bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effects of High Centrifugal Acceleration on Bluff-Body Stabilized Premixed Flames
Authors: Erdmann Timothy , Gutmark Ephraim , Caswell Andrew 
Published: October 2022

Abstract
An experimental study is conducted on bluff-body stabilized premixed flames in a curved, square cross-section duct. High flow velocities coupled with a small radius of curvature of the duct induce high centrifugal acceleration normal to the flame sheet. A cylindrical flame holder spans the width of the square cross-section and is positioned at the channel mid-height. Flame shear layers are stabilized on the radially inward (upper) and outward (lower) edges of the flame holder. Side-view high-speed Schlieren images and high-speed pressure measurements are captured. Static stability, overall pressure loss, and statistics and velocimetry results from the Schlieren images are reported, and results are compared to a straight configuration with no centrifugal acceleration. Two bluff-body diameters are studied to show the effect of flame holder diameter on static stability. For the curved configuration, blowout velocities are higher for the smaller bluff-body diameter, likely due to flow acceleration effects. Blowout velocities are lower for the curved configuration compared to the straight configuration which may be due to the destabilizing Rayleigh-Taylor (RT) effect on the upper flame layer. Overall pressure loss is slightly higher for the curved configuration than the straight configuration. High-speed Schlieren results show centrifugal acceleration causes significant structural and velocimetric asymmetry in the bluff-body wake. In the curved configuration, the upper flame layer displays destabilizing RT instabilities, and the lower flame layer displays stabilizing RT effects. The upper flame shows vigorous RT instabilities which broaden the flame brush and sustain a flame leading edge independent of inlet Reynolds number or velocity. Conversely, the lower flame exhibits suppression of Kelvin-Helmholtz and flame-generated instabilities in the wake, which confines the flame brush and significantly reduces transverse flame velocities. The lower flame edge profile moves toward the channel centerline with increasing inlet Reynolds number. The upper flame in the curved configuration shows higher flame edge velocities than the straight configuration while the lower flame shows velocities closer to zero. The empirical constant to the power law relation for upper flame edge velocities agrees with RT-dominated flame growth theory for this experimental scale and agrees with other RT-dominated flame studies.
UHBR Open-Test-Case Fan ECL5/CATANA: Numerical Investigation Near the Stability Limit Including Aerodynamic Mistuning
Authors: Fiquet Anne-Lise , Ottavy Xavier , Brandstetter Christoph 
Published: October 2022

Abstract
Non-synchronous blade vibration (NSV) has received enormous attention in turbomachinery research, since it can be safety critical and its occurrence is less predictable than typical aeroelastic instabilities such as flutter. Typical for front stages of core compressors, NSV arises due to the propagation of one or multiple aerodynamic disturbances, traveling around the circumference and locking-in with structural blade vibration modes. Recent studies have shown, that modern low-speed fan architectures are also susceptible for this type of instability. With a specific focus on such aeroelastic instabilities, the open-test-case fan stage ECL5 has been designed by Ecole Centrale de Lyon. It is representative of near-future UHBR fan concepts with carbon-fibre composite blades. To prepare the experiments planned for 2022, unsteady full-annulus simulations have been carried out. Depending on rotation speed, the emergence of aerodynamic disturbances traveling around the circumference at a typical convective speed is observed, such as reported in studies on NSV on different configurations. These aerodynamic disturbances are identified as a possible source for non-synchronous vibration. At design conditions, an unstable aerodynamic behavior is observed, with part-span stall cells developing within the operating range predicted by RANS simulations. A study of intentional aerodynamic mistuning, in form of an alternating leading edge pattern is presented. At design speed, influence on steady performance and the onset of part-span stall is observed. At part-speed, the evolution of small-scale vortical disturbances, which can be responsible for the onset of NSV is affected significantly, providing a possible method to suppress NSV.
Predictions of Falling Wavy Films Based on the Depth Averaged Thin Film Model and Its Application to Aeroengine Bearing Chamber
Authors: Singh K. , Nicoli A. , Jefferson-Loveday R. , Ambrose S. , Paleo Cageao P. , Johnson K. , Mouvanal S. , Cao J. , Jacobs A. 
Published: October 2022

