bluuebunny/crossref_metadata_2025 huggingface dataset:
The Preliminary CFD Design of a Compressor and Combustor System Towards a 100 kW Hydrogen Fuelled Micro Gas Turbine
Authors: Devriese C. , Pennings W. , de Reuver H. , Bastiaans R. , De Paepe W.
Published: November 2019

Within the context of an ever-increasing share of wind, solar and emerging tidal power, the need to store energy, not only on the short term, but also in the medium to long-term to balance out the power grid will become more important in the near future. One of the most promising routes for this mid- to long term storage, is to produce hydrogen through electrolysis using excess electricity and store it. Instead of using this hydrogen then to generate electricity in a conventional, large, power plant, a more efficient route is to use it in a Decentralised Energy System (DES) using micro Gas Turbines (mGTs). Although the mGT presents itself as a promising option to convert pure hydrogen into electricity in this DES framework, several challenges, linked to the necessary increase of Turbine Inlet Temperature (TIT) for efficiency increase to make the unit compatible and the use of pure hydrogen in the combustor, still need to be overcome. In this paper we present the first steps towards a fully hydrogen fuelled mGT. Firstly, a full thermodynamic cycle analysis was performed to determine the optimal operating parameters, such as compressor pressure ratio and mass flow rate, air-to-fuel ratio and TIT. Secondly, a full CFD design and optimisation of the compressor and the combustion chamber was performed (steady and transient RANS and LES). CFD simulations of the compressor and combustion chamber matched the 1D performance calculations and also reached the desired performance goals. This CFD supported validation of the component performance shows that the design of a pure hydrogen combustion chamber for mGT applications is possible.
A Pneumatic Probe for Measuring Spatial Derivatives of Stagnation Pressure
Authors: Clark C. J. , Grimshaw S. D.
Published: November 2019

This paper introduces a pneumatic 9-hole probe which can measure flow angles, stagnation and static pressures, and spatial derivatives of stagnation pressure. It does this through direct measurement at a single location, rather than empirical corrections using measurements at multiple points.

The new design resembles a 5-hole probe with 4 additional holes positioned around the side of the probe head. This arrangement enables the probe to distinguish between flows with stagnation pressure gradient and flows at an angle. Mapping between the inputs, the probe hole pressures, and outputs, the calibration reference measurements, is achieved with a trained neural network which takes the place of a conventional calibration map.

Measurements of an unknown wake are performed in a calibration tunnel. The 9-hole probe data is compared with measured reference data and a “conventional” analysis of the 5 forward facing holes. The 5-hole probe analysis results in a maximum yaw angle error of 8.4°, while the 9-hole probe matches the reference to within 0.8°. Mass-averaged stagnation pressure and kinetic energy loss coefficients, evaluated with the 5-hole probe analysis, result in errors of +2.8% and −48% respectively, while the 9-hole probe gives +0.5% and −4.5%.

The new probe is used to perform an area traverse of an inlet guide vane in a research compressor. The 5-hole probe analysis gives a ±5.5° variation in yaw angle across the wake and this reduces to ±1.0° when the 9-hole probe is used. Measurement of stagnation pressure gradient and curvature, based on single point measurements, is also demonstrated.
Using Machine Learning to Predict Core Sizes of High-Efficiency Turbofan Engines
Authors: Tong Michael T.
Published: November 2019

With the rise in big data and analytics, machine learning is transforming many industries. It is being increasingly employed to solve a wide range of complex problems, producing autonomous systems that support human decision-making. For the aircraft engine industry, machine learning of historical and existing engine data could provide insights that help drive for better engine design. This work explored the application of machine learning to engine preliminary design. Engine core-size prediction was chosen for the first study because of its relative simplicity in terms of number of input variables required (only three). Specifically, machine-learning predictive tools were developed for turbofan engine core-size prediction, using publicly available data of two hundred manufactured engines and engines that were studied previously in NASA aeronautics projects. The prediction results of these models show that, by bringing together big data, robust machine-learning algorithms and automation, a machine learning-based predictive model can be an effective tool for turbofan engine core-size prediction. The promising results of this first study paves the way for further exploration of the use of machine learning for aircraft engine preliminary design.
Enhancement of Film Cooling Effectiveness Using Dean Vortices
Authors: Chen Pingting , Wang Lang , Li Xueying , Ren Jing , Jiang Hongde , Simon Terrence
Published: November 2019

