bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultra-High Temperature Compliant Foil Bearings: The Journey to 870°C and Application in Gas Turbine Engines — Experiment
Authors: Heshmat Hooshang , Walton James F. , Nicholson Brian D.
Published: August 2018

In this paper, the authors present the results of recent developments demonstrating that ultra-high temperature compliant foil bearings are suitable for application in a wide range of high temperature turbomachinery including gas turbine engines, supercritical CO2 power turbines and automotive turbochargers as supported by test data showing operation of foil bearings at temperatures to 870°C (1600°F). This work represents the culmination of efforts begun in 1987, when the U.S. Air Force established and led the government and industry collaborative Integrated High Performance Turbine Engine Technology (IHPTET) program. The stated goal of IHPTET was to deliver twice the propulsion capability of turbine engines in existence at that time. Following IHPTET, the Versatile Affordable Advanced Turbine Engines (VAATE) program further expanded on the original goals by including both versatility and affordability as key elements in advancing turbine engine technology. Achieving the stated performance goals would require significantly more extreme operating conditions including higher temperatures, pressures and speeds, which in turn would require bearings capable of sustaining temperatures in excess of 815°C (1500°F). Similarly, demands for more efficient automotive engines and power plants are subjecting the bearings in turbochargers and turbogenerators to more severe environments. Through the IHPTET and VAATE programs, the U.S. has made considerable research investments to advancing bearing technology, including active magnetic bearings, solid and vapor phase lubricated rolling element bearings, ceramic/hybrid ceramic bearings, powder lubricated bearings and compliant foil gas bearings. Thirty years after the IHPTET component goal of developing a bearing capable of sustained operation at temperatures above 540°C and potentially as high as 815°C (1500°F) recent testing has demonstrated achievement of this goal with an advanced, ultra-high temperature compliant foilgas bearing. Achieving this goal required a combination of high temperature foil material, a unique elastic-tribo-thermal barrier coating (KOROLON 2250) and a self-adapting compliant configuration. The authors describe the experimental hardware designs and design considerations of the two differently sized test rigs used to demonstrate foil bearings operating above 815°C (1500°F). Finally, the authors present and discuss the results of testing at temperatures to 870°C (1600°F).
A Strategy of Mixture Preparation for Methane Direct-Fired sCO2 Combustors
Authors: Manikantachari K. R. V. , Martin Scott , Vesely Ladislav , Bobren-Diaz Jose O. , Vasu Subith , Kapat Jayanta
Published: August 2018

The reactor residence time required for a sCO2 combustor is comparatively higher than an equal power, airdiluted conventional combustor. Therefore, the strategies to reduce the reactor residence time are very important in the design of sCO2 combustors. The current work recommends a method to reduce the residence time requirement in the sCO2 combustion chamber. Here, the combustor is modelled by coupling the perfectly-stirred-reactor (PSR) and plug-flow-reactor (PFR) models along with the detailed Aramco 2.0 combustion chemical kinetic mechanism. The real gas effects are considered by using the Soave-Redlich-Kwong (SRK) equation of state incorporated in CHMEKIN-RG. Though, the CO emission level at the exit of the primary zone of the sCO2 combustor is lower or in some cases equal to the conventional combustor, the further decline of CO in the dilution zone is identified as very poor. Therefore, very high CO levels can be expected at the exit of the sCO2 combustor compared to conventional combustors. CO from the sCO2 combustor exhaust can be eliminated by lean operation of the combustor and the excess O2 retained in the re-cycled CO2 stream due to lean operation can be mixed with primary methane before entering the primary combustion zone. This strategy is shown to reduce the primary zone residence time requirement of sCO2 combustion. However, the minimum level of O2 in the re-cycled CO2 stream is approximately 5000 ppm and the minimum required residence time in this pre-mixing chamber is around 4 ms. Also, it is observed that the primary zone residence time requirement decreases linearly with respect to the O2 level in the re-cycled CO2 stream.
An Experimental Study for the Development of Mandrel-Free Hot-Spinning for Large Size Titanium Alloy Plate Forming
Authors: Imamura Yoshihide , Ikawa Ken , Motoyama Kojiro , Iwasaki Hayato , Hirakawa Takeo , Utsunomiya Hiroshi
Published: August 2018

A mandrel-free hot-spinning was developed as a near-net-shape titanium alloy plate forming technique. In this work, a Ti-6Al-4V alloy conical product with a wall angle of 34 degrees and 170mm height was formed from a large size Ti-6Al-4V plate (890∼920mm dia. × 30mm thick). The product was characterized metallurgically and mechanical properties were measured, and the shape of formed products was investigated. It was found that the mandrel-free hot-spinning is able to form a large size titanium alloy plate. Material properties including tensile strength and microstructure of the formed products satisfied the material specifications. Fatigue stress of the formed product was higher than that of the typical Ti-6Al-4V material. For a further improvement, a forming method using pre-formed material was proposed and which was successfully conducted with two types of preforms and found to be effective in the forming process.
Theoretical and Experimental Analyses of Directly Lubricated Tilting-Pad Journal Bearings With Leading Edge Groove
Authors: Hagemann Thomas , Schwarze Hubert
Published: August 2018

