bluuebunny/crossref_metadata_2025_split huggingface dataset:
CFD Investigation of the Flow of Trailing Edge Cooling Slots
Authors: Jiang Y. , Gurram N. , Romero E. , Ireland P. T. , di Mare L. 
Published: August 2018

Slot film cooling is a popular choice for trailing edge cooling in high pressure (HP) turbine blades because it can provide more uniform film coverage compared to discrete film cooling holes. The slot geometry consists of a cut back in the blade pressure side connected through rectangular openings to the internal coolant feed passage. The numerical simulation of this kind of film cooling flows is challenging due to the presence of flow interactions like step flow separation, coolant-mainstream mixing and heat transfer.
The geometry under consideration is a cutback surface at the trailing edge of a constant cross-section aerofoil. The cutback surface is divided into three sections separated by narrow lands. The experiments are conducted in a high speed cascade in Oxford Osney Thermo-Fluids Laboratory at Reynolds and Mach number distributions representative of engine conditions. The capability of CFD methods to capture these flow phenomena is investigated in this paper. The isentropic Mach number and film effectiveness are compared between CFD and pressure sensitive paint (PSP) data. Compared to steady k–ω SST method, Scale Adaptive Simulation (SAS) can agree better with the measurement. Furthermore, the profiles of kinetic energy, production and shear stress obtained by the steady and SAS methods are compared to identify the main source of inaccuracy in RANS simulations. The SAS method is better to capture the unsteady coolant-hot gas mixing and vortex shedding at the slot lip.
The cross flow is found to affect the film significantly as it triggers flow separation near the lands and reduces the effectiveness. The film is non-symmetric with respect to the half-span plane and different flow features are present in each slot. The effect of mass flow ratio (MFR) on flow pattern and coolant distribution is also studied. The profiles of velocity, kinetic energy and production of turbulent energy are compared among the slots in detail. The MFR not only affects the magnitude but also changes the sign of production.
Impact of Predicted Combustor Outlet Conditions on the Aerothermal Performance of Film-Cooled HPT Vanes
Authors: Cubeda S. , Mazzei L. , Bacci T. , Andreini A. 
Published: August 2018

Turbine inlet conditions in modern aero-engines employing lean-burn combustors are characterised by highly swirled flow and non-uniform temperature distributions. As a consequence of the lack of confidence in numerical predictions and the uncertainty of measurement campaigns, the use of wide safety margins is of common practice in the design of turbine cooling systems, thus affecting the engine performance and efficiency.
Previous experiences showed how only scale-resolving approaches such as Large-eddy and Scale-adapting simulations are capable of overcoming the limitations of RANS, significantly improving the accuracy in the prediction of flow and temperature fields at the combustor outlet. However it is worth investigating the impact of such differences on the aerothermal performance of the NGVs, as to understand the limitations entailed in the current approach for their thermal design. Industrial applications in fact usually rely on 1D, circumferentially-averaged profiles of pressure, velocity and temperature at the combustor-turbine interface in conjunction with Reynolds-averaged Navier-Stokes (RANS) models.
This paper describes the investigation performed on an experimental test case consisting of a combustor simulator equipped with NGVs. Three numerical modelling strategies were compared in terms of flow field and thermal loads on the film-cooled vanes: i) RANS model of the NGVs with inlet conditions obtained from a RANS simulation of the combustor; ii) RANS model of the NGVs with inlet conditions obtained from a Scale-Adaptive Simulation (SAS) of the combustor; iii) SAS model inclusive of both combustor and NGVs.
The results of this study show that estimating the aerodynamics at the NGV exit does not demand particularly complex approaches, whereas the limitations of standard RANS models are highlighted again when the turbulent mixing is key. High-fidelity predictions of the conditions at the turbine entrance proved to be very beneficial to reduce discrepancies in the estimation of local adiabatic wall temperature of even 100 K. However, a further leap forward can be achieved with an integrated simulation, capable of reproducing the transport of the unsteady fluctuations generated in the combustor up into the turbine, which plays a key role in presence of film cooling. This work therefore points out how keeping the analysis of combustor and NGVs separate can lead to a significantly misleading estimation of the thermal loads and ultimately to a wrong thermal design of the cooling system.
CFD Study Exploring Jet Configurations and Jet Pulsing for an Aeroengine Scoop-Based Oil Delivery System
Authors: Simmons Kathy , Harrison Luke , Korsukova Evgenia , Paleo Cageao Paloma 
Published: August 2018