Film cooling technology is widely used in gas turbines. Improvement of gas turbine thermal efficiency, specific power and specific thrust can be achieved by reducing the use of cooling air by improvements on film cooling technology. Experimental and numerical efforts have demonstrated that cooling effectiveness is reduced when kidney vortices created as the emerging film cooling jet flow interacts with the passage flow resulting in coolant lift-off and mixing. With higher blowing ratios, M, these kidney vortices become stronger and effectiveness worsens. Different technologies have been developed to enhance film cooling effectiveness by manipulating the kidney vortices. Some reduce local blowing ratios and local injection angles with expanded hole exits, called shaped holes. Others are employing hole geometries in an attempt to establish anti-kidney vortices in the flow field to weaken the effects of kidney vortices. Most of these film cooling technologies focus on methods that are within the present limits of manufacturing technology. However, with the additive manufacturing anticipated in the future, there will be more freedom in film cooling hole design. Exploiting this freedom, the present authors tried using curved holes to generate Dean vortices within the delivery line. These vortices have opposite direction of rotation to the vorticity of the kidney vortices and, thus, there is interaction between these vortices in the mixing region. It is shown that as a result of the inclusion of Dean vortices, the curved hole delivery leads to enhanced film cooling effectiveness.

Numerical results, including film cooling effectiveness values, tracking of vortices in the flow field, heat transfer coefficients, and net heat flux reduction are compared between the curved hole (CH), round hole (RH) and a laidback, fan-shaped hole (SH) with blowing ratios, M, of 0.5, 1.0, 1.5, 2.0 and 2.5. The laidback, fan-shaped hole represents the state of the art in film cooling hole design. Another curved hole (RCH) with the opposite (to the CH hole) curvature of delivery line is checked for comparison, with M = 1.5. The comparison shows that film cooling effectiveness values with the CH curved hole are higher than those with cylindrical film cooling holes at every blowing ratio studied. The curved hole has lower film cooling effectiveness values than the laidback, fan-shaped holes when M = 0.5 and 1.0, but shows advantages when the blowing ratio is higher than 1.0. With the interaction between Dean vortices and kidney vortices when using curved holes, a large amount of coolant re-attaches to the wall after moving streamwise for some distance, providing improved downstream film cooling performance. There is heat transfer enhancement for the curved hole case due to a higher kinetic energy transferred to the near-wall region, however. Nevertheless, the curved hole still displays a higher net heat flux reduction (NHFR) when the blowing ratio is high.
Implementation of Adaptive Gaussian Quadrature for Improved Accuracy of Boundary Element Methods Applied to Three Dimensional Geometries
Authors: Davies Michael , Saverin Joseph
Published: November 2019

An adaptive Gaussian quadrature method for characterizing flow over three dimensional bodies via a boundary element method using isoparametric quadrilateral elements with non-constant source and dipole strengths has been developed and tested. This method is compared to state-of-the-art methods: flat elements with constant strengths, flat elements with bilinear strengths, and twisted elements with constant dipole strengths. As such, an overview of current boundary element methods is provided.

The method developed here for twisted elements with non-constant source and dipole strengths is advantageous in that it both better approximates the actual geometry of the surface and the distribution of the dipole and source strengths. The majority of current methods are lacking at least one of these attributes.

The developed method has been validated by comparison to two known analytical solutions: a non-lifting ellipsoid and a Kármán-Trefftz airfoil. The flexible and robust procedure presented here results in improved accuracy of the solution to the Laplace equation around three dimensional bodies.
Second Law Analysis of an Energy Storage System Consisting of an Electrolysis Plant and the Graz Cycle With Internal H2/O2 Combustion
Authors: Dybe Simeon , Tanneberger Tom , Stathopoulos Panagiotis
Published: November 2019

The expansion of renewable energy generation must go hand in hand with measures for reliable energy supply and energy storage. A combination of hydrogen and oxygen as storing media provided from electrolysis at high pressure and zero emission power plants is a very promising option. The Graz cycle is an oxy-fuel combined power cycle that can operate with internal H2/O2 combustion and steam as working fluid. It offers thermal efficiencies up to 68.5% (LHV). This work applies a second law analysis to the Graz cycle and determines its exergetic efficiency. Exergy destruction is broken down to the cycle’s components thus providing insights on the location and magnitude of the cycle’s inefficiencies. A sensitivity analysis identifies the cycle’s exergetic and energetic efficiency as a function of representative parameters, offering an approach for future improvements. The combination of the cycle with an electrolysis plant is subsequently analyzed as an electric energy storage system. The round trip efficiency of the storage and back conversion system is computed by taking into account the additional compression of the reactants. As part of this analysis, the effect of the electrolyzer’s operational pressure is studied by comparing several commercial electrolyzers.
Experimental Evaluation of Heat Transfer in a High Temperature High Pressure Test Facility
Authors: Ramesh S. , Robey E. , Straub D. , Black J.
Published: November 2019