Flooded lubrication of tilting-pad journal bearings provides safe and robust operation for many applications due to a completely filled gap at the leading edge of each pad. While flooded conditions can be ensured by restrictive seals on the lateral bearing ends for any conventional bearing design, direct lubrication by leading edge grooves (LEG) placed on the pads represents an alternative to produce completely filled gaps at the entrance to the convergent lubricant film. Moreover, this design is flexible to apply different axial sealing baffles in order to influence the thermal equilibrium within the entire bearing. A theoretical model is presented that describes the specific influences of LEG design on the operating characteristics. First, in opposite to conventional tilting-pad journal bearing designs the LEG is a self-contained lube oil pocket which is generally connected to an outer annular oil supply channel. Consequently, each leading edge groove can feature a specific speed and load dependent effective pocket pressure and flow rate. As a consequence of this and the fact that the LEG is part of the pad, it directly influences its tilting angle. Secondly, the thermal inlet mixing model must consider the specific flow conditions depending on the main flow direction within the film as well as the one between outer annular channel and pocket. The novel LEG model is integrated into a comprehensive bearing code validated earlier for other bearing designs. The code is based on an extended Reynolds equation and a three-dimensional energy equation. The entire theoretical model is validated with test data from high performance journal bearing test rig for a four tilting-pad bearing in load between pivot orientation. The bearing is described by the following specifications: 0.5 nominal preload, 60% offset, 70° pad arc angle, 120 mm inner diameter, 72 mm pad length and 1.7 per mille relative bearing clearance. Measurements are conducted for rotational speeds between 4000 and 15000 rpm and specific bearing loads between 0.5 and 2.5 MPa. Within the investigated operating range good agreement between theoretical and experimental data is achieved if all boundary conditions are accurately considered. Additionally, the impact of single simplifications within the model are studied and evaluated. Finally, the test data is compared to results from the same test bearing with modified lubricant oil supply conditions in order to identify specific properties of LEG design. Here, the leading groove edge elements are replaced by conventional spray-bars. It is shown that an assessment of the comparison depends on the definition of reference conditions as the bearings require different oil flow rates for nominal operation due to their design.
Application of Conjugate Heat Transfer Analysis to Improvement of Cooled Turbine Vane and Blade for Industrial Gas Turbine
Authors: Horiuchi Takeshi , Taniguchi Tomoki , Tanaka Ryozo , Ryu Masanori , Kazari Masahide
Published: August 2018

In this paper, the Conjugate Heat Transfer (CHT) analysis, which utilizes commercial software STAR-CCM+ with detailed models and practical mesh size, was performed to the first stage cooled turbine airfoils for an industrial gas turbine produced by Kawasaki Heavy Industries, Ltd. (KHI). First its estimation accuracy was evaluated by comparing with the measurement results obtained with thermal index paint (TIP) and a pyrometer. After the validation of the CHT analysis, the metal temperature distribution was understood with the flow phenomena associated with it from the analysis results. To the parts where the metal temperature is locally high, then, the improvements of the cooling performance were considered with the CHT analysis and their effects were finally confirmed by measuring the metal temperature in the actual engine.

The investigation reveals that the CHT analysis, which is validated with measurement results, makes it possible for cooling designers to efficiently improve the cooling performance of turbine airfoils with the adequate estimation accuracy, thus enhancing their durability for the reliability of gas turbines.
Development of a Meanline Model for Preliminary Design of Recirculating Casing Treatment in Turbocharger Compressors
Authors: Favaretto Carlos Felipe F. , Anderson Mark R. , Li Shuo , Hu Leon
Published: August 2018

Recirculating casing treatment is a feature frequently adopted in automotive turbocharger compressor design to extend its operating range. In the low flow region of the map, surge margin can be enhanced by bleeding a fraction of the main flow from the impeller casing back to the stage inlet. In the high flow region, choke margin can be improved by bleeding flow from the stage inlet to a location downstream of the impeller throat. The benefits of recirculating casing treatment are more prominent at higher rotational speeds and are usually accompanied by an associated penalty in efficiency, which may or may not be acceptable. The challenge posed to the designers is to create a recirculating casing cavity configuration which enlarges the map width, while minimizing its impact on efficiency.

