bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non-Linear Vibration Behaviour of an Axial Compressor Rotor Blade
Authors: Peng Caetano , Miyakozawa Tomokazu , Schroeter Thomas , Schnitzler Jan , Lyndon Ian 
Published: August 2015

There has been some concern that the blades in the real engine operating environment may not always behave in a linear manner. The non-linearity can arise from friction contact surfaces (i.e. blade dovetails and discs), non-linear material properties (i.e. Young’s modulus, non-linear temperature dependence of modulus), component manufacturing variability, and component design geometry. The vibration forcing itself can also cause multi-modal responses when applied as multi-mode excitation. The present study aims at investigating the effects of static contact friction loads on the blade vibration responses. Moreover, some natural frequencies of the blade investigated here are commensurable and thus leading to internal resonance in the system and nonlinear interactions between involved modes.
This investigation shows that some blade vibration modes are more sensitive to the blade root friction loads than others. This sensitivity is associated with modeshape localisations. The other source of non-linear behavior is related to internal resonances. This particular blade geometry affects the blade stiffness in such a way that some natural frequencies are commensurable. For instance, there is an internal resonance between the first and second torsion modes. The modal frequency of second torsion is twice the first torsion frequency. Both the non-linearity effects associated with contact friction loads and internal resonances seem to result from the interactions of two or more natural vibration modes. There is a dominant modal response among the interacting modes. Fast Fourier Transforms (FFT) of response histories also reveals the contribution of individual modes in the multi-modal response. This paper attempts to address this non-linear blade behaviour by conducting both experimental tests and numerical simulations using an in-house forced response code.
Time Transformation Simulation of 1.5 Stage Transonic Compressor
Authors: Zori Laith , Galpin Paul , Campregher Rubens , Morales Juan Carlos 
Published: August 2015

The accurate prediction of the aerodynamic and aeromechanical performance in a modern transonic compressor often exceeds the capability of traditional steady state mixing plane simulation methods. Time accurate transient blade row simulation approaches are required when there is a close coupling of the flow between the blade rows, and for fundamentally transient flow phenomena such as aeromechanical analysis including blade flutter and forced response, aerothermodynamic analysis and aero-acoustic analysis.
Transient blade row simulations can be computationally impractical when all of the blade passages must be modeled to account for the unequal pitch between the blade rows. Most turbomachines consist of multiple stages, further exacerbating the computational challenge. In order to reduce the computational cost, time accurate pitch-change methods are utilized so that only a sector of the turbomachine (one or few passages per row) is modeled. The extension of the time-transformation pitch-change method to multistage machines has recently shown good promise in predicting both aerodynamic performance and resolving dominant blade passing frequencies for a subsonic compressor, while keeping the computational cost affordable.
In this work, a modified one and a half stage Purdue transonic compressor (modified for unequal pitch for all three blade rows) is examined. The goal is to assess the ability of the multistage time-transformation method to accurately predict the aerodynamic performance and transient flow details in the presence of transonic blade row interactions. The results from the multistage time-transformation simulation are compared in detail with a transient full-wheel simulation, a profile transformation simulation, as well as to a steady-state mixing-plane model. Flow details are examined including an FFT analysis of select signals, and the onset of stall is compared between all methods. The relative computational effort is compared between all of the analysis methods.
Numerical Investigation of the Return Channel of a High-Flow Centrifugal Compressor Stage
Authors: Franz Holger , Rube Christoph , Wedeking Matthias , Jeschke Peter 
Published: August 2015

Steady-state simulations of a high-flow centrifugal compressor stage with return channel for industrial applications are carried out to determine the flow conditions in a new compressor test rig at the RWTH Aachen University. Overall performance predictions, conducted by means of CFD simulations, will be shown and discussed in this paper. Furthermore, a detailed analysis of the stage components is presented, providing an insight into the flow phenomena responsible for the compressor performance. Thereby, the analysis focuses on the return channel.
The compressor has a shrouded impeller with 3D-twisted blades, operating at a high flow coefficient and moderate pressure ratios, as usual for multistage single-shaft compressors. The complete computational domain consists of an inlet duct, the impeller, a vaneless diffuser and return channel with bends to guide the flow. All CFD simulations have been carried out in advance of the test rig construction. The results of the simulations have been used to define the measurement locations within the test rig. Within this paper, the predicted flow phenomena in the return channel, which are strongly three-dimensional, are detailed and analyzed against the backdrop of their origin and their contribution to the overall losses. Furthermore, the available measurement results of the overall compressor performance are compared to the numerical simulations to validate the numerical setup.
The objective of this paper is to give a detailed analysis of the flow in the return channel of a new compressor test rig built up at the Institute of Jet Propulsion and Turbomachinery of the RWTH Aachen University. The investigation is conducted to get an insight into the formation processes of the dominant flow phenomena affecting the overall stage performance. These investigations can form the basis for developing new strategies for return channel improvements.
Acceptance Testing of Liquefied Natural Gas Compressors
Authors: Nyquist Roger , Andrews Mike , Hunter Andrew , Myagmar Oyuna 
Published: August 2015