Performance of film cooling holes is generally evaluated near ambient conditions, so scaling the film cooling performance from ambient to engine conditions is important. These performance metrics can be reported in terms of net heat flux reduction, heat transfer enhancement, and effectiveness. There are several challenges and penalties in conducting experiments on a real engine or even on a stationary flat plate test article at near engine conditions. In this study, an experimental methodology capable of delivering film cooling performance for the experiments conducted in the high-temperature high-pressure test facility at NETL will be explored. More specifically, this study focuses on various challenges that are present and how these concerns are addressed to evaluate the heat transfer coefficient on the test article. Steady state experiments were conducted on a flat plate test article whose surface temperature distribution was obtained using an IR camera calibrated with a combination of bench top experiments and in-situ calibrations based on embedded thermocouple measurements. A detailed radiation analysis is conducted to enable differentiation of heat transfer by convection from heat transfer by radiation. The estimated surface heat flux and heat transfer coefficient were found to be higher than the one obtained from flat plate correlation.
Demonstration of a Dynamic Clearance Seal in a Rotating Steam Test Facility
Authors: Messenger Andrew , Williams Richard , Ingram Grant , Hogg Simon , Reggentin Philip
Published: November 2019

This paper reports on the latest phase of the development of a new rotating machinery sealing technology, which was a successful seal test in a high temperature steam test facility at TU Brauschweig in Germany.

The “Aerostatic Seal” is a dynamic clearance seal that is capable of maintaining very small clearances with a rotor and has the potential for a wide range of rotating machinery applications. It has been developed in recent years at Durham University, UK, in collaboration with a major OEM, with a focus on steam turbine sealing, and has previously been reported on in a number of ASME Turbo Expo papers. Previous work has reported on the design tool, and two air test facilities; testing in steam addressed the effect of high temperature components and the working fluid, and was an opportunity to verify the design system.

The seal is a development of a retractable gland seal and so in a low load condition it is retracted from the rotor with a large rotor clearance and then when the pressure ratio is sufficient moves to an operational small clearance. At its operational clearance the seal is capable of moving with rotor vibrations which means the design clearance can be smaller than any expected rotor movement. The benefits include a significant reduction in leakage when compared to conventional sealing technologies and also the ability to react to large transients or thermal growths caused by rapid changes in machine loads and speeds. The seal is shown to operate well in this environment and this work moves the technology closer to deployment in industry.
On the Effect of Inflow Disturbances on the Flow Past a Linear LPT Vane Using Spectral/hp Element Methods
Authors: Cassinelli Andrea , Xu Hui , Montomoli Francesco , Adami Paolo , Vazquez Diaz Raul , Sherwin Spencer J.
Published: November 2019

The recent development and increasing integration of high performance computing, scale resolving CFD and high order unstructured methods offers a potential opportunity to deliver a simulation-based capability (i.e. virtual) for aerodynamic research, analysis and design of industrial relevant problems in the near future. In particular, the tendency towards high order spectral/hp element methods is motivated by their desirable dispersion-diffusion properties, that are combined to accuracy and flexibility for complex geometries. Previous work from the Authors focused on developing guidelines for the use of these methods as a virtual cascade for turbomachinery applications. Building on such experiments, the present contribution analyzes the performance of a representative industrial cascade at moderate Reynolds number with various levels and types of inflow disturbances, adopting the incompressible Navier-Stokes solver implemented in the Nektar++ software framework. The introduction of a steady/unsteady spanwise-nonuniform momentum forcing in the leading edge region was tested, to break the flow symmetry upstream of the blade and investigate the change in transition mechanism in the aft portion of the suction surface. To provide a systematic synthetic turbulence generation tool, a parallelised version of Davidson’s method is incorporated and applied for the first time in the software framework to a low pressure turbine vane. The clean results of the cascade are compared to various levels of momentum forcing and inflow turbulence, looking at blade wall distributions, wake profiles and boundary layer parameters. Low levels of background disturbances are found to improve the agreement with experimental data. The results support the confidence for using high order spectral methods as a standalone performance analysis tool but, at the same time, underline the sensitivity at these flow regimes to disturbances or instabilities in the real environment when comparing to rig data.
A Design for Fouling Oriented Optimization of an HPT Nozzle
Authors: Friso R. , Casari N. , Suman A. , Pinelli M. , Montomoli Francesco
Published: November 2019

Fouling and erosion are two problems that severely affect gas turbines. The shape of the blade, its roughness, and its structural stability can vary as a consequence of these phenomena. The outcomes of this occurrence can span from the efficiency reduction to the engine shut down according to the nature of the material ingested, to the concentration of contaminants in the air, the cleanliness of fuel and to the particular design of the machine.

In this work, an axial turbine airfoil is modified according to the requirement of less sensibility to the phenomena above mentioned, utilizing an automatic optimization algorithm. An artificial neural network surrogate approach is used for searching the optimal shape, minimizing the computational cost of the entire process. The optimum design of the blade is therefore achieved, in order to reduce the effects of deposition on the performance.

