bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Study on the Effect of Back Cavity on the Aerodynamic Behavior of a Non-Axisymmetric Casing Treatment for Transonic Axial Compressors
Authors: Martin Simon , Rodriguez Benoit 
Published: August 2024

Abstract
For decades, aeronautic engineers have studied the potential of Casing Treatments (CT) to improve the aerodynamic operability of tip-limited compressors. Axial Slot Casing Treatment (or ASCT) has shown very good results on modern transonic compressor. One possible variant of ASCT uses a circumferential back cavity that links the slots outside the compressor main flow path.
This study does a back-to-back comparison of two CT designs that differ only by the presence or the absence of the back cavity. The influence of both CT designs on a transonic rotor performances and aerodynamics are presented. CT flows are detailed and analyzed. The analysis focuses on fluid exchanges between the CT and the main flow path. This study is based on CFD simulation; CFD results are, at first, confronted with available experimental data and then analyzed.
Detailed CT flows analyses show that the presence of the cavity reduces the amplitude of the velocity fluctuations and allows for a more uniform redistribution of the recirculated mass flow. The presence of the back cavity reduces significantly the flow mass transfer between the main flow and the front part of the slots (situated before the rotor leading edge), as a consequence of the action of the transient vortex developing inside. In addition, the synchronization between the rotor blade passage and the extraction cycle, by the rear part of the slots, differs when back cavity is present or not. With the back cavity, the slot tends to extract mass flow mostly when it is close to the pressure side. Without the back cavity, the extraction is performed mostly in the middle of the blade channel. Because of these differences, the back cavity reduces the influence of the CT on rotor efficiency at the cost of a reduction in its capability to improve stall margin.
A Comparative Study of Model Predictive Control Approaches for Surge Mitigation in Centrifugal Compressors
Authors: Bonacchi Luigi Bono , Fiorucci Marta , Pencelli Manuel , Schillaci Guido , Politano Andrea , De Magistris Giovanni , Galeotti Daniele , Tonno Giovanni 
Published: August 2024

Abstract
Surge is a phenomenon that occurs in centrifugal compressors characterized by a sudden and severe drop in pressure and flow rate. To avoid the phenomena, an anti-surge valve (ASV) is installed in parallel with the compressor. The valve opening is manipulated by a control system to partially recycle the flow to the compressor inlet. Current industrial solutions for anti-surge control are based on a proportional-integral controller (PI). This approach presents several challenges, like parameter tuning, lack of constraints and difficulty in handling nonlinear dynamics. Therefore, the traditional solution is a suboptimal control that can potentially lead to surge events or unneeded ASV opening. One effective approach is the use of model predictive control (MPC), which offers the advantage of considering future system states and constraints, enabling proactive control actions to prevent surge. This study presents a comparative analysis of different MPC approaches while considering practical surge scenarios. The MPC formulations are implemented and tested using a dynamic model of a single stage gas compressor. The performance analysis involves inducing disturbances through rapid valve closures on the suction and discharge sides of the compressor. A comparison on how to deal with parameter retuning on real plant is performed. The results offer guidance for selecting the most suitable approach for centrifugal gas compressors in practical applications.
Mapping Maximum Exposure Temperatures on Automotive Turbocharger Wheels Using Thermal History Coatings
Authors: Hickey Jim , Peral David , Vacula Jan , Babák Martin , Araguas Rodriguez Silvia , Karagiannopoulos Solon , Feist Jörg 
Published: August 2024

Abstract
In this study, surface temperature maps of three turbocharger turbine wheels subject to three different tests, were generated using Thermal History Coatings (THCs). THCs are ceramic-based sensor coatings doped with a luminescent ingredient and the coating luminescence permanently changes with temperature. Therefore THCs can be used to assess temperatures post-test (i.e. offline). A parallel study was performed to optimize the THC application to the turbine wheels because of their complex geometry by deliberately altering the THC application parameters between the three wheels. An initial comparison of the THC data to Conjugate Heat Transfer (CHT) simulations of each test was also made.
The THC-derived temperature profiles measured reflected the test conditions each wheel was subject to. The wheel temperatures were generally hottest at the blade leading edges and decreased radially towards their hubs. The surface resolution of the temperature maps was 1–2 mm and there was good coverage across the wheel surfaces. Some THC erosion occurred at the leading edge of the wheel exposed to the most extreme environment, but the coating was not optimized for this particular test. The coating applied to one turbine wheel showed the most success, with excellent durability along the blade leading and precise blade-to-blade measurements. The initial CHT/THC comparison for this turbine wheel was very promising, with the vast majority of points showing a temperature difference &lt; 10 °C at like-for-like surface locations for the case of one wheel.
Concluding, THC technology was successfully used to profile temperatures of turbocharger turbine wheels. Future work aims to apply thermal history coating technology to further turbocharger development (e.g. E-Turbo applications) and on other inaccessible turbocharger components (e.g. bearing cartridges).
High-Fidelity Simulation of the Aerothermal Performances of a Turbofan Thrust Reverser
Authors: Grenouilloux Adrien , Bechane Yacine , Carmona Julien , Bénard Pierre , Lartigue Ghislain , Moureau Vincent , Ferrey Paul 
Published: August 2024

