bluuebunny/crossref_metadata_2025 huggingface dataset:
Loss and Thrust Modeling of Rocket Engine High Density Turbopumps
Authors: Gloger Jonathan , Lettieri Claudio , Souverein Louis
Published: January 2021

Turbopumps constitute an essential component of high thrust liquid rocket engines. They are characterized by a compact design, providing a large shaft power at high rotation rates. This is necessary to deliver the propellants at high pressure into the combustion chamber to generate the required engine thrust. Recirculating fluid around the pump has a major influence on axial loads and fluid dynamical losses, impacting turbopump performance and life. Therefore, simplified modelling approaches are required early on for the preliminary design of the pump impeller, and its side cavities and seals. Indeed, past experience within ArianeGroup for pumps and secondary circuits indicates that the coupling between the main flow and the leakage has to be considered at an early stage of the design. The empirical correlations of the flow in the cavities shall be carefully selected, accounting for the particularities of each new configuration. Furthermore, it is also recommended for the impeller design (e.g. for blade leading edge and pressure relieve orifices positioning), that the effects of leakage reinjection into the main flow shall be taken into account.

In order to obtain first estimates for early design optimization without the cost of full scale 360° high fidelity computational dynamic simulations (CFD), a reduced model is developed to predict losses and axial thrust on the rotor, including effects of fluid recirculation and reinjection. A two-step approach is followed: Firstly, an empirical model developed by Gülich et al. [1] is applied to characterize leakage loss analytically. Secondly, a reduced numerical model is implemented which features a single passage impeller geometry including seals and side wall gaps. The accuracy of both the analytical model and the simplified numerical model are verified in comparison to high fidelity CFD calculations, evaluating the loss contributions in the leakage path and axial thrust for a range of operating points.

In line with expectation, the highest impact on the pump performance are the volumetric losses due to the recirculation of pressurized fluid, with and efficiency decrease of up to 20 % in the investigated cases. The implemented analytical model captures the overall loss mechanisms with a 20 % uncertainty in the design point, disk friction is underpredicted and axial thrust is mostly over-predicted. Due to the simplified numerical model with the single passage impeller geometry including side cavities, the uncertainty can be decreased to about 5 %. At part load operation, the accuracy of both models reduces. It is noted, that thrust prediction is subject to the highest uncertainties.

The current work has provided a simplified numerical model that offers the higher flexibility required for the early design phase as compared to a full annulus CFD simulation of the pump, with an increased accuracy as compared to the analytical models.
Evaluation of the Capacity of RANS/URANS/LES in Predicting the Performance of a High-Pressure Turbine: Effect of Load and Off Design Condition
Authors: Dombard Jérôme , Duchaine Florent , Gicquel Laurent , Odier Nicolas , Leroy Kevin , Buffaz Nicolas , Le-Guyader Sébastien , Démolis Jacques , Richard Stéphane , Grosnickel Thomas
Published: January 2021

This paper aims at addressing design issues of turbomachinery configurations by use of Large-Eddy Simulation (LES). To do so, a research state-of-the-art high-pressure turbine stage, without technological details and for which experimental data are available, is computed with the three methods: i.e. RANS, URANS and LES. Starting from the nominal operating design, a database is acquired varying the design space (three Zweifel numbers), load (three pressure rates) and rotation speed (three reduced speeds). The analysis of the database is carried out incrementally from a design perspective. Numerical results are systematically compared to experimental ones.

Main conclusions are threefold: 1/ Calibrated RANS provides excellent results at the nominal operating point but lacks of accuracy at off design conditions. Only unsteady methods (both URANS and LES) allow a good agreement with experiment along the whole database. 2/ Although very good on the overall performances, LES provides radial profiles and 2D maps leaving room for improvement in comparison with the URANS predictions. 3/ LES and standard law-of-the-wall is validated against experiments in a high-pressure turbine without technological details but still representative of a realistic and recent industrial design. From an aero design point, this paper shows the interest in using URANS for off design conditions. It also represents a milestone for LES that had to be passed before addressing more complex issues which URANS hardly addresses.
Optimization of Large Offshore Wind Farm Layout Considering Reliability and Wake Effect
Authors: Li Xiangyu , Dao Cuong D. , Kazemtabrizi Behzad , Crabtree Christopher J.
Published: January 2021

Nowadays, the increasing demand of electricity and environmental hazards of the greenhouse gas lead to the requirement of renewable energies. The wind energy has been proved as one of the most successful sustainable energies. Recently, the development trend of the wind energy is to build large offshore wind farms (OWFs) with hundreds of wind turbines, which could generates more power in one wind farm. In the large OWF, the wake effect is a very important impact factor to the wind farms, especially for those with close spacing. Therefore, the wind farm layout, the location of the wind turbines (WTs) is very essential to the performance of the whole wind farm, especially for large OWFs. In this research, we focus on the optimization of the large OWF layout by considering performance of the OWF, such as the total output energy. Firstly, the model for wind farm performance evaluation is established by incorporating historical wind speed data and the wake effect which can affect the total wind farm output. Then, by using the metaheuristic algorithms, the genetic algorithm (GA), the OWF layout is optimized. This study can offer useful information to the wind farm manufactures in the large OWF design phase.
The Impact of Exceptional Points on the Reliability of Thermoacoustic Stability Analysis
Authors: Schäfer Felicitas , Guo Shuai , Polifke Wolfgang
Published: January 2021

