bluuebunny/crossref_metadata_2025_split huggingface dataset:
Systematic Experimental Evaluations Aimed at Optimizing the Geometry of Axial Casing Groove in a Compressor
Authors: Chen Huang , Koley Subhra Shankha , Li Yuanchao , Katz Joseph 
Published: November 2019

Abstract
Performance and flow measurements are carried out to investigate the impact of varying the geometry of axial casing grooves on the stall margin and efficiency of an axial turbomachine. Prior studies have shown that skewed semi-circular grooves installed near the blade leading edge (LE) have multiple effects on the flow structure, including ingestion of the tip leakage vortex (TLV), suppression of backflow vortices, and periodic variations of flow angle. To determine which of these phenomena is a key contributor, the present study examines the impact of several grooves, all with the same inlet geometry, but with outlets aimed at different directions. The “U” grooves that have circumferential exits aimed against the direction of blade rotation achieve the highest stall margin improvement of well above 60% but cause a 2.0% efficiency loss near the best efficiency point (BEP). The “S” grooves, which have exits aimed with the blade rotation, achieve a relatively moderate stall margin improvement of 36%, but they do not reduce the BEP efficiency. Other grooves, which are aligned with and against the flow direction at the exit from upstream inlet guide vanes, achieve lower improvements. These trends suggest that causing high periodic variations in flow angle around the blade leading edge is particularly effective in extending the stall margin, but also reduces the peak efficiency. In contrast, maintaining low flow angles near the LE achieves more moderate improvement in stall margin, without the maximum efficiency loss. Hence, of the geometries tested, the S grooves appear to have the best overall impact on the machine performance. Velocity measurements and flow visualizations are performed in an axial plane located downstream of the grooves, near the trailing edge of the rotor. Reduced efficiency or performance co-occurs with elevated circumferential velocity in the tip region, but differences in the axial blockage are subtle. Yet, near the BEP, the regions with reduced axial velocity, or even negative velocity between the TLV and the endwall, are wider behind the U grooves compared to the S grooves. The vorticity profiles also show that at low flow rates the TLV is ingested entirely by the grooves, in contrast to the best efficiency point, where a considerable fraction of the TLV rollup occurs downstream of the grooves.
Optimization of Inserts to Minimize Cross-Flow Impact in Impingement Heat Transfer
Authors: Curbelo Andres , Kapat Jayanta S. , Thorpe Steven J. , Maurer Michael 
Published: November 2019

Abstract
To increase gas turbine cycle efficiency it requires higher turbine inlet temperatures. Multiple cooling mechanisms are used in order to ensure the survival of hot-gas-path components. Impingement cooling is one of the most prevalent methods due to its ability to remove heat over a localized area with a high local heat transfer coefficient. However,, the same level of high heat transfer cannot be uniformly maintained over a large surface due to degradation of downstream jets by cross-flow created by post impingement flow from upstream jets. In order to avoid jet degradation and hence to enhance overall heat transfer, this study focuses on use of U-shaped guide vane inserts surrounding downstream impingement jets. A multi-objective numerical optimization approach is performed to perfect the U-shape guide vane insert where heat transfer and pressure ratio are maximized for a given coolant flow. Three models are obtained from the Pareto optimal front and compared through experimental testing. Temperature Sensitive Paint (TSP) is used to experimentally obtain the local Heat Transfer distributions for an average jet Reynolds number ranging from 75,000 to 150,000. Results show that utilizing U-shaped guided vane inserts can protect against cross-flow and thus enhance overall heat transfer at the target surface.
Numerical Study on Cooling Characteristics of Double-Row Cylindrical Holes on Upstream Endwall
Authors: Luo Ding , Lu Ruishan , Lei Jiang , Wright Lesley M. 
Published: November 2019

Abstract
In this paper film-cooling effectiveness of two rows of cylindrical holes located on the endwall upstream of a vane is investigated numerically. Five different cooling schemes, including three schemes of double rows cylindrical holes (β = −45°, 0°, 45°), and two schemes of Double-jet film cooling (DJFC) holes (β = −45°, 45° and β = 45°, −45°), are arranged on the endwall at four blowing ratios (M = 0.5, 1.0, 1.5, 2.0). Both primary effect (on downstream endwall) and secondary effect (on pressure and suction surfaces) of the endwall film cooling are considered. ICEM is used to mesh the computational domain, and simulation is carried out by ANSYS 14.0. The result shows that cooling jets with compound angles can effectively suppress lifting-off and increase film-cooling effectiveness. In addition, at low blowing ratios, it is difficult for jets no matter what directions to cool the neighborhood of the leading edge and the pressure side due to the effect of horseshoe vortices. However, passage vortices have different effects on the cooling jets with different compound angles which will result in different film coverage on both endwall and airfoil.
Numerical Study on Flow Characteristics of Liquid Jet in Airflows
Authors: Le Jiang , Zhenxia Liu , Yaguo Lyu , Pengfei Zhu 
Published: November 2019

