bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi-Fidelity Simulation for Secondary Air System Seal Design in Aero Engines
Authors: Nasti Adele , Voutchkov Ivan I. , Toal David J. J. , Keane Andrew J. 
Published: October 2022

Abstract
Secondary air system seals in aero engines sit at the intersection between all the major aspects of the physics of the system. Their behavior is affected by the air system, the thermal physics, the effect of flight loads and is highly dependent on the engine component movements, the operating conditions, and the supporting hardware. Due to the number of functional and physical interfaces in the engine, seal design is therefore a highly coupled multi-physics problem and requires multiple iterations during the design process to converge to a solution that meets system requirements and optimizes engine specific fuel consumption.
At different stages of the design process, simulation models with different levels of fidelity can be built. Due to the long runtimes of high-fidelity coupled multi-disciplinary models and to the iterative nature of the process, seal design in industry presents significant computational cost challenges, in particular in the phases of the design that require multiple simulation runs.
Multi-fidelity computational techniques for surrogate modelling and optimization such as Kriging and co-Kriging have been demonstrated on a number of industrial applications and have the potential to significantly reduce the number of function evaluations for computationally expensive optimization problems, improve the accuracy of the predictions of surrogate models and allow the development of improved simulation strategies for a specific product design.
This paper demonstrates the use of multi-fidelity simulation techniques on aero engine secondary air system seal design and shows how these techniques can be used in the context of system, sub-system and component design. This is achieved by combining results from a simple two-dimensional Finite Element Analysis with those from a coupled secondary air system-thermomechanical model.
Depending on the stage of the design process and on the specific design decisions being made, the use of computational power in simulation often comes down to a trade-off between reduced overall computational time and improved result accuracy. Multi-fidelity simulation frameworks provide the environment to drive holistic choices on the simulation strategy, reducing the cost of the design and offering agility in the industrial response to market changes or new technologies. Moreover, this methodology establishes an infrastructure for updating the virtual product at each step of the product lifecycle, allowing experimental or service data to feed the system-level simulation models to produce a digital twin.
A Turbo-Oriented Data-Driven Modification to the Spalart-Allmaras Turbulence Model
Authors: He Xiao , Zhao Fanzhou , Vahdati Mehdi 
Published: October 2022

Abstract
The Spalart-Allmaras turbulence model is one of the most popular models applied to compressors, but it often over-predicts compressor blockage size and hence under-predicts the compressor stall margin. In this paper, a novel modification to the SA model is proposed to improve the prediction of compressor near-stall flows. The modification is based on the dimensionless vortical pressure gradient, which identifies blockage cells featured by 3D swirling low-momentum flows under adverse pressure gradients. It unblocks the compressor passage by enhancing the eddy viscosity in the identified blockage cells; whereas in canonical 2D flows the modification is automatically switched off. The model coefficients are calibrated via Bayesian inference, which considers the uncertainties involved in experiments and CFD. The rotor exit radial profile data of NASA Rotor 67 at the peak efficiency (PE) and near stall (NS) conditions at the design speed are used for calibration. Validation on the NASA Rotor 67 case shows that the proposed model not only predicts a better agreement with the measured near-tip profiles compared to the original SA model, but also predicts more accurate stall margins at all operating speeds. Further validations are conducted on the TUDa-GLR-OpenStage transonic axial compressor and the low-speed BUAA Stage B rotor, where stall is driven by the rotor tip blockage cell. Results show that the proposed model predicts a more accurate stall margin at all operating speeds of TUDa-GLR-OpenStage and a more accurate tip blockage size of BUAA Stage B rotor. Finally, the proposed model is validated on the LMFA NACA65 cascade featured by corner separation. In combination with the quadratic constitutive relation (QCR), significant improvement in predicting the static pressure rise coefficient, the total pressure loss coefficient, the flow angle and the blade loading is achieved, indicating the model predicts a more accurate corner separation size. The proposed model, termed as SA-PGω in this work, is a promising engineering tool for future RANS simulations of compressor near-stall flows.
Multi-Objective Aerodynamic and Aeroelastic Coupled Design Optimization Using a Fully Turbulent Discrete Adjoint Harmonic Balance Method
Authors: Wu Hangkong , Wang Dingxi , Huang Xiuquan 
Published: October 2022

