bluuebunny/crossref_metadata_2025 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.
Assessment of Large Eddy Simulation Predictive Capability for Compound Angle Round Film Holes
Authors: Rodebaugh Gregory , Stratton Zachary , Laskowski Gregory , Benson Michael
Published: August 2015

Film cooling holes with a compound angle are commonly used on high pressure turbine components in lieu of axial holes to improve effectiveness or as a result of manufacturing constraints. Whereas large eddy simulation (LES) of axial holes is becoming more common place, assessment of LES predictive ability for compound angle hole has been limited. For this study, the selected compound angle round (CAR) hole configuration has a 30 degree injection angle, a 45 degree compound angle, and a density ratio of 1.5. The geometry, flow conditions, and experimental adiabatic effectiveness validation data are from McClintic et al. [28]. The low free stream Mach number of the experiment puts the flow in the incompressible regime. Two LES solvers are evaluated, Fluent and FDL3Di, on structured meshes with a range of blowing ratios simulated for plenum, inline coolant crossflow, and counter coolant crossflow feed holes. When a steady inlet profile is used for the main flow, LES agreement with the data is poor. The inclusion of a resolved turbulent boundary layer significantly improves the predictive quality for both solvers; consequently, resolved inflow turbulence is a required aspect for CAR hole LES. The remaining differences between the simulations and IR data are partly attributed to the steady coolant inlet profiles used for the counter and inline cross feeds.
Experimental and Numerical Investigations of the Heat Transfer and Flow Field in a Trailing Edge Cooling Geometry: Part 2 — LES and Hybrid RANS/LES Study
Authors: Ivanova Elizaveta , Ledezma Gustavo , Wang Guanghua , Laskowski Gregory M.
Published: August 2015

This paper presents the results of a numerical study on the predictive capabilities of Large Eddy Simulation (LES) and hybrid RANS/LES methods for heat transfer in the trailing edge (TE) geometry experimentally investigated in Part 1. The experimental validation data includes 2D wall contours and laterally-averaged values of adiabatic cooling effectiveness. The simulations were conducted at three different blowing ratio values. The comparison with the experimental data shows a general advantage of LES and hybrid RANS/LES methods against steady-state RANS. The results obtained by means of the WALE LES model and the Improved Delayed Detached Eddy Simulation (IDDES) hybrid RANS/LES method were comparable. The presented grid dependence study shows the importance of adequate grid resolution for the predictive capabilities of trailing edge cooling LES. Furthermore, the importance of considering TE slot lands simulation quality in the numerical method assessment is discussed. Potential directions of future research needed to improve simulation reliability are outlined.
Numerical Study of Deposition in a Full Turbine Stage Using Steady and Unsteady Methods
Authors: Zagnoli Daniel , Prenter Robin , Ameri Ali , Bons Jeffrey P.
Published: August 2015

A computational study was performed to investigate deposition phenomena in a high-pressure turbine stator and rotor stage. Steady mixing-plane and unsteady sliding mesh calculations were utilized. 3D, steady and unsteady RANS calculations were performed in conjunction with published experiments completed on identical turbine geometry in order to extract boundary conditions and to validate flow solutions. Particles were introduced into the flow domain and deposition was predicted using a Lagrangian particle tracking method with the critical viscosity model to predict deposition. For the steady method, in order to track particles from the mixing plane through the blade domain, particle positions were saved after passing through the vane domain and inserted into the blade domain using two different methods: averaged and preserved. Both methods yielded nearly identical results. For the unsteady simulation particles were tracked through a sliding mesh interface with particle position, velocity, and temperature preserved at exit of the vane domain and inlet of the blade domain. Deposition results for the steady mixing plane using both particle averaging techniques and unsteady sliding interface were compared for particles of different sizes. Large particles produced localized impact and deposit zones near the hub and tip of the pressure surface for all methods. Steady methods overpredicted impacts and deposits relative to unsteady methods by averaging out discrete unsteady vane wake motion which caused particle motion towards blade surfaces.
Experimental Investigation of H2-Air Mixtures in a Rotating Detonation Combustor
Authors: Anand Vijay , St. George Andrew , Driscoll Robert , Gutmark Ephraim
Published: August 2015