Exceptional points can be found for specific sets of parameters in thermoacoustic systems. At an exceptional point, two eigenvalues and their corresponding eigenfunctions coalesce. Given that the sensitivity of these eigenvalues to parameter changes becomes infinite at the exceptional point, their occurrence may greatly affect the outcome and reliability of numerical stability analysis. We propose a new method to identify exceptional points in thermoacoustic systems. By iteratively updating the system parameters, two initially selected eigenvalues are shifted towards each other, ultimately colliding and generating the exceptional point. Using this algorithm, we were able to identify for the first time a physically meaningful exceptional point with positive growth rate in a thermoacoustic model. Furthermore, our analysis goes beyond previous studies inasmuch as we employ a more realistic flame transfer function to model flame dynamics. Building on these results, we analyze the effect of exceptional points on the reliability of thermoacoustic stability analysis. In the context of uncertainty quantification, we show that surrogate modeling is not reliable in the vicinity of an exceptional point, even when large sets of training samples are provided. The impact of exceptional points on the propagation of input uncertainties is demonstrated via Monte Carlo computations. The increased sensitivity associated with the exceptional point results in large variances for eigenvalue predictions, which needs to be taken into account for reliable stability analysis.
Experimental Results of Local Shear Stresses and Friction Torque in an Open Rotor-Stator Disc System
Authors: Kuntze Alexander , Odenbach Stefan , Uffrecht Wieland
Published: January 2021

This contribution presents experimental investigations of friction torque in an open rotor-stator disc system by using two different measuring procedures. The first procedure based on a thermo electrical wall shear stress sensor. The sensor is investigated in two different substrates and different measuring parameters. A thermal model consisting of the supplied heating power, the thermal resistance toward the fluid, and into the substrate as well as the over temperature is used to achieve the heat transfer coefficient on the sensor surface. This heat transfer coefficient is attributed by a functional relationship to the wall shear stress. This relationship is firstly calibrated in a rectangular channel and subsequently validated at a fully turbulent flat plat flow.

The second measuring procedure based on the tangential displacement of the stator disc due the friction torque. The disc is attached at a torsion spring. The friction torque is achieved by the torsion spring constant and the tangential displacement of the stator disc. Both measuring procedures are compared and agree well with each other.

The used test rig has the possibility of reaching rotational Reynolds numbers representative for instance of a modern gas turbine. The investigations were carried out by a 0.5 m diameter rotor disc rotating up to 8500 rpm with a gap ratio between 0.008 and 0.04. The friction torque is measured on the stator disc and can be converted into moment coefficient. Moment coefficient on stator as well as measured pressure distributions are presented for different gap ratios and rotational Reynolds number.
Numerical Investigation of Conjugate Heat Transfer in an Effusion and Impingement Cooled Combustor Wall
Authors: Jackowski Thomas , Elfner Maximilian , Bauer Hans-Jörg
Published: January 2021

In this paper, a numerical investigation of conjugate heat transfer in a double-wall combustor will be presented. The model replicates the cooling air duct, the double wall with impingement and effusion cooling, as well as the hot gas duct. For simplification, the walls are modeled planar, and the test parameters were adapted from an upcoming experiment at the Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology. The geometry was scaled up by a factor of 8 through performing a similarity analysis. Aerodynamic and thermal boundary conditions were scaled to ambient pressure and low temperatures while maintaining dimensionless quantities from realistic operating conditions. The diameter of the cylindrical impingement cooling holes is D = 4mm. The effusion cooling holes are angled with α = 30° to the surface and have a cylindrical entrance diameter of E=2D. The outlet of the effusion cooling hole is fanshaped with an opening of 7° to each side as well as laidback by 7°. Both walls have a staggered pattern in which the rows of holes are repeated every 4th row.

A range of blowing ratios from Meff = 0.5 to 3.0 was set as operating conditions for the calculations. Besides, the distance between the impingement wall and the effusion wall was varied from Hcav = 3D to 7D to investigate the influence on heat transfer and aerodynamic behavior of the setup.

The results show an increase in the overall cooling effectiveness θ while reducing the cavity height Hcav. The overall cooling effectiveness θ increases with higher blowing ratios M but shows an absolute saturation above blowing ratios of approximately M > 2.0. Another significant finding is the aerodynamically unfavorable flow of the coolant into the effusion cooling holes and the identification of the flow path from the coolant.
Life Cycle Analysis for a Powertrain in a Concept for Electric Power Generation in a Hybrid Electric Aircraft
Authors: Schneider Michael , Dickhoff Jens , Kusterer Karsten , Visser Wilfried
Published: January 2021

In the recent decades, civil aviation was growing 4.7% per annum. In order to reduce emissions promoting the global warming process, alternative propulsion systems are needed. Full-electric propulsion systems in aviation might have the potential for emission-free flights using renewable energy. However, several research efforts indicate electric propulsion only seems feasible for small aircraft. Especially due to the low energy density of batteries compared to fossil fuels.

