bluuebunny/crossref_metadata_2025 huggingface dataset:
Robust Optimization of a Compressor Blade Through Combination of an Adjoint-Based Multistart Approach and Global Gaussian Process Regression
Authors: Karimian Aryan , Schmidt Robin , Janke Christian
Published: August 2024

The real geometry of compressor blades naturally deviates from the intended design due to the finite accuracy of manufacturing processes as well as abrasion and deformation in operation. Consequently, a deterministic design approach causes an inevitable performance degradation. Robust design optimization captures this effect by defining a probabilistic objective that is subject to uncertain geometrical features. However, the required process complexity inherently entails an increase in computational cost, which narrows the pool of available methods in the industrial context due to the extensive usage of costly three-dimensional computational fluid dynamics in aerodynamic investigation. The adjoint method provides a means for the cheap acquisition of gradient information and thus lays the foundation for efficient gradient-based local search procedures. Furthermore, a global approximation of the search space can be achieved by surrogate modeling techniques enabling a better understanding of the system behavior and guidance towards the global optimum.

This paper presents the development and application of a hybrid robust optimization algorithm to compressor aerodynamics through the combination of the respective advantages of an efficient gradient-based search methodology incorporating the adjoint method and the Gaussian process regression. As such, the proposed algorithm aims for the balance of local and global optimization. For this purpose, a favorable interaction between the involved methods was targeted while accounting for geometrical uncertainty determined from optical measured blades. The performance of the employed methods as well as their ensemble within the complete algorithm was validated and analyzed on a low- and high-dimensional test function. In addition, the algorithm was compared to the efficient global optimization algorithm (EGO) where the behavior and overall results were evaluated by suitable criteria regarding the compressor application case. Following the established strategy, robust design optimization of a rotor blade from a state-of-the-art high-pressure compressor was conducted. The algorithm’s decisions and especially the surrogate model were monitored and analyzed. Validation by means of a design of experiments resolving the uncertainty space revealed the nonlinear character of the compressor performance with respect to geometrical uncertainty. The applied algorithm yielded a robust optimum, which is superior to those acquired by previous local searches under equal conditions. Ultimately, the optimal blade aerodynamics were analyzed and compared to the nominal design, disclosing a systematic reduction of loss caused by secondary flow and supersonic effects. A definite adaptation to the operating point under investigation was observed, leading to a shortened characteristic, albeit with improvement in a wide operating range.
Prediction and Analysis of Turbulence Anisotropy in a Low-Pressure Turbine Cascade at Two Reynolds Numbers Based on Transitional DDES
Authors: Fard Afshar Nima , Möller Felix M. , Deutsch Johannes , Henninger Stefan , Morsbach Christian , Kožulović Dragan , Bechlars Patrick , Jeschke Peter
Published: August 2024

This study analyzes the influence of Reynolds number on the turbulence anisotropy behavior for the transitional flow over the MTU-T161 linear low-pressure turbine (LPT) cascade. Two operating points at Reynolds number Re = 90,000 and Re = 200,000, both at an isentropic exit Mach number of 0.6, are calculated using a transitional Delayed Detached Eddy Simulation (DDES) model. We focus our investigation on the separation-induced transition occurring on the suction side, its sensitivity to the Reynolds number and the capabilities of the transitional DDES approach for capturing the turbulent state. The computational model of the MTU-T161 cascade consists of a single blade passage, including the diverging viscous sidewalls. Synthetic turbulence is generated at the inlet of the domain to mimic realistic turbomachinery flow conditions.

We show that the transitional DDES model is able to capture the separation and transition mechanism correctly for both Reynolds numbers, when compared to experimental data. The main part of this paper consists of a detailed analysis of the turbulence anisotropy behavior with particular attention to the separation bubble when changing the Reynolds number. By increasing the Reynolds number from 90,000 to 200,000, the turbulence anisotropy state of the suction side flow changes only slightly. At the higher Reynolds number, the passage flow is mostly governed by two-component turbulence state, while the separation bubble and its influence on the passage flow become weaker. The turbulence anisotropy analysis reveals an almost two-component state very close to the wall region and a one-component turbulence state in the separated shear layer for both Reynolds numbers. Our results show the capability of the transitional DDES model to capture the correct trend of the Reynolds stresses and the anisotropy behavior by comparing the results to a previously published Large eddy simulation (LES). The DDES method is not successful in capturing the Klebanoff modes (streamwise fluctuations) in the pre-transitional region, when compared to LES. These results enhance our overall comprehension of the turbulence state within different separation bubble sizes. Furthermore, the results indicate that the transitional DDES model resolves the essential characteristics of turbulence while keeping the computational cost up to seven times lower than LES.
Optimised Pilot Burner With Intelligent Control to Achieve Sub 9 PPM Emissions for Siemens Energy SGT-300-1S 7.9 MWe Engine
Authors: Liu Kexin , Sadasivuni Suresh
Published: August 2024