The methodology here proposed is fully general and it is applied to an HPT nozzle in the present analysis.
An Experimental Study of Passage-to-Passage Flow Interactions in a Single Stage Axial Flow Research Turbine Rotor
Authors: Andichamy Veerandra C. , Camci Cengiz , Kim Yong W.
Published: November 2019

During the lifetime of a turbine stage, some of the blade tips may undergo changes due to mechanical rubbing with casing surface and also due to thermal oxidation. Understanding the effect these damaged blades have over the undamaged blades is essential to estimate the performance of the turbine stage in the operable tip clearance range. In this paper, the passage to passage aerodynamic interaction in a turbine stage is studied by modifying the tip gap of selected turbine blades and analyzing their effect on the neighboring blade passage flows. The experiments in this study are carried out in a single-stage low-speed axial turbine facility. All measurements are taken in the stationary frame of reference using a time-accurate differential dynamic pressure transducer mounted in a Kiel probe head. The experimental results from this study show that even with a significant increase on a selected blade’s tip clearance, its effect on the AFTRF turbine flow is only confined to its neighboring blade passage. The disturbances due to the altered tip clearance of one passage are not measurably propagated to its neighboring turbine passages. The changes made in one of the blades in a turbine stage do not significantly alter the aerodynamic performance of other blades. This result is particularly important for large-scale turbine research rigs such as AFTRF where the unsteady total pressure field is mapped in a time-efficient and phase-locked manner.
Innovative Mechanical Integrity Approaches for Steam Turbines: Industrial Needs
Authors: Almstedt Henning , Yiğit-Rohde Zeynep , Havemann Jürgen , Thiemann Thomas , Stadler Martin
Published: November 2019

The increased installation of renewable energy resources results in a requirement for higher steam turbine cycling capabilities. In addition, there is a strong demand to save our environment by improved efficiency, as well as acceptable life-cycle costs whilst keeping a high level of reliability and availability. Optimization using state of the art deterministic methods for dimensioning of components is the traditional way addressing such challenges. The use of more advanced methods like fracture mechanics, assisted by probabilistic design are innovative alternatives that have been pushed significantly in recent years.

However, to fully exploit the latest developments of advanced engineering methods, acceptance criteria are essential. Due to the lack of specific steam-turbine standards for several calculation tasks, today acceptance criteria are often based on OEM internal standards and are part of the specific OEM know-how.

New methods require the definition or modification of existing acceptance criteria. In case of lack of acceptance criteria one option is to refer to available standards for industries dealing with comparable components, materials and loading conditions. An example is the adaption of acceptance criteria from pressure-vessel codes for high-pressure steam turbine components. The obvious advantage is the ease of use, but the drawback might be an unnecessary conservatism in the design. Another option is the development of acceptance criteria for advanced methods.

The main intent of the paper is to contribute to the discussion of acceptance criteria for the application of advanced design methods for steam turbine components. A selected steam-turbine example is discussed, acceptance criteria are compared with available standards and the need for the development of component specific criteria are highlighted.
Theoretical and Experimental Investigation on Rotor Dynamic Behavior of Bladeless Turbine for Innovative Cycles
Authors: Silvestri Paolo , Traverso Alberto , Reggio Federico , Efstathiadis Theofilos
Published: November 2019

This paper focuses on rotor dynamic investigation of a bladeless turbine, or Tesla turbine, for application to innovative small scale cycles. Tesla rotor consists of a shaft with several co-rotating disks with small gaps between each other. The flow through the disks creates a momentum exchange by viscous effect, motoring the shaft.

Thanks to its simplicity and low cost, the Tesla expander is attractive for energy harvesting and waste heat recovery from low/medium temperature in small and micro scale applications. Rotor assembly and its parts may present dynamic criticalities, due to their structural characteristics: to predict and ensure low vibrations during operations, numerical and experimental studies have been carried out on some prototypes.

The activity started considering a non-rotating single Tesla disk both in free and real constrained configuration: an experimental modal analysis was performed, whose results were used to validate a disk numerical model. In this case, an analytical approach with a simplified geometry assumption was considered. All methods results were correlated each other and discrepancies have been identified and analysed.

Furthermore, the investigation of a single disk rotor vibrational behaviour has been extended from static conditions to rotating conditions. Numerical analysis has been carried on taking into account the effect of gyroscopic couples and centrifugal field generated by disk rotation. In parallel, a corresponding experimental activity has been done using a dedicated test rig which allowed to perform vibrational operational measurement while the disk was in motion. Campbell diagram of the single rotating disk on the shaft has been obtained from numerical and experimental analysis allowing to identify system dynamic behaviour and to deepen aspects related to critical speeds.

Finally, a whole rotor model has been developed, allowing the characterization of the dynamic behaviour of a fully assembled turbine rotor. The developed models, validated with experiments, are powerful tools that can predict the bladeless expander vibrational behaviour at the early phase of design.
A Reliable Pre-Processing for the Simulation of Friction Joints in Turbomachineries and its Validation: A Case Study With Policontact
Authors: Firrone Christian M. , Battiato Giuseppe
Published: November 2019

Industry and University collaborates to develop methods to simulate the nonlinear dynamics of components in rotating assemblies like turbine or compressor modules in the presence of friction joints. This collaboration produced fruitful results providing a family of numerical solvers with the goal of foreseeing the safety margins against High Cycle Fatigue failure. Softwares are therefore intended as design tools to exploit the damping effect of joints by controlling geometrical features, materials and contact loads. Contact models, reduction techniques to handle complex blade geometries modeled by Finite Element softwares, and numerical techniques to solve the nonlinear equations of motion are refined to provide the level of vibration amplitude as fast as possible by keeping the representativeness of the physical phenomena that are involved.

