bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibratory Behavior Prediction of a Mistuned Clustered Stator Vane: Non-Intrusive Stochastic Methods
Authors: Philippe Jonathan , Thouverez Fabrice , Blanc Laurent , Gruin Marion
Published: August 2015

The role of stator vanes is to straighten the air flow on each stage of axial compressors. They are so subject to dynamically fluctuating high pressure loads. Furthermore, monobloc clustered designs have been developed to facilitate manufacturing process and reduce costs, but they result in loss of cyclic symmetry properties and very low structural damping. This makes it more difficult to predict vibratory behavior, when taking high modal density and extreme sensitivity to mistuning into account, and even more essential to ensure structural strength in the context of fatigue. In most cases, mistuning due to geometrical and material tolerances is unknown. Here, a non-intrusive spectral stochastic method has been developed to predict the vibratory behavior of a clustered stator vane in which the Young modulus of some blades is associated with a random variable representing the mistuning effect. This method is based on a stochastic modal analysis which consists in projecting eigenfrequencies and modes shapes on a polynomial chaos basis. Computation of spectral coefficients is performed through non intrusive ways — making the method applicable to any problem — as Smolyak projection or regression by least square method. These two methods are compared based on criteria of computations costs, accuracy, robustness and convergence. These methods have been tested on a simplified stator vane model - based on a 2D Euler-Bernoulli beams assembly. Regression method provides rather accurate results unlike Smolyak projection whatever the initial configurations of the problem. Computation costs are reasonable but could increase really fast according to polynomial degree and stochastic dimension. Thus, regression method is an accurate, robust and fast enough method to predict the vibratory behavior of a mistuned clustered stator vane.
Dual Drive Booster for a Two-Spool Turbofan: Performance Effects and Mechanical Feasibility
Authors: Speak Trevor H. , Sellick Robert J. , Kloos Vadim , Jeschke Peter
Published: August 2015

A novel two-spool turbofan engine configuration is described which uses a booster powered by both the LP and HP spool. Design and off-design performance analysis shows the operating characteristics of the configuration and a mechanical feasibility study of the gearbox is presented.

The trends towards ever higher engine overall pressure ratio and bypass ratio have resulted in a combination of higher pressure ratio and lower blade speed in the booster compressor of conventional two spool turbofans. This combination gives rise to many stages in the booster and/or lower booster efficiency and also a higher degree of off-design miss-match between the core compressors. The current paper describes an engine architecture which aims to alleviate both these issues by powering the booster compressor from both LP and HP spools through an epicyclic gear system. We have called this engine architecture the Dual Drive Booster. The concept gives the engine designer greater flexibility to optimize component performance and work split, resulting in the potential for lower cruise SFC and higher hot day take-off thrust capability than current engine configurations.

The gear system is described along with the mathematical derivation of the booster rotational speed in terms of LP and HP spool speeds. Both design point and off-design performance modelling has been conducted and comparison is made between a conventional turbofan and a turbofan fitted with the Dual Drive Booster. The results show a significant enhancement in take-off thrust due to the better speed match of the booster. The paper also describes the results of a preliminary study into the design and mechanical feasibility of the engine architecture and gear system.

The presented concept is an alternative to the conventional turbofan and should be considered during the conceptual design of future aircraft engines.
Robust Design Optimization Applied to a High Pressure Turbine Blade Based on Surrogate Modelling Techniques
Authors: Wagner Frank , Kühhorn Arnold , Parchem Roland
Published: August 2015

To achieve reverse objectives in engine design, advanced modelling and analysis methods are among the key research technologies. In the presented work, a robust design optimization of a first stage high pressure turbine blade has been carried out. This blade derives from a current production of a Rolls-Royce aero engine.

The motivation of this work is to show that the methodology of robust design optimization can be applied to high pressure turbine blades. A fully automated workflow, which encapsulated the integral blade design and analysis process, has been used. The main workflow objective is a representative life value of the external surface of the blade. In addition, the workflow enables the engineering uses to consider sub objectives like mass, efficiency and life at critical locations of the blade. These can also be taken into account in the multi-objective robust design optimization. This research also focuses on the use of surrogate models, with attention to the delivery of a physically correct result. For this purpose, the validation of the applied methods has a huge significance and a toolbox was created to generate and evaluate the quality of the surrogate models.

In the present case sixteen geometry parameters were considered. In order to show that this methodology is not limited to geometry variation, parameters for material specification and for boundary conditions were varied in addition. The surrogate model was trained by the workflow generated DoE-data and could be used for different kinds of optimization.

