bluuebunny/crossref_metadata_2025_split huggingface dataset:
Probabilistic FE-Analysis of Cooled High Pressure Turbine Blades: Part A — Holistic Description of Manufacturing Variability
Authors: Högner Lars , Voigt Matthias , Mailach Ronald , Meyer Marcus , Gerstberger Ulf 
Published: November 2019

Abstract
Modern high pressure turbine (HPT) blade design stands out due to its high complexity comprising three-dimensional blade features, multi-passage cooling system (MPCS) and film cooling to allow for progressive thermodynamic process parameters. During the last decade, probabilistic design approaches have become increasingly important in turbomachinery to incorporate uncertainties such as geometric variations caused by manufacturing scatter and deterioration.
Within this scope, the first part of this two-part paper introduces parametric models for cooled turbine blades that enable probabilistic FE analysis taking geometric variability into account to aim at sensitivity and robustness evaluation. The statistical database is represented by a population of more than 400 blades whose external geometry is captured by optical measurement techniques and 34 blades that are digitized by computed tomography (CT) to record the internal geometry and the associated variability, respectively. Based on this data, parametric models for airfoil, profiled endwall (PEW), wedge surface (WSF) and MPCS are presented.
The parametric airfoil model which is based on traditional profile theory is briefly described. In this regard, a methodology is presented that enables to adapt this airfoil model to a given population of blades by means of Monte-Carlo based optimization. The endwall variability of hub and shroud are parametrized by radial offsets that are applied to the respective median endwall geometry. WSFs are analytically represented by planes. Variations of the MPCS are quantified based on the radial distribution of cooling passage centroids. Thus, an individual MPCS can be replicated by applying adapted displacement functions to the core passage centroids. For each feature that is considered within the present study, the accuracy of the parametric model is discussed with respect to the variability that is present in the investigated blade population and the measurement uncertainty.
Within the scope of the second part of this paper (cf. Högner et al. [1]), the parametric models are used for a comprehensive statistical analysis to reveal the parameter correlation structure and probability density functions (PDFs). This is required for the subsequent probabilistic finite element analysis involving real geometry effects.
Aerothermal Optimization of Turbine Squealer Tip Geometries With Arbitrary Cooling Injection
Authors: De Maesschalck C. , Andreoli V. , Paniagua G. , Gillen T. , Barker B. 
Published: November 2019

Abstract
The optimization of the turbine rotor tip geometry remains a vital opportunity to create more efficient and durable engines. Balancing the aerodynamic and thermal aspects, while maintaining the mechanical integrity is key to reshape one of the most vulnerable and life determining parts of the entire turbine. The ever-increasing turbine gas temperatures, combined with the difficulty of cooling the tip and the aerodynamically penalizing nature of the overtip leakage vortex, makes the design of the tip a truly multi-disciplinary challenge.
While many earlier efforts focused on uncooled geometries, or studied the aerothermal impact with a fixed cooling configuration, the current paper presents the outcome of a multi-objective optimization where both the squealer rim geometry as well as the cooling injection pattern was allowed to vary simultaneously. This study explores a significantly wider design space, seeking a further synergistic aerothermal benefit through the combination of a quasi-fully arbitrary cooling arrangement, with mutating squealer rim structures.
Specifically, the current manuscript presents the results of over 330 cooled and uncooled squealer tip geometries. The high pressure turbine tip was automatically altered using a novel parametrization strategy adopting a maximum of 40 design variables to vary the squealer rim structures, as well as the size and location of the various cooling holes. The aerodynamic and thermal characteristics of every design were evaluated through Reynolds-Averaged Navier-Stokes CFD simulations with the k-ω SST model for the turbulence closure, adopting an unstructured hexahedral grid typically containing more than 8 million cells. A multi-objective differential evolution algorithm was used to obtain a Pareto front of designs which maximize the aerodynamic efficiency, while minimizing the overtip thermal loads. Eventually, a detailed investigation and robustness study was performed on a set of prime squealer geometries, to further investigate the aerodynamic flow topology, and the effect of various cooling injection schemes on the heat transfer patterns.
Development and Validation of a Hybrid Simulation Model for Darrieus Vertical-Axis Wind Turbines
Authors: Bianchini Alessandro , Balduzzi Francesco , Haack Leopold , Bigalli Simone , Müller Bernhard , Ferrara Giovanni 
Published: November 2019