Abstract
In the present study, the evolution of a falling wavy film with upstream forced excitation is investigated using the depth averaged thin film model, known as Eulerian Thin Film Model (ETFM). Because of the depth averaging of the governing equations, coarse grids can be used in the wall normal direction. Consequently, this model is computationally efficient when compared to fully resolving thin films and hence highly advantageous for industrial simulations. In the case of a falling wavy film, film thickness and film velocity are closely coupled. A coupled solver that solves the depth averaged continuity and momentum equations simultaneously has been implemented with the provision to apply smoothing to the curvature of surface tension term to improve the accuracy and robustness of the model. The implemented model provides a stable solution for explicit as well as implicit temporal formulations. The performance of the newly implemented ETFM model is evaluated by comparing numerical results with experimental measurements and high-fidelity VOF simulations. The newly implemented model is found to be reliable in predicting free surface film profiles. It is 150 to 415 times computationally cheaper when compared to high-fidelity VOF simulations. The implemented and validated model is successfully used to predict a wavy film on the inlet of a representative aeroengine bearing chamber. The model is able to capture key flow physics on the front face of a static insert, which forms part of the bearing chamber inlet, and agrees well with experimental visualization of oil flow on the insert.
Impact of Upstream and Downstream Excitation and Multi-Row Interaction on the Mistuned Forced Response Behavior of an Embedded Compressor Rotor: Higher-Order Mode Aeromechanics
Authors: Hegde Shreyas , Zori Laith , Campregher Rubens , Kielb Robert 
Published: October 2022

Abstract
The current papers discuss the impact of separating the upstream and downstream forcing function contributions in an embedded compressor rotor. Previously, the authors have discussed separating the influence at a torsional mode crossing, and this paper expands this study to a higher-order mode crossing. This crossing occurs at a slower speed, and higher-order crossings are difficult to predict due to their low response for this configuration. The paper focuses on the multi-row interaction at multiple operating points and the mistuned blade response prediction. The computational model for this analysis uses the time transformation method within the commercial code CFX to help simplify the computational domain. The configuration chosen for this study is that the number of rotor blades and downstream stator blades have a common multiple, which allows the usage of a small number of passages in these rows. However, the upstream stator count does not satisfy this criterion. Hence, the time tilting method helps account for this difference in pitch and simplifies the computational domain. Both the upstream and the downstream rows excite the embedded rotor at different crossings. Additionally, the effect of wave reflection from a downstream or upstream row is considered. The responses are characterized at multiple operating points, i.e., nominal loading and high loading.
The second section of this paper describes the details of the in-house mistuning code utilized to predict the blade responses of the individual rotor blades in the system. One of the inputs to this code is the modal force obtained using unsteady CFD. The in-house code is based on the FMM, which couples both aerodynamic and structural dynamics to predict the blade responses. The key conclusions from this study were: 1) Physical wave reflections from the downstream stator were constructive at both the operating points. 2) The analysis at the 88EO crossing helped quantify the impact of physical wave reflections from a downstream rotating row. The influence was found to be destructive at both operating points, 3) The 3-row case with the downstream rotor in the computational model yielded the most accurate prediction of the blade response supporting earlier conclusions by the same authors that a downstream row was essential to predict the forcing function accurately.
Influence of Purge Flow Injection on the Performance of an Axial Turbine With Three-Dimensional Airfoils and Non-Axisymmetric Endwall Contouring
Authors: Schäflein Lukas , Janssen Johannes , Brandies Henri , Jeschke Peter , Behre Stephan 
Published: October 2022

Abstract
In this paper, we present the evaluation of the aerodynamic robustness to rim seal purge flow of an optimized 1.5-stage axial turbine configuration with a bowed stator profile and endwall contouring. Performance maps obtained by experiments and numerical simulations show that the efficiency benefit gained by this optimized configuration is partially reduced, but not eliminated, by the injection of purge flow through the cavity downstream of the first stator. Measurements with five-hole probes and hot-wire probes, as well as unsteady RANS simulations, give detailed insights into the physical effects of the purge flow inside the rotor passage. There, when no purge flow is injected, the optimized configuration diminishes the formation of loss-inducing secondary flow structures near the hub and the casing. When purge flow is injected, however, new strong secondary flow structures are induced near the hub. These vortices generate additional losses and thereby partially negate the efficiency benefits gained by the optimization. From the data, we found that this influence of the purge flow is limited to the lower half of the channel height. The data also shows that the optimized configuration is able to reduce the vorticity near the casing regardless of the purge flow injection, which in turn leads to an efficiency increase in this area. Together, these effects lead to a reduction of the previously gained efficiency benefit by the optimized configuration when it is subjected to purge flow injection. However, compared to a baseline configuration with cylindrical endwalls also subject to purge flow injection, the overall efficiency is still increased by 0.38%.
Hydrogen Thermal-Powered Aircraft Combustion and Propulsion System
Authors: Palies Paul P. 
Published: October 2022