In the lack of specialized meanline tools, early stages of recirculating casing cavity design are mostly reliant on results from expensive CFD runs or test data from existing designs, if available. This paper presents the development of a meanline model suitable for preliminary design. The model was compared with CFD results for an automotive turbocharger compressor. The authors believe the proposed model can be a valuable tool for reducing development costs in the preliminary design stages of recirculating casing treatment configurations.
Integration of 3D-CFD Component Simulation Into Overall Engine Performance Analysis for Engine Condition Monitoring Purposes
Authors: Klein C. , Wolters F. , Reitenbach S. , Schönweitz D.
Published: August 2018

For an efficient detection of single or multiple component damages, the knowledge of their impact on the overall engine performance is crucial. This knowledge can be either built up on measurement data, which is hardly available to non-manufacturers or –maintenance companies, or simulative approaches such as high fidelity component simulation combined with an overall cycle analysis.

Due to a high degree of complexity and computational effort, overall system simulations of jet engines are typically performed as 0-dimensional thermodynamic performance analysis, based on scaled generic component maps. The approach of multi-fidelity simulation, allows the replacement of single components within the thermodynamic cycle model by higher-order simulations. Hence, the component behavior becomes directly linked to the actual hardware state of the component model. Hereby the assessment of component deteriorations in an overall system context is enabled and the resulting impact on the overall system can be quantified.

The purpose of this study is to demonstrate the capabilities of multi fidelity simulation in the context of engine condition monitoring.

For this purpose, a 0D-performance model of the IAE-V2527 engine is combined with a CFD model of the appropriate fan component. The CFD model comprises the rotor as well as the outlet guide vane of the bypass and the inlet guide vane of the core section. As an exemplarily component deterioration, the fan blade tip clearance is increased in multiple steps and the impact on the overall engine performance is assessed for typical engine operating conditions.

The harmonization between both simulation levels is achieved by means of an improved map scaling approach using an optimization strategy leading to practicable simulation times.
On the Identification and Decomposition of the Unsteady Losses in a Turbine Cascade
Authors: Lengani D. , Simoni D. , Pichler R. , Sandberg R. , Michelassi V. , Bertini F.
Published: August 2018

The present paper describes the application of Proper Orthogonal Decomposition (POD) to Large Eddy Simulation (LES) of the T106A low-pressure-turbine profile with unsteady incoming wakes at two different flow conditions. Conventional data analysis applied to time averaged or phase-locked averaged flow fields is not always able to identify and quantify the different sources of losses in the unsteady flow field as they are able to isolate only the deterministic contribution. A newly developed procedure allows such identification of the unsteady loss contribution due to the migration of the incoming wakes, as well as to construct reduced order models able to highlight unsteady losses due to larger and/or smaller flow structures carried by the wakes in the different parts of the blade boundary layers. This enables a designer to identify the dominant modes (i.e. phenomena) responsible for loss, the associated generation mechanism, their dynamics and spatial location.

The procedure applied to the two cases shows that losses in the fore part of the blade suction side are basically unaffected by the flow unsteadiness, irrespective of the reduced frequency and the flow coefficient. On the other hand, in the rear part of the suction side the unsteadiness contributes to losses prevalently due to the finer scale (higher order POD modes) embedded into the bulk of the incoming wake. The main difference between the two cases has been identified by the losses produced in the core flow region, where both the largest scale structures and the finer ones produces turbulence during migration. The decomposition into POD modes allows the quantification of this latter extra losses generated in the core flow region, providing further inputs to the designers for future optimization strategies.
High Fidelity Spectral/hp Element Methods for Turbomachinery
Authors: Cassinelli Andrea , Montomoli Francesco , Adami Paolo , Sherwin Spencer J.
Published: August 2018

The high order spectral/hp element methods implemented in the software framework Nektar++ are investigated for scale-resolving simulations of LPT profiles. There is a growing demand for high fidelity methods for turbomachinery to move towards numerical “experiments”. The study contributes at building best practices for the use of emerging high fidelity spectral element methods in turbomachinery predictions, with focus on the numerical details that are specific of these classes of methods. For this reason, the T106A cascade is used as a base reference application because of availability of data from previous investigations. The effects of polynomial order (p-refinement), spanwise domain extent and spanwise Fourier planes are considered, looking at flow statistics, convergence and sensitivity of the results. The performance of the high order spectral/hp element method is also assessed through validation against experimental data at moderately high Reynolds number. Thanks to the reduced computational cost, the proposed methods will have a strong impact in turbomachinery, paving the way to its use for design purposes and also allowing for a deeper understanding of the flow physics.
Numerical and Experimental Investigation of the CeCOST Swirl Burner
Authors: Hodzic Erdzan , Yu Senbin , Subash Arman Ahamed , Liu Xin , Liu Xiao , Szasz Robert-Zoltan , Bai Xue-Song , Li Zhongshan , Alden Marcus
Published: August 2018