With reduction of gas turbine core size, clearances between internal components are reduced and directing oil jets for bearing lubrication becomes more difficult. If direct access to the bearings or scallops is impeded, the inclusion of oil scoops becomes highly desirable for lubricant supply. With a scoop-based system oil is targeted at a scooped rotor, collected and fed along axial passages and delivered at a different axial location thus enhancing design opportunities. The proportion of oil from the supply jet retained by the scoop system is an important design parameter that can be characterised by the concept of capture efficiency. Previous investigations have focussed on a proposed scoop device’s operating conditions and oil jet configurations; this study proposes new methods of utilising the jets to improve scoop capture efficiency. A parametric study of a 2D scoop geometry was conducted using the Computational Fluid Dynamics (CFD) software ANSYS Fluent. The simulation utilised the Volume of Fluids (VOF) approach for multiphase modelling and the k-ω SST model to account for turbulence.
In the configuration studied the oil was supplied via two nozzles separated by 10 degrees circumferentially. An uneven flow rate between two oil jets in tandem allowed for the identification of jet interaction effects. A transition in capture efficiency responses was also highlighted between shallow and steep jet angles. The knowledge of individual jet behaviour may immediately improve existing tandem jet configurations.
Further, the concept of pulsing the jets was investigated, the idea being initiated following observation of high speed imaging of a scoop system tested experimentally. The imaging shows that most of the uncaptured oil is deflected or splashed following interaction with the scoop. Turning the oil off for part of the cycle potentially reduces or eliminates this. By defining and implementing an optimised time scheme for the pulsation of a single jet, the capture efficiency was improved by 10%. Compensating for the associated flow rate reduction by increasing the jet velocity resulted in a further 5% increase in capture efficiency. The development of pulsed jets for practical applications has the potential to significantly improve oil scoop capture efficiency.
Investigation of H2/CH4-Air Flame Characteristics of a Micromix Model Burner at Atmosphere Pressure Condition
Authors: Liu Xunwei , Shao Weiwei , Tian Yong , Liu Yan , Yu Bin , Zhang Zhedian , Xiao Yunhan 
Published: August 2018

For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potential low NOx emission solution for gas turbine combustors, especially for advanced gas turbines with high turbine inlet temperature. Compared with conventional lean premixed flames, multiple distributed slim and micro flames could lead to a lower NOx emission performance for shortening residence time of high temperature flue gas and generally a more uniform temperature distribution.
This work aims at micromix flame characteristics of a model burner fueled with hydrogen blending with methane under atmosphere pressure conditions. The model burner assembly was designed to have six concentrically millimeter-sized premixed units around a same unit centrally. Numerical and experimental studies were conducted on mixing performance, flame stability, flame structure and CO/NOx emissions of the model burner. OH radical distribution by OH-PLIF and OH chemiluminescence (OH*) imaging were employed to analyze the turbulence-reaction interactions and characters of the reaction zone at the burner exit. Micromix flames fueled with five different hydrogen content H2-CH4 (60/40, 50/50, 40/60, 30/70, 0/100 Vol.%) were investigated, along with the effects of equivalence ratio and heat load. Results indicated that low NOx emissions of less than 10 ppm (@15% O2) below the exhaust temperature of 1920 K were obtained for all the different fuels. Combustion oscillation didn’t occur for all the conditions. It was found that at a constant flame temperature, the higher the hydrogen content of the fuel, the higher the turbulent flame speed and the weaker the flame lift effect. Combustion noise and NOx emissions also increase with increasing hydrogen content. The OH/OH* signal distribution indicated that a pure methane micromix flame showed a lifted and weaken distributed feature.
Automated Meshing Algorithm for Generating As-Manufactured Finite Element Models Directly From As-Measured Fan Blades and Integrally Bladed Disks
Authors: Kaszynski Alex A. , Beck Joseph A. , Brown Jeffrey M. 
Published: August 2018

