bluuebunny/crossref_metadata_2025 huggingface dataset:
An Instrumented High-Speed Rotor With Embedded Telemetry for the Continuous Spatial Pressure Profile Measurement in Gas Lubricated Bearings: A Proof of Concept
Authors: Shalash K. , Schiffmann J.
Published: November 2019

Gas lubricated bearings are capable of supporting high speed rotors with satisfactory load capacities. Pressure is one of the constitutional quantities governing the flow field in gas lubricated bearings. Knowledge of the pressure is of principal importance in the fundamental understanding of such bearings and for the calibration of reduced order models. These measurements can be done from the bearing side using pressure taps in the bushings, however, the measurement points will yield a spatially sampled profile consisting of discrete points relative to the bearing bushing. This measurement technique is simple, yet, several details cannot be captured. In order to acquire a continuous scan of the pressure field inside the bearing, it is necessary to measure from the rotor side. Such onboard measurement technique is challenging due to constraints in volume, G-force, and data and power transmission through the rotor. This paper presents an instrumented measurement rotor with embedded pressure probes and a wireless telemetry, which is capable of the continuous pressure field measurement inside a high-speed externally pressurized gas journal bearing. The bearing under investigation has a diameter of 40mm, L/D = 1, and was tested up to 37.5 krpm. The bearing is of the annular type, with 2×18 Ø0.1mm restrictor orifices. Measurements at discrete points using pressure taps inside the test bearing were also performed for the sake of comparison. The measurements from both sides (bushing and rotor) were in good agreement at quasi-static conditions. At higher operational speeds, it was necessary to perform an in-situ system identification and calibration for the embedded pressure probes using the bearing side measurements as a reference. The in-situ system identification technique was successful to reconstruct the attenuated pressure signals for a wide range of supply pressures and rotor speeds. The instrumented rotor was proven qualified to perform time-resolved pressure measurements within the gas film of journal bearings up to 37.5 krpm.
The Effect of Vanes and Blades on Ingress in Gas Turbines
Authors: Hualca Fabian P. T. , Horwood Josh T. M. , Sangan Carl M. , Lock Gary D. , Scobie James A.
Published: November 2019

This paper presents experimental and computational results using a 1.5-stage test rig designed to investigate the effects of ingress through a double radial overlap rim-seal. The effect of the vanes and blades on ingress was investigated by a series of carefully-controlled experiments: firstly, the position of the vane relative to the rim seal was varied; secondly, the effect of the rotor blades was isolated using a disc with and without blades.

Measurements of steady pressure in the annulus show a strong influence of the vane position. The relationship between sealing effectiveness and purge flow-rate exhibited a pronounced inflexion for intermediate levels of purge; the inflexion did not occur for experiments with a bladeless rotor. Shifting the vane closer to the rim-seal, and therefore the blade, caused a local increase in ingress in the inflexion region; again this effect was not observed for the bladeless experiments.

Unsteady pressure measurements at the periphery of the wheel-space revealed the existence of large-scale pressure structures (or instabilities) which depended weakly on the vane position and sealing flow rate. These were measured with and without the blades on the rotor disc. In all cases these structures rotated close to the disc speed.
On the Development of a Pressure Actuated Leaf Seal for Turbomachinery Applications
Authors: Pedraza-Valle Ernesto , Papageorgiou Georgios , Bowsher Aaron , Crudgington Peter F. , Sangan Carl M. , Keogh Patrick S. , Scobie James A.
Published: November 2019

In gas turbines, seals that reduce the leakage between high and low pressure regions are critical for improved performance. Damaging rubs between the rotating and non-rotating parts of turbomachinery shaft seals occur due to thermal and assembly misalignments, and rotordynamic vibration during engine start-up and shut-down transients. These rubs lead to increased seal leakage and hence to reduced overall turbine efficiency and life span. The Film Riding Pressure Actuated Leaf Seal (FRPALS) is a non-contacting compliant seal under development to adapt to varying clearances without rubbing, while maintaining low leakage.

