bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis Technique to Determine the Underlying Wave Structure of Combustion Instabilities From Surface Mounted High Response Static Pressure Sensors
Authors: Hale Alan A. , Cothran Wesley D. , Sabo Kevin M.
Published: August 2018

Screech is an acoustic combustion instability that drives pressure oscillations much greater than normal combustion turbulent fluctuations. Discrete Fourier Transforms (FTs) are commonly utilized to analyze high resolution pressure sensor data. This isolated sensor analysis approach provides valuable frequency information, but since sensors are usually not located at peak amplitudes, resultant waves may be rotating and maximum amplitudes may be difficult to determine. Understanding the underlying counter-traveling or counter-rotating resultant wave structure is useful to develop screech mitigation strategies and necessary to quantify the impact of fuel schedule or geometry changes. A screech wave analysis methodology (SWAM) is developed for transverse, longitudinal, and complex modes. Typically, only two or three sensors are located in a transverse plane and in a longitudinal plane. The SWAM approach utilizes all the sensors in an analysis plane to provide an integrated sensor analysis. SWAM results are evaluated based upon exact wave solutions, and demonstrated with test data.
Mixing Losses in Steady and Unsteady Simulations of Turbomachinery Flows
Authors: Schlüß Daniel , Frey Christian
Published: August 2018

The aim of the present work is to facilitate insight into the modeling errors in the context of blade row coupling approaches which capture unsteady flow phenomena at different levels of detail. The focus is on RANS-based steady mixing plane computations as well as time domain and frequency domain unsteady computations. The concept of mixing loss is revisited to quantify the amount of unsteadiness in a flow field. Following an idea by Fritsch and Giles, we compute a second order approximation of the mixing losses which are generated at blade row interfaces. The resulting formula decomposes the entropy jump into contributions of circumferential and temporal fluctuations. The mathematical derivation, however, is based upon simpler arguments. It is shown that Fritsch and Giles’ main result can be extended to non-ideal gases. Moreover, the second order mixing loss formula is applied to time and frequency domain unsteady simulations. It is shown that an additional term has to be computed which accounts for the interaction of evanescent acoustic modes if the method is applied to unsteady flows. The methodology decomposes the overall mixing entropy into contributions of single perturbation types and harmonics. This may be used to assess whether unsteady flow phenomena of interest are adequately resolved and, in particular, to quantify the unsteadiness contained in the unresolved harmonics. A detailed investigation of the transonic IGV-rotor configuration of DLR’s Rig 250 compressor demonstrates the approach.
Numerical and Experimental Study of the Emissions During Methanol Combustion
Authors: Levy Y. , Erenburg V. , Roizman A. , Sherbaum V.
Published: August 2018

The study focuses on the emission of pollutants generated during combustion of methanol, including the formation of formaldehyde and acrolein, the two main additional hazardous pollutants formed during the combustion of methanol. The study is based on chemical kinetic analysis using the CHEMKIN code (1D-reactor model) and ANSYS code for numerical computation. A parallel experimental combustion study was performed using a laboratory scaled swirl stabilized combustor model using methanol fuel. The combustor model was built in order to calibrate and test the developed theoretical models. The chemical kinetic analysis, using the CHEMKIN code, showed that under the investigated conditions, the maximum acrolein concentration at the exhaust was 0.12ppmv. Currently, there is no emission standard that we know of that refers to acrolein. However, it may very well be that due to the high toxify of acrolein, even such a low value may be too high. The results from the CFD simulations about the acrolein concentration at the exhaust revealed very low values, less than 0.01ppm, and consequently were not presented. Formaldehyde emission was evaluated by chemical kinetics studies, CFD analyses, and measured experimentally using two different analyzers. It is shown that the current common standard for the allowable limit of formaldehyde, which is based on the absolute amount exhausted, is too low and will limit the use of methanol only to small power units.
Numerical Investigation of Gas Turbine Combustor Liner Film Cooling Slots
Authors: Kiyici Firat , Topal Ahmet , Hepkaya Ender , Inanli Sinan
Published: August 2018

A numerical study, based on experimental work of Inanli et al. [1] is conducted to understand the heat transfer characteristics of film cooled test plates that represent the gas turbine combustor liner cooling system. Film cooling tests are conducted by six different slot geometries and they are scaled-up model of real combustor liner. Three different blowing ratios are applied to six different geometries and surface cooling effectiveness is determined for each test condition by measuring the surface temperature distribution. Effects of geometrical and flow parameters on cooling effectiveness are investigated. In this study, Conjugate Heat Transfer (CHT) simulations are performed with different turbulence models. Effect of the turbulent Prandtl Number is also investigated in terms of heat transfer distribution along the measurement surface. For this purpose, turbulent Prandtl number is calculated with a correlation as a function of local surface temperature gradient and its effect also compared with the constant turbulent Prandtl numbers. Good agreement is obtained with two-layered k–ϵ with modified Turbulent Prandtl number.
Multi-Objective Optimization of the Cooling Configuration of a High Pressure Turbine Blade
Authors: Wagner Frank , Kühhorn Arnold , Janetzke Timm , Gerstberger Ulf
Published: August 2018

Due to the increasing turbine inlet temperature and in order to improve the overall efficiency it is necessary to optimize the cooling design of the hot gas components of an aero engine.

