8th Annual ACC Users Group Conference (2016)
This work describes the application of CFD to predict the wind field and determine the optimal setup for wind screens. This way, it was possible to improve the performance of the Air Cooled Condensers (ACC) and ultimately of the overall power plant.
http://acc-usersgroup.org/presentations/2016-conference/
http://acc-usersgroup.org/wp-content/uploads/2016/11/Cosimo-Bianchini_CFD-Analysis-for-Mitigating-Wind-Effects-on-ACC-Performance.pdf
ASME Turbo Expo 2016 – GT2016-56003
This paper summarizes the main results sorted out from a Design of Experiment (DoE) based on a validated Computational Fluid Dynamics (CFD). Several tip recessed geometries applied to an unshrouded impeller were considered in conjunction with two tip clearance levels. The computations show that recessed tip geometries have positive effects when considering high flow coefficient values while in part-load conditions the gain is reduced. Starting from the results obtained when studying tip cavities, a single rim tip squealer geometry was then analysed: the proposed geometry leads to performance improvements for all the tested conditions considered in this work.
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2554847
https://www.researchgate.net/publication/308500203_Effects_of_Impeller_Squealer_Tip_on_Centrifugal_Compressor_Performance
Proceedings of ASME Turbo Expo 2015 – GT2015-42473
The continuously growing request for high operational flexibility and extreme customization also for large scale steam turbine creates new challenges in the design of steam machineries. Most components in fact need to be operated, and hence verified, in conditions far from those they were originally designed for. Constant upgrade of selection tools for the assembly of the engine is thus required to extend correlations applicability range for both averaged aerodynamic performance and unsteady effects of critical components.
In this context a trip valve of a medium sized steam turbine was analyzed by means of CFD analysis. The investigation had two principal objectives: the estimate of aerodynamic losses within the valve and the evaluation of fluctuating loads effects.
For the time averaged behavior, first pressure losses across the strainer band were evaluated through a detailed simulation of the filter geometry in a simplified configuration to characterize an equivalent distributed momentum loss in the complete domain. Steady state solutions of the flow within the valve and the diffuser were then obtained for the entire range of operations to evaluate the global valve loss coefficient.
The unsteady steam behavior is predicted by means of the Scale Adaptive Simulation principle to evaluate major characteristic frequencies and verify fluctuations amplitudes on critical points.
Finally an acoustic propagation analysis is performed to estimate possible interactions between aerodynamic forcing and proper acoustic modes both verifying sufficient decoupling between aerodynamic and acoustic proper frequencies and analysing the forced acoustic response when subjected to registered pressure fluctuations.
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2428700
14th EDF/Pprime Workshop: Futuroscope, October 8 & 9, 2015
“Influence of design and materials on journal and thrust bearing performance”
The purpose of the article is to compare the operational characteristic of a direct lube tilting pad bearing measured during a component level test with steady state CFD predictions. Simulations assume that oil-air flow is identical on each pad. Both volume of fluid method (VOF) and single phase analyses have been conducted to allow the comparison with the “static” variables (zero order) such as pad babbitt temperatures, oil pressure/temperature, flow rate, and power losses. As regards the identification of linearized rotordynamic coefficient, the “Instrumental Variable Filter” (IVF) experimental method was used in the frequency domain; dynamic force controlled excitation express the small perturbation around equilibrium position (1st order), and proximity probes opportunely placed recorded the corresponding displacement. The ratio of these terms provides the complex dynamic impedance (whose real part represent the stiffness while the imaginary the damping) exercised by the oil film whose entities are compared with a 2D Reynolds simulation. The coherence with this iterative technique has finally allowed to optimize the size of the sprayer to ensure the maximum covering of oil film from the leading edge to the exit of each individual pad.
https://www.researchgate.net/publication/332268162_CFD_analysis_for_the_design_of_a_sprayer_for_direct_lube_tilting_pad_journal_bearing_Analyse_CFD_pour_la_conception_d’une_buse_de_pulverisation_pour_un_palier_a_patins_oscillants_avec_une_lubrificatio
Sono tutti giovani, ma già vantano collaborazioni con big dell’industria quali General Electric Nuovo Pignone, Eli Lylli e Trenitalia. Hanno tenacia da vendere gli ingegneri (tra i 30 e i 37 anni) che stanno trasformando in spin-off universitario la loro “creatura” nata nel 2008, la società Ergon Research.
Journal of Engineering for Gas Turbines and Power 138(2), Sep 2015
Transaction of ASME Turbo Expo 2015 GT2015-42003
Jet array is an arrangement typically used to cool several gas turbine parts. Some examples of such applications can be found
in the impingement cooled region of gas turbine airfoils or in the turbine blade tip clearances control of large aero-engines. In the open literature, several contributions focus on the impingement jets formation and deals with the heat transfer phenomena that take place on the impingement target surface. However, deficiencies of general studies emerges when the internal convective
cooling of the impinging system feeding channels is concerned.
In this work an aero-thermal analysis of jet arrays for active clearance control was performed; the aim was the definition of a correlation for the internal (i.e. within the feeding channel) convective heat transfer coefficient augmentation due to the coolant extraction operated by the bleeding holes. The data were taken from a set of CFD RANS simulations, in which the behaviour of the cooling system was investigated over a wide range of fluid-dynamics conditions. More in detail, several different holes arrangements were investigated with the aim of evaluating the influence of the hole spacing on the heat transfer coefficient distribution. Tests were conducted by varying the feeding channel Reynolds number in a wide range of real engine operative conditions. An in depth analysis of the numerical data set has underlined the opportunity of an efficient reduction through the local suction ratio of hole and feeding pipe, local Reynolds number and manifold porosity: the dependence of the heat transfer coefficient enhancement factor from these parameter is roughly exponential.
