bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Mainstream Cross Flow on Film Cooling Performance and Jet Flow Field
Authors: Li Yifei , Zhang Yang , Su Xinrong , Yuan Xin
Published: August 2017

The influence of the cross flow in mainstream on film cooling performance and jet flow field is investigated experimentally and numerically. To show the effect of cross flow in mainstream without the influence of the other secondary flows, a curved test section is constructed to generate a cross flow, simulating the curved turbine passage. Both the straight and the curved passage are used to show the differences of cooling performance for shaped holes with and without the cross flow, with blowing ratio varying from M = 0.5 to M = 2.5. Pressure sensitive paint is used to measure the adiabatic cooling effectiveness, and the ink trace measurement is conducted to present the friction lines on the endwall platform. Numerical simulations are performed to show the flow field. The cross flow is accelerated in a curved passage and migrates the fluid near the endwall platform. Due to the cross flow in the mainstream, the deflection angle changes a lot along the normal direction to the endwall, and dominates the spatial distribution of coolant. Although the cooling trace follows the trend of wall surface streamlines, the migration of coolant is slower than the deviation of the friction line, and the difference increases with increasing blowing ratios. The cross flow enhances the lateral dispersion, decreasing the peak value of cooling effectiveness but increasing the laterally averaged cooling effectiveness. Higher blowing ratios lead to a higher intensity of a counter-rotating vortex pair that limits lateral dispersion near the outlet of cooling hole. But the effect of cross flow dominates the flow pattern downstream. The cooling performance has a significant difference with the influence of the cross flow. This study is essential to understand the interaction of the cross flow and the film cooling in gas turbines.
A Parametrization Describing Blisk Airfoil Variations Referring to Modal Analysis
Authors: Backhaus Thomas , Maywald Thomas , Schrape Sven , Voigt Matthias , Mailach Ronald
Published: August 2017

This paper will present a way to capture the geometric blade by blade variations of a milled from solid blisk as well as the manufacturing scatter. Within this idea it is an essential task to digitize the relevant airfoil surface as good as possible to create a valid surface mesh as the base of the upcoming evaluation tasks. Since those huge surface meshes are not easy to handle and are even worse in getting quantified and easy interpretable results, it should be aimed for an easily accessible way of presenting the geometric variation.

The presented idea uses a section based airfoil parametrization that is based on an extended NACA-airfoil structure to ensure the capturing of all occurring characteristic geometry variations. This Paper will show how this adapted parametrization method is suitable to outline all the geometric blade by blade variation and even more, refer those airfoil design parameters to modal analysis results such as the natural frequencies of the main mode shapes. This way, the dependencies between the modal and airfoil parameters will be proven.
Accurate Estimation of Profile Losses and Analysis of Loss Generation Mechanisms in a Turbine Cascade
Authors: Lengani D. , Simoni D. , Ubaldi M. , Zunino P. , Bertini F. , Michelassi V.
Published: August 2017

The paper analyzes losses and the loss generation mechanisms in a low-pressure turbine cascade by Proper-Orthogonal-Decomposition (POD) applied to measurements. Total pressure probes and time resolved particle image velocimetry (TR-PIV) are used to determine the flow field and performance of the blade with steady and unsteady inflow conditions varying the flow incidence. The total pressure loss co-efficient is computed by traversing two Kiel probes upstream and downstream of the cascade simultaneously. This procedure allows a very accurate estimation of the total pressure loss coefficient also in the potential flow region affected by incoming wake migration. The TR-PIV investigation concentrates on the aft portion of the suction side boundary layer downstream of peak suction. In this adverse pressure gradient region the interaction between the wake and the boundary layer is the strongest, and it leads to the largest deviation from a steady loss mechanism. POD applied to this portion of the domain provides a statistical representation of the flow oscillations by splitting the effects induced by the different dynamics. The paper also describes how POD can dissect the loss generation mechanisms by separating the contributions to the Reynolds stress tensor from the different modes. The steady condition loss generation, driven by boundary layer streaks and separation is augmented in presence of incoming wakes by the wake-boundary layer interaction and by the wake dilation mechanism. Wake migration losses have been found to be almost insensitive to incidence variation between nominal and negative (up to −9deg), while at positive incidence the losses have a steep increase due to the alteration of the wake path induced by the different loading distribution.
Performance Simulation of an Integrated Organic Rankine Cycle and Air Inter-Cooling System for Heavy-Duty Diesel Truck Engines
Authors: Chen Haoxiang , Zhuge Weilin , Zhang Yangjun , Chen Tao , Zhang Lei
Published: August 2017