As a conclusion, it has been demonstrated that the methodology can be used for the engineering design process of turbine blades, while delivering physically correct results. The different techniques for surrogate modelling were examined and compared. With the help of these surrogate models, an optimization of life, mass and efficiency with 22.5 million evaluations was possible. Finally, an overview of the methodology for the case of a real world turbine blade could be given, and an improved blade in the sense of multi-objective robust design was found.
Unsteady Operative Conditions of Bleeding Lines in Heavy Duty Axial Gas Turbine
Authors: Cioffi Marco
Published: August 2015

The proper design and operation of air bleeding pipes (blow-off lines) from axial compressors in heavy duty gas turbines is relevant to protect the compressor during start-ups and shut-downs by avoiding dangerous flow instabilities in the first stages. The blow-off lines are usually equipped by valves, which are closed during normal gas turbine operation and opened at low rotor speed. During gas turbine shut-downs the blow-off valves open instantaneously.

In this paper the unsteady flow behavior in blow-off lines following the valve opening is presented together with numerical results based on available field data. The paper main scope is to address and to help the design of experimental activities on production gas turbines and to make available some simple numerical tools to be adopted during the industrial design of an axial compressor and its auxiliary systems. The performed analysis results have been used to define the structural requirements and the correct positioning of the measuring probes installed in blow-off lines. In addition the presented models are part of the compressor design loop, used to compute a fast evaluation of the limiting mass flow rate, which characterizes the blow-off pipes as gas turbine safety devices.
Disc Temperature Modelling Using Reduced Order Proper Orthogonal Decomposition Models
Authors: van Paridon Andrew , Bacic Marko , Ireland Peter T. , Daniel Ron
Published: August 2015

This paper presents a novel approach to modelling disc temperature distributions for use in health monitoring applications. The method combines singular value decomposition techniques with a series of low order transfer functions to predict the thermal response over a typical flight cycle. The model inputs reflect typical online measurements; engine speed, altitude, and compressor exit temperature. The model’s complexity has been reduced by projection and truncation of the reference data and its decompositions. The model predicts transient temperatures anywhere within the disc’s profile to an accuracy of 20K, and similarly the thermal gradient can be calculated in any direction within the 2D cross-section. The result is a simple model that is suitable for application in a FADEC system, with the accuracy necessary to safely extend a disc’s life through online calculation of fatigue damage incurred for individual flights. The paper concludes by comparing the model with an earlier method using a grey box physics approach.
Design and Development of a Full-Scale Generic Transient Heat Transfer Facility (THTF) for Air System Validation
Authors: van Paridon Andrew , Dann Andrew , Ireland Peter , Bacic Marko
Published: August 2015

This paper describes the design and development of a major new facility capable of reproducing flow conditions for large civil aero engine turbine and compressor segment cavities. The facility reproduces in 3-D, typical secondary air system cruise temperatures, pressures and mass flows. The facility allows better understanding of the circumferential heat transfer effects of air system flows on turbine and compressor casings, as these have a significant influence on both steady-state and transient blade tip clearance behavior. Different air system architectural solutions are considered and 1-D transient air system modelling is used to design architecture to ensure that they meet tight performance requirements in terms of allowable pressure and temperature ripples when subject to fast switching of flows. An explanation of the design of the double-skin pressure vessel using 2-D axisymmetric thermo-mechanical analysis to understand the life-limiting features of the design is discussed. Finally we conclude the paper with some experimental results from rig commissioning and the use of these results in the determination of engine casing transients is discussed.
Aerodynamic Optimization of the Nozzle for the Last Stage of Steam Turbine
Authors: Macálka Aleš , Synáč Jaroslav , Váchová Jana , Hajšman Miroslav
Published: August 2015

In order to meet the requirements of rising energy demand, one goal in the design process of modern steam turbines is to achieve high efficiencies. A major gain in efficiency is expected from the optimization of the last stage of a low pressure turbine (LP).

This paper focuses on aerodynamic study by compound lean, axial sweep and hub end-wall of nozzle. The objective function is to maximize efficiency and minimize the leaving losses under the assumption of constant mass flow rate.

The aerodynamic design process involves commercial 3D CFD tools. The maximization of the objective functions is achieved by means of a Design of Experiment (DoE) method “Optimal Space Filling” based on “Latin Hypercube Sampling”.

Finally, the optimized design is analyzed by a transient (Time Transformation) CFD simulation. Furthermore, the detailed flow pattern of the optimized and the initial design is analyzed and compared.
Hybrid RANS-LES Modeling of a Hot Streak Generator Oriented to the Study of Combustor-Turbine Interaction
Authors: Andreini A. , Facchini B. , Insinna M. , Mazzei L. , Salvadori S.
Published: August 2015

Turbine entry conditions are characterized by unsteady and strongly non-uniform velocity and temperature and pressure fields. The uncertainty and the lack of confidence associated to these conditions require the application of wide safety margins during the design of the turbine cooling systems, which are detrimental for the efficiency of the engine. These issues have been further complicated by the adoption of lean-burn technology in modern aeroengines, identified by many manufacturers as the most promising solution for a significant reduction of NOx emission. Such devices are in fact characterized by a very compact design, whereas the strong swirl component generated by the injector is maintained up to the end of the flametube due to the absence of dilution holes, which in conventional combustors provides the required pattern factor.

