bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-Dimensional Visualization of Flow Characteristics Using a Magnetic Resonance Imaging (MRI) in a Lattice Cooling Channel
Authors: Tsuru Tomoko , Ishida Katsuhiko , Fujita Junya , Takeishi Kenichiro
Published: August 2018

Flow structures in lattice cooling channels are investigated experimentally by measuring three-dimensional velocity components over entire duct. The lattice cooling structure is formed by crossing two sets of parallel inclined ribs. Heat transfer is enhanced when coolant flows through the narrow sub-channels between the ribs. According to the past literature, longitudinal vortex structures are formed inside the sub-channels due to interactions between crossing flows. In this study, three-dimensional velocity field measurement is performed using MRI scanner to clarify the flow mechanism. The rib inclination angle is varied from 30 to 60 degrees. Reynolds number is set at approximately 8,000 based on the whole duct inlet hydraulic diameter and bulk velocity. Working fluid is 0.015mol/L copper sulfate aqueous solution.

Measured results show that coolants in the upper and lower sub-channels interact not only at the both ends of the duct, but also at diamond-shaped openings formed by opposite sub-channels. The exchange of momentum between the upper and lower sub-channels occurs at the openings, leading to sustained longitudinal vortex in each sub-channel as mentioned in the literature. When the ribs are arranged with obtuse angle, a large vortex spreads across the contact surface, while the vortex structure independently stays in each sub-channel for acute rib angle.

The measured velocity fields are compared with numerically-simulated ones using a RANS solver. Overall flow pattern is captured, but flow interaction between the upper and lower sub-channels is underestimated.
Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution and Indirect Noise
Authors: Giusti Andrea , Magri Luca , Zedda Marco
Published: August 2018

Indirect noise generated by the acceleration of combustion inhomogeneities is an important aspect in the design of aeroengines because of its impact on the overall noise emitted by an aircraft and the possible contribution to combustion instabilities. In this study, a realistic rich-quench-lean combustor is numerically investigated, with the objective of quantitatively analyzing the formation and evolution of flow inhomogeneities and determine the level of indirect combustion noise in the nozzle guide vane (NGV). Both entropy and compositional noise are calculated in this work. A high-fidelity numerical simulation of the combustion chamber, based on the Large-Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) combustion model, is performed. The contributions of the different air streams to the formation of flow inhomogeneities are pinned down and separated with seven dedicated passive scalars. LES-CMC results are then used to determine the acoustic sources to feed an NGV aeroacoustic model, which outputs the noise generated by entropy and compositional inhomogeneities. Results show that non-negligible fluctuations of temperature and composition reach the combustor’s exit. Combustion inhomogeneities originate both from finite-rate chemistry effects and incomplete mixing. In particular, the role of mixing with dilution and liner air flows on the level of combustion inhomogeneities at the combustor’s exit is highlighted. The species that most contribute to indirect noise are identified and the transfer functions of a realistic NGV are computed. The noise level indicates that indirect noise generated by temperature fluctuations is larger that the indirect noise generated by compositional inhomogeneities, although the latter is not negligible and is expected to become louder in supersonic nozzles. It is also shown that relatively small fluctuations of the local flame structure can lead to significant variations of the nozzle transfer function, whose gain increases with the Mach number. This highlights the necessity of an on-line solution of the local flame structure, which is performed in this paper by CMC, for an accurate prediction of the level of compositional noise.

This study opens new possibilities for the identification, separation and calculation of the sources of indirect combustion noise in realistic aeronautical gas turbines.
Optimal Design of a Gas Turbine Cogeneration Plant by a Hierarchical Optimization Method With Parallel Computing
Authors: Yokoyama Ryohei , Shinano Yuji , Wakayama Yuki , Wakui Tetsuya
Published: August 2018

To attain the highest performance of energy supply systems, it is necessary to rationally determine types, capacities, and numbers of equipment in consideration of their operational strategies corresponding to seasonal and hourly variations in energy demands. Mixed-integer linear programming (MILP) approaches have been applied widely to such optimal design problems. The authors have proposed a MILP method utilizing the hierarchical relationship between design and operation variables to solve the optimal design problems of energy supply systems efficiently. In addition, some strategies to enhance the computation efficiency have been adopted: bounding procedures at both the levels and ordering of the optimal operation problems at the lower level. In this paper, as an additional strategy to enhance the computation efficiency, parallel computing is adopted to solve multiple optimal operation problems in parallel at the lower level. In addition, the effectiveness of each and combinations of the strategies adopted previously and newly is investigated. This hierarchical optimization method is applied to an optimal design of a gas turbine cogeneration plant, and its validity and effectiveness are clarified through some case studies.
Numerical Investigation of Transient Heat Transfer Experiments Under Rotation
Authors: Goehring Michael , Hartmann Christopher , von Wolfersdorf Jens
Published: August 2018

