD), in order to survey the impact of the vortex design method on the stall behavior of axial flow turbomachinery. The studies are based on 3D laser Doppler anemometer studies and global performance measurements, supplemented with literature data. CVD bladings are characterized by radially outward flow on the suction side due to spanwise changing circulation, and increased near-tip solidity and/or loading. These features were found to increase the near-tip endwall flow blockage and loss at the design flow rate, and to hasten stall. On this basis, it has been concluded that CVD tends to be disadvantageous from the viewpoint of the stall behavior. It was confirmed that forward blade sweep is a remedial strategy for moderating the stall-hastening effects of CVD, while retaining the favorable features of CVD.
Heat Transfer in Leading Edge, Triangular Shaped Cooling Channels With Angled Ribs Under High Rotation Numbers
Authors: Liu Yao-Hsien , Huh Michael , Rhee Dong-Ho , Han Je-Chin , Moon Hee-Koo
Published: August 2009

The gas turbine blade/vane internal cooling is achieved by circulating the compressed air through the cooling channels inside the turbine blade. Cooling channel geometries vary to fit the blade profile. This paper experimentally investigated the rotational effects on heat transfer in an equilateral triangular channel (Dh = 1.83cm). The triangular shaped channel is applicable to the leading edge of the gas turbine blade. 45° angled ribs are put on the leading and trailing surfaces of the test section to enhance heat transfer. The rib pitch-to-height ratio (P/e) is 8 and the height-to-hydraulic diameter ratio (e/Dh) is 0.087. Effect of the angled ribs under high rotation numbers and buoyancy parameters are also presented. Results show that due to the radially outward flow, heat transfer is enhanced with rotation on the trailing surface. By varying the Reynolds numbers (10000–40000) and the rotational speeds (0–400 rpm), the rotation number and buoyancy parameter reached in this study are 0–0.58 and 0–1.9, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the equilateral triangular channel.
Aircraft Engine On-Line Diagnostics Through Dual-Channel Sensor Measurements: Development of a Baseline System
Authors: Kobayashi Takahisa , Simon Donald L.
Published: August 2009

In this paper, a baseline system which utilizes dual-channel sensor measurements for aircraft engine on-line diagnostics is developed. This system is composed of a linear on-board engine model (LOBEM) and fault detection and isolation (FDI) logic. The LOBEM provides the analytical third channel against which the dual-channel measurements are compared. When the discrepancy among the triplex channels exceeds a tolerance level, the FDI logic determines the cause of the discrepancy. Through this approach, the baseline system achieves the following objectives: 1) anomaly detection, 2) component fault detection, and 3) sensor fault detection and isolation. The performance of the baseline system is evaluated in a simulation environment using faults in sensors and components.
Effects of Fuel-Nozzle Configurations on Particulate-Matter Emissions From a Model Gas Turbine Combustor
Authors: Asai Tomohiro , Koizumi Hiromi , Yoshida Shohei , Inoue Hiroshi
Published: August 2009

The present paper describes particulate-matter (PM) emissions from a model gas turbine combustor at atmospheric pressure, focusing on the effects fuel-nozzle configurations have on PM emissions. In this experiment, three types of fuel nozzles were employed: standard, annular, and multi-type. The annular and multi-type were designed as low-PM-emission fuel nozzles, based on our preliminary experimental results using the standard nozzle. Gas oil and fuel oil containing 0.2 wt% of carbon residue were used as the test fuels. The PM concentrations and particle-size distributions were measured with an electrical low-pressure impactor. The experimental results revealed that the PM concentrations for the annular and multi-type were dramatically reduced compared with that for the standard nozzle, demonstrating their PM-reducing effect. We found that the high-concentration regions seemed to be formed by soot aggregation, from the spatial-profile measurements of PM emissions from gas oil combustion. The high-concentration regions for the low-PM-emission fuel nozzles were located further upstream and they were on a smaller scale than that for the standard nozzle. This suggests that their PM-reducing effect may be due to their upstream location and the smaller-scale of their high-concentration regions.
Efficiency Analyses of a Coal Gasification Molten Carbonate Fuel Cell With a Gas Turbine Combined Cycle Including CO2 Recovery
Authors: Yoshiba F. , Koda E.
Published: August 2009