This paper presents the measurements of the FRPALS in a test rig specifically designed to test novel shaft seals for turbomachinery. The rig features a 254 mm diameter rotor with a maximum surface speed of 200 m/s. Pressure drops of up to 3.5 bar can be achieved. The results of initial testing at zero rotational speed are presented for the FRPALS in a reverse orientation. The opening and closing translations of the leaves have been measured using eddy current displacement probes targeting the movable parts of the seal. The seal clearance has been shown to remain constant for a range of applied pressure drops, which indicates the stable operation of the seal, though resulting in contact with the rotor at 1.5 bar. Mass flow leakage measurements have also demonstrated the sealing performance of the FRPALS. They show the potential of the seal to film ride subject to design modifications to maintain a more uniform film thickness. The steady-state Reynolds equation for lubrication has been used to predict the pressure along the seal clearance. The predictions have been compared with pressure measurements from a transducer located in the clearance fluid thin film.
Shielded Swirl Versus Piccolo Tube Inlet Thermal Anti-Icing System
Authors: Anderson Morris
Published: November 2019

This study presents a CFD comparison of a piccolo tube inlet anti-icing system with benchmark flight test data and a shielded swirl design.

Aircraft engine inlets must prevent ice accretion that could cause damage or inhibit safe operation. A common way to meet this requirement is to heat the inlet with hot air distributed with a piccolo tube or a swirl anti-icing system. Piccolo tube systems generally use less engine bleed air but are more complex and heavier than swirl systems.

The CFD model for this study includes all the inlet key characteristics such as piccolo tube holes, material properties, and thickness. The model is evaluated in a two-step process. Water collection rates for flight in icing conditions are calculated. These results are then mapped onto a conjugate heat transfer film runback model. The CFD results include surface temperatures and the amount of liquid film runback that flows off the heated surface.

Benchmark test data is presented illustrating good inlet surface temperature agreement with the piccolo tube CFD model for flight in both dry air and icing conditions.

This CFD modeling approach is also applied to a unique shielded swirl anti-icing system. The results of this study confirm that a shielded swirl anti-icing system can be designed to provide the same level of anti-icing protection that is achieved with a piccolo tube configuration without overheating the inlet or requiring more engine bleed flow.
Effects of Dust Composition on Particle Deposition in an Effusion Cooling Geometry
Authors: Crowe Evan D. , Bons Jeffrey P.
Published: November 2019

In this study the effects of dust composition on particle deposition in an effusion cooling geometry were investigated through a series of experiments. Single mineral dusts made from five different minerals, Quartz, Dolomite, Albite, Salt, and Gypsum, were milled to similar size distributions (approx. 0–10μm diameter). These dusts were then used in particle deposition tests on a flat plate effusion hole test article which was heated in a kiln to 1116K and supplied with coolant flow heated to 950K. Percent mass flow reduction per gram and deposit morphology were recorded for each test. Results for the different minerals varied greatly ranging from 7.8% to 160% reduction in mass flow per gram injected, with the albite dust producing the greatest blockage. The different dusts also produced varying shapes of deposits. These five dusts were then combined to form a dust blend with the same mass fractions found in AFRL02, a commercially available test dust, and additional tests were conducted using this dust. Results from the tests using the OSU mixed AFRL02 were compared with an estimated blockage per gram found by taking a weighted average of the blockage per gram for each single mineral dust on a percent volume basis. When tested, the mixed AFRL02 produced a lower blockage per gram than the estimate, indicating that an estimate based on volume fraction alone is not sufficient to predict the deposition of dusts composed of a mixture of minerals.
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

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

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

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

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

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

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

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

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

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

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

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

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.
Probabilistic FE-Analysis of Cooled High Pressure Turbine Blades: Part A — Holistic Description of Manufacturing Variability
Authors: Högner Lars , Voigt Matthias , Mailach Ronald , Meyer Marcus , Gerstberger Ulf
Published: November 2019

Modern high pressure turbine (HPT) blade design stands out due to its high complexity comprising three-dimensional blade features, multi-passage cooling system (MPCS) and film cooling to allow for progressive thermodynamic process parameters. During the last decade, probabilistic design approaches have become increasingly important in turbomachinery to incorporate uncertainties such as geometric variations caused by manufacturing scatter and deterioration.

