bluuebunny/crossref_metadata_2025 huggingface dataset:
Compact Combustion Systems Using a Combination of Trapped Vortex and High-G Combustor Technologies
Authors: Zelina J. , Anderson W. , Koch P. , Shouse D. T.
Published: August 2009

Major advances in combustor technology are required to meet the conflicting challenges of improving performance, increasing durability and maintaining cost. Ultra-short combustors to minimize residence time, with special flame-holding mechanisms to cope with increased through-velocities are likely in the future. This paper focuses on vortex-stabilized combustor technologies that can enable the design of compact, high-performance combustion systems. Compact combustors weigh less and take up less volume in space-limited turbine engine for aero applications. This paper presents the UCC, a novel design based on TVC work that uses high swirl in a circumferential cavity to enhance mixing rates via high cavity g-loading on the order of 3000 g’s. The UCC design integrates compressor and turbine features which will enable a shorter and potentially less complex gas turbine engine. Ultimately, it is envisioned that this type of combustion system can be used as the main combustor and/or as a secondary combustor between the high pressure and low pressure turbine to operate as a reheat cycle engine. The focus on this paper includes experimental results of the UCC for a variety of conditions: (1) the addition of turbine vanes in the combustor flowpath, (2) a comparison of JP-8 and FT fuel performance in the combustor, (3) the use of trapped-vortex-like air addition to increase combustor flammability limits, and (4) combustor performance related to two different fuel injector designs. Lean blowout fuel-air ratio limits at 20% the value of current systems were demonstrated. Combustion efficiency was measured over a wide range of UCC operating conditions. This data begins to build the design space required for future engine designs that may use these novel, compact, high-g combustion systems.
Development and Testing of High Temperature Silicon Nitride Microturbine Rotors
Authors: Pujari Vimal , Vartabedian Ara , Wayman Gregg
Published: August 2009

Development and testing of gas turbine quality high temperature silicon nitride (NT154) components will be described. An advanced CNC green (using pressed powder blanks prior to densification) machining based complex shape forming methodology has been developed and successfully deployed to fabricate gas turbine quality rotor, vane ring and shroud components to net shape with high yield and required dimensional tolerances. Utilizing a systems approach involving green blank properties, type of cutting tools and machining parameters, the process has been optimized to achieve required as machined surface finish, dimensional control and part integrity. Integral bladed micro turbine rotors (IBR) and vane rings have been fabricated with dimensional control within 100 microns, surface finish within 1–2 microns. IBRs so formed have been successfully spin tested at room temperature at 40% above designed speed approaching maximum stress in the vicinity of 400 MPa.
API 617’s Requirements on Centrifugal Compressors: A Purchaser’s Viewpoint
Authors: Taherimoghaddam Mahdi
Published: August 2009

Centrifugal compressor’s long delivery times as well as high capital and operating expenditures have classified them as projects critical equipment. Purchasers normally employ American Petroleum Institute (API) standard API 617 as the convenient backbone for customizing their centrifugal compressor’s purchasing specification within oil, gas, and petrochemical industry. Centrifugal compressor’s mechanical and performance integrity guaranteed by the manufacturer at the contract stage is based on purchaser’s specific project requirements reflected in material requisition. Accordingly, purchasers share the responsibility of a suitable design. Among those API 617 clauses applicable to centrifugal compressors, some of them require purchaser’s decision on certain details and features, which should be finalized prior to order placement. It is tried to provide a perspective of the latest edition of API 617 (July 2002) as it is applied to centrifugal compressors from a purchaser’s viewpoint. Moreover, it attempts to address critical sections of the standard and share practical comments on specific clauses.
Stochastic Crack Growth Analysis on Turbine Disk Based on FEM
Authors: Hu Dianyin , Wang Rongqiao
Published: August 2009

Finite element method (FEM) is proved feasible to obtain structural fracture parameters compared with theoretical results of compact tension specimen (CT). Damage tolerance analysis on the turbine disk component was performed based on FEM, where critical crack length was determined through developing the program used to simulate crack growth. Crack growth life of the turbine disk was predicted based on the crack growth model obtained from the experiments. The predicted life agrees with the literature result, which verifies that the method to predict the component’s crack growth life is reasonable and feasible based on FEM. Then, considering random characteristics of material and load, stochastic crack growth of the turbine disk was studied by utilizing orthogonal regression design method. Furthermore, the effect of different random variables on crack growth rate was investigated through the sensitivity analysis in order to improve the component’s reliability.
Prediction of Inter-Turbine Burner (ITB) Performance With Curved Radial Vane Cavity at Various Equivalence Ratios
Authors: Thornburg Hugh J. , Sekar Balu , Zelina Joseph , Lin Charlie , Holder Richard
Published: August 2009