Clean technology has become a key feature due to increasing environmental concerns. Swirling flows, being directly associated with combustion performance and hence minimized pollutant formation, are encountered in most propulsion and power-generation combustion devices. In this study, the development process of the conceptual swirl burner developed at the Swedish National Centre for Combustion and Technology (CeCOST), is presented. Utilizing extensive computational fluid dynamics (CFD) analysis, both the lead time and cost in manufacturing of the different burner parts were significantly reduced. The performance maps bounded by the flashback and blow-off limits for the current configuration were obtained and studied in detail using advanced experimental measurements and numerical simulations. Utilizing high speed OH-chemiluminescence, OH/CH2O-PLIF and Large Eddy Simulation (LES), details of the combustion process and flame-flow interaction are presented. The main focus is on three different cases, a stable case, a case close to blow-off and flashback condition. We show the influence of the flame on the core flow and how an increase in swirl may extend the stability limit of the anchored flame in swirling flow burners.
Thermo-Mechanical Modeling of Abradable Coating Wear in Aircraft Engines
Authors: Nyssen Florence , Batailly Alain
Published: August 2018

In modern turbomachine designs, the nominal clearances between rotating bladed-disks and their surrounding casing are reduced to improve aerodynamic performances of the engine. This clearance reduction increases the risk of contacts between components and may lead to hazardous interaction phenomena. A common technical solution to mitigate such interactions consists in the deposition of an abradable coating along the casing inner surface. This enhances the engine efficiency while ensuring operational safety. However, contact interactions between blade-tips and an abradable layer may yield unexpected wear removal phenomena. The aim of this work is to investigate the numerical modeling of thermal effects within the abradable layer during contact interactions and compare it with experimental data. A dedicated thermal finite element mesh is employed. At each time step, a weak thermo-mechanical coupling is assumed: thermal effects affect the mechanics of the system, but the mechanical deformation of the elements has no effect on temperatures. Weak coupling is well appropriated in the case of rapid dynamics using small time step and explicit resolution schemes. Moreover, only heat transfer by conduction is considered in this work. To reduce computational times, a coarser spatial discretization is used for the thermal mesh comparing to the mechanical one. The time step used to compute the temperature evolution is larger than the one used for the mechanical iterations since the time constant of thermal effect is larger than contact events. The proposed numerical modeling strategy is applied on an industrial blade to analyze the impact of thermal effects on the blade’s dynamics.
Model Predictive Control for Gas Turbine Engines
Authors: Pandey Amit , de Oliveira Maurício , Moroto Robert H.
Published: August 2018

The use of Model Predictive Control (MPC) is commonplace in many industrial applications. The anticipative nature of MPC and the inclusion of physical constraints into the control framework presents many advantages over classical control strategies. Despite these advantages, obtaining an accurate open-loop model of the underlying process is often a difficult and time consuming process. In this paper, a methodology is introduced to identify linear open-loop models of gas turbine engines from closed-loop data. The closed-loop data can be obtained by any sufficiently informative experiment from a plant in operation or simulation. We present simulation results here. These open-loop models are then used in the design of model predictive controllers at a number of operating points of the turbine. The predictive controllers we designed include physical constraints on the fuel and air flow into the turbine. The performance of these predictive controllers is compared in simulation against existing classical control techniques in a number of typical operating scenarios including off loads, on loads and set point changes.
CMAS Effects on Ship Gas-Turbine Components/Materials
Authors: Shifler D. A. , Choi S. R.
Published: August 2018

Recent inspection of shipboard gas-turbine components under the platform has indicated the apparent presence of CMAS (calcium, magnesium, alumino-silicate) and its related attack. This type of attack has often been observed in aero gas turbine engines when sand and similar siliceous matter is ingested into the engine and the sand debris melts due to high engine operating temperature greater than 1150°C. Initial chemical analysis shows that the CMAS-affected areas of ship engine components versus aero engine components are similar. However, this phenomenon commonly observed in advanced aeroengines are not supposed to occur in the ship engine components since their probable temperature is known to be much lower than 1150°C (i.e., melting temperature of CMAS). As a consequence, some important questions arise as to: What caused this “CMAS” attack in ship engine components? Was this initiated by hot corrosion, which created a molten salt pool at a sufficient temperature to trigger CMAS attack? Did sodium chloride mixed with dust and debris lower the temperature at which molten CMAS would initiate?

Past research provides a basic understanding of hot corrosion, but may ignore other reactants and other species inherently associated with ‘natural CMAS’ and mechanisms contributing to hot corrosion or CMAS attack. Further examination of ship and aero components will discern the local structure chemical profile of the component coatings, the chemical compositions of the alloy substrates, and the interface between the coating and the molten “CMAS” by several methods. Integrated computational materials engineering (ICME) and validating experiments will assist in developing degradation mechanisms.