The efficiency of an integrated coal gasification system equipped with a molten carbonate fuel cell, a gas turbine and a steam turbine (IG/MCFC) is calculated. Coal is conveyed to a gasifier furnace by CO2 and changed to coal gas by adding oxygen; a methyldiethanolamine (MDEA) method is applied to initiate a cleanup procedure of the coal gas. A water-gas shift converter is employed to heat up the coal gas. The cathode gas of the MCFC is composed of CO2 and O2 with a composition of 66.7/33.3 (noble cathode gas composition). The magnitude of the system’s electrical power output is assumed to be that of a 300 MW class. The calculated net efficiency of the 2.2 MPa pressurised system reached a 60.1% high heating value (HHV) without CO2 recovery. The 2.2 MPa pressurised system, however, has a short lifetime limited by the shortening of electrodes. For this reason, a further 0.15 MPa pressurised system (low pressurised system) efficiency is recorded which has a more promising shortening time of the electrodes. The net efficiency of the low pressurised system is 51.9% HHV without CO2recovery. Since the coal is gasified using oxygen and the cathode gas of the MCFC is composed of CO2/O2, the system’s exhaust gas only includes CO2, thus the system is ready for the recovery and storage of carbon dioxide (Carbon Capture and Storage ready, CCS ready). For the purpose of estimating the net efficiency with CO2 recovery, a liquid form of CO2 with a pressure of 10MPa is assumed. Using the 2.2 MPa pressurised system, the net efficiency including the consumption of CO2 compression and liquefaction is evaluated at 58.2% HHV. Another simple CO2 closed system configuration without gas turbine is proposed; the net efficiencies of the 2.2 MPa and the 0.15 MPa system including the consumption of CO2 liquefaction are determined at 56.4% and 50.3% HHV, respectively. According to the calculation results, a high efficiency system with CO2 recovery is possible by applying the noble cathode gas in the IG/MCFC systems.
Leveraging the Strengths of Commercial Finite Element Modeling Codes and Custom Engineered Software to Solve Atypical Rotordynamic Problems
Authors: Ransom David
Published: August 2009

Commercial finite element modeling codes have evolved over the past few decades into very user friendly environments, easily handling the many complications of finite element simulation. The significant steps of model generation (preprocessing), problem solution (analysis) and results viewing (post-processing) are easily handled for most of the typical finite element problems. However, there are still occasions when the necessary solution requirements fall outside the capabilities of any single finite element code. In this case, it is beneficial to the engineer to use some of the features of the commercial code, filing in the gaps with custom engineered software. This is especially true for the field of rotordynamics. In this paper, several of the complications involved in the finite element simulation of rotordynamics are discussed, and methods for leveraging the strengths of both commercial and custom engineered software are provided. The objective is to assist the practical engineer in the simulation of more complicated rotordynamic systems, including transient non-linear systems and three-dimensional coupled rotor-structure interaction systems.
High Altitude Recuperated 50 kWe Turboprop Study
Authors: Rodgers Colin
Published: August 2009

Specialized requirements exist for advanced high altitude unmanned air vehicles (UAV’s) capable of extended durations the propulsion units of which can only be served by either air-breathing highly turbocharged piston, and or, gas turbines engines with high thermal efficiency and light weight. These UAV requirements encompass ground surveillance, air sampling, and global atmospheric missions proposed in a variety of roles previously performed by larger manned aircraft. Some applications demand up to several days loitering endurance at altitudes over 65000ft, with which existing production propulsion engines are either incapable of meeting or require extensive modifications. Highly turbocharged piston engines and low specific fuel consumption turbofans have been developed for these specialized duties and record breaking global circumnavigation piloted aircraft. Recuperated cycle gas turbines thermal efficiencies of the order 40% are necessary to match those of current highly turbocharged piston engines which are difficult to attain with conventional uncooled metallic turbine rotors even at standard sea level day conditions. It is believed however that above the tropopause with sub zero air inlet temperatures, thermal efficiencies of 40% can rationally be attained with small relatively light weight recuperated gas turbine turboprops. The performance details and flowpath configuration of a two candidate recuperated turboprop designs are presented as specifically optimized for the propulsion of a long endurance UAV operating at 65000ft altitude, fueled with hydrogen.
Simulated Foreign Object Damage on Blade Aerofoils: Real Damage Investigation
Authors: Duo´ Pierangelo , Pianka Christian , Golowin Andrej , Fueller Matthias , Schaefer Roger , Bernhardt Ulf
Published: August 2009