The majority of natural gas compressors operate on gas mixtures with molecular weights (MW) less than air. For these machines, performance acceptance tests are run on air at reduced speed. For multistage compressors, each stage is tested individually. The test speeds and inlet temperatures are selected to closely match the inlet to exit density ratios and the machine Mach numbers per the ASME PTC10 test code. The specified test inlet pressure (limited by the test variable speed motor power capacity) is always high enough to assure that the test Reynolds number is above the required PTC10 minimum; the density ratio and machine Mach number do not depend on inlet pressure. The air test data is converted to the specified natural gas conditions using similarity laws, and an in-house stage matching program is used to determine the overall machine performance.
For compressors used in liquefied natural gas (LNG) transport, the MW of the natural gas mixture is lower than air. However, the inlet temperatures are so low that an air test at typical ambient temperatures needs to be run at a speed higher than design to closely match density and machine Mach number ratios. It is impractical to run air tests at higher than design speeds (especially for 60 Hz machines), thus these machines are tested on air at design speed.
As before, the air test data is reduced to the specified natural gas conditions using the similarity laws. An additional “compressibility” correction is made to account for the mismatch of density ratio between test and design conditions. Running a test at lower than the required PTC10 speed means that the test density ratio will be lower than the corrected density ratio and the stage would pass more flow than the test data conversion indicates. The method used to account for the density ratio mismatch, i.e. a “compressibility” correction is discussed in detail in this paper.
Debris Tolerant Compliant Foil Bearings for High-Speed Turbomachines
Authors: Hunsberger Andrew , Walton James F. , Heshmat Hooshang 
Published: August 2015

High-speed turbomachines such as air cycle machines (ACM), auxiliary power units (APU) and turbogenerators as used in aerospace systems operate in hot and harsh environments. Such operating conditions often dictate the application of compliant foil bearings to provide reliable, low power loss performance. Many such turbomachines in operation today were developed, validated and commissioned into service more than 30 years ago. While these machines are still valuable and highly effective, in some cases premature failures have been observed by the end user. In particular, equipment that has seen use in environments with high concentrations of airborne particulates such as sand, dust and other debris (i.e. Middle East) appear to be particularly vulnerable. Exponential gains in load carrying capacity, damping characteristics and temperature limitations have been demonstrated from compliant foil bearings over the past 30 years and retro-fitting these higher performance complaint foil bearings into legacy turbomachines can provide drastic improvements in system performance, increase mean time between service and reduce, and reduce failure rates.
In this paper the authors will present results from testing of an ACM which was developed and initially commissioned into service more than 30 years ago for use in the F/A-18 but remains active in aerospace and military service today [1]. Testing of the fully refurbished ACM and its new cantilever leaf style foil gas bearing components was conducted under normal and abusive conditions such as might be encountered in operational use. The ACM foil bearings came with a Teflon coating. The performance of the cantilever leaf style compliant foil bearings was compared a tension dominated or compliant bump foil style bearing with a Korolon™ polyimide type coating. During component level testing, the compliant bump foil bearings demonstrated lower starting torque, temperature rise, and more consistent and reliable performance than the cantilevered leaf foil bearings under the same operating conditions. System testing of the ACM with both types of bearings under identical conditions was also conducted. Under baseline conditions, cantilevered-leaf bearings were observed to operate at temperatures of 72°C higher than those of the compliant bump foil bearings. The lower operating temperature of the compliant bump foil design indicated lower power loss with compliant bump foil bearings as confirmed by 10% lower turbine pressure and flow required to reach the same speed condition. In dust ingestion testing, the cantilevered-leaf bearings showed a temperature spike due ingestion of dust, leading to failure of the thrust bearings, whereas, the compliant bump foil bearings were unaffected by dust ingestion and operated reliably with minimal signs of wear or damage.
Stress Relaxation Modelling
Authors: Riva Andrea , Maldini Maurizio 
Published: August 2015