The environment complexity is also to be taken into account to determine whether salt-induced CMAS attack or CaO-induced hot corrosion may be dominant. The mechanisms need to be further studied and defined. The current work will address a series of systematic approaches to the aforementioned CMAS issues and will also present some recent results on CMAS-related effects on components and an elected alloy material system.
Effect of End-Wall Vortex Generator Jet Parameters on Flow Control in High Subsonic Compressor Cascade
Authors: Chen Cong , Yu Jianyang , Chen Fu
Published: August 2018

In order to explore the control mechanism of vortex generator jet, which is located in the passage (PVGJ), on the separation flow, the influence of the pitch angle, skew angle, locations and jet-to-inflow ratio are studied using numerical methods in a high subsonic compressor cascade. The changing of the flow pattern is also analyzed in detail. The results show that the control effect of the end-wall vortex generator jet located in the passage is better than the leading edge one and the aerodynamic performance is effectively improved. The maximum total pressure loss coefficient decreases by 12% and the static pressure coefficient increases by 5.2% while the jet-to-inflow ratio is only 0.3%. The control effect is sensitive to the change of jet parameters. When 0 deg < β < 80 deg, 20 deg < α < 50 deg,, x < 0.5B, y < 0.15t, the vortex generation jet could acquire an ideal control effect. As the jet mass increases, the total pressure loss coefficient gradually reduces. The VGJ prevent separation mainly by bringing high momentum fluid into the near wall region and by promoting momentum transport through turbulent mixing in previous studies. Both the LVGJ and PVGJ mainly take advantage of jet vortex to prevent the cross flow from interacting with the suction side boundary layer.
Heat Transfer Coefficient and Film Cooling Effectiveness on the Partial Cavity Tip of a Gas Turbine Blade
Authors: Jeong Jin Young , Kim Woobin , Kwak Jae Su , Park Jung Shin
Published: August 2018

Leakage flow between the rotating turbine blade tip and the fixed casing causes high heat loads and thermal stress on the tip and near the tip region. For this study, new squealer tips called partial cavity tips, which combine the advantages of plane and squealer tips, were suggested, and the effects of the cavity shape on the tip heat transfer coefficient and film cooling effectiveness were investigated experimentally in a low speed linear cascade. The suggested blade tips had a flat surface near the leading edge and a squealer cavity from the mid-chord to trailing edge region to achieve the advantages of both blade tip types. The heat transfer coefficient was measured via the 1-D transient heat transfer technique using an IR camera, and the film cooling effectiveness was obtained via the pressure sensitive paint (PSP) technique. Results showed that the heat transfer coefficient and film cooling effectiveness on the partial cavity tips strongly depended on the cavity shape. Near the leading edge, the heat transfer coefficients for the partial cavity tip cases were lower than that for the squealer tip case. However, the heat transfer coefficient on the cavity surface was higher for the partial cavity tip cases. The D10 tip showed a similar distribution of film cooling effectiveness to that of the PLN tip near the leading edge and the DSS tip near the mid-chord region. However, the overall averaged film cooling effectiveness of the DSS tip was higher than that of the D10 tip.
A Combined Application of Negative Bowed Blade and Endwall Unsteady Pulsed Holed Suction in a Highly Loaded Compressor Cascade
Authors: Chen Shaowen , Zhang Hongxin , Meng Qinghe , Wang Songtao , Wang Zhongqi
Published: August 2018

With the increasing continually of blade load, a serious three-dimensional (3D) unsteady flow separation is caused in the design of modern advanced aero-engine compressor. The flow separation has a strong influence on the aerodynamic behavior of the flow in the compressor passage such as reducing the pressure rise capability and overall efficiency, and even resulting in stall and surge. Consequently, it is very necessary to apply some effective techniques for suppressing the 3D flow separation in order to improve the aerodynamic performance of aero-engine compressors. The endwall unsteady pulsed holed suction (EUPHS) is first developed. Additionally, the negative bowed blade is a convention passive flow control method. It can make the flow of the midspan move toward the endwall by changing the radial pressure distribution and improve flow behavior of the midspan. Therefore, with the aim of further improving the aerodynamic performance and flow behavior, the EUPHS combined with the negative bowed blade as a new promising compound flow control (CFC) technique is proposed. In this study, only two bleeding holes on the endwalls (one on the upper endwall and another on the lower endwall) are used to achieve suction in a highly loaded compressor cascade. The improvements in aerodynamic performance by endwall steady constant holed suction (ESCHS), EUPHS and CFC are investigated and compared firstly. Some related parameters such as suction-to-inlet time-averaged suction flow ratio and excitation frequency are also discussed and analyzed in detail. The results show that CFC has more potential advantages than ESCHS and EUPHS in reducing the total pressure loss coefficient and is a promising flow control technology to further enhance aerodynamic performance. Based on the optimal suction-to-inlet time-averaged suction flow ratio and excitation frequency, the total pressure loss coefficients for CFC are reduced by 17.7%.
Development of a Steady-State Experimental Facility for the Analysis of Double-Wall Effusion Cooling Geometries
Authors: Murray Alexander V. , Ireland Peter T. , Romero Eduardo
Published: August 2018

The continuous drive for ever higher turbine entry temperatures is leading to considerable interest in high performance cooling systems which offer high cooling effectiveness with low coolant utilisation.

