bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Investigation of Axial Compressor With Aggressive Flow Path Near Stall Condition
Authors: Ming Lele , Wu Yadong , Ouyang Hua 
Published: January 2021

Abstract
Rotating stall is an unsteady flow phenomenon in flow rate reduction process of axial compressor. Single or multiple stall cells can be found in blade passage, rotating circumferentially at frequency ranging from 20% to 80% of compressor rotating frequency. Rotating stall may further lead to surge, then mass flow and pressure ratio of the compressor decrease rapidly while vibration amplitude of bearing fulcrum increases significantly, which would affect safety operation of the aero-engine. This paper reports the study on a multistage compressor with special-shaped aggressive flow path, which is significantly different from the conventional compressor with its meridian flow path midline parallel or nearly parallel to the rotating shaft axis.
To study rotating stall and surge characteristics of multistage compressor with inlet distortion, this paper takes a 4.5-stage axial compressor as research object which has special S-shaped meridian flow path. On SJTU compressor test facility, the author carries out multidisciplinary tests on compressor dynamic performance (stator LE/TE and inter-stage fluctuating pressure measured by fluctuating pressure transducers, vibration measured by acceleration transducers, and dynamic stress measured by pasting strain transducers on the surface of stator blade). And in subsequent surge experiment, stall and surge signals at different rotating speeds are successfully captured. With above test data, axial, radial and circumferential instability development characteristics are studied by time domain correlation analysis, frequency domain power spectrum and coherence analysis, which preliminarily reveals the generation, development, propagation and elimination characteristics of rotating stall and surge.
Meanwhile, in view of time-frequency characteristics of two instability transition processes, time-frequency analysis method based on Choi-Williams distribution model is adopted to capture instantaneous frequency characteristics. The results show that instability phenomenon exhibits quasi-exponential change in instability transition processes. Compared with traditional methods, time-frequency method is more effective in characterizing strong time-varying instability signals such as rotating stall and surge.
Acceleration Method for Evolutionary Optimization of Variable Cycle Engine
Authors: Hao Wang , Zhou Li , Zhang Xiaobo , Wang Zhanxue 
Published: January 2021

Abstract
Variable cycle engine (VCE) is considered as one of the best options for advanced military or commercial supersonic propulsion system. Variable geometries enable the engine to adjust performance over the entire the flight envelope but add complexity to the engine. Evolutionary algorithms (EAs) have been widely used in the design of VCE. The initial guesses of the engine model are generally set using design point information during evolutionary optimization. However, the design point information is not suitable for all situations. Without suitable initial guesses, the Newton-Raphson solver will not be able to reach the solution quickly, or even get a convergent solution. In this paper, a new method is proposed to obtain suitable initial guesses of VCE model during evolutionary optimization. Differential evolution (DE) algorithm is used to verify our method through a series of optimization cases of a double bypass VCE. The result indicates that the method can significantly reduce the VCE model call number during evolutionary optimization, which means a dramatic reduction in terms of evolution time. And the robustness of the optimization is not affected by the method. The method can also be used in the evolutionary optimization of other engines.
Windmilling Characteristics of a Contra-Rotating Fan
Authors: Madasseri Payyappalli Manas , Karmakar Arghya , Pradeep A. M. 
Published: January 2021

Abstract
In the present experimental study, a low aspect ratio, low hub-tip ratio contra-rotating axial fan is investigated to understand its performance under windmilling conditions. Two configurations are tested; in the first configuration (event A), the front rotor of the contra-rotating fan is powered and the rear rotor is allowed to windmill; in the second configuration (event B), the rear rotor of the contra-rotating fan is powered and the front rotor is allowed to windmill. The spanwise distribution of the loading coefficient and the flow angles at different streamwise positions reveal the details of the flow development across the rotors. The performances of event A and event B are nearly similar; however, event A stalls earlier than event B. Though the average total pressure drops across the windmilling rotor for both the events, a small spanwise region behaves as a fan or a stirrer. Thus, a “neutral radius” on the windmilling rotor is identified for both events A and B. The neutral radius appears close to the tip for event A and it appears close to the hub for event B. On the windmilling rotor in either events, the span regions close to the tip for event A behaves as a fan and the span regions close to the hub for event B behaves as a stirrer. It is also observed that the neutral radius shifts its position to a lower span location as the flow coefficient reduces. Thus, the flow coefficient is a significant parameter that decides the position of the neutral radius. Further, the unsteady pressure measurements recorded at the casing captures the fundamental phenomena during the stall inception. The paper thus relates the similarities and unveils the contrasting features of the windmilling events A and B. In summary, this paper discusses the performance, flow physics and stall inception characteristics of a contra-rotating axial fan under windmilling conditions.
Improved LP-Stage Design for Industrial Steam Turbines
Authors: Brunn Oliver , Harbecke Ulrich , Mokulys Thomas , Salit Victor , Schwarz Mark Andre , Dornbusch Felix 
Published: January 2021