The operating range and wave speed performance of a Rotating Detonation Combustor (RDC) is characterized for hydrogen-air mixtures for three fuel injection schemes and two air injection schemes. The fuel injection scheme is altered by changing the total number of injection orifices and the individual orifice area, while maintaining the same fuel mass flux across the three schemes. The operability, performance and combustion-induced pressure rise due to the addition of a back-pressurizing convergent nozzle is also characterized. While the operating range is largely unaffected by changes in the length-to-diameter ratio of the fuel injector orifices, higher length-to-diameter ratios correspond to a lower number of pop-out events. Pop-out event is defined as a transitional RDC operation where there is a sudden abatement of the continuously propagating detonation wave, once established inside the combustor. Increased air injection area diminishes the operability, while producing high stochasticity in the performance of the RDC. The length-to-diameter ratio of the fuel orifices has a significant impact on the number of detonation waves that can exist in the chamber. For the highest length-to-diameter ratio of the fuel orifices, and at the highest air flow rates, the RDC supports multiple detonation waves inside the chamber. Without the convergent nozzle attachment, 80% of Chapman-Jouguet (C-J) detonation speed is achieved for all three fuel injection schemes. C-J detonation wave speed is achieved in the annulus when the RDC is back-pressurized using the nozzle. The ratio of reactant fill-height to the detonation cell-width tapers at the lean and rich operating conditions, while peaking at an equivalence ratio of around 1.2. The detonation-induced static pressure rise produced in the RDC is found to be dependent on the air flow rate and the equivalence ratio of the reactants.
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.
Gas Turbine Analytics Using Archival Data Sets
Authors: Holcomb Chad M. , Bitmead Robert R.
Published: August 2015

Transient behavior of machinery is becoming increasingly recognized as a major factor in predicting life of components and exposing degradation or faults that are not observable from steady state measurements. The methods developed here are directed to trawling archival data records to reconstruct a sufficiently informative experiment in lieu of dedicated testing. The central novel observation is the modification to subspace system identification methods to permit their application to multiple concatenated, but non-contiguous data sets, which jointly can be sufficiently rich for identification while individual records are not. This is a break from traditional system identification, where one uses a single contiguous synchronous input-output record.
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.
Micro Gas Turbine Firing Kerosene and Ammonia
Authors: Iki Norihiko , Kurata Osamu , Matsunuma Takayuki , Inoue Takahiro , Suzuki Masato , Tsujimura Taku , Furutani Hirohide
Published: August 2015

A demonstration test with the aim to show the potential of ammonia-fired power plant is planned using a micro gas turbine. 50kW class turbine system firing kerosene is selected as a base model. A standard combustor is replaced by a prototype combustor which enables a bi fuel supply of kerosene and ammonia gas. Diffusion combustion is employed in the prototype combustor due to its flame stability. Demonstration test of co-firing of kerosene and ammonia gas was achieved to check the functionality of the each component of the micro gas turbine. The gas turbine started firing kerosene and increased its electric power output. After achievement of stable power output, ammonia gas was started to be supplied and its flow rate increased gradually. 21kW power generation was achieved with 30% decrease of kerosene by supplying ammonia gas. Ammonia gas supply increases NOx in the exhaust gas dramatically. However post-combustion clean-up of the exhaust gas via SCR can reduce NOx successfully.
Variance Based Global Sensitivity Analysis for Uncorrelated and Correlated Inputs With Gaussian Processes
Authors: Srivastava Ankur , Subramaniyan Arun K. , Wang Liping
Published: August 2015