The double-wall system discussed here, is an optimised amalgamation of more conventional cooling methods including impingement cooling, pedestals, and film cooling holes in a more closely packed array characteristic of effusion cooling. The system entails two walls, one with the impingement holes, and the other with the film holes. These are mechanically connected via the bank of pedestal thereby allowing conduction between the walls and increasing coolant wetted area and turbulent flow. However, in the open literature, data — and particularly experimental data — on such systems is sparse.

This study presents a newly commissioned experimental heat transfer facility designed to investigate double-wall cooling geometries. The paper discusses some of the key features of the steady-state facility, including the use of infrared thermography to obtain overall cooling effectiveness measurements. The facility is designed to achieve both Reynolds and Biot (to within 10%) number similarity to those seen at engine conditions.

The facility is used to obtain overall cooling effectiveness measurements for a circular pedestal, double-wall test piece at three coolant mass-flow conditions with the results presented and discussed. A fully conjugate CFD model of the facility was also developed providing greater insight into the internal flow field. Additionally, a computationally efficient, decoupled conjugate method developed by the authors for analysing such double-wall systems is run at conditions to match the experiments. The results of the simulations are encouraging, particularly given how computationally efficient the method is, with area-weighted, averaged overall effectiveness within a small margin of those obtained from the experimental facility.
Unsteady Conjugate Heat Transfer Investigation of a Multistage Steam Turbine in Warm-Keeping Operation With Hot Air
Authors: Łuczyński Piotr , Toebben Dennis , Wirsum Manfred , Mohr Wolfgang F. D. , Helbig Klaus
Published: August 2018

In recent decades, the rising share of commonly subsidized renewable energy especially affects the operational strategy of conventional power plants. In pursuit of flexibility improvements, extension of life cycle, in addition to a reduction in start-up time, General Electric has developed a product to warm-keep high/intermediate pressure steam turbines using hot air. In order to optimize the warm-keeping operation and to gain knowledge about the dominant heat transfer phenomena and flow structures, detailed numerical investigations are required. Considering specific warm-keeping operating conditions characterized by high turbulent flows, it is required to conduct calculations based on time-consuming unsteady conjugate heat transfer (CHT) simulations.

In order to investigate the warm-keeping process as found in the presented research, single and multistage numerical turbine models were developed. Furthermore, an innovative calculation approach called the Equalized Timescales Method (ET) was applied for the modeling of unsteady conjugate heat transfer (CHT). The unsteady approach improves the accuracy of the stationary simulations and enables the determination of the multistage turbine models. In the course of the research, two particular input variables of the ET approach — speed up factor (SF) and time step (TS) — have been additionally investigated with regard to their high impact on the calculation time and the quality of the results. Using the ET method, the mass flow rate and the rotational speed were varied to generate a database of warm-keeping operating points.

The main goal of this work is to provide a comprehensive knowledge of the flow field and heat transfer in a wide range of turbine warm-keeping operations and to characterize the flow patterns observed at these operating points. For varying values of flow coefficient and angle of incidence, the secondary flow phenomena change from well-known vortex systems occurring in design operation (such as passage, horseshoe and corner vortices) to effects typical for windage, like patterns of alternating vortices and strong backflows. Furthermore, the identified flow patterns have been compared to vortex systems described in cited literature and summarized in the so-called blade vortex diagram. The comparison of heat transfer in the form of charts showing the variation of the Nusselt-numbers with respect to changes in angle of incidence and flow coefficients at specific operating points is additionally provided.
Detached-Eddy Simulation Applied to the Tip-Clearance Flow in a Last Stage Steam Turbine Blade
Authors: Sun Tianrui , Petrie-Repar Paul , Vogt Damian M.
Published: August 2018

Prediction of the aerodynamic stability of rotor blades at the last stage of steam turbines is of great importance and widely studied. Considering the large span and low natural frequency of these blades, flow at the tip region has a remarkable effect on blade flutter characteristics. However, the transonic tip-clearance flow in these blades has a complex structure of vortices. To obtain a deep understanding of the transonic tip-clearance flow structure in steam turbines, the Detached-Eddy Simulation (DES) is applied in this paper. DES is a hybrid LES/RANS method that activates LES in specified flow regions and applies URANS in other regions of the flow field. As far as we are aware, the tip-clearance flow structure of real-scale last stage steam turbine by high-fidelity numerical method had not been much analyzed in open literature. In this paper, the transonic tip-clearance flow structure in modern last stage of steam turbines is analyzed by both URANS and DES approaches. The open steam turbine model designed by Durham University is chosen as the research model. The flow solver applied is the commercial software ANSYS CFX. From the DES result, the tip leakage vortex and the induced vortices are presented. Based on the comparison between tip-clearance flow structure captured by the two approaches, the URANS method is not able to resolve all induced vortices. Therefore, the distribution of aerodynamic loading on the blade surface is different between URANS and DES results. The present study serves as a basis for investigating the influence of the tip-clearance flow structure on blade aeroelasticity.
Criteria for Best Performance of Pre-Optimized Solid Dampers
Authors: Gastaldi Chiara , Gola Muzio M.
Published: August 2018