The combustion processes present in modern propulsion systems exhibit very complex turbulent chemically reacting unsteady multiphase flow with fuel spray evaporation and heat and mass transfer. The understanding and design of such systems represents a challenging research area. Ultra-short compact, high performance combustion systems are desirable for advanced propulsion systems. AFRL has proposed placing an Ultra-Compact Combustor (UCC) between a high pressure turbine stage and low pressure turbine stage, to create an innovative Inter-Turbine Burner (ITB) concept. This analysis focuses on ITB combustor technologies that can enable the development of compact, high-performance combustion systems. Compact combustors weigh less and require less volume for space-limited turbine engine aero applications. For turbulent conditions flame speed is directly proportional to the square root of G and high G flames exhibit increased flame speeds, which can aid in the design of shorter combustion systems. This paper presents the Ultra-Compact Combustor (UCC), a novel design based on a high G flame driven by high swirl in a circumferential cavity (CC) utilized to enhance mixing rates via high G-loading on the order of 3000 G’s within the CC. Flow field predictions utilizing FLUENT are presented for the UCC-ITB for a variety of operating conditions: (1) the addition of curved Radial Vanes (CRV) in the combustor flow path, (2) a comparison performance of the combustor at various fuel/air ratios. The effect of various equivalence ratios on the resulting G load distribution, predicted total pressure loss, the entrainment and the calculated exit temperature profile are discussed. The analysis and comparison with available rig test data supplements the understanding of the design space required for future engine designs that may use these novel, compact, high-G combustion systems.
Effects of Turbine Tip Clearance on Gas Turbine Performance
Authors: Bringhenti Cleverson , Barbosa Joa˜o Roberto
Published: August 2009

There are many different sources of loss in gas turbines. The turbine tip clearance loss is the focus of this work. In gas turbine components such as compressor and turbine the presence of rotating blades necessitates a small annular tip clearance between the rotor blade tip and the outer casing. This clearance, although mechanically necessary, may represent a source of large loss in a turbine. The gap height can be a fraction of a millimeter but can have a disproportionately high influence on the stage efficiency. A large space between the blades and the outer casing results in detrimental leakages, while contact between them can damage the blades. Therefore, the evaluation of the sources of the performance degradation independently presents useful information that can aid in the maintenance action. As part of the overall blade loss the turbine tip clearance loss arises because at the blade tip the gas does not follow the intended path and therefore does not contribute to the turbine power output and interacts with the outer wall boundary layer. Increasing turbine tip clearance causes performance deterioration of the gas turbine and therefore increases fuel consumption. The increase in turbine tip clearance may as a result of rubs during engine transients and the interaction between the blades and the outer casing. This work deals with the study of the influence of the turbine tip clearance on a gas turbine engine, using a turbine tip clearance model incorporated to an engine deck. Actual data of an existing engine were used to check the validity of the procedure. This paper refers to a single shaft turbojet engine under development, operating under steady state condition. Different compressor maps were used to study the influence of the curve shapes on the engine performance. Two cases were considered for the performance simulation: constant corrected speed and constant maximum cycle temperature.
Towards Improved Prediction of Aero-Engine Combustor Performance Using Large Eddy Simulations
Authors: James S. , Anand M. S. , Sekar B.
Published: August 2009

The paper presents an assessment of large eddy simulation (LES) and conventional Reynolds averaged methods (RANS) for predicting aero-engine gas turbine combustor performance. The performance characteristic that is examined in detail is the radial burner outlet temperature (BOT) or fuel-air ratio profile. Several different combustor configurations, with variations in airflows, geometries, hole patterns and operating conditions are analyzed with both LES and RANS methods. It is seen that LES consistently produces a better match to radial profile as compared to RANS. To assess the predictive capability of LES as a design tool, pretest predictions of radial profile for a combustor configuration are also presented. Overall, the work presented indicates that LES is a more accurate tool and can be used with confidence to guide combustor design. This work is the first systematic assessment of LES versus RANS on industry-relevant aero-engine gas turbine combustors.
Application of Detached Eddy Simulation to a Subsonic Compressor Rotor
Authors: Gu Chunwei , Feng Fan , Li Xuesong , Chen Meilan
Published: August 2009

An attempt is made in the present paper to apply DES (Detached Eddy Simulation), which is based on S-A model of RANS, for investigating the flow field around a subsonic compressor rotor with a tip clearance of 2% blade height. Comparison of the results by DES and S-A model shows that DES model can capture more intensive vortex flow, such as tip leakage flow, double leakage flow, as well as interaction between the leakage flow and wake flow downstream of the rotor passage. DES model predicts more complicated flow at the separation region near the hub. DES simulation for different operation conditions also reveals interesting details. The shedding angle and strength of the tip leakage flow changes with the blade loading. The starting point of the leakage vortex moves towards the leading edge when the blade loading increases. Double leakage is observed only at the design and higher loading conditions, and is not at a lower loading condition. The tip leakage vortex splits into two branches downstream of the rotor blade due to interaction with the wake flow. Instantaneous results show unsteadiness of the tip leakage vortex. Alternating regions of higher and lower loss is found along the time-averaged leakage vortex trajectory. Obvious is also the unsteadiness in the separation region near the hub.
Film Cooling in a Separated Flow Field on a Novel Lightweight Turbine Blade
Authors: Okita Yoji , Nakamata Chiyuki , Kumada Masaya , Ikeda Masahiro
Published: August 2009