A smooth two-pass internal gas turbine cooling channel is numerically investigated. Transient conjugated non-rotating and rotating URANS simulations are executed. The transient thermochromic liquid crystal (TLC) approach is supported with these simulations as the temporally changing rotational buoyancy effects can be examined. The Reynolds number is 25,000, the rotation number is 0.24 and the initial buoyancy number is 0.63 (according to an inlet-to-wall density ratio of 0.23). As heat is transferred, the temperatures and heat fluxes change with increasing time, and so do the local buoyancy effects. The computational results are evaluated as averaged segmental values. They are compared to the experimental results from literature that have been determined for constant wall temperature experiments (various experimental runs with different constant wall temperatures). Especially in the first passage, there is a good agreement between the numerically gained results and the experimental data. The more complex flow inside the bend leads to more diverse characteristics and the second passage is only slightly effected.
Effects of Fan Inflow Distortions on Heat Exchange in Air-Cooled Condensers: Unsteady Computations With Synthetic Blade Model
Authors: Angelini G. , Bonanni T. , Corsini A. , Delibra G. , Tieghi L. , Volponi D.
Published: August 2018

Heat exchange in air-cooled condensers (ACC) is achieved by forced convection of fresh air on bundle of tubes by means of forced-draft axial-flow fans. These fans are characterized by low solidity and low hub ratio, large diameters, relatively low rotational velocity, high efficiencies. This combination usually leads to fans with non-stalling characteristics, with pressure rise continuously rising when reducing the flow rate, at least in standard (ISO or AMCA) test rigs. In real-life installations, in fact, it is quite difficult to characterize these fans, due to the practical difficulties arising in setting up a proper test rig and to control the boundary conditions of the system, in particular the fan inflow conditions.

Here we focus on a real-life setting of ACC, numerically simulated with URANS. In this work the fan is simulated with a Synthetic Blade Model presented in [1]. This model is derived from actuator disk theory, and allows to simulate the unsteady movement of the blades and compute a non-constant azimuthal distribution of lift and drag forces, partially accounting for non-constant deviation in the blade-to-blade passage, while drastically reducing the mesh requirements. In this way it is possible to model the shedding of wakes behind the blades and their interaction with the heat exchanger. The flow will be assumed to be incompressible, due to the low Mach number and heat transfer will be treated assuming temperature to be a passive scalar convected by the flow.

Duty point of the fan and heat exchange in the ACC will be studied while inflow conditions, in order to account for free inflow with a constant velocity distribution as well as distortions due to lateral wind. Computations will be carried out on the Virtual Test Rig of developed at Sapienza within the OpenFOAM 2.3.x library with a URANS approach and k-ε closure.
A Method for Parametric Analysis of Stability Boundaries for Nonlinear Periodic Vibrations of Structures With Contact Interfaces
Authors: Petrov E. P.
Published: August 2018

A method for parametric analysis of the stability loss boundary has been developed for periodic regimes of nonlinear forced vibrations for a first time. The method allows parametric frequency-domain calculations of the stability loss together with the vibration amplitudes and design parameter values corresponding to the stability boundaries. The tracing algorithm is applied to obtain the trajectories of stability loss points as functions of design parameters. The parametric stability loss is formulated for cases when: (i) the design parameters characterise the properties of nonlinear contact interfaces (e.g. gap, contact stiffness, friction coefficient, etc.) and (ii) the design parameters describe linear components of the analysed structure (e.g. parameters of geometric shape, material, natural frequencies, modal damping etc.) and (iii) these parameters describe the excitation loads (e.g. their level, distribution or frequency). An approach allowing the multiparametric analysis of stability boundaries is proposed. The method uses the multiharmonic representation of the periodic forced response and aimed at the analysis of realistic gas-turbine structures comprising thousands and millions degrees of freedom. The method can be used for the effective search of isolated branches of the nonlinear solutions and examples of detection and search of the isolated branches are given: for relatively small and for large-scale finite element models. The efficiency of the method for calculation of the stability boundaries and for the search of isolated branches is demonstrated on simple systems and on a large-scale model of a turbine blade.
On Possibilities of Using Relative Shaft Vibration Signals for Rotating Blades Monitoring
Authors: Liska Jindrich , Vasicek Vojtech , Jakl Jan
Published: August 2018

Ensuring the reliability of the steam turbine is the key for its long life. For this purpose monitoring systems are standardly used. Early detection of any failure can avoid possible economical and material losses. A monitoring of rotating blades vibration belongs to the very important tasks of the turbomachinery state assessment. Especially in terms of the last stages of low-pressure part, where the longest blades are vibrating at most. Commonly used methods for blade vibration monitoring are based on contact measurement using strain gauges or non-contact approach based on blade tip timing measurement.

Rising demand for low-cost monitoring systems has initiated development of a new approach in blade vibration monitoring task. The presented approach is based on usage of relative rotor vibration signals. Its advantage is in using of standardly installed sensors making this approach economically interesting for the turbine operators compared to the traditionally used methods, mentioned above.