The current paper discusses the strategy of optimizing a rotor blade cooling configuration of a small civil aero engine, comprising of films and internal turbulators (ribs). An insight into the parametrization is given including the location of the films and ribs as well as the number of the films and ribs. The parameter reduction results in 18 input parameters for the optimizations to limit the number of parameters to an acceptable level.

Two optimizations are carried out with the primary objectives of non-dimensional mass flow and overall cooling effectiveness. Different optimization algorithms are used, namely AMGA and NSGA-II, and compared afterwards. A further optimization is carried out with direct objectives of mass flow and mean surface temperature using the AMGA algorithm.

The outputs from the optimizations are presented as a pareto-front. These plots are used for a comparison of the optimization algorithms and formulations respectively. Finally, the differences are discussed and the advantages and disadvantages of the algorithms used are highlighted.
New Facility Setup for the Investigation of Cooling Flow, Viscous and Rotational Effects on the Interstage Seal Flow Behavior of a Gas Turbine
Authors: Guida R. , Lengani D. , Simoni D. , Ubaldi M. , Zunino P.
Published: August 2018

A new rig has been designed and commissioned at the University of Genova to study the flow field within a turbine interstage cavity and its interaction with the main flow path. The rig is a large scale one-and-half stages, rotating test facility, opportunely designed to reproduce the main features characterizing the cavity flows developing in real low pressure modules of turbogas engines. The effects due to swirl factor and the coolant injected into the cavity to prevent the thermomechanical failure of the disks have been investigated. The rig allows the evaluation of the leakage mass flow rate and the measurement of the seal discharge coefficient in the different operating conditions, as well as the characterization of viscous, rotational and coolant related effects on the main flow path, especially in terms of secondary flow structures and vane row efficiency. Pressure signals acquired into the cavity provide a direct measure of the pressurization level of the fore and rear cavities, as well as the analysis of the effects induced by rotation and coolant flow on the pressure drop provoked by the teeth. Results clearly show that once the cooling flow rate reaches a datum threshold level an iso-pressure condition (with respect to the main flow at the vane leading edge) is established into the fore part of the cavity, and the gas ingestion from the main annulus is avoided. This “purged” condition significantly modifies the near wall flow developing across the vane. The boundary layer entering the vane row is not sucked into the cavity, and simultaneously at the vane exit plane there is poor interaction between the cavity flow and the near wall flow leaving the vane. Total pressure measurements upstream and downstream of the vane clearly highlight the modification of the secondary flow structures for the different conditions tested. Overall, results reported into the paper demonstrate the capability of the new rig to provide a direct estimation of the discharge coefficient of a realistic turbine cavity system for different coolant flow rates and swirl factors, as well as to understand the effects on the flow path near wall behavior due to cavity-main flows interaction, that should be properly accounted for during the design phases, and should be properly reproduced during cascade testing.
Evaluation of the Fuel Saving Potential Regarding Recuperated Helicopter Flight Conditions
Authors: Zhang Chengyu , Kerler Martin , Gümmer Volker
Published: August 2018

Incorporating recuperators into turbine engines which enables the heat transfer between exhaust gas and compressed air, indicates considerable potential for lower emissions and SFC (specific fuel consumption). However as a matter of fact, they have not yet found wide acceptance in aircraft applications. One of the main potential disadvantages is because in such situations system overall weight needs to be strictly controlled, and there are concerns that the beneficial fuel saving may not offset the additional bulk and weight of the recuperator.

In this work, aimed at evaluating the performance of the recuperated rotorcraft and investigating the influence of a recupeator on the whole system, a comprehensive simulation framework has been developed which mainly contains three modules for various flight conditions: Helicopter performance module (HPM), GasTurb engine simulation module and the recuperator weight estimation. Specifically, HPM calculates the helicopter power requirement for different flight conditions (altitude, speed, etc.), and GasTurb is used to simulate the performance of conventional and recuperated turbine engine, and compute the corresponding engine operating point to meet the power demand. The recuperator weight estimation is mainly based on previous studies as a function of mass flow and effectiveness. The methodology is adopted for a typical twin engine light helicopter configuration.

In comparison with the conventional non-recuperated cycle, the authors studied the fuel saving potential of the recuperated cycle for different recuperator effectiveness under various flight conditions, and a trade-off analysis was also conducted to identify the flight time required to compensate the additional recuperator weight.