Automated tetrahedral meshing from manifold tessellated optical scan data is investigated to determine its viability as an approach for finite element analysis. This approach avoids the costs of constructing a volumetric representation of the scan data that can be meshed with conventional grid generation approaches. This paper demonstrates an auto-meshing algorithm for inserted airfoil and integrally bladed rotor hardware. These automatically generated models are compared to experimentally obtained frequencies and mode shapes for validation.
In an effort to compare the fidelity as well as the effect of mesh density on analytical convergence rate, manually generated all-hexahedral models are compared against the auto-meshed tetrahedral finite element models. CPU time, solution accuracy, and mesh convergence are evaluated to determine the viability of automatically generated tetrahedral meshes versus the standard approach of manually generating hex-dominant meshes. This paper demonstrates that given the power of modern CPUs, automatically generated all-tetrahedral meshes can serve as a viable alternative to manually generated hex-dominant finite element models, especially when these meshes can be refined for solution convergence within the auto-mesher. This new approach effectively solves both the mesh convergence problem while demonstrating that models based on as-measured geometry can be rapidly built with virtually no human interaction.
Three-Dimensional Visualization of Flow Characteristics Using a Magnetic Resonance Imaging (MRI) in a Lattice Cooling Channel
Authors: Tsuru Tomoko , Ishida Katsuhiko , Fujita Junya , Takeishi Kenichiro 
Published: August 2018

Flow structures in lattice cooling channels are investigated experimentally by measuring three-dimensional velocity components over entire duct. The lattice cooling structure is formed by crossing two sets of parallel inclined ribs. Heat transfer is enhanced when coolant flows through the narrow sub-channels between the ribs. According to the past literature, longitudinal vortex structures are formed inside the sub-channels due to interactions between crossing flows. In this study, three-dimensional velocity field measurement is performed using MRI scanner to clarify the flow mechanism. The rib inclination angle is varied from 30 to 60 degrees. Reynolds number is set at approximately 8,000 based on the whole duct inlet hydraulic diameter and bulk velocity. Working fluid is 0.015mol/L copper sulfate aqueous solution.
Measured results show that coolants in the upper and lower sub-channels interact not only at the both ends of the duct, but also at diamond-shaped openings formed by opposite sub-channels. The exchange of momentum between the upper and lower sub-channels occurs at the openings, leading to sustained longitudinal vortex in each sub-channel as mentioned in the literature. When the ribs are arranged with obtuse angle, a large vortex spreads across the contact surface, while the vortex structure independently stays in each sub-channel for acute rib angle.
The measured velocity fields are compared with numerically-simulated ones using a RANS solver. Overall flow pattern is captured, but flow interaction between the upper and lower sub-channels is underestimated.
Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution and Indirect Noise
Authors: Giusti Andrea , Magri Luca , Zedda Marco 
Published: August 2018