During operating service, gas turbine aero-engines can ingest small hard particles which typically produce damage to the aerofoils. If the damage found is a tear or a perforation at the leading edge, it is known as a Foreign Object Damage or FOD and this leads to a reduction of the subsequent High-Cycle-Fatigue (HCF) strength. The objective of research work in this area is to assess the effect of FOD on the residual fatigue strength of compressor blades and to provide predictive tools for engineering judgment. The methodology followed is normally to carry out experimental simulation of FOD, followed by fatigue tests to assess subsequent performance. To date, research related to fatigue following FOD events has concentrated on HCF loading and the impact geometry is frequently that of a sphere against a flat surface or the edge of a blade-like specimen. Both of these aspects do not correspond to the worst cases of real FOD. Here it is intended to investigate the effect of a V-notch geometry, which is more representative of severe FOD found in service. Alongside this, numerical models can be used to simulate the damage and to evaluate the residual stress field. In addition analytical model are used to predict the residual fatigue strength. The current work explains the development of a new rig impact test and discusses the improvements necessary to obtain a sufficient repeatability of the impacts. From the experience gained with a gas gun, an alternative method using a pistol and a barrel, capable of achieving the necessary velocity of simulated FOD, was developed. The applied velocity was in the range of 250m/s to 300m/s and a technique to describe the impact is here discussed. Furthermore the introduction of a high speed camera has allowed to have a complete description of the impact scene and to better understand the impact. The impacted blades were measured and HCF tested. As a result, this has produced a large scatter in the residual fatigue strength. The current method to describe a notch using a 2D approach, which was applied to several geometries of notches, is here critically reviewed. The proposed method would incorporate a more sophisticated method, which reconstruct the real geometry using optical measurement. This latter measurement can fully describe the 3D geometry, showing particularly zones inside the notch where compressive residual might appears. Tears and shear of the material can also be described by applying this technique. The findings are compared with the residual HCF strength and the results are compared to special cases of HCF to justify the results out of theoretical prediction.
Investigation of an Air Supply Centrifugal Fan for Air Cushion Vehicle: Impeller Design and Validation
Authors: Lee Yu-Tai , Ahuja Vineet , Hosangadi Ashvin , Slipper Michael E. , Mulvihill Lawrence P. , Birkbeck Roger , Coleman Roderick M.
Published: August 2009

A design method is presented for re-designing the double-discharge, double-width, double-inlet (DWDI) centrifugal impeller for the lift fans of a hovercraft. Given the current high performance of impellers, the design strategy uses a computational method, which is capable of predicting flow separation and vortex-dominated flow fields, enabling a detailed comparison of all aerodynamic losses. The design method, assuming a weak interaction between the impeller and the volute, employs a blade optimization procedure and several effective flow path modifications. Simplified CFD calculations were performed on fans with two existing impellers and the newly designed impeller to evaluate the impeller design criterion. The calculation was made with the impeller/volute coupling calculation and a frozen impeller assumption. Further refined CFD calculations, including the gap between the stationary bellmouth and the rotating shroud, revealed a reduction in the new impeller’s gain in efficiency due to the gap. The calculations also further supported the necessity of matching the volute and the impeller to improve the fan’s overall efficiency. Measured data of three fans validated CFD predictions in pressure rise at design and off-design conditions. CFD calculations also demonstrated the Reynolds number effect between the model- and full-scale fans. Power reduction data were compared between the measurements and the predictions along with the original design requirements.
Influence of a Broken-Away TBC on the Flow Structure and Wall Temperature of an Effusion Cooled Multi-Layer Plate Using the Conjugate Calculation Method
Authors: Bohn Dieter , Krewinkel Robert
Published: August 2009

Within Collaborative Research Center 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants” at RWTH Aachen University an effusion-cooled multi-layer plate configuration is investigated numerically by application of a 3-D in-house fluid flow and heat transfer solver, CHTflow. Previous conjugate calculations have shown a considerably decreased surface temperature for a hole geometry with a broken-away TBC, but could not attribute this effect conclusively to the decreased surface or the changed fluid flow conditions resulting from the changed outlet geometry. For this work, both conjugate calculations and calculations with adiabatic wall temperatures are conducted to analyse the flow in and around a hole with a fan-shaped outlet. The adiabatic calculations will exclude the effect of the solid body, making a quantification of its effects possible. The geometrical setup and the fluid flow conditions derive from modern gas turbine combustion chambers and bladings and are the same for both types of calculations. The numerical grid contains the coolant supply (plenum), the solid body for the conjugate calculations and the main flow area on the plate. The effusion-cooling is realized by finest drilled holes with a diameter of 0.2 mm that are shaped in the region of the thermal barrier coating. The flow field and the resulting temperature distributions on the hot gas surface will be discussed in detail for the two approaches, two blowing ratios and two different fan-shapes. Finally, the results will be discussed from the point-of-view of optimising the cooling effectivenss for effusion cooling geometries. The results will show that only for the smallest blowing ratio and the largest cooling hole exit area the decreased surface area of the TBC is the dominant factor.
Performance Research of High Temperature Compact Offset Strip Fin Heat Exchanger
Authors: Wang Lijin , Zhang Huisheng , Weng Shilie , Lin Wenguang
Published: August 2009

