bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design and Optimization of Leading-Edge Tubercles for a Transonic Axial Compressor
Authors: Schulz Yannik , Kohl Joop Moritz , Kuestner Christoph , Seume Joerg R. 
Published: August 2024

Abstract
In nature, the front of the flippers of humpback whales are structured with protuberances, so-called tubercles, giving them excellent manoeuvrability. Inspired by this, tubercles can be implemented on the leading edge of compressor blades as a form of passive flow control, improving performance and possibly stall margin.
In the present work, the effect of leading-edge tubercles in a single-stage transonic compressor is investigated numerically. The base compressor operates at a mass flow rate of up to 0.83 kg/s and is capable of reaching pressure ratios of up to 1.8 and isentropic efficiencies of up to 87% while the flow is accelerated to relative inlet Mach numbers of up to 1.5.
The tubercles are initially implemented on the leading edges of the rotor blades and stator vanes via a sinusoidal function and hence as a function of amplitude and wavelength. A genetic algorithm is then used to optimize the compressor aerodynamic performance by means of steady-state CFD at design-point conditions of a mass flow rate of 0.8 kg/s and a speed of 77,000 rpm. By computing and comparing the performance maps of the reference and the optimized compressor, off-optimization point performance can be assessed. An in-depth analysis of the flow field allows the identification of the underlying effects behind the performance improvement for the tubercle-shaped topology: the creation of counter rotating vortices, laminar separation bubbles and the reduction in tip leakage vortex size at suction side-incidence.
Study of Secondary Cooling Effect on the Endwall Region With Various Trailing Edge Cutback Configurations
Authors: Yang Xi , He Wenbin , Zhang Ke , Wu Junmei , Lei Jiang 
Published: August 2024

Abstract
Designing the cooling schemes for the endwall region of 1st stage vanes is a challenging task due to the requirement of low NOx emissions and the presence of strong secondary flows. Considering the adequate use of coolant, the coolant injections from the trailing edge cutback not only cool the vane surface but also protect the downstream endwall region. This is called the secondary effect of cooling and is worth studying. In the present paper, distributions of cooling effectiveness on the endwall surface are measured using the PSP technique. Discrete slots are implemented near the airfoil trailing edge to provide the coolant with three compound angles (β = 15°, 30°, and 45°). Two positions of cutback slots are studied: trailing edge pressure side cutback (PC) and central cutback (CC). Experiments are conducted in a five-passage linear cascade in a suction-type wind tunnel with the inlet Reynolds number of 1 × 105 based on the axial chord length. Effects of mass flow ratio (MFR = 1%–4%) are also considered. Aerodynamic losses are obtained by solving the Reynolds-averaged Navier-Stokes equations to assess the interaction of coolant and mainstream. Results show that, with the increase of MFR, the cooling performance on the endwall surface is improved greatly. At a higher MFR, as the compound angle increases, the coolant coverage is expanded significantly and the high cooling effectiveness region gradually shrinks towards the trailing edge. In addition, the influence of cutback slot position behaves differently.
Direct Numerical Simulation of Air-Cooled and Air-Heated Channels
Authors: Modesti Davide , Pirozzoli Sergio 
Published: August 2024

Abstract
We develop a theoretical framework for predicting friction and heat transfer coefficients in variable-properties forced-air convection, as typical of turbine blade cooling. To do this, we borrow concepts from high-speed wall turbulence, also featuring large temperature and density variations. Using the mean momentum balance and mean thermal balance equations we develop integral transformations that account for the effect of the variable fluid properties, and apply the inverse transformations to calculate the friction and heat transfer coefficients. The proposed theory is validated using a direct numerical simulation dataset spanning both heating and cooling conditions, and the predicted friction and heat transfer coefficients match DNS data with 1–2% accuracy.
Design and Testing of a Compact, Reverse Brayton Cycle, Air (R729) Cooling Machine
Authors: Teichel Sönke , Karaefe Renan Emre , Çokşen Ahmet 
Published: August 2024