Abstract
This publication deals with the improvement of the design and life steam testing of a low-pressure steam turbine module for utilization in industrial applications. Extensive numerical investigations were carried out and validated with experimental measurements. For the validation of the final blade design, the LP module was integrated and tested in a 12.5MW steam turbine test rig. During the balancing of the rotor in a vacuum chamber, tip-timing and strain gage measurements were conducted for testing the mechanical behavior of the airfoils. In the succeeding assembly of the steam turbine, tip-timing probes and flow measurement probes were integrated around the LP module to evaluate the blade load and performance under realistic conditions. To obtain a good understanding of the improved performance and mechanical behavior the thermodynamic tests were carried out under no-load, part load and design load conditions to cover the whole operating range of the LP stages. The paper also describes how an existing rotor from the test rig could be retrofitted, to accommodate the new turbine stages with additive manufacturing of the base material on the shaft.
Numerical Investigation on the Nonlinear Dynamics of Anisotropic Breathing Cracked Rotor Systems
Authors: Zheng Zhaoli , Li Zixuan , Zhang Di , Xie Yonghui , Zhang Zheyuan 
Published: January 2021

Abstract
The nonlinear breathing crack behaviors and anisotropy of the bearing are important sources of severe vibration of rotor systems. However, the rotor system considering both of these factors has not gained sufficient attention in the existing studies. In this paper, the nonlinear dynamics of such anisotropic breathing cracked rotor system is investigated based on three-dimensional finite element model (FEM). Firstly, the equations of motion of the rotor system are established in the rotating frame to facilitate the modeling of the breathing crack. The fixed-interface component mode synthesis (CMS) is used to reduce the system’s degrees of freedom (DOFs). Then, in the process of solving the equations by harmonic balance method (HBM) and Newton-Raphson method, an original method for fast calculating tangent stiffness matrix is proposed. Finally, the effects of the crack depth, the anisotropy of bearing and relative angle between bearings on the nonlinear dynamics of the system are studied. The results show that the breathing behavior will complicate the vibration and introduce additional transverse stiffness. The increase of crack depth will deteriorate the vibration. The anisotropy and relative angle of bearing will lead to the splitting and merging of the resonant peaks, respectively.
Near Wall Resolution Requirements for High-Order FR/CPR Method for Wall-Resolved Large Eddy Simulations
Authors: Bhaskaran Rathakrishnan , Ledezma Gustavo 
Published: January 2021

Abstract
This study aims to establish near wall resolution requirements for wall-resolved Large Eddy Simulations (LES) using the Flux Reconstruction / Correction Procedure via Reconstruction (FR/CPR) method. The FR/CPR method is relatively new and its numerical capabilities for LES are not well established. A high-order unstructured LES solver (GENESIS) based on the FR/CPR approach is used to study two canonical near wall turbulent flow problems. The first problem concerns spatial development of a turbulent flat plate boundary layer. The grid resolution requirement for various polynomial orders is established and the skin-friction and near wall turbulence is compared to theory and Direct Numerical Simulation (DNS) results. The second problem studied is the two-dimensional wall film case of Kacker and Whitelaw (1968, 1969). This is a thermal mixing problem consisting of a two-dimensional jet for various mass flow ratios and plate thicknesses. This study focuses on one of the cases from this data set, corresponding to a thick plate. Well resolved LES simulations show an excellent agreement with measured adiabatic film effectiveness. The effect of polynomial order and grid resolution is investigated and near wall resolution requirements are established.
Laminar Flame Speeds of Oxy-Methane Flames With CO2 Dilution at Elevated Pressures
Authors: Turner Mattias A. , Kulatilaka Waruna D. , Petersen Eric L. 
Published: January 2021

