bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unsteady Simulations of a Trailing-Edge Slot Using Machine-Learnt Turbulence Stress and Heat-Flux Closures
Authors: Lav Chitrarth , Sandberg Richard D. 
Published: January 2021

Abstract
The trailing edge slot is a canonical representation of the pressure-side bleed flow encountered in high pressure turbines. Predicting the flow and temperature downstream of the slot exit remains challenging for RANS and URANS, with both significantly overpredicting the adiabatic wall-effectiveness. This over-prediction is attributable to the incorrect mixing prediction in cases where the vortex shedding is present. In case of RANS the modelling error is rooted in not properly accounting for the shedding scales while in URANS the closures account for the shedding scales twice, once by resolving the shedding and twice with the model for all the scales. Here, we present an approach which models only the stochastic scales that contribute to turbulence while resolving the scales that do not, i.e. scales considered as contributing to deterministic unsteadiness. The model for the stochastic scales is obtained through a data-driven machine learning algorithm, which produces a bespoke turbulence closure model from a high-fidelity dataset. We use the best closure (blowing ratio of 1.26) for the anisotropy obtained in the a priori study of Lav, Philip & Sandberg [A New Data-Driven Turbulence Model Framework for Unsteady Flows Applied to Wall-Jet and Wall-Wake Flows, 2019] and conduct compressible URANS calculations. In the first stage, the energy equation is solved utilising the standard gradient diffusion hypothesis for the heat-flux closure. In the second stage, we develop a bespoke heat-flux closure using the machine-learning approach for the stochastic heat-flux components only. Subsequently, calculations are performed using the machine-learnt closures for the heat-flux and the anisotropy together. Finally, the generalisability of the developed closures is evaluated by testing them on additional blowing ratios of 0.86 and 1.07. The machine-learnt closures developed specifically for URANS calculations show significantly improved predictions for the adiabatic wall-effectiveness across the different cases.
Generation Mechanism of Broadband Whoosh Noise in an Automotive Turbocharger Centrifugal Compressor
Authors: Dehner Rick , Sriganesh Pranav , Selamet Ahmet , Miazgowicz Keith 
Published: January 2021

Abstract
The present study focuses on the acoustics of a turbocharger centrifugal compressor from a spark-ignition (SI) internal combustion (IC) engine for passenger car applications. Whoosh noise is typically the primary concern for this type of compressor, which is loosely characterized by broadband sound elevation in the 4 to 13 kHz range. To identify the generation mechanism of broadband whoosh noise, the present study combines three approaches: three-dimensional (3D) computational fluid dynamics (CFD) predictions, experiments, and modal decomposition of 3D CFD results. CFD predictions include four operating points at the (relatively low) 80 krpm rotational speed, spanning from near choke to the peak pressure ratio, along with an additional point at the peak whoosh noise (from experiments) at 140 krpm. Predicted compressor performance, along with noise in the compressor inlet duct agree reasonably well with the corresponding experimental results.
After establishing the accuracy of predictions, flow structures and time-resolved pressures are closely examined in the vicinity of the main blade leading edge. This reveals the presence of rotating instabilities that may interact with the rotor blades to generate noise. An azimuthal modal decomposition is performed on the predicted pressure field to determine the number of cells and the frequency content of these rotating instabilities.
The strength of the rotating instabilities and the frequency range in which noise is generated as a consequence of the rotor-rotating instability interaction, is found to correspond well with the qualitative trend of the whoosh noise that is measured several duct diameters upstream of the rotor blades. The variation of whoosh frequency range between low (4 to 6 kHz at 80 krpm) and high (4 to 13 kHz at 140 krpm) rotational speeds is interpreted through this analysis. It is also found that the whoosh noise primarily propagates along the duct as acoustic azimuthal modes. Hence, the inlet duct diameter, which governs the cut-off frequency for multi-dimensional acoustic modes, determines the lower frequency bound of the broadband noise.
Performance Improvement of a Supercritical CO2 and Transcritical CO2 Combined Cycle for Offshore Gas Turbine Waste Heat Recovery
Authors: Zhou Aozheng , Ren Xiaodong 
Published: January 2021