The primary contribution of this research is to clarify the feasibility of a novel lightweight turbine blade with internal and external cooling, which is invented aiming at drastic reduction of weight. With a considerably thinner airfoil, an extensive separation bubble is formed on the pressure side and film cooling performance in such a flow field has to be investigated. Experimental results with a curved duct setup, which simulates the flow field around the proposed airfoil, show that a film cooling is still an effective measure of cooling even in the vastly separated region and it behaves quite similarly to the conventional correlation except for lower blowing ratios where the thermal field is strongly affected by the intense recirculation flow. Comparisons between the experimental and numerical results verify that an affordable RANS simulation is useful to investigate the detailed physics of this flow field. With the numerical modeling, a cooling performance of the proposed blade under a typical engine operating condition is simulated and the metal temperatures of the blade are also predicted with a fluid-solid conjugate calculation. The resultant thermal distribution in the airfoil suggests that the trailing edge portion is inevitably most critical in the temperature and also a considerable thermal gradient across the blade is induced. Thermal profile, however, is partly recovered with some of the film coolant being bypassed from the pressure side to the suction side.
Lifing of Turbomachinery Blades: A Process Driven Approach
Authors: Rao J. S. , Narayan R. , Ranjith M. C.
Published: August 2009

Turbomachinery blades pass through several resonances during start up and shut down operations that cause cumulative damage leading to failures. It is important to estimate life of these blades at design stage so as to reduce prototype testing time. While the technologies required for lifing have been established, it is still a time consuming process to achieve the final result with calculations from different groups involved in solid and fluid mechanics and heat transfer. Here an attempt is made to reduce the design cycle time by way of combining these multifaceted technologies and develop a process driven approach to determine life using Hyper Works platform.
Proposal of United Combustion Model for Premixed and Diffusion Flames and Its Evaluation
Authors: Inage Shin-Ichi
Published: August 2009

A premixed flame assisted by the burning of a diffusion flame is used in gas-turbine combustors to reduce NOx emissions. A united model that can be applied to the premixed and diffusion flames is therefore required to simulate the combustion phenomena. This paper proposes such a united model based on the author’s premixed combustion model for reactive progress variable equation. The proposed model has the following features. 1) It includes the laminar flame speed and the gradient of the mixture fraction as parameters. When the gradient of the mixture fraction is close to zero, the model is also close to the previous premixed combustion model as an asymptotic form. 2) It considers the effects of pressure in the combustor, unburned gas temperature, and flame stretch on combustion based on the laminar flame speed. 3) It can be applied to all types of turbulence models like the k-ε model, large eddy simulations, and direct simulations in the case of wrinkled laminar flames. The effect of turbulence is considered through the turbulent eddy viscosity of all turbulence models. To verify the accuracy of the model, the opposed diffusion flame presented by Tsuji and Yamaoka was numerically simulated, as an example of a laminar diffusion flame. Further, a turbulent diffusion flame, which was assisted by the burning of a pilot jet, was demonstrated using the united combustion model as an example of the turbulent diffusion flame discussed by Barlow and Frank. The flame was known as Sandia Flame D. Model results were in good agreement with the experimental data and this agreement confirmed the proposed united model was able to accurately simulate both diffusion flames.
Customer Adapted Maintenance Plan (CAMP): A Process for Optimization of Gas Turbine Maintenance
Authors: Wa¨rja Mathias , Slottner Pontus , Bohlin Markus
Published: August 2009