A reliable compromise between speed and accuracy must be confirmed by several ‘gates’ to pass through during all the simulation process, in particular during pre-processing phase.

The objective of this paper is to propose a good practice made of a list of actions to check the goodness of the mathematical basis to obtain reliable results from simulation.

Experience gained thanks to the long-lasting collaboration between Politecnico di Torino and GE Avio for the development of the software Policontact provides a case study of an effective synthesis between two requirements that are often opposed to each other: complex mathematical models to simulate the nonlinear forced response of rotating components on one side and a robust, confident implementation of an easy-to-use tool intended for industrial staff with complementary background on the other side.
Multi-Fidelity Global-Local Optimization of a Transonic Compressor Rotor
Authors: Mondal Sudeepta , Joly Michael M. , Sarkar Soumalya
Published: November 2019

In aerodynamic design, accurate and robust surrogate models are important to accelerate computationally expensive CFD-based optimization. Machine learning techniques can also enable affordable exploration of high-dimensional design spaces with targeted selection of sparse high-fidelity data. In this paper, a multi-fidelity global-local approach is presented and applied to the surrogate-based design optimization of a highly-loaded transonic compressor rotor. The key idea is to train multi-fidelity surrogates with fewer high-fidelity RANS predictions and more rapid and inexpensive lower-fidelity RANS evaluations. The framework also introduces a global-local search algorithm that can spin-off multiple local optimization threads over narrow and targeted design spaces, concurrently to a constantly adapting global optimization thread. The approach is demonstrated with an optimization of the transonic NASA rotor 37, yielding significant increase in performance within a dozen of optimization iterations.
Characterization of an Additively Repaired Ti-6Al-4V Alloy
Authors: Gyekenyesi Andrew L. , Shrestha Sulochana , Kannan Manigandan , Morscher Gregory , Scott-Emuakpor Onome E.
Published: November 2019

A major disadvantage regarding integrally bladed rotors (IBRs: also referred to as blisks) is the ability to repair damage. Since it is a single part, anything beyond a minor dent requires full removal and either an expensive replacement or a complicated repair. Repair approaches gaining attention include additive metal build-up techniques such as blown powder directed energy deposition (DED). As a start and to attain confidence in such repairs, the characterization of additively modified specimens is required. The work presented here involved the tensile and fatigue testing of stock, annealed Ti-6Al-4V and DED repaired specimens. Thin, dog-bone standard test coupons, consisting of half stock material and half additively manufactured (AM) material with a bond line in the center of the specimen gauge section, were mechanically characterized via tensile and fatigued tests. The behaviors of these “50/50 AM repaired” Ti-6A1-4V coupons were compared to 100% stock Ti-6A1-4V coupons. In addition, metallography and post-test fractography were performed to study the microscopic characteristics and failure initiation sites with special attention to the grain structures in the vicinity of the bond lines. The AM repaired coupons did show a slight degradation in mechanical properties compared to the stock material of this study (tensile strength and elongation as well as fatigue life), with the microstructural dissimilarities explaining the variances. Even so, the AM repaired specimen properties were acceptable and compared favorably to other published results for stock annealed Ti-6A1-4V.
Combustion and Emission Characteristics of a Lean Axial-Stage Combustor
Authors: Stiehl Bernhard , Worbington Tyler , Miegel Alexander , Martin Scott , Velez Carlos , Ahmed Kareem
Published: November 2019

Gas turbine engines with high operational flexibility represent an important area of research. In support of this, the stage change of NOx emissions at high-temperature, full-load conditions are the main target of this research study. To overcome the challenge of decreasing the residence time of hot exhaust gas in the burner, the approach of axial-staged combustion has been used, which aims to burn at lean conditions. A main combustion stage with a conventional burner is followed by a jet-in-crossflow (JIC) stage downstream. This second combustion stage, the test section, burns well over a third of the total fuel amount, which is added by a jet inlet. The entire combustor is designed to run at a pressure of 5 bar, featuring a challenging point of experimental operation. Hence, a steady Computational Fluid Dynamics (CFD) model was created in Star-CCM+ to analyze the JIC stage. A structured mesh grid with local refinement domains was used along with RANS equations, Realizable k-ε turbulence, Complex Chemistry model with Laminar Flame Concept (LFC) applied. The findings of the computational model include a detailed description of the flow field, focusing on vortex formation and penetration depth. Three vortex types and local pressure losses in the shear domain were identified. Results were compared with similar data from literature and a very good match was proven. Optical laser diagnostics should work well to capture the predicted flow penetration. The highest local reaction rates were observed inside a thin flame front between 4 and 6 diameters downstream of the jet. The jet showed a limited expansion into the available channel domain, resulting in a low total heat release and a methane conversion of 52%. Along with production of just under 1% CO, the potential of axial-staged combustion has been outlined by two boundary cases, using either equilibrium main burner stage NOx, which showed a reduction of high incoming NOx, or setting incoming NOx fractions to zero, which yielded a total production of only 17 ppm NOx in the JIC stage.
Experimental and Numerical Assessment of the Impact of Part-Span Connectors on Turbine Efficiency and Flow Field
Authors: Brüggemann C. , Schatz M. , Vogt D. M. , Popig F.
Published: November 2019