Waste heat recovery using Organic Rankine cycle (ORC) systems has been regarded as the most potential technology for diesel engine fuel economy improvement. The compactness of ORC system is very important, so reducing the total volume of heat exchangers of the ORC system is the main challenge for ORC applications in truck engines. This paper proposes a new ORC system for waste heat recovery of truck diesel engines. The ORC system uses the hot compressed intake air and the exhaust gas as heat sources. The conventional air intercooler is substituted with the pre-heater of the ORC system. Hence the condenser of the ORC system can be installed at the original place of the intercooler, which could make the system integration much easier. A one-dimension simulation model of the combined diesel engine and ORC power system is set up. In combined ORC-engine system the output power of turbine is combined with the output power of crack shaft at a specific gear ratio to increase effective power of the engine system. The combined ORC-engine system performance is analyzed at common operating conditions and compared with the original engine. Results show that the combined system thermal efficiency is increased by 8.38% and the brake special fuel consumption (BSFC) reduces by 7.82% at peak. In design point, net output power of ORC system is 28.72kW, which increases thermal efficiency by 9.31% and reduces BSFC from 199.76 g/(kW·h) to 182.76 g/(kW·h). In addition, the cost of ORC system is estimated, and Payback time is 4.92 years.
Analysis of Performance Sensitivity to Geometrical Variations of a Modern Helicopter Engine Combustor Using LES Simulations
Authors: Vignat Guillaume , Taliercio Guillaume , Lamouroux Jean , Da Veiga Sébastien , Savary Nicolas , Duchaine Patrick
Published: August 2017

When a gas turbine combustor is manufactured, small geometrical differences between production runs are unavoidable. These geometrical differences potentially influence performances such as service life, lighting, lean blow off, pollutant emissions. To ensure performances, manufacturing tolerances are kept tight enough so as to neglect their impact. However, loosening some key manufacturing tolerances can result in lower manufacturing costs, while maintaining combustion performances at a satisfactory level. The present study aims at challenging some cost-driving manufacturing tolerances of Safran Helicopter Engines new turboshaft combustor, using state-of-the-art 3D numerical tools. The objective is to guarantee robust and long lasting combustor performances at a reasonable manufacturing cost. To this purpose, an optimized Latin Hypercube Sampling of 30 geometrical configurations around the nominal geometry has been simulated with a 3D LES solver. Simulation parameters had to be chosen to keep computation costs manageable and to have a high representability when comparing geometries. These aspects are checked using theoretical considerations and comparisons with both experimental data and previously validated simulations. The temperature field at the combustion chamber exhaust has been analyzed in detail using metamodeling. In particular, the Radial Temperature Distribution Factor (RTDF) at the combustor outlet appears to be robust. Such large designs of numerical experiments (DonE) are computationally expensive but they provide a reliable tool to assess the robustness of a combustor design, and define optimized manufacturing tolerances.
Periodic Unsteady Tip Clearance Vortex Development in a Low Speed Axial Research Compressor at Different Tip Clearances
Authors: Lange Martin , Rolfes Matthias , Mailach Ronald , Schrapp Henner
Published: August 2017

Since the early work on axial compressors the penalties due to radial clearances between blades and side walls are known and an ongoing focus of research work. The periodic unsteadiness of the tip clearance vortex, due to its interaction with the stator wakes, has only rarely been addressed in research papers so far. The current work presents experimental and numerical results from a four stage low speed research compressor modeling a state of the art compressor design. Time-resolved experimental measurements have been carried out at three different rotor tip clearances (gap to tip chord: 1.5%, 2.2%, 3.7%) to cover the third rotor’s casing static pressure and exit flow field. These results are compared with either steady simulations using different turbulence models or harmonic RANS calculations to discuss the periodical unsteady tip clearance vortex development at different clearance heights. The prediction of the local tip leakage flow is clearly improved by the EARSM turbulence model compared to the standard SST model. The harmonic RANS calculations (using the SST model) improve the prediction of time-averaged pressure rise and are used to analyze the rotor stator interaction in detail. The interaction of the rotor tip flow field with the passing stator wakes cause a segmentation of the tip clearance vortex and result in a sinusoidal variation in blockage downstream the rotor row.
Evaluation of Property Methods for Modeling Direct-Supercritical CO2 Power Cycles
Authors: White Charles W. , Weiland Nathan T.
Published: August 2017

Direct supercritical CO2 (sCO2) power cycles have received considerable attention in recent years as an efficient and potentially cost-effective method of capturing CO2 from fossil-fueled power plants. These cycles combust natural gas or syngas with oxygen in a high pressure (200–300 bar), heavily-diluted sCO2 environment, such that the fluid entering the turbine is 90–95% CO2, with the balance composed primarily of H2O, CO, O2, N2 and Ar. After recuperation of the turbine exhaust thermal energy, water is condensed from the cycle, and the remainder is recompressed for either return to the combustor or for enhanced oil recovery (EOR) or storage. The compression power requirements vary significantly, depending on the proximity of the operating conditions to the CO2 critical point (31 °C, 73.7 bar), as well as to the level of working fluid dilution by minor components. As this has a large impact on cycle and plant thermal efficiency, it is crucial to correctly capture the appropriate thermo-physical properties of these sCO2 mixtures when carrying out performance simulations of direct sCO2 power plants. These properties are also important to determining how water is removed from the cycle, and for accurate modeling of the heat exchange within the recuperator.