Maintaining high levels of availability and reliability are essential objectives for many industries, especially those that are subject to high costs due to shutdowns of critical systems, e.g. gas turbines. To utilize these systems as effectively as possible, preventive maintenance must be optimized. Determining what is optimal is, however, a multi-variable task requiring detailed knowledge about the components in the system and their different damage mechanisms. These factors have always affected the condition of the gas turbine and maintenance actions, but only recently has it been possible to estimate and measure them correctly for individual components during operation. In the past, it was necessary to construct maintenance intervals from the most critical component (or components), requiring the highest maintenance frequency. An additional worst-case scenario margin was also necessary, taking into account factors such as possible load variation, differences in environment (affecting e.g. power turbine temperatures) and other sources of uncertainty. These uncertainties together have determined traditional maintenance planning, with maintenance packages each containing a set of maintenance activities for a set of components being predetermined and preplanned. With the new CAMP approach, the maintenance strategy is to reach a Retirement For Cause (RFC) strategy, where components are not replaced until a potential failure has been detected. This requires measurement techniques that can monitor how the gas turbine is operated, prognostics capabilities that foresee maintenance needs, and test methods that can determine the state of a component during maintenance events. One important part of CAMP is therefore a prognostic tool which tells us the condition, and therefore the maintenance needs, of individual components within the gas turbine. To handle this information and efficiently make a preventive maintenance plan, software for gas turbine maintenance optimization has been developed. The software can not only calculate the most efficient point in time for a maintenance action, it can also adjust the maintenance plan to any customer’s specific demands. This paper describes the model, gathering and processing of information, risk assessment performance and the result from an optimization which groups maintenance actions as a result of customer prioritized demands. It also describes the software layout and how it is used.
CFD Simulation of Noise in Gas Turbine Combustors by Means of Turbulence Refluctuation Method
Authors: Tiribuzi Stefano
Published: August 2009

The paper describes a numerical simulation methodology based on CFD for deriving and analyzing the spectral and spatial characteristics of combustion noise in industrial gas turbine combustors. ENEL is testing the combustion section of a medium size pure hydrogen-fed gas turbine, during which pressure fluctuation levels are also measured to asses the combustion stability. Pressure probes are located in colder zones only, but information on the fluctuations levels throughout the whole component are also desired. For this purpose, a simple empirical and, to the knowledge of the author, original method, based solely on CFD modelling, was developed for reproducing in a realistic way the spatial and transient characteristics of the acoustic flow field inside the combustor volumes. The method employs a sparse and persistent excitation on a wide frequency spectrum, by imposing a stochastic fluctuating component to the velocity computed on each grid node throughout the entire computational domain. The intensity of this additional component is proportional to the local level of the modelled turbulent velocity, so the method will be shortly designated as PRMT (Partial Refluctuation of Modelled Turbulence). This method requires that all the acoustically connected volumes be included in the computational domain and that transients be protracted for a time sufficient to provide meaningful spectral information. KIEN, an in-house low diffusive URANS code capable of simulating 3D reactive flows, was used. The adopted Very Rough Grid approach made it possible to protract the simulated transient for a long time, with an affordable computing time. Comparison with in-plant measured data shows that the refluctuation method provides a realistic qualitative description of the noise spectrum. The spatial distribution of computed acoustic field is also derived and analyzed.
Investigation of Flame Stability Characteristics of the EV Burner on the GT13E2 Engine
Authors: Biagioli F. , Schiessel P. , Fischer L.
Published: August 2009

The development and optimization of dry low NOx combustors for industrial gas turbines could largely benefit from better understanding of the way the burners stabilize lean premixed turbulent flames. This has motivated the present work where the stabilization properties of turbulent (partially) premixed flames in the annular combustor of the ALSTOM GT13E2 gas turbine equipped with the EnVironmental (EV) burner are studied. The study benefits from the results of a previous analysis where the flame anchoring properties have been determined in single EV burner configuration, using a one-dimensional boundary layer type model and Large Eddy Simulation (LES). These properties, which are confirmed by experiments on single burner atmospheric and high pressure test rigs, consist in two possible stabilization modes for the flame: a) anchored just downstream the exit of the burner or b) displaced inside it, depending if the bulk equivalence ratio is below or above a characteristic value. The change from one flame stabilization mode to the other implies a change in the NOx characteristic versus flame temperature due to different levels of unmixedness (higher when the flame is stabilized inside the burner). Such a change in the NOx characteristic is found also in the GT13E2, indicating that flames in the combustor of this engine have same stabilization properties as seen on single burner rigs. It is seen that low frequency pulsations—typically anticipating the approaching of the lean stability limit—becomes discernible on the GT13E2 as soon as the equivalence ratio falls below the characteristic value separating the two flame stabilization modes. This finding gives the opportunity of more effective extrapolation of single burner test rig data to engine conditions. Finally, a simple model which can determine the effect of propane content in natural gas on the conditions where the transition between the two stabilization modes takes place is developed.
Gas Turbine Temperature Prediction Using Unsteady CFD and Realistic Non-Uniform 2D Combustor Exit Properties
Authors: Felten Fre´de´ric N. , Kapetanovic Semir , Holmes D. Graham , Ostrowski Michael
Published: August 2009