This study presents the results of measurements in an industrial steam turbine test rig operated at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) in Stuttgart, Germany. In order to ensure safe operation over a wide range of operating conditions the last and penultimate rotor blade rows of this turbine feature Part-Span Connectors (PSC). The PSC provide additional coupling and mechanical damping during operation, however, they present a major obstacle to the flow, thus causing additional aerodynamic loss. The focus of the present work is on the aerodynamic impact of the PSC on the flow field of the last stage. To capture this impact, an extensive measurement campaign over a wide range of operating points was performed using two last blade row configurations that are identical with regard to the blade design, except for the fact that one features free-standing blades while the second is equipped with PSC. A performance assessment of these two configurations based on detailed probe measurements and overall turbine efficiency is presented. Additionally, a detailed comparison of 3D CFD-results employing an equilibrium steam (EQS) model and a non-equilibrium steam (NES) model for both configurations is shown with good agreement to the test data. However, comparing the two models reveals major differences whenever there is condensation occurring close to the evaluation plane, thus the advantage of applying the NES model is presented.
3D Printing in Turbomachinery: Overview of Technologies, Applications and Possibilities for Industry 4.0
Authors: Novotny Vaclav , Spale Jan , Stunova Barbora Bryksi , Kolovratnik Michal , Vitvarova Monika , Zikmund Petr
Published: November 2019

Customization and providing tailored products, while keeping highly automated production with minimum manufacturing personnel, is a general trend, and one of the expectations of manufacturing companies from developed countries to stand in competition against cheap mass production. This trend, often also called “industry 4.0”, is taking advantage of many innovative and quickly developing technologies like AM or 3D printing. Applications of 3D printing are also getting into the field of turbomachinery.

The first part of the paper provides a review of current 3D printing technologies with respect to applications in turbomachinery field. Several technologies, mostly for producing a metal or plastic product, exist and can be considered. Applications for the components range from single Watts to hundreds MW scale and similarly for various other operating conditions.

The second part briefly describes possible practical applications concerning multiple situations as research and development, customization of end-product, operative field-testing, or temporary replacements.
Pipeline Compressors Dry Gas Seal Retrofits
Authors: Sihra Inderpal , Goldswain Ian , Twist Christina , Pacheco Jorge
Published: November 2019

Methane emissions are classed as one of the most important contributors to climate change. This greenhouse gas has a global warming potential 21 times that of Carbon Dioxide. In the Oil and Gas industry, pipeline compressor emissions have been identified as an important source of methane released into the atmosphere. Wet seals (oil seals) technology will not meet new targets being set for methane emissions. John Crane has therefore developed a new dry gas seal design with a significantly narrower cross section to allow historically high value compressor assets to continue to function without the need for extensive redesign or replacement.

This dry gas seal has been specifically engineered to replace wet seals within older centrifugal pipeline compressors. The main reasons associated with conversion from wet seals to dry gas seals include: moving to non-contacting technology which reduces seal wear issues, reduced operating costs from removal of oil seal supporting systems including degassing equipment, lower energy consumption due to the shear losses associated with oil seals, reduced maintenance costs by having a simpler supporting system and less frequent routine maintenance, and reduced emissions.

Wet seals are typically compact in nature and are therefore very flexible in how they can be installed into a compressor. Traditional dry gas seals occupy a larger cross-sectional footprint and therefore it was necessary to develop a brand new gas seal that can retrofit into the same cavity without the need for expensive and prohibitive machining of the compressor shaft or housing. The resulting gas seal design is significantly compact when compared to a standard gas seal, yet provides sealing at maximum pipeline compressor duties of up to 120barg and 100m/s.