Abstract
Efforts to reduce the contribution of refrigeration to global warming have resulted in a phase-down of the use of fluorinated refrigerants. The alternative, natural refrigerants, used in vapor compression refrigeration machines (VCR), such as propane (R290) and ethane (R170) have significantly lower Global Warming Potential (GWP) and are less harmful to the environment. However, these refrigerants are flammable, which does not make them the preferred choice for some applications like electronics cooling. An alternative refrigeration cycle, the so called Reverse Brayton Cycle (RBC), does not require a refrigerant that undergoes a phase change and can work with air as a refrigerant (R729). Air has the advantages that it is completely harmless and easily accessible. It can be used for direct cooling, which has the potential to allow more effective and uniform cooling, faster cooldown, and a less complex cooling cycle. Despite its significant efficiency disadvantage at cooling temperatures above −50°C, this can make R729 an attractive refrigerant for innovative and simple refrigeration systems in applications where efficiency is not the most critical parameter. In this paper, the design considerations of compact, electrically driven RBC cooling machines (about 2 kWe) are discussed. Preliminary system design is presented for two different potential applications, one at high cooling temperatures (25 °C), the other at low cooling temperatures (−90 °C). The design process of the turbine stage of a RBC cooling machine including a method for matching compressor and turbine are presented. A demonstrator was built and tested, achieving a cool down of about 28 °C. Despite the deviation to the simulation, the test data supports the applied methodology.
Effect of Tilt on Thermo-Hydrodynamic Model of a Thrust Air Foil Bearing
Authors: Pourashraf Talieh , Bonello Philip , Lancaster Craig 
Published: August 2024

Abstract
Air Foil Thrust bearings are essential parts of high efficiency turbomachinery and are often used to support rotating machines in the axial direction. Predicting the thermo-elastic behavior of hydrodynamic thrust bearings is particularly crucial because of the common heat management challenge. Previous research works demonstrate that the thickness of the lubricating gap is significantly influenced by the thermal deformation of the runner. They did not, however, consider the impact of the disk’s misalignment in addition to its thermally induced deformation. In this study, a thermo-hydrodynamic model for an air foil thrust bearing will be provided in order to predict the pressure and temperature distribution in the bearing while accounting for rotor disc misalignment. Based on the proposed model, the performance of the bearing has been investigated. The results show that ignoring the effect of thermally induced bending of the disk will lead to unreliable prediction of bearing behavior. The same applies to the neglect of tilt, although at this stage of the modelling the degree of tilt is prescribed, unlike the thermal bending of the disk.
Dimaxer: A Fast High Order Unsteady Simulating System on GPUs for Turbomachinery
Authors: Liu Boyang , Peng Jun , Lu Yi , Liu Kai , Zhang Yang 
Published: August 2024

Abstract
The space-time extension kinetic energy preserving flux reconstruction method (STE-KEP-FR) and the “Magazine” type computational model can achieve fast solution of high-order accuracy large eddy simulation (LES) on small-scale machine GPUs. In this paper, a completely autonomous CFD industrial software Dimaxer developed based on this method is used to perform 5th order accuracy LES on typical turbomachinery flow cases such as VKI LS59, VKI LS89, T106C, S809, and flat plate film cooling with cylindrical hole to assess the solution speed. As well as LES on coarse and fine meshes with lower order schemes are conducted on VKI LS59 and VKI LS89 to study the requirement of the mesh and order under a given error tolerance. All the simulations are conducted on multiple Nvidia-RTX4090 desktop GPUs. The results show that for typical flow problems of turbomachinery with Renolds number ranging from hundreds to millions, wall-resolved LES numerical simulation can be achieved at an affordable computational cost (∼1 GPU hour), showing good industrial application prospects.
Combustion Modelling of the T100 Micro-Gas Turbine Burner Including the Influence of the Stretch and Heat Loss/Gain Effects on the Flame
Authors: Generini Giulio , Andreini Antonio , Bianchi Enrico 
Published: August 2024

