bluuebunny/crossref_metadata_2025 huggingface dataset:
A Mistuned Forced Response Analysis of an Embedded Compressor Blisk Using a Reduced Order Model
Authors: Gutierrez Mauricio , Petrie-Repar Paul , Kielb Robert E. , Key Nicole L.
Published: August 2018

Accuracy when assessing mistuned forced response analyses is still a mayor concern. Since a full coupled analysis is still very computational expensive, several simplifications and reduced order models are carried out. The use of a reduction method, the assumptions and simplifications, generate different uncertainties that challenge the accuracy in the results. Experimental data are needed for validation and also to understand the propagation of these uncertainties. This paper shows a detailed mistuned forced response analysis of a compressor blisk. The blisk belongs to the Purdue Three-Stage (P3S) Compressor Research Facility. Two different stator-rotor-stator configurations of 38 and 44 upstream stator vanes are taken into consideration. Several loading conditions are analyzed at three different speed lines. A reduced order model known as subset nominal mode (SNM), has been used for all the analyses. This reduction takes as a basis a set of modes within a selected frequency spectrum. A detailed comparison between the predicted and measured results have been performed, showing a good agreement for the high loading conditions.
Durability Assessment of Additive Manufactured Compressor Disk Considering Material Defects Distribution
Authors: Wang Jier , Hu Dianyin , Zhang Long , Liu Xi , Wang Rongqiao
Published: August 2018

Additive Manufacturing (AM) applications are poised to rapidly expand in aero-engines, providing opportunities to manufacture complex geometries which are unobtainable through traditional manufacturing techniques. The powder based AM process, selective laser melting (SLM), results in susceptibility to defects such as porosity, lack of fusion, and unmelted powder. These random defects often serve as fatigue crack initiation sites, thus influencing fatigue crack initiation and growth behavior. Consequently, the influence of random defects on high cycle fatigue performance for the AM titanium compressor disk is investigated in this study. First, the relationships between the defect area and the fatigue performances involving fatigue limit and the crack propagation threshold are quantified. Second, the effect of defect probability distribution is examined. Finally, the durability analyses on SLM titanium compressor disks in Ti-6A1-4V alloy are performed based on the fatigue life prediction model for defect-containing AM material. Then sensitivity analysis is conducted to determine the critical defect size influencing the fatigue limit and fatigue life.
Towards Structural Topology Optimization of Rotor Blisks
Authors: Boccini Enrico , Meli Enrico , Rindi Andrea , Pinelli Lorenzo , Peruzzi Lorenzo , Arnone Andrea
Published: August 2018

The current trend in turbomachinery is pushing forward more and more efficient machines, increasing speeds, reducing components mass and improving their vibrational behaviour. Structural topology optimization is a challenging and promising approach to satisfy all these demands, with a very remarkable economic impact. This approach enables the creation of structures characterized by complex three-dimensional geometries, which are usually difficult or impossible to be produced using traditional manufacturing processes. However, thanks to innovative technologies, as new additive manufacturing techniques, it is now possible to effectively exploit topology optimization to develop innovative components. The aim of this work is to demonstrate the applicability of structural topology optimization techniques in turbomachinery, to improve the dynamic performances and vibrational behaviour of critical components. A 3D mock-up blade geometry based on T106 profile has been designed to reproduce a typical rotor blade in design conditions. The blade has been mounted on a rough disk model, to obtain a rotor blisk in order to ensure a wide design space for the optimization. The optimization has been carried out by applying mean and fluctuating loads coming from a 3D unsteady computation of 1.5stage (stator-rotor-stator) together with the centrifugal stresses. The unsteady loads acting on the rotor skin are due to the wake of the upstream stator and the potential field generated by the downstream stator. A new concept design for the blisk has been developed and the optimized geometry has been compared to the original one to highlight the improvements in terms of mass reduction and improved dynamic behaviour. This paper will confirm the suitability of this approach to turbomachinery components and a prototype of optimized geometry will be ready to be manufactured through innovative additive manufacturing techniques for high resistance alloys.
Modelling the Effect of External Flue Gas Recirculation on NOx and CO Emissions in a Premixed Gas Turbine Combustor With Chemical Reactor Networks
Authors: Prakash V. , Steimes J. , Roekaerts D. J. E. M. , Klein S. A.
Published: August 2018

