bluuebunny/crossref_metadata_2025_split huggingface dataset:
System Parameter Identification of a Colored-Noise-Driven Rijke Tube Simulator
Authors: Vishnoi Neha , Gupta Vikrant , Saurabh Aditya , Kabiraj Lipika 
Published: October 2022

Abstract
In this paper, we report an experimental investigation on the influence of colored noise (generated by the Ornstein-Uhlenbeck process) on thermoacoustic coupling in an electroacoustic Rijke tube simulator. In the absence of noise, the simulator exhibits subcritical Hopf bifurcation. Although, noise in a practical system has a finite correlation time, yet the system identification methods are based on the assumption of white noise. In this study, we investigate the effects of correlation time and intensity of colored noise on the estimation of the growth rates of acoustic oscillations determined using Fokker Planck equation in stable, bistable and linearly unstable regions. Subsequently, we compare the findings against results obtained considering white noise approximations. We report the observed deviation of the estimated growth rates from the actual values as a function of noise intensity and correlation time. We find that with the colored noise model, the deviation in the estimated growth rates lies within the range of 0–10% compared to the deviation of 5–25% observed considering the white noise approximation. We also report that increasing noise amplitudes leads up to a deviation of approximately 30% in the estimated growth rates from the actual values.
The Effect of Rectangular Confinement Aspect Ratio on the Flame Transfer Function of a Turbulent Swirling Flame
Authors: Ånestad Aksel , Ahn Byeonguk , Nygård Håkon T. , Worth Nicholas A. 
Published: October 2022

Abstract
The Flame Transfer Function (FTF) has been experimentally investigated for a premixed, turbulent and highly swirled flame in rectangular enclosures with varying aspect ratio. A range of equivalence ratios and inlet bulk velocities are considered to vary the length of the flame. Increasing confinement is also shown to increase flame length. More confined flames become increasingly asymmetric, with significant changes to the mean flame shape. Characteristic peaks and dips are observed in the FTF gain for several configurations, caused by constructive and destructive interference between different sources of flow perturbations. Changes in the geometrical confinement distinctly affects these interactions, with FTFs in the most confined chamber containing more pronounced peaks and dips. Analysis of the phase-averaged dynamics has been conducted for two limiting operational conditions in the least and most confined enclosures: a short flame at a low bulk velocity and high equivalence ratio condition; and a long flame at a high velocity and low equivalence ratio condition. The analysis of the short flames shows similar behaviour in both enclosures, both in terms of the global response and the local structure of the heat release rate oscillations. Small differences in local response symmetry in the flame due to the close confinement do not affect the global flame response. By comparison, close confinement significantly affects the symmetry of the flame dynamics in the long flame. However, the changes in symmetry do not significantly modify the response, and more important is the change in flame length, which significantly alters the cut-off frequency, reducing the gain at high frequencies.
Novel Fuel Injector Geometry for Enhancing the Fuel Flexibility of a Dry Low NOx MicroMix Flame
Authors: Kroniger Daniel , Horikawa Atsushi , Okada Kunio , Ashida Yuji 
Published: October 2022

Abstract
A novel fuel injector is presented for enhancing the fuel flexibility of the dry micromix (MMX) combustion principle. Originally having been developed for pure hydrogen fueling, the micromix combustion is based on a non-premixed type jet-in-crossflow mixing for inherent safety against flashback, as well as flame miniaturization and multiplication for suppressing NOx emissions. This study investigates the potential of the novel geometry regarding the operation with higher natural gas content fuels. In experiments at atmospheric pressure conditions it could be shown that the new injector extends the fuel flexibility down to between 60 and 80 vol.% H2. The responsible flow phenomena are verified with numerical RANS simulations at engine pressure conditions using a detailed chemistry model. An experimental validation of numerical methods at atmospheric conditions based on OH chemiluminescence distributions showed that the unsteady LES model can predict the micromix flame more accurately regarding to its ignition point than the steady RANS model, although the reaction progress is underestimated by both models, which in comparison to the experiment results in a more stretched flame.
Large Eddy Simulation of Turbulent Flow Through a Compressor Cascade
Authors: Haider Rizvi Syed Anjum , Mathew Joseph 
Published: October 2022