This paper presents a quantitative evaluation of ten different property methods that can be used for modeling direct sCO2 cycles in Aspen Plus®. REFPROP is used as the de facto standard for analyzing indirect sCO2 systems, where the closed nature of the cycle leads to a high purity CO2 working fluid. The addition of impurities due to the open nature of the direct-sCO2 cycle, however, introduces uncertainty to the REFPROP predictions. There is a limited set of mixtures available for which REFPROP can be reliably used and there are a number of species present in a coal-fired direct-fired sCO2 cycle that REFPROP cannot accommodate. Even with a relatively simplified system in which the trace components are eliminated, simulations made using REFPROP require computation times that often preclude its use in parametric studies of these cycles. Consequently, a series of comparative analyses were performed to identify the best physical property method for use in Aspen Plus® for direct-fired sCO2 cycles. These property methods are assessed against several mixture property measurements, and offer a relative comparison to the accuracy obtained with REFPROP. This study also underscores the necessity of accurate property modeling, where cycle performance predictions are shown to vary significantly with the selection of the physical property method.
Investigation of Loss Impact From Production-Like Features in a Compressor Duct Under Engine Realistic Conditions
Authors: Wallin Fredrik , Ross Mark H. , Rusche Max , Morris Scott , Ray Steven
Published: August 2017

An experimental and numerical investigation of the flow in a compressor duct with engine-realistic in-production features is presented in this paper. The experimental testing was conducted in the ND-FSCC test facility at University of Notre Dame, Indiana, USA. A baseline duct was also tested for back-to-back comparison.

The ducts were heavily instrumented; duct inlet and exit flowfields were scanned using a five-hole pressure probe that provided total pressure, velocities and flow angles. Based on the five-hole probe total pressures, duct losses could be assessed. Furthermore the duct inlet boundary layers were traversed and turbulence intensity levels were assessed. For the CFD analysis of the production-like duct, a highly complex computational grid, resolving all the geometrical features present, was used. A previously validated surface roughness model was used to account for the cast aero-surfaces.

Both experimental and numerical results show that there is a significant increase in loss for the production-like duct when compared to the baseline duct loss. The CFD results agree very well with experimental results for the baseline duct, which makes it possible to use the experimental data recorded for the production-like duct to validate CFD tools for real geometry effects, such as interface steps and surface roughness for example.
A Critical Analysis of the Differences Among Design Methods for Low-Speed Axial Fans
Authors: Castegnaro Stefano
Published: August 2017

Some methodological differences exist among the design methods for axial-flow fans. These differences generate confusion in the mind of the unexperienced fan designer, who is unaware of which method ensures the achievement of the required pressure rise at highest efficiency. In this work three important differences that appear comparing the classic methods of fan blading design are highlighted and analyzed: i) the choice of the airfoil, ii) the choice of the solidity distribution, and iii) the computation of the stagger angle of the blade elements. A fourth aspect regards the selection of the rotor number of blades. This aspect is treated in relation to the dubious applicability of the drag annulus correlation by Howell to low hub-to-tip ratio fan design and analysis. CFD simulations are performed on three case-study rotor-only fans, comparing blades systematically designed varying the airfoils (British C4 vs American NACA-65), the solidity distribution (Diffusion Factor criterion against the arbitrary selection of the blade-element lift coefficient) and the computation of the stagger angle (with respect to the inlet flow velocity or the mean one). The accuracy of XFOIL-predicted data at low Reynolds number (e.g., 300000) in designing small-to-medium fans is discussed as well. For each of the previous design aspects, results suggest the best indication among those suggested in the classic literature to achieve fan requirements.
Large Eddy Simulation of Transitional Flow in a Compressor Cascade
Authors: Rizvi Syed Anjum Haider , Mathew Joseph
Published: August 2017

At off-design conditions, when the blade Reynolds number is low, a significant part of the blade boundary layer can be transitional. Then, standard RANS models are unable to predict the flows correctly but explicit transition modeling provides some improvement. Since large eddy simulations (LES) are improvements on RANS, the performance of LES was examined by simulating a flow through a linear, compressor cascade for which experimental data are available — specifically at the Reynolds number of 210,000 based on blade chord when transition processes occur over a significant extent of the suction surface.