Abstract
Spherically expanding, laminar flame experiments have been conducted for oxy-methane mixtures diluted in CO2. Test conditions consisted of pressures of 5 atm and 10 atm, an ambient initial temperature of 298 K, and a full range of equivalence ratios from lean to rich. Schlieren imaging was used to image the flames. The mixtures tested in this study contained helium for the purpose of increasing the Lewis number to suppress onset of thermal-diffusive instabilities. Flame speeds ranged from 24.3 to 30.4 cm/s at 5 atm initial pressure and from 17.9 to 22.6 cm/s at 10 atm, resulting in an approximately 26% decrease in flame speed across all tested equivalence ratios as a result of the doubling in initial pressure. Predicted flame speeds from AramcoMech2.0 tended to be higher than the experimental data by 3% at 5 atm initial pressure and 8% at 10 atm initial pressure, indicating that the performance of the mechanism is quite good for this mixture, but diminishes slightly as pressure increases.
Reduced-Order Modelling of Rotating Stall
Authors: Schlüter Dominik , Grewe Robert P. , Wartzek Fabian , Liefke Alexander , Werner Jan , Kunkel Christian , Gümmer Volker 
Published: January 2021

Abstract
Rotating stall is a non-axisymmetric disturbance in axial compressors arising at operating conditions beyond the stability limit of a stage. Although well-known, its driving mechanisms determining the number of stall cells and their rotational speed are still marginally understood. Numerical studies applying full-wheel 3D unsteady RANS calculations require weeks per operating point. This paper quantifies the capability of a more feasible quasi-2D approach to reproduce 3D rotating stall and related sensitivities.
The first part of the paper deals with the validation of a numerical baseline the simplified model is compared to in detail. Therefore, 3D computations of a state-of-the-art transonic compressor are conducted. At steady conditions the single-passage RANS CFD matches the experimental results within an error of 1% in total pressure ratio and mass flow rate. At stalled conditions, the full-wheel URANS computation shows the same spiketype disturbance as the experiment. However, the CFD underpredicts the stalling point by approximately 7% in mass flow rate. In deep stall, the computational model correctly forecasts a single-cell rotating stall. The stall cell differs by approximately 21% in rotational speed and 18% in circumferential size from the experimental findings. As the 3D model reflects the compressor behaviour sufficiently accurate, it is considered valid for physical investigations.
In the second part of the paper, the validated baseline is reduced in radial direction to a quasi-2D domain only resembling the compressor tip area. Four model variations regarding span-wise location and extent are numerically investigated. As the most promising model matches the 3D flow conditions in the rotor tip region, it correctly yields a single-cell rotating stall. The cell differs by only 7% in circumferential size from the 3D results. Due to the impeded radial migration in the quasi-2D slice, however, the cell exhibits an increased axial extent. It is assumed, that the axial expansion into the adjacent rows causes the difference in cell speed by approximately 24%. Further validation of the reduced model against experimental findings reveals, that it correctly reflects the sensitivity of circumferential cell size to flow coefficient and individual cell speed to compressor shaft speed. As the approach reduced the wall clock time by 92%, it can be used to increase the physical understanding of rotating stall at much lower costs.
Soot Formation and Emission From Jet A-1 and a 30% HEFA Blend in a Multisector Combustor at Realistic Operating Conditions
Authors: Hassa Christoph , Magens Eggert , Voigt Lena , Diers Olaf , Otterpohl Ingo , Heinze Johannes 
Published: January 2021

Abstract
The production and emission of soot from Kerosene JET-A1 and a blend of a different JET-A1 and 30% HEFA was investigated in a realistic multisector combustor of Rolls-Royce Deutschland. Soot concentration measurements were performed at the exit as well as in the optically accessible primary zone of the combustor. There, information of soot mass concentration is available from measurements using Laser induced incandescence and Laser extinction. At the exit of the combustor, soot particles were measured with a scanning mobility particle sizer. This resulted in particle size distributions from which soot number and mass concentrations were calculated.
Within the pressurized combustor, low load points, scaled cruise and high load points were operated. For the investigated operating range which reaches to ∼50% of max pressure but preserves engine AFR, up to 75% reduction of both soot particle mass and number EI were observed for the HEFA blend in part load and 50% at the scaled high-power condition. However at the end of the primary zone, a reduction increasing with soot concentration and fuel load was recorded. This guides attention to the different oxidation characteristics for the fuels in the investigated combustor. Accordingly, larger particles were consistently measured at the exit for the HEFA blend.
Vibration Analyses of an Axial Turbine Wheel With Intentional Mistuning
Authors: Beirow Bernd , Kühhorn Arnold , Weber Robby , Popig Frederik 
Published: January 2021

