bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vibrational Response Analysis of Rotating Mistuned Bladed-Disk Using a Deconvolution Method Based on Blade Tip Timing
Authors: Xiao Zhicheng , Xiao Jiaguangyi , Meng Yiming , Wang Shang , Chai Pengfei , Ouyang Hua 
Published: August 2024

Abstract
The blade tip timing measurement of rotating mistuned bladed-disk vibration is modeled and analyzed by a newly proposed method. The motion of the blades is simplified by a 2-degree-of-freedom lumped mass model responding to traveling wave excitations. A deconvolution algorithm is established to recognize the amplitudes and natural frequencies of system modes based on the undersampled tip displacement data collected by several circumferentially distributed probes. Theoretical analysis shows that the algorithm could obtain accurate amplitudes given a sufficient candidate vector that includes the orders of dominant vibrational components. The robustness is demonstrated by a numerical study which reveals that the uncertainty of the magnitude caused by normally distributed random noise with 0.1 standard deviation is within ±5% as long as the leakage effect is insignificant. The proposed method is applied to analyze a 2F/4EO vibration of a fan in a real aero-engine test. The response curves generated by the present method successfully reconstruct the feature of multiple peaks observed in the measurements. More importantly, the maximum amplitude obtained by the present method agrees with that measured by the strain gauge, while the traditional SDOF method underestimates the value by 38.2% on average.
Numerical Analysis of a Two-Phase Turbine: a Comparative Study Between Barotropic and Mixture Models
Authors: Kumar Amit , Parisi Simone , Agromayor Roberto , Walther Jens Honore , Haglind Fredrik 
Published: August 2024

Abstract
Two-phase turbines offer the potential to significantly enhance the performance of power generation and refrigeration systems. However, their development has been hindered by comparatively lower efficiencies resulting from additional loss mechanisms absent in single-phase turbines. In this context, Computational Fluid Dynamics (CFD) emerges as a crucial tool to predict the performance of two-phase turbines and guide the design process towards higher efficiency. To date, most multiphase CFD studies on turbomachinery have focused on condensation in the final stages of steam turbines, and on cavitation in hydraulic pumps and turbines. These applications, however, are not representative of the conditions in two-phase turbines, where a liquid-dominated mixture undergoes a large expansion ratio, leading to a significant increase in the gas phase volume fraction throughout the entire flow. Recognizing the lack of an established modeling approach, this paper aims to identify a suitable modeling methodology for two-phase turbines. Our evaluation is centered around two models: the mixture model and the barotropic model. The validity and accuracy of these two modeling approaches is assessed using existing experimental data from a single-stage impulse turbine operating with several mixtures of water and nitrogen as working fluid. The results indicate that both the mixture and barotropic models are consistent and accurately predict the nozzle mass flow rate, yet, both models systematically overpredict the nozzle exit velocity and rotor torque. Adding correction terms for windage and unsteady pumping losses significantly improves the torque predictions, bringing them within the uncertainty range of the experimental data. In addition, refining the models to account for the effect of slip presents a promising avenue to enhance the prediction of nozzle exit velocity and overall performance of two-phase turbines.
Multi-Point Aerodynamic Optimization of a Backward-Curved Impeller Fan
Authors: Motamedi Zokae Hamid , Tabor Gavin , Moxey David , Page Martin , Stokes Martin 
Published: August 2024

Abstract
Centrifugal fans find widespread application in building ventilation and air-conditioning systems. Nonetheless, they face challenges in meeting the growing need for energy efficiency, better performance, and reduced noise levels. These limitations stem from the inherent constraints imposed by the circular arc blade design. In this paper, aerodynamic optimization of a backward-curved centrifugal fan was carried out. For this purpose, 3D computational fluid dynamics (CFD) simulations of the initial fan were first validated against test data. Then, using five geometric design parameters, the blade flow angle distribution, from leading edge (LE) to trailing edge (TE), was optimized within its operating range by means of a surrogate-based optimization technique. Efficiencies at different operating points of the fan were selected as objectives while the constraints of the optimization practice include flowrates as well as blade thicknesses of the initial geometry. The suggested optimum geometry generated from this process was independently simulated by CFD to assess the meta-model predictions. The computed results demonstrated up to a 1.7% increase in efficiency in its operating range compared to the initial model. Moreover, studying the features of the flow passing through the blades indicated an improved aerodynamic behavior with reduced separation zones for the optimized geometry compared with the initial one. Geometric comparison of initial and optimized geometries also revealed a curvature redistribution in the fan blades.
Numerical Study on the Console Hole Film Cooling Performance With Varied Hole Inlet Shape
Authors: Luo Yiming , Li Haiwang , Zhou Zhiyu , Xie Gang , Meng Long 
Published: August 2024