The obtained results suggested that the recuperated cycle possesses great potential, especially for long duration and large range mission, but it may not be necessarily suitable for all types of helicopter missions.
Nonlinear Analysis of Rotordynamic Fluid Forces in the Annular Plain Seal by Using Extended Bulk-Flow Analysis: Influence of Static Eccentricity and Whirling Amplitude
Authors: Yamada K. , Ikemoto A. , Uchiumi M. , Inoue T.
Published: August 2018

Rotor-dynamic fluid force (RD fluid force) of turbo-machinery is one of the causes of the shaft vibration problem. Bulk flow theory is the method for analyzing this RD fluid force, and it has been widely used in the design stage of machine. Conventional bulk flow theory has been carried out under the assumption of concentric circular shaft’s orbit with small amplitude. However, actual rotating machinery’s operating condition often does not hold this assumption, for example, existence of static load on the machinery causes static eccentricity. In particular, when such a static eccentricity is significant, the nonlinearity of RD fluid force may increase and become non-negligible. Therefore, conventional bulk flow theory is not applicable for the analysis of RD fluid force in such situation. In this paper, RD fluid force of the annular plain seal in the case of circular whirling orbit with static eccentricity is investigated. The case with both the significant static eccentricity and the moderate whirling amplitude is considered, and the perturbation analysis of the bulk-flow theory is extended to investigate RD fluid force in such cases. In this analysis, the assumption of the perturbation solution is extended to both static terms and whirling terms up to the third order. Then, the additional terms are caused by the coupling of these terms through nonlinearity, and these three kinds of terms are considered in the extended perturbation analysis of the bulk flow theory. As a result, a set of nonlinear analytical equations of the extended perturbation analysis of the bulk flow theory, for the case with both the significant static eccentricity and the moderate whirling amplitude, is deduced. RD fluid force for such cases are analyzed, and the occurrence of constant component, backward synchronous component and super-harmonic components in RD fluid force is observed in addition to the forward synchronous component. The representation of RD fluid force coefficients (RD coefficients) are modified for the case with significant static eccentricity, and the variation of RD fluid force coefficients for the magnitude of static eccentricity is analyzed. These analytical results of RD fluid force and its RD coefficients are compared with the numerical results using finite difference analysis and experimental results. As a result, the validity of the extended perturbation analysis of the bulk-flow theory for the case with both the significant static eccentricity and the moderate whirling amplitude is confirmed.
An Acoustic Travelling Wave System for the Analysis of Blisk Mistuning
Authors: Grant Joshua J. , Cosmo Mitchell R. , Hou Jianfu F. , Smith Evan O. , de Baar Jouke H. S.
Published: August 2018

One of the few acoustic travelling wave systems (TWS) in the world has been developed by Defence Science and Technology Group Australia (DST). This system uses acoustic excitation of blisks by means of a high-powered speaker cluster. The response to this acoustic excitation is measured by a laser doppler vibrometer which shows the natural frequencies and mode shapes of the blisk. To date, this system has been verified and validated on a simple, twelve-bladed research blisk with a maximum error of 3.78% from FEM modal and harmonic analysis. Furthermore, the system has been refined and tested on a current in-service blisk with an accuracy of approximately 1%. This study outlines how the TWS has been used to investigate the effects of mistuning on blisks. Promising results have been achieved with the system able to accurately identify changes in resonant behaviour due to mistuning with correlation to finite element modelling predictions. The limitations are also outlined, along with suggested areas of research and improvement. This may ultimately result in the ability to verify manufacturer blending limits and assess the effect of foreign object damage and repairs on the dynamic response characteristics of a blisk without a complex and labour intensive mechanical spin rig investigation.
Investigation of Thermal Effect on Bypass Transition on a High-Pressure Turbine Guide Vane
Authors: Cação Ferreira Tânia S. , Vasilakopoulos Nikolaos , Arts Tony
Published: August 2018

The role of gas-to-wall temperature ratio on bypass transition along a highly loaded turbine guide vane is investigated through time-resolved heat flux measurements for different flow conditions. The tests are conducted in the von Karman Institute (VKI) isentropic compression tube (CT-2) facility. High response thin films mounted on the vane (VKI LS89 airfoil) coupled with analog circuits are used for the heat flux measurements. The first detectable wall heat flux fluctuations denote the onset of transition which is also evaluated by both the heat transfer coefficient and the intermittency factor distributions along the suction side. The exit Mach number is kept constant during each test by means of a downstream sonic throat while the gas-to-wall temperature ratio is varied from 1.14 to 1.51 by changing the inlet gas temperature. Four test cases are considered for different exit Mach numbers (0.52 and 0.86) and freestream turbulence intensity levels (0.8% and 5.3%) while the isentropic exit chord Reynolds number is maintained at 106. In the present test campaign, the length and the evolution of the phenomenon indicate a measurable effect of the gas-to-wall temperature ratio for test cases with mild pressure gradients.
3D Computational Analysis of a Compressor for Heavy Duty Truck Engine Turbochargers
Authors: Abel Matthias , Newton Peter , Martinez-Botas Ricardo F. , Wöhr Michael , Müller Markus , Leweux Johannes
Published: August 2018

This paper presents a detailed analysis of a centrifugal compressor stage with a vaned diffuser for application in a heavy duty engine turbocharger. The analysis is carried out in order to investigate the capability of a steady-state 3D CFD to predict the pressure distribution resulting from the flow through the stage.