In order to create a compact seal, John Crane has significantly reduced the cross section of the rotating (mating) and stationary (primary) sealing faces. This change brings about an increased level of complexity associated with dry gas seal design. In-house FEA and CFD simulations have been used to optimize the seal design and groove patterns. Results documenting the extensive design and simulation activities will be presented to demonstrate effective separation of the sealing faces throughout the entire seal performance envelope. A number of tests were specifically designed to thoroughly validate the seal design by simulating compressor field conditions. The product has undergone a series of testing through its entire performance envelope for pressure, speed and temperature. Specific accelerated tests were also designed to replicate the seal lifetime. The paper will describe the test setup and present the validation results.
Experimental Validation of Friction Models for Rotor-Rubbing
Authors: Jauregui Juan , De Santiago Duran Oscar
Published: November 2019

The work presented here is a continuation of a set of experiments that were designed for predicting friction forces during rotor rubbing. The experimental set up consisted of a rotor rubbing a fixed surface. The surface had two force sensors, one aligned with the tangential force, and the other aligned in the radial direction. This set up allowed us to measure the friction component and the normal force. The measurements were complemented with a couple of accelerometers mounted on the bearings, and the accelerations and the friction force were measured simultaneously. All the data were analyzed using the Continuous Wavelet Transform (CWT) and the cross-correlation function. The CWT produces a spectrogram that is useful for identifying the nonlinear behavior of the phenomenon. The cross-correlation is used to measure the similarities between the friction force and the acceleration measurements. At low friction levels, experimental results show a sub-synchronous vibration at half of the rotating speed. This pattern is always present regardless of the friction source, but it is impossible to reproduce this effect using current friction models.

The experimental results were compared to numerical results, these results were computed with the Muszynska’s model that is based on the physics of the phenomenon, but their predictions differ significantly from the experimental results. One of the reasons for these discrepancies lay on the fact that rotor-rubbing models consider the friction as an external force instead of modifying the system parameters.
Optical Coarse Droplet Measurement and Wet Loss Analysis on the Wet Air Flow Through the Subsonic Blade Cascade Channel
Authors: Sasao Yasuhiro , Takata Ryo , Miyake Satoshi , Tabata Soichiro , Yamamoto Satoru
Published: November 2019

In order to understand the details of the mechanism of the occurrence of wetness loss between blade rows, the blades of an HP nuclear turbine were modeled in an atmospheric subsonic wind tunnel, and a flow field with wet loss was analyzed in its totality using a three-hole Pitot tube and Phase Doppler Particle Analyzer (PDPA) system.

In the secondary flow loss region and the end wall loss region, a significant increase in pressure loss was confirmed under wet conditions. Analysis by measurement and the Eulerian-Lagrangian coupled solver showed that these loss increases can occur due to the agitation of water droplets and water films in the passage vortex or corner vortex.

Finally, this report contains a breakdown of profile loss, thermodynamic loss and acceleration loss of the wet air flow through the sub-sonic blade row.
Scaling Methodology of the FAA Burner for Pre-Qualification Fire Tests of Aircraft Engine Panels
Authors: Béland Mathieu , deChamplain Alain , Kalla Smail , Robert Etienne
Published: November 2019

The main objective of this work is to design a small kerosene burner to study the fireproofing capacity of aircraft composite materials exposed to an open flame. The standards AC20-135 and ISO-2685 describe how the fireproofing tests have to be performed and serve as guidelines to set the requirements for the design of a small kerosene burner as a less costly alternative to the larger FAA burner. The burner is fed with liquid jet-A fuel and air, which is flowing around the injector in a cylindrical chamber. The combustion generates an unconfined flame. The fuel injector selected is a Delavan spill-return pressure atomizer. There is a custom 3D printed plastic axial swirler at the inlet of the combustion area to promote better mixing between air and jet-A droplets. A computational fluid dynamic analysis (CFD) is presented to better understand the aerodynamic of the burner and to design adequately the swirler. The design of the burner allows changing easily the swirler to test swirlers with different vane angles. An experimental test bench is designed to test the effect of these swirlers on the heat flux measurements under multiple combinations of burner power and equivalence ratio at four axial locations. The experimental investigation allows selecting the final configuration and parameters for the burner. The chosen swirler has 15 vanes that are oriented at the exit at 25° to the burner axis. The best axial location for the measurements from the burner face to the position of the calorimeter is at 7.6 cm (3 in.). It is possible to generate a flame with a diameter smaller than 6.4 cm (2.5 in.) while reaching the required heat flux of 116 kW/m2. This accommodates smaller coupon sizes for the composite material and reduces cost for pre-certification FAA testing. To achieve this flame configuration, the burner power should be set between 10 kW and 20 kW with an equivalence ratio from 0.7 to 0.9.
Liquid Jet in Crossflow: Effect of Momentum Flux Ratio on Spray and Vaporization Characteristics
Authors: Kamin Manu , Khare Prashant
Published: November 2019