Abstract
The shaped holes are widely used to improve the film cooling performance in gas turbine thermal protection. Among them, the converging slot-hole (console) is a well-performed shaped hole, but its cooling effectiveness can be severely deteriorated near the centerline at a small incident degree. In this paper, the geometry of the console, particularly the inlet shape, was adjusted using numerical simulation methods to improve the cooling performance of the console. Different consoles with varying inlet widths but the same inlet area were tested on a flat plate with an injection angle of 30 degrees, and the blowing ratios ranged from 0.5 to 2.0. The mainstream Reynolds number was set to 10000 based on the film hole inlet diameter, and the density ratio was 1.5. The RANS equations were closed by the RNG k-ε model and the structured grid consisting of 7.64 million cells was adopted to provide a relatively accurate predictive result. It is found that kidney vortices near the centerline of the typical console are responsible for the severe deterioration in cooling performance, resulting in the loss of coolant protection in the downstream centerline region and exhibiting trace bifurcation. These kidney vortices mainly originate from flow separation generated when coolant flows from the plenum into the hole. Widening the inlet width of the console increases the spacing between kidney vortices within the hole. This reduces the mutual induction between the vortices and suppresses their development within the hole, ultimately eliminating the kidney vortices along the downstream centerline. In the flow field of the console with a larger inlet width, the predominant structures are anti-kidney vortices. Although this leads to a slightly shorter length of coolant trace, an appropriate increase in the console inlet width can increase the area-averaged cooling effectiveness by up to 117.3% within the downstream range of 40D.
Effect of Swirling Number and Direction on Flame Morphology and Combustion Performance in a Centrally Staged Swirl Combustor
Authors: Xu Honghao , Li Zongfu , Pang Liyao , Zhao Ningbo , Zheng Hongtao 
Published: August 2024

Abstract
Swirl flow is a prominent technology for effectively controlling combustion stability, combustion intensity, and various other aspects in a gas turbine combustor, while the interaction between the two stages of the swirler affects the flame morphology within the recirculation zone, subsequently influencing the combustion performance. In the present work, focusing on the interaction between the main and pilot stages of the swirler, as well as the regularity that influences the combustion flow field, experimental research and numerical simulations are conducted in the single-sector centrally staged model combustors with different swirling numbers and directions of the pilot stage, while the swirling parameters of the primary stage remain constant. Under constant operating conditions, the flow characteristics of the combustion flow field, the development of high-temperature zones, the evolution of flame morphology, and variations in combustor performance are analyzed. The above analysis is carried out with the swirling numbers of the pilot stage respectively maintained at 0.44, 0.55, and 0.68, as well as the swirling direction of the two stages set as either identical or opposite. Simultaneously, the flame cooperation mechanism between the main and pilot stages is explored. Flame within the combustors exhibit stratified structure. Under a constant swirling direction, changing swirling number causes a variation in opening angle between inner shear layers, then altering fuel distribution, opening angles of flames, as well as confluence between inner and outer main flames. In co-swirl condition, as swirling number of pilot stage increases, total pressure losses rise while PF decreases. Effect of swirling direction combination on PF varies across different swirling numbers of pilot stage. At a swirling number of 0.44, counter-swirl results in a slightly lower PF than co-swirl. Nevertheless, at swirling numbers of 0.55 and 0.68, co-swirl proves more effective in achieving lower PF.
Flashback Prevention in a Hydrogen-Fueled Reheat Combustor by Water Injection Optimized With Global Sensitivity Analysis
Authors: Rouco Pousada Pablo , Doan Nguyen Anh Khoa , Aditya Konduri , Düsing Michael , Ciani Andrea , Langella Ivan 
Published: August 2024

Abstract
This paper presents an investigation of the effects of water injection within a simplified version of the Ansaldo GT36 reheat system. The investigation is carried out under realistic operating conditions of 20 atm and using large eddy simulation (LES) coupled with the thickened flame model (TFM) and an adaptive mesh refinement. The water injection conditions are optimized by performing a parametric study based on global sensitivity analysis and a surrogate model based on Gaussian process is employed as a way to reduce computational cost. In particular, the influence on the system performance of four design parameters, namely Sauter mean diameter, water mass flow and the angles of the spray’s hollow cone, is tested to achieve an optimized solution. In the ‘dry’ case, the LES simulations show several flashback events, which are a defining aspect of the considered conditions, and attributed to compressive pressure waves resulting from autoignition in the core flow near the crossover temperature. The use of water injection is found to be effective in suppressing the flashback occurrence. In particular, the global sensitivity analysis shows that the external angle of the spray cone and the mass flow of water are the most important design parameters for flashback prevention. Moreover, NOx was shown to be reduced by about 17% by the use of the water injection at the tested conditions. Once an optimised condition with water injection is found, a recently proposed method to downscale the combustor to lower pressures is applied and tested. Additional LES are performed for this purpose at the ‘dry’, unstable condition and the ‘wet’, stable condition. Results show that similar dynamics, respectively unstable and stable, is predicted at 1 atm, suggesting the robustness of the method. This provides avenues for experimentally testing combustion dynamics at simplified conditions which are still representative of high-pressure practical configurations.
Instability Amplitude Suppression in a Double Orifice Flow Through External Periodic Forcing
Authors: Singh Ashutosh , Mukherjee Isha , Nair Vineeth 
Published: August 2024