Dynamic mathematical model of high temperature compact offset strip fin heat exchanger (COSFHE) is established, and Volume-Resistance characteristic simulation model is built based on the distributed and lumped parameter technique. This model can meet the requirement to quick dynamic simulation. Under the same operating condition, the steady-state and transient simulation are studied for the same configuration COSFHE with different fin materials. The results show that they have almost the same steady state performances and totally different transient performances. This will provide reference for the design and optimization of COSFHE control system.
Jet Shear Layer Size and Number Influences on Grid Plate Direct Fuel Injection Shear Layer Mixing Low NOx Gas Turbine Combustion With Fuel Staging for Power Turn Down
Authors: Andrews Gordon E. , Ahmed S. A. R.
Published: August 2009

The scale up of jet shear layer low NOx concepts for compact gas turbine applications is considered using natural gas as the fuel with all experiments at one atmosphere pressure and 600K air inlet temperature. A 76mm diameter cylindrical combustor with 4 round jet shear layers was compared with a near double scale combustor with 140mm diameter and 4 round jet shear layers with the same total blockage as for the smaller combustor. This is compared with 16 round jet shear layers of the same diameter as for the smaller combustor. The shear layer air holes were fuelled by eight radial inward fuel injection holes in each shear layer jet. All three designs had acceptable combustion efficiencies, but the NOx emissions were considerably higher for the 4 shear layer design in the larger combustion. When the same shear layer hole size was used and the number increased in the larger combustor the NOx emissions were identical. Changing the shape of the hole from circulat to slot for the same area, considerably reduced the NOx in the four hole 76mm combustor, but had little effect on the 16 hole 140mm combustor. Fuel staging within the array of shear layers was successfully demonstrated for four levels of fuel staging. There was some intermixing of air from the unfuelled jets, but this had only a small effect on the combustion efficiency and flame stability. A practical range of simulated power turndown was demonstrated with little NOx penalty. This was achieved with no wall between the staged shear layer regions and hence leads to very compact combustor designs.
Evolution of the Laminar Boundary Layer Over a Flat Plate Under a Free Stream Turbulence Intensity of 1.3%
Authors: Walsh E. J. , Brighenti F. , McEligot D. M.
Published: August 2009

The evolution of the laminar boundary layer over a flat plate under a free stream turbulence intensity of 1.3% is analysed. The effect of free stream turbulence on the onset of transition is one of the important sources leading to bypass transition. Such disturbances are of great interest in engineering for the prediction of transition on turbine blades. The study concentrates on the early part of the boundary layer, starting from the leading edge, and is characterised by the presence of streamwise elongated regions of high and low streamwise velocity. It is demonstrated that the so called “Klebanoff modes” are not entirely representative of the flow structures, due to the time-averaged representations used in most studies. For the conditions of this investigation it is found that the urms and the peak disturbances remain constant in the early stages of the transition development. This region, in which the streaks strength is constant, is problematic for many theories as it is not known where on a surface to initiate a growth theory calculation, and hence the prediction of transition onset is difficult. The observation that a constant urms region exists within the boundary layer under these conditions may be the source of great difficulty in predicting transition onset under turbulence levels around 1%. This region suggests that the streaks are either continuously generated and damped, or do not grow during the early stage of transition, and highlights the importance of continuous influence of the free stream turbulence along the boundary layer edge. This work concludes that the first is more likely, and furthermore the measurements are shown to agree with recent direct numerical simulations.
Effect of Coolant Ejection in Rectangular and Trapezoidal Trailing Edge Cooling Passages
Authors: Wright Lesley M. , Gohardani Amir S.
Published: August 2009