The LES were performed with an explicit filtering approach, applying a low-pass filter to achieve sub-grid-scale modeling. Explicit 8th-order difference formulas were used to obtain high resolution spatial derivative terms. An O-grid was wrapped around the blade with suitable clustering for the boundary layer and regions of large changes along the blade. Turbulent in-flow was provided from a precursor simulation of homogeneous, isotropic turbulence. Two LES and a DNS were performed. The second LES refines the grid in the vicinity of the separation bubble on the suction surface, and along the span. Surface pressure distributions from all simulations agree closely with experiment, thus providing a much better prediction than even transition-sensitive RANS computations. Wall normal profiles of axial velocity and fluctuations also agree closely with experiment. Differences between LES and DNS are small, but the refined grid LES is closer to the DNS almost everywhere. This monotonic convergence, expected of the LES method used, demonstrates its reliability.

The pressure surface undergoes transition almost immediately downstream of the leading edge. On the suction surface there are streaks as expected for freestream-turbulence-induced transition, but spots do not appear. Instead, a separating shear layer rolls up and breaks down to turbulence at re-attachment. Both LES capture this process. Skin friction distribution reveals the transition near the re-attachment to occur over an extended region, and subsequent relaxation is slower in the LES. The narrower transition zone in the DNS is indicative of the essential role of smaller scales during transition that should not be neglected in LES. Simulation data also reveal that an assumption of laminar kinetic energy transition models that Reynolds shear stress remains small in the pre-transitional region is supported. The remaining differences in the predictions of such models is thus likely to be the separation-induced transition which preempts the spot formation.
Investigation Into the Thermal Limitations of Steam Turbines During Start-Up Operation
Authors: Topel Monika , Laumert Björn , Nilsson Åsa , Jöcker Markus
Published: August 2017

Liberalized electricity market conditions and concentrating solar power technologies call for increased power plant operational flexibility. Concerning the steam turbine component, one key aspect of its flexibility is the capability for fast starts. In current practice, turbine start-up limitations are set by consideration of thermal stress and low cycle fatigue. However, the pursuit of faster starts raises the question whether other thermal phenomena can become a limiting factor to the start-up process. Differential expansion is one of such thermal properties, especially since the design of axial clearances is not included as part of start-up schedule design and because its measurement during operation is often limited or not a possibility at all.

The aim of this work is to understand differential expansion behavior with respect to transient operation and to quantify the effect that such operation would have in the design and operation of axial clearances. This was accomplished through the use of a validated thermo-mechanical model that was used to compare differential expansion behavior for different operating conditions of the machine. These comparisons showed that faster starts do not necessarily imply that wider axial clearances are needed, which means that the thermal flexibility of the studied turbine is not limited by differential expansion. However, for particular locations it was also obtained that axial rubbing can indeed become a limiting factor in direct relation to start-up operation. The resulting approach presented in this work serves to avoid over-conservative limitations in both design and operation concerning axial clearances.
Demonstration of a Dynamic Clearance Seal in a Rotating Test Facility
Authors: Messenger Andrew , Williams Richard , Ingram Grant , Hogg Simon , Tibos Stacie , Seaton Jon , Charnley Bernard
Published: August 2017

The successful demonstration of the “Aerostatic Seal” in a half scale rotating facility is described in this paper. The Aerostatic seal is a novel dynamic clearance seal specifically designed for steam turbine secondary gas path applications. The seal responds to radial rotor excursions, so a reduced clearance can be maintained compared to conventional labyrinth seal without damage to the seal. This enables increased turbine performance through reduced leakage and increased tolerance of turbine transient events typically found during start up. The seal is an extension of the existing retractable seal design already deployed in commercial steam turbines.

The seal was tested in the Durham Rotating Seals Rig, which was developed specifically to test this device. The rig featured a rotor designed to run with large eccentricities to model high speed radial rotor excursions, and the seal was instrumented to measure the real time seal response to the rotor.

The experimental campaign has conclusively demonstrated the ability of the seal to dynamically respond to the rotor position. The key result is that the seal is able to track the rotor position at high speed, and hence maintain a mean seal clearance that is lower than the rotor eccentricity. Overall this work marks a key milestone in the development of the Aerostatic Seal, and leads the way to testing in a steam environment and application in steam turbine plant.
Ansaldo GT26 Sequential Combustor Performance in Long-Term Commercial Operation
Authors: Zahirovic Selma , Knapp Klaus
Published: August 2017