Within this scope, the first part of this two-part paper introduces parametric models for cooled turbine blades that enable probabilistic FE analysis taking geometric variability into account to aim at sensitivity and robustness evaluation. The statistical database is represented by a population of more than 400 blades whose external geometry is captured by optical measurement techniques and 34 blades that are digitized by computed tomography (CT) to record the internal geometry and the associated variability, respectively. Based on this data, parametric models for airfoil, profiled endwall (PEW), wedge surface (WSF) and MPCS are presented.

The parametric airfoil model which is based on traditional profile theory is briefly described. In this regard, a methodology is presented that enables to adapt this airfoil model to a given population of blades by means of Monte-Carlo based optimization. The endwall variability of hub and shroud are parametrized by radial offsets that are applied to the respective median endwall geometry. WSFs are analytically represented by planes. Variations of the MPCS are quantified based on the radial distribution of cooling passage centroids. Thus, an individual MPCS can be replicated by applying adapted displacement functions to the core passage centroids. For each feature that is considered within the present study, the accuracy of the parametric model is discussed with respect to the variability that is present in the investigated blade population and the measurement uncertainty.

Within the scope of the second part of this paper (cf. Högner et al. [1]), the parametric models are used for a comprehensive statistical analysis to reveal the parameter correlation structure and probability density functions (PDFs). This is required for the subsequent probabilistic finite element analysis involving real geometry effects.
Aerothermal Optimization of Turbine Squealer Tip Geometries With Arbitrary Cooling Injection
Authors: De Maesschalck C. , Andreoli V. , Paniagua G. , Gillen T. , Barker B.
Published: November 2019

The optimization of the turbine rotor tip geometry remains a vital opportunity to create more efficient and durable engines. Balancing the aerodynamic and thermal aspects, while maintaining the mechanical integrity is key to reshape one of the most vulnerable and life determining parts of the entire turbine. The ever-increasing turbine gas temperatures, combined with the difficulty of cooling the tip and the aerodynamically penalizing nature of the overtip leakage vortex, makes the design of the tip a truly multi-disciplinary challenge.

While many earlier efforts focused on uncooled geometries, or studied the aerothermal impact with a fixed cooling configuration, the current paper presents the outcome of a multi-objective optimization where both the squealer rim geometry as well as the cooling injection pattern was allowed to vary simultaneously. This study explores a significantly wider design space, seeking a further synergistic aerothermal benefit through the combination of a quasi-fully arbitrary cooling arrangement, with mutating squealer rim structures.

Specifically, the current manuscript presents the results of over 330 cooled and uncooled squealer tip geometries. The high pressure turbine tip was automatically altered using a novel parametrization strategy adopting a maximum of 40 design variables to vary the squealer rim structures, as well as the size and location of the various cooling holes. The aerodynamic and thermal characteristics of every design were evaluated through Reynolds-Averaged Navier-Stokes CFD simulations with the k-ω SST model for the turbulence closure, adopting an unstructured hexahedral grid typically containing more than 8 million cells. A multi-objective differential evolution algorithm was used to obtain a Pareto front of designs which maximize the aerodynamic efficiency, while minimizing the overtip thermal loads. Eventually, a detailed investigation and robustness study was performed on a set of prime squealer geometries, to further investigate the aerodynamic flow topology, and the effect of various cooling injection schemes on the heat transfer patterns.
Development and Validation of a Hybrid Simulation Model for Darrieus Vertical-Axis Wind Turbines
Authors: Bianchini Alessandro , Balduzzi Francesco , Haack Leopold , Bigalli Simone , Müller Bernhard , Ferrara Giovanni
Published: November 2019

The increasing interest in deep-water floating applications and in wind turbine installations in turbulent flows, is putting vertical-axis wind turbines back again in research agendas. However, due to the lack of activities in past years, the accuracy and robustness of available design tools is much lower than the corresponding ones for horizontal-axis rotors.