Abstract
A study of large eddy simulations (LES) for compressor blade flows has been undertaken and assessed by comparisons with the measurements of Hobson et al. (AIAA J. Prop. Power, 17, 154 (2001)) on a linear cascade of controlled-diffusion airfoils at Reynolds numbers based on blade chord and inflow velocity of 210 000, 380 000 and 640 000. LES of the latter two conditions are reported here. LES is by an explicit filtering method. Compressible flow equations in curvilinear coordinates were solved with 8th-order, central, finite differences and 2nd order Runge-Kutta integration. At 380 000 there is close quantitative agreement of the blade surface pressures and blade normal profiles of velocity magnitudes and fluctuations. Features of the initial development of the suction surface boundary layer is typical of transition induced by freestream turbulence, but end-stage turbulent spots are missing because of premature completion of transition over a mid-chord separation bubble. At 640 000 this separation is absent and turbulent spots appear before transition is completed. Blade surface pressure distribution from the LES agrees closely with that from experiment and is consistent with absence of separation, as are velocity profiles. Velocity profiles from experiment however had shown substantial open separation from the suction surface. This discrepancy had been noted before and was supposed to be an endwall effect, but our LES, including one with endwalls, does not support that view.
Sensitivity Study on Species Diffusion Models in Turbulent Combustion of Hydrogen/air Jet in Crossflow Structure
Authors: Sun Xiaoxiao , Martin Harry , Gauthier Pierre , Sethi Bobby 
Published: October 2022

Abstract
CFD approach has been intensively used for novel hydrogen combustion technologies as well as emissions prediction. In order to minimise time and costs, simplified combustion CFD models have been developed to take into account of the effect of turbulence-chemistry interactions, coupled with both RANS and LES models. These models often employ assumptions that have been validated for conventional fuels such as Jet-A1 and natural gas. It is clear that the preferential diffusion and thermal diffusion play a vital role in hydrogen laminar premixed flames. Conventionally, it is believed that for high Re cases, turbulent diffusion is dominant, preferential diffusion and thermal diffusion only have a minor effect. For highly turbulent non-premixed flames, these effects have not been fully investigated. The appropriate modelling of these effects is essential for reaction rate, flame temperature and emissions prediction. There is a need to study the sensitivity of different species diffusion models for hydrogen-air flames.
Within the current study, a single micromix injector burning a hydrogen air mixture with an overall equivalence ratio of 0.4 has been simulated in a systematic RANS campaign, and compared with LES. The RANS campaign employs two combustion models: FGM with the kinetic rate closure and Complex Chemistry (CC) with both the laminar flame concept (LFC) and eddy dissipation concept (EDC) closures. The LES employs the same combustion models. The sensitivity of Lewis and Schmidt numbers have been investigated for FGM and EDC model. As expected, FGM is insensitive to the value of Le and Sc whereas for LFC, significant changes have been observed between Le = 0.25 and 0.5, Sc = 0.5 and 0.75. Several species diffusion coefficient models have been used with both LFC and EDC, including: mixture averaged, multi-component and multi-component with thermal diffusion coefficients. All three approaches of modelling molecular diffusivity yielded flame lengths and temperatures of a similar order. The micromix flame was found to be a mixture of both premixed and non-premixed, with jets of strongly premixed and non-premixed originating from the hydrogen injectors.
The sensitivity of turbulent Sc and Le numbers has also been studied with LFC models. It was clearly shown that these changes lead to more significant variation in flame length and temperature compared to those caused by different molecular diffusivity models. LES results with various multi-component diffusion models are compared, the results are in better agreement relative to RANS with different models. The similarity in flame length and insensitivity to CC closure type demonstrates the dominance of turbulence in determining flame structure, through turbulent mixing.
On the Impact of the Turbulence Model on the Secondary Flow Structure of a Highly-Loaded Compressor Stage
Authors: Toracchio Riccardo , Fontaneto Fabrizio , Hillewaert Koen 
Published: October 2022