Heat transfer coefficients are experimentally determined in various trailing edge cooling channels. A rectangular channel (AR = 3:1) with fully developed flow is used as a baseline for the study with the Reynolds number varying from 20,000 to 80,000. The heat transfer coefficients in this channel are compared to those in a similar rectangular channel with coolant extraction, which would likely be encountered in a trailing edge cooling passage. The heat transfer trends in the rectangular channel are compared to those obtained in a passage with a trapezoidal (or wedge-shaped) cross-section. The heat transfer coefficients are also obtained in the channel without coolant extraction and with extraction from the narrow side of the channel. The effect of V-shaped rib turbulators is also considered in the rectangular and trapezoidal cooling passages. In addition, the effect of entrance condition is considered with the wedge-shaped channel. Heat transfer coefficients obtained with hydrodynamically developed flow are compared to those with flow through a contraction into the heated section of the channel. In the rectangular channel without ejection, the heat transfer coefficients are uniform across the span of the channel; however, with coolant ejection, the heat transfer coefficients increase near the ejection slots. In addition, in the trapezoidal channels, the heat transfer coefficients are uniform across the cross-section of the smooth channel. When coolant is extracted for trailing edge ejection, the outer surface sees the most significant heat transfer enhancement. The outer surface of the smooth, trapezoidal channel is most profoundly affected by the entrance condition, and the effect of the entrance condition is marginal in trapezoidal channels with ribs and ejection.
Windage Power Losses From Spiral Bevel Gears With Varying Oil Flows and Shroud Configurations
Authors: Johnson Graham , Chandra Budi , Foord Colin , Simmons Kathy
Published: August 2009

In many aero-engines the power to drive accessories is transmitted through high speed bevel gears in a chamber in the center of the engine. The windage power loss (WPL) associated with these gears makes a significant contribution to the overall heat generation within the chamber. Shrouding the gears provides an effective method of reducing this WPL and managing the flow of lubricating oil. Experimental and computational programs at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems are providing an improved understanding of shroud performance and design. This paper presents results from a pair of shrouded meshing gears run at representative speeds and oil flow in a rig with speed and torque measurement. A previously published study of a single bevel gear operating in air [1] found a reduction in torque of up to 70% from shrouding. In this work the addition of oil and the pinion gear did not lead to high torque due to the build up of oil under the shrouds, but the reduction in torque due to fitting the shrouds is significantly less than was found for the same gear in air alone. In order to isolate the various parameters, further testing with a single gear was carried out. A fully (360 degree) shrouded gear shows a big improvement over an unshrouded gear when running in air alone, but much of this benefit disappears as soon as a very small amount of oil is introduced under the shroud. This implies that the oil is recirculating under the shroud. Increasing the oil flow beyond this initial level increases the torque by the amount required to accelerate the oil mass flow up to the peripheral speed of the gear. Providing a full width slot in the shroud downstream of the oil jet allows the oil to escape without any recirculation and restores much of the benefit of the shroud. Further insight into the oil behavior is obtained from torque measurements and observations through a transparent shroud and with various slot configurations. Video observation shows evidence of a vortex flow under the shroud that carries some of the oil towards the inner diameter of the gear. The three main windage contributors, air alone, recirculation of oil under the shroud and acceleration of the feed oil are quantified and methods for achieving the optimum design are discussed.
Passive Control of the Inlet Acoustic Boundary of a Swirled Turbulent Burner
Authors: Tran Nicolas , Ducruix S. , Schuller T.
Published: August 2009

The efficiency of perforated panels inserted in the injection line of a swirled turbulent burner is investigated as a passive control solution for combustion instabilities. Perforated panels backed by a cavity are widely used as acoustic liners, mostly in the hot gas region of combustion chambers to reduce pure tone noise levels. This paper focuses on the implementation of this technology in the injection line of a burner. The system is used to control the inlet acoustic reflection coefficient of the burner to stabilize the combustion. This method is shown to be particularly efficient because high acoustic fluxes issued from the combustion region are concentrated on a small surface area in the injection line. Theoretical results are used to design two types of perforated plates featuring similar acoustic damping properties when submitted to low amplitude pressure fluctuations (linear regime). However it is shown that their behavior largely differs when facing large pressure fluctuations levels (non linear regime) typical of those encountered during self-sustained combustion oscillations. Design criteria are given to control the reflection coefficient of perforated panels submitted to high pressure fluctuations levels and damp thermo-acoustic oscillations. While developed on a laboratory scale swirled combustor, this method is more general and could easily be adapted to practical combustors.
A Scale Independent Model for Turbine Surface Cooling
Authors: LaFleur Ronald S.
Published: August 2009