Abstract
With increasing requirements for high-loading and high-efficiency turbomachines, blades become thinner and thinner and thus design optimizations considering both aerodynamic performances and aeroelastic stability become more and more necessary. In this study, a fully turbulent discrete adjoint harmonic balance (HB) solver is developed using algorithmic differentiation (AD), validated by a discrete linear solver, and then adopted to perform multi-disciplinary coupled design optimizations. To this end, a framework of multi-objective adjoint design optimizations is developed to improve both aerodynamic performances and aeroelastic stability of turbomachinery blades. This framework is divided into two steps including the aeroelastic design initialization and aerodynamic Pareto front determination. First, the blade profiles are optimized to improve the aeroelastic stability only and constrain the change of aerodynamic performances. Second, the optimized blade profiles in the first step are used as the initial ones and then further optimized with the objective function of aerodynamic parameters and the constraints of aeroelastic parameters. The effectiveness of the multi-objective design optimization method is demonstrated using the transonic NASA Rotor 67 subjected to a hypothetical vibration mode. The results show that the multi-objective adjoint design optimization method can improve not only aerodynamic performances but also flutter stabilization.
Detection of the Onset of Trip Symptoms Embedded in Gas Turbine Operating Data
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Bechini Giovanni 
Published: October 2022

Abstract
Nowadays, the importance of gas turbine monitoring and diagnostics pushes OEM operators to exploit historical data to search for early indicators of incipient failures.
One of the most disrupting events that affect GT operation is gas turbine trip, since its occurrence causes a reduction of equipment remaining useful life as well as revenue loss because of business interruption. Thus, early detection of incipient symptoms of gas turbine trip is crucial to ensure efficient operation and lower operation and maintenance costs.
This paper presents a data-driven methodology aimed at investigating and disclosing the onset of trip symptoms. The goal of the methodology is the identification of the time point at which trip symptoms are triggered, by exploring multiple scenarios characterized by different trigger positions. For each scenario, a time window of the same length is considered before and after the trigger time point. For classification purposes, the former is supposed to be representative of normal operation and thus is labeled as “No trip”, whereas the latter is labeled as “Trip”. A Long Short-Term Memory (LSTM) neural network is employed as the classification model. A predictive model is first trained for each scenario and subsequently tested on new observations (i.e., trip events) by considering the whole available timeframe. Finally, trips are clustered into homogeneous groups according to their most likely trigger position, which identifies the time point of onset of trip symptoms.
The methodology is applied to two real-world case studies composed of a collection of trips, of which the causes are different, taken from various fleets of Siemens gas turbines. Data collected from multiple sensors during three days of operation before trip occurrence are employed and analyzed.
The methodology provides the most likely trigger position for four clusters of trips within the two days before trip occurrence with a confidence in the range 66%–97%.
Application of Adjoint-Enhanced First Order Second Moment Method for Robust Design Optimization of a High Pressure Compressor Rotor
Authors: Dittmann Max , Schmidt Robin , Meyer Marcus 
Published: October 2022

Abstract
This paper applies the computationally advantageous combination of a differential analysis technique and the adjoint method in the context of uncertainty quantification to the gradient-based robust design optimization of aerofoils. First, the accuracy and feasibility of the method is evaluated using an analytical test function. The method is subsequently applied to the robust design optimization of a rotor blade under geometric uncertainty, that is based on a parametrized population of optically 3D scanned blades. A significant improvement of the robustness w.r.t. the isentropic efficiency of the rotor is reported.
The Influences of Trailing Edge Base Pressure on the Profile Loss of Low-Pressure Turbine Blades
Authors: Kodama Hidekazu , Funazaki Ken-Ichi 
Published: October 2022