Abstract
RANS turbulence models still represent a weak point of industrial simulations of turbomachinery flows. In presence of a large blade loading the turbulence model can impact severely on the prediction of the end-wall flow and secondary structures in the blade passage, with an important effect on the computed global performance and flow stability. This paper presents a turbulence model comparison for the characterization of a highly-loaded low-pressure compressor at multiple operating points using 3D RANS simulations. The turbulence models mostly employed for the design and analysis of axial compressors are considered, with the aim of providing a clear physical description of their impact on the critical flow features of the machine. It will be shown that no single turbulence model is generally better than others and the prediction depends on the operating point, with increasing discrepancies as the mass-flow is reduced.
Interaction Mechanism of Transonic Squealer Tip Cooling With the Effect of High-Speed Relative Casing Motion
Authors: Xie Wenbo , Jiang Hongmei , Lu Shaopeng , Peng Xu , Zhang Qiang 
Published: October 2022

Abstract
The relative casing motion can significantly influence the turbine blade tip aerothermal performance. In this study, experimental investigation was conducted in a newly developed high-speed disk rotor rig which can mimic engine realistic highspeed casing relative motion while enabling full optical access to a transonic turbine blade tip surface. Spatially-resolved tip heat transfer data, including heat transfer coefficient and film cooling effectiveness, were obtained for a cooled transonic squealer tip by infrared transient thermal measurement. Combined with closely coupled RANS CFD analysis, this paper reveals an interesting interaction mechanism between the cooling injections from the pressure side and the cavity floor with and without the effect of relative casing motion. Both experimental data and CFD results show a consistent trend in both heat transfer and cooling performance. With the cavity cooling only, the cooling performance reduces with the effect of relative casing motion. However, with additional cooling injection from the pressure side, a significant improvement in the combined cooling performance with the relative casing motion can be observed. Such opposite trend highlights the importance of relative casing motion when ranking different tip cooling designs. With the consideration of relative casing motion, extra tip cooling benefit can be obtained by combining cooling injections from two different locations.
Knowledge-Based Process Design Optimisation in Blisk Manufacturing
Authors: Landwehr Markus , Ganser Philipp , Vinogradov Georg , Bergs Thomas 
Published: October 2022

Abstract
The manufacturing process of blade-integrated disks (blisks) represents one of the most challenging tasks in turbomachinery manufacturing. The requirement is to machine complex, thin-walled blade geometries with high aspect ratios made of difficult-to-cut materials. In addition, extremely tight tolerances are required, since the smallest deviations can lead to a reduction in efficiency of the blisk in the later use.
Nowadays, the ramp-up phase for the manufacturing of a new blisk is time and cost intensive. To find a suitable manufacturing process that meets the required tolerances of the blisk, many experimental tests with different process parameters and strategies are necessary. The used approach is often trial and error which offers limited testing opportunities, is time consuming and wastes resources.
Therefore, the objective of this paper is to develop a knowledge-based process design optimization in blisk manufacturing. For this purpose, this paper picks up the results from our previous work. Based on these results, an experimental validation of the two process design tasks “number of blocks” and “block transition” is conducted. As part of the validation, the results of machining tests on a demonstrator blisk made of Inconel 718 are presented and discussed.
Effects of Part-to-Part Flow Variations on Overall Effectiveness and Life of Rotating Turbine Blades
Authors: Knisely Brian F. , Berdanier Reid A. , Wagner Joel H. , Thole Karen A. , Arisi Allan R. , Haldeman Charles W. 
Published: October 2022