Indirect noise generated by the acceleration of combustion inhomogeneities is an important aspect in the design of aeroengines because of its impact on the overall noise emitted by an aircraft and the possible contribution to combustion instabilities. In this study, a realistic rich-quench-lean combustor is numerically investigated, with the objective of quantitatively analyzing the formation and evolution of flow inhomogeneities and determine the level of indirect combustion noise in the nozzle guide vane (NGV). Both entropy and compositional noise are calculated in this work. A high-fidelity numerical simulation of the combustion chamber, based on the Large-Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) combustion model, is performed. The contributions of the different air streams to the formation of flow inhomogeneities are pinned down and separated with seven dedicated passive scalars. LES-CMC results are then used to determine the acoustic sources to feed an NGV aeroacoustic model, which outputs the noise generated by entropy and compositional inhomogeneities. Results show that non-negligible fluctuations of temperature and composition reach the combustor’s exit. Combustion inhomogeneities originate both from finite-rate chemistry effects and incomplete mixing. In particular, the role of mixing with dilution and liner air flows on the level of combustion inhomogeneities at the combustor’s exit is highlighted. The species that most contribute to indirect noise are identified and the transfer functions of a realistic NGV are computed. The noise level indicates that indirect noise generated by temperature fluctuations is larger that the indirect noise generated by compositional inhomogeneities, although the latter is not negligible and is expected to become louder in supersonic nozzles. It is also shown that relatively small fluctuations of the local flame structure can lead to significant variations of the nozzle transfer function, whose gain increases with the Mach number. This highlights the necessity of an on-line solution of the local flame structure, which is performed in this paper by CMC, for an accurate prediction of the level of compositional noise.
This study opens new possibilities for the identification, separation and calculation of the sources of indirect combustion noise in realistic aeronautical gas turbines.
Effects of Fan Inflow Distortions on Heat Exchange in Air-Cooled Condensers: Unsteady Computations With Synthetic Blade Model
Authors: Angelini G. , Bonanni T. , Corsini A. , Delibra G. , Tieghi L. , Volponi D. 
Published: August 2018

Heat exchange in air-cooled condensers (ACC) is achieved by forced convection of fresh air on bundle of tubes by means of forced-draft axial-flow fans. These fans are characterized by low solidity and low hub ratio, large diameters, relatively low rotational velocity, high efficiencies. This combination usually leads to fans with non-stalling characteristics, with pressure rise continuously rising when reducing the flow rate, at least in standard (ISO or AMCA) test rigs. In real-life installations, in fact, it is quite difficult to characterize these fans, due to the practical difficulties arising in setting up a proper test rig and to control the boundary conditions of the system, in particular the fan inflow conditions.
Here we focus on a real-life setting of ACC, numerically simulated with URANS. In this work the fan is simulated with a Synthetic Blade Model presented in [1]. This model is derived from actuator disk theory, and allows to simulate the unsteady movement of the blades and compute a non-constant azimuthal distribution of lift and drag forces, partially accounting for non-constant deviation in the blade-to-blade passage, while drastically reducing the mesh requirements. In this way it is possible to model the shedding of wakes behind the blades and their interaction with the heat exchanger. The flow will be assumed to be incompressible, due to the low Mach number and heat transfer will be treated assuming temperature to be a passive scalar convected by the flow.
Duty point of the fan and heat exchange in the ACC will be studied while inflow conditions, in order to account for free inflow with a constant velocity distribution as well as distortions due to lateral wind. Computations will be carried out on the Virtual Test Rig of developed at Sapienza within the OpenFOAM 2.3.x library with a URANS approach and k-ε closure.
On Possibilities of Using Relative Shaft Vibration Signals for Rotating Blades Monitoring
Authors: Liska Jindrich , Vasicek Vojtech , Jakl Jan 
Published: August 2018

Ensuring the reliability of the steam turbine is the key for its long life. For this purpose monitoring systems are standardly used. Early detection of any failure can avoid possible economical and material losses. A monitoring of rotating blades vibration belongs to the very important tasks of the turbomachinery state assessment. Especially in terms of the last stages of low-pressure part, where the longest blades are vibrating at most. Commonly used methods for blade vibration monitoring are based on contact measurement using strain gauges or non-contact approach based on blade tip timing measurement.
Rising demand for low-cost monitoring systems has initiated development of a new approach in blade vibration monitoring task. The presented approach is based on usage of relative rotor vibration signals. Its advantage is in using of standardly installed sensors making this approach economically interesting for the turbine operators compared to the traditionally used methods, mentioned above.
This paper summarizes the symptoms of blade vibration phenomenon in relative shaft vibration signals, the impact of operating conditions on the blade vibration amplitude and its comparison to blade tip-timing measurement results. In addition of several examples, the article also describes an evaluation of proposed method in operation of steam turbine with power of 170MW.
Experimental and Numerical Investigation of Optimized Blade Tip Shapes: Part II — Tip Flow Analysis and Loss Mechanisms
Authors: Pátý Marek , Cernat Bogdan , De Maesschalck Cis , Lavagnoli Sergio 
Published: August 2018