Bearing in mind complexity and costs associated to the experimental investigation of combustor-turbine interaction, CFD has become a key and complementary tool to understand the physical phenomena involved. Due to the well-known limitations of the RANS approach and the increase in computational resources, hybrid RANS-LES models, such as Scale Adaptive Simulation (SAS), are proving to be a viable approach to resolve the main structures of the flow field.

This paper reports the main findings of the numerical investigation of a hot streak generator for the study of combustor-turbine interaction. The results were compared to experimental data obtained from a test rig representative of a lean-burn, effusion cooled, annular combustor, developed in the context of the EU project FACTOR. Steady RANS and unsteady SAS runs were carried out in order to assess the improvements related to hybrid models. Additional simulations were performed to investigate the effect of the periodicity assumption and the impact of liner cooling modelling on the exit conditions.
Impact of Swirl Flow on Combustor Liner Heat Transfer and Cooling: A Numerical Investigation With Hybrid RANS-LES Models
Authors: Mazzei L. , Andreini A. , Facchini B. , Turrini F.
Published: August 2015

This paper reports the main findings of a numerical investigation aimed at characterizing the flow field and the wall heat transfer resulting from the interaction of a swirling flow provided by lean burn injectors and a slot cooling system, which generates film cooling in the first part of the combustor liner. In order to overcome some well-known limitations of RANS approach, e.g. the underestimation of mixing, the simulations were performed with hybrid RANS-LES models, namely SAS-SST and DES-SST, which are proving to be a viable approach to resolve the main structures of the flow field. The numerical results were compared to experimental data obtained on a non-reactive three sector planar rig developed in the context of the EU project LEMCOTEC.

The analysis of the flow field has highlighted a generally good agreement against PIV measurements, especially for the SAS-SST model, whereas DES-SST returns some discrepancies in the opening angle of the swirling flow, altering the location of the corner vortex. Also the assessment in terms of Nu/Nu0 distribution confirms the overall accuracy of SAS-SST, where a constant over-prediction in the magnitude of the heat transfer is shown by DES-SST, even though potential improvements with mesh refinement are pointed out.
Best Strategies for the Development of a Holistic Porosity Model of a Heat Exchanger for Aero Engine Applications
Authors: Yakinthos K. , Misirlis D. , Vlahostergios Z. , Flouros M. , Donnerhack S. , Goulas A.
Published: August 2015

In an attempt to manage CFD computations in aero engine heat exchanger design, this work presents the best strategies and the methodology used to develop a holistic porosity model, describing the heat transfer and pressure drop behavior of a complex profiled tubular heat exchanger for aero engine applications. Due to the complexity of the profile tube heat exchanger geometry and the very large number of tubes, detailed CFD computations require very high CPU and memory resources. For this reason the complex heat exchanger geometry is replaced in the CFD computations by a simpler porous medium geometry with predefined pressure loss and heat transfer.

The present work presents a strategy for developing a holistic porosity model adapted for heat exchangers, which is capable to describe their macroscopic heat transfer and pressure loss average performance. For the derivation of the appropriate pressure loss and heat transfer correlations, CFD computations and experimental measurements are combined. The developed porosity model is taking into consideration both streams of the heat exchanger (hot and cold side) in order to accurately calculate the inner and outer pressure losses, in relation to the achieved heat transfer and in conjunction with the selected heat exchanger geometry, weight and operational parameters. For the same heat exchanger, RAM and CPU requirement reductions were demonstrated for a characteristic flow passage of the heat exchanger, as the porosity model required more than 80 times less computational points than the detailed CFD model. The proposed porosity model can be adapted for recuperation systems with varying heat exchanger designs having different core arrangements and tubes sizes and configurations, providing an efficient tool for the optimization of the heat exchangers design and leading to an increase of the overall aero engine performance.
Turbine Tone Noise Prediction Using a Linearized CFD Solver: Comparison With Measurements
Authors: Serrano González Adolfo , Fernández Aparicio José Ramón
Published: August 2015

The capability of a Linearized CFD Method for predicting turbine tone noise is investigated through comparison with measurements. To start with, a benchmark problem on flat plates is presented, and results are put together with those published by other authors. Then, numerical predictions are compared with measurements from two Low Pressure Turbines (LPTs), which have been tested in different facilities. The first specimen is a three stage cold flow rig, noise tested in the CTA facility (Bilbao, Spain) in 2012, and funded by the Clean Sky EU Program. The second is the ANTLE LPT rig, full scale, cold flow, noise tested in the TSTF in Rolls-Royce (Derby, United Kingdom) in 2005 and funded by the SILENCE(R) EU Funded Program. The comparison includes multi-stage effects, clocking sensitivities and acoustic scattering through Outlet Guide Vanes (OGVs).
An Analysis of a Deposition Tolerant Cooling Approach for Nozzle Guide Vanes
Authors: Kingery J. E. , Ames F. E. , Downs J. , Acharya S. , Barker B. J.
Published: August 2015