For this reason, hybrid propulsion systems came into focus, combining the benefits of all-electric and conventional propulsion system concepts. It is also considered as bridging technology, system test and basis for component development — and therewith paves the way towards CO2 free aviation. In the ‘HyFly’ project (supported by the German Luftfahrtforschungsprogramm LuFo V-3), the potential of a hybrid electric concept for a short/mid-range 19 PAX aircraft is assessed — not only on system but also on single component basis. In a recent study, the propulsion architecture and the operating mode of the gas turbine and the electric components have been defined [1].

In this paper, the advantages of the hybrid propulsion architecture and a qualitative assessment of component life are presented. Methods for life time prediction for the aircraft engine, the electric motor, the reluctance generator and the battery are discussed. The impact of turbine inlet temperature on life consumption is analyzed. The life cycle of the aircraft engine and the electric components including gradual component deterioration and consequent performance degradation is simulated by using an in-house gas turbine simulation tool (GTPsim). Therefore, various effects on electric propulsion system can be predicted for the entire drivetrain system in less than one hour.
A General-Purpose Test Facility for Evaluating Gas Lubricated Thrust Bearings
Authors: Gary Keith , Ertas Bugra , Delgado Adolfo
Published: January 2021

The design, construction, operational capabilities, and proof of concept results are presented for a test rig used to evaluate gas-lubricated thrust bearings. The following work is motivated by a desire to utilize the working fluid of high-performance turbomachinery, such as gas turbines, for bearing lubricant. Auxiliary equipment required to cool, pump, and clean oil for a typical thrust bearing is eliminated by taking advantage of the turbomachinery’s working fluid as bearing lubricant. The benefit of removing such auxiliary equipment is obvious when considering cost and weight of turbomachines, yet the working fluid of gas turbines typically has very low viscosity compared to oil which introduces load capacity and stability challenges. It is therefore necessary to build a facility capable of testing gas-lubricated thrust bearings to advance the technology. The test rig design in this work allows for 7 to 15 inch (180–380 mm) diameter thrust bearings, static loads up to 30,000 lbf (135 kN), and speeds up to 20 krpm. The test facility also provides up to 500 psig (3.45 MPa) static air pressure to enable testing of hydrostatic and hybrid (hydrodynamic combined with hydrostatic) bearings. This paper describes the test rig operating principle, details experimental procedures to obtain measurements, and provides test results necessary to prove the test rig concept by means of a hybrid gas bearing.
Numerical and Analytical Investigation of Heat Transfer Mechanisms and Flow Phenomena in an IP Steam Turbine Blading During Startup
Authors: Bohn Dieter , Betcher Christian , Kusterer Karsten , Weidtmann Kristof
Published: January 2021

As a result of an ever-increasing share of volatile renewable energies on the world wide power generation, conventional thermal power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction and determination of the metal temperature distribution inside these components is crucial. Therefore, boundary conditions in terms of local fluid temperatures as well as heat transfer coefficients with sufficient accuracy are required. As modern numerical modeling approaches, like 3D-Conjugate-Heat-Transfer (CHT), provide these thermal conditions with a huge calculation expense for multistage turbines, simplified methods are inevitable. Analytical heat transfer correlations are thus the state-of-the-art approach to capture the heat transport phenomena and to optimize and design high efficient startup curves for flexible power market.

The objective of this paper is to understand the predominant basic heat transfer mechanisms such as conduction, convection and radiation during a startup of an IP steam turbine stage. Convective heat transport is described by means of heat transfer coefficients as a function of the most relevant dimensionless, aero-thermal operating parameters, considering predominant flow structures. Based on steady-state and transient CHT-simulations the heat transfer coefficients are derived during startup procedure and compared to analytical correlations from the literature, which allow the calculation of the heat exchange for a whole multistage in an economic and time-saving way.