Abstract
This paper focuses on the application of an extension for Zimont’s Turbulent Flame Closure (TFC) model turbulent flame speed formulation to include stretch and heat loss and gain effects on the flame. The effects are introduced, by tabulating the consumption speed of laminar 1D counter-flow flames in a “fresh-to-burnt” configuration for different stretch and heat loss/gain values. The consumption speed look-up table is then used to compute the flame turbulent flame speed within the tabulated-chemistry Flamelet Generated Manifolds (FGM) combustion model. Existing models, such as the Extended Turbulent Flame Closure (ExtTFC), are able to account for stretch and heat loss effects downstream of the reaction zone. A new model, named ExtTFCcomplete, is presented taking into account, in the construction of the consumption speed look-up table, the heat loss and gain effects both on the combustion products and reactants.
The necessity of evaluating the heat loss/gain effects on the reactants derives from the flow and geometrical characteristics of the Ansaldo Green Tech AE-T100 micro-gas turbine (mGT) burner, the object of this study. The reverse-flow inlet air and the main line fuel distribution plenum geometry demand to consider the heat loss/gain effects on the mixture before entering the combustion chamber to correctly catch the flame characteristics.
In a first step, the performances of the proposed model are validated by comparing computational fluid dynamics (CFD) simulations predictions to experimental data of an atmospheric turbulent premixed bluff-body stabilized CH4/air flame. The model is then numerically applied to the AE-T100 burner, emphasizing how the extension significantly improves the flame shape prediction with respect to the original Zimont model.
Experimental Analysis on Performance of Air/Oil Centrifugal Breathers for Aircraft Engines Under Different Operating Conditions
Authors: Di Matteo Mariano , Berten Olivier , Hendrick Patrick 
Published: August 2024

Abstract
This paper investigates the separation efficiency of modern aeroengine air/oil breathers, focusing on identifying configurations that enhance existing geometries. The study systematically varies parameters such as air flow rates and rotational speed, using well-known particle size distributions for testing different configuration. The experimental campaign involves various breathers with metallic grids of different geometries and mesh sizes, evaluating performance parameters such as pressure drops, oil consumption, and droplet cut-off size. The insertion of a metallic grid with a narrow mesh is found to offer a favorable trade-off in terms of pressure drops, oil consumption, and particle size at the separator exit. Results indicate that while increasing pressure drops of a reasonable amount, the selected geometries significantly reduce oil consumption and size of droplet at the exit of the breather.
Insights Into Turbocharger Centrifugal Compressor Stability Using High-Fidelity CFD and a Novel Impeller Diffusion Factor
Authors: Liu Yiming , Spence Stephen , Horsley John , Mann Stuart , Stuart Charles 
Published: August 2024

Abstract
Turbocharger technologies are widely applied in the modern automotive industry to meet increasingly stringent carbon emission standards. To support the continuous enhancement of these tactics, delivering improvement to the performance and stability of turbocharger compressors at low mass flow rate regimes is of paramount importance.
The present paper investigated the stability of a turbocharger compressor stage equipped with a ported shroud, using high-fidelity CFD simulations. It was found that the recirculated flow passing through the ported shroud device had primary influence on the flow condition in the vicinity of the impeller tip region (80% to 100% span). This discovery facilitated the definition of a modified impeller diffusion factor (DF), which was applied to the CFD results for three different compressor geometry configurations to lead to the provision of quantitative metrics for impeller stability. Furthermore, the observed change in the limiting impeller DF along the compressor surge line indicated that the dominant components governing the instability of the entire stage had switched, i.e., the stalling behavior of the compressor stage had transitioned from impeller dominated stall to vaneless diffuser dominated stall. Additionally, the limiting impeller DF clearly showed that one of the compressor configurations with a change in the hub endwall recess around the rear of the impeller improved the impeller stability by 3%. By comparison, another configuration with a change to strut geometry in the ported shroud recirculation channel reduced the impeller stability by 10%.
The present work addressed the gap in the understanding about the stability of different compressor configurations equipped with a ported shroud, and was useful for determining the changes in compressor global and local instability through a quantitative parameter based on a modified definition of DF.
Large Eddy Simulations for the Prediction of Fuel-Bound NOx Emissions: Application to NH3 and NH3-CH4 Blends at Different Operating Conditions
Authors: Meloni Roberto , Mazzotta Luca , Pucci Egidio , Morris Steve , Goktepe Burak , Mashruk Syed , Borello Domenico , Valera-Medina Agustin 
Published: August 2024