Abstract
Various afterburners, ramjets, and combustors exhibit vortex shedding lock-in with an acoustic mode of the duct. In the present study, we experimentally analyse the effect of external forcing on the flow through a square duct containing two circular orifices (double-orifice cavity). As the mean flow is altered, the system transitions from a noisy state to periodic oscillations (lock-in) through a quasiperiodic regime. Periodic forcing of the system close to its instability frequency leads to amplitude suppression via synchronous quenching and 1:1 lock-in. The phase lock-in happens via phase drifting and phase slipping. We also observe asynchronous quenching on forcing the system far from the instability frequency. However, the phase lock-in asynchronous quenching happens via phase drifting and phase trapping. These approaches serve as effective active control strategies for instability control. Synchronisation maps are presented and the dynamics of transition is explored using return maps. In this study, we introduce phenomenological oscillatory models of these phenomena that effectively depict the transition between different lock-in regimes, including the occurrence of a saddle-node bifurcation near the natural frequency and torus death for forcing at a frequency far from the natural frequency. We also study a model that transforms the continuous domain into a discrete map. Synchronisation maps obtained from both models are compared and validated with the experimental results.
Experimental Investigation on the Effect of Nozzle Bluntness Thickness on the Combustion Characteristics of a High-Speed Parallel Jet Mild Combustor
Authors: Yang Ningjing , Xiong Yan , Liu Zhigang , Xu Xiang 
Published: August 2024

Abstract
The safe, stable, and low-emission combustion of high-content hydrogen and pure hydrogen fuels is a crucial aspect of the gas turbine combustion system for achieving carbon-neutral and ultimately carbon-free combustion. However, employing high hydrogen content and even hydrogen as a fuel in combustors presents unique challenges due to distinct fuel characteristics compared to natural gas. This study parametrically investigates the impact of three different nozzle bluntness thicknesses on the reaction zone morphology, combustion stability, and NOx emission characteristics of the high-speed parallel jet MILD combustor. The findings demonstrate that the effect of bluntness thickness variation on the reaction zone morphology can be classified into two distinctive stages: the reaction zone morphology is dominated by the flow field at relatively low hydrogen content and equivalence ratios and by the chemical reactivity of the reactants at higher hydrogen content and equivalence ratios. Meanwhile, the change in lip thickness affects combustion stabilization. The trend of the dynamic pressure main frequency with hydrogen contents and equivalence ratios for the combustor with different lip thicknesses varies in the same way that the trend of the liftoff height of the reaction zone does. Despite significant differences in thermoacoustic characteristics among different bluntness thicknesses, total nitrogen oxide emissions remain relatively unchanged. Total NOx emissions were all less than 10 ppm@15%O2 when the combustion chamber adiabatic flame temperature was less than 2000 K.
Exploiting Active Subspace for Modeling Uncertainty and Optimization in Fan-Shaped Film Cooling Simulation
Authors: Cai Feixue , Zhou Hua , Yao Min , Ren Zhuyin 
Published: August 2024

Abstract
The numerical studies for film cooling performance have gained considerable interest for the development of advanced gas turbines and aero-engines. However, the accuracy of Reynolds-Averaged Navier-Stokes simulations is significantly influenced by the uncertainties associated with turbulence modeling closure coefficients. The traditional Monte Carlo methods for uncertainty quantification are computationally prohibitive as the cost of constructing an accurate response surface increases exponentially with the number of input parameters. The active subspace method, developed recently as a means of dimension reduction, incurs a moderate cost when dealing with high-dimensional uncertain inputs. In this study, the active subspace (AS) method is applied to quantify the modeling uncertainties related to SST turbulence modeling parameters in a fan-shaped film cooling simulation. The results reveal that the quantified modeling uncertainties exhibit distinct characteristics across different blowing ratios, and the response functions are constructed based on the primary control parameters. Subsequently, the turbulence model parameters are optimized to minimize the computational error based on the response functions. In the optimized test point, the average relative errors decrease to 1.3% and 0.3%, respectively, under blowing ratios of 0.5 and 2.5 after optimization. Furthermore, a set of unified model parameters is optimized and applied across different blowing ratios (0.5, 1.5, 2.5), resulting in average relative error of 4.3%, 3.7%, and 3.1%, respectively, demonstrating the advantages of the AS method for modeling uncertainty quantification and optimization in film cooling simulation.
Flow and Heat Transfer in a Rotating Disc Cavity With Axial Throughflow at High Speed Conditions
Authors: Wang Ruonan , Chew John W. , Gao Feng , Marxen Olaf 
Published: August 2024