Abstract
The supercritical CO2 (S-CO2) and transcritical CO2 (T-CO2) combined cycle is a promising technology for the waste heat recovery of the offshore gas turbine. In this paper, a new system layout is proposed to investigate the thermodynamic and economic performances improvement of the S-CO2-T-CO2 combined cycle. Compared to the original systems, the residual heat of the topping S-CO2 cycle is recovered and extra recuperation is added to the bottoming T-CO2 cycle. Sensitivity analysis of different systems is carried out based on the mathematical model and multi-objective optimization is conducted. The net power out and the net present value (NPV) are chosen as the objective functions of thermodynamic and economic aspects. The results reveal that at the design point, the improved system has more than 8.23% increment on the net power output and 3.55% increment on the NPV. Besides, the optimized net power output of the improved system attains at least 5.16% increment with 3.15% increment for the optimized NPV at the same time. The improved system can be applied in some practical cases from both the thermodynamic and economic views.
Pressurized SOFC System Fuelled by Biogas: Control Approaches and Degradation Impact
Authors: Ferrari Mario L. , Zaccaria Valentina , Kyprianidis Konstantinos 
Published: January 2021

Abstract
This paper shows control approaches for managing a pressurized Solid Oxide Fuel Cell (SOFC) system fuelled by biogas. This is an advanced solution to integrate the high efficiency benefits of a pressurized SOFC with a renewable source. The operative conditions of these analyses are based on the matching with an emulator rig including a T100 machine for tests in cyber-physical mode (a real-time model including components emulated in the rig, operating in parallel with the experimental facility and used to manage some properties in the plant, such as the turbine outlet temperature set-point and the air flow injected in the anodic circuit). The T100 machine is a microturbine able to produce a nominal electric power output of 100 kW. So, the paper presents a real-time model including the fuel cell, the off-gas burner, and the recirculation lines. Although the microturbine components are planned to be evaluated with the hardware devices, the model includes also the T100 expander for machine control reasons, as detailed presented in the devoted section. The simulations shown in this paper regard the assessment of an innovative control tool based on the Model Predictive Control (MPC) technology. This controller and an additional tool based on the coupling of MPC and PID approaches were assessed against the application of Proportional Integral Derivative (PID) controllers. The control targets consider both steady-state (e.g. high efficiency solutions) and dynamic aspects (stress smoothing in the cell). Moreover, different control solutions are presented to operate the system during fuel cell degradation. The results include the system response to load variations, and SOFC voltage decrease. Special attention is devoted to the fuel cell system constraints, such as temperature and time-dependent thermal gradient. Considering the simulations including SOFC degradation, the MPC was able to decrease the thermal stress, but it was not able to compensate the degradation. On the other hand, the tool based on the coupling of the MPC and the PID approaches produced the best results in terms of set-point matching, and SOFC thermal stress containment.
Performance Simulation of Roughness Induced Module Variations of a Jet Propulsion by Using Pseudo Bond Graph Theory
Authors: Göing Jan , Bode Christoph , Friedrichs Jens , Seehausen Hendrik , Herbst Florian , Seume Joerg R. 
Published: January 2021

Abstract
A scientific method is developed to determine the impact of a deteriorated HPC (high-pressure compressor) on the overall performance of a turbofan jet engine. Initially, the HPC performance with roughness variations on vanes and blades is simulated by using 3D CFD (Computational Fluid Dynamics) at different operating points. Afterwards, the overall performance of the full jet engine is computed by the in-house 1D performance tool ASTOR (AircraftEngine Simulation for Transient Operating Research). ASTOR is based on the Pseudo Bond Graph approach to model and connect miscellaneous components with the equations of motion and dynamic volumes. By solving this differential equation system, transient performance is calculated in higher accuracy compared to common Reduced Order Models (ROM). Transient load cases are modelled to analyse the impact of deteriorated HPC on the overall performance. Furthermore, similarities and differences to the steady performance are considered. The maximum deviation of EGT between an engine with a new and deteriorated HPC during a fast acceleration is 32% while it is 27% at steady operation. Also a trade-off between an increasing EGT and a decreasing pressure downstream of the LPT is analysed. Finally, relations between the engine performance, Reynolds-number and roughness are analysed to classify the performance drop due to a HPC with roughness.
Design and Testing of a Hot Gas Blower for Solid Oxide Fuel Cell Applications
Authors: Honkatukia Juha , Jaatinen-Värri Ahti , Turunen-Saaresti Teemu , Grönman Aki , Sallinen Petri , Backman Jari 
Published: January 2021