In support of reduction in emissions, Siemens Energy Industrial Turbomachinery Ltd (SEITL) developed the optimised pilot burner for its SGT-300 engine to produce ultra-low emissions for a wider range of engine load. The optimised pilot burner has been developed based on the standard pilot burner, with the size of the pilot gaseous fuel injection holes optimised, resulting in a significant reduction in its effective area. To validate the design change, a single-shaft SGT-300 engine (SGT-300-1S) configured with the optimised pilot burners and the rest of the combustion hardware as standard was tested at various operating conditions including natural turndown as well as with turndown control temperature at part load by Variable Guide Vane (VGV) modulation. An intelligent control algorithm for combustion was used, and its settings for the optimised pilot burners were refined by pilot split mapping during engine testing. The same engine configured with standard pilot burners was also tested to provide reference data. Extensive instrumentation and measurement equipment were used in the engine test to measure NOx, CO, and Unburnt Hydrocarbon (UHC) emissions and combustion system performance, such as fuel supply pressures and temperatures, combustion hardware metal temperatures, and combustor and casing dynamic pressure. Engine test results show that the optimised pilot burner, when operated with the refined intelligent control method for combustion system, can achieve a wide load range of sub 9 ppmvd emissions for the SGT-300-1S engine.
Suppression of Combustion Oscillations in Hydrogen-Enriched Can-Type Combustors Through Fuel Staging
Authors: Jung Junwoo , Kim Daesik , Wang Yuangang , Park Soonbeen , Sohn Chae Hoon , Kim Minkuk , Hwang Jeongjae , Kang Dowon , Lee Wonjune , Kim Hanseok
Published: August 2024

To achieve decarbonization in power-generating gas turbines, the technology of mixing hydrogen with natural gas is garnering significant attention. However, when blending natural gas with hydrogen, the altered combustion characteristics can lead to combustion instability in gas turbine combustors. Although fuel staging can effectively suppress combustion instability for can-type combustors, further research on mitigation strategies for hydrogen co-firing and their predictive methods is required. This study involves hydrogen co-firing experiments using a full-scale can-type combustor. Moreover, the resulting suppression of combustion instability is analyzed through fuel staging by utilizing three-dimensional (3D) computational fluid dynamics (CFD) and one-dimensional (1D) thermo-acoustic analysis. The experiments used a full-scale industrial can-type combustor with a five-around-one nozzle configuration. Hydrogen was blended with natural gas up to a volume fraction of 30%, maintaining a constant thermal power. Fuel staging was applied by controlling two out of five outer nozzles along with the remaining three. Before the 1D thermo-acoustic analysis, the internal flame structure of the combustor was examined through 3D CFD analysis. Based on the results, a multi-input multi-output (MIMO) system was constructed for 1D thermo-acoustic analysis of the can-type combustor. The application of time delays derived from 3D CFD analysis to the 1D model revealed that differences in flame time delays across the nozzles cause combustion instability suppression observed in fuel staging.
NASA HECC Geometry and Performance Review Part 3: A Numerical and Experimental Investigation of Tip Clearance Effects on the Vaneless Diffuser Configuration
Authors: Harrison Herbert M. , Nguyen-Huynh Tammy , Mathison Randall M.
Published: August 2024