This paper furthers recent research by these authors. The starting point is the pre-optimization of solid dampers, which ensures that all dampers bound to misbehave are excluded since the early design stage. The authors now enlarge the scope of their investigations to explore those damper configurations selected inside the admissible design area. The purpose of the paper is to present a set of criteria apt to select a damper configuration which not only avoids unwanted situations, but in addition guarantees high performance under different design conditions.

The analysis starts with the definition of a set of requirements a high performance damper should meet. In detail the present investigation seeks to answer the following questions:

– in the low excitation regime, what is the frequency shift and the stiffening effect each damper can provide?

– for increasing excitation levels, which damper will start slipping sooner?

– in the high excitation regime, which damper provides the maximum dissipation?

Like pre-optimization, it does not involve nonlinear Finite Element calculations, and unlike existing optimization procedures, is not linked to a specific set of blades the damper may be coupled to. The numerical prediction of the blade-damper coupled dynamics is here used only for validation purposes.

The approach on which this paper rests is fully numerical, however real contact parameters are taken from extensive experimental investigations made possible by those purposely developed test rigs which are the distinctive mark of the AERMEC Lab of Politecnico di Torino.
Model Based Diagnostics of AE-T100 Micro Humid Air Turbine Cycle
Authors: Mahmood Mariam , Martini Alessio , Massardo Aristide F. , De Paepe Ward
Published: August 2018

Micro gas turbines (mGT) are emerging power sources for distributed generation facilities with promising features like environment friendliness, high fuel flexibility, cost effectiveness and efficient cogeneration of heat and power (CHP). However, curtailed heat demand during summers reduces the plant operating hours per year and negatively affects the overall economic feasibility of a CHP project. The micro Humid Air Turbine (mHAT) cycle is one of the novel cycles to increase the electrical efficiency of the gas turbine by utilizing the exhaust gas heat in periods of low heat demand, thus avoiding the system shutdown. However, the water injection system can introduce additional pressure losses in the mGT cycle, which may lead to compressor surge and it may also affect the recuperator performance in the long run due to corrosion. Hence, numerical simulation and diagnostic tools are essential for cycle optimization of mHAT and prediction of performance degradation.

This work is focused on the real time application of the AE-T100 model for the mHAT system located at the Vrije Universiteit Brussel (VUB), which is based on the T100 mGT equipped with a spray saturation tower. The AE-T100 model is a steady-state simulation tool for mGT cycles, which has been developed within a collaboration between the University of Genova (Unige) and Ansaldo Energia, and has been successfully applied at the Ansaldo Enegia test rig (AE-T100) for the diagnostic purpose. For this study, the basic AE-T100 model has been modified to simulate the humidified cycle according to the VUB plant configuration. The modified AE-T100 model has been validated against the experimental data obtained from the mHAT unit at nominal and part load.

Once the model was validated using real operating conditions, it has been used for monitoring the recuperator performance over large number of tests in dry mode, conducted over the past five years, as well as initial tests in wet mode, from the VUB-mHAT system. This work has proved the modeling capability of the AE-T100 tool to simulate the mHAT cycle with reasonable accuracy and first diagnostic application of the AE-T100 tool, in dry mode. However, the lack of data available at present in wet mode does not allow to provide a complete and robust diagnostics of this novel cycle under wet operation.

Hence, this preliminary analysis will provide basis for more detail diagnostics of the mHAT cycle using AE-T100 tool, over a longer time period under wet operation, in future.
Simulation and Analysis of Oil Scoop Capture Efficiency
Authors: Yaguo Lyu , Le Jiang , Zhenxia Liu , Jianping Hu
Published: August 2018

Under-race lubrication is the main method for the main shaft bearing of aero-engine which with higher performance. Oil scoop is an important part of the under-race lubrication structure, which plays an important role in capturing oil coming out of a stationary jet nozzle, and the efficiency of oil capture has great influence on the performance of the under-race lubrication. In this paper, a reasonable numerical simulation method is used to calculate a certain radial oil scoop. The velocity distribution of the internal air field in the lubrication structure and the oil distribution of the oil-gas two phase flow field were calculated and the scoop efficiency under different working conditions were calculated. The scoop efficiency under the three oil jet nozzles was verified by the test data. Finally, the influence of the shaft rotation speed, the oil flow rate and the number of the oil nozzles on the scoop efficiency of the radial scoop is analyzed, and the reason of these regularities is analyzed in detail. The result of this study may provide an idea or method for the optimization and improvement of oil scoop with similar structure.
Experimental Investigation on the Flow and Heat Transfer of an Air-Air Primary Surface Heat Exchanger
Authors: Dong Wei , Zhang Shengbao , Guo Zhiqiang , Yu Xiao
Published: August 2018