The increasing amount of renewable energy and emission norms challenge gas turbine power plants to operate at part-load with high efficiency, while reducing NOx and CO emissions. A novel solution to this dilemma is external Flue Gas Recirculation (FGR), in which flue gases are recirculated to the gas turbine inlet, increasing compressor inlet temperature and enabling higher part load efficiencies. FGR also alters the oxidizer composition, potentially leading to reduced NOx levels. This paper presents a kinetic model using chemical reactor networks in a lean premixed combustor to study the impact of FGR on emissions. The flame zone is split in two perfectly stirred reactors modelling the flame front and the recirculation zone. The flame reactor is determined based on a chemical time scale approach, accounting for different reaction kinetics due to FGR oxidizers. The recirculation zone is determined through empirical correlations. It is followed by a plug flow reactor. This method requires less details of the flow field, has been validated with literature data and is generally applicable for modelling premixed flames. Results show that due to less O2 concentration, NOx formation is inhibited down to 10–40% and CO levels are escalated up to 50%, for identical flame temperatures. Increasing combustor pressure leads to a rise in NOx due to thermal effects beyond 1800 K, and a drop in CO levels, due to the reduced chemical dissociation of CO2. Wet FGR reduces NOx by 5–10% and increases CO by 10–20%.
Analysis of Deformation of Mistuned Bladed Disks With Friction and Random Crystal Anisotropy Orientation Using Gradient-Based Polynomial Chaos Expansion
Authors: Rajasekharan Rahul , Petrov E. P.
Published: August 2018

Single crystal blades used in high pressure turbine bladed disks of modern gas-turbine engines exhibit material anisotropy. In this paper the sensitivity analysis is performed to quantify the effects of blade material anisotropy orientation on deformation of a mistuned bladed disk under static centrifugal load. For a realistic, high fidelity model of a bladed disk both: (i) linear, and (ii) non-linear friction contact conditions at blade roots and shrouds are considered. The following two kinds of analysis are performed: (i) local sensitivity analysis, based on first order derivatives of system response w.r.t design parameters, and (ii) statistical analysis using polynomial chaos expansion. The polynomial chaos expansion is used to transfer the uncertainty in random input parameters to uncertainty in static deformation of the bladed disk. An effective strategy, using gradient information, is proposed to address the “curse of dimensionality” problem associated with statistical analysis of realistic bladed disk.
High-Fidelity Sensitivity Analysis of Modal Properties of Mistuned Bladed Disks Regarding Material Anisotropy
Authors: Koscso Adam , Dhondt Guido , Petrov E. P.
Published: August 2018

A new method has been developed for sensitivity calculations of modal characteristics of bladed disks made of anisotropic materials. The method allows the determination of the sensitivity of the natural frequencies and mode shapes of mistuned bladed disks with respect to anisotropy angles that define the crystal orientation of the monocrystalline blades using full-scale finite element models. An enhanced method is proposed to provide high accuracy for the sensitivity analysis of mode shapes. An approach has also been developed for transforming the modal sensitivities to coordinate systems used in industry for description of the blade anisotropy orientations.

The capabilities of the developed methods are demonstrated on examples of a single blade and a mistuned realistic bladed disk finite element models. The modal sensitivity of mistuned bladed disks to anisotropic material orientation is thoroughly studied.
Forced Response Reduction of a Blisk by Means of Intentional Mistuning
Authors: Beirow Bernd , Kühhorn Arnold , Figaschewsky Felix , Bornhorn Alfons , Repetckii Oleg V.
Published: August 2018

The effect of intentional mistuning has been analyzed for an axial turbocharger blisk with the objective of limiting the forced response due to low engine order excitation (LEO). The idea behind the approach was to increase the aerodynamic damping for the most critical fundamental mode in a way that a safe operation is ensured without severely losing aerodynamic performance. Apart from alternate mistuning a more effective mistuning pattern is investigated, which has been derived by means of optimization employing genetic algorithms. In order to keep the manufacturing effort as small as possible only two blade different geometries have been allowed which means that an integer optimization problem has been formulated. Two blisk prototypes have been manufactured for the purpose of demonstrating the benefit of the intentional mistuning pattern identified in this way: A first one with and a second one without employing intentional mistuning. The real mistuning of the prototypes has been experimentally identified. It is shown that the benefit regarding the forced response reduction is retained in spite of the negative impact of unavoidable additional mistuning due to the manufacturing process. Independently, further analyzes have been focused on the robustness of the solution by considering increasing random structural mistuning and aerodynamic mistuning as well. The latter one has been modeled by means of varying aerodynamic influence coefficients (AIC) as part of Monte Carlo simulations. Reduced order models have been employed for these purposes.
Surrogate Modeling of Manufacturing Variation Effects on Unsteady Interactions in a Transonic Turbine
Authors: Brown Jeffrey M. , Beck Joseph , Kaszynski Alexander , Clark John
Published: August 2018

This effort develops a surrogate modeling approach for predicting the effects of manufacturing variations on blade unsteadiness and performance of a transonic turbine. CFD results from a set of 105 as-manufactured turbine blade geometries are used to train and validate the surrogate models. Blade geometry variation is characterized with point clouds created from a structured light optical measurement system and as-measured CFD grids are generated through mesh morphing of the nominal design grid data. Results from a Reynolds-averaged Navier-Stokes flow solver with the two-equation Wilcox turbulence model are used as training and validation data. Principal Component Analysis (PCA) of the measured airfoil geometry variations is used to create reduced basis of independent surrogate model parameters. Results of the surrogate are compared to the CFD results. It is shown that the surrogate model typically captures between 60% and 80% of the full CFD predicted variance. Three new approaches are introduced to improve the accuracy of the surrogate. A zonal PCA approach is defined which improves surrogate accuracy by focusing on key regions of the airfoil. A training point reduction strategy is proposed that is based on the kd-tree nearest neighbor search algorithm and reduces the required training points by 25%. A second reduction approach uses k-means clustering to effectively select training points from the 105 blade population and is used to reduce the required training points by up to 66%.
Numerical Study on Local Heat Transfer in a Rotating Cooling Channel
Authors: Ren Min , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2018