Typical Computational Fluid Dynamics (CFD) studies performed on High Pressure Turbines (HPT) do not include the combustor domain in their analyses. Boundary conditions from the combustor exit have to be prescribed at the inlet of the computational domain for the first HPT nozzle. It is desirable to include the effect of combustor non-uniformities and flow gradients in order to enhance the accuracy of the aerodynamics and heat transfer predictions on the nozzle guide vanes and downstream turbine blades. The present work is the continuation of steady and quasi-unsteady studies performed previously by the authors. A fully unsteady nonlinear approach, also referred to as sliding mesh, is now used to investigate a first HPT stage and the impact of realistic non-uniformities and flow gradients found along the exit plane of a gas turbine combustor. Two Turbine Inlet Boundary Conditions (TIBC) are investigated. Simulations using a two-dimensional TIBC dependant on both the radial and circumferential directions are performed and compared to baseline analyses, where the previous two-dimensional TIBC is circumferentially averaged in order to generate inlet boundary conditions dependant only on the radial direction. The two elements included in the present work, combustor pitchwise non-uniformities and full unsteady blade row interactions are shown to: (1) alter the gas temperature profile predictions up to ±5%; (2) modify the surface temperature predictions by ±8% near the trailing edge of the vane suction side; (3) increase the overall pressure losses by roughly 1%, and (4) modified the ingestion behavior of the purge cavity flow. In addition, keeping in mind the tradeoff between improved predictions and computational cost, the use of an unsteady sliding mesh formulation, instead of a quasiunsteady frozen gust, reveals the importance of the two-way unsteady coupling between adjacent blade rows for temperature and pressure predictions.
Steady State Analysis of a SOFC/GT Hybrid Power Plant Test Rig
Authors: Panne Tobias , Widenhorn Axel , Aigner Manfred
Published: August 2009

In the present paper a steady state analysis of a SOFC/GT hybrid cycle test rig is shown. In the test rig the SOFC stack is replaced by a hardware simulator. Therefore the cycle can be investigated without the risk of damaging the cell. One focus of the numerical studies presented here is the influence of the SOFC stack size on the commercial Turbec T100 gas turbine and the system parameters, i.e., power output and electrical efficiency. The results are used to define the stack size for the test rig simulator. Based on the test rig configuration another focus of this paper is to work out the effect of several system parameters, like ambient conditions or pressure losses, on the hybrid system. Here the discussion will concentrate on the gas turbine operating behavior. Furthermore the power balance between fuel cell and gas turbine. Therefore the SOFC boundary conditions are changed to analyze there influence on the system performance. For the presented studies a validated steady state in-house simulation tool is used.
Clearance Reduction and Performance Gain Using Abradable Material in Gas Turbines
Authors: Giovannetti Iacopo , Bigi Manuele , Giannozzi Massimo , Sporer Dieter R. , Cappuccini Filippo , Romanelli Marco
Published: August 2009

An improvement in the energy efficiency of industrial gas turbines can be accomplished by developing abradable seals to reduce the stator/rotor gap to decrease the tip leakage flow of gases in the hot gas components of the turbine. “ABRANEW” is a project funded by the European Commission aimed at developing a high temperature abradable material capable of controlled abrasion and resistant to erosion and oxidation. In order to define the basic parameters such as the component shape, the existing gap, the expected gap reduction, the seal thickness and other geometric parameters, a comprehensive review of the design of the blade/shroud/casing system was performed.
Numerical and Experimental Investigation on a Low-Speed Compressor Cascade With Circulation Control
Authors: Fischer S. , Saathoff H. , Radespiel R.
Published: August 2009

Experimental and numerical results for the flow through a stator cascade with active flow control are discussed. By blowing air through a slot close to the trailing edge of the aerofoils, the deflection angle as well as the static pressure rise in the stator are increased. The aerofoil design is representative for a 1st-stage stator geometry of a multi-stage compressor adapted for low–speed applications. To allow a reasonable transfer of the high-speed results to low-speed wind tunnel conditions, a corresponding cascade geometry was generated applying the Prandtl–Glauert analogy. With this modified cascade numerical simulations and experiments have been conducted at a Reynolds number of 5 · 105. As a reference case two-dimensional flow simulations without circulation control are considered using a Navier–Stokes solver. In the related wind tunnel tests three–dimensional conditions occur in the test rig. Nevertheless five–hole probe measurements in the wake of the blade mid section show a good agreement with the theoretical characteristics. Additional investigation along the whole blade span gives a deeper insight into the flow topology. For design conditions different blowing rates are applied. The wind tunnel tests confirm the positive benefit, which is predicted by two-dimensional calculations. The offset between simulated and measured pressure rise decreases with increasing blowing mass flows due to the reduction of the axial velocity ratio. This result is related to a redistribution of the passage flow which can only be explained in a three–dimensional analysis including the side wall influence. The benefit of the circulation control at varying blowing rates is finally characterized by the efficiency and the static pressure rise per injected energy.
Modelling of Film Cooling for Turbine Blade Design
Authors: Tartinville B. , Hirsch Ch.
Published: August 2009