Methods for efficient variance based global sensitivity analysis of complex high-dimensional problems are presented and compared. Variance decomposition methods rank inputs according to Sobol indices which can be computationally expensive to evaluate. Main and interaction effect Sobol indices can be computed efficiently in the Kennedy & O’Hagan framework with Gaussian Processes (GPs). These methods use the High Dimensional Model Representation (HDMR) concept for variance decomposition which presents a unique model representation when inputs are uncorrelated. However, when the inputs are correlated, multiple model representations may be possible leading to ambiguous sensitivity ranking with Sobol indices. In this work we present the effect of input correlation on sensitivity analysis and discuss the methods presented by Li & Rabitz in the context of Kennedy & O’ Hagan framework with GPs. Results are demonstrated on simulated and real problems for correlated and uncorrelated inputs and demonstrate the utility of variance decomposition methods for sensitivity analysis.
A Contribution to the Reduced-Order Analysis of Bladed Disks Using Combined Approximations for Quick Campbell Diagrams Assessment
Authors: de Cazenove Jean , Mbaye Moustapha , Ousty Jean-Philippe , Cogan Scott
Published: August 2015

This paper proposes an original approach to the reduced-order modelling of integrally bladed disks. It is proposed to build a reduction basis which is independent from the rotational speed, from only one modal, cyclic-symmetry calculation performed at rest, and a few static computations. Based on previous works, a polynomial expansion is used which leads to a parametric approximation of the stiffness matrix for the entire operating range. Furthermore, the Kirsch Combined Approximation (KCA) method is used for building the final reduction basis. This method is based on successive approximations of the negative binomial expansion applied to the reanalysis eigenproblem. After giving a general overview of the main theoretical aspects, the paper focuses on the reanalysis problem based on the combined approximations method. Finally, the application of the extended reduction method to the case of a real bladed disk is presented. It is shown that the use of combined approximations provides a very accurate estimation of a Campbell diagram, and allows substantial computational time savings.
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.
High Effectiveness, Low Pressure Drop Recuperator for High Speed and Power Oil-Free Turbogenerator
Authors: Córdova José Luis , Walton James F. , Heshmat Hooshang
Published: August 2015

Development of a compact radial recuperator prototype for a previously demonstrated 8 kW turboalternator has been completed. Its novel geometry has resulted in measured heat transfer effectiveness that surpasses 90% at the operating conditions of the engine, with acceptable pressure penalty (< 35 kPa) that can be easily accommodated by the compressor. Unrecuperated, the oil-free, high-speed micro-turboalternator, operating at 180,000 rpm and featuring compliant-foil bearings, presented a thermal (or cycle) efficiency of 12%. With the recuperator, thermal efficiency of approximately 30% is possible. The recuperator configuration is unique from both a geometric and a heat transfer point of view. Its radial (axisymmetric) configuration allows for compact system integration, concentric to the existing engine/combustor hardware assembly. While the addition of the recuperator prototype has increased the overall weight of the system, and hence reduced its specific power from the previously reported 1.6 kW/kg (1 hp/lbm) to approximately 0.9 kW/kg, the unprecedented gain in efficiency by such a compact device justifies its implementation. Furthermore, it is anticipated that continuing prototype refinement, along with the use of novel manufacturing technologies and materials (e.g. 3D printing and ceramics) will result in a significant increase in power density. Performance characterization has been performed for mass flow rates up to 0.08 kg/s and gas inlet temperatures up to 925 K, which are representative of meso-scale turbine engines. Scalability of the device has also been evaluated, down to a 1 kW engine, and up to MW order.
Evaluation of Air Filtration Options for an Industrial Gas Turbine
Authors: Perullo Christopher A. , Barron Josh , Grace Dale , Angello Leonard , Lieuwen Tim
Published: August 2015