Effect of rotation on turbine blade internal cooling is an important factor in gas turbine cooling systems. To obtain the distribution of the heat transfer and the flow field in a rotating cooling channel, a series of computational simulations using the realizable k-ε model are utilized. The channel Reynolds number based on the channel diameter is 25000. The rotation number ranges from 0 to 0.20. The investigated density ratio Δρ/ρ ranges from 0.05 to 0.33 and the range of radius-to-passage hydraulic diameter r/D is from 10 to 40. The results show that the heat transfer on the trailing side shows an overall augmentation while that on the leading side decreases in the cooling channel. When the channel is stationary, the density ratio has little effect on the thermal performance. And for the rotating channel, the heat transfer on the trailing side and leading side both increases when the density ratio increases. The heat transfer both on the trailing side and leading side decreases when the radius-to-passage hydraulic diameter (r/D) increase. And the radius has a greater effect when the rotation number is higher.
Rotordynamics Experimental Validation of a Sliding-Blade Architecture for an Inside-Out Ceramic Turbine
Authors: Landry C. , Picard B. , Parent-Simard T. , Plante J.-S. , Picard M.
Published: August 2018

The integration of monolithic ceramic blades into sub-megawatt microturbines is a low-cost option for increasing Turbine Inlet Temperature and efficiency. The Inside-Out Ceramic Turbine (ICT) is a promising concept for the integration of ceramic blades by loading each blades in compression using a carbon-polymer composite rim to convert the blade radial loads to tangential hoop stress. High tangential velocities lead to elevated radial displacement of the rim and, therefore, the rotor hub needs to be able to maintain the contact with the blades for a large range of radial displacements. This displacements comes with hub structural challenges and rotordynamics considerations. For these reasons, blade tip speed have been previously limited to about 360 m/s. This paper presents a hub design that allows high radial displacement using the combination of inclined blade roots, inclined hub grooves and an axial spring. The contact between the blade root and the hub is maintained through the inclined planes by the axial forces from the spring creating internal friction in the rotor that can induce sub-synchronous rotordynamics instabilities. The onset of instabilities is investigated experimentally with cold spin tests of a simplified ICT prototype. The results first show that the concept remains stable up to the maximum speed tested of 127 kRPM (tip speed of 387 m/s) if the spring is designed such that it remains in contact with the blade roots at all time. On the other hand, when reducing the preload sufficiently to test the limits of the concept, the rotor first mode became unstable at 120 kRPM resulting in failure of the prototype. These results suggest that, provided a sufficient spring preload to prevent excessive relative motion, the blades can reach the desired radial displacements, removing the main constraint on ICT tip speed.
Investigation of Stress-Strain Behavior of a Component Under Variable Frequency Non-Proportional Loading
Authors: Hu Yifeng , Chen Gang , Wang Weizhe
Published: August 2018

With the flexibility operation demand of the plants, the load change becomes more and more often. The torsion loading due to load change becomes larger and more frequent. The influence of torsion loading frequency (the number of repeating cycles in a unit time) on the stress-strain behavior of component was numerically investigated under non-proportional loadings. A hollow cylinder specimen was chosen in this study. And three conditions of non-proportional loadings (Case1, Case2 and Case3) were chosen. The relationships between cyclic stress response and cyclic strain response were obtained for Case1, Case2 and Case3. The numerical results revealed that the distortion of stress-strain response curve was intensified with the increase of torsion loading frequency. The cyclic softening behaved in the first 2 cycles for the tension and torsion stress responses; however, the characterizations of the cyclic hardening and the cyclic softening for the material appeared after the starting 2 cycles. Furthermore, with the increase of cycle number and torsion loading frequency, there is a significant difference between the tension stress response and the torsion stress response.
Effects of Asymmetry on Thermoacoustic Modes in Annular Combustors: A Higher-Order Perturbation Study
Authors: Mensah Georg A. , Magri Luca , Orchini Alessandro , Moeck Jonas P.
Published: August 2018