The present paper documents a cooling analysis for an innovative cooling approach designed to reduce the potential for particle deposition while effectively and efficiently using cooling air. The design eliminates showerhead cooling in the stagnation region through the use of incremental impingement (Busche et al. [1]) on the pressure surface, stagnation region and near suction surface. The incremental impingement terminates by collecting and discharging the spent cooling air through a slot. An approach called counter cooling (Ames et al. [2]) is used to cool the suction surface. Counter cooling uses cooling air sparingly by matching the heat up of cooling air with the effective use of full coverage film cooling. Finally, the design promotes the use of a covered trailing edge to improve the thermal protection in that region. The vane is designed with a generous leading edge diameter to allow the integration of double wall cooling. The aft loaded pressure distribution helps to minimize the aerodynamic losses associated with film cooling discharge. The heat load analysis incorporates engine relevant inlet turbulence levels (14%) predicting turbulent augmentation using the algebraic turbulence model of Ames et al. (1999) [3] and the transition model of Mayle (1991) [4]. The internal boundary conditions for the incremental impingement and counter cooling sections, including pressure drop, were based on the research of Busche [1] et al. The trailing edge cooling boundary conditions were based on the work of Jaswal and Ames [5]. The film cooling effectiveness levels were interpolated from the database documented by Busche et al [6]. The cooling design results in moderately high levels of overall effectiveness while using cooling air in a very efficient manner. The objective of the finite element cooling analysis is to help advance the readiness of incremental impingement and counter cooling for use in vane cooling designs. The cooling design is expected to be fabricated and tested in a warm cascade experiment to demonstrate potential of the technologies for integration into engine component designs.
Failure Analysis and Life Assessment of Thermal Fatigue Crack Growth in a Nickel-Base Superalloy Based on EBSD Method
Authors: Kobayashi Daisuke , Miyabe Masamichi , Achiwa Masahiro
Published: August 2015

In the case of failure incidents involving important components, it is necessary to clarify the fracture mechanism by failure analysis. In the case of conventional steel materials, according to the individual fracture mode the fracture surfaces have unique fracture morphology corresponding to tensile, impact, creep and fatigue conditions. We can identify the mechanism of a fracture by observing its fracture surface, and this is known as the fractography. However regarding nickel-base superalloys, any differences in fracture morphology are unfortunately barely distinguishable, which makes it difficult to conduct fractography.

In this paper, in order to characterize the damage behavior of IN738LC, the misorientation analysis within grains by using the electron backscattered diffraction (EBSD) method across almost all the whole range of specimens has been carried out. As a result, it was found that the cross section of fracture samples have unique distinguishable morphology corresponding to the individual fracture mode. Furthermore, the striations corresponding to the fatigue crack growth rate was found in the crack cross-sectional sample. It was considered that the EBSD striation observed on the cross section reveals the fatigue crack growth rate, as with striations found in the fatigue fracture surface such as conventional steel materials.

On the case study of the actual (service and damaged) gas turbine blade, the EBSD analysis as the fractography revealed the mechanism of cracking and the fatigue crack growth rate. Thus, it is concluded that the misorientation analysis of damage materials allows the qualitative estimation of the fracture mode and the quantitative life assessment of the fatigue crack growth.
Formation and Transport of Secondary Flows Caused by Vortex-Blade Interaction in a High Pressure Turbine
Authors: Wei Zuo-Jun , Qiao Wei-Yang , Chen Ping-Ping , Liu Jian
Published: August 2015

As modern turbines are designed with low aspect ratio and high blade loading, secondary flow interactions become more important. In the present work, numerical simulation is performed in a two-stage high-pressure turbine with divergent meridional passage to investigate the transport and interaction of secondary vortex from the first stage rotor within the second stage’s stator. Scale-Adaptive Simulation model coupled with Shear Stress Transport model (SAS-SST turbulence model) is used to capture the flow structures caused by the interaction in the second stator. Coupled with the passage vortex of the first rotor, the shed vortex rotates opposite in the direction and has comparable strength. As both of these vortices convect downstream to the stator bladerow, each deforms into two legs on the pressure and suction sides in the passage. In the passage due to the cross pressure gradient by blade loading, all the low-momentum fluid contained in these vortices moves towards the suction side. Besides, with the existing static pressure gradient in radial direction and vortex dynamics, the suction-side leg and the pressure-side leg move in different radial directions. The suction side leg of incoming passage vortex moves towards the endwall along the suction surface and interacts with the developing passage vortex of the second stator. The incoming shed vortex moves towards the midspan and rolls up the boundary layer fluid from suction surface. Due to the interactions between the incoming shed vortices from the hub and casing and the boundary layer of second stator, two counter-rotating vortices are formed near the midspan. Additional high loss is found there at the outlet plane, which has a comparable magnitude to the endwall secondary loss. The pressure side leg of the incoming passage vortex remains in a certain span with that of the incoming shed vortex and is not engulfed by the developing passage vortex.
Systematic Fluid Selection for Organic Rankine Cycles (ORC) and Performance Analysis for a Combined High and Low Temperature Cycle
Authors: Rödder Maximilian , Neef Matthias , Laux Christoph , Priebe Klaus-P.
Published: August 2015