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2430863
Proceedings of ASME Turbo Expo 2015 – GT2015-42594
In the present paper the combined effects of rotation and channel orientation on heat transfer and pressure drop along two scaled up matrix geometries suitable for trailing edge cooling of gas turbine airfoils are investigated.
Experimental tests were carried out under static and rotating conditions. Rotating tests were performed for two different orientations of the matrix channel with respect to the rotating plane: 0deg and 30deg. This latter configuration is representative of the exit angle of a real gas turbine blade. Test models are designed in order to replicate an internal geometry suitable for blade trailing edge cooling, with a 90deg turning flow before entering the matrix array which has an axial development.
Both the investigated geometries have a cross angle of 45deg between ribs and different values of sub-channels and rib thickness: one has four sub-channels and lower rib thickness (open area 84.5%), one has six sub-channels and higher rib thickness (open area 53.5%). Both geometries have a converging angle of 11.4deg.
Matrix models have been axially divided in 5 aluminium elements per side in order to evaluate the heat transfer coefficient in 5 different locations in the main flow direction. Metal temperature was measured with embedded thermocouples and thin-foil heaters were used to provide a constant heat flux during each test.
Heat transfer coefficients were measured applying a steady state technique based on a regional average method and varying the sub-channel Reynolds number Res from 2000 to 10000 and the sub-channel Rotation number Ros from 0 to 0.250 in order to have both Reynolds and Rotation number similitude with the real conditions.
A post-processing procedure, which takes into account the temperature gradients within the model, was developed to correctly compute average heat transfer coefficients starting from discrete temperature measurements.
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2428299
Proceedings of ASME Turbo Expo 2015 – GT2015-42479
The continuous challenge to develop more efficient and cleaner combustion systems for energy production, promotes the exploitation of traditional fossil fuels in alternative energy cycles capable of abating pollutant emissions. Integrated coal gasification combined cycle (IGCC) technology for instance permits to convert standard coal and other carbon based fuels into hydrogen-rich syngas. These gases are generally used to fuel standard gas turbine engines typically designed for natural gas combustion. Due to the increased propensity to flashback with high hydrogen content, lean premixed burners usually need a specific redesign to ensure adequate flow velocity at the burner exit section so as to extend lean blow out limits.
However design practices for flashback prevention are far from being established especially for these unconventional fuels and it is therefore of interest to rely on CFD analysis to establish flame stabilization process and to predict incipient flashback.
The purpose of this work is to assess the accuracy and reliability of a CFD methodology to describe the flame anchoring process and exhaust pollutant emissions in a high hydrogen syngas version of a standard swirled lean premixed burner which has been tested in a tubular test rig.
Considered numerical setup is based on the use of the Flamelet-Generated Manifolds (FGM) method which is a good choice to combine computational efficiency and detailed chemistry modelling. This work aims at providing a first assessment of the FGM model as implemented in Fluent v15 in the framework of RANS turbulence approach. Four different operating conditions at increasing pressure levels are tested and a detailed sensitivity analysis of the combustion model is provided exploring flamelet generation parameters, turbulence-chemistry interaction closures and methods to assign progress variable variance.
A specifically developed detailed chemical mechanism for H2 was implemented and used to verify NOx emission predicting capabilities of three alternative methods: lookup table generated integrating with presumed PDF, automatic reactor network model based on CFD aero-thermal solution and Fluent native NOx model. Obtained results are validated against available experimental data.
https://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2428151
Journal of Engineering for Gas Turbines and Power 138(3) Sep 2015
Transaction of ASME Turbo Expo 2015 – GT2015-43135
Combustor liner of present gas turbine engines is subjected to high thermal loads as it surrounds high temperature combustion
reactants and is hence facing the related radiative load. This generally produces high thermal stress levels on the liner, strongly limiting its life expectations and making it one of the most critical components of the entire engine. The reliable prediction of such thermal loads is hence a crucial aspect to increase the flame tube life span and to ensure safe operations.
The present study aims at investigating the aero-thermal behavior of a GE DLN1 (Dry Low NOx) class flame tube and in
particular at evaluating working metal temperatures of the liner in relation to the flow and heat transfer state inside and outside the combustion chamber. Three different operating conditions have been accounted for (i.e. Lean-Lean partial load, Premixed full load and Primary load) to determine the amount of heat transfer from the gas to the liner by means of CFD. The numerical predictions have been compared to experimental measurements of metal temperature showing a good agreement between CFD and experiments.
https://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2430864
European Turbomachinery Conference 2015
A computational analysis of the acoustic response of a double seat valve employed in the control stage of an industrial steam turbine was performed to verify possible criticalities in terms of mechanical stresses. Unsteady CFD was exploited to evaluate the unsteady pressure loads on selected positions. Turbulent flow simulations adopt the Scale Adaptive Simulation principle, as implemented in Ansys CFX 14.5 code, to partially resolve turbulence spectrum. 180 deg symmetric computational models were used, after verification that principal flow features of the full geometry were adequately reproduced, to maintain grid size below 20M cells. Purely acoustic computations exploiting the homogeneous Helmoltz equation were conducted first to identify natural acoustic modes and secondly to verify the forced response subjected to the unsteady pressure loads computed by CFD. Investigated frequency range is extended from 5 to 1000 Hz to comprehend all relevant structural modes. 4 different flow conditions were investigated to represent the entire operating range both in terms of characteristic Reynolds and Mach number. Obtained results shows that principal forcing frequency is characterized by a constant Strouhal number based on plug diameter and bulk flow velocity while main load amplitude is proportional to Reynolds number. Acoustic modes correspond to much higher frequencies so that the forced response does not generate critical stress levels on both valve stem and chest.