As part of an undergraduate course in design of thermodynamic systems, a highly loaded turbine, such as a power turbine or high bypass turbofan, is modeled as a modified Brayton cycle. On a smaller scale, the vane, blade, liner and seal surfaces of modern high pressure turbine (HPT) parts are exposed to gas path temperatures that far exceed the base metal material-life capability. A cooling method such as compressor bleed allows high combustion temperatures to attain high turbine output but is considered a negative on overall cycle performance. The required cooling flow must be included as its impact on the cycle-scale calculations can be significant. At the thermodynamic education level, the cooling model for part surfaces must be such that expertise in heat transfer is not required. At the same time, the cooling model for the cycle must represent key influences of cooling technologies. To bridge this educational gap, a scale independent model for surface cooling is required. This is important because thermodynamic cycle conditions impact detailed surface cooling features and, in the opposite direction, surface-material cooling demands are calculated in the cycle model. The cooling issues are scale independent when characteristic temperatures track the engine and surface cooling design. A surface cooling model is shown with five cooling technologies working in tandem: film cooling, thermal barrier coating (TBC), base metal conduction, passage convection cooling and backside convection cooling. Six new definitions for cooling technology effectivenesses are introduced. The result is a basis for communicating the impact of small scale cooling design on large scale engine performance. Two applications at different scales, the cooling demand for a rotor stage and the film decay over a 1st vane surface patch, are used to demonstrate the model and show where counter-intuitive results may arise.
Semi-Inverse Design Applied to an Eight Stage Transonic Axial Flow Compressor
Authors: Hield Paul
Published: August 2009

Semi-Inverse Design is a class of Computational Fluid Dynamics (CFD) procedures for calculating aerofoil geometry from prescriptions of pressure loading and thickness distribution; when describing an aerofoil in three dimensions a stacking axis is also needed. All sixteen blade rows of an eight stage transonic axial flow compressor have been simultaneously designed in a single inverse 3D CFD calculation. The tip Mach number of the first rotor was just over sonic with a peak value in excess of 1.25. Apart from the substitution of geometric by aerodynamic aerofoil boundary conditions, the CFD model is the same as that used for direct analysis and includes rotor and stator clearance gaps as well as stator shroud leakage flows. This has profound implications for 3D CFD in the context of the total design process at a system level. The technique allows 3D CFD to behave like a design point through flow in the sense that we can now ask the question of 3D CFD - “what is the performance of a turbo-machine that has this design intent?” as opposed to “does this set of aerofoils meet the design intent and if they do what is its performance? And if they do not how should they be changed?” Inverse design provides a means of conveying design intent up through the “fidelity levels” from 1-D and 2-D, through Low Fidelity 3D CFD to High Fidelity CFD. Thus the desired loading distribution may be determined cheaply using 2D blade to blade analysis, either by iterative direct analysis (the current approach) or using a semi-inverse technique in 2D. As an illustration of this, a 1-D tool will be presented which produces estimates of aerofoil shape and surface velocities in real time to enable the designer to manipulate the loading distributions which are then used in Inverse 3D CFD to realize the final geometry.
Pressure Dependence of Soot Formation in Diffusion Flames
Authors: Joo Hyun I. , Gu¨lder O¨mer L.
Published: August 2009

The effects of pressure on soot formation and the structure of the temperature field were studied in co-flow methane-air laminar diffusion flames over a wide pressure range, from atmospheric to 6 MPa (60 atm) in a high-pressure combustion chamber. The selected fuel mass flow rates provided diffusion flames in which the soot was completely oxidized within the visible flame envelope and the flame was stable at all pressures considered. The spatially resolved soot volume fraction and soot temperature were measured by spectral soot emission as a function of pressure. The visible (luminous) flame height remained almost unchanged, about 9 mm, from 1 to 10 MPa, whereas it increased considerably from atmospheric to 1 MPa. Between 1 MPa and 6 MPa, the cross-sectional area of the flame (measured from the radius defined by either the maximum soot or maximum temperature annuli) showed an inverse dependence on pressure. Peak soot concentrations showed a strong dependence on pressure from 1 MPa to 4 MPa; however this dependence got relatively weaker between 4 MPa and 6 MPa.
Second Vane Total Pressure Loss Due to Endwall Iceform Contouring
Authors: LaFleur Ronald S.
Published: August 2009