Abstract
The interaction between the fuel jet, the oil jet and the airflow is involved in the afterburner (or ramjet combustion chamber) and the lubricating oil system of the aero-engine respectively. The latter mainly studies the penetration depth of the oil jet into the airflow, the oil jet breakup position and so on. In the under-race lubrication system, the oil jet is deflected due to the high-speed rotation of the oil scoop and some droplets, ligaments are separated. The deflection of the oil jet and the splash of droplets may affect the oil capture efficiency of the under-race lubrication system. At the same time, the configuration of the oil jet nozzle will also have a certain impact on the oil capture efficiency. Therefore, it is necessary to carry out research on the flow characteristics of the oil jet in the airflow, and provide reference for the oil jet nozzle configurations of the under-race lubrication system. In this paper, the calculation results show that the Couple Level-Set and Volume of Fluid (CLSVOF) method is better than the Volume of Fluid (VOF) method. The correlations between the coordinate of the oil jet breakup positions and the liquid-air momentum ratio were concluded. The equation of the trajectory curve was derived for the jet column trajectory before breakup. The difference of the oil jet flow characteristics between single jet nozzle and the twin jet nozzle and the tandem jet nozzle configuration is also studied. Finally, the design method under the tandem jet nozzle configuration is given.
Heat Transfer During Impact of Elastoplastic and Cohesive Particles
Authors: Yu Kuahai , Tafti Danesh , Yang Xi , Xin Shihong 
Published: November 2019

Abstract
This paper presents a theoretical study of the heat transfer during particles colliding with a surface considering the material elastoplastic properties and adhesion forces of particles. The model divides the impact processes into three stages, the elastic stage, the elastic-plastic stage, and full plastic stage, and assumes that the recovery stage is fully elastic. The rebound velocities of particles are obtained by the comparison of initial kinetic energy and total energy losses, and the major loss mechanisms in the form of adhesion forces and plastic deformation of particles. During each stage of the collision, the impact duration of collision is predicted numerically by integrating the differential equations of contact forces and particle motion. Elastic impact duration and heat transfer of a 4.76 mm stainless steel particle with 304 stainless steel surface agrees well with a previous analytical model. The result shows that at higher impact velocity, a larger percentage of time is spent in the compression stage. Sand particles under 50 μm impacting a nickel based super alloy surface (DD3) from room temperature to 1273 K are evaluated. Time duration decreases with an increase in impact velocity and a decrease in particle size. Heat transfer at particle impact is determined primarily by the contact area and time duration, besides the temperature difference and thermal conductivity. Heat transfer of plastic impact is noticeably smaller than the Sun and Chen’s analytical model, and the difference increases with increase in impact velocity. Adhesion forces affect the time duration significantly at low impact velocity. Heat transfer for 20 μm sand particles at 1073 K, 1173 K and 1273 K is about 1.12, 1.15 and 1.25 times that at room temperature, and about 1.07, 1.08 and 1.15 times the impact duration at room temperature.
Role of Turbulence in Precessing Vortex Core Dynamics
Authors: Karmarkar Ashwini , Frederick Mark , Clees Sean , Mason Danielle , O’Connor Jacqueline 
Published: November 2019

Abstract
Precessing vortex cores (PVC), arising from a global instability in swirling flows, can dramatically alter the dynamics of swirl-stabilized flames. Previous study of these instabilities has identified their frequencies and potential for interaction with the shear layer instabilities also present in swirling flows. In this work, we investigate the dynamics of precessing vortex cores at a range of swirl numbers and the impact that turbulence, which tends to increase with swirl number due to the increase in mean shear, has on the dynamics of this instability. This is particularly interesting as stability predictions have previously incorporated turbulence effects using an eddy viscosity model, which only captures the impact of turbulence on the base flow, not on the instantaneous dynamics of the PVC itself. Time-resolved experimental measurements of the three-component velocity field at ten swirl numbers show that at lower swirl numbers, the PVC is affected by turbulence through the presence of vortex jitter. With increasing swirl number, the PVC jitter decreases as the PVC strength increases. There is a critical swirl number below which jitter of the PVC vortex monotonically increases with increasing swirl number, and beyond which the jitter decreases, indicating that the strength of the PVC dominates over turbulent fluctuations at higher swirl numbers, despite the fact that the turbulence intensities continue to rise with increasing swirl number. Further, we use a nonlinear van der Pol oscillator model to explain the competition between the random turbulent fluctuations and coherent oscillations of the PVC. The results of this work indicate that while both the strength of the PVC and magnitude of turbulence intensity increase with increasing swirl number, there are defined regimes where each of them hold a stronger influence on the large-scale, coherent dynamics of the flow field.
Numerical Investigation of the Effect of Inlet Flow Angle on Film Cooling Performance for the Blade Tip With Suction Surface Squealer Rim
Authors: Yu Zhiqiang , Liu Jianjun , Li Chen , An Baitao 
Published: November 2019