Abstract
The knowledge of the pressure at the base of the trailing edge (base pressure) is important for the prediction of profile loss of low-pressure turbine (LPT) blades. It is known that base pressure varies with a surface velocity profile and a Reynolds number, and that a lower base pressure increases the losses, and a higher base pressure decreases the losses. However, in the airfoil design, it is difficult to predict the base pressure. This is because the physical mechanism to determine the base pressure level is not well understood. This paper aims at clarifying the mechanism to determine the base pressure level for a low speed LPT cascade and investigating the influences of the base pressure on the profile loss by using the results of numerical simulations. In the study, two kinds of LPT blade design with different levels of the base pressure are used. One is the design with the base pressure higher than the far downstream static pressure (Blade A) and another is the design with the base pressure lower than the far downstream static pressure (Blade B). Based on the findings from the study, the correlation parameter BP calculated by the numerical simulation results is proposed for the prediction of base pressure. The prediction method using the parameter BP is applied to low speed cascade test data and compared with the measured base pressure. It is concluded that the method reasonably predicts the base pressure for blades with no laminar separation and predicts the base pressure within the range of an engineering allowable error for blades with a closed separation bubble.
Autoignition Delay Time Measurements and Chemical Kinetic Modeling of Hydrogen/Ammonia/Natural Gas Mixtures
Authors: Baker Jessica B. , Rahman Ramees K. , Pierro Michael , Higgs Jacklyn , Urso Justin , Kinney Cory , Vasu Subith 
Published: October 2022

Abstract
In recent years, hydrogen-carrying compounds have accrued interest as an alternative to traditional fossil fuels due to their function as zero-emission fuels. As such, there is interest in investigating hydrogen-carrying compounds to improve understanding of the fuels’ characteristics for use in high-pressure systems. In the current study, the oxidation of ammonia/natural gas/hydrogen mixtures was carried out to study CO formation profiles as well as the ignition delay times behind reflected shock waves in order to refine chemical kinetic models. Experiments were carried out in the University of Central Florida’s shock tube facility by utilizing chemiluminescence to obtain OH* emission and laser absorption spectroscopy to obtain CO profiles. Experimental results were then compared with the GRI 3.0 mechanism, as well as the proprietary UCF 2022 mechanism utilizing CHEMKIN-Pro software. In general, both models were able to capture the trend in autoignition delay times and CO time histories for natural gas and ammonia mixtures. However, for ammonia-hydrogen mixtures, GRI 3.0 failed to predict ignition delay times whereas the UCF 2022 mechanism was able to capture the IDTs within the uncertainty limits of the experiments. A sensitivity analysis was conducted for different mixtures to understand the important reactions at the experimental conditions. Finally, a reaction pathway analysis was carried out to understand important ammonia decomposition pathways in the presence of hydrogen and natural gas.
Numerical Investigation of the Effects of Tip Clearance and Rotor Cavities on the Performance of a 1.5-Stage High-Work Turbine
Authors: Hansen Thorsten , Munktell Erik , Scheuerer Georg , Zwiener Kim 
Published: October 2022

Abstract
The paper presents CFD simulations about the effects of tip clearance and rotor cavities on the performance of a 1.5-stage high-work turbine. The experimental test case to which the simulation results are compared is the 1.5-stage unshrouded high-work turbine investigated by Behr et al. [1]. The authors performed the simulations on three homogeneously refined meshes. The results on the three meshes were used to quantify discretisation errors applying Richardson extrapolation. The mesh-related discretisation errors for the mass flow rate, total pressure ratio, and mechanical efficiency were below 0.2 % on the finest mesh. The simulation results agreed well with the experimental data. In particular, the loss topologies induced by the hub and shroud passage vortices and the tip-leakage vortex compared well to the measured contours. The simulations showed a consistent and realistic response to the addition of the rotor cavities, with increased mass flow rates and reduced efficiency, shifting the hub passage vortices upwards. Increasing the tip gap decreased the efficiency and strengthened the tip-leakage vortex; decreasing the tip gap had the opposite effect.
Breaking 70% Net Electric Combined Cycle Efficiency With CMC Gas Turbine Blades
Authors: Martelli Emanuele , Girardi Marco , Chiesa Paolo 
Published: October 2022