The use of Computational Fluid Dynamics for modern turbine blade design requires the accurate representation of the effect of film cooling. However, including the cooling holes in the computational domain requires a substantial meshing effort and leads to a drastic increase in the computing time. Therefore, it is here proposed to represent the effect of cooling holes by adding a local source term at the hole exit. The major advantage of such a method is that it does not require any additional meshing effort and induces only a small increase in computational time. Results obtained with this approach are compared to experimental data and to results obtained with the full meshing of the cooling holes on a series of test cases. Though details of the flow structure downstream of the holes cannot be perfectly captured, this method allows an accurate prediction of the overall flow and performance modifications induced by the presence of the cooling holes.
Overspray and Interstage Fog Cooling in Compressor Using Stage-Stacking Scheme: Part 2—Case Study
Authors: Wang Ting , Khan Jobaidur R.
Published: August 2009

A stage-by-stage wet-compression theory and algorithm have been developed for overspray and interstage fogging in the compressor. This theory and algorithm are used to calculate the performance of an 8-stage compressor under both dry and wet compressions. A 2D compressor airfoil geometry and stage setting at the mean radius are employed. Six different cases with and without overspray have been investigated and compared. The stage pressure ratio enhances during all fogging cases as does the overall pressure ratio, with saturated fogging (no overspray) achieving the highest pressure ratio. Saturated fogging reduces specific compressor work, but increases the total compressor power due to increased mass flow rate. The results of overspray and interstage spray unexpectedly show that both the specific and overall compressor power do not reduce but actually increase. Analysis shows this increased power is contributed by increased pressure ratio and, for interstage overspray, “recompression” contributes to more power consumption. Also it is unexpected to see that air density actually decreases, instead of increases, inside the compressor with overspray. Analysis shows that overspray induces an excessive reduction of temperature that leads to an appreciable reduction of pressure, so the increment of density due to reduced temperature is less than decrement of air density affected by reduced pressure as air follows the polytropic relationship. In contrast, saturated fogging results in increased density as expected. After the interstage spray, the local blade loading immediately showed a significantly increase. Fogging increases axial velocity, flow coefficient, blade inlet velocity, incidence angle, and tangential component of velocity. The analysis also assesses the use of an average shape factor in the generalized compressor stage performance curve when the compressor stage information and performance map are not available. The result indicates that using a constant shape factor might not be adequate because the compressor performance map may have changed with wet compression. The results of non-stage-stacking simulation are shown to underpredict the compressor power by about 6% and net GT output by about 2% in the studied cases.
Investigating Circumferential Non-Uniformities in Throughflow Calculations Using an Harmonic Reconstruction
Authors: Thomas J. P. , Le´onard O.
Published: August 2009

The computation time and the extraction of useful information remain severe drawbacks to systematic use of modern three-dimensional Navier-Stokes codes in a design procedure of multistage turbomachines. That explains why throughflow simulation is still widely used at industrial scale. The main limitation of throughflow is however the need for empirical models to reproduce blade-flow interactions and major 3D flow features. The purpose of this work is to investigate the degree to which empiricism could be reduced by using the averaged-passage equations of Adamczyk, combined with an harmonic closure strategy. To that aim, results of a computation performed with a steady three-dimensional Navier-Stokes code are used to calculate some of the additional terms of the circumferentially-averaged equations, the so-called circumferential stresses. The importance of the latter to bring back the mean effect of circumferential non-uniformities is proven by injecting them into a throughfow simulation. The frequency spectrum of these terms is next investigated and it is demonstrated that an harmonic reconstruction can model the circumferential stresses.
Forced Response and Surge Behaviour of IP Core-Compressors With Ice-Damaged Rotor Blades
Authors: Dhandapani Sridar , Vahdati Mehdi , Imregun Mehmet
Published: August 2009

This paper deals with performance, forced response and surge issues arising in ice-damaged IP compressor assemblies. In addition to the inherent blade-passing excitation, damaged rotor blades may cause low engine-order excitation for both upstream and downstream blade rows, the strength of which depends on the severity, location and circumferential distribution of the damage. Similarly, performance and surge stability are related to the nature of the blockage caused by the damaged blades. Several symmetric and asymmetric damage configurations were studied using a 49-bladed rotor assembly in order to quantify the consequences of ice damage and assess the maximum amount of damage that can be tolerated. Both single-row part-annulus and multi-row whole-annulus models were used in the numerical study.
Analyses and Optimization of a Propulsion Cycle for Unmixed High Bypass Turbofan
Authors: Ghenaiet Adel
Published: August 2009