The Ansaldo GT26 reheat gas turbine features the sequential combustion system with further improvements for extended fuel flexibility, increased operational flexibility and even lower NOx emissions compared to its predecessor, GT26 (2006). Better overall sequential combustor performance is achieved through an improved sequential burner and fuel lance. The design optimizations resulted in an improved fuel/oxidant mixing for lower NOx and CO emissions over a broad load range and extended fuel flexibility with regards to highly reactive fuels. The wide operation window is extended thanks to integrated acoustic damping devices, reducing combustion pulsations and extending lifetime. The improved hardware passed through an extensive testing and validation program on the high pressure full-scale test rig and validation engine. The performance of the Ansaldo GT26 sequential combustor in long-term operation is assessed based on data of two commercial engines and presented in this paper. For both engines, a broad operating window with reduced sequential combustor acoustic load was demonstrated, reconfirming the effectiveness of the damping devices. The emission compliance test ratified emission levels significantly below the site-specific guarantee limits, showing single digit NOx emissions at 15%-vol. O2 at base load. Natural gases with different heating values and C2+content were supplied and varied during continuous engine operation, revealing combustor insensitivity to lower Wobbe numbers. Long-term monitoring data bear witness to unchanged performance of the two engines since commissioning.
LES Loss Prediction in an Axial Compressor Cascade at Off-Design Incidences With Free Stream Disturbances
Authors: Leggett John , Priebe Stephan , Shabbir Aamir , Sandberg Richard , Richardson Edward , Michelassi Vittorio
Published: August 2017

It is well known that an axial compressor cascade will exhibit variation in loss coefficient, described as a loss bucket, when run over a sweep of incidences, and that higher levels of free stream turbulence are likely to suppress separation bubbles and cause earlier transition (see e.g. [23]). However, it remains difficult to achieve accurate quantitative prediction of these changes using numerical simulation, particularly at off-design conditions, without the added computational expense of using eddy-resolving techniques. The aim of the present study is to investigate profile losses in an axial compressor under such conditions using wall-resolved Large Eddy Simulation (LES) and RANS. The work extends on previous work by Leggett et al.[11] with the intention of furthering our understanding of loss prediction tools and improving our quantification of the physical processes involved in loss generation. The results show that while RANS predicts losses with good accuracy the breakdown of these losses are attributed to different processes, meaning that optimisation of a compressor cascade profile, based solely on RANS, may be hard to achieve.
Seedgas Investigation of Turbine Stage and Seal Performance at Varying Cavity Purge Rates and Operating Speeds
Authors: Dahlqvist Johan , Fridh Jens
Published: August 2017

The topic of hub cavity purge is investigated in a high-pressure axial low-reaction turbine stage. Both the sealing ability of the purge flow and the performance impact associated with its injection into the main flow are studied. Three operating speeds are investigated, namely a high loading case, the peak efficiency, and a high speed case, and purge flow rates across a wide range. The operating points coincide with investigations previously reported, where the flow field and stage efficiency was quantified using pneumatic probes. Comparative measurements are also performed, varying a leakage flow through the rotor below the hub platform.

The purge flow is now seeded with CO2 in order to measure its distribution throughout the stage, as it is injected into the wheelspace upstream of the rotor, allowing for quantification of the sealing effectiveness. This is done at a number of defined locations along the stator-side wall in the wheel space, resolving the radial variation through the cavity. Important radial variations of effectiveness are observed, confirming that the flow is in the regime of merged boundary layers, due to the narrow cavity, as compared to typical gas turbine operation with separated boundary layers. The trends are found to be related to operating speed and platform leakage.

With known sealing effectiveness, industry correlations may be adapted to make use of the variation of necessary purge rate to obtain a certain degree of sealing at a given operating point, and thereby optimize the efficiency.

In addition to quantification of potential hot-gas ingestion, the paper initiates an investigation of the transport of the purge flow in the main annulus, through sampling on the hub, as well as area traverse downstream of the rotor. The amount of sealing gas leads to opportunity to quantify the cooling performance of the purge flow in the main annulus. Both the cooling performance in the main annulus and cavity are shown to be significantly influenced by the rotor leakage, while its effect on efficiency is minor.
Multiobjective Optimal Design of a Gas Turbine Cogeneration Plant by a Revised Hierarchical Optimization Method
Authors: Yokoyama Ryohei , Shinano Yuji , Wakayama Yuki , Wakui Tetsuya
Published: August 2017

To attain the highest performance of energy supply systems, it is necessary to rationally determine design specifications in consideration of operational strategies corresponding to energy demands. Mixed-integer linear programming (MILP) approaches have been applied widely to such optimal design problems. A MILP method utilizing the hierarchical relationship between design and operation variables have been proposed to solve them efficiently. However, it cannot necessarily be effective to multi-objective optimal design problems because of the existence of a large number of competing design candidates. In this paper, the hierarchical MILP method is revised from the viewpoint of computation efficiency so that it can be applied practically to multi-objective optimal design problems. At the lower level, the order of the optimal operation problems to be solved is changed based on incumbents obtained previously to increase a lower bound for the optimal value of the combined objective function and reduce the number of the optimal operation problems to be solved. At the upper level, a lower bound for the optimal value of the combined objective function is incorporated into the solution method to reduce the number of the design candidates to be generated. This revised hierarchical MILP method is applied to a multiobjective optimal design of a gas turbine cogeneration plant, and its validity and effectiveness are clarified.
Influence of Cross-Sectional Shape on the Flow in a Highly Bent Research Intake Duct for Jet Engines
Authors: Haug Jakob P. , Rademakers Rudolf P. M. , Stößel Marcel , Niehuis Reinhard
Published: August 2017