Abstract
The increasing interest in deep-water floating applications and in wind turbine installations in turbulent flows, is putting vertical-axis wind turbines back again in research agendas. However, due to the lack of activities in past years, the accuracy and robustness of available design tools is much lower than the corresponding ones for horizontal-axis rotors.
Moving from this background, the study presents the development of a hybrid simulation model able to simulate H-type Darrieus turbines with low computational effort and an accuracy higher than that of conventional low-fidelity models. It is based on the coupling of unsteady RANS CFD with the Actuator Line theory to replace the airfoils. The present tool has been implemented within the commercial solver ANSYS® FLUENT® and it is then of practical interest for a large number of potential users. With respect to other examples in the literature, the present approach includes some new findings in the correct manipulation of airfoil polars that notably increased its accuracy. The validation of the model is assessed by means of two different study cases featuring a simplified 1-blade rotor and a real 3-blade turbine, for which both detailed CFD simulations and experiments were available. The model was able to produce accurate results — both in terms of aggregate power production and of flow field description — for turbines with a medium-low chord-to-radius ratio and the tipspeed ratios typical of turbine operation.
Profile Loss of Ultra-Highly Loaded Turbine Cascade at Transonic Flow Condition
Authors: Tsujita Hoshio , Kaneko Masanao 
Published: November 2019

Abstract
The aerodynamic performance of turbine components constituting the gas turbine engine is seriously required to be improved in order to reduce environmental load. The energy recovery efficiency in turbine component can be enhanced by the increase of turbine blade loading. In this study, as the first stage to investigate the aerodynamic performance of an ultra-highly loaded turbine cascade (UHLTC) with a turning angle of 160 degrees at transonic flow regime, two-dimensional steady compressible flows in UHLTC were analyzed numerically by using a commercial CFD code to focus on the profile loss. In the computations, the isentropic exit Mach number was varied in the wide range from 0.3 to 1.8 in order to examine the effects of exit Mach number on the shock wave formation and the associated profile loss generation. The computed results were examined in detail by comparing with those for a typical transonic turbine cascade. The detailed examination for the present computed results clarified the variation of shock pattern with the increase of exit Mach number and the loss “plateau” behavior in the present UHLTC.
Finite Element Transient Modelling for Aero-Thermo-Mechanical Analysis of Whole Gas Turbine Engine
Authors: Giuntini Sabrina , Andreini Antonio , Facchini Bruno 
Published: November 2019

Abstract
It is here proposed a numerical procedure aimed to perform transient aero-thermo-mechanical calculations of large power generation gas turbines.
Due to the frequent startups and shutdowns that nowadays these engines encounter, procedures for multi-physics simulations have to take into account the complex coupled interactions related to inertial and thermal loads, and seal running clearances. In order to develop suitable secondary air system configurations, guarantee structural integrity and maintain actual clearances and temperature peaks in pre-established ranges, the overall complexity of the structure has to be reproduced with a whole engine modelling approach, simulating the entire machine in the real operating conditions.
In the proposed methodology the aerodynamic solution providing mass flows and pressures, and the thermo-mechanical analysis returning temperatures and material expansion, are performed separately. The procedure faces the aero-thermo-mechanical problem with an iterative process with the aim of taking into account the complex aero-thermo-mechanical interactions actually characterizing a real engine, in a robust and modular tool, combining secondary air system, thermal and mechanical analysis. The heat conduction in the solid and the fluid-solid heat transfer are computed by a customized version of the open source FEM solver CalculiX®. The secondary air system is modelled by a customized version of the embedded CalculiX® one-dimensional fluid network solver.
In order to assess the physical coherence of the presented methodology the procedure has been applied to a test case representative of a portion of a real engine geometry, tested in a thermal transient cycle for the assessment of the interaction between secondary air system properties and geometry deformations.
Numerical and Experimental Aerodynamic Investigation of a Low Pressure Steam Turbine Module
Authors: Bellucci Juri , Peruzzi Lorenzo , Arnone Andrea , Arcangeli Lorenzo , Maceli Nicola 
Published: November 2019

Abstract
This work aims to deepen the understanding of the aerodynamic behavior and the performance of a low pressure steam turbine module. Numerical and experimental results obtained on a three-stage low pressure steam turbine (LPT) module are presented. The selected geometry is representative of the state-of-the-art of low pressure sections for small steam turbines. The test vehicle was designed and operated in different operating conditions with dry and wet steam. Different types of measurements are performed for the global performance estimation of the whole turbine and for the detailed analysis of the flow field. Steady and unsteady CFD analyses have been performed by means of viscous, three-dimensional simulations adopting a real gas, equilibrium steam model. Measured inlet/outlet boundary conditions are used for the computations. The fidelity of the computational setup is proven by comparing computational and experimental results. Main performance curves and span-wise distributions show a good agreement in terms of both shape of curves/distributions and absolute values. Finally, an attempt is done to point out where losses are generated and the physical mechanisms involved are investigated and discussed in details.
Assessment of an Enhanced Thin Film Model to Capture Wetting and Drying Behavior in an Aero-Engine Bearing Chamber
Authors: Singh Kuldeep , Sharabi Medhat , Ambrose Stephen , Eastwick Carol , Jefferson-Loveday Richard , Cao Jing , Jacobs Adrian 
Published: November 2019