As it is impractical to investigate the whole range of conditions, the first objective of this paper is to define the operating points, which are most relevant to the real operation of the compressor, to be used in this paper. In order to do this, the engine operation is weighted in terms of the total fuel consumption across a reference route: Portland-Pendleton-Portland. After the definition of the primary operating points, a CFD setup is created with regard to previous work on steady-state 3D CFD of a centrifugal compressor stage. The CFD analysis is validated against extensive hot-gas test stand data. The experimental data include the static pressure distribution in the diffuser shroud, determined with an array of 256 pressure transducers. A maximum discrepancy between the CFD and the experiment of around 1.6% difference is achieved for all primary operating points.
Numerical Investigation of Unsteady Film Cooling on the Turbine Shroud With the Blade Passing
Authors: Gao Chao , Liu Cun-liang , Liu Hai-yong , Guo Qi-ling , Wang Rui-dong , Zhu Hui-ren
Published: August 2018

Numerical simulations have been performed on the turbine shroud unsteady film cooling under the blade passing. There are many published experimental studies for turbine shroud heat transfer and a few computational fluid dynamics data. In this paper, unsteady RANS method has been performed to study the effect of the blade rotation speeds and the film blowing ratios on the behavior of film cooling effectiveness. And the sliding mesh in Fluent was used to achieve relative rotation between blade and shroud. These results are reported for blowing ratios of 1.0, 1.5, 2.0, blade rotation speeds of 1600 rpm, 1800rpm, 2089rpm, 2400rpm. The results show that the time instantaneous film cooling effectiveness on the shroud have a notable different distribution with the steady blade case. And at the rotation results, the film cooling effectiveness is even coverage with the blowing ratio increasing. The time-averaged film cooling effectiveness on the shroud increases by increasing the blowing ratio on all blade rotational velocities. And in this study, the blade at different rotation speeds, the distribution of time-averaged film cooling effectiveness has a significantly reduce on the shroud because of the relative movement of blade and shroud.
Effect of Temperature Ratio on Jet Impingement Heat Transfer in Active Clearance Control Systems
Authors: Da Soghe Riccardo , Bianchini Cosimo , D’Errico Jacopo , Tarchi Lorenzo
Published: August 2018

Impinging jet arrays are typically used to cool several gas turbine parts. Some examples of such applications can be found in the internal cooling of high pressure turbine airfoils or in the turbine blade tip clearances control of aero-engines. The effect of wall-to-jets temperature ratio on heat transfer is generally neglected by the correlations available in the open literature.

In present contribution, the impact of the temperature ratio on the heat transfer for a real engine Active Clearance Control system, is analyzed by means of validated CFD computations. At different jets Reynolds number and considering several impingement array arrangements, a wide range of target wall-to-jets temperature ratio (TR) is accounted for. Computational results prove that both local and averaged Nusselt numbers reduce with increasing temperature ratios.

An in-depth analysis of the numerical data show that the last mentioned evidence is motivated by both the heat transfer incurring between the spent coolant flow and the fresh jets and the variation of gas properties with temperature through the boundary layer. A scaling procedure, based on TR power law, was proposed to estimate the Nusselt number at different wall temperature levels necessary to correct available open-literature correlations, typically developed with small temperature differences, for real engine applications.
The Role of Vortex Shedding in the Trailing Edge Loss of Transonic Turbine Blades
Authors: Melzer A. P. , Pullan G.
Published: August 2018

The loss of Square, Round, and Elliptical turbine trailing edge geometries, and the mechanisms responsible, is assessed using a two-part experimental program. In the first part, a single blade experiment, in a channel with contoured walls, allowed rapid testing of a range of trailing edge sizes and shapes. In the second part, turbine blade cascades with a sub-set of sizes of the trailing edge geometries tested in part one were evaluated in a closed-loop variable density facility, at exit Mach numbers from 0.40 to 0.97, and exit Reynolds numbers from 1.5 x105 to 2.5 x106. Throughout the test campaign, detailed instantaneous Schlieren images of the trailing edge flows have been obtained to identify the underlying unsteady mechanisms in the base region. The experiments reveal the importance of suppressing transonic vortex shedding, and quantify the influence of this mechanism on loss. The state and thickness of the blade boundary layers immediately upstream of the trailing edge are of critical importance in determining the onset of transonic vortex shedding. Elliptical trailing edge geometries have also been found to be effective at suppressing transonic vortex shedding. For trailing edges that exhibit transonic vortex shedding, a mechanism is identified whereby reflected shed shockwaves encourage or discourage vortex shedding depending on the phase with which the shocks return to the trailing edge, capable of modifying the loss generated.
Dynamic Analysis and Reduction of a Cyclic Symmetric System Subjected to Geometric Nonlinearities
Authors: Martin Adrien , Thouverez Fabrice
Published: August 2018

The search for ever lighter weight has become a major goal in the aeronautical industry as it has a direct impact on fuel consumption. It also implies the design of increasingly thin structures made of sophisticated and flexible materials. This may result in nonlinear behaviours due to large structural displacements. Stator vanes can be affected by such phenomena, and as they are a critical part of turbojets, it is crucial to predict these behaviours during the design process in order to eliminate them.