Abstract
Thrust reversers (TR) are one of the primary braking systems of aircrafts. They rely on a deflection of the airflow exiting the engine to generate a counter-thrust. Current steady-state numerical approaches used in the design phase, such as RANS (Reynolds-Averaged Navier-Stokes), fail to correctly predict the aerothermal performances of impinging configurations. This paper presents a methodology for the Large-Eddy Simulation (LES) of a representative reduced-scaled TARGET configuration. It relies on a two-step workflow to get the maximum accuracy at an optimal cost. First, a Low-Mach number variable density simulation is conducted. Despite not taking into account compressible effects, the accumulated statistics are used to perform feature-based mesh adaptation. A dedicated procedure based on the homogenization of the dissipation of the turbulent kinetic energy and on the boundary layer resolution allows to generate a grid with a controlled number of cells. The grid is refined in regions of prime interest for the study of this configuration, i.e. in the mixing layer and the impinging region, while it is coarsened in the far field. Then, the second step relies on the use of an explicit compressible solver to solve for the flow dynamics. Statistics are converged on this grid for later post-processing and comparison with experimental data.
Further Studies in Hydrogen Micromix Combustor Technologies for Aircraft Applications
Authors: French Ainslie , Mingione Giuseppe , Schettino Antonio , Cutrone Luigi , Roncioni Pietro , Vitagliano Pier Luigi 
Published: August 2024

Abstract
Within the context of future aircraft turbine engine development technology, hydrogen has fast become one of the most favored candidates as an alternative fuel due to the possibility of producing extremely low levels of pollutants in particular NOx. The principal component of such an engine technology is the hydrogen micromix combustor which provides a solution to safe hydrogen combustion which avoids auto-ignition and flashbacks by addressing novel methods of hydrogen-air mixing. The current design concepts include a typical injection manifold consisting of multiple concentric arrays of micromix combustors which produce hundreds of miniature low temperature diffusion flames at very low NOx levels.
The present paper builds on previous studies of a typical micromix combustor which was evaluated using turbulent chemical interaction models by examining the effects on pollutant levels using laminar diffusion flamelets employing the Flamelet Generated Manifold model. Results for several different combustion kinetic mechanisms obtained with the latter method are compared with those obtained using the more classical turbulent chemical interaction models. The effects of the chosen segregated model for the convective fluxes and the adiabatic boundary conditions are also studied.
The above methods are extended to simulations of combustion chamber fluxes at high pressures ranging from 15 to 20 atmospheres which are relevant to the development of future ultra-high bypass ratio engines which are envisaged to come into service around 2050. In line with these future developments, additional micromix combustor geometries are examined.
Advanced Methods for Assessing Flow Physics of the TU Darmstadt Compressor Stage: Part 2 – Uncertainty Quantification of RANS Turbulence Modeling
Authors: Matha Marcel , Möller Felix M. , Bode Christoph , Morsbach Christian , Kügeler Edmund 
Published: August 2024

Abstract
In this second paper of the two-part series, we quantify the turbulence modeling uncertainty for the transonic TU Darmstadt (TUDa) compressor. The present work applies the Eigenspace Perturbation Framework (EPF), as it is the only published physics-based framework capable of addressing the model-form uncertainty in turbulence closure modeling. To sample from the possible solution space and obtain the modelling uncertainty, we perform simulations perturbing the eigenvalues of the Reynolds stress tensor in addition to simulations using an unperturbed turbulence model. We show, that the shape of the Reynolds stress tensor ellipsoid has significant impact on the evolution of turbulence, flow separation, vortex systems, shock-boundary layer interaction and finally the overall performance of the compressor. We compare the estimated uncertainties with available measurements and transitional Delayed Detached-Eddy Simulations (DDES). This allows us to assess the confidence of the chosen turbulence model and to evaluate the sharpness and coverage of the resulting uncertainty bounds. Thus, the EPF is comprehensively validated and suggestions for its future applicability with respect to turbomachinery components are made.
A Combined LES and PIV Investigation of Trenched Fan-Shaped Hole Aerodynamics
Authors: Barigozzi Giovanna , Zamiri Ali , Gamba Stefano , Spozio Ilaria , Chung Jin Taek 
Published: August 2024