This paper summarizes the symptoms of blade vibration phenomenon in relative shaft vibration signals, the impact of operating conditions on the blade vibration amplitude and its comparison to blade tip-timing measurement results. In addition of several examples, the article also describes an evaluation of proposed method in operation of steam turbine with power of 170MW.
Experimental and Numerical Investigation of Optimized Blade Tip Shapes: Part II — Tip Flow Analysis and Loss Mechanisms
Authors: Pátý Marek , Cernat Bogdan , De Maesschalck Cis , Lavagnoli Sergio
Published: August 2018

The leakage flows within the gap between the tips of unshrouded rotor blades and the stationary casing of high-speed turbines are the source of significant aerodynamic losses and thermal stresses. In the pursuit for higher component performance and reliability, shaping the tip geometry offers a considerable potential to modulate the rotor tip flows and to weaken the heat transfer onto the blade and casing. Nevertheless, a critical shortage of combined experimental and numerical studies addressing the flow and loss generation mechanisms of advanced tip profiles persists in the open literature.

A comprehensive study is presented in this two-part paper that investigates the influence of blade tip geometry on the aerother-modynamics of a high-speed turbine. An experimental and numerical campaign has been performed on a high-pressure turbine stage adopting three different blade tip profiles. The aerothermal performance of two optimized tip geometries (one with a full three-dimensional contoured shape and the other featuring a multi-cavity squealer-like tip) is compared against that of a regular squealer geometry.

In the second part of this paper, we report a detailed analysis on the aerodynamics of the turbine as a function of the blade tip geometry. Reynolds-averaged Navier-Stokes simulations, adopting the Spalart-Allmaras turbulence model and experimental boundary conditions, were run on high-density unstructured meshes using the Numeca FINE/Open solver. The simulations were validated against time-averaged and time-resolved experimental data collected in an instrumented turbine stage specifically set up for the simultaneous testing of multiple blade tips at scaled engine-representative conditions. The tip flow physics is explored to explain variations in turbine performance as a function of the tip geometry. Denton’s mixing loss model is applied to the predicted tip gap aerodynamic field to identify and quantify the loss reduction mechanisms of the alternative tip designs. An advanced method based on the local triple decomposition of relative motion is used to track the location, size and intensity of the vortical flow structures arising from the interaction between the tip leakage flow and the main gas path. Ultimately, the comparison between the unconventional tip profiles and the baseline squealer tip highlights distinct aerodynamic features in the associated gap flow field. The flow analysis provides guidelines for the designer to assess the impact of specific tip design strategies on the turbine aerodynamics and rotor heat transfer.
Assessment of External Heat Transfer Modeling of a Laboratory-Scale Combustor Inside a Pressure-Housing Environment
Authors: Rodrigues P. , Gicquel O. , Darabiha N. , Geigle K. P. , Vicquelin R.
Published: August 2018

Many laboratory-scale combustors are equipped with viewing windows to allow for characterization of the reactive flow. Additionally, pressure housing is used in this configuration to study confined pressurized flames. Since the flame characteristics are influenced by heat losses, the prediction of wall temperature fields becomes increasingly necessary to account for conjugate heat transfer in simulations of reactive flows. For configurations similar to this one, the pressure housing makes the use of such computations difficult in the whole system. It is therefore more appropriate to model the external heat transfer beyond the first set of quartz windows. The present study deals with the derivation of such a model which accounts for convective heat transfer from quartz windows external face cooling system, free convection on the quartz windows 2, quartz windows radiative properties, radiative transfer inside the pressure housing and heat conduction through the quartz window. The presence of semi-transparent viewing windows demands additional care in describing its effects in combustor heat transfers. Because this presence is not an issue in industrial-scale combustors with opaque enclosures, it remains hitherto unaddressed in laboratory-scale combustors. After validating the model for the selected setup, the sensitivity of several modeling choices is computed. This enables a simpler expression of the external heat transfer model that can be easily implemented in coupled simulations.
A Detailed Analytical Study of Hydrogen Reaction in a Novel Micromix Combustion System
Authors: Ben Abdallah Ramzi , Sethi Vishal , Gauthier Pierre Q. , Rolt Andrew Martin , Abbott David
Published: August 2018

Liquid hydrogen is considered a technically feasible fuel for all gas turbine applications including propulsion systems [1]. However, the exceptional combustion properties of hydrogen will make fundamental changes to gas turbine combustion systems essential. Micromixing, with a novel cross-flow fuel-injection feature and a large plurality of injection holes offers miniaturised diffusive combustion without the risk of auto-ignition or flashback. A detailed analytical study has been performed to explore combustion behaviour of hydrogen in the micro-diffusion combustor concept. The aims are to investigate a broad range of analytical tools and sensitivities related to hydrogen micromix combustion numerical modelling. Comparative studies based on a number of RANS and LES simulations were carried out to down-select suitable numerical models for species transport, turbulence, chemistry and thermochemistry. Simulation results were found to be particularly sensitive to the species diffusion effects. The study was then extended to identify proper thermal boundary conditions capable of replicating experimental work. A thorough discussion of the findings is provided. The study has generated a novel micromix-injector geometry promising to yield ultra-low NOx emissions. This paper sheds light on the difficulties encountered in modelling the combustion of a gaseous fuel (hydrogen) in a novel micro-diffusion combustion chamber and suggests effective approaches to overcome them. It also identifies additional benefits related to hydrogen as a fuel.
Dry Low NOx Emissions Operability Enhancement of a Heavy-Duty Gas Turbine by Means of Fuel Burner Design Development and Testing
Authors: Cerutti Matteo , Giannini Nicola , Ceccherini Gianni , Meloni Roberto , Matoni Emanuele , Romano Christian , Riccio Giovanni
Published: August 2018