This paper presents a reduced order modelling process suited for the study of geometric nonlinearities. The method is derived from a classical Component Mode Synthesis with fixed interfaces, in which the reduced nonlinear terms are obtained through a STEP procedure using an adapted basis composed of linear modes completed by modal derivatives. The whole system is solved using a harmonic balance procedure and a classic iterative nonlinear solver. The application is implemented on a schematic stator vane model composed of nonlinear Euler-Bernoulli beams under von Kàrmàn assumptions.
Robust Fluid Topology Optimization Using Polynomial Chaos Expansions: TOffee
Authors: Gaymann A. , Montomoli F. , Pietropaoli M.
Published: August 2018

The paper presents an innovative solution to robust topology optimization developed for components that can be manufactured by additive manufacturing. Topology optimization has been used in fluid dynamics to optimize geometries based on a target set of performances required for the flow paths. These target performances can be defined as pressure losses or heat exchanges for example, and multiple optimized geometries can be found in the literature.

However, none of these cases considered the impact of stochastic variations and are based on a deterministic optimization. It means the optimization has been done for a single boundary condition value. Would this boundary be random, as it is the case in real life gas turbines, then the optimized geometry, optimized for a single set of boundary conditions, will underperform.

Robust topology optimization obtains a geometry able to cope with these random variations. The robust optimization method has been implemented in an in-house solver TOffee and relies on a multi-objective function.

2D and 3D robust optimized geometries are obtained and their performance compared to deterministic cases over a range of boundary conditions. Superiority of robust geometries as compared to deterministic geometries is shown. Robust topology optimization presents a great interest in the gas turbine industry due to the greater performance obtained by the optimized geometries while taking into consideration random variations of boundary conditions, making the simulations closer to real life conditions.

For the first time in this work it is shown a fluid topology optimization solution with sedimentation that are inherently able to cope with uncertainty.
Reduction of the Design Space to Optimize Blade Fir-Tree Attachments
Authors: Alinejad F. , Botto D. , Gola M. , Bessone A.
Published: August 2018

The blade attachment, both dovetail or fir-tree, transfers the centrifugal load from the blade to the disc, generating high mean and peak stresses in notches as well as on contact surfaces. Hence, the strength of the attachment is one of the main concern of the designers for improving the performance of the engine and several optimization procedure have been put forward to minimize the state of stress in the attachment for a given centrifugal load. The optimization process is generally driven by a parametric model. The selection of the proper parameters and their variation ranges represent one of the main issues for the process to converge in a reasonable amount of time. Simulation methods and optimization algorithms have been improved a lot in the past years. Nevertheless, the computational effort of the finite element analysis involved in the optimization procedure of complex geometries remains a critical task. Moreover, an accurate evaluation of the local contact stresses is highly dependent on the mesh refinement, increasing the computing time of the whole optimization process. Moreover, a multi-objective optimization, in addition to robustness design approach, is the designer tool to improve the attachment performance.

The searching domain reduction of the optimization process improves the computational performance reducing the convergence time of the solution. To achieve this goal, a preliminary selection of the design space has been performed by means of an analytical approach.

This paper describes a new design criterion based on one dimensional approach. The criterion has been implemented in an in-house tool that takes faster decisions, if compared with a two or a three dimensional model, about the number of possible feasible solutions. During the geometrical optimization phase of the blade fir-tree attachment, in which a parametric model is used, the authors try to handle the geometrical non-feasibility with a combination of Latin Hypercube Sampling (LHS) and an adaptive penalty method. The optimization is done via the genetic algorithm and the computational time of the reduced domain is compared with the original one.
Investigations on the Influence of Rib Orientation Angle on Film Cooling Performance of Compound Holes
Authors: Ye Lin , Liu Cun-liang , Liu Hai-yong , Zhu Hui-ren , Luo Jian-xia
Published: August 2018