Moving from this background, the study presents the development of a hybrid simulation model able to simulate H-type Darrieus turbines with low computational effort and an accuracy higher than that of conventional low-fidelity models. It is based on the coupling of unsteady RANS CFD with the Actuator Line theory to replace the airfoils. The present tool has been implemented within the commercial solver ANSYS® FLUENT® and it is then of practical interest for a large number of potential users. With respect to other examples in the literature, the present approach includes some new findings in the correct manipulation of airfoil polars that notably increased its accuracy. The validation of the model is assessed by means of two different study cases featuring a simplified 1-blade rotor and a real 3-blade turbine, for which both detailed CFD simulations and experiments were available. The model was able to produce accurate results — both in terms of aggregate power production and of flow field description — for turbines with a medium-low chord-to-radius ratio and the tipspeed ratios typical of turbine operation.
Profile Loss of Ultra-Highly Loaded Turbine Cascade at Transonic Flow Condition
Authors: Tsujita Hoshio , Kaneko Masanao
Published: November 2019

The aerodynamic performance of turbine components constituting the gas turbine engine is seriously required to be improved in order to reduce environmental load. The energy recovery efficiency in turbine component can be enhanced by the increase of turbine blade loading. In this study, as the first stage to investigate the aerodynamic performance of an ultra-highly loaded turbine cascade (UHLTC) with a turning angle of 160 degrees at transonic flow regime, two-dimensional steady compressible flows in UHLTC were analyzed numerically by using a commercial CFD code to focus on the profile loss. In the computations, the isentropic exit Mach number was varied in the wide range from 0.3 to 1.8 in order to examine the effects of exit Mach number on the shock wave formation and the associated profile loss generation. The computed results were examined in detail by comparing with those for a typical transonic turbine cascade. The detailed examination for the present computed results clarified the variation of shock pattern with the increase of exit Mach number and the loss “plateau” behavior in the present UHLTC.
Finite Element Transient Modelling for Aero-Thermo-Mechanical Analysis of Whole Gas Turbine Engine
Authors: Giuntini Sabrina , Andreini Antonio , Facchini Bruno
Published: November 2019

It is here proposed a numerical procedure aimed to perform transient aero-thermo-mechanical calculations of large power generation gas turbines.

Due to the frequent startups and shutdowns that nowadays these engines encounter, procedures for multi-physics simulations have to take into account the complex coupled interactions related to inertial and thermal loads, and seal running clearances. In order to develop suitable secondary air system configurations, guarantee structural integrity and maintain actual clearances and temperature peaks in pre-established ranges, the overall complexity of the structure has to be reproduced with a whole engine modelling approach, simulating the entire machine in the real operating conditions.

In the proposed methodology the aerodynamic solution providing mass flows and pressures, and the thermo-mechanical analysis returning temperatures and material expansion, are performed separately. The procedure faces the aero-thermo-mechanical problem with an iterative process with the aim of taking into account the complex aero-thermo-mechanical interactions actually characterizing a real engine, in a robust and modular tool, combining secondary air system, thermal and mechanical analysis. The heat conduction in the solid and the fluid-solid heat transfer are computed by a customized version of the open source FEM solver CalculiX®. The secondary air system is modelled by a customized version of the embedded CalculiX® one-dimensional fluid network solver.

In order to assess the physical coherence of the presented methodology the procedure has been applied to a test case representative of a portion of a real engine geometry, tested in a thermal transient cycle for the assessment of the interaction between secondary air system properties and geometry deformations.
Numerical and Experimental Aerodynamic Investigation of a Low Pressure Steam Turbine Module
Authors: Bellucci Juri , Peruzzi Lorenzo , Arnone Andrea , Arcangeli Lorenzo , Maceli Nicola
Published: November 2019