This paper describes the development phases of an annular type combustor for heavy-duty gas turbine applications. High cycle efficiency and low emissions are required over a wide range of load conditions, with the consequence of reducing margin to thermo-acoustic instability onset and lean blow-out. In addition, in lean premixed combustors, the increased fuel air mixing times required to keep emissions low, may lead to undesired ignition or flashback into the fuel burner ducts.

All these aspects are matter of this work and focus is on fuel burner design modifications which allowed dry emissions reduction while maintaining a sufficiently wide safe operation window.

A synergic effort has been put in place, involving experimental campaigns and CFD simulations, with the purpose of assessing design changes initially and doing screening. In the meanwhile, numerical practices have taken benefits form the experience growth. Results of past work on similar components has been leveraged too.

Test campaign involved different scale facilities, from single burner through full annular combustor up to full scale prototype engine. The progressive reduction of viable option for combustor components design changes, due to high impact of such modifications during the gas turbine late development phases, forced designers to concentrate efforts onto fuel burner optimization, looking for efficient ways to implement modifications and assess their effectiveness of combustion system performances.

Emissions trends, blow-out and flashback margin for several burner designs are reported. Numerical analysis results are also shown, which revealed to be well aligned with the experimental outcomes, allowing burner optimized solution to be identified. Finally, characterization with respect to fuel gas composition is shown as well as sensitivity to different operating conditions.
Experimental and Numerical Analysis of Unsteady Flow Structure in a Centrifugal Compressor With Variable Vaned Diffuser
Authors: Xue Xiang , Wang Tong , Shao Yuchang , Yang Bo , Gu Chuangang
Published: August 2018

The unsteady flow at small flow rates is always the most important of typical unsteady phenomena in centrifugal compressors, since it is closely related to the operating safety and efficiency. To study the mechanism of stall and surge generation, an experimental research on an industrial centrifugal compressor with variable vaned diffuser is carried out to study the unsteady flow structure from design point to surge. A multi-phase dynamic pressure measurement is conducted, based on 23 dynamic pressure sensors mounted on the shroud side casing surface of the compressor. The sensors are circumferentially distributed in a non-uniform manner at seven different radial positions, including the impeller region, the vaneless region and the diffuser throat region. Real-time data is recorded during the whole valve-adjusting process. The characteristics of pressure fields at some specific operating conditions are focused on, especially the pre-stall, stall precursor, stall and surge conditions. According to the multiphase data association, the originating position of the stall precursor can be determined. The features of the unsteady flow structure are also obtained, such as the surge pattern and the propagation direction of stall cells. In addition, when the diffuser vane setting angle (OGV) is turned up, the core factors to trigger total instability will change. In order to visually show how the tip leakage and separation vortex in the impeller gradually affect the flow structure in the vaned diffuser region and even the whole machine, numerical simulation and dynamic mode decomposition (DMD) method are used to study the flow mechanisms. The numerical simulation result is well matched with the experimental result. With the help of the DMD method, a few low-frequency tip leakage vortex structures are extracted from the unsteady numerical result over a period of time, which correlate with the experimental result. Meanwhile, on this issue, the feasibility of dynamic experimental analysis combined with multi-channel numerical simulation analysis is verified and discussed. Through the two analytic methods, a detailed understanding of the unsteady flow structure in the centrifugal compressor with variable vaned diffuser is obtained.
Intentional Response Reduction by Harmonic Mistuning of Bladed Disks With Aerodynamic Damping
Authors: Willeke Sebastian , Schwerdt Lukas , Panning-von Scheidt Lars , Wallaschek Jörg
Published: August 2018

A harmonic mistuning concept for bladed disks is analyzed in order to intentionally reduce the forced response of specific modes below their tuned amplitude level. By splitting a mode pair associated with a specific nodal diameter pattern, the lightly damped traveling wave mode of the nominally tuned blisk is superposed with its counter-rotating complement. Consequently, a standing wave is formed in which the former wave train benefits from an increase in aerodynamic damping.