Gas turbines ingest large quantities of air during operation. As a result, large quantities of foreign particles ranging in size from smoke (0.01 to 1.0 micron) to pollen (10 micron) enter the unit and can contribute to both fouling and erosion depending on particle size. Fouling and erosion both lead to reductions in unit output and efficiency resulting in increased operational cost. Operators have historically combatted fouling through a combination of online water washes, more effective off-line water washes, and air filtration. As is the case with almost all engineering problems, the trade-off between the cost and effectiveness of these methods must be evaluated. Online washing is somewhat effective but has led to first stage blade erosion and unit trips in some cases. Off-line washing is more effective at cleaning the unit, but requires the unit to be shut down for extended periods of time. Air filtration can help prevent foreign particles from entering the unit, but higher efficiency filters are generally associated with a larger inlet pressure drop, leading to decreased unit output; this is balanced against reduced fouling rates. These tradeoffs between the costs associated with higher efficiency filters and the frequency of compressor washing need to be evaluated on a plant-by-plant basis to determine the best combination of air filtration and compressor washing programs. This paper presents a field study carried out to determine the effectiveness of high efficiency filters in preventing compressor fouling. Fourteen units at four sites were monitored over a 9 month to 3 year time period to determine the changes in unit performance and the impact of water washes on unit performance for both pre and final filters of lower and higher efficiency ratings. Results to date indicate that higher efficiency filters are effective at reducing the need for off-line water washes and potentially reduce life-cycle cost. Reduced output from the higher pressure drop, high efficiency filters is offset by the better performance retention offered from reduced fouling rates.
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.
The Effect of Environment on TBC Lifetime
Authors: Pint Bruce A. , Unocic Kinga A. , Haynes J. Allen
Published: August 2015

While the water vapor content of the combustion gas in natural gas-fired land based turbines is ∼10%, it can be 20–85% with coal-derived (syngas or H2) fuels or innovative turbine concepts for more efficient carbon capture. Additional concepts envisage working fluids with high CO2 contents to facilitate carbon capture and sequestration. To investigate the effects of changes in the gas composition on thermal barrier coating (TBC) lifetime, furnace cycling tests (1 and 100h cycles) were performed in air with 10, 50 and 90 vol.% water vapor and CO2-10%H2O and compared to prior results in dry air or O2. Two types of TBC’s were investigated: (1) diffusion bond coatings (Pt diffusion or Pt-modified aluminide) with commercial electron-beam physical vapor-deposited yttria-stabilized zirconia (YSZ) top coatings on second-generation superalloy N5 and N515 substrates and (2) high velocity oxygen fuel (HVOF) sprayed MCrAlYHfSi bond coatings with air-plasma sprayed YSZ top coatings on superalloys X4, 1483 or 247 substrates. For both types of coatings exposed in 1h cycles, the addition of water vapor resulted in a decrease in coating lifetime, except for Pt diffusion coatings which were unaffected by the environment. In 100h cycles, environment was less critical, perhaps because coating failure was chemical (i.e. due to interdiffusion) rather than mechanical. In both 1h and 100h cycles, CO2 did not appear to have any negative effect on coating lifetime.
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.
An Experimental Study on Film Cooling Performance Behind Barchan Dune-Shaped Ramps Using PSP and PIV Techniques
Authors: Zhou Wenwu , Hu Hui
Published: August 2015

A novel Barchan-dune-assisted film cooling configuration was proposed and examined in present study. The effects of mass flux ratio, location, and height of Barchan dunes on film cooling effectiveness were investigated in great detail using the Pressure Sensitive Paint (PSP) and Particle Image Velocimetry (PIV) techniques. The PSP measurement results showed that the Barchan-dune-assisted film cooling configuration (H=0.5D, DB=−0.9D) can greatly enhance the film cooling effectiveness for flow from a cylindrical hole in relatively high mass flux ratio (M>0.85), which was explained by the PIV results in this study. Meanwhile the effects of Barchan dune location and height indicated that the film cooling performance of the Barchan-dune-assisted configuration is closely related to the height and location of the dune. It is wiser to choose Barchan dune of H=0.5D when it is placed upstream of the coolant hole, however the H=0.3D configuration is a better choice for placing the dune downstream.
Corrosion Testing of a Subsea Motor and Stator Winding Insulation System
Authors: Poerner Melissa , Grignard Jean-François , Krahn John , Duranty Lionel , Galioto Steven
Published: August 2015