Abstract
Trenches implemented in the thermal barrier coating have been proved to be a feasible solution to increase the thermal performance of film cooling holes. The performance of this solution can be maximized by properly selecting the trench design. The present paper reports the results of a combined experimental and numerical investigation carried out on a flat plate model with a set of three 7-7-7 fan-shaped holes. The Particle Image Velocimetry (PIV) technique was used to measure the in-plane mean and fluctuating velocity components in the trench region on the mid-hole section for variable injection conditions corresponding to various coolant to mainstream blowing ratios M in the range between 0.5 and 2.0. Cases at a momentum flux ratio I = 1.5 were used to cross check the prediction capability of a Large Eddy numerical simulation (LES) for two trench geometries previously thermally tested. PIV and LES result to be in good agreement. Both contribute to the understanding of the complex aerodynamics taking place inside the trench, supporting the thermal analysis. In particular, the presence of a vortical structure in the cavity downstream corner in the mid-hole section and the absence of counter-rotating vortex pair are the main reasons for the better performance of the deeper and shorter trench (Case#2).
Multidisciplinary Analysis of the Impact of Blade Geometric Deviations on Compressor Performance Based on Fluid-Solid Grid Coordinated Deformation
Authors: Tong Zhaoxu , Zhang Huiying , Zhou Yan , Xie Rong , Xu Shengli 
Published: August 2024

Abstract
Machining errors are widely presented in the blade manufacturing process, and their influence on compressor performance cannot be overlooked. Accurate assessment of this influence is of great significance. In this study, an analytical framework is proposed to quantify the impact of radial machining errors on the aerodynamic and structural performance of blades. This framework integrates fluid-solid grid coordinated deformation methods with Backpropagation Neural Network surrogate model technology. NASA Rotor 67 is utilized as a case study to quantify the uncertainty associated with radial machining errors. The results indicate that, compared to the prototype, the relative standard deviation of isentropic efficiency, pressure ratio, and mass flow rate for the compressor are 0.278%, 0.192%, and 0.138%, respectively, while the relative standard deviation of the maximum von Mises stress on the blade reaches 2.85%. Isentropic efficiency, pressure ratio, and mass flow rate exhibit approximate monotonic positive correlations with each other, whereas all three parameters demonstrate a monotonic negative correlation with the maximum von Mises stress. Precision control of leading edge thickness is advantageous for enhancing isentropic efficiency and reducing von Mises stress levels at the blade root region, and meticulous attention should be given to the machining accuracy of leading edge thickness.
The Aerodynamic Interaction of Seal Leakage and Mainstream Flows in a Compressor Cascade With Non-Axisymmetric Endwall
Authors: Li Jian , Qiang Xiaoqing 
Published: August 2024

Abstract
In response to the escalating efficiency demands of the forthcoming generation of aircraft engines, the pursuit of higher bypass ratios and pressure ratios has led to an ongoing reduction in the size of the core engine. However, this scale-down of the core engine size is met with inherent challenges, as certain critical geometric characteristics, such as seal and tip clearances, cannot be proportionally reduced. This results in an increased proportion of leakage losses within the overall compressor losses. Additionally, the reduction in blade height and an increase in load lead to a significant rise in end-wall losses. Consequently, the control of flow near the end-wall region has become a major focus in the development of axial flow compressors. As a passive approach of flow control, nonaxisymmetric end-wall contouring has exhibited its efficacy in reducing losses within axial compressors and turbines. It operates by changing the pressure distribution near the end-wall to influence corner separation, consequently reducing end-wall losses. Typically, non-axisymmetric contouring is designed solely under the consideration of the compressor blade. In the actual axial compressor geometric, the presence of seal clearance leads to leakage flow interacting with the mainstream. The distinctive flow pattern produced by the seal leakage flow at the end-wall may diminish the efficiency gains that nonaxisymmetric end-wall contouring could otherwise achieve. Therefore, the objective of this study is to investigate the interaction mechanisms between seal leakage flow and the mainstream flow in a profiled end-wall compressor cascade with seal cavity. The non-axisymmetric end-wall contour employed in this study is derived through numerical optimization at a Mach number of 0.6 for a compressor cascade without seal cavity. Numerical results have been validated against experimental data, demonstrating the effectiveness of this end-wall contour in reducing end-wall losses for the cascade under both design and off-design conditions. The comparative analysis of the flow characteristics between the datum and end-wall contoured cascades with and without seal cavity is conducted. Particular emphasis is placed on investigating the alterations in flow structures induced by seal leakage flow on the end-wall contoured blades and the reciprocal influence of the end-wall contouring on the seal leakage flow. This research will provide valuable insights for the future design of shrouded compressors employing non-axisymmetric end-wall contouring.
A Numerical Study on the Aerodynamic Performance of a Shrouded Low-Pressure Turbine With Solid and Honeycomb Lands
Authors: Hur Min Seok , Kim Tong Seop , Kim Dong Hyun , Jung Il Young 
Published: August 2024