Unlike previous analyses of randomly perturbed configurations, the mode-specific stabilization is intentionally promoted through adjusting the harmonic content of the mistuning pattern. Through a re-orientation of the localized mode shapes in relation to the discrete blades, the response is additionally attenuated by an amount of up to 7.6 %. The achievable level of amplitude reduction is analytically predicted based on the properties of the tuned system. Furthermore, the required degree of mistuning for a sufficient separation of a mode pair is derived.
Ignition Dynamics in an Annular Combustor With Gyratory Flow Motion
Authors: Ye Chenran , Wang Gaofeng , Fang Yuanqi , Ma Chengbiao , Zhong Liang , Moreau Stephane
Published: August 2018

In concepts of integrated design of combustor and turbine, an annular combustor model is developed and featured with multiple oblique-injecting swirling injectors to introduce gyratory flow motion in the combustion chamber. The ignition process is experimentally investigated to study the effects of introducing circumferential velocity component Uc to the light-round sequence. Experiments are carried out with premixed propane/air mixture in ambient conditions. The light-round sequence is recorded by a high-speed camera, which provides detailed flame azimuthal positions during the sequence and gives access to the light-round time τ and the circumferential flame propagation speed Sc. The results have also been compared with that obtained from a straight-injecting annular combustor. The effects of bulk velocity Ub, thermal power P and equivalence ratio Φ are also explored. Due to the gyratory flow motion induced by oblique injection, the flame fronts only propagate along the direction of circumferential flow. Both of the circumferential flame propagation speed increase with increasing bulk velocity in two injection types. It seems mainly to depend on bulk velocity, regardless of Φ, in oblique-injecting combustor when compared with the straight one. It indicates that the circumferential velocity component would play a dominant role in light-round sequence when it is sufficient higher than the displacement flame speed.
Effects of Inlet Chamber Structure of the Control Stage on the Unsteady Aerodynamic Force
Authors: Gao Keke , Wang Chongyu , Xie Yonghui , Zhang Di
Published: August 2018

Blade fatigue fracture is the main factor affecting the safe operation of the turbine and the aerodynamic exciting force caused by partial admission accelerates the fatigue failure of the control stage blade. In this paper, based on the three-dimensional unsteady flow research of 300MW control stage, a new type of inlet chamber structure is proposed, which can reduce the local aerodynamic exciting force effectively. The performance of original structure and new structure is compared at 0.7 partial admission operation condition in details. Firstly, the paper gives the overall performance of the control stage under the two structures. It is proved that the new inlet chamber structure proposed in this paper only has a slight influence on the overall performance, which is shown as mass flow, power and efficiency. Secondly, distributions of flow parameters such as pressure, static entropy and axial velocity at the stator inlet and rotor inlet are given in the paper. The new structure is found to alleviate the sudden change of flow parameters such as pressure at the inlet steam chamber transition region. Finally, five key points of axial aerodynamic force and seven key points of tangential aerodynamic force are captured to illustrate the influence of partial admission on instantaneous aerodynamic exciting force. Further, the mechanism of new inlet chamber structure on local aerodynamic exciting forces is explained. The result shows that the new inlet chamber structure can reduce the local axial aerodynamic exciting force up to 13% and reduce the local tangential aerodynamic exciting force up to 29.7%, which is beneficial to improve the safety and reliability of the turbine operation.
Blade Vibration Monitoring in a Low-Pressure Steam Turbine
Authors: Przysowa Radosław
Published: August 2018

A tip-timing system is used in a coal power station to investigate and mitigate excessive blade vibrations in the exit stage of the low-pressure steam turbine. There are presented hardware and software solutions used to monitor blade responses as well as the analyses of amplitude and frequency trends observed during the 5-year collaborative project, including operation at the nominal speed and during the shutdowns and start-ups. The transition from data acquisition to the embedded system with the partial reuse of tip-timing algorithms and LabView code is demonstrated. The proposed system processes the data coming from the turbine blades in real time and operates autonomously or under the supervision of the PC-based client program connected to the network. Acquired data are stored in a cyclic buffer and can be transferred to the host. The stack pattern is used to distinguish blades and calculate rotating reference. Tip deflection is analysed statistically and evaluated against defined reference patterns.
Skin Friction Measurements of Transition in High Reynolds Number, Adverse Pressure Gradient Flow
Authors: Holley Brian M. , Hardin Larry W. , Tillman Gregory , Lin Ray-Sing , Joo Jongwook
Published: August 2018

A combined experimental and analytical modeling effort has been carried out to measure the skin friction response of the boundary layer in high Reynolds number adverse pressure gradient flow. The experiment was conducted in the United Technologies Research Center (UTRC) Acoustic Research Tunnel, an ultra-low freestream turbulence facility capable of laminar boundary layer research. Boundary layer computational fluid dynamics and stability modeling were used to provide pre-test predictions, as well as to aid in interpretation of measured results. Measurements were carried out at chord Reynolds numbers 2–3 × 106, with the model set at multiple incidence angles to establish a range of relevant leading edge pressure gradients. The combination of pressure gradient and flight Reynolds number testing on a thin airfoil has produced a unique data set relevant to propulsion system turbomachinery.
Three-Dimensional Vaneless Diffuser Rotating Stall Numerical Study
Authors: Grapow Filip , Liśkiewicz Grzegorz
Published: August 2018

Centrifugal compressor efficiency is the key to increasing incomes from its operation. There are several flow instabilities which can negatively affect a compressor, one of them being the rotating stall, as it decreases efficiency and mass flow while it can also lead to a surge. Among others, this can occur in the vaneless diffuser. A thorough understanding of this phenomenon and the ability to model its behaviour can lead to a robust protection system assuring high efficiency even at lower mass flow rates.