Gas-turbine combustion chambers typically consist of nominally identical sectors arranged in a rotationally symmetric pattern. However, in practice the geometry is not perfectly symmetric. This may be due to design decisions, such as placing dampers in an azimuthally non-uniform fashion, or to uncertainties in the design parameters, which break the rotational symmetry of the combustion chamber. The question is whether these deviations from symmetry have impact to the thermoacoustic-stability calculation. The paper addresses this question by proposing a fast adjoint-based perturbation method. This method can be integrated into numerical frameworks that are industrial standard such as lumped-network models, Helmholtz- and linearized Euler-equations. The thermoacoustic stability of asymmetric combustion chambers is investigated by perturbing rotationally symmetric combustor models. The approach proposed in this paper is applied to a realistic three-dimensional combustion chamber model with an experimentally measured flame transfer function, which is solved with a Helmholtz solver. Results for modes of zeroth, first, and second azimuthal mode order are presented and compared to exact solutions of the problem. A focus of the discussion is set on the loss of mode-degeneracy due to symmetry breaking and the capability of the perturbation theory to accurately predict it. In particular, an “inclination rule” that explains the behavior of degenerate eigenvalues at first order is proven.
Prediction of Aerodynamically Induced Blade Vibrations in a Radial Turbine Rotor Using the Nonlinear Harmonic Approach
Authors: Kovachev Nikola , Waldherr Christian U. , Mayer Jürgen F. , Vogt Damian M.
Published: August 2018

Resonant response of turbomachinery blades can lead to high cycle fatigue (HCF) if the vibration amplitudes are excessive. Accurate and reliable simulations of the forced response phenomenon require detailed CFD and FE models that may consume immense computational costs.

In the present study, an alternative approach is applied, which incorporates nonlinear harmonic (NLH) CFD simulations in a one-way fluid-structure interaction (FSI) workflow for the prediction of the forced response phenomenon at reduced computational costs. Five resonance crossings excited by the stator in a radial inflow turbocharger turbine are investigated and the aerodynamic excitation and damping are predicted using this approach. Blade vibration amplitudes are obtained from a subsequent forced response analysis combining the aerodynamic excitation with aerodynamic damping and a detailed structural model of the investigated turbine rotor. A comparison with tip timing measurement data shows that all predicted values lay within the range of the mistuned blade response underlining the high quality of the utilized workflow.
Environmental Impact on the Life Cycle for Turbine Based Biomass CHP Plants
Authors: Bartocci Pietro , Bidini Gianni , Laranci Paolo , Zampilli Mauro , D'Amico Michele , Fantozzi Francesco
Published: August 2018

Biomass CHP plants represent a viable option to produce distributed energy in a sustainable way when the overall environmental benefit is appraised on the whole life cycle. CHP plants for bioenergy conversion may consist of a gasification (IGC – Integrated Gasification Cycle) or pyrolysis (IPRP – Integrated Pyrolysis Regenerated Plant) pre-treatment unit, producing a syngas that feeds an internal combustion engine or a gas turbine. The external combustion mode is also an option, where exhaust gases from biomass combustion provide heat to either a traditional steam cycle, an ORC (Organic Rankine Cycle) or an EFGT (Externally Fired Gas Turbine). This paper focuses specifically on turbines based technologies and provides a LCA comparison of 4 main technologies suitable for the small scale, namely: EFMGT, ORC, IGC and IPRP. The comparison is carried out considering 3 different biomasses, namely a Short Rotation Forestry, an agricultural residue and an agro industrial residue at 2 different scales: micro scale (100 kw) and small scale (1 MW), being higher scales barely sustainable on the life cycle. From data derived from the Literature or experimental campaign (tests at the IPRP and gasification facilities at the University Perugia), LCA analysis were carried out and the different scenarios were compared based on two impact categories: global warming and human health. Input and output of the derived LCI are referred to the functional unit of 1 kWh electric for upstream, core and downstream processes. Results show the contribution of main processes and are discussed comparing scale, technology and feedstock.
Thermal Boundary Layer Response to Periodic Fluctuations
Authors: Saavedra J. , Paniagua G. , Chazot O.
Published: August 2018

Unsteady effects impact the aerothermal performance of the turbine blade rows, originating noise, mechanical and thermal fatigue. Blade row interactions are due to the relative motion between nearby rows of airfoils, the periodic occurrence of flow distortions generated by the airfoil rows or combustors. The detailed characterization of the thermal boundary layer under periodic fluctuations is vital to improve the performance of cooled turbine airfoils. In the present contribution, we performed series of Unsteady Reynolds Averaged Navier-Stokes simulations to investigate the wall heat flux response to periodic flow velocity fluctuations, on a flat plate of 0.5 m. We investigated the boundary layer response to sudden flow acceleration and periodic flow perturbations, caused by inlet total pressure variations. Because of the flow acceleration the boundary layer is first stretched, resulting in an increase of the wall shear stress. Later on, due to the viscous diffusion, the low momentum flow adjusts to the new free stream conditions. The behavior of the boundary layer at low frequency is similar to the response to an individual deceleration followed by one acceleration. However, at higher frequencies the mean flow topology is completely altered. One would expect that higher acceleration rates would cause a further stretching of the boundary layer that should cause even greater wall shear stresses and heat fluxes. However, we observed the opposite; instead, the amplitude of the skin friction coefficient is abated, while the peak level is one order of magnitude smaller than at low frequency. Two counteracting effects influence the response of both the momentum and the thermal boundary layer. In one hand, the stagnant flow quantities propagate at characteristic velocities guiding the establishment of the mean flow conditions. On the other hand, the diffusion across the boundary layer leads the final response of the near wall region. However, the dynamic pressure gradients imposed in the mean flow modulate the viscous properties of the boundary layer through local flow acceleration, transforming the expected pattern.
Using Mobile Quiz Application to Enhance Learning in Combustion Kinetics Course for Students of Mechanical Engineering and Transport Systems
Authors: Djordjevic Neda
Published: August 2018