The simulations point out that the local convective heat transfer coefficient generally increases with increasing axial and circumferential Reynolds’ number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The heat transfer coefficients at vane, blade, hub and labyrinth-sealing surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds’ number. The comparison illustrates that the analytical correlations underestimate the convective heat transfer by approx. 40% on average. Results show that special correlation-based approaches from the literature are a particularly suitable and efficient procedure to predict the heat transfer within steam turbines in the thermal design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.
The Effect of Thermal Barrier Coating Surface Temperature on the Adhesion Behavior of CMAS Deposits
Authors: Clark Robert A. , Plewacki Nicholas , Gnanaselvam Pritheesh , Bons Jeffrey P. , Viswanathan Vaishak
Published: January 2021

The interaction of thermal barrier coating’s surface temperature with CMAS (calcium magnesium aluminosilicate) like deposits in gas turbine hot flowpath hardware is investigated. Small Hastelloy X coupons were coated in TBC using the air plasma spray (APS) method and then subjected to a thermal gradient via back-side impingement cooling and front-side impingement heating using the High Temperature Deposition Facility (HTDF) at The Ohio State University (OSU). A 1-D heat transfer model was used to estimate TBC surface temperatures and correlate them to intensity values taken from infrared (IR) images of the TBC surface. TBC frontside surface temperatures were varied by changing back-side mass flow (kept at a constant temperature), while maintaining a constant hot-side gas temperature and jet velocity representative of modern commercial turbofan high-pressure turbine (HPT) inlet conditions (approximately 1600K and 200 m/s, or Mach 0.25). In this study, Arizona Road Dust (ARD) was utilized to mimic the behavior of CMAS attack on TBCs. To identify the minimum temperature at which particles adhere, the back-side cooling mass flow was set to the maximum amount allowed by the test setup, and trace amounts of 0–10 μm ARD particles were injected into the hot-side flow to impinge on the TBC surface. The TBC surface temperature was increased through coolant reduction until noticeable deposits formed, as evaluated through an IR camera. Accelerated deposition tests were then performed where approximately 1 gram of ARD was injected into the hot side flow while the TBC surface temperature was held at various points above the minimum observed deposition temperature. Surface deposition on the TBC coupons was evaluated using an infrared camera and a backside thermocouple. Coupon cross sections were also evaluated under a scanning electron microscope for any potential CMAS ingress into the TBC. Experimental results of the impact of surface temperature on CMAS deposition and deposit evolution and morphology are presented. In addition, an Eulerian-Lagrangian solver was used to model the hot-side impinging jet with particles at four TBC surface temperatures and deposition was predicted using the OSU Deposition model. Comparisons to experimental results highlight the need for more sophisticated modeling of deposit development through conjugate heat transfer and mesh morphing of the target surface. These results can be used to improve physics-based deposition models by providing valuable data relative to CMAS deposition characteristics on TBC surfaces, which modern commercial turbofan high pressure turbines use almost exclusively.
Low Fidelity, Numerical Simulation of Gas Turbine Propulsion Across Off Design Conditions
Authors: De Luca Mark John , Taylor Ian J.
Published: January 2021

This paper presents the first section of work carried out as part of a larger research investigation into the feasibility of engine type architecture for specific mission profiles, pertaining to next generational concepts of spacecraft propulsion. Significant work has been undertaken to improve the capability of an existing simulation code, HyPro, used to model all aspects of propulsion technologies, with a focus being given to developing gas turbine type components. The paper explores the implementation of an approach that circumvents the requirements for detailed component mapping and eliminates the need for a fixed, specified design point, presenting early stage validation data of the methodology selected for the modelling, which will go towards justifying its inclusion to the code library.
Nozzle Passage Endwall Effectiveness Values With Various Combustor Coolant Flow Rates: Part 1 — Flowfield Velocity and Coolant Concentration Measurements
Authors: Nawathe Kedar P. , Zhu Rui , Lin Enci , Kim Yong W. , Simon Terrence W.
Published: January 2021

The stators of the first stage of a gas turbine are exposed to severe temperatures. The coolant streams introduced to prevent the stators from thermal damage further complicate the highly three-dimensional flow in the vane passage. Recent results have shown that, in addition to these coolant streams, the coolant streams injected for cooling the combustor also influence the flow physics and the cooling effectiveness in the first-stage stator vanes passage. However, the effects of changing the mass flow rate of these combustor coolant streams on the passage flowfield have not been studied. As understanding the coolant transport is necessary for analyzing changes in cooling effectiveness in the vane passage, detailed aerodynamic and thermal measurements along the whole vane passage are required. This two-part paper presents such measurements taken in a first-stage nozzle guide vane cascade for a variety of combustor coolant and endwall film coolant flow rates. The experiments were conducted in a low-Mach-number facility with engine-representative Reynolds numbers and large-scale high-level turbulence. The objective of the first part of the paper is to describe the flow that influences endwall and vane surface cooling effectiveness distributions, which are presented in the second part of this paper. The measurements show changes in the passage flowfield due to changes in both combustor coolant and endwall film coolant flow rates. Overall, the flow-physics remains largely unaffected by changes in coolant flow rates except in the endwall-vane surfaces region where the combustor coolant flow rate dominates changes in coolant transport. This is shown to have a high impact on endwall and vane surface cooling.
Fretting Wear of T800 Coating in Aero-Engine Applications
Authors: Lavella Mario , Botto Daniele
Published: January 2021

High cycle fatigue in blades is triggered by oscillating forces. Devices such as shrouds, that exploit dry friction, are commonly introduced in the blade assembly to reduce the blade vibrations. If severe wear occurs, the effectiveness of the dry friction damping decreases, vibrations increase, and the number of cycles to failure of the blade diminishes. Mating surfaces in shrouds undergo high loads combined with relative displacement of low amplitude. This is the typical condition known as fretting. Coatings are commonly applied on damping surfaces of turbine blades to mitigate wear.