In this paper, the simulated flow was viscous and compressible. Much attention was devoted to providing boundary conditions that would not affect flow conditions at the diffuser outlet. The transient simulation was conducted in order to observe sequential stages of the VDRS onset and growth. Pressure signals from different points in the diffuser have been analysed with the CWT method in the purpose of detecting oscillations frequency change in time.

Results have shown that the complex structure and time evolution of the VDRS indeed require the application of three-dimensional methods. As the mass flowrate was continuously decreased a sudden change in number of the rotating stall cells was observed together with an appearance of new strong peak of the pressure oscillation.
Analysis of Unstable Radial Compressor Operation in a System With Large Plenum Volume: Mathematical Modelling and Experimental Results
Authors: Jaeschke Andrzej , Kabalyk Kirill , Grapow Filip , Liskiewicz Grzegorz
Published: August 2018

The paper focusses on the numerical and experimental investigation of the operation of a centrifugal compressor connected to a large plenum volume. The experimental study consisted of measurements of time-averaged and transient pressure values in a system based on the DP1.12 blower. The numerical analysis was based on the Greitzer model. The model parameters were determined so as to achieve best fit with the experimental signal. It was observed that out of two optimal solutions, one resolved the first harmonic of oscillations significantly better than the other. The obtained values of the B parameter varied with the operation point, which is contrary to the formal definition of this quantity. The values of angular Helmholtz frequency ωh were not sensitive to the change of operation point. This paper improves our understanding of the meaning of model parameters, which is a crucial step towards a more accurate prediction and prevention of surge.
Investigation and Assessment of the Performance of Various Recuperative Cycles Based on the Intercooled Recuperation Concept
Authors: Salpingidou Christina , Vlahostergios Zinon , Misirlis Dimitrios , Flouros Michael , Donus Fabian , Yakinthos Kyros
Published: August 2018

This work is focused on investigations of Intercooled Recuperation configurations for aero engines. The investigated configurations were the Conventional Recuperation, where the recuperator was placed downstream the low-pressure turbine (LPT), the Alternative Recuperation, where the recuperator was mounted between the intermediate pressure turbine (IPT) and LPT, and the Staged Heat Recovery concept, in which two recuperators were mounted, one between IPT and LPT and the other downstream the LPT. These concepts were further assessed with the use of an additional combustor between IPT and LPT. All recuperator concepts that have been developed within the framework of various research projects by Aristotle University of Thessaloniki and MTU Aero engines AG were utilized, named as the NEWAC, CORN and STARTREC concepts. Additionally, a new recuperator design was introduced using a secondary fluid as heat transfer medium. The configurations thermodynamic assessment was focused on specific fuel consumption reduction, while the configurations effect on NOx emissions was also investigated. The results showed that the most promising recuperator concept, with respect to low TSFC values compared with a reference GTF engine of 2050 year technology level, is the recuperator with the secondary fluid heat transfer medium.
Statistical Analysis of Component Failures: A 16-Year Survey on More Than 550 Wind Turbines
Authors: Ferrari Lorenzo , Soldi Guido , Bianchini Alessandro , Dalpane Enzo
Published: August 2018

A good prediction of the failure ratio of wind turbine components is pivotal in order to define a correct maintenance program and reduce the downtime periods. Even a small failure can lead to long downtime periods and high repairing costs. The installation sites, which generally have limited accessibility, and the necessity of special facilities to reach the components inside the nacelle, also play a major role in the correct management of wind turbines.

In this study, a detailed survey on the failures occurred to the wind turbines managed by the Italian operator “e2i energie speciali” (more than 550 machines) over 16 years was performed and the results were analyzed in detail. Each failure was classified by considering the damaged component and the related downtime period. The analysis allowed the determination of several useful results such as the trend of failure occurrence with machine age and the identification of components and macro-components which are more critical in terms of both number of occurrences and downtime periods. The combination of component failure occurrences and related downtime periods was also computed to estimate which component is most critical for wind turbine operation.
Numerical Study on NOx Reduction in Pulse Detonation Combustion by Using Steam Injection Decoupled From Detonation Development
Authors: Hanraths Niclas , Tolkmitt Fabian , Berndt Phillip , Djordjevic Neda
Published: August 2018