Abstract
Ammonia and its blend with natural gas and/or hydrogen will play a significant role in decarbonizing the energy sector in the next decades. Moreover, green fuels can help in reducing the fluctuations introduced by intermittent renewable sources providing an interesting alternative to the storage by the adoption of P2x2P schemes. The challenge GT manufactures are asked to solve is mainly related to the minimization of NOx emissions and the discovery of the optimal operating windows of the engines taking into consideration the potential fuel composition fluctuations associated with the availability of ammonia and other carbon-free fuels. In this context, the definition of dedicated numerical tools able to predict the combustor performance becomes crucial for the re-design of burner architecture allowing detailed analysis of technical solutions prior to experimental tests. The availability of detailed measurements, even at lab scale, represents a milestone for the improvement of these tools, especially for the Computational Fluid Dynamics codes.
In the present paper, a Computational Fluid Dynamics (CFD) methodology for the calculation of NOx emissions is developed and validated against unique data collected at Cardiff University’s Gas Turbine Research Center for blends involving methane and ammonia, considering also different pressure levels. The novelty of this methodology, based on the switch between the “in-flame” – “post-flame” contributions, lies in its extension and application for the first time to the fuel-bound NOx formation path. Thus, the main goal of this investigation is the validation of the proposed approach in the framework of this NOx mechanism, hence allowing to overcome the limits of the pre-tabulated combustion models in the prediction of this pollutant. Further, the method is implemented along a computationally cheap model like the FGM, providing an additional benefit in terms of delivery time especially in the context of applied research.
Regarding the results, the findings show good agreement with the data: for most of the considered cases, not only the trend is captured, but the numerical results offer also a good quantitative prediction of the tests.
Validation of the Numerical Simulation of Rotor/Stator Interactions in Aircraft Engine Low-Pressure Compressors
Authors: Favretti Isabelle , Roux Louis , Batailly Alain 
Published: August 2024

Abstract
This contribution focuses on the validation of a numerical strategy developed jointly by Safran and Polytechnique Montréal for the simulation and the analysis of blade-tip/casing contact interactions in low-pressure compressor stages. A large experimental campaign provided data (including strain measurements on the blade and abradable coating wear profiles) for several contact configurations involving four distinct blades and one type of abradable coating. The numerical strategy is here improved by introducing a new cut-off criterion to ensure the physical relevance of the presented results, specifically by keeping the maximum stress within the blade below the material’s yield stress. Similarly to previous publications involving a single contact configuration, the numerical model is first calibrated for one of the four blades of interest. It is seen that the results using the numerical model — critical speed, relative wear depth between leading edge and trailing edge, maximum stress levels within the blade — are in good agreement with the experimental observations. Using the same calibration, numerical simulations are then blindly run for the three other blades. The results demonstrate that numerically predicted key quantities align well with experimental data. Additionally, the numerical model provides an accurate relative assessment of a blade’s sensitivity to contact in agreement with experimental observations. This paper thus presents the first blind validation of a numerical strategy dedicated to blade-tip/casing contact interactions. Simultaneously, it also demonstrates that this model may be considered for the early discrimination of blade profiles depending on their sensitivity to contact.
Development and Validation of a Numerical Multiphysics Algorithm for Wall Condensation Heat Transfer for Steam Turbines Starting Phases
Authors: Rafanelli Isacco , Andreini Antonio , Facchini Bruno , Diurno Tommaso , Tomasello Stella Grazia , Girezzi Gabriele 
Published: August 2024