In many modern aircraft concepts, civil as well as military ones, the engine is fully integrated into the fuselage. This integration often requires a highly bent intake duct. Due to the high degree of curvature and also the diffusive character of the intake duct, the inflow at the engine’s fan is non-uniform and may feature severe flow distortions. The size, strength, and pattern of these flow distortions may affect the engine’s compressor system and its safety margins. In this paper five highly bent intake duct geometries are analyzed by means of CFD. They evolve from the same baseline geometry but are defined by different crosssectional shapes. With this variation of the cross-sections, the influence of the cross-sectional shape on the aerodynamics of the intake duct is investigated qualitatively. Based on these analyses a sixth intake duct geometry was created as test vehicle for experimental investigation of intake-compressor interaction within the engine test facility. The defining cross-sectional shapes were selected in order to achieve a flow distortion at the duct outlet plane, that is small enough to ensure a safe engine operation, but is still strong enough to provoke interaction of the distorted flow and the compressor flow. The setup for these fully numerical investigations is based on previous studies of the aerodynamics of intake ducts at the Institute of Jet Propulsion. It is shown that the entrance cross-section has a strong influence on the flow throughout the whole intake duct. Additionally, it could be determined that the flow distortion caused by the strong curvature of the intake duct can be reduced in size and strength by a proper combination of cross-sectional shapes.
Thermomechanical Component Mode Synthesis for Blade Casing Interaction Prediction
Authors: Guerin Nicolas , Thouverez Fabrice , Gibert Claude , Legrand Mathias , Almeida Patricio
Published: August 2017

Increasing the efficiency of turbomachines is a major concern as it directly translates into lower environmental impact and improved operational costs. One solution is to reduce the blade-casing operating clearance in order to mitigate aerodynamic losses at the unavoidable cost of increased structural unilateral contact and friction occurrences. In centrifugal compressors, the dynamic behaviour of the structures interacting through unilateral contact and friction is not yet fully understood. In fact, the heat generated during such events may affect the dynamics through thermal stresses.

This paper presents a complete thermomechanical modelling strategy of impeller rotor and casing, and of blade-tip/casing contact events. A fully coupled thermomechanical modal synthesis technique is introduced and applied to turbomachinery-related models. The blisk is reduced via a hybrid modal synthesis technique combining the Craig-Bampton method and the characteristic constraint mode method. The casing model is reduced using an axisymmetric harmonic modal synthesis. Both strategies involve thermomechanical modes embedding thermal dilatation effects. The contact modelling algorithm is then introduced. It handles unilateral contact and friction occurrences together with heating effects. This algorithm uses the above mentioned reduced-order models as input data to avoid CPU-intensive simulations.

The results show that the thermomechanical behaviour of the structures is well preserved by the reduction strategy proposed. Contact simulations on simple cases show qualitative results in accordance with expectations.

Further work is needed in order to validate the strategy based on experimental results. However, this methodology opens the way to extended multiphysics simulations of contact events in turbomachinery.
Pulsations in Gas Turbine Operation: Identification and Modeling With the Purpose of Online Engine Monitoring and Optimization
Authors: Weidner Frank S. , Lipperheide Moritz , Wirsum Manfred C. , Bernero Stefano , Gassner Martin
Published: August 2017

Lean premixed combustion has become state of the art technology in gas turbines for power generation because of its very low emission potential in the context of tightening pollutant emissions regulations. Lean premixed combustion is yet also prone to combustion instabilities, resulting in thermo-acoustically induced acoustic pressure oscillations (pulsations). Understanding pulsation behavior over an enginés lifetime is of interest to accurately monitor the engine status, as wear and degradation typically affect combustion behavior and result in changes of both pulsations and emissions. Such improved understanding can be exploited for optimizing both the engine operation concept and the design of relevant hardware parts. In return, pulsation and hardware optimization may lead to reduced degradation and thus inherently more robust long-term operational behavior.