The organic Rankine cycle (ORC) is an established thermodynamic process that converts waste heat to electric energy. Due to the wide range of organic working fluids available the fluid selection adds an additional degree of freedom to the early design phase of an ORC process. Despite thermodynamic aspects such as the temperature level of the heat source, other technical, economic and safety aspects have to be considered. For the fluid selection process in this paper, 22 criteria were identified in six main categories while distinguishing between elimination and tolerance criteria. For an ORC design, the suggested method follows a practical engineering approach and can be used as a structured way to limit the number of interesting working fluids before starting a detailed performance analysis of the most promising candidates. For the first time the selection process is applied to a two-stage reference cycle which uses the waste heat of a large reciprocating engine for cogeneration power plants. It consists of a high temperature and a low temperature cycle in which the condensation heat of the high temperature (HT) cycle provides the heat input of the low temperature (LT) cycle. After the fluid selection process the detailed thermodynamic cycle design is carried out with a thermodynamic design tool that also includes a database for organic working fluids. The investigated ORC cycle shows a net thermal efficiency of about 17,4% in the high temperature cycle with Toluene as the working fluid and 6,2% in low temperature cycle with iso-Butane as the working fluid. The electric efficiency of the cogeneration plant increases from 40,4% to 46,97% with the both stages of the two-stage ORC in operation.
Volume of Fluid (VOF) Analysis of Oil-Jet Lubrication for High-Speed Spur Gears Using an Adaptive Meshing Approach
Authors: Fondelli Tommaso , Andreini Antonio , Da Soghe Riccardo , Facchini Bruno , Cipolla Lorenzo
Published: August 2015

In high speed gearbox systems, the lubrication is generally provided using nozzles to create small oil jets that feed oil into the meshing zone. It is essential that the gear teeth are properly lubricated and that enough oil gets into the tooth spaces to permit sufficient cooling and prevent gearbox failure. A good understanding of the oil behaviour inside the gearbox is therefore desirable, to minimize lubrication losses and reduce the oil volume involved, and ensure gearbox reliability.

In order to reach these objectives, a comprehensive numerical study of a single oil jet impinging radially on a single spur gear teeth has been carried out using the Volume of Fluid (VOF) method. The aims of this study are to evaluate the resistant torque produced by the oil jet lubrication, and to develop a physical understanding of the losses deriving from the oil-gear interaction, studying the droplets and ligaments formation produced by the breaking up of the jet as well as the formation of an oil film on the surface of the teeth.

URANS calculations have been performed with the commercial code ANSYS FLUENT and an adaptive mesh approach has been developed as a way of significantly reducing the simulation costs. This method allows an automatic mesh refinement and/or coarsening at the air-oil interface based on the volume of fluid gradient, increasing the accuracy of the predictions of oil break-up as well as minimizing numerical diffusion of the interface. A global sensitivity analysis of adopted models has been carried out and a numerical set-up has been defined. Finally several simulations varying the oil injection angle have been performed, in order to evaluate how this parameter affects the resistant torque and the lubrication performances.
The One-Dimensional Meanline Design of Radial Turbines for Small Scale Low Temperature Organic Rankine Cycles
Authors: White M. , Sayma A. I.
Published: August 2015

This paper presents a complete radial turbine design methodology intended for the design of a small scale organic Rankine cycle (ORC) turbo expander. The design methodology is comprised of 1D meanline design, coupled with REFPROP for real fluid properties, and 3D geometrical construction of the turbine rotor, stator and volute. A novel method to predict the rotor passage velocity distribution also enables the rotor passage to be effectively designed to ensure a smooth expansion without requiring CFD analysis. The design method is used to construct two test turbines with target isentropic total-to-static efficiencies of 85%. The first expands air from 282.3kPa and 1073K with a total-to-static pressure ratio of 3 and mass flow rate of 0.1kg/s. The ORC turbine expands R245fa from 350K and 623kPa, with a pressure ratio of 2.5 and mass flow of 0.7kg/s. Comparison with design point CFD validates the turbine design program, predicting a mass flow rate of 0.104kg/s for the air turbine at the design point with a total-to-static isentropic efficiency of 84.73%. At the design mass flow rate and rotational speed, the ORC turbine achieves a total-to-static pressure ratio of 2.51 and a total-to-static isentropic efficiency of 84.87%.
Uncertainty Quantification for an Industrial Mistuned Bladed Disk With Geometrical Nonlinearities
Authors: Capiez-Lernout Evangéline , Soize Christian , Mbaye Moustapha
Published: August 2015