This study investigates the wear mechanism of contact interfaces coated by Tribaloy® T-800, a coating greatly used in aeroengines. The experimental campaign was performed with a point contact test rig. The investigation was carried out using as test parameters temperature, normal load and fretting amplitude. Nine sets of parameters were analyzed at different test durations. Friction coefficients were computed using the hysteresis loops measured during the fretting tests. The worn surfaces were measured by an optical equipment based on focus variation and the volume losses were accurately measured. The wear region was observed by scanning electron microscopy at the end of each test.

At room temperature, the friction coefficient was found substantially independent of the normal load. The wear rates at room temperature were higher than at high temperature. Observation of the worn surfaces by scanning electron microscopy revealed several brittle cracks. The damage mechanism changes from brittle (at room temperature) to ductile (at high temperature). The volume loss as a function of the dissipated energy was found independent of the normal load, showing that dissipated energy is a better variable rather than the number of wear cycles to show results of wear tests.
Effect of Altitude on Turbomachinery Vibration in an Aircraft Compression-Ignition Engine
Authors: McGowan Ryan C. , Fellows David W. , Bodony Daniel J. , Mojica Jovany R. , Pieri James J. , Kweon Chol-Bum M. , Gibson Joseph A. , Meininger Rik D. , Musser Marshall R.
Published: January 2021

To investigate the effect of altitude on vibrations in a turbocharger, an aircraft compression-ignition engine was operated in both a sea level cell and an altitude chamber up to 25,000 ft (7620 m). The turbocharger was instrumented with a nonintrusive stress measurement system to analyze the frequencies, magnitudes, and critical speeds of the blade bending modes as the ambient pressure, ambient temperature, and engine power varied. The measurements were also compared to data from accelerometers mounted on the compressor housing. At sea level conditions, the largest deflection amplitudes were associated with excitations of the first blade bending mode. These deflections grew in amplitude as the altitude increased and the turbocharger/engine worked harder to produce the required pressure rise and power. There was also evidence of a higher-order mode being excited at elevated altitudes. By understanding the factors contributing to resonance and flutter in aircraft turbomachinery, modeling and prediction tools can be improved to update operating envelopes for current designs and minimize these phenomena in future, aviation-specific designs.
Application of a Convolutional Neural Network for Wave Mode Identification in a Rotating Detonation Combustor Using High-Speed Imaging
Authors: Johnson Kristyn B. , Ferguson Donald H. , Tempke Robert S. , Nix Andrew C.
Published: January 2021

Utilizing a neural network, individual down-axis images of combustion waves in a Rotating Detonation Engine (RDE) can be classified according to the number of detonation waves present and their directional behavior. While the ability to identify the number of waves present within individual images might be intuitive, the further classification of wave rotational direction is a result of the detonation wave’s profile, which suggests its angular direction of movement. The application of deep learning is highly adaptive and therefore can be trained for a variety of image collection methods across RDE study platforms. In this study, a supervised approach is employed where a series of manually classified images is provided to a neural network for the purpose of optimizing the classification performance of the network. These images, referred to as the training set, are individually labeled as one of ten modes present in an experimental RDE. Possible classifications include deflagration, clockwise and counterclockwise variants of co-rotational detonation waves with quantities ranging from one to three waves, as well as single, double and triple counter-rotating detonation waves. After training the network, a second set of manually classified images, referred to as the validation set, is used to evaluate the performance of the model. The ability to predict the detonation wave mode in a single image using a trained neural network substantially reduces computational complexity by circumnavigating the need to evaluate the temporal behavior of individual pixels throughout time. Results suggest that while image quality is critical, it is possible to accurately identify the modal behavior of the detonation wave based on only a single image rather than a sequence of images or signal processing. Successful identification of wave behavior using image classification serves as a stepping stone for further machine learning integration in RDE research and comprehensive real-time diagnostics.
Aeromechanical Analysis of a Complete Wind Turbine Using Nonlinear Frequency Domain Solution Method
Authors: Naung Shine Win , Rahmati Mohammad , Farokhi Hamed
Published: January 2021

The high-fidelity computational fluid dynamics (CFD) simulations of a complete wind turbine model usually require significant computational resources. It will require much more resources if the fluid-structure interactions between the blade and the flow are considered, and it has been the major challenge in the industry. The aeromechanical analysis of a complete wind turbine model using a high-fidelity CFD method is discussed in this paper. The distinctiveness of this paper is the application of the nonlinear frequency domain solution method to analyse the forced response and flutter instability of the blade as well as to investigate the unsteady flow field across the wind turbine rotor and the tower. This method also enables the aeromechanical simulations of wind turbines for various inter blade phase angles in a combination with a phase shift solution method. Extensive validations of the nonlinear frequency domain solution method against the conventional time domain solution method reveal that the proposed frequency domain solution method can reduce the computational cost by one to two orders of magnitude.
A Comparison of Unsteady RANS and DES for Simulating an Axial Compressor Stage
Authors: Miller Edward A. , Cave Michael J. , Williams David M. , Thayalakhandan Khandan
Published: January 2021