Abstract
This article presents an assessment study of the propulsion system, the fuel distribution system, and the injector/combustor technologies enabling to eliminate CO2 emissions in aviation. In addition, the discussion is on NOx reduction methods and mitigation technologies, and a concept to fully eliminate NOx is proposed. To design and deploy an advanced thermal-powered aircraft based on liquid hydrogen fuel in future, it is important to provide key estimates that support feasibility of the methods and technologies developed and explored in this paper. This is conducted here for a typical narrow-body aircraft that will be retrofitted and considered. Once the design space and performance requirements are introduced, a compact low emission combustor including all components is discussed to operate with hydrogen swirled combustion to equip the turbofan engines of this conceptualized aircraft. The fuel tank is not only discussed with respect to the difference in power per unit volume and per unit mass between Sustainable Aviation Fuel (SAF) and H2 but also taking into account the Breguet range. This demonstrates that the volume of the tanks does not need to be four times more voluminous between H2 and SAF. The paper also presents a thermodynamics performance analysis for SAF fuel that is used to retrofit the engine with hydrogen fuel keeping inlet and outlet combustor stagnation temperatures equivalent. A method to derive the required flow split for future premixed combustor is described and conserve identical thermal power between SAF and H2 fuels. Flame stabilization critical challenges are also introduced.
Prediction of Thermoacoustic Instability and Fluid-Structure Interactions for Gas Turbine Combustor
Authors: Xia Yu , Sharkey Patrick , Verma Ishan , Khaware Alok , Cokljat Davor 
Published: October 2022

Abstract
This work simulates a laboratory-scale 3D methane/air burner, which features a bluff body stabilized, lean partially premixed flame experiencing strong limit cycle oscillations. A thin steel liner is installed around the combustion chamber, which heavily interacts with the flow field and produces large amplitude structural deformation via Fluid-Structure Interactions (FSI). An unsteady RANS approach uses the Shear Stress Transport turbulence model and a Flamelet Generated Manifold combustion model to predict the thermoacoustic oscillations in the turbulent reacting flow. The solver also has a built-in finite element Structure Model, which solves the structural governing equations simultaneously with the CFD-computed, finite volume flow equations. This way, a fully coupled, two-way FSI simulation can be performed to predict the thermoacoustic instabilities and the associated solid deformations in the burner. Overall, the predicted strongest pressure oscillation and wall displacement modes (frequency and amplitude) are all in good agreement with the experimental data across different operating conditions. The established workflow may support realistic gas turbine combustor design and prognosis.
Unsteady Structure of Compressor Tip Leakage Flows
Authors: Maynard Joshua M. , Wheeler Andrew P. S. , Taylor James V. , Wells Roger 
Published: October 2022

Abstract
Direct numerical simulations (DNS) are performed of a cantilevered stator blade to identify the unsteady and turbulent flow structure within compressor tip flows. The simulations were performed with clearances of 1.6 and 3.2 percent of chord. The results show that the flow both within the gap and at the exit on the suction side are highly unsteady phenomena controlled by fine-scale turbulent structures. The signature of the classical tip leakage vortex is a consequence of time-averaging and does not exist in the true unsteady flow. Despite the complexity, we are able to replicate the flow within the tip-gap using a validated quasi-three-dimensional model. This enables a wide range of quasi-3D DNS simulations to study the effects of blade tip corner radius and Reynolds number. Tip corner radius is found to radically alter the unsteady flow in the tip; it affects both separation bubble size and shape, as well as transition mechanisms in the tip flow. These effects can lead to variations in tip mass flow of up to10 percent and a factor of2 variation in dissipation within the tip gap.
Heat Transfer and Pressure Loss Correlations for Leading Edge, Jet Impingement Using Racetrack-Shaped Jets With Filleted Edges
Authors: Kulkarni Ritwik V. , Wright Lesley M. 
Published: October 2022

Abstract
This paper presents an experimental investigation of heat transfer and pressure loss for leading edge jet impingement using racetrack shaped jets. The majority of literature considers jet impingement using square, or sharp edged orifices, to create the jets. However, for gas turbine cooling applications, the edge of the jet orifices generally has some degree of filleting (or rounding) along the edges. The rounding may be a result of casting the airfoils or material wear due to long-term operation. In addition, within the engine, it is likely the jet orifice is not perfectly round. Engineers need data under realistic engine configurations to improve the utilization of coolant while adequately protecting the airfoil. The current experimental study is a parametric investigation of heat transfer and pressure loss for leading edge jet impingement. In this investigation, the effects of jet Reynolds number (Re = 10,000–100,000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (z/d = 2–4), surface curvature (D/d = 2.67–5.33), and jet fillet-to-jet plate thickness (r/l = 0.16–0.5) are each considered. The inclusion of the fillet at both the inlet and outlet of the jet plate yields reduced heat transfer compared to the square edged jets. However, the fillets significantly improve the discharge coefficients associated with the racetrack shaped orifices. With the extensive testing completed in this study, design correlations have been developed to predict the surface Nusselt number and discharge coefficients including the geometrical parameters investigated in this study. The newly developed correlations accurately capture the geometrical effects and their deviations from the current experimental results are 10% and 19% for the Nusselt numbers and discharge coefficients, respectively. Engine designers can predict the level of heat transfer and pressure loss for leading edge jet impingement using these correlations.
Droplet Impact on a Curved Moving Liquid Film
Authors: Sinha Avick , Ramakrishnan Vaibhav , Johnson Kathy 
Published: October 2022