Abstract
Numerical investigations have been performed to study the effect of incidence angle on the aerodynamic and film cooling performance for the suction surface squealer tip with different film-hole arrangements at τ = 1.5% and BR = 1.0. Meanwhile, the full squealer tip as baseline is also investigated. Three incidence angles at design condition (0 deg) and off-design conditions (± 7 deg) are investigated. The suction surface, pressure surface, and the camber line have seven holes each, with an extra hole right at the leading edge. The Mach number at the cascade inlet and outlet are 0.24 and 0.52, respectively. The results show that the incidence angle has a significant effect on the tip leakage flow characteristics and coolant flow direction. The film cooling effectiveness distribution is altered, especially for the film holes near the leading edge. When the incidence angle changes from +7 deg to 0 and −7 deg, the ‘re-attachment line’ moves downstream and the total tip leakage mass flow ratio decreases, but the suction surface tip leakage mass flow ratio near leading edge increases. In general, the total tip leakage mass flow ratio for suction surface squealer tip is 1% greater than that for full squealer tip at the same incidence angle. The total pressure loss coefficient of suction surface squealer tip is larger than that for full squealer tip. The full squealer tip with film holes near suction surface and the suction surface squealer tip with film hole along camber line show high film cooling performance, and the area averaged film cooling effectiveness at positive incidence angle +7 deg is higher than that at 0 and −7 deg. The coolant discharged from film holes near pressure surface only cools narrow region near pressure surface.
A Novel Structural Health Monitoring System Using Surface Acoustic Sensor Network and Guided Lamb Waves
Authors: Borate Prabhav , Thatte Azam 
Published: November 2019

Abstract
This paper focuses on the development of a structural health monitoring system based on guided Lamb waves propagating over the structure and a network of surface acoustic sensors in communication at high frequencies. A time-of-flight (ToF), algorithm and a probabilistic diagnostic imaging and calibration method is developed to detect miniscule material losses or material adhesion as well as the defects like small scale holes and cracks in turbomachinery components like blades, rotors, plates and pipes. Using an advanced ToF algorithm, precise differences in timescales for arrival of symmetric / antisymmetric lamb wave packets are found for all possible combinations of actuator-sensor pairs. This leads to a deterministic mathematical construct for damage localization for various actuator-sensor pairs at focal points. In the probabilistic diagnostic imaging (PDI) method, field value is assigned based on fusion of wave signals rendered by various actuator-sensor paths to indicate the probability of the presence of a damage at a particular location on the structure. Correlation coefficients between healthy and damaged data for each of the actuator-sensor path is used to calculate the field value for each pixel on the structure. Damage calibration curve is developed by progressively increasing the damage and obtaining a magnitude of the probability density function of the severity of the damage. Proposed approach has been validated using experimental data for multiple damage cases on plates, internal surfaces of pipes and impeller blade to successfully detect submillimeter scale holes and cracks, material adhesion as well as rate of pipeline erosion and corrosion.
Reduced-Scale Model Design for a High-Speed Rotor System Based on Similitude Theory
Authors: Zhou Biao , Liang Haotian , Miao Hui , Zang Chaoping 
Published: November 2019

Abstract
Reduced-scale models are often established based on similitude theory as an alternative to the direct experimental observation on the prototype, which is usually oversized or requires unacceptable expenses. Much insight into the similitude theory applied to various fields in structural engineering, vibration and impact problems has been gained to date. However, the efficient dynamic similarity design of complex rotors remains elusive. This paper is devoted to developing a reduced-scale model based on similitude theory from a high-speed rotor system prototype. Three critical speeds within the range of operating speeds characterize this flexible rotor. A reduced scaling design strategy for the complex rotor system is proposed as a two-step scheme. Similarity conditions relating the critical design parameters (such as rotor geometry, support stiffness, etc.) between the reduced-scale model and the prototype are derived. The scaling factors are accordingly determined by a dimensional analysis in combination with the governing equation of rotordynamics. This leads to a downsized rotor model with distorted geometric configuration whose operation speed is efficiently narrowed down. Dynamic similitude is assured by proportionally scaling down the three critical speeds while the rotor mode shapes still maintain high correlation between the prototype and downscaled model. The resultant reduced-scale model of the rotor system will practically guide the construction of the essential part of a whole engine dynamics test rig for laboratory use.
Design and Prototype Test Data for a 300 kW AMB-Supported Turbine Generator for Natural Gas Pressure Letdown
Authors: Khatri Rasish , Hawkins Larry , Ortiz Neri Massimiliano , Cangioli Francesco , Biliotti Davide 
Published: November 2019