The primary surface heat exchanger (PSHE) is a kind of small size, light weight, high integration heat exchanger. The characteristics of the complex internal structure, complex flow pattern and the flow interaction have a great influence on the heat transfer of the air-air primary surface heat exchanger. Five cross-corrugated air-air primary surface heat exchangers with different core configurations are designed and fabricated applying additive manufacturing technology. The cross angle θ of upper and lower corrugated plates is 0°, 15°, 30°, 45°, respectively. An experimental investigation on the flow and heat transfer performance is carried out. The comparison of test results of overall heat transfer coefficient and the pressure drop for different primary heat exchangers is presented. The test results show that the pressure drop is significantly increased with the cross angle increasing, and the heat transfer performance does not show the linear increasing with the cross angle increasing.
Numerical Investigation on Single-Restricted Swirling Flows in an Innovative Combustor
Authors: Hu Bin , Zhang JunHua , Deng AiMing , Zhao Wei , Zhao QingJun
Published: August 2018

The size and fuel consumption as well as the pollutant emissions of gas turbine combustors have to be significantly reduced in the future, which brings new challenges to the design of combustors. An innovative gas turbine combustor, named Short Helical Combustor (SHC) has been proposed by B. Ariatabar et al. The major feature of SHC is that the swirling flow originated from a single swirler is only restricted by one side in circumferential direction which is greatly different than traditional combustors. The present work of this paper is to investigate the features of the single-restricted swirling flows in a model SHC by adjusting the axial distance (L) between adjacent swirlers. The relevant results show that, 1. In non-reacting flows, with the increase of L, the flow field downstream the swirler successively presents four modes: traditional mode, single-vortex mode, critical mode and double-vortices mode. When L = 0, a pair of counterrotating vortices exists in combustor. When 0.27H < L < 0.67H, only one vortex exists downstream the swirler. When 0.68H < L < 1.73H, another counter-rotating vortex gradually appears close to the unrestricted side. 2. With the increasing of L, the aerodynamic boundary is gradually formed on the unrestricted side in the reacting and non-reacting flows, which is the primary reason for the formation of vortex B. 3. The specific value of L of critical mode in reacting flows is larger than that in non-reacting flows because the gas expansion caused by combustion goes against the formation of aerodynamic boundary. 4. The velocity direction of the flows downstream the recirculation varies at different vortex modes in reacting and non-reacting flows. In non-reacting flows, the flow direction changes almost 180° as L is increased from 0.27H–1.73H. In reacting flows, the flow direction gradually varies from circumference to axis as L is increased from 0.27H–1.73H. The present work details the feature of the flow field in SHC, which is great meaningful to the design and improvement of the combustor.
Numerical Investigation of a Sweeping Jet Actuator for Active Flow Control in a Compressor Cascade
Authors: Meng Qinghe , Chen Shaowen , Li Weihang , Wang Songtao
Published: August 2018

Sweeping Jet Actuator (SJA) was introduced as a potential active flow control method for reducing three-dimension (3D) flow separations in a compressor cascade. Unlike some other actuators, SJA needs no valves or moving parts to convert its steady compressed air source into sweeping jets that oscillates from side to side through the millimeter-sized outlet nozzle. The rather simple and small structure makes it possible to place SJA into the blades. In this study, a 3D numerical simulation using unsteady RANS codes was conducted to investigate the effects of SJA on the flow pattern and the aerodynamic loss mechanism in a compressor cascade. Firstly, the reliability of a commercial Computational Fluid Dynamic (CFD) code was validated and the computed results showed good agreements with experimental data from the literature. Secondly, some possible affecting factors, such as actuating pressure, position of SJA exit and jet skew angle, were analyzed and discussed in detail. Moreover, the effectiveness of active flow control under different locations and stream directions of SJA was studied for obtaining a further understanding of the mechanism of SJA for controlling flow separations. In addition, the generation and interaction of internal secondary flows in the compressor cascade were also investigated, and the oscillating jet process of SJA was presented. The numerical results indicate that using SJA delays effectively the corner flow separation, thus decreases the aerodynamic loss of the compressor cascade. For the optimum scheme within the present research, the reduction of overall time-averaged total pressure loss coefficient achieves about 5.6% compared with the original case without SJA. The streamwise position of SJA has a more remarkable influence in improving performance than the other SJA schemes. The considerable improvements of flow separation in the corner region is considered to be one of the main reasons in overall performance increase.