Abstract
The study focuses on the design and testing of a centrifugal blower to be used for recirculating hot anode off-gas in solid oxide fuel cells (SOFC). SOFCs operate at high temperatures, even at 800 °C and typically, the anode off-gas is led out of the SOFC stack. However, nowadays it is commonly known that the efficiency of the SOFC system can be improved by recirculating the anode off-gas.
Up until recent years, the problem with the recirculation has been that there are no suitable blowers feasible enough to sustain the high temperature of the anode off-gas. In this study, a 500 W centrifugal blower having a design pressure ratio of 1.126 was designed and tested using a 50 kW SOFC application as a basis of the design, but the designs can also be applied to other applications, e.g. recirculation needs of hot air.
The blower was first tested using inlet air at room temperature and then using heated inlet air at about 300 °C. In the design phase, cooling was found one of the main challenges when hot inlet air is used. The results obtained from the test runs were well-matched with the design values.
Firing Trials of the Siemens SGT-300 Dry Low Emissions Combustion System Using High Calorific Value Fuels
Authors: Calladine Kristopher , Rogerson Jim , Hubbard Phill , Sadasivuni Suresh K. , Bulat Ghenadie 
Published: January 2021

Abstract
The current paper presents an extension of the fuel flexibility of the Siemens SGT-300 Dry Low Emissions combustion system to include High Calorific Value fuels, achieved using the engine’s current standard combustion hardware.
Results from high pressure rig tests show that the standard SGT-300 DLE combustor can reliably operate on High Calorific Value fuels with temperature corrected Wobbe Index up to 63MJ/m3, which corresponds to Grade A LPG (60%vol. C3H8, 40%vol. C4H10). Metal temperatures of the combustion hardware when operating on High Calorific Value fuels are within life acceptance criteria for the Siemens SGT-300 industrial gas turbine. NOx emissions throughout the load range of the engine comply with the EU Industrial Emissions Directive. At part load, a reduced requirement for piloting compared to Natural Gas yields relatively low temperatures at the burner face and low NOx emissions. NOx emissions at full load, which tend to increase with increasing heating value, are higher than for Natural Gas but lower than for diesel and heavy fuel oils.
Unsteady Analysis of Inlet Hot Streaks Clocking Effects in a 1-1/2 Turbine Stage
Authors: Jin Yejia , Ma Hongwei , Yu Xinghang 
Published: January 2021

Abstract
Migration of inlet hot streaks and the clocking effects are investigated by three-dimensional unsteady numerical simulations in a 1-1/2 turbine stage. Two hot streak circumferential positions with respect to first-stage stator, passage centered and vane centered, are simulated. Results indicate that hot streaks tend to accumulate on rotor blade pressure side and move towards shroud, causing hot spots on these parts. Separation of hot and cold fluid is observed in rotor, thus influence of hot streaks spreads to second-stage stator. Hot streaks are broken into fragments by rotor blade wakes and rotor-stator interactions in second-stage stator. Impinging hot streaks on first-stage stator passages results in separation of hot and cold lats longer in rotor, but area-averaged temperature at rotor outlet is relatively lower. Hot streaks keep a higher temperature through rotor, yet area-averaged temperature has a quicker drop in second-stage stator. Impinging hot streaks on first-stage stator vanes brings a more uniform temperature distribution at rotor and turbine outlet while a higher area-averaged temperature at the same time. Hot streaks adhere to the first-stage stator vane surfaces and move towards hub due to tip leakage, causing extra heating to these parts compared with passage centered hot streaks. Rortex, as a new way to identify vortexes in fluid, is employed to understand how vortexes contribute to migration and dissipation of hot streaks. Also, Proper Orthogonal Decomposition analysis is applied to identify flow features that impact migration and dissipation of hot streaks, and a few connections between the flow features and POD modes are made.
The Effect of Radial Skew Angles of Blade Angle Slots on the Stability and Performance of an Axial Flow Compressor
Authors: Zhang HaoGuang , Liu WenHao , Chu WuLi , Wang EnHao 
Published: January 2021