Abstract
In the present work, a wetting and drying model is coupled with Eulerian Thin-Film model (ETFM) to analyze the wetting and drying behavior inside the bearing chamber. In the enhanced model, an additional source term is included to account for the contact angle effect. These models were coupled with volume-of-fluid (VOF) such that the core region is resolved by VOF and region close to the chamber walls, where a thin film is expected is resolved by either ETFM or enhanced ETFM model. Numerical studies are conducted for a shaft speed of 5,000 rpm, lubricant and air flow rates of 100 1/hr and 10 g/s respectively, at a scavenging ratio of 4. In the case of enhanced ETFM model lubricant to surface contact angle was varied from 10° to 45°. The performance of enhanced ETFM model is evaluated to capture drying and wetting behavior on a flat plate and found to be satisfactory. Film thickness prediction of enhanced ETFM model is found to be comparable with the VOF predictions reported in the literature. The effect of contact angle on the spreading of oil and film thickness is found to be small for the investigated conditions on an aero-engine bearing chamber.
Predicting the Operability of Damaged Compressors Using Machine Learning
Authors: Taylor J. V. , Conduit B. , Dickens A. , Hall C. , Hillel M. , Miller R. J. 
Published: November 2019

Abstract
The application of machine learning to aerospace problems faces a particular challenge. For successful learning a large amount of good quality training data is required, typically tens of thousands of cases. However, due to the time and cost of experimental aerospace testing, this data is scarce. This paper shows that successful learning is possible with two novel techniques: The first technique is rapid testing. Over the last five years the Whittle Laboratory has developed a capability where rebuild and test times of a compressor stage now take 15 minutes instead of weeks. The second technique is to base machine learning on physical parameters, derived from engineering wisdom developed in industry over many decades.
The method is applied to the important industry problem of predicting the effect of blade damage on compressor operability. The current approach has high uncertainty, it is based on human judgement and correlation of a handful of experimental test cases. It is shown using 100 training cases and 25 test cases that the new method is able to predict the operability of damaged compressor stages with an accuracy of 2% in a 95% confidence interval; far better than is possible by even the most experienced compressor designers. Use of the method is also shown to generate new physical understanding, previously unknown by any of the experts involved in this work. Using this method in the future offers an exciting opportunity to generate understanding of previously intractable problems in aerospace.
Prediction of Rotating Stall During Startup for Axial Compressors
Authors: Mito Ryosuke , Yamashita Satoshi 
Published: November 2019

Abstract
In a compressor used for power generation, a rotating stall due to an operating point mismatch between the front and rear stages occurs at front stages in low-speed condition during startup. IGV, VSV opening schedule and bleed flow rates are determined in order to obtain stable operating conditions, with the occurrence of pressure fluctuations or blade excitation force derived from the rotating stall.
The setting of the number of stages for variable stator vane, the vane opening and the bleed flow rate are largely based on the rig test and experience of the actual machine, however we focused on the capability study for direct simulation with unsteady CFD for the rotating stall. If this can be predicted in advance, it makes it possible to reduce the number of stages of the variable stator vanes, the capacity of the thyristor, and to make the bleed chambers and piping compact, leading to cost reductions.
The method of rotating stall prediction during startup condition, and the comparison between predicted and actual measurements on how this number changes with different starting conditions and different machines, are shown in this paper. CFD shows the different stall cell position, the number of stall cells and the pressure fluctuation level in each condition, and these results were consistent with the measurement data. Furthermore, we have found that these phenomena can be controlled by variable stator vane angle during start up.
Experimental and Numerical Investigation of Small Scale Tesla Turbines
Authors: Renuke Avinash , Vannoni Alberto , Pascenti Matteo , Traverso Alberto 
Published: November 2019

Abstract
Interest in small scale turbines is growing mainly for small scale power generation and energy harvesting. Conventional bladed turbines impose manufacturing limitations and higher cost, which hinder their implementation at small scale. This paper focuses on experimental and numerical performance investigation of Tesla type turbines for micro power generation. A flexible test rig for Tesla turbine fed with air as working fluid has been developed, of about 100W net mechanical power, with modular design of two convergent-divergent nozzles to get subsonic as well as supersonic flow at the exit. Seals are incorporated at the end disks to minimize leakage flow. Extensive experiments are done by varying design parameters such as disk thickness, gap between disks, radius ratio and outlet area of exhaust with speeds ranging from 10000 rpm to 40000 rpm. A quasi-1D model of the whole setup is created and tuned with experimental data to capture the overall performance. Major losses, ventilation losses at end disks, nozzle and exhaust losses are evaluated experimentally and numerically. Effect of design parameters on the performance of Tesla turbines is discussed.
Evaluating Splitter Blade Designs to Avoid Impeller Failure in a High-Speed Unshrouded Centrifugal Compressor
Authors: Curtin Alex , Berdanier Reid A. , Kunz Robert F. , Jonson Michael L. 
Published: November 2019

