Proceedings 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.

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.

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.

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

https://www.researchgate.net/publication/272833359_Heat_Transfer_Augmentation_Due_to_Coolant_Extraction_on_the_Cold_Side_of_Active_Clearance_Control_Manifolds

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.

https://www.researchgate.net/publication/283479817_Aeroacoustic_analysis_of_a_steam_turbine_double_seat_control_valve