Recently, a methodology allowing a stochastic nonlinear reduced-order model to be constructed in the context of the nonlinear mistuning induced by geometric nonlinearities has been proposed. The present work is devoted to an industrial application for which the centrifugal stiffening due to rotational effects is also included. The nonlinear mistuned forced response is investigated in the time-domain by using a spatial cyclic load over a given excitation frequency range. The geometric nonlinear mistuned analysis is performed over the frequency range by using the Fast-Fourier Transform of the time response. A sensitivity analysis is conducted with respect to the load level, giving rise to secondary resonances, which appear outside the excitation frequency range and which can exhibit a particular sensitivity to uncertainties. Such new complex dynamical situation, induced by the coupling between the geometrical nonlinearities and the mistuning phenomenon, is analyzed in details.
Synthesis of Experimental and Theoretical Analysis of Pneumatic Hammer Instability in an Aerostatic Bearing
Authors: Arghir Mihai , Hassini Mohamed-Amine , Balducchi Franck , Gauthier Romain
Published: August 2015

The present work is focused on the pneumatic hammer instability in an aerostatic bearing with shallow recesses and orifices of four different diameters. Operating conditions were zero rotation speed, zero load and different supply pressures. The diameters of the tested orifices were large compared to the usual practice and correspond to a combined inherent and orifice restriction. The theoretical analysis was based on the CFD evaluation of the ratio between the recess and the feeding pressure and on the “bulk flow” calculation of the rotordynamic coefficients of the aerostatic bearing. Calculations showed an increase of the direct stiffness with decreasing the orifice diameter and increasing the supply pressure and, on the other hand, a decrease toward negative values of the direct damping with decreasing the orifice diameter. These negative values of the direct damping coefficient indicate pneumatic hammer instabilities. In parallel, experiments were performed on a floating bearing test rig. Direct stiffness and damping coefficients were identified from multiple frequency excitations applied by a single shaker. Experiments were performed only for the three largest orifices and confirmed the decrease of the direct damping with the orifice diameter and the supply pressure. The identification of the rotordynamic coefficients was not possible for the smallest available orifice because the aerostatic bearing showed self-sustained vibrations for all feeding pressures. These self-sustained vibrations are considered the signature of the pneumatic hammer instability. The paper demonstrates that aerostatic bearings with shallow recesses and free of pneumatic hammer instabilities can be designed by adopting orifice restrictors of large size diameter.
Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part A — Experimental Results
Authors: Kuschel Marcus , Drechsel Bastian , Kluß David , Seume Joerg R.
Published: August 2015

Exhaust diffusers downstream of turbines are used to transform the kinetic energy of the flow into static pressure. The static pressure at the turbine outlet is thus decreased by the diffuser, which in turn increases the technical work as well as the efficiency of the turbine significantly. Consequently, diffuser designs aim to achieve high pressure recovery at a wide range of operating points.

Current diffuser design is based on conservative design charts, developed for laminar, uniform, axial flow. However, several previous investigations have shown that the aerodynamic loading and the pressure recovery of diffusers can be increased significantly if the turbine outflow is taken into consideration. Although it is known that the turbine outflow can reduce boundary layer separations in the diffuser, less information is available regarding the physical mechanisms that are responsible for the stabilization of the diffuser flow.

An analysis using the Lumley invariance charts shows that high pressure recovery is only achieved for those operating points in which the near-shroud turbulence structure is axi-symmetric with a major radial turbulent transport component. This turbulent transport originates mainly from the wake and the tip vortices of the upstream rotor. These structures energize the boundary layer and thus suppress separation. A logarithmic function is shown that correlates empirically the pressure recovery vs. the relevant Reynolds stresses. The present results suggest that an improved prediction of diffuser performance requires modeling approaches that account for the anisotropy of turbulence.
Investigation of Different Surge Handling Strategies and its Impact on the Cogeneration Performance for a Single-Shaft Gas Turbine Operating on Syngas
Authors: Montemayor Javier Beltran , Axelsson Lars-Uno
Published: August 2015

The increasing demand for decentralized power has led to a growing interest in smaller gas turbines for cogeneration applications. One benefit of decentralized power generation is the possibility to utilize fuels that are locally available. One example is syngas, which has gained increasing interest during the recent years. Compared to natural gas the syngas fuels have a large amount of dilutants, such as nitrogen and carbon dioxide, which results in a very low energy density. Hence, significant larger fuel flow is required. However, the added fuel flow will decrease the compressor surge margin and eventually drive the compressor towards surge. Several methods exist to address this issue including variable inlet guide vanes, increased turbine throat area, compressor bleeding and decreased combustor outlet temperature.