Abstract
A 300 kW integrated and fully-sealed turbine generator for natural gas pressure letdown (PLD) was developed by Baker Hughes, a GE company (BHGE), in conjunction with Calnetix Technologies. This paper describes the design and analysis of the generator, magnetic bearings, and touchdown bearings, with a focus on the dynamic performance and key characteristics of the machine. The permanent magnetic (PM) synchronous generator is supported by PM-biased, homopolar magnetic bearings and has a maximum continuous operating speed (MCOS) of 31.5 krpm. A touchdown bearing system is implemented using rolling element bearings, with soft mount supports. Also described is a thrust load balancing scheme that uses the thrust bearing coil current for reference. A time transient simulation showing the effect of process conditions on the AMB dynamics is shown. Preliminary data from the prototype mechanical run test are shown, including transfer functions measured using the magnetic bearings, Campbell diagram, and touchdown bearing drop test results.
Application of Artificial Neural Networks for Monitoring and Optimum Operation Prediction of Solar Hybrid MGT Systems
Authors: Somehsaraei Homam Nikpey , Iaria Davide , Al Zaili Jafar , Assadi Mohsen , Sayma Abdulnaser , Ghavami Mohsen 
Published: November 2019

Abstract
Hybrid energy system consisting of a parabolic dish solar concentrator and a micro gas turbine (MGT) has been considered as promising distributed generation technology, since it can be operated as a stand-alone system for power or combined heat and power (CHP) applications in remote areas with no connection to the grid. The main concern when it comes to distributed generation is the ability of maintaining high availability. Therefore, given the intermittency of the solar resource, the availability of consistent and computationally fast tools for modelling and monitoring of solar micro gas turbines is essential for adequate and optimum operation.
This paper presents the application of artificial neural networks (ANNs) for performance prediction and monitoring of a hybrid solar MGT system. For this purpose, a validated in-house tool, developed for evaluating the performance of solar-hybrid MGT, was used to generate simulated data at various operational conditions by varying solar irradiation and ambient conditions. The obtained data was used to train the ANN model. The prediction accuracy of the ANN model was tested using a data set, which were not used during the training process. The results showed that the ANN model can predict the solar hybrid MGT performance with high accuracy and could serve as an accurate baseline model for monitoring applications.
Finally, the developed ANN model was integrated with an optimization algorithm. A case study was conducted using the developed ANN model for multi-objective optimization of the hybrid solar MGT. By varying turbine inlet temperature and rotational speed, the system performance at part load operation were analysed resulting in a Pareto front for maximum electrical efficiency and minimal operational cost. Multi-objective genetic algorithm (GA) based on controlled elitism concept was applied to find the optimum solution.
Conjugate Heat Transfer Analysis to Assess Overall Cooling Effectiveness of High Pressure Turbine Nozzle With Optimized Film Cooling Hole Arrangements
Authors: Kang Young Seok , Rhee Dong-Ho , Lee Sanga , Cha Bong Jun 
Published: November 2019

Abstract
Conjugate heat transfer analysis method has been highlighted for predicting heat exchange between fluid domain and solid domain inside high-pressure turbines, which are exposed to very harsh operating conditions. Then it is able to assess the overall cooling effectiveness considering both internal cooling and external film cooling at the cooled turbine design step. In this study, high-pressure turbine nozzles, which have three different film cooling holes arrangements, were numerically simulated with conjugate heat transfer analysis method for predicting overall cooling effectiveness.
The film cooling holes distributed over the nozzle pressure surface were optimized by minimizing the peak temperature, temperature deviation. Additional internal cooling components such as pedestals and rectangular rib turbulators were modeled inside the cooling passages for more efficient heat transfer. The real engine conditions were given for boundary conditions to fluid and solid domains for conjugate heat transfer analysis. Hot combustion gas properties such as specific heat at constant pressure and other transport properties were given as functions of temperature. Also, the conductivity of Inconel 718 was also given as a function of temperature to solve the heat equation in the nozzle solid domain.
Conjugate heat transfer analysis results showed that optimized designs showed better cooling performance, especially on the pressure surface due to proper staggering and spacing hole-rows compared to the baseline design. The overall cooling performances were offset from the adiabatic film cooling effectiveness. Locally concentrated heat transfer and corresponding high cooling effectiveness region appeared where internal cooling effects were overlapped in the optimized designs. Also, conjugate heat transfer analysis results for the optimized designs showed more uniform contours of the overall cooling effectiveness compared to the baseline design. By varying the coolant mass flow rate, it was observed that pressure surface was more sensitive to the coolant mass flow rate than nozzle leading edge stagnation region and suction surface.
The CHT results showed that optimized designs to improve the adiabatic film cooling effectiveness also have better overall cooling effectiveness.