In subsea applications, turbomachinery is subjected to severe gas and liquid mixtures. This is due to the fact that equipment installed on the ocean floor is severely limited. Typical gas/liquid separators and gas processing equipment are not used to clean the gas before it enters the turbomachinery. This means that the turbomachines can have multiphase mixtures and also corrosive gases such as hydrogen sulfide or carbonic acid (carbon dioxide and water) present in their flow streams among other contaminants. In many of these subsea applications, the electric motor driving the turbomachine is cooled using the process gas. Therefore the internals of the motor must withstand the attack of the corrosive mixtures and erosion with multiphase flow. A series of environmental static tests were conducted on a full scale subsea prototype motor to evaluate the performance of various materials when subjected to corrosive gas mixtures. These tests were conducted at various time intervals with different levels of pressure and temperature to simulate the conditions of a subsea environment gas flow. This paper reviews the test matrix and the test set-up used to conduct these tests. Also, it highlights the safety measures used to manage the inherent risks of testing with large quantities of corrosive and toxic gases mixtures and the different techniques that were implemented to follow the trends of the health of the insulation system.
An Extended Reynolds Equation Including the Lubricant Inertia Effects: Application to Finite Length Water Lubricated Bearings
Authors: Dousti Saeid , Fittro Roger L.
Published: August 2015

Water lubricated bearings used in nuclear coolant pumps and sub-sea applications exhibit large lubricant inertia forces in the magnitude order of viscous forces. To model these bearings the traditional Reynolds equation is not adequate. An extended Reynolds equation is developed in this study which takes into account the turbulence and inertia effects: both convective and temporal. The most complete form of temporal inertia which applies to the turbulent regime as well, is developed that consists of primary and secondary temporal inertia terms. The convective inertia model follows Constantinescu’s approach [1,2]. The turbulence model is also Constantinescu’s which is tuned with a CFD work. The dynamic coefficients including the lubricant added mass coefficients of a full cylindrical fixed geometry water bearing are obtained. It is observed that the convective inertia increases the load capacity and stability of the bearing. Significant lubricant added mass coefficients comparable to the shaft mass are calculated, which exhibit destabilizing effects in general.
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.
The Effects of Different Pin-Fin Arrays on Heat Transfer and Pressure Loss in a Narrow Channel
Authors: Siw Sin Chien , Fradeneck Austen D. , Chyu Minking K. , Alvin Mary Anne
Published: August 2015

This paper describes a detailed experimental investigation of a narrow rectangular channel based on the double-wall cooling concept that can be applicable to a gas turbine airfoil. The channel has dimensions of 63.5 mm by 12.7 mm, corresponding to an aspect ratio of 5:1. The pin diameter, D, is 12.7 mm, and the ratio of pin-height-to-diameter, H/D is 1. The inter-pin spacing is varies in both spanwise and streamwise directions to form two inline, and two staggered pin-fin configurations. The Reynolds number, based on the hydraulic diameter of the pin fin and the mean bulk velocity, ranges from 6,000 to 15,000. The experiments employ a hybrid technique based on transient liquid crystal imaging to obtain the distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. The heat transfer on both the endwall and pin-fin surfaces revealed similar pattern compared to the typical circular pin-fin array, which were conducted at higher Reynolds number. The total heat transfer enhancement of current pin-fin array is approximately four times higher than that of fully developed smooth channel with low pressure loss, which resulted in much higher thermal performance compared to other pin-fin array as reported in the literature.
A Development Method and Applications of the Most Severe Engine Parameters for Airworthiness Certification
Authors: Li Huihui , Tang Bin
Published: August 2015