A combustion kinetics course offered as an elective for master students of mechanical engineering and transport systems can have quite a heterogeneous group of participating students with respect to their foreknowledge of organic chemistry, thermochemistry and basics of combustion. To deal with this challenge a mobile quiz application in form of a multiple choice questions with extensive explanations have been employed in order to motivate and facilitate needs-oriented self-learning. A survey showed that students felt strongly that the mobile app affected their learning positively, helped them to consolidate their knowledge during the semester and also to test it during the preparation for the oral exam. The students also reported being additionally motivated by being able to use a smartphone to enhance learning, given that such tools are presently still scarce. They perceived the technology-assisted learning enhancement through the app as innovative and very useful.
Physical Interpretation of Machine Learning Models Applied to Film Cooling Flows
Authors: Milani Pedro M. , Ling Julia , Eaton John K.
Published: August 2018

Current turbulent heat flux models fail to predict accurate temperature distributions in film cooling flows. The present paper focuses on a machine learning approach to this problem, in which the Gradient Diffusion Hypothesis (GDH) is used in conjunction with a data-driven prediction for the turbulent diffusivity field αt. An overview of the model is presented, followed by validation against two film cooling datasets. Despite insufficiencies, the model shows some improvement in the near-injection region. The present work also attempts to interpret the complex machine learning decision process, by analyzing the model features and determining their importance. These results show that the model is heavily reliant of distance to the wall d and eddy viscosity vt, while other features display localized prominence.
Gas Turbine Fouling Tests: Review, Critical Analysis and Particle Impact Behavior Map
Authors: Suman Alessio , Casari Nicola , Fabbri Elettra , Pinelli Michele , di Mare Luca , Montomoli Francesco
Published: August 2018

Fouling affects gas turbine operation and airborne or fuel contaminants, under certain conditions, become very likely to adhere to surfaces if impact takes place. Particle sticking implies the change in shape in terms of roughness of the impinged surface. The consequences of these deposits could be dramatic: these effects can shut an aircraft engine down or derate a land-based power unit. This occurrence may happen due to the reduction of the compressor flow rate and the turbine capacity, caused by a variation in the HPT nozzle throat area (geometric blockage due to the thickness of the deposited layer and the aerodynamic blockage due to the increased roughness, and in turn boundary layer).

Several methods to quantify particle sticking have been proposed in literature so far, and the experimental data used for their validation vary in a wide range of materials and conditions. The experimental analyses have been supported by (and have given inspiration to) increasingly realistic mathematical models. Experimental tests have been carried out on (i) a full scale gas turbine unit, (ii) wind tunnel testing or hot gas facilities using stationary cascades, able to reproduce the same conditions of gas turbine nozzle operation and finally, (iii) wind tunnel testing or hot gas facilities using a coupon as the target.

In this review, the whole variety of experimental tests performed is gathered and classified according to composition, size, temperature and particle impact velocity. Using particle viscosity and sticking prediction models, over seventy (70) tests are compared with each other and with the model previsions providing a useful starting point for a comprehensive critical analysis. Due to the variety of test conditions, the related results are difficult to be pieced together due to differences in particle material and properties.

The historical data of particle deposition obtained over thirty (30) years are classified using particle kinetic energy and the ratio between particle temperature and its softening temperature. Qualitative thresholds for the distinction between particle deposition, surface erosion and particle break-up, based on particle properties and impact conditions, are identified. The outcome of this paper can be used for further development of sticking models or as a starting point for new insight into the problem.
Aerodynamic Design System for Non-Axisymmetric Boundary Layer Ingestion Fans
Authors: Kumar Sandeep , Turner Mark G. , Siddappaji Kiran , Celestina Mark
Published: August 2018