The iceformation design method generates an endwall contour, altering the secondary flows that produce elevated endwall heat transfer load and total pressure losses. Iceformation is an analog to regions of metal melting where a hot fluid alters the isothermal surface shape of a part as it is maintained by a cooling fluid. The passage flow, heat transfer and geometry evolve together under the constraints of flow and thermal boundary conditions. The iceformation concept is not media dependent and can be used in analogous flows and materials to evolve novel boundary shapes. In the past, this method has been shown to reduce aerodynamic drag and total pressure loss in flows such as diffusers and cylinder/endwall junctures. A prior paper [1] showed that the Reynolds number matched iceform geometry had a 24% lower average endwall heat transfer than the rotationally symmetric endwall geometry of the Energy Efficiency Engine (E3). Comparisons were made between three endwall geometries: the ‘iceform’, the ‘E3’ and the ‘flat’ as a limiting case of the endwall design space. This paper adds to the iceformation design record by reporting the endwall aerodynamic performances. Second vane exit flow velocities and pressures were measured using an automated 2-D traverse of a 1.2 mm diameter five-hole probe. Exit plane maps for the three endwall geometries are presented showing the details of the total pressure coefficient contours and the velocity vectors. The formation of secondary flow vortices is shown in the exit plane and this results in an impact on exit plane total pressure loss distribution, off-design over- and under-turning of the exit flow. The exit plane contours are integrated to form overall measures of the total pressure loss. Relative to the E3 endwall, the iceform endwall has a slightly higher total pressure loss attributed to higher dissipation of the secondary flow within the passage. The iceform endwall has a closer-to-design exit flow pattern than the E3 endwall.
Application of an Enhanced 1D Network Model to Calculate the Flow Properties of a Pre-Swirl Secondary Air System
Authors: Benra F.-K. , Dohmen H. J. , Schneider O.
Published: August 2009

Former investigations [10] were focused on the design point of the secondary air system. This paper discusses further enhancements to the modelling to describe the flow in the pre-swirl cavity more precisely at off design flow conditions. Special focus was drawn to mixing of the pre-swirl nozzle flow with the flow in the cavity. Together with the description of the friction losses and the surging effects of the boundary layers with new modules in a 1D network model the flow in the mixing region is now appropriately reproduced. 3D CFD investigations were used for calibration of the correlation approach. The 1D network model so enhanced was then used to simulate the flow in the pre-swirl test rig at the University of Duisburg-Essen over a wide range of operating conditions. A comparison of the experimental results from the test rig to the results of the enhanced 1D network model reveals that the crucial parameters can be now determined over the complete operating range of the test rig. It is demonstrated that the accuracy of the estimated pressure ratio, the temperature and the swirl ratio of the pre-swirl system is now much better.
Impact of Boundary Conditions on the Reconstructed Flame Transfer Function for Gas Turbine Combustion Systems
Authors: Kostrzewa Krzysztof , Widenhorn Axel , Noll Berthold , Aigner Manfred , Krebs Werner , Huth Michael , Kaufmann Peter
Published: August 2009

In order to achieve low levels of pollutants modern gas turbine combustion systems operate in lean and premixed modes. However, under these conditions self-excited combustion oscillations due to a complex feedback mechanism between pressure and heat release fluctuations can be found. These instabilities may lead to uncontrolled high pressure amplitude oscillations which can damage the whole combustor. The flame induced acoustic source terms are still analytically not well described and are a major topic of thermo-acoustic investigations. For the analysis of thermo-acoustic phenomena in gas turbine combustion systems flame transfer functions can be utilized. The purpose of this paper is to introduce and to investigate modeling parameters, which could influence a novel computational approach to reconstruct flame transfer functions known as the CFD/SI method. The flame transfer function estimation is made by application of a system identification method based on Wiener-Hopf formulation. Varying acoustic boundary conditions, combustion models and time resolutions may strongly affect the reconstructed flame response characterizing overall system dynamics. The CFD/SI approach has been applied to a generic gas turbine burner to derive a flame response. 3D unsteady simulations excited with white noise have been performed and the reconstructed flame transfer functions have been validated with experimental data. Moreover, the impact on the reconstructed flame transfer functions because of different boundary condition configurations has been examined.
CFD and Thermo-Mechanical Analysis for Heat Exchanger Used in Aero Engine
Authors: Jeong Ho Seung , Cho Jong Rae , Kim Lae Sung , Ha Man Yeong , Jeong Ji Hwan , Kim Kui Soon , Lindquist Torbjorn , Walsh Philip
Published: August 2009