Abstract
As firing temperatures in gas turbine engines continue to increase to achieve high efficiencies, components in the main gas path must be protected with cooling flows to ensure lifing targets are met. Manufacturing variations, however, influence the performance and life characteristics of components with the same nominal design. This study presents blade flow and overall cooling effectiveness measurements for nine true-scale, aero engine turbine blades with realistic manufacturing variations. Flow measurements were made through each blade at a fixed pressure ratio to determine flow variability between holes and between blades. Infrared thermography was used to capture spatially-resolved temperature measurements reported as overall effectiveness on the same nine blades under high-speed rotating conditions at the Steady Thermal Aero Research Turbine Laboratory. Thermal performance was correlated with blade flow performance indicating substantial blade-to-blade variations resulting from manufacturing differences. Measurements also indicated wide variations in cooling jet trajectories as well as overall cooling effectiveness. Finally, the observed blade-to-blade variations in effectiveness were scaled to engine conditions with lifing estimates showing some blades would be expected to last only half as long as others due to manufacturing variability.
A Numerical Investigation of Reheat Hydrogen Combustion in a Simplified Geometrical Configuration From Atmospheric Pressure to Full Load Conditions
Authors: Gruber Andrea , Heggset Tarjei , Duesing Michael , Ciani Andrea 
Published: October 2022

Abstract
An increasing amount of recent experimental evidence indicates that sequential combustion is particularly well-suited for burning highly-reactive fuels like hydrogen, while maintaining low emissions. A convenient feature of the sequential combustion system, resulting in a fundamental advantage compared to alternative approaches, is the possibility of controlling the second-stage flame position through its combustion characteristics, defined by a complex balance of propagation versus spontaneous ignition, based mainly on the reactants’ inlet temperature. At full-load conditions, requiring high pressure and high flame temperature, fuel mixtures with a hydrogen content approaching 100% still bring significant challenges, it is therefore of key importance for the further development of hydrogen-firing capabilities of the gas turbine to improve our present understanding of the interaction between flame propagation and spontaneous ignition and of its role in controlling flame stability and emissions. A series of DNS and LES calculations, featuring complex chemical kinetics and a fully-compressible representation of the reactive flow, are performed on simplified geometrical configurations, yet representative of a sequential combustion system. The present research effort provides novel insight about the combustion characteristics of hydrogen reheat flames at nominal part- and full-load conditions, defining their structure and stabilization mechanism for a range of reactants temperature, as well as modelling guidelines for a reliable numerical approach to reheat combustion.
Effect of Flare Geometry on the Flow Field of Radial-Radial Swirlers
Authors: Bay Ayşe , Kıyıcı Fırat , Perçin Mustafa 
Published: October 2022

Abstract
In this study, an experimental investigation is conducted to assess the impact of the flare geometry on the mean flow field generated by radial-radial swirlers. Two-dimensional two-component PIV measurements are performed on the mid-plane of a non-reacting planar combustor test section. Three-dimensional numerical simulations are conducted for selected cases to support experimental observations. In a previous study conducted in the same setup, counter-rotating radial-radial swirlers without flare extension were investigated. In this study, in addition to the previously studied baseline swirler geometry, four different swirlers are investigated with three different flare geometries (a rounded flare geometry with a radius of 4 mm and two chamfered flares at angles of 27.5° and 45°) with the rounded one having both co- and counter-rotating configurations. Analysis of the time-averaged flow fields reveals that there is an increase in radial velocity values and a decrease in axial velocity values as a result of the introduction of the flare geometry, which results in a sudden expansion of the swirling jet. When different flare geometries are compared, almost identical flow fields are observed and the formation of a CRZ is not observed for any geometry that employs a flare geometry. Although the maximum negative axial velocity values decrease for geometries with flare, due to the increase of the recirculation radius, the recirculating mass flow rate is higher than the baseline swirler. On the other hand, the recirculating mass flow rate is higher in the co-rotating swirler configuration due to stronger adverse pressure gradient along the central axis of the jet when compared to counter-rotating configuration. Coherent flow structures are identified by using the snapshot POD method and different mode shapes obtained for swirlers with and without flare geometry are reported. It is shown that the change of the sense of rotation and flare geometry does not bring about any differences in the POD modes and their energy contents for the given swirl number and confinement conditions.
Leakage Characteristics of a Stepped Balance Piston Labyrinth Seal in Supercritical CO2
Authors: Wilkes Jason , Smith Natalie R. , Wygant Karl , Patil Abhay , Kulhanek Chris 
Published: October 2022