Recently, the focus has been laid on the characteristics of pollutant emissions from pulse detonation combustion. Initial studies indicate possibly high nitrogen oxides (NOx) emissions, so the assessment of potential primary reduction methods is advisable. The present work considers the following reduction methods: lean combustion, nitrogen and steam dilution as well as flue gas recirculation. Since such changes in the combustion mixture reduce its reactivity and thus detonability, they can impair a reliable operation in technical systems. In order to explore the potential and limitations of each of these reduction methods, they are compared for mixtures featuring an identical characteristic detonation cell size at given initial conditions. Furthermore, building upon the use of steam dilution, a modified method to add steam to the combustible mixture is investigated. In order to avoid the strong reduction of mixture detonability by steam addition and ensure a robust detonation formation, steam is injected into the already developed detonation front. It was found that, for sufficiently even steam distribution, NOx reduction comparable to a premixed dilution could be achieved. This approach enables the realization of NOx reduction in pulse detonation combustion also for such conditions, for which premix dilution is not feasible. Therefore, combining the premix dilution with post-shock injection offers a promising strategy to substantially reduce NOx emissions from pulse detonation combustion, while at the same time ensuring its reliable operation.
Numerical and Experimental Investigation of Acoustic Characteristics of Model Ultra High Bypass Ratio Counter Rotating Fan
Authors: Rossikhin Anton , Druzhinin Iaroslav , Khaletskii Iurii , Mileshin Victor
Published: August 2018

A computational investigation of acoustic characteristics of model ducted counter-rotating fan COBRA-1 with ultra-high bypass ratio BPR = 20, developed in CIAM in the framework of European Project COBRA (Innovative Counter rOtating fan system for high Bypass Ratio Aircraft engine), is presented in the paper. Calculations of acoustic characteristics of the fan were performed at five operational conditions. For three of them the sums of rotation frequencies of rotors corresponded to those expected for approach conditions, and they differed from each other by relations between frequencies of rotors, and for other two the sums of rotation frequencies corresponded to cutback and sideline operational conditions. Numerical investigations were conducted using the method of 3D numerical calculation of interaction between fan rows implemented in 3DAS (3 Dimensional Acoustics Solver) CIAM in-house solver. The data were compared with the results of the experiments conducted in the CIAM test rig C-3A. The results of comparison show satisfactory qualitative and, in some positions of microphones, quantitative agreement between the results of the simulation and the experiment. Both results demonstrate strong influence of relation between rotation frequencies of rotors on acoustic characteristics and significant dominance of noise radiated from the nozzle over the noise radiated from the inlet.
Design and Application of a Multi-Disciplinary Pre-Design Process for Novel Engine Concepts
Authors: Reitenbach S. , Krumme A. , Behrendt T. , Schnös M. , Schmidt T. , Hönig S. , Mischke R. , Moerland E.
Published: August 2018

Central targets for jet engine research activities comprise the evaluation of improved engine components and the assessment of novel engine concepts for enhanced overall engine performance in order to reduce the fuel consumption and emissions of future aircraft. Since CO2 emissions are directly related to engine fuel burn, a reduction in fuel consumption leads to lower CO2 emissions. Therefore improvements in engine technologies are still significant and a multi-disciplinary pre-design approach is essential in order to address all requirements and constraints associated with different engine concepts. Furthermore, an increase in effectiveness of the preliminary design process helps reduce the immense costs of the overall engine development.

Within the DLR project PEGASUS (Preliminary Gas Turbine Assessment and Sizing) a multi-disciplinary pre-design and assessment competence of the DLR regarding aero engines and gas turbines was established. The application of modern preliminary design methods allows for the construction and evaluation of innovative next generation engine concepts.

The purpose of this paper is to present the developed multi-disciplinary pre-design process and its application to three aero engine models. First, a state of the art twin spool mixed flow turbofan engine model is created for validation purposes. The second and third engine models investigated comprise future engine concepts: a Counter Rotating Open Rotor and an Ultra High Bypass Turbofan. The turbofan used for validation is based on publicly available reference data from manufacturing and emission certification.

At first the identified interfaces and constraints of the entire pre-design process are presented. An important factor of complexity in this highly iterative procedure is the intricate data flow, as well as the extensive amount of data transferred between all involved disciplines and among the different fidelity levels applied within the smoothly connected design phases. To cope with the inherent complexity data modeling techniques have been applied to explicitly determine the required data structures of those complex systems. The resulting data model characterizing the components of a gas turbine and their relationships in the design process is presented in detail.

Based on the established data model the entire engine pre-design process is presented. Starting with the definition of a flight mission scenario and the resulting top level engine requirements thermodynamic engine performance models are developed. By means of these thermodynamic models, a detailed engine component pre-design is conducted. The aerodynamic and structural design of the engine components are executed using a stepwise increase in level of detail and are continuously evaluated in the context of the overall engine system.
An Innovative Approach Towards Fouling Modeling: Microscale Deposition Pattern and its Effect on the Flow Field
Authors: Casari Nicola , Pinelli Michele , Suman Alessio
Published: August 2018

Solid particle ingestion is one of the main compressor degradation mechanisms for both heavy-duty and aero-propulsion gas turbines. Particles impacting the inner surfaces of the machine can stick there forming deposits. The presence of such deposits reflects on the reduction in performance of the machinery.