To investigate the effects of the inclined ribs on internal flow structure in film hole and the film cooling performance on outer surface, experimental and numerical studies are conducted on the effects of rib orientation angle on film cooling of compound cylindrical holes. Three coolant channel cases, including two ribbed cross-flow channels (135° and 45° angled ribs) and the plenum case, are studied under three blowing ratios (0.5, 1.0 and 2.0). 2D contours of film cooling effectiveness as well as heat transfer coefficient were measured by transient liquid crystal measurement technique (TLC). The steady RANS simulations with realizable k-ε turbulence model and enhanced wall treatment were performed. The results show that the spanwise width of film coverage is greatly influenced by the rib orientation angle. The spanwise width of the 45° rib case is obviously larger than that of the 135° rib case under lower blowing ratios. When the blowing ratio is 1.0, the area-averaged cooling effectiveness of the 135° rib case and the 45° rib case are higher than that of the plenum case by 38% and 107%, respectively. With the increase of blowing ratio, the film coverage difference between different rib orientation cases becomes smaller. The 45° rib case also produces higher heat transfer coefficient, which is higher than the 135° rib case by 3.4–8.7% within the studied blowing ratio range. Furthermore, the discharge coefficient of the 45° rib case is the lowest among the three cases. The helical motion of coolant flow is observed in the hole of 45° rib case. The jet divides into two parts after being blown out of the hole due to this motion, which induces strong velocity separation and loss. For the 135° rib case, the vortex in the upper half region of the secondary-flow channel rotates in the same direction with the hole inclination direction, which leads to the straight streamlines and thus results in lower loss and higher discharge coefficient.
In-Situ Assessment of Fracture in SiCf/SiC Under Computed X-Ray Tomography
Authors: Bache M. R. , Nicholson P. I. , Williams E.
Published: August 2018

The use of X-ray computed tomography (XCT) for detecting sub-critical damage and ultimate failure mechanisms in a ceramic matrix composite is demonstrated. To this end, an initial XCT investigation of a CMC sample, using a commercially available in-situ mechanical loading rig, is presented. As an important step toward a better understanding of the mechanical behaviour of these materials, in-situ XCT inspection was performed on a macroscopic scaled test coupon, i.e. sampling a significant number of fibre bundles, whilst the material was subjected to monotonic tensile load. The observation of inherent processing artefacts, and the tracking of resultant damage in the structure of CMCs, was demonstrated, supported by post test inspections using optical and scanning electron microscopy. Further consideration is given to the requirements for developing XCT systems for in-situ inspection of CMC materials.
Multi-Lead Direct Current Potential Drop (DCPD) for In-Situ Health Monitoring of Ceramic Matrix Composites
Authors: Singh Yogesh P. , Presby Michael J. , Manigandan Kannan , Morscher Gregory N.
Published: August 2018

The method of direct current potential drop (DCPD) can be utilized as an effective, and convenient approach for in-situ damage detection, and as a non-destructive evaluation technique. We present the results from use of a multiprobe DCPD technique for in-situ damage detection in loading of a SiC/SiC composite. It is shown that in three different modes of loading (monotonic, fatigue, and cyclic load-unload), the sensing capabilities of DCPD technique compares well to the techniques of modal acoustic emission (AE) and digital image correlation (DIC). It was also found that DCPD technique provides a far earlier warning of failure under fatigue loading than the other two methods. In addition, we show that strategically placed multiple voltage leads on the specimen surface provides a promising way of qualitatively determining the crack initiation site. Therefore, the use of multiple lead DCPD method, together with other techniques, provides a viable option for sensing damage in ceramic matrix composites (CMCs) with complex geometries, and for applications at higher temperatures.
Utilization of a Thermo-Mechanical Model Coupled With Multi-Objective Optimization to Enhance the Start-Up Process of Solar Steam Turbines
Authors: Topel Monika , Vitrano Andrea , Laumert Björn
Published: August 2018

The need to mitigate the climate change has brought in the last years to a fast rise of renewable technologies. The inherent fluctuations of the solar resource make concentrating solar power technologies an application that demands full flexibility of the steam turbine component. A key aspect of this sought steam turbine flexibility is the capability for fast starts, in order to harvest the solar energy as soon as it is available. However, turbine start-up time is constrained by the risk of low cycle fatigue damage due to thermal stress, which may bring the machine to failure. Given that the thermal limitations related to fatigue are temperature dependent, a transient thermal analysis of the steam turbine during start process is thus necessary in order to improve the start-up operation.

This work focuses on the calculation of turbine thermo-mechanical properties and the optimization of different start-up cases in order to identify the best solution in terms of guaranteeing reliable and fast start-ups. In order to achieve this, a finite element thermal model of a turbine installed in a concentrating solar power plant was developed and validated against measured data. Results showed relative errors of temperature evolutions below 2%, making valid the assumptions and simplifications made. Since there is trade-off between start-up speed and turbine lifetime consumption, the model was then implemented within a multi-objective optimization scheme in order to test and design faster start-ups while ensuring safe operation of the machine. Significant improvements came up in terms of start-up time reduction up to 30% less than the standard start-up process.
Unsteady Effects on the Experimental Determination of Overall Effectiveness
Authors: Rutledge James L. , Baker William P.
Published: August 2018