Non-uniformities at the engine inlet call for novel design techniques to cater to the performance and aeromechanical challenges. The purpose of the fan system is to mitigate the effects of distortion in the flow and to provide thrust to the vehicle. This paper discusses a harmonic based open source design system (NAX) and demonstrates its capabilities for applications in a boundary layer ingesting fan system. First, a primary baseline design was obtained using a typical axisymmetric design approach for the rotor and OGV (Outlet Guide Vanes). This baseline design now serves as the basis for further development, based on user-defined design features. Subsequently, using this baseline design, a circumferentially non-axisymmetric design of the OGV is obtained by means of inducing perturbations in blade leading edge metal angles using Fourier coefficients and phase values. The other parameters that can be varied radially as Bezier curves and tangentially as Fourier modes are: trailing edge metal angle, chord, lean, sweep, curvature and thickness. A smooth spanwise curvature controlled 3D design of OGV is discussed using the open-source geometry generator, T-Blade3. The OGV geometry files along with the detailed documentation are also available for download on the T-Blade3 website and NAX source code on Github website. This design is further optimized to improve the non-axisymmetric geometric distribution against the distorted flow conditions. The design system proposed here helps in exploration of user-specified parametric design space for development of a non-axisymmetric fan stage. Further, since the design system is modular in nature, it can easily be integrated at multiple process levels for other types of turbomachinery design applications.
Development of a New Low-Cost Tandem VGT Concept for Turbocharger Applications
Authors: Erdmenger Rodrigo R. , Menter Katya , Giepman Rogier , Clancy Cathal , Vadvadgi Aneesh , Lavertu Tom , Leonard Thomas , Spence Stephen
Published: August 2018

The air handling system for large diesel/gas engines such as those used on locomotive, marine, and power generation applications require turbochargers with a high reliability and with turbomachinery capable to adjust to different operating conditions and transient requirements. The usage of variable geometry turbocharging (VGT) provides flexibility to the air handling system but adds complexity, cost and reduces the reliability of the turbocharger in exchange for improved engine performance and transient response. For this reason, it was desirable to explore designs that could provide the variability required by the air handling system, without the efficiency penalty of a conventional waste gate and with as little added complexity as possible.

The current work describes a new low-cost variable geometry turbine design to address these requirements. The new tandem nozzle concept proposed is applicable to both axial and radial turbines, and has been designed using conventional 1D models and 2D/3D CFD methods. The concept has furthermore been validated experimentally on two different test rigs. In order to avoid the long lead times of procuring castings, the nozzle for the axial turbine was manufactured using new additive manufacturing techniques. Both the axial turbine and the radial turbine designs showed that the concept is capable to achieve a mass flow variability of more than 15% and provide a robust and cost-effective alternative to conventional VGT designs by significantly reducing the number of moveable parts.
Development of a Non-Contacting Mechanical Seal for High Performance Turbocharger Applications
Authors: Nelson Daniel A.
Published: August 2018

This paper presents the design and development of a non-contacting dry-gas mechanical seal for high performance automotive turbocharger applications. Turbochargers are increasingly being incorporated into high performance automobile engines to improve fuel efficiency, enhance energy recovery, and increase horsepower as compared with similar sized naturally aspirated engines. Minimizing the wear rate of tribological surfaces in the turbomachinery is critical to maximizing the reliability and durability of the turbocharger.

A dry-gas seal for turbochargers and related technologies with 2 to 4 cm shafts has been developed. The seal provides a complete barrier between the bearing oil and compressor flow path and is capable of reverse pressure and high speed. The seal performance was evaluated for speeds between 60,000 to 80,000 RPM, pressure differentials between −0.8 (reverse pressure) to 6 bar, and temperatures between 20 to 200 °C. Structural and thermal response of the seal components to the operating conditions are analyzed using finite element methods and the tribological behavior of the seal rings are analyzed using computational fluid dynamics. The design is experimentally validated in a seal test stand. This novel approach reduces turbocharger blowby and shows no measurable wear when compared with piston ring seals.
LES Study of the Laminar Heat Transfer Augmentation on the Pressure Side of a Turbine Vane Under Freestream Turbulence
Authors: Kanani Yousef , Acharya Sumanta , Ames Forrest
Published: August 2018

Vane pressure side heat transfer is studied numerically using Large Eddy Simulation (LES) on an aft loaded vane with a large leading edge over a range of turbulence conditions. Numerical simulations are performed in a linear cascade at exit chord Reynolds number of Re = 5.1 × 105 at low (Tu≈0.7%), moderate (Tu≈7.9%) and high (Tu≈12.4%) freestream turbulence with varying length scales as prescribed by the experimental measurements of Varty and Ames (2016). Heat transfer predictions (i.e. Stanton number based on exit condition) on the vane pressure side are in a very good agreement with the experimental measurements and the heat transfer augmentation due to the freestream turbulence is well captured. At Tu≈12.4%, freestream turbulence enhances the Stanton number on the pressure surface without boundary layer transition to turbulence by a maximum of about 50% relative to the low freestream turbulence case (Tu≈0.7%). Higher freestream turbulence generates elongated structures and high-velocity streaks wrapped around the leading edge that contain significant energy. Amplification of the velocity streaks is observed further downstream with max r.m.s of 0.3 near the trailing edge but no transition to turbulence or formation of turbulence spots is observed on the pressure side. The heat transfer augmentation at the higher freestream turbulence is primarily due to the initial amplification of the low-frequency velocity perturbations inside the boundary layer that persist along the entire chord of the airfoil. Stanton numbers appear to scale with the streamwise velocity fluctuations inside the boundary layer. Görtler vortices are not observed for this airfoil geometry.
Real Time Gas Turbine Engine Particulate Ingestion Sensor for Particle Size and Composition
Authors: Papadopoulos George , Bivolaru Daniel , Lin Jiaji
Published: August 2018