Abstract
This study investigates splitter blade failures experienced during testing of an unshrouded transonic centrifugal compressor. Specifically, when the impeller was deeply throttled using an upstream inlet guide vane to introduce significant pre-swirl, the splitter blades exhibited cracking near the root of the leading edge. The observed failures are of particular interest because the impeller does not exhibit a mode shape typical of this type of failure corresponding to either the upstream IGV or downstream diffuser vane count, nor the anticipated surge frequencies. Accordingly, modal analysis and CFD modeling were performed leading to an understanding of the failure mechanism, and a successful splitter blade cut-back solution was implemented. Specifically, excitation sources developed from a CFD model of the IGV and impeller were used in a blade flutter calculation, in order to determine the aerodynamic damping and unsteady loading on the blade. The CFD model indicates that shockwaves arise near the splitter leading edge for this off-design condition. Due to interactions with the high incidence/separated boundary layer, these shockwaves exhibit streamwise unsteadiness, thereby leading to the observed failure mechanisms. It was determined that by cutting back the splitter blade at the leading edge, the failure could be avoided while minimally affecting the overall stage performance.
Study on Effect of Axial Overlap on Tip Leakage Flow Structure in Tandem Bladed Low Speed Axial Flow Compressor
Authors: Singh Ajey , Mistry Chetan S. 
Published: November 2019

Abstract
This paper discusses the effect of axial overlap on tip leakage flow behavior in a low speed tandem bladed axial compressor. Tandem bladed axial flow compressors provide an efficient way of obtaining a higher pressure rise with minimum number of stages as compared to a conventional design. The single stage tandem rotor compressor is designed to achieve a stage loading coefficient of 1.04 and flow coefficient of 0.9. A tip clearance of 3% (of span) is provided for the current study and it is maintained constant for all axial overlap configuration studies. A computational study of the designed stage was performed to investigate the behavior of tip leakage flow with different axial overlap and its effect on the overall performance of the stage. The application of tandem blading is only justified by prescribing high aerodynamic loading on both blades which increases the concern for associated tip leakage and corner separation losses. The study reveals the interaction of tip leakage flow from the fore and aft blade with the end wall flow and its influence on the main stream flow. The presence of an aft blade behind the fore seeks additional caution for optimum management of tip leakage flow. The leakage flows from the individual blades tend to roll up along with the shroud boundary layer resulting in the formation of momentum deficit fluid in the flow passage and at exit of rotors. The penetration of momentum deficit fluid in the main stream flow is directly related to the leakage flow structure from the fore and aft blade and also their interaction with the end wall flow. The axial overlap is seen to influence the leakage flow structure in two different ways. Firstly, it is observed that the initiation of tip leakage vortex of aft blade shifts from 30% to 10% of chord measured from leading edge, as axial overlap varies from 5% to −5% of chord in the tip region respectively. Secondly, a change in axial overlap also causes a change in passage geometry of the tandem blade interaction zone which has a first order influence on the mass flow rate through it. The accelerated flow through the passage geometry sustains high loading on the aft blade. It can also be utilized for mitigating the low momentum incoming fluid resulting from the mixing of tip leakage and end wall flow. The appropriate realization of these two effects has a potential to minimize the losses occurring due to tip leakage flow in the tandem compressor rotor and to achieve the benefit of higher loading with minimum number of stages.
Evaluating the Aerodynamic Impact of Circumferentially Grooved Fan Casing Treatments With Integrated Acoustic Liners on a Turbofan Rotor
Authors: Bozak Richard F. , Podboy Gary G. 
Published: November 2019

Abstract
NASA is investigating the potential of integrating acoustic liners into fan cases to reduce fan noise, while maintaining the fans aerodynamic performance. An experiment was conducted to quantify the aerodynamic impact of circumferentially grooved fan cases with integrated acoustic liners on a 1.5 pressure ratio turbofan rotor. In order to improve the ability to measure small performance changes, fan performance calculations were updated to include real gas effects including the effect of humidity. For all fan cases tested, the measured difference in fan isentropic efficiency was found to be less than the measurement repeatability for a torque-based efficiency calculation (≈ 0.2%), however, an unintended tip clearance difference between configurations makes it difficult to determine if circumferentially grooved fan cases degraded fan performance. Fan exit turbulence measurements showed a 1.5% reduction in total turbulence intensity between hardwall and circumferentially grooved fan cases in the tip vortex region, which is attributed to a disruption in the formation of the tip leakage vortex. This decrease in fan exit turbulence could potentially lead to a 1–2dB reduction in broadband rotor-stator interaction noise. Reduced aerodynamic performance losses associated with over-the-rotor liners could enable further fan noise reduction.