Tip clearance effects in centrifugal compressors have been extensively investigated to understand the losses associated with the flow in the impeller tip clearance gap between the rotating blades and the stationary shroud. In Part 3 of this multipart investigation, experimental data and validated numerical simulations from Parts 1 and 2 were used to analyze the effects of the size of the tip clearance gap on the High Efficiency Centrifugal Compressor performance and aerodynamics. Four tip clearance gaps ranging from 0.012-in to 0.030-in (2.0% to 4.9% of the impeller exit blade height) were considered at both design and off-design operating conditions. The total pressure ratio and efficiency of the stage are found to decay linearly with increasing tip gaps. The sensitivity of the impeller performance to the tip gap was found to vary with the rotational speed of the compressor. Spanwise surveys of flow angle, total pressure, and total temperature collected at the impeller exit at design speed are used to validate numerical simulations at each experimental tip gap condition. Numerical simulations show that increased turbulence kinetic energy near the shroud at larger tip gaps leads to spanwise mixing of high entropy fluid near the impeller trailing edge which decreases the useful work input by the impeller. The data presented have been made available to the public in the HECC Data Archive located at https://storage.googleapis.com/hecc-data/NASA-HECC-Data-Archive.zip.
Performance Evaluation of a Direct Air-Cooled Supercritical Recompression Brayton Cycle Using CO2/n-Butane As the Working Fluid Operating Under Off-Design Conditions
Authors: Wang Xurong , Zhang Longwei , Qi Jianhui , Fan Xiaowei , Dai Yiping
Published: August 2024

In order to improve the air-cooled supercritical carbon dioxide (CO2) Brayton cycle for solar power systems, the use of mixed working fluid is a potential direction. The thermal stability of the CO2-based mixture at the operating temperatures, however, has not received as much attention as the thermodynamic performance. In this study, the degradation of CO2/n-Butane mixture is investigated using ReaxFF simulation method. Based on design results and off-design model of a direct air-cooled supercritical CO2/n-Butane Brayton cycle, the influence of thermal decomposition of the working fluid is evaluated on the cycle thermodynamic behavior. The results show that the fluid degradation greatly reduces the ability of the power cycle to absorb heat input from the solar field. When the totally decomposition of CO2/n-Butane mixture occurs, the net electricity is decreased by 32% at the design ambient temperature, while the cycle thermal efficiency is near the design-point efficiency. In addition, the impact of fluid degradation is much greater than above-design ambient temperature on the off-design performance of the supercritical Brayton cycle. This study indicates that the design of novel CO2-based mixture Brayton cycles should simultaneously take into account the cycle performance and thermal stability of the potential CO2 mixture.
Assessment of a BLI-Tolerant Aft-Fan at Design and Near Stall Conditions - From Preliminary to Detailed Aerodynamic Design
Authors: Mennicken Maximilian , Schnell Rainer , Kožulović Dragan
Published: August 2024

Boundary layer ingestion (BLI) is a promising concept to decrease the climate impact of civil aviation. One propulsion unit architecture considers a wake filling propulsor in the rear of the fuselage aiming at a higher fuel-efficiency. The flow entering the propulsion unit features stagnation pressure and swirl distortions. The fuselage boundary layer causes a stagnation pressure variation orthogonal to the fuselage. Moreover, the fuselage upsweep leads to a circumferential non-homogeneous stagnation pressure distribution and causes a swirl distortion. This study focuses mainly on three parts. Firstly, a new and numerically efficient design and assessment methodology for distortion tolerant fans is presented. The new methodology requires approximately 3 CPUh to assess fans in BLI conditions which is four orders of magnitude lower than the assessment by time-resolved calculations. Secondly, a distortion tolerant fan stage is assessed at the aerodynamic design point. The study shows that the new design methodology is able to capture the flow redistribution due to the stagnation pressure distortion and the local operating point variation around the circumference. Compared to the design conditions which feature purely radial distortion, the two-dimensional distortion leads to a fan efficiency decrease of 1.16%. The additional decrease of fan efficiency associated with the swirl distortion is 0.35%. Thirdly, a similar analysis is conducted at near stall conditions. The two-dimensional stagnation pressure distortion leads to a 2.5% lower fan efficiency compared to the purely radial distortion while the swirl distortion leads to a further decrease of 0.44%. Therefore, the fan performance is mainly driven by the stagnation pressure distortion rather than by the swirl distortion. At both operating conditions and both distortions, the fan attenuates the distortion which manifests in a decrease in distortion intensity of minimum 30% up to 40%.
Techno-Economic and Environmental Evaluation of Steam Generators Availability in Enhanced Oil Recovery Applications
Authors: Al Busaidi Waleed
Published: August 2024