Experimental studies of turbine engine sand, dust, and ash ingestion have shown that certain constituents, typically those containing Calcium, Magnesium, Aluminum, and Silicon (CMAS) compound minerals and/or Chlorides and Sulfates, are particularly detrimental to engine turbine components. These reactive media undergo a phase change from solid to semi-solid as they pass through the combustion section of the engine under certain conditions characterized by size and mass. The phase change allows them to adhere to various turbine components including but not limited to stator vanes, rotor blades and shrouds. Unfortunately, with no on-board sensing technology the only warning signs that the flight crew has to an impeding airborne particle ingestion problem are lagging indicators. Hence, a sensor system that can measure the composition, size and concentration of particles being ingested by a gas turbine while in flight can provide pilots the warning they need to avoid damage mechanisms, both in the military where operational limits are always pushed to the maximum, and in the commercial area where safety is paramount. The current paper reports on the development of an in-situ sensor system that can be integrated at several places within an engine (e.g. aircraft inlet, engine inlet, engine bypass, engine gas path) with minimum modifications and provide measurements of composition, size and concentration for particles ingested by the engine.
Rapid Visualization of Compressor Blade Finite Element Models Using Surrogate Modeling
Authors: Bunnell Spencer , Thelin Christopher , Gorrell Steven , Salmon John , Ruoti Christopher , Hepworth Ammon
Published: August 2018

The design process for compressor blades is a highly iterative and often slow process. This research applied and measured the impact of using surrogates to quickly model the stresses on a compressor blade. By modeling distinct points on a finite element (FE) model with unique surrogates, the stress field of the entire FE model was quickly predicted. This required that the distinct points remain in the same relative location on each blade used in training the surrogate. This research studied the ability of mesh morphing, and using the surface nodes as those distinct points, to satisfy this requirement. The results show that mesh morphing performed well on the tested compressor blades. The research also found that the surrogate accuracy depended not only on the number of training samples, but also the number and types of parameters being emulated. The surrogate models achieved less than 5% error on all the tested blades. Finally, the method provided a 96% decrease in time required for a structural iteration of a compressor blade. Such speeds eliminate bottlenecks that may occur in the structural design process. The combination of mesh morphing and surrogate modeling in compressor blade analysis enables exploration of various geometric parameters and their effect on structural responses. Application of this process would produce a more thoroughly refined and understood compressor blade design.
Fuel Composition Effects on Forced Ignition of Liquid Fuel Sprays
Authors: Wei Sheng , Sforzo Brandon , Seitzman Jerry
Published: August 2018

In gas turbine combustors, ignition is achieved by using sparks from igniters to start a flame. The process of sparks interacting with fuel/air mixture and creating self-sustained flames is termed forced ignition. Physical and chemical properties of a liquid fuel can influence forced ignition. The physical effects manifest through processes such as droplet atomization, spray distribution, and vaporization rate. The chemical effects impact reaction rates and heat release. This study focuses on the effect of fuel composition on forced ignition of fuel sprays in a well-controlled flow with a commercial style igniter. A facility previously used to examine prevaporized, premixed liquid fuel-air mixtures is modified and employed to study forced ignition of liquid fuel sprays. In our experiments, a wall-mounted, high energy, recessed cavity discharge igniter operating at 15 Hz with average spark energy of 1.25 J is used to ignite liquid fuel spray produced by a pressure atomizer located in a uniform air coflow. The successful outcome of each ignition events is characterized by the (continued) presence of chemiluminescence 2 ms after spark discharge, as detected by a high-speed camera. The ignition probability is defined as the fraction of successful sparks at a fixed condition, with the number of events evaluated for each fuel typically in the range 600–1200. Ten fuels were tested, including standard distillate jet fuels (e.g., JP-8 and Jet-A), as well as many distillate and alternative fuel blends, technical grade n-dodecane, and surrogates composed of a small number of components. During the experiments, the air temperature is controlled at 27 C and the fuel temperature is controlled at 21 C. Experiments are conducted at a global equivalence ratio of 0.55. Results show that ignition probabilities correlate strongly to liquid fuel viscosity (presumably through droplet atomization) and vapor pressure (or recovery temperature), as smaller droplets of a more volatile fuel would lead to increased vaporization rates. This allows the kernel to transition to a self-sustained flame before entrainment reduces its temperature to a point where chemical rates are too slow. Chemical properties of the fuel showed little influence, except when the fuels had similar physical properties. This result demonstrates that physical properties of liquid fuels have dominating effects on forced ignition of liquid fuel spray in coflow air.
Performance Desensitization for a High-Speed Axial Compressor
Authors: Souleimani Yassine , Vo Huu Duc , Yu Hong
Published: August 2018