Computational fluid dynamics (CFD) of industrial-scale, axial compressor geometries has traditionally been performed using steady state methods such as the mixing plane approach. With the surge in the development of large-scale, massively-parallel computing platforms, fully 3D unsteady approaches are rapidly growing in popularity. The fully 3D, unsteady approach involves building a full 3D domain for each blade row, and then coupling the stationary and rotating domains using a sliding interface. In the literature, there are various methods for solving this 3D unsteady problem, such as the Unsteady Reynolds Averaged Navier-Stokes (URANS) and the Detached Eddy Simulation (DES) methods. While these methods are well documented for a variety of real-world problems, there have been limited efforts to compare the effectiveness of these methods for fully 3D, unsteady turbomachinery problems.

In this study, the first stage of an industrial-scale axial compressor was simulated using: i) the URANS approach, and ii) the DES approach. The compressor geometry consisted of an inlet housing, inlet guide vanes (IGV), a rotor, and a stator. The RANS model for both simulations was the k-epsilon model. For both of these cases, sliding mesh interfaces were located between the IGV and rotor, and between the rotor and stator. The results of the URANS and DES approaches were time-averaged and their predictions were compared. Throughout the study, our goal was to provide important insights into the performance of the URANS and DES approaches, and to highlight the essential differences.
Non-Circular and Non-Cylindrical Streamvanes
Authors: Gillespie John , Lowe K. Todd
Published: January 2021

We show that desired swirl distributions may be obtained in non-circular and non-cylindrical inlet ducts by tailored vane distributions designed with an a priori method, and further explain dominant physics for the spatial evolution of swirl in expanding or contracting ducts. Virginia Tech has developed the StreamVane™ device for producing swirl distortion, as well as the ScreenVane™ device for producing combined swirl and pressure distortions. Up to now, all StreamVane and ScreenVane devices have designed to fit in a right, circular cylindrical duct. This is usually the simplest geometry to use for testing the response (in terms of performance and stall margin changes, as well as aeromechanics) of turbofan engines to inlet distortion.

However, many potential applications exist for generating or removing swirl distortions in ducts that are not cylindrical. For example, turboshaft engines generally do not have a cylindrical inlet to install a StreamVane in front of. Yet, inlet distortion is still very relevant to the performance of the engine. With a non-cylindrical StreamVane, inlet distortions generated by various flight conditions can be tested in conjunction with the real aircraft inlet. Further applications exist both within and outside of the field of turbomachinery for flow conditioning purposes. Four separate conceptual designs were created and analyzed: a converging duct (nozzle), a diverging duct (diffuser), a square duct, and an annular duct. Twin vortex swirl profiles were specified for all of the cases except the annular duct, which was designed to create a single vortex.

However, in a real application, these swirl profiles would instead be specified by the end-user depending on what is required for the test. As in circular cylindrical StreamVanes, the end-user has the option of selecting any physically consistent swirl profile. All of the concept designs were checked with CFD analysis in ANSYS CFX. The square and annular StreamVanes showed comparable performance to a baseline StreamVane in a cylindrical duct (RMS errors of 1.5° or less). The StreamVanes placed in a nozzle and diffuser demonstrated that swirl patterns may also be created in converging and diverging ducts, and that the varying cross sectional area has a non-negligible influence on the development of the swirl profile. A simple explanation has been made for this altered flow development has been, and is shown to make good quantitative predictions of the changes in swirl with downstream location.

The demonstration of the capability to create StreamVanes for applications that do not use cylindrical ducts should open a variety of possibilities, while building on existing experiences.
Theoretical Study on Static Performance of Herringbone Grooved Aerodynamics Foil Bearing
Authors: Dong ZeDa , Cheng Cheng , Xu Fangcheng
Published: January 2021

In this paper, the mathematical model of herringbone grooved aerodynamic foil bearings is established, and the finite difference method is used to obtain the discretized form of Reynolds equation. The static characteristics of bearings, such as film pressure, film temperature, are obtained by solving the Reynolds equation and energy equation. The bearing load capacity and friction power consumption are obtained by calculating the film thickness and film pressure distribution in the bearing gap. The influence of the bearing operational parameters, such as eccentricity and rotation speed, and the bearing structural parameters, such as groove width, groove depth ratio, groove number and helix angle, on the bearing load capacity and friction power consumption of bearings are analyzed. The methods of improving bearing load capacity and reducing friction power consumption are obtained. Simultaneously, by comparing the bearing load capacity and friction power consumption of herringbone grooved gas foil bearings and gas foil bearings (GFBs) without herringbone grooves, the influence of herringbone grooves on the bearing performance is obtained.
Very Large Eddy Simulation of Film Cooling Effectiveness on Trailing Edge Cutback
Authors: Yan Xin
Published: January 2021