Modern gas turbine bolts experience severe operational conditions due to high temperatures and elevated axial stresses, generated by the tightening couple applied during the turbine assembly. In such conditions the relaxation of the initial stress due to viscous phenomena has to be taken into account in order to guarantee the proper operation of the turbine.
Relaxation modelling can either be based on strain controlled relaxation tests or load controlled creep tests. Both solutions present difficulties: relaxation tests entail critical experimental issues, whereas creep tests may not be significant for the given strain controlled operational condition of a gas turbine bolt. Some of these problems will be described in the paper and solutions will be provided.
The performances of several models for stress relaxation quantification will be compared, highlighting advantages and disadvantages of each approach. In particular, great emphasis will be given to those aspects which are relevant for bolt design or tightening load calculation. For instance, some important requirements are: firstly, the possibility to implement the given model easily in finite element calculations; secondly, the possibility to accurately calculate the relaxation in the second life of a serviced bolt after re-tightening; lastly, the possibility to reduce as much as possible the time required for the experimental tests.
In order to evaluate the coefficients of the different models considered in the study, creep tests were performed at 450°C and 475°C with applied stresses producing a strain ε = 1% in a time range of 1000–10000h and stress relaxation tests were performed at the same temperatures with initial strain in the range of 0.2%. After some stress relaxation, the specimens were reloaded at the initial stress several times in order to simulate the aforesaid service conditions of bolts.
In the paper it will be shown how a valid model, capable of predicting the stress relaxation with acceptable accuracy, can be fed either by creep or relaxation tests, provided that the experimental tests and the related data elaboration are conducted with the proper methodology. This scenario provides the engineer responsible for material model creation with a remarkable flexibility, essential to fulfill the requirements of modern GT design, in terms of accuracy, promptness of data collection and possibility of FEM implementation.
Kinetic Modeling of Plasma-Enhanced Vitiated Combustion
Authors: Joklik Richard G. , Gokulakrishnan Ponnuthurai , Klassen Michael S. 
Published: August 2015

Plasma-enhanced combustion can improve the performance of combustion systems for which ignition and flameholding are issues through augmentation of radical species concentrations. Electron impact generates electronically excited N2 and O2, both of which participate in reactions that create atomic oxygen and nitrogen. OH and H concentrations are also altered, both through equilibration of the radical pool, and through direct production pathways from the excited N2 and O2. In the case of vitiated combustion, it has been demonstrated that the presence of NO in the oxidizer stream enhances ignition. However, the impact of the plasma-enhanced radical pool on the effects of vitiation is unknown. It was the goal of this work to explore the impact of plasma-generated species on vitiated kinetics, and the resulting effect on ignition.
In this paper we describe the development and validation of a model for ethylene-air ignition by a nanosecond pulsed-plasma. The model employs a zero-dimensional simulation of the plasma to predict the radical concentrations produced by the plasma. These concentrations are then used as input to an ignition delay time calculation using a kinetic mechanism for vitiated combustion that has been previously developed by the authors. The modeling results show that the O-atom, H-atom, N-atom and C2H3 production by the plasma are important in determining ignition delay. The ignition delay time calculations show that both vitiation and plasma effects are important in determining ignition delay, with the plasma effect becoming dominant as the plasma strength is increased, especially in the low-temperature oxidation regime. Thus in designing practical plasma-assisted combustion systems, an understanding of these effects is important in determining the plasma requirements to achieve the desired level of combustion enhancement.
Experimental and Numerical Investigations of the Heat Transfer and Flow Field in a Trailing Edge Cooling Geometry: Part 1 — Experimental Study With IR Thermography and PIV
Authors: Wang Guanghua , Estevadeordal Jordi , DeLancey James , Bailey Jeremy , Kopriva James , Laskowski Gregory 
Published: August 2015

Airfoil Trailing Edge (TE) cooling is critical for turbine blade and nozzle lifing and safety. Gas turbines overall efficiency enhancement requires further increasing of the turbine inlet temperature and decreasing of cooling flow usage. This requires more advanced TE designs to meet the inherent conflicting requirements. Aerodynamic requirements of thin TE, particularly in jet engines, lead to Pressure Side (PS) cutback of the TE with a span-wise slot forming uniform cooling film over the cutback/floor region.
This study focused on the PS cutback TE film effectiveness and flow field measurements of a standard geometry with t/s=0.9. The measurements were conducted in a subsonic open loop wind tunnel with a generic setup to cover different TE running conditions. IR camera is used to measure the TE coupon surface temperature distribution. The test conditions are characterized by a constant main flow Mach number with constant gas temperature. CO2 at constant temperature is used as the coolant to reach the realistic blowing ratio and density ratio. Inlet boundary layer is measured by the Particle Image Velocimerty (PIV) to characterize the TE flow conditions and study the underlying flow physics. The experimental data for 2D wall contours and laterally-averaged profiles of adiabatic film effectiveness, velocity vector field and boundary layer profiles were discussed. These data will be used to provide inlet boundary conditions and validate CFD simulations in Part 2.
Advanced Axial Compressor Airfoils Design and Optimization
Authors: Jiang Bin , Zheng Qun , Zhang Hai , Zhang Xiaolong , Chen Zhongliang , Qiu Yi , Li Mingshi 
Published: August 2015