Over last years, several methods have been developed in order to study the problem from the numerical standpoint. Examples of these techniques are the mesh morphing approach and the added-roughness-and-thickness method. In this work, an innovative procedure is proposed in order to evaluate the losses and the variation in the fluid flow due to the deposits. Particularly, an algorithm capable of determining the microscale deposition pattern has been developed. By using this methodology, a comprehensive analysis of the variation of the performance of the compressor over time can be carried out. The deposition severity and the subsequent roughness variation can be kept into account in a very detailed and precise fashion. Furthermore, this approach overcomes the difficulties that may arise by using a mesh morphing technique. The computational grid is not modified and thus its quality is retained, without re-meshing requirements, even for large deposits. The local roughness variation is accounted for without extra-effort.

The procedure developed, shown here in deposition problems, can be easily extended to erosion or even icing problems. The only parameter to be changed is the model that takes care of the particle-wall interaction, using an erosion rather than an icing law.
Aero-Thermal Performance of a Rotor Blade Cascade With Film Cooling in Passage Endwall
Authors: Fu Jinglun , Hossain Jahed , Kapat Jayanta
Published: August 2018

This paper describes the numerical investigations on the aerodynamic and thermal performance of a rotor blade cascade with multiple film cooling rows in the passage. First, the experimental data on an annular cascade with upstream film cooling was compared with the numerical results to validate the numerical method. The CFD simulations of the models with a row of film holes at four different locations on the hub endwall were performed respectively. The aerodynamic and thermal performance under the interaction of the secondary flow and endwall film cooling are analyzed based on the CFD predicted streamlines of mainstream flow and film injection, the contours of total pressure loss on the sections located in the passage and at the blade exit, the pitch-averaged film cooling effectiveness and film cooling effectiveness contours. The results show that film holes placed at low level of iso-Mach line tends to provide a better cooling with a smaller amount of coolant.
Automated Design Optimization of a Small-Scale High-Swirl Cavity-Stabilized Combustor
Authors: Briones Alejandro M. , Burrus David L. , Sykes Joshua P. , Rankin Brent A. , Caswell Andrew W.
Published: August 2018

A numerical optimization study is performed on a small-scale high-swirl cavity-stabilized combustor. A parametric geometry is created in CAD software that is coupled with meshing software. The latter automatically transfers meshes and boundary conditions to the solver, which is coupled with a post-processing tool. Steady, incompressible three-dimensional simulations are performed using a multi-phase Realizable k-ϵ Reynolds-averaged Navier-Stokes (RANS) approach with the non-adiabatic flamelet progress variable (FPV). There are nine input parameters based on geometrical control variables. There are five output parameters, viz., pattern factor (PF), RMS of the profile factor deviation, averaged exit temperature, averaged exit swirl angle, and total pressure loss. An iterative design of experiments (DOE) with a recursive Latin Hypercube Sampling (LHS) is performed to filter the most important input parameters. The five major input parameters are found with Spearman’s order-rank correlation and R2 coefficient of determination. The five input parameters are used for the adaptive multiple objective (AMO) optimization. The AMO algorithm provided a candidate design point with the lowest weighted objective function. This design point was verified through CFD simulation. The combined filtering and optimization procedures improve the baseline design point in terms of pattern and profile factor. The former halved from that of the baseline design point whereas the latter turned from an outer peak to a center peak profile, closely mimicking an ideal profile. The exit swirl angle favorably increased 25%. The averaged exit temperature and the total pressure losses remained nearly unchanged from the baseline design point.
Measurements of Periodic Reynolds Stress Oscillations in a Forced Turbulent Premixed Swirling Flame
Authors: Douglas Christopher , Lim Jamie , Smith Travis , Emerson Benjamin , Lieuwen Timothy , Jiang Naibo , Fugger Christopher , Yi Tongxun , Felver Joseph , Roy Sukesh , Gord James
Published: August 2018

This work is motivated by the thermoacoustic instability challenges associated with ultra-low emissions gas turbine combustors. It demonstrates the first use of high-speed dual-plane orthogonally-polarized stereoscopic-particle image velocimetry and synchronized OH planar laser-induced fluorescence in a premixed swirling flame. We use this technique to explore the effects of combustion and longitudinal acoustic forcing on the time- and phase-averaged flow field — particularly focusing on the behavior of the Reynolds stress in the presence of harmonic forcing. We observe significant differences between ensemble averaged and time averaged Reynolds stress. This implies that the large-scale motions are non-ergodic, due to coherent oscillations in Reynolds stress associated with the convection of periodic vortical structures. This result has important implications on hydrodynamic stability models and reduced order computational fluid dynamics simulations, which do show the importance of turbulent transport on the problem, but do not capture these coherent oscillations in their models.