An increasingly common experimental method allows determination of the overall effectiveness of a film cooled turbine component. This method requires the Biot number of the experimental model to match that of the engine component such that the nondimensional surface temperature, ϕ, is matched to that of the engine component. The matched Biot number requirement effectively places a requirement on the thermal conductivity of the model and the traditional implementation places no requirement on the model’s density or specific heat. However, such is not the case if such a model is exposed to unsteadiness in the flow such as with film cooling unsteadiness. In this paper, we develop an additional nondimensional parameter that must also be theoretically matched to conduct overall effectiveness experiments with unsteady film cooling. Since finding suitable materials with an acceptable combination of thermodynamic properties for a typical low temperature experiment can be difficult, simulations were conducted to determine the impact of imperfectly matched parameters achievable with common materials. Because the disparity between the diffusion and unsteadiness time scales can hinder numerical simulation, a novel analytical solution to the heat equation with relevant unsteady Robin type boundary conditions is developed. Particular solutions are examined to determine the sensitivity of the temperature response of a turbine blade (or a model of one) to its material properties and the form of the unsteady variation in the convection parameters. It is shown that it is possible to obtain useful experimental results even with imperfectly matched parameters.
Application of Surrogate Models and Probabilistic Design Methodology to Assess Creep Growth Limit of an Uncooled Turbine Blade
Authors: Hadadian Armin , Prabhakar Sairam , Sjodin Bjorn , Taylor Keith
Published: August 2018

Predictive lifing with probabilistic treatment of key variables represents a promising approach to realizing the digital gas turbine of the future. In this paper, we present a predictive model for creep life assessment of an uncooled turbine blade. The model development methodology draws on well-established machine learning principles to develop and validate a surrogate model for creep life from engine performance parameters. Verified creep life results, obtained from 3D non-linear thermo-mechanical finite element simulation for varying engine operating conditions are used as the basis for model development. The selection of model response surface order is studied over a range of models by evaluating normalized residual error on training and uncorrelated validation data sets. A model that is fully quadratic in the data set features is shown to have excellent predictive capability, yielding nominal creep life predictions to within ± 3% on the validation data set. This work then considers probabilistic techniques to evaluate the impact of uncertainty associated with each key factor on the predicted nominal creep life in order to achieve a mandated life target with a defined probability of failure.
Thermomechanical Model Reduction for Efficient Simulations of Rotor-Stator Contact Interaction
Authors: Guérin Nicolas , Thorin Anders , Thouverez Fabrice , Legrand Mathias , Almeida Patricio
Published: August 2018

Turbomachinery rotor-stator unilateral contact induced interactions play a growing role in lifecycle analysis and thus motivate the use of accurate numerical prediction tools. Recent literature confirmed by ongoing in-house experiments have shown the importance of thermomechanical coupling effects in such interactions. However, most available (possibly reduced-order) models are restricted to the sole mechanical aspects.

This work describes a reduction technique of thermomechanical models involving unilateral contact and frictional contact occurrences between rotor and stator components. The proposed methodology is grounded on Guyan and Craig–Bampton methods for the reduction of the structural dynamics in conjunction with Krylov subspace techniques, and specifically the Craig–Hale approach, for the reduction of the thermal equations.

The method has the capability to drastically reduce the size of the model while preserving accuracy. It stands as a reliable strategy to perform simulations of thermomechanical models with localized mechanical and thermal loads.
Development of a Dry Low NOx Combustor for Dual Gaseous Fuels of Natural Gas and Petroleum Gas
Authors: Asai Tomohiro , Miura Keisuke , Abe Kazuki , Matsubara Yoshinori , Koganezawa Tomomi , Hirata Yoshitaka , Hayashi Akinori , Yoshida Shohei
Published: August 2018

Liquefied petroleum gas (LPG) will be suitable for satisfying part of the growing global energy demands. The widespread utilization of LPG as a gas turbine fuel for power generation requires an advanced combustor that achieves dry low nitrogen oxides (NOx) combustion and flashback-resistant combustion. This paper describes the development of a “multi-cluster combustor” as an advanced dry low NOx and flashback-resistant combustion technology for dual gaseous fuels of natural gas and petroleum gas. The dual gaseous fuel capability will contribute to expanding fuel flexibility. The purpose of this paper is to evaluate the feasibility of the dual gaseous fueled combustion with the multi-cluster combustor with the same configuration. The combustor was tested in a single-can combustor test stand at medium pressure with both fuels. In the tests, natural gas consisted mainly of methane with a content of over 90 vol.%, and petroleum gas consisted almost entirely of propane. The test results showed that the combustor achieves dry low NOx combustion of both fuels within their stable ranges without flashback. This paper concluded from the test results that the multi-cluster combustor possesses the potential capability to achieve dry low NOx and flashback-resistant combustion of dual gaseous fuels of natural gas and petroleum gas. As the next step, further tests will be required with petroleum gas including butane and for high pressure conditions.
A Novel COGAG Propulsion System for Marine Ships
Authors: Xu Zhenzhong , Wen Xueyou , Zhao Ningbo
Published: August 2018