Abstract
This work focuses on the optimal cycle design criteria for heavy duty gas turbines employing CMC blades. A combined cycle model with detailed description of the cooled gas turbine is used to determine the optimal Turbine Inlet Temperature and pressure ratio for two values of maximum allowed CMC wall temperatures (1300, 1500 °C). Results indicate that the maximum efficiency of the combined cycle is achieved with pressure ratio above 60, posing the need of adopting two shafts for the gas turbine and high temperature materials for the high-pressure compressor. Net electric efficiency above 70% (LHV basis) can be approached with CMC blade wall temperatures of 1300 °C (TIT = 2000 °C) and efficiency values approaching 72% with CMC blade wall temperatures of 1500 °C and TIT of 2200 °C. Compared to current H-class gas turbines, the simple cycle efficiency increases by about 10 percentage points (&gt; 53% vs. 43% LHV basis) and the net specific work/net power output by 66%–110% depending on the pressure ratio and TIT. The most critical challenge to achieve such performance appears to be the temperature gradient across the blade wall and the temperature capability (maximum surface temperature and temperature gradient) of the blade coatings.
Ignition Chemistry of Syngas Highly Diluted in CO2
Authors: Cooper Sean P. , Mathieu Olivier , Mohr Darryl J. , Petersen Eric L. 
Published: October 2022

Abstract
Syngas is a desirable, high-hydrogen fuel source for combustors utilizing the Allam-Fetvedt cycle involving supercritical-CO2 (sCO2). Minimal data are available with high concentrations of CO2, with much of the available data being few in number and reported over very narrow temperature ranges. Considerable model disagreements have been shown at intermediate pressures (10–100 atm), while good agreement is seen for higher pressures (&gt; 100 atm). Further examination of literature data highlights that the ignition delay time (IDT) characteristics of syngas at these pressures show little dependence on pressure, mixture composition, and equivalence ratio. To verify these observations, literature experiments were replicated using a high-pressure shock tube facility. Ignition delay time data were collected for syngas mixtures for pressures of 20 and 40 atm with 85% CO2 mixtures at stoichiometric conditions and H2:CO fuel ratios of 1:1 and 1:4. Literature results are limited to IDTs less than 500 μs, and data presented herein expand these data to considerably longer IDTs over a wider temperature range. Some disagreement with literature data is seen, and sources of discrepancy from the literature results are discussed. However, similar trends are seen for syngas ignition delay time characteristics and chemical kinetic models do not replicate this behavior. In particular, AramcoMech 2.0 replicates IDT near 40 atm for a H2:CO fuel ratio of 1:1, but is significantly under reactive for the 1:4 fuel ratio. To this end, a detailed sensitivity analysis using the AramcoMech 2.0 chemical kinetics mechanism highlights important chemical reactions. Of these reactions, significant model improvements are shown using the reaction rate suggested by Tsang and Hampson for CO+HO2 ⇌ CO2+OH.
Stress Blended Eddy Simulations for Hydrogen-Air Rotating Detonation Engine With Wall Heat Transfer
Authors: Elasrag Hossam A. , Gallagher Timothy , Rankin Brent A. , Schumaker S. Alexander 
Published: October 2022