Abstract
The parametric numerical study was performed to explore the effect of radial skew angles of blade angle slot casing treatment (CT) on the stability and performance of an axial flow subsonic compressor. Five kinds of blade slot casing treatment with difference radial skew angles (0 degree, 30 degrees, 45 degrees, 60 degrees, and 75 degrees) were designed in the numerical investigations. The unsteady calculated results show that among the radial skew angles of 0 degree, 30 degrees, 45 degrees, 60 degrees, the bigger the radial skew angle of the slots is, the greater the stall margin improvement (SMI) generated by the slots is, and the slots with 60 degrees radial skew angle can generate 58.86% SMI. Moreover, the SMI for the slots with 60 degrees radial skew angle is 29.64% more than that for the slots with 75 degrees radial skew angle. Besides, the slots with radial skew angle of 75 degrees cause the least penalty in peak efficiency among five kinds of radial skew angle, and the peak efficiency for the slots with 75 degrees radial skew angle is 0.88% higher than that for smooth wall casing treatment. The slots with 0 degree radial skew angle generate the biggest peak efficiency loss of 5.94% among five kinds of radial skew angle.
The flow field analyses show that the recirculated flows formed in the slots can generate momentum transport effects on the flow field in the blade tip. Under the effects of the momentum transport, the momentum balance between the tip leakage flow (TLF) and main flow (MF) is changed, and the momentum balance determines the trajectory of the TLF and the mainstream/tip leakage flows interface. As a result, the flow condition in the tip channel is also changed. By changing the radial skew angle of slots, the slots behave different capacities of momentum transport on the tip flow field, and the momentum balance between tip leakage flow and main flow is changed differently. So, the trajectory of the TLF and the mainstream/tip leakage flows interface are deflected differently. Different improvements of the compressor stability are obtained by the slots with different radial skew angles. The slots with radial skew angle of 60 degrees can largely deflect the trajectory of TLF and the mainstream/tip leakage flows interface to the blade suction surface. It improves the flow condition of the blade tip channel, and the slots generate 58.86% SMI. However, after the slots with radial skew angle of 0 degree and 30 degrees are applied, the tip leakage vortex breakdown is occurred. So, they generate few improvements of the stall margin. Furthermore, the interaction between recirculated flows inside slots and main flows inevitably causes additional flow losses. With the increase of radial skew angle, the efficiency loss caused by slot CT decreases. Thus, the slots with 75 degrees radial skew angle generate the least peak efficiency loss among five kinds of radial skew angle.
Effects of the Large Eddy Simulation Calculation Parameters on Prediction of Profile Loss in an Axial Cascade at Off-Design Incidence
Authors: Lee Yuntae , Teramoto Susumu , Toki Takahiko , Okamoto Koji 
Published: January 2021