For commercial aircraft engines, airworthiness certification is essential and the very first step before entry into service. Airworthiness requirements mainly consider the safety of the aircraft and mandate the aviation products to safely operate under all possible conditions. Therefore, during an airworthiness certification process, the relevant analyses and verifications are generally carried out by considering the most adverse operating conditions. A method for obtaining the most severe engine parameters which represent the possibly most adverse conditions is presented in this paper. Furthermore, it is used to complete the calculation of a set of most severe parameters, including rotor speed, turbine temperature, pressure, shaft torque, etc. Finally, this paper describes applications of these most severe parameters in the certification of the engine airworthiness regulation-CCAR/FAR33. Two examples are provided to illustrate the difference between using the general parameters and the most severe parameters. These examples demonstrate that application of most severe engine parameters to comply with the airworthiness requirements is the most practical way to guarantee the true safety.
Unsteady Effects of Profiled Endwalls on a 1.5 Stage Axial Turbine
Authors: Tang Huimin , Liu Shuaiqiang , Luo Hualing , Hou Weitao
Published: August 2015

Using a profiled endwall is an effective method to reduce secondary losses in axial turbines. This approach has been widely investigated in the past decade on many real engines. Much of the previous analysis, however, was conducted in a steady state, with mixing plane conditions where the effects of unsteady interaction between inter-blade rows could not be taken into account. Since a profiled endwall has notable influences on the secondary flow and trailing shed vorticity, it is unavoidable that the profiled endwall may also alter the unsteady flow field. Previously, we executed an optimization procedure [27] to design profiled endwalls for a one-and-half stage, high work axial turbine. Steady state results indicate an improvement in stage efficiency due to profiled endwalls on both the stator one and rotor one. In this work, the effects of profiled endwalls on the turbine unsteady flow features have been analyzed by conducting unsteady simulations. Numerical results indicate that profiled endwalls on the upstream stator not only reduce the secondary loss and trailing edge shed vorticity of the stator, but also reduce the secondary losses of the downstream rotor by affecting the development of the passage vortex. However, a profiled endwall on a rotor has nearly no influence on the upstream stator performance. Transient results indicate that with the profiled endwalls of S1, the periodic fluctuations of flow fields are reduced, due to a weaker stator/rotor unsteady interaction. With profiled endwall of R1, the fluctuations of a flow fields become stronger over time, which means a profiled endwall of R1 can introduce significant unsteady effects to the turbine. Unsteady effects of profiled endwalls will be experimentally confirmed before this design is applied to a real turbine.
Bayesian Calibration for Power Splitting in Single Shaft Combined Cycle Plant Diagnostics
Authors: Jiang Xiaomo , Mendoza Eduardo , Lin TsungPo
Published: August 2015

Condition monitoring and diagnostics of a combined cycle gas turbine power plant has become an important tool to improve its availability, reliability, and performance. However, there are two major challenges in the diagnostics of performance degradation and anomaly in a single shaft combined cycle power plant. First, since the gas turbine and steam turbine in such a plant share a common generator, each turbine’s contribution to the total plant power output is not directly measured, but must be accurately estimated to identify the possible causes of plant level degradation. Second, multivariate operational data instrumented from a power plant need to be used in the plant model calibration, power splitting and degradation diagnostics. Sensor data always contains some degree of uncertainty. This adds to the difficulty of both estimation of gas turbine to steam turbine power split and degradation diagnostics. This paper presents an integrated probabilistic methodology for accurate power splitting and the degradation diagnostics of a single shaft combined cycle plant, accounting for uncertainties in the measured data. The method integrates the Bayesian inference approach, thermodynamic physics modeling, and sensed operational data seamlessly. The physics-based thermodynamic heat balance model is first established to model the power plant components and their thermodynamic relationships. The model is calibrated to model the plant performance at the design conditions of its main components. The calibrated model is then employed to simulate the plant performance at various operating conditions. A Bayesian inference method is next developed to determine the power split between the gas turbine and the steam turbine by comparing the measured and expected power outputs at different operation conditions, considering uncertainties in multiple measured variables. The calibrated model and calculated power split are further applied to pinpoint the possible causes at individual components resulting in the plant level degradation. The proposed methodology is demonstrated using operational data from a real-world single shaft combined cycle power plant with a known degradation issue. This study provides an effective probabilistic methodology to accurately split the power for degradation diagnostics of a single shaft combined cycle plant, addressing the uncertainties in multiple measured variables.