Advanced compressor airfoils design and optimization have been investigated for the axial compressor of gas turbine at high subsonic condition, which aim to decrease losses and to increase compressor operating ranges. The design and optimization processes are carried out based on (CDP_HEU) the Compressor Design Platform of Harbin Engineering University, in which a geometric code for the airfoil description, grid generation, blade-to-blade solver and the interface codes were combined. The influence of the higher airfoil Reynolds numbers flow of the land/marine based compressors is compared with aero engine and the impact of these differences on the location of boundary layer transition are taken into account by γ-Reθ transition model in ANSYS/CFX solver. The optimization objective function is a compromise of the total pressure losses at design-point and at off-design conditions of a large incidence angle range. The effects of optimization variables selection, objective functions and numerical optimization algorithms on the design results are analyzed and discussed in this paper.
The superior performance of the optimized airfoil is demonstrated by a comparison with conventional controlled diffusion airfoils (CDA) at a wide range of inlet flow angles, inlet Reynolds numbers and inlet Mach numbers that maximum value can reach 0.77. The aerodynamic advantage of the optimized airfoils have been presented, which include the leading edge shock wave losses and the profile losses etc.
The optimized results indicate that a significant improvement in compressor efficiency and stability for land/marine gas turbine could be reached by the proposed optimized airfoils instead of conventional airfoils. Moreover, different optimized variables, objective function and optimization algorithm are recommended which could improve the optimization efficiency remarkably with the same design effect.
CFD Simulation of Lab Seal Tooth Tip Geometry Variations to Reduce Leakage
Authors: Chougule Hasham H. , Mirzamoghadam Alexander 
Published: August 2015

A modification of a conventional straight four-tooth labyrinth seal with inclined teeth including single and double stepped notches is proposed. The variants are to be numerically modeled and evaluated for potential leakage reduction through the seal as a result of the developing flow field. The CFD methodology for numerical investigation is first validated by comparison with literature data from static labyrinth seal experiments. The objective is to numerically analyze the proposed “Notched Inclined Teeth” with solid and honeycomb lands and verify the leakages. Another objective is to compare these leakages with the “Stepped Double Notched Straight Tooth” variant discussed by the present authors in a previous paper.
Results indicate that the proposed modifications — single and double stepped notched inclined teeth, systematically reduce the seal leakage compared to the baseline straight and forward inclined teeth due to higher turbulence, higher blockages by introducing vortex in leakage flow through step and cavities, and higher flow resistance as compared to baseline model.
Aerodynamic Turbine Upgrade for W501D5, and SGT6-3000E (W501D5A) Gas Turbines
Authors: Ayoung-Chee Frank , Bhatia Akash , Humphrey Chris , Abdel-Karim Hisham 
Published: August 2015

The W501D5, W501D5A, and SGT6-3000E gas turbines have been in operation for almost 30 years and continue to be a reliable workhorse for many power suppliers. As these units age, operating costs and power production become key drivers in order to maximize profits and improve dispatch rates. Performance upgrades for this mature frame allows customers to benefit from proven technology used in advanced frames in order to lower their overall combustion turbine operating costs and provide improved thermal performance.
The W501D5 and W501D5A fleet contain approximately 150 units with the fleet leader having over 235,000 reported operating hours. These units are configured in both combined and simple cycle operation, and are located in 60 Hertz power markets throughout the world. This upgrade product focuses on improving efficiency and increasing power for both frames.
The purpose of this paper is to describe the Si3D Aerodynamic Turbine Upgrade for the W501D5, W501D5A and SGT6-3000E Gas Turbines. This product is intended to improve turbine performance with an upgrade to the turbine stage 1 and 2 components (row 1 blade, row 1 vane, and row 2 vane) using the latest 3D aerodynamic tools. The Si3D product will provide customers with an increase in engine power and improved thermal efficiency through a combination of improved aerodynamic design, advanced sealing, cooling improvements, and advanced materials.
This product uses the same concept, analytical tools, and processes as the SGT5-2000E and SGT6-2000E Si3D upgrade, which to date has been installed in over 80 new apparatus and service units achieving over 840,000 equivalent operating hours. While actual results may vary, installation of this product in a W501D5, W501D5A, or SGT6-3000E may provide up to 8.0 MW gas turbine power and 320 BTU/kW-hr gas turbine heat rate improvement. Recent verification testing of the first time application of the Si3D upgrade has just been completed on a W501D5 unit with favorable results.