Abstract
Large Eddy Simulation (LES) has already been widely applied for unsteady flow simulations (e.g., axial cascade simulation), showing its superiority in the case of turbulent flow fields. However, there are several obstacles in the practical use of LES as a cascade design tool for gas turbine engines. Several calculation parameters such as the inlet turbulence, spanwise extents, and many other boundary conditions, affect calculation results for LES simulation and can cause reliability problems. This study concentrates on investigating the effects of LES calculation parameters on the prediction of profile loss at high air inlet angle off-design condition. The LES flow field results were found to be sensitive to four parameters (i.e., inlet turbulence, spanwise domain extent, time step size, and outlet domain). The inlet turbulence affects the size of the laminar separation bubble, while the spanwise domain extent affects the velocity fluctuations of the wake in correspondence of the large-scale vortices shedding. The time step size affects the velocity fluctuations of the wake because of the number of times that the low-pass filter is applied. Finally, the outlet domain extent affects the whole calculation domain (from the leading edge to the wake). Overall, the results show that all four calculation parameters can change the flow characteristics, affecting the prediction of profile loss at off-design condition when using LES.
Effect of Boundary Layer Suction on the Corner Separation in a Highly Loaded Axial Compressor Cascade
Authors: Liang Tian , Liu Bo , Spence Stephen 
Published: January 2021

Abstract
Control of corner separation in axial compressor blade rows has attracted much interest due to its potential to improve compressor efficiency and the energy utilization in turbomachinery. This paper investigates the effectiveness and mechanisms of boundary layer suction in controlling the corner separation of a highly loaded axial compressor cascade. Numerical simulations have been carried out to investigate the effect of different suction schemes on the loss downstream of the cascade and the change in incidence characteristics with the variation of the suction flow rate. The results show that the effectiveness of flow suction in controlling the flow separation depends heavily on the proportion of the blade for which it is applied. It was found that suction along part of the blade span on the suction surface could effectively remove the separation at the region of the span influenced by the suction slot. However, this resulted in a deterioration of the flow field at other parts of the span. The full span suction scheme on the suction surface not only eliminated the separation of the boundary layer in the middle of the blade, but also significantly improved the flow uniformity near the end-wall.
Despite the improvement in flow uniformity using the full-span suction scheme, a three-dimensional (3D) corner separation still existed due to the strong cross-passage pressure gradient. To improve the flow field uniformity further, two combined suction schemes with one spanwise slot on the suction surface and another slot on the end-wall were designed in order to fully remove both the separated flow on the blade suction surface and the 3D corner separation. It was found that the total pressure loss coefficient was reduced significantly by 63.8% with suction flow rates of 1.88% and 0.82% for the slots on the suction surface and the end-wall respectively. Further work showed that the behavior of the loss coefficient is different as the combination of suction flow rates is changed for different incidence. The cascade loss at high incidence operation can be more effectively reduced with suction control on the end-wall. When implementing combined suction, it is necessary to determine the best combination of suction flow rate according to the incidence level.
Multidisciplinary Design Optimization of a Low-Noise and Efficient Next-Generation Aero-Engine Fan
Authors: Jaron Robert , Moreau Antoine , Guérin Sébastien , Enghardt Lars , Lengyel-Kampmann Timea , Otten Tom , Nicke Eberhard 
Published: January 2021

Abstract
Due to the increasing bypass ratios of modern engines, the fan stage is increasingly becoming the dominant source of engine noise. Accordingly, it is becoming more and more important to develop not only efficient but also quiet fan stages. In this paper the noise emission of a fan for an aero-engine with a bypass ratio of 19 is reduced within a multidisciplinary design optimization (MDO) by means of an hybrid noise prediction method while at the same time optimizing the aerodynamic efficiency. The aerodynamic performance of each configuration in the optimization is evaluated by stationary Reynolds-Averaged Navier-Stokes (RANS) simulations. These stationary flow simulations are also used to extract the aerodynamic excitation sources for the analytical fan noise prediction. The resulting large database of the optimization provides new insights into which extent an MDO can contribute to the design of both quiet and efficient fan stages. In addition to that the hybrid approach of numerical flow solutions and analytical description of the noise sources enables to understand the noise reduction mechanisms. In particular, the influence of rotor blade loading on the aerodynamic efficiency and the noise sources as well as the potential of configurations with a comparatively low number of outlet guide vanes (OGV) is explored. The acoustic results of selected configurations are confirmed by unsteady RANS simulations.