The trailing edge of high pressure gas turbine blade in aeroengine is usually designed as thin as possible to achieve higher aerodynamic efficiency. However, as the inlet temperature of modern gas turbine is continuously increasing, thermal stress in a thin trailing edge will become much significant, resulting in possibilities of erosion and creep problems. To find a balance between these two conflicting goals, one method is the use of pressure-side cutback, which extends into the coolant slot to get film cooling and also achieves a thin trailing edge. Due to the interactions between mainstream and coolant flow, film cooling effect on trailing edge cutback is significantly affected by the vortex shedding downstream the cooling slot. To resolve the coherent flow structures and understand their role on film cooling effect on trailing-edge cutback, this paper implemented a Very Large Eddy Simulation (VLES) model into the solver ANSYS Fluent with user defined functions. By introducing a resolution control factor, the turbulence viscosity predicted by transient SST k-ω model was corrected and the VLES computations were realized in the whole computational region. With the VLES method, film cooling effectiveness distributions on trailing-edge cutback at three blowing ratios were computed and compared against the experimental data. The coherent unsteadiness in cutback region was visualized to reveal the mixing process between mainstream and coolant flow. The numerical accuracies between different unsteady prediction methods, i.e. URANS (Unsteady Reynolds Averaged Navier-Stokes), SAS (Scale-Adaptive Simulation), DES (Detached Eddy Simulation), DDES (Delayed-Detached Eddy Simulation), SBES (Stress-Blended Eddy Simulation), and VLES were compared with respect to the resolutions of cooling effect and vortex shedding. The results show that the periodic vortex shedding induced by the interactions between mainstream and coolant is the main factor that affecting the cooling performance on cutback. VLES method has a comparable accuracy in predicting the film cooling effect on trailing edge cutback with DDES and SBES approaching. In the detached shear layer, VLES method exhibits a good ability to resolve coherent unsteadiness caused by vortex shedding. Compared with URANS and SAS methods, the VLES method has a higher accuracy in resolving the periodic vortex shedding and film cooling effectiveness distributions, especially in low blowing ratio cases.
Uncertainty Quantification of Mass and Aerodynamic Rotor Imbalance for Offshore Wind Turbines
Authors: Ward Nicholas J. , Ekwaro-Osire Stephen , Dias João Paulo
Published: January 2021

One promising way to address turbine durability issues is early detection of mass and aerodynamic imbalances. More probabilistic methods are necessary to improve the accuracy of rotor imbalance diagnostics. The research question that this work addresses is: can current imbalance detection for an offshore wind turbine be improved through uncertainty quantification of its operating conditions? An uncertainty quantification strategy was proposed to model uncertainties in wind speed, pitch angle, and blade mass density using assumed probability density functions based on available data/information. These input parameters served as random variables that were fed into an aeroelastic software to model dynamic and power output variables for multiple imbalance scenarios. 4% variation in wind speed exhibited power differences as much as 500-kW for given imbalance cases. Additionally, the results indicated that a 10% variation in pitch angle, and blade mass density demonstrated power differences of 20-kW and 10-kW respectively due to imbalance in one blade. In addition, probability distributions for power output and dynamic loading indicated that turbine underperformance and excessive blade loading occurred approximately 40–52% and 45–77% of the time respectively depending on the imbalance scenario. This imbalance detection strategy could serve as a useful tool to help minimize turbine operation uncertainties.
Data-Tuned Fuzzy Logic Controller Applied to a Horizontal Axis Wind System
Authors: Dambrosio Lorenzo
Published: January 2021

This paper deals with the control problem concerning the output voltage frequency and amplitude regulation of a wind system power plant not connected to the supply grid. The wind system configuration includes a horizontal-axis wind-turbine which drives a synchronous generator. An appropriate modeling approach has been adopted for both the wind-turbine and the synchronous generator. The proposed controller makes use of the fuzzy logic environment in order to take advantage of the wind plant system informations integrated into a limited number of equilibrium condition points (input variable - output variable pairs). The fuzzy logic controller described in the present paper merges the most appropriate fuzzy rules clusters, based on the steady state working conditions. Then, thanks to a Least Square Estimator algorithm, the proposed control algorithm evaluates, for each sample time, the linear relation between control law correction and control tracking error levels. In order to demonstrate robustness of the suggested fuzzy control algorithm, two sets of results have been provided: the first one consider a fuzzy base with equally spaced rules, whereas, in the second set results, the number of fuzzy rules is reduced by a 25%.
Gas Turbine Direct Exhaust Gas Integration in Process Industry: Applications Review
Authors: Cichocki Marek , Salamonik Ilona , Bielecki Marcin , Fadlun Ever , Rusowicz Artur
Published: January 2021

The typical combined heat and power plants requires the introduction of additional heating medium. The alternative solution is the direct integration of the exhaust gases from heat engine. High temperature, surplus oxygen and low water content of the Gas Turbines exhaust gases enabled the successful integration at industrial scale as: preheated combustion air for industrial furnaces, heat source for drying and for absorption chillers. The article comprises the reference list for direct exhaust gas integration of GTs produced by Baker Hughes formerly GE), the processes overview, GTs selection criteria, as well as the review of documented GTs applications in process industry focusing on technical and economic considerations.