Abstract
Hybrid stress blended eddy simulations (SBESs) are performed for the AFRL rotating detonation engine burner with detailed finite rate chemistry. The near wall boundary layer flow is modeled using URANS k-ω-SST model and the turbulent internal flow is modeled using Large Eddy Simulation (LES) dynamic Smagorinsky model. Using one-dimensional (1D) detonation tubes, the chemical mechanism and the chemistry integration algorithm are validated against the Chapman Jouguet (CJ) conditions and the Zel’dovich-von Neumann-DÖring (ZND) calculations with reasonably good accuracy. The impact of spatial and temporal resolutions on the wave propagation speed (WPS) and the von Neumann (VN) peak is studied using 1D detonation tube simulations. Using second order (SO) spatial accuracy, the SO temporal scheme over-predicts the VN peak with numerical dispersion near the pressure’s peak, while the first order (FO) temporal scheme is found to add the correct numerical dissipation. The SO and FO profiles show identical wave structure at different resolutions in the expansion region downstream of the compression shock’s peak. With FO temporal scheme, the VN peak was found to vary within 2%–6% band within a spatial resolution range of 0.5–0.001 mm and within 2%–20% band within a temporal resolution range of 1E−7 s – 1E−8 s. The spatial and temporal resolutions, however, are found to have a smaller impact on the WPS (varies within 2%–5%). For three-dimensional (3D) simulations the SO and FO comparisons with data were overall comparable. The results show very good agreement with the measurements mean static pressure data, WPS, specific thrust and specific impulse. The SO temporal scheme predicted a WPS with a mean error of approximately 11%–10% while the FO temporal scheme mean error is 6%. Back-flow due to the detonation wave in the air and fuel plenums are quantified to be 10% and 15%, respectively. The impact of wall heat transfer modeling on the detonation wave is studied. As the wall temperature increases more deflagration burning in the refill zone occurs ahead of the detonation wave. The fraction of heat released by deflagration and detonation is quantified for each case using cut-off values of 5 atm and 10 atm. Although the impact of wall heat transfer on WPS is found to be small, the fraction of heat released by deflagration increased by 10% for 600 K isothermal wall temperature compared to the 300 K isothermal wall temperature. For local static temperatures &gt; 300 K, the fraction of heat released in the deflagration mode was 75%, 53%, and 40%, for the adiabatic walls, 600 K, and 300 K isothermal walls, respectively. The current numerical study shows that accurate wall heat transfer modeling is important for rotating detonation engine (RDE) numerical simulations.
Characterization of an Apparatus to Study Solid Deposit Formation in Lubricating Oils at High Temperatures
Authors: Juárez Raquel , Gutierrez Noble , Petersen Eric L. 
Published: October 2022

Abstract
When exposed to excessively high temperatures, the lubricating oils in turbines undergo extreme oxidation and thermal degradation processes that eventually result in the formation of solid deposits that can, in turn, cause operational problems. This work describes the testing and characterization process of a newly constructed test rig that studies the propensity of lubricants to form such deposits. In the test rig, the lubricant flows through a heated tube, thermally degrades or oxidizes, and forms solid deposits that adhere to the heated surface. An oil flow rate calibration curve as a function of pump speed was developed using two oils, Castrol GTX 20W-50 and Mobil DTE 732. The steady-state axial temperature distribution along the heated tube was measured for temperature settings of up to 475°C and flow rates of 10.4, 12.2, and 13.9 mL/min using Mobil DTE 732. The results showed that the surface temperature is not constant, but that it varies axially as is expected from the heat transfer in the thermal entrance region of a pipe with laminar flow. Examples of the results of tests performed with the apparatus using Mobil DTE 732 and Castrol GTX 20W-50 flowing at 10.4 mL/min with surface temperatures between 328 and 489°C are presented. Based on these tests, it is clear that the induction time for solid-deposit formation can be unambiguously determined using the experimental apparatus. The induction times of the sample tests described were found to be 638 ± 10 min and 86 ± 10 min for Mobil DTE 732 and Castrol GTX 20W-50, respectively.