The study presented here is conducted for one specific gas turbine of GE’s GT24/GT26 fleet with sequential annular combustion. Based on operational data of the examined gas turbine, a semi-empirical modeling approach is introduced to describe the pulsations measured in the first (EV) combustion chamber. The target is to reproduce measured pulsation amplitudes as well as their different behaviors with engine load. The modeling presented here has been focused on pulsations in a distinctive frequency range below 1kHz. A model based on a small set of data obtained from initial commissioning is able to represent the pulsation behavior within a normalized root mean square error of 11%. Validation with long-term engine data shows that predicted pulsation levels are reasonably matching the initial operation period but increasingly deviate with engine operating time. By using additional data from later engine commissioning and adjustments, the robustness of the model is sensibly increased. Model accuracy on the training dataset remains similar at around 11%, but validation on the long-term data shows a significant decrease of the normalized root mean square error from over 21% to below 16%. Additional model improvements to further reduce prediction errors on long-term data have been also identified.
Investigation on the Excitation Characteristics and Dynamic Response of the Multi-Support Flexible Rotor With Misalignment
Authors: Xiao Sen , Wu FaYong , Ma YanHong , Hong Jie
Published: August 2017

Aiming at the misaligned problems of high-speed flexible multi-supported rotor system, considering the structural characteristics and load characteristics of the rotor, the unbalanced excitation of the rotor with misalignment is presented and quantitatively described. The mechanical model of the high-speed flexible rotor system with multi-support under misaligned excitation is established. Based on the finite element method, the dynamic equation of the rotor system is given and the dynamic response characteristics of rotor systems are studied. The results show that the misalignment for the highspeed multi-support flexible rotor system can not only lead to 2X excitation and support stiffness nonlinearity, but also bring additional unbalanced excitation to the rotor system. The 2X frequency component is one typical feature for the rotor system with bearing misalignment. The vibration response of the rotor showed a trend of “increased slowly first, then reduced quickly as the rotation frequency increased”, and it turns to be more obvious with the increasing of the nonlinear stiffness and unbalance.
Three Spool High Efficiency Small Scale Gas Turbine Concept
Authors: Malkamäki Matti , Jaatinen-Värri Ahti , Uusitalo Antti , Grönman Aki , Honkatukia Juha , Backman Jari , Hartikainen Toni
Published: August 2017

Decentralized electricity and heat production is a rising trend in small-scale industry. There is a tendency towards more distributed power generation. The decentralized power generation is also pushed forward by the policymakers.

Reciprocating engines and gas turbines have an essential role in the global decentralized energy markets and improvements in their electrical efficiency have a substantial impact from the environmental and economic viewpoints. This paper introduces an intercooled and recuperated three stage, three-shaft gas turbine concept in 850 kW electric output range. The gas turbine is optimized for a realistic combination of the turbomachinery efficiencies, the turbine inlet temperature, the compressor specific speeds, the recuperation rate and the pressure ratio. The new gas turbine design is a natural development of the earlier two-spool gas turbine construction and it competes with the efficiencies achieved both with similar size reciprocating engines and large industrial gas turbines used in heat and power generation all over the world and manufactured in large production series. This paper presents a small-scale gas turbine process, which has a simulated electrical efficiency of 48% as well as thermal efficiency of 51% and can compete with reciprocating engines in terms of electrical efficiency at nominal and partial load conditions.
Development, Numerical Investigation and Experimental Validation of a New Recuperator Design for Aero Engines Applications
Authors: Vlahostergios Zinon , Misirlis Dimitrios , Flouros Michael , Salpingidou Christina , Donnerhack Stefan , Goulas Apostolos , Yakinthos Kyros
Published: August 2017

Targeting the development of more efficient aero engine designs, various concepts have been considered through the previous years, among which is the Intercooled Recuperative Aero engine (IRA) concept. In the IRA concept a system of heat exchangers is mounted in the hot-gas exhaust nozzle, downstream of the low-pressure turbine focusing on the exploitation of the waste heat exhaust gasses for preheating the compressor discharge air just before the latter enters the combustion chamber, resulting in fuel consumption and pollutants emission reduction. In the present work a new heat exchanger design for use as a recuperator is proposed for possible implementation in the IRA engine, based on an annular configuration design which is more easily integrated in an aero engine. The new recuperator external pressure losses are computationally and experimentally investigated for laboratory conditions, providing very good agreement. Additionally, the pressure losses just before the recuperator were further minimized by introducing riblet films inside the exhaust conical nozzle. The optimized recuperator characteristics were included in a thermodynamic analysis of the IRA engine and it was shown that considerable improvement in fuel consumption and pollutant emissions reduction could be achieved.
Reproducible Inflow Modifications for a Wind Tunnel Mounted Research Hawt
Authors: Bartholomay Sirko , Fruck Wolf-Leonard , Pechlivanoglou George , Nayeri Christian Navid , Paschereit Christian Oliver
Published: August 2017