Abstract
Due to the rising interest in using renewable energy for environmental impact reduction, steam turbines are facing with a radical change in design practices and operability. In particular, the unpredictable and variable production of renewable plants drives to frequent shutdowns and fast start-ups of steam turbines, which have a huge impact on structural integrity. During start-up phases, the high temperature steam could face with a below-saturation wall temperature causing condensation and then high temperature gradients on solid components.
Hence, the proper thermal gradient evolution and condensing mass prediction are quite relevant in steam turbine design. Nowadays, numerical Conjugate Heat Transfer (CHT) analysis is a good industrial practice to quantify the thermal distribution in turbomachinery components. On the other hand, the usual bottleneck of these analyses is the fluid timestep and the required temporal discretization that is one or two order of magnitude smaller than the solid one: therefore a fully coupled unsteady is still unaffordable in terms of computational costs.
In this context, this work presents a low dimensional multiphysics approach which models the condensation phenomenon through correlations and the solid heat transfer through discrete 1D transient heat equation. Furthermore, a 3D CHT by employing the eulerian wall film multiphase approach is presented and compared with the developed algorithm.
Finally, the numerical results obtained are compared with field data on a real unit where the inlet section, as usual, is subjected to the described condensation phenomenon.
Scale Cooling -- A Novel Fractal Cooling Structure for Turbine Vanes
Authors: Chi Zhongran , Wang Longfei 
Published: August 2024

Abstract
Additive manufacturing technology provides the possibility of more efficient turbine cooling structures. In this work, a novel structure for turbine air-cooled vane based on fractal structure, named Scale Cooling Structure, was proposed. Fractal channel arrays are arranged on the leading edge, pressure side, and suction side of the novel vane. The design of the fractal channel units takes into account the internal cooling effect, film cooling effect, manufacturing accessibility of the channels, and adaptability to non-uniform thermal loads. The initiated cooling structure allows for the use of larger wall thickness to improve strength.
A parameterized design and automated mesh generation technique based on in-house code was developed for the vanes installed with Scale Cooling Structure. And typical turbine vanes with impingement-film cooling structure and Scale Cooling Structure were evaluated by both IR measurement and conjugate heat transfer CFD analysis. Experimental studies have shown that the local overall cooling effectiveness at the leading edge of the Scale Cooling Structure vane is obviously improved compared to the prototype design with impingement-film structure. The consistency between the IR measurements and the CHT CFD results is favorable.
It is found that the improvement in cooling performance of Scale Cooling Structure is mainly due to the improvement of film cooling. Its internal cooling relies on enhanced heat transfer at the branching positions of fractal channels. The Scale Cooling Structure is more sensitive to insufficient coolant supply pressure. It is suggested that the entire pressure difference between the cooling air and the mainstream shall be utilized by the Scale Cooling Structure, which can provide sufficient backflow margin while enhancing internal cooling.
Experimental Investigation of Randomly Oriented Wire Mesh Damper Performance
Authors: Pietrowski Seth P. , Villanueva Bryce , Kauffman Jeffrey L. 
Published: August 2024

Abstract
Wire mesh dampers can provide excellent damping for extreme environments and structures that repeatedly experience large vibrations. As a subset of friction damping, the fundamental technology has been explored through extensive material and empirical testing. Compared to more traditional friction dampers, however, the performance of wire mesh dampers remains relatively unexplored, both empirically and analytically. Limited studies address meshes aligned in very specific, repeating arrangements; this paper seeks to characterize performance for randomly oriented wire meshes. This paper explores the damping behavior across the parameter space of several mesh dampers, varying mesh parameters like wire diameter, mesh density, and compression force. Specific properties include the mesh effective stiffness and damping performance, measured across several compression set curves. Experiments show that a mesh compressed against a plate structure adds significant damping to the structure, and higher compression levels increase both the added damping and added stiffness effects of the mesh. Randomly oriented wire meshes provide a potential avenue for further study and implementation in extreme environments.