This paper deals with a parametric study and an optimization for the design variables of a high bypass unmixed turbofan equipping commercial aircrafts. The objective of the first part of this study is to highlight the effects of the principal design parameters (bypass ratio, compression ratios, turbine inlet temperature etc..) on the uninstalled performance, in terms of specific thrust and specific fuel consumption. The second part concerns the optimization, aiming at finding the optimum design parameters concurrently minimizing the specific fuel consumption at cruise, and meeting the thrust requirement at takeoff. The cycle analyzer (on-design and off-design) as coupled to the optimization algorithm MMFD by adopting a random multi-starts search strategy is shown to be stable and converging. The predefined requirements and constraints have dictated utilizing an engine with a high-bypass ratio, high-pressure ratio and a moderate turbine inlet temperature. In general, the obtained results compare fairly well with typical data available for an equivalent ‘reference’ engine. This elaborated methodology is shown to be consistent with the conceptual design requirements and accuracy, because, it does not use components’ characteristics, and operates on simplifying assumptions. This present methodology can be readily adapted for other configurations of aero-engines as well, and easily integrated in a multi-disciplinary design approach.
Numerical Investigation of Fluid Flow and Heat Transfer in a Turbine Blade With Serpentine Passage and Latticework Cooling
Authors: Su Sheng , Liu Jian-Jun , Fu Jing-Lun , Hu Jie , An Bai-Tao
Published: August 2009

This paper describes 3D numerical simulations of a turbine rotor blade with complex internal cooling structure. Conjugate heat transfer method is used to get an accurate blade temperature distribution. The cooling structure consists of a rib roughened serpentine channel near the leading edge, latticework cooling channels in the middle part and slots at the trailing edge. Both the rib roughened channel and the latticework cooling channels can enhance the heat transfer. Furthermore, the latticework cooling channels can enhance the blade strength. Different cooling structures are simulated and analyzed, including changing the configuration of the latticework cooling channels, and whether to apply two holes to the blade tip or not. The effects of different internal cooling configurations are as follows. Firstly, blade temperature distribution is highly disordered: low temperature at the U turning of the serpentine passage, medium temperature at the location of latticework in a relatively uniform distribution, and a few hot spots on the trailing edge. Secondly, tip holes can improve the cooling in serpentine passage by improving fluid flow at the U turning with a negative impact on the cooling of latticework and trailing edge slots. Thirdly, smaller width to height ratio of the sub passage in latticework channels increases coolant flow resistance and leads to an improved latticework cooling with also a negative impact on the cooling of trailing edge slots.
Hybrid Gas Bearings With Controlled Supply Pressure to Eliminate Rotor Vibrations While Crossing System Critical Speeds
Authors: San Andre´s Luis , Ryu Keun
Published: August 2009

Micro-turbomachinery (MTM) implements gas bearings in compact units of enhanced mechanical reliability. Gas bearings, however, have little damping and wear quickly during transient rub events. Flexure pivot tilting pad bearings offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability; and when modified for hydrostatic pressurization, demonstrate superior rotordynamic performance over other bearing types. External pressurization stiffens gas bearings thus increasing system critical speeds, albeit reducing system damping. Most importantly, measurements demonstrate that external pressurization is not needed for rotor super critical speed operation. In practice, the supply pressure could be shut off at high rotor speeds with substantial gains in efficiency. The paper introduces a simple strategy, employing an inexpensive air pressure regulator to control the supply pressure into the hybrid bearings, to reduce or even eliminate high amplitudes of rotor motion while crossing the system critical speeds. Rotor speed coast-down tests with the pressure controller demonstrate the effectiveness of the proposed approach. A simple on-off supply pressure control, i.e. a sudden increase in pressure while approaching a critical speed, is the best since it changes abruptly the bearing stiffness coefficients and moves the system critical speed to a higher speed. A rotordynamic analysis integrating predicted bearing force coefficients forwards critical speeds in agreement with the test results. Predicted rotor responses for the controlled supply conditions show an excellent correlation with measured data. The experiments validate the predictive tools and demonstrate the controllable rotordynamic characteristics of flexure pivot hybrid gas bearings.
Influence of Swept Wing on Axial Steam Turbine Static Cascade Aerodynamics
Authors: Feng Ziming , Han Wanjin , Zhong Jingjun , Yan Hongming
Published: August 2009

Super-critical steam turbine high pressure stage static blade cascade is as the prototype blade to numerical simulations. The prototype blade has aft-loading and big front-edge radius characteristics. Different swept blades are made by changing the sweep angle and sweep height in order to study the effect of blade sweep on aerodynamic characteristics of super-critical steam turbine high pressure stage blade. The numerical simulation sweep angle are made of fore-angel 10°, 20°, 30° and aft-angle 10°, 20°, 30°, sweep height are made of 10%, 20%, 30% blade height. The steam turbine aerodynamics are analyzed such as static pressure coefficient of swept blade profiles, total pressure coefficient of swept blade at blade trailing edge, contour of mass averaged static pressure on meridional surface and velocity streamlines along hub and suction surface by CFD software CFX®. The numerical simulation results indicate the fore-swept blades increase the low energy fluid centralizing in endwall corner and the endwall secondary flow loss, but the loss is decreased at mid-span, comparing to the baseline. But aft-swept blades decrease the low energy fluid centralizing in endwall corner and the endwall secondary flow loss, but the loss is increased at mid-span, comparing to the baseline. Either the fore-sweep height or the aft-sweep angle can increase the above results. At the same time the swept blade aerodynamics also are computed at 10, −10 degree incidence, the results indicate it keep down the aft-loading characteristics of baseline.
Experimental and Numerical Investigation of Fluid Dynamics of the Bounded and Unbounded Triangular Jets
Authors: Riahi Reza , Bagheri Farshid , Farhanieh Bijan
Published: August 2009