Considering the increasing development of naval destroyers and the obvious advantages of marine gas turbine, this paper designs a novel COGAG (Combined Gas-turbine And Gas-turbine) propulsion system which mainly consists of four GT25 marine gas turbines and one CCG (Cross Connection Gears) for the large destroyer. Firstly, the overall configuration and key devices of COGAG propulsion system are introduced briefly. Then, the typical operating patterns of COGAG propulsion system under different condition are discussed in detail. Finally, many experimental information are further presented. All the results show that the developed COGAG propulsion system not only has higher flexibility and reliability, but also can effectively improve the fuel economy of marine ships.
Investigation on the Modal Characteristics of the Rubbing Rotor System With Additional Constraint
Authors: Hong Jie , Yu Pingchao , Zhang Dayi , Ma Yanhong , Liu Jixing
Published: August 2018

The rub-impact can bring about the impact load and friction force onto the rotor, and produce the additional constraint effect as well. The additional constraint effect, which is also called stiffness effect, can increase the stiffness of the rotor system. Consequently, the modal characteristics of the rotor system are changed. This paper aims to understand the modal characteristics of the rubbing rotor system with additional constraint. The governing equation for a modified Jeffcott rotor with additional constraint is established first. Based on the complex nonlinear modes concept and harmonic balance method, the solution method for nonlinear modes of the rubbing rotor system is derived, then the method is validated through a 2-dof collision system. Finally, the modal characteristics of the rubbing rotor and influence of the key parameters are analyzed in detail. The results reveal that the rubbing rotor system possesses two potential mode motions, i.e. forward whirl with positive modal frequency and backward whirl with negative modal frequency. Both the modal frequency values of these two mode motions increase with the modal amplitude increases, but their values are limited to an interval range. The modal damping of the forward whirl mode motion is always greater than zero, while the modal damping of the backward whirl mode motion may be less than zero, indicating the backward whirl mode motion can be unstable in some cases.
A Simplified and Efficient Analysis of Morton Effect
Authors: Gu Lili
Published: August 2018

The Morton Effect refers to a phenomenon of special instability for rotors supported by fluid-film-bearings and present with asymmetric heating for the journal part. This problem tends to occur when rotors exhibit synchronous vibrations. Originating from the temperature gradients during the eccentric orbiting of rotor journals, the Morton Effect has been a latent threaten to rotor stability since the fluid-bearing-supported rotating machinery was first in service. This paper extends the modeling scope to a general scenario when the heating source is not limited only to the viscous shearing effect. Such an extension could apply to the Newkirk effect, a problem induced by light rubbing but exhibiting similar phenomenon as the Morton Effect. The simplified coupled model enables the coupling between the thermal field and structural vibrations directly. To better understand the roles played by the thermal factors in the Morton Effect, this paper extracts the influence of temperature increase in the bearing fluid film on bearing dynamic coefficients. The investigation results show that the temperature rise, an accompany of increased speeds, has a significant influence on the cross-coupled stiffness coefficients but a negligible impact on other components of dynamic coefficients. In general, the speed plays a dominant role in the change of dynamic coefficients. In the end, the coupled dynamic model is validated by a case study of a mid-span rotor model investigated in the literature. Good agreements with the reference imply that the model assembled here is effective and reliable for the analysis of the Morton Effect.
Impact of Turbine Blade Stagger Angle Adjustment on the Efficiency and Performance of Gas Turbines During Off-Design and Dynamic Operation
Authors: Schobeiri Meinhard T.
Published: August 2018

Gas turbines in general and aircraft engines in particular undergo frequently dynamic operations. These operations include the routine start-up, load change and shut downs to cover their operation envelope. The frequency of the dynamic operation depends on the size of the engines and the field of application. Engines for commuter aircrafts and particularly helicopter engines operate more often in an off-design mode compared to large commercial aircraft engines and power generation gas turbines. During these routine operations, the compressor mass flow, the pressure ratio, the combustion chamber fuel and air mass flow as well as turbine mass flow change. These changes affect the engine aerodynamic performance and its efficiency. To avoid the inception of rotating stall and surge, high performance gas turbines are equipped with mechanisms that adjust the stator stagger angles thus aligning the stator exit flow angle to the rotor inlet angle, which reduces an excessive incidence. The reduction of incidence angle not only preserves the stable operation of the compressor but it also prevents the compressor efficiency from deterioration. The existence of an inherent positive pressure gradient may cause the boundary layer separation on compressor blades leading to the rotating stall and surge. Such condition, however, does not exist in a turbine, and therefore, there has been no compelling reason to apply the blade adjusting method to the turbine component. For the first time, the impact of turbine blade stagger angle adjustment on the gas turbine efficiency during the operation is shown in this paper. Given a statistically distributed load condition, the extensive dynamic simulation reported in this paper shows how the efficiency can be positively affected through proper blade adjustment. For the time dependent operation, the code GETRAN developed by the author was enhanced to include the turbine blade adjustment as a function of time. To conduct the dynamic simulation with turbine stator stagger angle adjustment during a dynamic operation, the full geometry of the Brown Boveri GT-9 gas turbine was utilized. Starting from the reference stagger angle, it is varied within an incidence range of ± 3 degree. Detailed simulation results show the substantial efficiency improvement through stator stagger blade adjustment.