This paper examines the operability of a generic all-radial single-shaft gas turbine in the 2 MW power range when running on syngas with different heating values. The above methods to combat the decreased surge margin will be analyzed using detailed cycle simulations and their advantages and disadvantages will be discussed. It was found that the increased throat area is the most beneficial of the four methods. The net power output is nearly the same as for natural gas operation and the heat rate is the lowest of the four methods.
Analysis of Long-Term Gas Turbine Operation With a Model-Based Data Reconciliation Technique
Authors: Rudolf Christian , Wirsum Manfred , Gassner Martin , Bernero Stefano
Published: August 2015

The continuous monitoring of gas turbines in commercial power plant operation provides long-term engine data of field units. Evaluation of the engine performance is challenging as, apart from variations of operating points and environmental conditions, the state of the engine is subject to changes due to the ageing of engine components. The measurement devices applied to the unit influence the analysis by means of their accuracy, which may itself alter with time. Furthermore, the available measurements do usually not cover all necessary information for the evaluation of the engine performance. To overcome these issues, this paper describes a method to systematically evaluate long term operation data without the incorporation of engine design models since the latter do not cover performance changes when components are ageing. Key focus of the methodology thereby is to assess long-term emission performance in the most reliable manner.

The analysis applies a data reconciliation method to long-term operating data in order to model the engine performance including non-measured variables and to account for measurement inaccuracies. This procedure relies on redundancies in the data set due to available measurements and the identification of suitable additional constituting equations that are independent of component ageing. The resulting over-determined set of equations allows for performing a data set optimization with respect to a minimal cumulated deviation to the measurement values, which represents the most probable, real state of the engine. The paper illustrates the development and application of the method to analyse the gas path of a commercial gas turbine in a combined cycle power plant with long-term operating data.
A CFD Analysis of the Effects of Two-Phase Flow in a Two-Stage Centrifugal Compressor
Authors: Halbe Chaitanya V. , O’Brien Walter F. , Cousins William T. , Sishtla Vishnu
Published: August 2015

The performance of a compressor is known to be affected by the ingestion of liquid droplets. Heat, mass and momentum transfer as well as the droplet dynamics are some of the important mechanisms that govern the two-phase flow. This paper presents numerical investigations of three-dimensional two-phase flow in a two-stage centrifugal compressor, incorporating the effects of the above mentioned mechanisms. The results of the two-phase flow simulations are compared with the simulation involving only the gaseous phase. The implications for the compressor performance, viz. the pressure ratio, the power input and the efficiency are discussed. The role played by the droplet-wall interactions on the rate of vaporization, and on the compressor performance is also highlighted.
Effect of Hole Diameter on Nozzle Endwall Film Cooling and Associated Phantom Cooling
Authors: Zhang Luzeng , Yin Juan , Liu Kevin , Hee-Koo Moon
Published: August 2015

Flow fields near the turbine nozzle endwall are highly complex due to the passage vortices and endwall cross flows. Consequently, it is challenging to provide proper cooling to the endwall surfaces. An effective way to cool the endwall is to have film cooling holes forward of the leading edge, often called “inlet-film cooling”. This paper presents the results of an experimental investigation on how the film hole diameter affects the film effectiveness on nozzle endwall and associated phantom cooling effectiveness on airfoil suction side. The measurements were conducted in a high speed linear cascade, which consists of three nozzle vanes and four flow passages. Double staggered rows of film injections, which were located upstream from the nozzle leading edge, provided cooling to the contoured endwall surfaces. Film cooling effectiveness on the endwall surface and corresponding phantom cooling effectiveness on the airfoil suction side were measured separately with a Pressure Sensitive Paint (PSP) technique through the mass transfer analogy. Four different film hole diameters with the same injection angle and the same pitch to diameter ratio were studied for up to six different MFR’s (mass flow ratios). Two dimensional film effectiveness distributions on the endwall surface and two dimensional phantom cooling distributions on the airfoil suction side are presented. Film/phantom cooling effectiveness distributions are pitchwise/spanwise averaged along the axial direction and also presented. The results indicate that both the endwall film effectiveness and the suction side phantom cooling effectiveness increases with the hole diameter (as decreases in blowing ratio for a given MFR) up to a specific diameter, then starts decreasing. An optimal value of the film hole diameter (blowing ratio) for the given injection angle is also suggested based on current study.
Experimental and Computational Study of Flow and Heat Transfer Inside a Heated Exhaust Strut
Authors: Crawford James , Birk A. M.
Published: August 2015