In the present study, the fluid characteristics of triangular turbulent jet flow are considered experimentally and numerically. The results of spatially developed three-dimensional jet, issued from an equilateral triangular nozzle are presented. The jet is discharged to both bounded and unbounded domains. Because of the wind tunnel set up restrictions, the experimental study has done just for the bounded domain. The hot-wire anemometry is used for experimental study. A numerical method employing control volume approach with collocated grid arrangement which couples the velocity and pressure fields with SIMPLEC algorithm is introduced to discrete the governing equations of fluid flow. The turbulent stresses are approximated using k-ε model. Both bounded and unbounded domains have been studied using a numerical code. The velocity field is presented using profiles and contours. Comparison of numerical and experimental results for the bounded domain shows a good agreement. The flow pattern results show that the strong mixing and flow entrainment from free boundaries into the jet takes place and eventuates to expand the jet highly at the unbounded domain.
Shrink Fit Effects on Rotordynamic Stability: Experimental Study
Authors: Jafri Syed Muhammad Mohsin , Vance John M.
Published: August 2009

This paper presents an experimental study of internal friction effects on two different test rotors with shrink fit and interference fit joints. One of the setups was a single-disk rotor with an interference fit joint to the main shaft through a mechanically adjustable tapered sleeve; the other setup was a two-disk rotor with a variable cross-section shaft, having the two disks shrunk fit into an aluminum sleeve at the ends. The slippage in these types of joints is known to be a potential source of sub-synchronous rotordynamic instability in rotating machines. The experimental results from the rotor setups show the presence of strong unstable sub-synchronous rotor vibrations initiated at operating speeds above the first critical speeds of the rotor-bearing systems. The experiments with the two-disk rotor demonstrated that different distributions of shrink fit at two locations (loose fit at one end; tight fit at the other end) were necessary to produce rotordynamic instability. The instability in that case caused complete wreckage of the test rig, showing that the sub-synchronous vibrations caused by slippage at interference fit joints are potentially dangerous to the safe operation of rotating machines. Furthermore, a critical radial interference (shrink fit) of 1 mils (25.4 μm) at speed was identified to cause an onset of instability in several of the experiments.
Adaptive Control of Combustion Instabilities in Annular Combustors
Authors: Illingworth Simon J. , Morgans Aimee S.
Published: August 2009

An adaptive control algorithm based on Lyapunov’s direct method has been implemented in a low-order thermoacoustic network model of an axisymmetric annular combustor. The pressure perturbation at a fixed axial location downstream of the flame — provided by multiple pressure measurements around the combustor circumference — acts as the control input. Control is achieved via modulation of the fuel flow rate at multiple fuel valve locations. New expressions for the controller’s adaptation rates are derived by specifying the desired control settling time: these adaptation rates are functions of known parameters only. Time domain simulations show that the controller successfully stabilises both longitudinal and circumferential modes (including the simultaneous control of multiple unstable modes), even from within the limit cycle. The adaptive controller successfully retains control following a large change in the combustor operating conditions.
The Effect of Clearance Flow of Variable Area Nozzles on Radial Turbine Performance
Authors: Tamaki Hideaki , Goto Shinya , Unno Masaru , Iwakami Akira
Published: August 2009

The flow behind the variable area nozzle for radial turbines was measured with a 3-hole yaw probe and calculated with CFD. Two nozzle throat-areas were investigated: the smallest and the largest opening for the variable nozzle. Test results agreed with the calculated results qualitatively. The leakage flow through the tip clearance of the nozzle vane significantly affected the flow field downstream of the nozzle vane with the smallest opening. However, the effect on leakage flow on the flow field downstream of the nozzle vane with the largest opening was very weak. In the flow field of the largest opening nozzle, the effect of wake s dominant. The effect of the clearance of the nozzle vane on the turbine performance was estimated by a 1D-model and the strong influence on the turbine efficiency was confirmed at smallest opening. The flow fields in the impeller downstream of the nozzle vane at the smallest opening with and without the nozzle clearance were investigated with CFD. The setting angle of the nozzle vane without clearance was adjusted to match the operating point of the turbine with the nozzle clearance. In order to extract the specific work from the impeller, the nozzle vane with the vane clearance requires the larger vane setting angle than that without clearance. The increase of the vane setting angle increases the incidence loss and deteriorates turbine efficiency.