This paper describes a method of creating inhomogeneous inflow conditions to a horizontal axis wind turbine installed in the settling chamber of the large wind tunnel of the TU Berlin. Thereby, a steady gust (i.e. spatial velocity gradient, constant over time) is created which covers half of the swept area of the turbine. For purposes of analysis, a hotwire traversing system was used and measurements were correlated to on-blade angle of attack, velocity and blade root bending moment measurements. Moreover, the paper presents wake measurements at one downstream plane behind the turbine.
Structural Topology Optimization of Turbomachinery Components Using New Manufacturing Techniques and Innovative Materials
Authors: Boccini Enrico , Meli Enrico , Rindi Andrea , Corbò Simone , Falomi Stefano , Iurisci Giuseppe
Published: August 2017

Structural topology optimization is an innovative approach in turbomachinery to satisfy the increasing demand for higher rotational speeds, light components and optimized natural frequencies, with a remarkable economic impact. Although this approach has never been extensively applied before to rotating machines, it is very promising for the mechanical optimization of rotor and stator components. This approach enables the creation of complex three-dimensional geometries, which are usually difficult or impossible to be built using traditional manufacturing methods. Thanks to innovative technologies and to the use of innovative materials, it is now possible to effectively exploit topology optimization. It allows to change the topology of the structures, significantly improving material distribution within a given design space for a given set of boundary conditions and loads. In this work, the authors have deeply investigated the applicability of topology optimization to the fields of turbomachinery and rotordynamics.
Damage Development in SiCf/SiC Composites Through Mechanical Loading
Authors: Bache Martin R. , Jones J. Paul , Quiney Zak , Gale Louise
Published: August 2017

Sophisticated mechanical characterisation is vital in support of a fundamental understanding of deformation in ceramic matrix composites. On the component scale, “damage tolerant” design and lifing philosophies depend upon laboratory assessments of macro-scale specimens, incorporating typical fibre architectures and matrix under representative stress-strain states.

Standard SiCf/SiC processing techniques inherently introduce porosity between the individual reinforcing fibres and between woven fibre bundles. Subsequent mechanical loading (static or cyclic) may initiate cracking from these stress concentrations in addition to fibre/matrix decohesion and delamination. The localised coalescence of such damage ultimately leads to rapid failure.

Proven techniques for the monitoring of damage in structural metallics, i.e. optical microscopy, potential drop systems, acoustic emission (AE) and digital image correlation (DIC), have been adapted for the characterisation of CMC’s tested at room temperature. As processed SiCf/SiC panels were subjected to detailed X-ray computed tomography (XCT) inspection prior to specimen extraction and subsequent static and cyclic mechanical testing to verify their condition. DIC strain measurements, acoustic emission and resistance monitoring were performed and correlated to monitor the onset of damage during loading, followed by intermittent XCT inspections throughout the course of selected tests.
A 3D Shape Design and Optimization Method for Natural Laminar Flow Nacelle
Authors: Zhong Yongjian , Li Songyang
Published: August 2017

With the rapid development of high bypass ratio turbofan engine, the proportion of the nacelle drag increases obviously in the total drag of the aircraft with the increase of nacelle surface area. And the frictional resistance is one of the major contributors of drag. Under the same Reynolds number, the friction resistance in turbulent boundary layer is about 10 times larger as that in laminar boundary layer. Therefore, a correctly profiled engine nacelle will delay the transition in the boundary layer and allow laminar flow to extend back, resulting in a substantial drag reduction. In the previous conference paper (9th reference), a 2D nacelle longitudinal profile-line geometry generator, which allows curvature and slope-of-curvature to be continuous was developed and presented. This established an optimization system to minimize nacelle frictional drag. One of the nacelle profile-line is optimized to achieve minimum drag coefficient, and then is stacked with the other original profile-lines to form the 3D isolated nacelle aerodynamic shape. Finally, a total 23% of nacelle outer surface maintains a laminar flow and its frictional drag coefficient is less than initial shape.

This paper proposes a new 2D nacelle longitudinal profile-line design method, based on PARSEC parameterization, with can generate the profile-line rapidly and precisely. Conservation Full Potential Equation was used to calculate the aerodynamic distribution and obtain the transition location. Then adaptive simulated annealing genetic algorithm was adapted to search 2D profiles of low drag, which would be applied to narrow down design space in 3D nacelle optimization. Second, 2D profiles were stacked circumferentially, by NURBS surface generator, to form the 3D nacelle aerodynamic shape, and an optimization system was established, in combination with the 3D nacelle generator, γ–Reθ transition model, Kriging surrogate model and adaptive simulated annealing algorithm, for natural laminar flow nacelle design. Finally, a total 34% of nacelle surface maintains a laminar flow and its frictional drag coefficient is less than initial shape. The generated optimized loft was evaluated by CFD to determine if the low drag of this optimized nacelle shape can be maintained under different Mach numbers and angles of attack.