Abstract
This paper examines how leakage flow from the blade tip of shrouded blades influences the aerodynamic performance of a two-stage shrouded LPT, considering various labyrinth seal configurations. The investigation was conducted through a steady-state 3D RANS analysis. The blade tip architecture includes two types of labyrinth seals (stepped and straight seals) and two types of casing (solid and honeycomb land). The evaluation of aerodynamic performance for both the turbine stages and the labyrinth seal was based on fundamental parameters including stage efficiency, leakage fraction, and discharge coefficient. Our investigations were classified into two topics. Firstly, the aerodynamic performance of unshrouded and shrouded blades was compared in a wide range of clearance sizes. For both blade types, as the clearance size increases, the leakage flow increases, and the isentropic efficiency of all stages decreases. However, the shrouded turbine showed a lower decrease in stage efficiency as the clearance increased in comparison to the unshrouded turbine. Secondly, the effects of casing type (solid and honeycomb lands) were compared and complex flow phenomena occurring in the tip leakage were analyzed. For this particular study’s findings, it was observed that in the case of a stepped seal, the use of honeycomb land resulted in increases in both leakage flow and discharge coefficient compared to solid land, consequently leading to a decrease in stage efficiency. However, when it came to the straight seal, the utilization of honeycomb land decreased both leakage flow and discharge coefficient, thus contributing to an increase in efficiency.
Evaluation of Mechanical Properties of Additively Manufactured Beams With Lattice Structures
Authors: Pir Inci , Sahin Serhat Arda , Tufekci Mertol , Tufekci Ekrem 
Published: August 2024

Abstract
The use of lattice structurses is becoming more common day by day. Limitations such as being expensive and time-consuming have led to a search for new solutions in the industry. In light of these limitations, the widespread use of 3D printing technology methods is evaluated. 3D printing technology has advantages in terms of design flexibility, quick prototyping, lightness and the ability to produce complex shapes. 3D printing is used to systematically investigate different geometries in line with the requirements of sustainable product development, leading to the production of auxiliary structures that are both strong and lightweight. This research investigates the mechanical properties of various lattice structures that were previously modelled and analysed through analytical methods in the literature. The samples with five different auxetic structures are manufactured using the Fused Deposition Modelling (FDM) 3D printing technique, with Acrylonitrile Butadiene Styrene (ABS) as the selected material. The manufactured samples are subjected to a three-point bending test to assess their mechanical characteristics, including the flexural modulus, flexural strength, and elongation at break, and the effect of the in-plane geometry on the mechanical behaviour is evaluated.
Effect of Heat Treatment and Multiple Passes Through Resonance on Damping and Vibration Frequencies of Additively Manufactured Structure With Inherent Damping
Authors: Moneta Grzegorz , Cieslak Slawomir , Wdowinski Wojciech , Malicki Maciej , Szalkowski Sebastian , Fedasz Michal , Piecka Sebastian , Raczko Konrad , Pilczynski Jakub 
Published: August 2024

Abstract
To meet current market demands, modern engines need: to operate with higher load, operate at higher firing temperatures, to startup and shutdown faster and more frequently. Therefore, the blade must be more often designed as the resonance-proof component under circumstances of the variable engine speed and varying thermal conditions. One of solutions to this challenge is damping optimization through advanced design of parts. Additive Manufacturing (AM) provides additional design space and capabilities for blading engineers. Introduction of inherent damping (energy dissipation between loose, non-melted metal powder particles) can increase damping by more than one order of magnitude comparing to ‘solid’ component. On the other hand AM parts often require additional Heat Treatment (HT) or Hot Isostatic Pressing (HIP) to reduce residual stresses and porosity. Additionally, components are affected by multiple passes through resonance and long-term exposure to vibrations during their service life. All these factors can cause changes in the powder: wear, compaction, fragmentation of compaction, micro-welding, sintering, sinter cracking and fragmentation. These changes are affecting damping and dynamic characteristics of structure.
Several mock-up components have been studied. Three designs have been manufactured using Laser Powder Bed Fusion (LPBF) technology: a baseline ‘solid’ beam, beam with one large cavity with loose powder, beam with sixteen small pockets with pins surrounded by loose powder. All beams in as-built condition where then scanned using Computed Tomography (CT). Then, the damping ratio has been assessed for all components using electrodynamic shaker — the response was measured by laser vibrometer. The third beam (with sixteen small pockets) was subjected to Heat Treatment, CT-scanned and tested again. Several sweeps through resonance were executed and CT-scans were performed on this mock-up. The results of shaker tests show significant damping ratio changes: almost complete disappearance of inherent damping after HT, partial restoration of inherent damping after first resonance passing and damping changes during further runs. Performed CT-scans show formation of the powder sinter after HT and progressive sinter fragmentation caused by resonance passing cycles.