Enhanced oil recovery technology become one of the key players in oil and gas applications targeting a high production value with a minimum cost. However, this necessitates the need for high reliable and efficient steam generators to recover the heavy oil. Thus, this paper followed a novel integrated approach to improve the availability of the OTSGs using both regression statistical analysis and failure-modes analysis. This was validated using actual data and the steam system availability has been compared before and after the trial. Furthermore, the second part of this study involved a sensitivity study at design and off-design conditions to identify the dominant factors with the highest impact on the reliability of steam system and its interaction with the hydrocarbons recovery. This can help to obtain the optimum operating point considering efficiency, cost, and CO2 emissions of OTSGs. The data show an average yearly availability of steam generators by about 74% with an average steam loss of about 673 ton/day and a potential of 218 m3/d of oil. This has caused approximately 24.4 MUSD as annual deferment cost. Finally, a new method has been also developed to assess the possibility of scaling formation in the steam generators and it has been also validated using actual pigging data. One of the main features of this approach is that it can be used to identify the optimum required cleaning frequency with less downtime and maintenance cost. Moreover, the upward trend of stack temperature data shows a degradation in the absorbed heat ratio by around 2.0% with an increase of about 6020 sm3/d in the fuel consumption. This also indicates the need for routine washing of the convection section finned and bare tubes. Environmentally, the high fuel rate leads to increase CO2 emission by 8164.8 ton per year. Additionally, the CO2 trend shows a sharp increase in the emission rate between 95% and 100% steam output by roughly 9.1% driven by a dramatic increase in the fuel consumption comparing with estimated additional hydrocarbons recovery revenue rate of around 6.9%.
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

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

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

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 < 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

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

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

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

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

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

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

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

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

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.
Characteristics of Deterministic and Stochastic Unsteadiness of Trailing Edge Cutback Film Cooling Flows
Authors: He Xiao , Montomoli Francesco , Michelassi Vittorio , Panizza Andrea , Pulga Leonardo
Published: August 2024

Trailing edge cutback film cooling flows are ubiquitous in small and medium gas turbines, but they are difficult to predict accurately due to the inherent deterministic and stochastic unsteadiness that controls the effectiveness of the cooling system. To help develop accurate closure models for such flows, the characteristics of both types of unsteadiness and their effects on the mean flows are analyzed in this research. Zonal detached eddy simulation (ZDES) is performed on a trailing edge cutback flow model, and the numerical results are validated against the measured data. Then, by using spectral proper orthogonal decomposition (SPOD) reconstruction, the original dataset is segregated into deterministic and stochastic unsteadiness. The characteristics of the stress tensor and the heat flux of each type of unsteadiness are analyzed in detail, and notable differences between the two unsteadiness are identified in terms of the stress tensor anisotropy and distribution of unsteady kinetic energy and heat flux. By propagating the unsteadiness through the Reynolds-Averaged Navier-Stokes (RANS) equations, the effect of different unsteadiness on the mean flow prediction is quantified. An accurate calculation of the total stress tensor reduces the prediction error in the velocity field by 79% and cooling effectiveness by 55%. An accurate prediction of the total heat flux vector reduces the prediction error in cooling effectiveness further by 37%. These findings provide valuable knowledge for the physical understanding, turbulence modeling and aerothermal design of cutback trailing edge flows.
Design and Simulation Model of a Direct Supply Cryogenic LH2 Fuel Aircraft System for Airborne Applications
Authors: Thilker Fynn , Tramposch Andreas , Giuliani Fabrice
Published: August 2024