The flow and heat transfer inside a short airfoil shaped turbine exhaust strut was studied experimentally and computationally. A combination of transient and steady IR thermographic techniques were used to measure the heat transfer, and showed that the streamwise evolution of the heat transfer could be reliably described using a power law type relationship. Steady RANS CFD using the realizable k-epsilon was unable to accurately predict the observed heat transfer, with the main limitations of the model being a) a fundamental inability to calculate secondary flows and b) an underestimation of the restriction on boundary layer growth rates imposed by the opposing walls. The experiments showed that heat transfer rates were much higher in thinner regions of the strut, and lower in thicker regions. The CFD predicted an essentially uniform heat transfer rate, independent of the local strut thickness.
Research on Meta-Model Based Global Design Optimization and Data Mining Methods
Authors: Guo Zhendong , Song Liming , Li Jun , Li Guojun , Feng Zhenping
Published: August 2015

The turbomachinery cascades design is a typical high dimensional computationally expensive and black box (HEB) problem, for which a meta-model based design optimization and data mining method is proposed and programmed in this work. The method combines an EI-based global algorithm with two data mining techniques of self-organizing map (SOM) and analysis of variance (ANOVA); 3D blade parameterization method and RANS Solver technique. NASA Rotor 37, a typical axial transonic rotor blade, is selected for the research. Firstly, the SOM is employed to explore the interactions between critical performance indicators. Based on SOM analysis, a design optimization with 19 design variables is carried out to maximize the isentropic efficiency of Rotor 37 configuration with constraints prescribed on the total pressure ratio and mass flow rate. An EI-based global algorithm is programmed for above optimization process and the number of CFD evaluations needed amount to only 1/5 of that required when employing a modified differential evolution algorithm as the optimizer. Throughout the optimization the isentropic efficiency is increased by 1.74% and a subsequent analysis of the redesign reveals that the performance of the rotor blade is significantly improved. And then, the ANOVA is employed to explore the correlations among design variables and objective function as well as the constraints. It is confirmed that the shock wave has the most significant influence on the aerodynamic performance of transonic rotor blades, the combination of proper 2D section profiles and 3D radial stacking is effective for improving the performance of rotor blade. Meanwhile, isentropic efficiency and total pressure ratio of transonic compressor blade is found to be in slight trade-off relation due to the effect of 3D sweep in tip sections. Furthermore, an ANOVA-based optimization strategy is tried, which can obtain remarkable optimal designs with much less computational resource. On a whole, it’s demonstrated that the meta-model based design optimization strategy by coupling data mining techniques is promising for solving HEB problems like the design of turbomachinery cascades.
Numerical Simulation of Icing on the Rotating Blade
Authors: Dong Wei , Zhu JianJun , Wang Rui , Chen Yong
Published: August 2015

The physical processes involved in ice accretion on the rotating blade are complex. It is important to develop high fidelity numerical method and simulate the icing process on the blade under icing conditions. This paper presents a numerical study on the icing process on the rotating blade. The flow field around the blade is obtained using ANSYS FLUENT. The trajectories of supercooled water droplets and the collection efficiency are calculated by Eulerian approach. Heat and mass balance on the rotating blade surface is taken into account in icing process simulations. The NASA Rotor 67 blade is chosen as the computational model. The collection efficiency on the blade surface is computed and the impingement characteristics are analyzed. The 3D icing accretion on Rotor 67 blade is predicted at design point. The ice shapes of accretion time of 5s, 10s and 15s are simulated and the ice shapes at different span positions of the rotating blade are compared.
An Experimental Study of Impingement Heat Transfer on the Surfaces With Micro W-Shaped Ribs
Authors: Rao Yu , Chen Peng , Zhu Jiaqi
Published: August 2015

The paper proposed an idea of using micro-W-shaped ribs on a test plate to improve the impingement heat transfer performance in a multiple-jet impingement cooling system. An experimental study has been conducted on the heat transfer characteristics of multiple-jet impingement onto a flat plate and a roughened plate with micro W-shaped ribs under maximum cross flow scheme. Transient liquid crystal thermography method has been used to obtain the detailed impingement heat transfer distribution for the Reynolds numbers from 15,000 to 30,000.The effects of micro W ribs on the local Nusselt number and the related pressure loss were investigated experimentally. The jet-to-plate spacing H/d=1.5 was used in the experiments for both the flat and the micro-W-rib roughened plate. The experiments showed that the micro W ribs on the plate can enhance the impingement heat transfer globally and locally, and increase the heat transfer uniformity, which are due to the facts that the micro W ribs on the test plate increase the near-wall turbulent mixing by interacting with the wall jets and cross flow. The pressure loss is negligibly increased compared to the impingement onto the flat plate.