Abstract
In an integrally geared compressor, there is a net thrust load on the pinion shaft from gear loads and aerodynamic forces. The net thrust on the pinion is resolved with either a thrust bearing or a thrust collar (rider ring). As the pressure increases, this increases the aerodynamic force proportionally. In high-pressure systems this can overwhelm the thrust bearing or thrust collar if thrust is mismanaged. In a recent test program for an sCO2 integrally geared compander (compressor/turbine), a balance piston was created on the opposite end of the turbine to provide an equalizing thrust; while this is not novel, the balance piston provided a test apparatus for measuring the leakage on a 20 tooth stepped labyrinth seal operating at pressures in excess of 250 bar (3600 psi).
The stepped balance piston seal is a 20 tooth tooth-on-rotor balance piston seal. This type of seal was selected since it was predicted to have substantially less leakage than a comparably sized straight through labyrinth seal. Comparisons between the two designs will be made, showing that the leakage of the stepped balance piston seal is considerably lower. The tooth clearance on the seal was selected to be 30 mils radial. While this seems large, a stack-up tolerance assessment showed that this magnitude of clearance was appropriate to prevent rotor stator contact.
During the testing campaign, data was recorded showing the leakage across this stepped balance piston seal at pressures in excess of 250 bar (3600 psi) with a pressure ratio of 2. This leakage data was measured, and will be compared to leakage data predicted with CFD. Two measurement methods are presented for the stepped balance piston seal: an orifice plate and valve.
The predicted seal leakage from a straight through seal was four times that of the predicted stepped labyrinth seal. The measured flow from the stepped seal was on the same order as the CFD prediction and offered adequate rotordynamic performance.
Flame Transfer Functions for Turbulent, Premixed, Ammonia-Hydrogen-Nitrogen-Air Flames
Authors: Wiseman Samuel , Gruber Andrea , Dawson James R. 
Published: October 2022

Abstract
Ammonia is a promising hydrogen and energy carrier but also a challenging fuel to use in gas turbines, due to its low flame speed, limited flammability range, and the production of NOx from fuel-bound nitrogen. Previous experimental and theoretical work has demonstrated that partially-dissociated ammonia (NH3/H2/N2 mixtures) can match many of the laminar flame properties of methane flames. Among the remaining concerns pertaining to the use of NH3/H2/N2 blends in gas turbines is their thermoacoustic behavior. This paper presents the first measurements of flame transfer functions (FTFs) for turbulent, premixed, NH3/H2/N2-air flames and compares them to CH4-air flames that have a similar unstretched laminar flame speed and adiabatic flame temperature. FTFs for NH3/H2/N2 blends were found to have a lower gain than CH4 FTFs at low frequencies. However, the cut-off frequency was found to be greater, due to a shorter flame length. The results suggest that NH3/H2/N2 blends may excite different thermoacoustic modes in gas turbines. In addition, the dependence of the flame response on forcing amplitude was measured for a forcing frequency of 650 Hz and the linearity of the NH3/H2/N2 flame response up to high forcing amplitudes suggests that particularly high-amplitude limit cycles may occur. For both CH4 flames and NH3/H2/N2 flames the confinement diameter was found to have a strong influence on peak gain values. The effect on the FTF phase was modest, except in the case of extreme confinement, where almost all of the flame is close to the wall, and in the case of a significant change in the flame stabilisation. Chemiluminescence resolved along the longitudinal direction shows a suppression of fluctuations when the flame first interacts with the wall followed by a subsequent recovery, but with a significant phase shift. Nevertheless, simple Strouhal number scalings based on the flame length and reactant bulk velocity at the dump plane result in a reasonable collapse of the FTF cut-off frequency and phase curves.