Abstract
The last stage bladed disk of a steam turbine is analyzed with respect to both flutter susceptibility and limitation of forced response. Due to the lack of variable stator vanes unfavorable flow conditions may occur which can lead to flow separation in some circumstances. Consequently, there is the risk of flutter in principle, particularly at nominal speed under part load conditions. For this reason, intentional mistuning is employed by the manufacturer with the objective to prevent any self-excited vibrations. A first step in this direction is done by choosing alternate mistuning, which keeps the manufactural efforts in limits since only two different blade designs are allowed. In this sense, two different series of blades have been made. However, it is well known that small deviations from the design intention are unavoidable due to the manufacturing procedure, which could be proved by bonk tests carried out earlier. The influence of these additional but unwanted deviations is considered in numerical simulations. Moreover, the strong dependence of blade frequencies on the speed is taken into account since centrifugal stiffening effects significantly attenuate the blade-to-blade frequency difference in this particular case.
Focusing on the first flap mode it could be shown that a mitigation of flutter susceptibility is achieved by prescribing alternate mistuning, which indeed evokes an increase of originally small aerodynamic damping ratios. Nevertheless, the occurrence of negative damping ratios could not be completely precluded at part load conditions. That is why optimization studies are conducted based on genetic algorithms with the objective function of maximizing the lowest aerodynamic damping ratios. Again only two different blade designs are admitted. Finally, mistuning patterns could be identified causing a tremendous increase of aerodynamic damping ratios. The robustness of the solutions found could be proved by superimposing additional random mistuning.
The CFD Design and Optimisation of a 100 kW Hydrogen Fuelled mGT
Authors: Devriese Cedric , Penninx Gijs , de Ruiter Guido , Bastiaans Rob , De Paepe Ward 
Published: January 2021

Abstract
Against the background of a growing deployment of renewable electricity production, like wind and solar, the demand for energy storage will only increase. One of the most promising ways to cover the medium to long-term storage is to use the excess electricity to produce hydrogen via electrolysis. In a modern energy grid, filled with intermittent power sources and ever-increasing problems to construct large power plants in densely populated areas, a network of Decentralised Energy Systems (DES) seems more logical. Therefore, the importance of research into the design of a small to medium-sized hydrogen fuelled micro Gas Turbine (mGT) unit for efficient, local heat and electricity production becomes apparent. To be able to compete with Reciprocating Internal Combustion Engines (RICEs), the mGT needs to reach 40% electrical efficiency. To do so, there are two main challenges; the design of an ultra-low NOX hydrogen combustor and a high Turbine Inlet Temperature (TIT) radial turbine. In this paper, we report on the progress of our work towards that goal. First, an improvement of the initial single-nozzle swirler (swozzle) combustor geometry was abandoned in favour of a full CFD (steady RANS) design and optimisation of a micromix type combustion chamber, due to its advantages towards NOx-emission reduction. Second, a full CFD design and optimisation of the compressor and turbine is performed. The improved micromix combustor geometry resulted in a NOx level reduction of more than 1 order of magnitude compared to our previous swozzle design (from 1400 ppm to 250 ppm). Moreover, several design parameters, such as the position and diameter of the hydrogen injection nozzle and the Air Guiding Panel (AGP) height, have been optimized to improve the flow patterns. Next to the combustion chamber, CFD simulations of the compressor and turbine matched the 1D performance calculations and reached the desired performance goals. A CFD analysis of the impact of the tip gap and exhaust diffuser cone angle led to a choice of these parameters that improved the compressor and turbine performance with a limited loss in efficiency.
Numerical Investigation of an In-Wall Cooling Design Approach for Improved Thermal Efficiency of Additively Manufactured Gas Turbine Ring Segments
Authors: Wimmer Thomas , Mick York , Weigand Bernhard 
Published: January 2021

Abstract
Raising the combustion temperature continues to be a major driver for increasing the overall efficiency of industrial gas turbines. Therefore, active cooling has become a necessity as gas temperatures have surpassed the allowable temperature of the base material. Thus, cooling schemes need to be improved for higher heat loads. However, the thermal efficiency of cooling schemes, which can be manufactured employing conventional machining is limited. With the geometrical freedom offered by Additive Manufacturing (AM), advanced cooling designs for gas turbine parts have become viable and can provide superior thermal efficiency. A promising cooling design approach which exploits this freedom is In-Wall cooling. Here cooling channels are placed within the structural wall close to the heat-loaded surface. In order to develop this design approach further, In-Wall cooling schemes for a ring segment have been modeled numerically with different topologies and varying design parameters. These include wall thickness, channel pitch, size and length, and several more. The design parameters’ influence on thermal efficiency of In-Wall cooling schemes are quantified. The wall thickness between channels and the heat loaded surface is adapted locally. The employed approach leads to a more homogeneous temperature distribution and is reported in the paper. This work can help designers to focus on the most important factors when designing a new In-Wall cooling scheme and shows how the capabilities of AM can be employed in gas turbine cooling design.