A comprehensive study is conducted to identify the effects of momentum flux ratio on the spray and vaporization characteristics of liquid jet injected in air crossflow at elevated temperatures, a configuration relevant to high-speed propulsion systems, such as ramjets and afterburners. The physical setup consists of a straight chamber with a triangular bluff body down-stream of the liquid injection location. The numerical simulations are based on an Eulerian-Lagrangian framework, where the gas phase flow behaviors such as recirculation zones, turbulence statistics, mixing of vaporized liquid and gas streams are resolved by solving the complete set of three-dimensional conservation equations of mass, momentum, energy and species, and the liquid phase is treated using the blob approach and tracked in a Lagrangian coordinate system. Turbulence closure is achieved using Large Eddy Simulation (LES) technique. Primary breakup of the liquid jet is simulated using the K-H wave breakup model, and the Taylor Analogy Breakup (TAB) model is used for secondary breakup. Two-way coupling between the liquid and gas phases is implemented in the LES framework to systematically model the exchange of mass, momentum and energy between the two phases. The formulation is validated against experimental measurements of liquid jet penetration and sauter mean diameter for a Weber number of 68 and momentum flux ratio of 9 at two temperatures, 298K and 573K. Results show excellent agreement with measurements for both cases. Next, simulations are conducted for a range of momentum flux ratios from 10–140 to identify the detailed gas and spray fields for vaporizing flow cases. This study helps to estimate the penetration of the liquid jet, droplet distribution, and then, location of the core of evaporated liquid in the gas-phase are quantitatively identified.
Low Fidelity Design and Analysis Parametric Tool for General Centrifugal Compressors
Authors: Muppana Sai , Siddappaji Kiran , Abdallah Shaaban , Turner Mark
Published: November 2019

Performance prediction and blade generation in a preliminary design stage of centrifugal compressors is critical to have a successful design. In this paper, a one-dimensional meanline design and analysis tool has been developed for single-rotor and novel multi-rotor centrifugal impellers. Loss models used for performance prediction of single stage compressors have been extended to single hub multi-rotor compressors to evaluate isentropic efficiency and pressure ratio. Stage conditions like work ratio and stator turning angle are given as input parameters and the tool computes flow properties along the meanline and also, generates velocity triangles, streamlines, smooth definition of blade angles at different spanwise sections. The tool acts a preprocessor for Tblade3 which is an in-house 3D parametric blade geometry generator to create blades. A 0D tool has been developed for multi-rotor impellers to provide an estimate of work ratio. 0D coupled with 1D tool can provide a good preliminary design point. The process of 0D to blade generation has been automated enabling it to connect with high-fidelity analysis. The motivation to create this tool is to calculate flow angles, metal angles, velocity triangles, ease of parametric modification and reduce aero-design cycle time. This tool is modular which adds the flexibility of capability extension. The code is validated with DLR centrifugal compressor experimental data. The 1D tool is also used to calculate performance and blade angles for the novel single hub multi-rotor centrifugal compressor demonstrating the versatility of the low fidelity tool. The tool suite is written in Python and is open source https://github.com/msaisiddhartha/CIMdes.
Integrated Turbine Design Using Evolutionary Strategies to Minimize Fuel Burn
Authors: Hartfield Roy J. , Cervantes Noel
Published: November 2019

This paper describes the use of an Evolutionary Strategies optimization scheme to optimize the rotor blade section of a high-pressure turbine stage for minimum fuel burn. The goal is to determine if the blade optimization can result in an overall engine performance upgrade by minimizing the fuel required. To ascertain the overall effect of turbine improvement on fuel burn specifically, the remainder of the engine is modeled using the Numerical Propulsion System Simulation tool. The result is a 0.082% improvement in fuel burn. The paper details the resulting configuration and identifies some strategies which are emerging for improving turbine design.
Potential of Semi-Closed Cycles for UAV Propulsion
Authors: Tacconi Jacopo , Visser Wilfried , Verstraete Dries
Published: November 2019

Conventional Brayton cycles have demonstrated to be significantly less efficient than alternative propulsion systems (spark ignition, diesel, fuel cells, etc.) for low power output applications, such as for small size UAVs.

The gas turbine performance could be enhanced through the introduction of heat exchangers, with the consequent increase of the overall engine weight. Semi-closed cycles have documented advantages of higher thermal efficiency and degree of compactness than traditional intercooled-recuperated open cycles.

This paper discusses advantages and applicability of semi-closed cycles to a small gas turbine, designed for a medium altitude UAV mission. In particular, size and altitude effects have been accounted in the performance evaluation of two different semi-closed cycle arrangements designed for an output shaft power of 100 hp (74.57 kW).

Resultant performance has been compared with equivalent simple recuperated and intercooled-recuperated open cycles. Furthermore, a final engine performance comparison has been made with data obtained from a similar analysis performed on a larger engine, with a power output of 300 hp (223.71 kW) and designed for an extremely high altitude UAV application.

While promising results have been obtained for the larger case study, where semi-closed cycles have demonstrated superior performance and higher engine compactness than conventional solutions, similar trends have not been displayed for the smaller engines, as consequence of the strong size effects observed in the turbomachinery performance. For the 100 hp engine the semi-closed cycles are slightly outperformed by the open cycle engines.