The development of efficient and sustainable aircraft engine fuel systems has become one of the primary aspects in achieving the long-term goal of net-zero CO2 emissions from aviation by 2050. This involves not only the choice of the operating fuel but also its storage and processing conditions. Previous studies suggest that using liquid hydrogen (LH2) can offer longer endurance for air vehicles and an effective engine cooling due to its high specific heat value compared to high-pressure systems. This work is part of the LIQORNE (LIQuid hydrogen for airbORNE application) project, which investigates a hydrogen aircraft fuel system with a direct cryogenic LH2 supply. In this regard, a system model has been developed, focusing on continuously feeding LH2 into the engine and recovering redundant fuel and engine heat for gasification and hydrogen expansion improvement. This approach helps to control the risk of icing and boil-off in the system components and allows for a more lightweight and compact system. By implementing continuous fuel circulation and incorporating a flow control valve near the engine injection, it is realistic to verify and achieve shorter full-throttle response times. The potential of this architecture lies in its efficiency and flexibility, as it uses LH2 not only as a combustion fuel but also utilizes the redundant fuel for cooling, tank pressure control, and heating for optimal expansion before injection. To provide initial approximations of the system’s behavior, this paper describes a simulation model created with Simscape software for a small twin-engine medium-haul aircraft. This model focuses on component dimensions, including tank, pipes, and pump in terms of their thermodynamic behavior. The fuel properties are based on the thermophysical database CoolProp, enabling accurate calculations of phase proportion, temperature, and pressure based on real gas parameters. Through validation against previous state-of-the-art studies, the model is expected to yield initial dimensions of the system volume. Consequently, a comparison of system weight between liquid and pressure-driven architectures can be conducted, along with an assessment of potential efficiency improvements. It will also verify the feasibility of boil-off regulation by the fuel system alone. Due to the parametric model design, various study cases can be applied to find the optimum operating point and adapt to different applications.
Transfer Functions for the Inverse Design of Turbomachinery for Thermal Power Storage
Authors: Folkers Steffen , Schuster Sebastian , Brillert Dieter
Published: August 2024

This paper is part of a priority program developing inverse design methods for thermal power storage. Turbomachinery for use in thermal power storage face specific challenges. These lay in the unconventional working fluids employed and the operating conditions of the machines. This paper discusses the inverse design of turbomachines using an approach that combines optimized aerodynamic design with its feasibility in transfer functions. The transfer functions consider the aerodynamic design by means of the Cordier diagram. It provides correlations between several basic parameters necessary for the preliminary design and can thus be used as a basis for transfer functions. To ensure the feasibility of the design the mechanical stability of the rotor and the flow stability inside the flow path are implemented as limits on the design. A set of additional design constraints are included to simplify the design process in order to enable the automated method. A selection method is applied to select the most optimal machine applicable. This way a machine can be designed for any given problem without further assumptions or other input by the designer. The machines designed by this method are analyzed through variation of the input parameters. The most important parameter has been shown to be the specific work on the working fluid. The speed of sound of the fluid was shown to possess a limited impact on the design while the volume flow through the machine showed no impact.
Experimental and Numerical Study of Thermoacoustic Instability Characteristics and Mechanisms of Swirling Flame With Outer Flame
Authors: Qi Yuanhong , Hu Bin , Shi Qiang , Ren Sanqun , Zhao Wei , Zhao Qingjun
Published: August 2024

Previous research has identified that a stable outer flame existing in swirling flame can enhance the flameout characteristics of swirl combustion. However, it may exhibit thermoacoustic instability under low equivalence ratio conditions. In this study, the combustion instability characteristics of swirling flame with outer flame under different operating conditions were investigated. The sound pressure was captured by microphone, and the OH* chemiluminescence was acquired at 10 kHz simultaneously. The results indicate that the amplitude of pressure pulsation induced by combustion instability undergoes a process of formation, development, weakening and disappearance starting from higher equivalence ratio until flameout. The instability frequency increases linearly from 560 Hz to 720 Hz as the airflow rate increases, and then gradually converges until the flow rate is sufficiently high. Subsequently, Reynolds stress model (RSM) and Flamelet Generated Manifold (FGM) combustion model were employed to conduct unsteady RANS simulation for an unstable condition. The flame pattern captured by simulation is generally consistent with OH-PLIF observations. By examining the flow field structure, it was observed that the air separated when it left the inner and outer swirl nozzles — a phenomenon not previously reported in other studies — suggesting its potential as a novel approach for studying swirling combustion dynamics. Furthermore, pressure spectrum characteristics obtained from simulation results exhibit similarities to experimental findings. The physical field of a single pressure pulsation period was investigated. It is founded that the pressure pulsation in the combustion chamber causes the fuel passage periodically releases fuel pellets into the combustion chamber, which resulting in variations in heat release. Dual spiral vortex and PVC in the inner swirl nozzle were captured. The fuel pellet reacts violently in the downstream of the flame under the enrolling action of large-scale coherent structure and the transport effect of jet air. This feature is highly consistent with the spectral proper orthogonal decomposition (SPOD) mode derived from the chemiluminescence data.