Abstract
The European Commission has set targets to reduce the emissions of CO2 and NOx by 75% and 90% respectively, per passenger kilometre, by 2050. Computational modelling of elements within the aero-engine will play a key role in achieving this goal. Currently, the computational models used to characterise impact outcomes from droplets splashing on wall films in bearing chambers are based on correlations obtained for droplet impacts on plane films. The present study bridges that gap, being the first experimental study investigating droplet impact on a film moving on a curved surface.
Experiments were conducted on a curved channel where the variation in the channel curvature provided the opportunity to investigate droplet impact at three different curvatures with three corresponding impact angles. Two droplet diameters of 2.34 mm and 1.90 mm were obtained using two different needle sizes attached to a syringe. The height of the syringe from the liquid film was varied to investigate the effect of droplet impact velocity. Five flow rates were considered to investigate the effect of film thickness on droplet impact. To investigate the dynamics of the droplet impact a high-speed imaging technique was used.
Qualitatively, two different impingement outcomes were observed, namely, crown formation and crown splashing. The key difference between the two outcomes is in the production of secondary droplets from the crown in crown splashing. Quantitatively, it was observed that at lower angles of impingement (less oblique), the transition from crown formation to crown splashing agrees strongly with previous literature for impact on static films and films on an angled plane where the transition value of the splashing parameter is 2100 based on the absolute velocity of the droplet. At the higher angles of impingement (more oblique), the critical splashing parameter (K) value was found to increase, as with droplet impact on an inclined surface or liquid film, but to a significantly higher value (2800 at 38°) than was typically obtained for an inclined plane (2400 at comparable angle). This indicates that the transition from crown formation to splashing at the highest radius of curvature is different to that of inclined planes at higher angles.
Investigating impact event duration, the present study suggests that with the increase in the impact energy, the time required for the film to come back to its original state increases.
The Modelling of Roughness Effect on the Performance of a Controlled Diffusion Airfoil
Authors: Delvaux Grégory , Toracchio Riccardo , Boufidi Elissavet , Croner Emma , Fontaneto Fabrizio 
Published: October 2022

Abstract
The manufacturing and operational roughness of aerodynamic profiles impacts both the laminar and the turbulent boundary layers state, directly affecting the aerodynamic and thermal performance of typical turbomachinery components. By better understanding the underlying physical mechanisms, the present work aims at building a more refined and comprehensive model to take the effects of surface finish into account. The model is implemented into the MIT Multiple blade Interacting Streamtube Euler Solver (MISES) and is validated against experimental results for different roughness levels, Reynolds number and Mach number regimes. In the proposed model, the roughness effects on the turbulent boundary layer (BL) state are included through the modification of the turbulent skin friction law, while the roughness level is implemented through a new definition of ks that accounts for the influence of the roughness skewness. Particular emphasis is placed on the modelling of the transitionally rough regime. Finally, roughness effects on transition are modelled by implementing the Mayle rough-induced onset transition criterion. Results are validated in terms of the total pressure loss coefficient and the outlet flow angle, leading to a marked improvement in terms of agreement with the experimental data.
Effects of Novel Roughened Wall of Swirl Cooling in Gas Turbine on Heat Transfer Characteristics and Pressure Drop
Authors: Elwekeel Fifi , Abdala Antar , Zheng Qun 
Published: October 2022

Abstract
In the present study the effects of ribbed and grooved walls of swirl cooling chamber on heat transfer and fluid flow characteristics are investigated. This study presents ten roughened wall shapes that are compared with a smooth wall in a swirl cooling chamber. The roughened wall shapes are circumferential and longitudinal with and without cut. The circumferential cases consist of four cases. The first case is called (CG) which has eight grooves along chamber surface. The second case is called (CGC) which has eight cut grooves along chamber surface. The third case (CR) and the fourth case (CRC) have eight ribs without and with cut along chamber surface. While the longitudinal cases, consist of six cases. The first four cases (LG, LGC, LR and LRC) have six longitudinal grooves and ribs without and with cut. The last two longitudinal cases (LRG and LRGC) have hybrid grooves and ribs without and with cut along chamber surface. The comparison is conducted by CFX software and the study parameters are bulk temperature, averaged circumferential heat transfer ratio, friction factor, global thermal performance factor and turbulence kinetic energy. The results show that heat transfer of cases LG, CG and CGC are enhanced by about 2.7, 2.6 and 2.5 higher than smooth case; respectively. The global thermal performance factor is increased by using rough walls in swirl cooling chamber, the global thermal performance factor of LG case reaches 2.8 times higher than that for smooth case. The maximum heat transfer characteristics can be achieved by a grooved wall of case LG compared with the other internal cooling techniques.