The increase in compressor tip clearance over the lifespan of an aero-engine leads to a long-term degradation in its fuel consumption and operating envelope. A highly promising recent numerical study on a theoretical high-speed axial compressor rotor proposed a novel casing treatment to decrease performance and stall margin sensitivity to tip clearance increase. This paper aims to apply and analyze, through CFD simulations, this casing treatment concept to a representative production axial compressor rotor with inherently lower sensitivity to tip clearance increase and complement the explanation on the mechanism behind the reduction in sensitivity. Simulations of the baseline rotor showed that the lower span region contribute as much to the pressure ratio sensitivity as the tip region which is dominated by tip leakage flow. In contrast, the efficiency sensitivity is mainly driven by losses occurring in the tip region. The novel casing treatment was successfully applied to the baseline rotor through a design refinement. Although the casing treatment causes some penalty in nominal performance, it completely reversed the pressure ratio sensitivity (i.e. pressure ratio increases with tip clearance) and reduced the efficiency sensitivity. The reversed pressure ratio sensitivity is explained by a rotation in the core flow in the lower span region indirectly induced by the flow injection from the casing treatment. The lower efficiency sensitivity comes from a reduction in the amount of fluid that crosses the tip clearance of two adjacent blades, known as double leakage. The casing treatment’s beneficial effect on stall margin sensitivity is less obvious because of the stall inception type of the baseline rotor and its change in the presence of the casing treatment.
Thermal Performance of the Realistic Leading Edge Cooling Passage of a Turbine Blade
Authors: Song Inhwan , Son Changmin , Yang Jangsik , Lee Changyong , Lee Kidon
Published: August 2018

The present study focuses on evaluating the thermal performance of the realistic leading edge cooling passage of a turbine blade, experimentally. The detailed heat transfer distributions and pressure loss of the cooling passage are measured with and without rib turbulators for direct comparison.

The experimental model is representing the realistic leading edge cooling passage, which has a converging duct with triangular cross sectional shape. Therefore, the aspect ratio and the cross sectional area of the triangular passage vary significantly along the coolant flow direction. A Perspex test model is designed at 1.3 times large scale to meet Reynolds number similarity. The test model is installed with 45-degree rib turbulators at constant space-to-height ratio of P/e = 10. The experiments are carried out at the Reynolds numbers of 20,000, 40,000 and 80,000. The transient heat transfer test technique using thermochromic liquid crystals (TLCs) was applied to measure the detailed surface heat transfer distributions. The local mixed bulk temperatures (Tmb) are defined using the air thermocouples positioned in the centerline along the cooling passage. The static pressures are measured from the pressure taps machined as a part of the test model so that friction factors of the ribbed cooling passage are also evaluated. The friction factors are influenced by the characteristics of 3 dimensional converging duct of the experimental model. The full surface heat transfer coefficients, friction factors, and overall thermal performance of the cooling passage are reported for the comparison with the other cooling configurations.
LPV Based Sliding Mode Control for Limit Protection of Aircraft Engines
Authors: Yang Shubo , Wang Xi
Published: August 2018

Limit protection, which frequently exists as an auxiliary part in control systems, is not the primary motive of control but is a necessary guarantee of safety. As in the case of aircraft engine control, the main objective is to provide the desired thrust based on the position of the throttle; nevertheless, limit protection is indispensable to keep the engine operating within limits.

There are plenty of candidates that can be applied to design the regulators for limit protection. PID control with gain-scheduling technique has been used for decades in the aerospace industry. This classic approach suggests linearizing the original nonlinear model at different power-level points, developing PID controllers correspondingly, and then scheduling the linear time-invariant (LTI) controllers according to system states. Sliding mode control (SMC) is well-known with mature theories and numerous successful applications. With the one-sided convergence property, SMC is especially suitable for limit protection tasks. In the case of aircraft engine control, SMC regulators have been developed to supplant traditional linear regulators, where SMC can strictly keep relevant outputs within their limits and improve the control performance.

In aircraft engine control field, we all know that the plant is a nonlinear system. However, the present design of the sliding controller is carried out with linear models, which severely restricts the valid scope of the controller. Even if the gain scheduling technique is adopted, the stability of the whole systems cannot be theoretically proved.

Research of linear parameter varying (LPV) system throws light on a class of nonlinear control problems. In present works, we propose a controller design method based on the LPV model to solve the engines control problem and achieve considerable effectiveness.

In this paper, we discuss the design of a sliding controller for limit protection task of aircraft engines, the plant of which is described as an LPV system instead of LTI models. We define the sliding surface as tracking errors and, with the aid of vertex property, present the stability analysis of the closed-loop system on the sliding surface. An SMC law is designed to guarantee that the closed-loop system is globally attracted to the sliding surface. Hot day (ISA+30° C) takeoff simulations based on a reliable turbofan model are presented, which test the proposed method for temperature protection and verify its stability and effectiveness.