The leakage flows within the gap between the tips of unshrouded rotor blades and the stationary casing of high-speed turbines are the source of significant aerodynamic losses and thermal stresses. In the pursuit for higher component performance and reliability, shaping the tip geometry offers a considerable potential to modulate the rotor tip flows and to weaken the heat transfer onto the blade and casing. Nevertheless, a critical shortage of combined experimental and numerical studies addressing the flow and loss generation mechanisms of advanced tip profiles persists in the open literature.
A comprehensive study is presented in this two-part paper that investigates the influence of blade tip geometry on the aerother-modynamics of a high-speed turbine. An experimental and numerical campaign has been performed on a high-pressure turbine stage adopting three different blade tip profiles. The aerothermal performance of two optimized tip geometries (one with a full three-dimensional contoured shape and the other featuring a multi-cavity squealer-like tip) is compared against that of a regular squealer geometry.
In the second part of this paper, we report a detailed analysis on the aerodynamics of the turbine as a function of the blade tip geometry. Reynolds-averaged Navier-Stokes simulations, adopting the Spalart-Allmaras turbulence model and experimental boundary conditions, were run on high-density unstructured meshes using the Numeca FINE/Open solver. The simulations were validated against time-averaged and time-resolved experimental data collected in an instrumented turbine stage specifically set up for the simultaneous testing of multiple blade tips at scaled engine-representative conditions. The tip flow physics is explored to explain variations in turbine performance as a function of the tip geometry. Denton’s mixing loss model is applied to the predicted tip gap aerodynamic field to identify and quantify the loss reduction mechanisms of the alternative tip designs. An advanced method based on the local triple decomposition of relative motion is used to track the location, size and intensity of the vortical flow structures arising from the interaction between the tip leakage flow and the main gas path. Ultimately, the comparison between the unconventional tip profiles and the baseline squealer tip highlights distinct aerodynamic features in the associated gap flow field. The flow analysis provides guidelines for the designer to assess the impact of specific tip design strategies on the turbine aerodynamics and rotor heat transfer.
Dry Low NOx Emissions Operability Enhancement of a Heavy-Duty Gas Turbine by Means of Fuel Burner Design Development and Testing
Authors: Cerutti Matteo , Giannini Nicola , Ceccherini Gianni , Meloni Roberto , Matoni Emanuele , Romano Christian , Riccio Giovanni 
Published: August 2018

This paper describes the development phases of an annular type combustor for heavy-duty gas turbine applications. High cycle efficiency and low emissions are required over a wide range of load conditions, with the consequence of reducing margin to thermo-acoustic instability onset and lean blow-out. In addition, in lean premixed combustors, the increased fuel air mixing times required to keep emissions low, may lead to undesired ignition or flashback into the fuel burner ducts.
All these aspects are matter of this work and focus is on fuel burner design modifications which allowed dry emissions reduction while maintaining a sufficiently wide safe operation window.
A synergic effort has been put in place, involving experimental campaigns and CFD simulations, with the purpose of assessing design changes initially and doing screening. In the meanwhile, numerical practices have taken benefits form the experience growth. Results of past work on similar components has been leveraged too.
Test campaign involved different scale facilities, from single burner through full annular combustor up to full scale prototype engine. The progressive reduction of viable option for combustor components design changes, due to high impact of such modifications during the gas turbine late development phases, forced designers to concentrate efforts onto fuel burner optimization, looking for efficient ways to implement modifications and assess their effectiveness of combustion system performances.
Emissions trends, blow-out and flashback margin for several burner designs are reported. Numerical analysis results are also shown, which revealed to be well aligned with the experimental outcomes, allowing burner optimized solution to be identified. Finally, characterization with respect to fuel gas composition is shown as well as sensitivity to different operating conditions.