This work aims to deepen the understanding of the aerodynamic behavior and the performance of a low pressure steam turbine module. Numerical and experimental results obtained on a three-stage low pressure steam turbine (LPT) module are presented. The selected geometry is representative of the state-of-the-art of low pressure sections for small steam turbines. The test vehicle was designed and operated in different operating conditions with dry and wet steam. Different types of measurements are performed for the global performance estimation of the whole turbine and for the detailed analysis of the flow field. Steady and unsteady CFD analyses have been performed by means of viscous, three-dimensional simulations adopting a real gas, equilibrium steam model. Measured inlet/outlet boundary conditions are used for the computations. The fidelity of the computational setup is proven by comparing computational and experimental results. Main performance curves and span-wise distributions show a good agreement in terms of both shape of curves/distributions and absolute values. Finally, an attempt is done to point out where losses are generated and the physical mechanisms involved are investigated and discussed in details.
Assessment of an Enhanced Thin Film Model to Capture Wetting and Drying Behavior in an Aero-Engine Bearing Chamber
Authors: Singh Kuldeep , Sharabi Medhat , Ambrose Stephen , Eastwick Carol , Jefferson-Loveday Richard , Cao Jing , Jacobs Adrian
Published: November 2019

In the present work, a wetting and drying model is coupled with Eulerian Thin-Film model (ETFM) to analyze the wetting and drying behavior inside the bearing chamber. In the enhanced model, an additional source term is included to account for the contact angle effect. These models were coupled with volume-of-fluid (VOF) such that the core region is resolved by VOF and region close to the chamber walls, where a thin film is expected is resolved by either ETFM or enhanced ETFM model. Numerical studies are conducted for a shaft speed of 5,000 rpm, lubricant and air flow rates of 100 1/hr and 10 g/s respectively, at a scavenging ratio of 4. In the case of enhanced ETFM model lubricant to surface contact angle was varied from 10° to 45°. The performance of enhanced ETFM model is evaluated to capture drying and wetting behavior on a flat plate and found to be satisfactory. Film thickness prediction of enhanced ETFM model is found to be comparable with the VOF predictions reported in the literature. The effect of contact angle on the spreading of oil and film thickness is found to be small for the investigated conditions on an aero-engine bearing chamber.
Predicting the Operability of Damaged Compressors Using Machine Learning
Authors: Taylor J. V. , Conduit B. , Dickens A. , Hall C. , Hillel M. , Miller R. J.
Published: November 2019

The application of machine learning to aerospace problems faces a particular challenge. For successful learning a large amount of good quality training data is required, typically tens of thousands of cases. However, due to the time and cost of experimental aerospace testing, this data is scarce. This paper shows that successful learning is possible with two novel techniques: The first technique is rapid testing. Over the last five years the Whittle Laboratory has developed a capability where rebuild and test times of a compressor stage now take 15 minutes instead of weeks. The second technique is to base machine learning on physical parameters, derived from engineering wisdom developed in industry over many decades.

The method is applied to the important industry problem of predicting the effect of blade damage on compressor operability. The current approach has high uncertainty, it is based on human judgement and correlation of a handful of experimental test cases. It is shown using 100 training cases and 25 test cases that the new method is able to predict the operability of damaged compressor stages with an accuracy of 2% in a 95% confidence interval; far better than is possible by even the most experienced compressor designers. Use of the method is also shown to generate new physical understanding, previously unknown by any of the experts involved in this work. Using this method in the future offers an exciting opportunity to generate understanding of previously intractable problems in aerospace.
Prediction of Rotating Stall During Startup for Axial Compressors
Authors: Mito Ryosuke , Yamashita Satoshi
Published: November 2019

In a compressor used for power generation, a rotating stall due to an operating point mismatch between the front and rear stages occurs at front stages in low-speed condition during startup. IGV, VSV opening schedule and bleed flow rates are determined in order to obtain stable operating conditions, with the occurrence of pressure fluctuations or blade excitation force derived from the rotating stall.

The setting of the number of stages for variable stator vane, the vane opening and the bleed flow rate are largely based on the rig test and experience of the actual machine, however we focused on the capability study for direct simulation with unsteady CFD for the rotating stall. If this can be predicted in advance, it makes it possible to reduce the number of stages of the variable stator vanes, the capacity of the thyristor, and to make the bleed chambers and piping compact, leading to cost reductions.

The method of rotating stall prediction during startup condition, and the comparison between predicted and actual measurements on how this number changes with different starting conditions and different machines, are shown in this paper. CFD shows the different stall cell position, the number of stall cells and the pressure fluctuation level in each condition, and these results were consistent with the measurement data. Furthermore, we have found that these phenomena can be controlled by variable stator vane angle during start up.