Majority of referenced applications for industrial furnace are in the steam methane reformers used in fertilizer industry, as well as steam crackers in petrochemical industries. Several GTs were integrated with crude oil furnace in refinery. Direct drying utilizing exhaust gas from GT, is commonly applied in ceramic, wood derivative, pulp & paper and inorganic chemicals industries. Integrating GTs with absorption chillers was introduced to serve the district heating and cooling system.

The described solutions allowed to reduce specific energy consumption by 7–20% or the costs of energy consumption associated with large volume production by 15–30%. The reduction of specific energy consumption allows to decrease the amount of CO2 emitted. The overall efficiency of cogeneration plant above 90% was achieved.
The Influence of Element Thermal Conductivity, Shape, and Density on Heat Transfer in a Rough Wall Turbulent Boundary Layer With Strong Pressure Gradients
Authors: Gramespacher Christoph , Albiez Holger , Stripf Mattias , Bauer Hans-Jörg
Published: January 2021

Formation mechanisms for turbine roughness are manifold, including erosion, corrosion, deposition, and spallation or more recently additive manufacturing processes. Consequently, the resulting surfaces differ remarkably not only in roughness shape, height, and density, but also in element thermal conductivity. Because the roughness elements extend into the boundary layer, their temperature distribution has a direct influence on the thermal boundary layer and thus on the resulting convective heat transfer. In the current study, heat transfer distributions along a flat plate with more than 20 deterministic rough surface topographies that differ in element eccentricity, height and density are measured. For each surface roughness, measurements are conducted using two different element thermal conductivities (0.2 W/(mK) and 30 W/(mK)), two pressure distributions, four Reynolds numbers between 3 × 105 and 7.5 × 105 and various inlet turbulence intensities in the range of 1.5% to 8%. The pressure distributions resemble a typical suction and pressure side, respectively. Results show a heat transfer increase of up to 60% for the high thermal conductivity surfaces and up to 50% for the low conductivity ones. While heat transfer on the high conductivity surfaces is always higher than on the low conductivity ones, the difference becomes smaller with decreasing element density.
Monitoring Damage in Non-Oxide Composites at High Temperatures Using Carbon-Containing CVD SiC Monofilament Fibers As Embedded Electrical Resistance Sensors
Authors: Panakarajupally Ragav P. , Elrassi Joseph , Manigandan K. , Singh Yogesh P. , Morscher Gregory N.
Published: January 2021

Electrical resistance has become a technique of interest for monitoring SiC-based ceramic composites. The typical constituents of SiC fiber-reinforced SiC matrix composites, SiC, Si and/or C, are semi-conducive to some degree resulting in the fact that when damage occurs in the form of matrix cracking or fiber breakage, the resistance increases. For aero engine applications, SiC fiber reinforced SiC, sometimes Si-containing, matrix with a BN interphase are often the main constituents. The resistivity of Si and SiC is highly temperature dependent. For high temperature tests, electrical lead attachment must be in a cold region which results in strong temperature effects on baseline measurements of resistance. This can be instructive as to test conditions; however, there is interest in focusing the resistance measurement in the hot section where damage monitoring is desired. The resistivity of C has a milder temperature dependence than that of Si or SiC. In addition, if the C is penetrated by damage, it would result in rapid oxidation of the C, presumably resulting in a change in resistance. One approach considered here is to insert carbon “rods” in the form of CVD SiC monofilaments with a C core to try and better sense change in resistance as it pertains to matrix crack growth in an elevated temperature test condition. The monofilaments were strategically placed in two non-oxide composite systems to understand the sensitivity of ER in damage detection at room temperature as well as elevated temperatures. Two material systems were considered for this study. The first composite system consisted of a Hi-Nicalon woven fibers, a BN interphase and a matrix processed via polymer infiltration and pyrolysis (PIP) which had SCS-6 monofilaments providing the C core. The second composite system was a melt-infiltrated (MI) pre-preg laminate which contained Hi-Nicalon Type S fibers with BN interphases with SCS-Ultra monofilaments providing the C core. The two composite matrix systems represent two extremes in resistance, the PIP matrix being orders of magnitude higher in resistance than the Si-containing pre-preg MI matrix. Single notch tension-tension fatigue tests were performed at 815°C to stimulate crack growth. Acoustic emission (AE) was used along with electrical resistance (ER) to monitor the damage initiation and progression during the test. Post-test microscopy was performed on the fracture specimen to understand the oxidation kinetics and carbon recession length in the monofilaments.