The multi-physics analysis using both the CFD and thermo-mechanical analysis is carried out to estimate the life of the heat exchanger which is operated under the conditions of high temperature and high pressure. First CFD analysis is carried out to obtain the distribution of flow, pressure and temperature around heat exchanger. The distribution of pressure, temperature and heat transfer coefficient obtained from the CFD analysis is transferred to the thermo-mechanical analysis using finite element analysis technique and is used as data to calculate the mechanical and thermal stress distribution in the heat exchanger. For the CFD analysis, it is considered a segment of heat exchangers using the symmetric and periodic conditions. For the thermo-mechanical analysis, the present finite element model considered both a segment and a half of full geometry by using the symmetric and periodic conditions. Alloy 625 is used for the present heat exchanger design due to its high strength at the elevated temperatures. The temperature-dependent physical properties of Alloy 625 for the thermo-mechanical analysis are used in a temperature ranges of 300∼1100K. Fatigue analysis is performed using a Goodman-diagram to assess the life of the present heat exchanger.
Optimisation of Non-Axisymmetric Endwalls in Compressor S-Shaped Ducts
Authors: Naylor Edward M. J. , Ortiz Duen˜as Cecilia , Miller Robert J. , Hodson Howard P.
Published: August 2009

This paper presents a new design methodology for strutted S-shaped compressor ducts that allows for more aggressive designs whilst maintaining current levels of duct loss. A baseline duct geometry was selected which had a radius change to length ratio which is 26% larger than current engine design limits. A large-scale low-speed model of the baseline duct was experimentally tested. The flow in the corner between the hub and the strut was found to separate due to the high local diffusion causing an increase in duct loss. Area ruling was applied to the baseline duct and was predicted to reduce the size and extent of the strut-hub corner separation, but the duct design was compromised. The duct loss coefficient at mid-pitch was predicted to increase compared to that of the baseline design. Non-axisymmetric endwall profiling was then used on the duct wall, locally to the strut, to remove the strut-hub corner separation and thus reduce net duct loss, without compromising the duct design away from the strut. The endwall geometry was produced by numerical optimisation. It was shown that the net duct loss was insensitive to casing profiling but highly sensitive to hub profiling. The optimal hub geometry was experimentally tested and shown to completely remove endwall strut-hub corner separation. The profiling was found to reduce the net duct loss by 16%. The paper shows that the key benefit to endwall profiling is that it can be used to safely increase the size of the design space in which aeroengine duct designers can operate.
Probabilistic Analysis of Accelerated Life Tests for Thermal Barrier Coatings
Authors: Riesch-Oppermann Heinz , Hu¨lsmeier Patricia
Published: August 2009

Reliability of thermal barrier coatings (TBCs) of turbine blades and vanes is gaining importance, because the continuous improvement of gas turbine efficiency and CO2 reduction requires an increase in turbine inlet temperatures. To predict the reliable operation of TBCs, lifetime tests using selected material systems have to be conducted. Tests under real operating conditions are often difficult to realise and too time-consuming, since the expected lifetime of several years exceeds the time available for further technological development. To overcome this dilemma, accelerated tests are performed under more severe loading conditions and lifetimes are extrapolated from acceleration to use conditions. Due to the natural variance in the lifetime test data, extrapolation to use conditions is prone to statistical uncertainty. For a reliable lifetime prediction, it is essential to take these uncertainties into account. Probabilistic methods have to be used for this purpose. In the present paper, a Bayesian approach is selected for the probabilistic analysis of the extrapolation uncertainty. This approach is based on the well-known likelihood function, but makes different use of it compared to a classical statistical approach. The first advantage of the Bayesian approach is that it does not suffer from sample size limitations. Since life tests are expensive and time-consuming, the number of available data is generally limited, leading to large uncertainties and making classical statistical procedures questionable, because they are usually based on large sample approximations. As a second advantage, the Bayesian approach allows to eliminate nuisance parameters, which contribute to the lifetime prediction uncertainty, but are not interesting in its own respect. The presented example of using a Bayesian approach is the analysis of cyclic oxidation test data; a commonly used lifetime test for TBC systems. The lifetime of coated specimens is determined under overload conditions for several temperature levels above the operating temperature and the lifetime under use conditions is extrapolated from these data. In a first (analysis) step it is shown, how the uncertainties in the expected lifetime at the various test temperatures can be quantified using Bayesian credibility intervals. In the second (prediction) step, the uncertainty in the extrapolated lifetime is assessed by using an Arrhenius-type acceleration model. It is shown that neglecting the uncertainty in the Arrhenius activation energy leads to a pronounced underestimation of the uncertainty in the extrapolated lifetime.