Abstract
Flow and heat transfer in a compressor rotating disc cavity with axial throughflow is investigated using wall-modelled large-eddy simulations (WMLES). These are compared to measurements from recently published experiments and used to investigate high Reynolds number effects. The simulations use an open-source CFD solver with high parallel efficiency and employ the Boussinesq approximation for centrifugal buoyancy. Kinetic energy effects (characterised by Eckert number) are accounted for by scaling the thermal boundary conditions from static temperature to rotary stagnation temperature. The WMLES shows very encouraging agreement with experiments up to the highest Reynolds number tested, Reϕ = 3.0 × 106. A further simulation at Reϕ = 107 extends the investigation to an operating condition more representative of aero engine high pressure compressors. The results support the scaling of shroud heat transfer found at lower Reϕ, but disc heat transfer is higher than expected from a simple extrapolation of lower Reϕ results. This is associated with transition to turbulence in the disc Ekman layers and is consistent with the boundary layer Reynolds numbers at this condition. The introduction of swirl in the axial throughflow, as may occur at engine conditions, could reduce the boundary layer Reynolds numbers and delay the transition.
Computational Study of Flow Characteristics of an Inducer Dropleg Configuration for Pulp Pumping Applications
Authors: Dhanasegaran Radheesh , Tiitinen Kalle , Vahteri Timo 
Published: August 2024

Abstract
The present work numerically investigates the flow characteristics and performance of a dropleg-inducer configuration for medium consistency (MC) pulp pumping applications. The study employed a commercial CFD solver package to carry out the steady-state single-phase Newtonian fluid (water) simulations using RANS-based k-ε turbulence model. Three different normalized axial spacing of the inducer from the dropleg exit (L/D = 0.75, 1.15 & 1.5) were studied for three normalized rotational speeds (Ṅ = 0.6, 1 & 1.2) considering both design and off-design operating conditions. The results are discussed in the context of velocity streamlines at different planes, contours of velocity and turbulence intensity, and plots of performance parameters such as power consumed, and power number thereby allowing for an assessment of the inducer’s performance with changing distances from the dropleg and different rotational speeds considering the operational range of the MC pump. The findings reveal that change in the axial spacing and rotational speeds significantly impacts the flow pattern within the dropleg and the inducer passage. Consequently, these changes affect the turbulence characteristics and the power consumption by the inducer, which will in turn affect the overall performance of the MC pump.
Assessment of Measurement Techniques for Adiabatic Cooling Effectiveness in Transonic Flow Over a Flat Plate
Authors: Zeng Wei , Dai Siming , Liu Yisu , Ma Haiteng 
Published: August 2024

Abstract
Adiabatic cooling effectiveness, as a primary indicator of film cooling performance, still suffers from the disputable measurement principle in transonic flow. The two measuring techniques in the state of the art, linear regression method and dual linear regression technique, produce different results, due to their distinct treatment of local recovery temperature. To resolve this controversy, this paper first established a criterion for judging the two methods, based on similarity/dimensional analysis. It is concluded that adiabatic cooling effectiveness is uniquely determined by six dimensionless numbers: Mach number, Reynolds number, Prandtl number of the mainstream, blowing ratio, momentum ratio and temperature ratio between coolant and mainstream. Then, the two methods were gauged against the judging criterion through transient thermal measurements by infrared thermography, for transonic flow over a flat plate with film cooling. All the six dimensionless numbers were fixed during experiments. Only the value of mainstream temperature and coolant temperature varied by 8K and 14K respectively. It is shown that adiabatic cooling effectiveness obtained by linear regression method is roughly unaltered at different mainstream and coolant temperatures, when the coolant-to-mainstream temperature ratio is fixed. However, results measured by dual linear regression technique display noticeable variation (by a maximum of 0.3) under the same circumstance. This is because the assumption of this technique conflicts with the similarity principle. Therefore, linear regression method aligns much better with the judging criterion based on dimensional analysis, than dual linear regression technique, and is hence recommended to measure adiabatic cooling effectiveness in transonic flow.