Journal of Engineering for Gas Turbines and Power GTP-062602 June 2015, Vol. 137

Transaction of ASME Turbo Expo GT2014-25386

The transition-piece of a gas turbine engine is subjected to high thermal loads as it collects high temperature combustion products from the gas generator to a turbine. This generally produces high thermal stress levels in the casing of the transition piece, 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 transition-piece life span and to assure safe operations. The present study aims to investigate the aerothermal behavior of a gas turbine engine transition-piece and in particular to evaluate working temperatures of the casing in relation to the flow and heat transfer situation inside and outside the transition-piece. Typical operating conditions are considered to determine the amount of heat transfer from the gas to the casing by means of computational fluid dynamics (CFD). Both conjugate approach and wall fixed temperature have been considered to compute the heat transfer coefficient (HTC), and more in general, the transition-piece thermal loads. Finally a discussion on the most
convenient HTC expression is provided.

http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=1920336

https://www.researchgate.net/publication/263277737_Thermo_Fluid_Dynamic_Analysis_of_a_Gas_Turbine_Transition-Piece

 

Proceedings of ASME Turbo Expo 2014 – GT2014-26982

The continuously growing request for high operational flexibility also for large scale steam turbine creates new challenges for control valve design. Such components, subjected to large static loads, may also experience strong vibrations due to unsteady turbulent fluctuations downstream the throttling section, which need to be confined sufficiently far from structural natural frequencies in the entire range of operating conditions. This work is focused on a computational analysis of the unsteady steam flow developing within a realistic double-seat control valve employed in industrial steam turbine. Actual operating conditions are considered both in terms of steam inflow pressure and temperature, flow rates and plug height. Three plug heights were considered: two corresponding to almost closed plug thus subjected to choked flow, and the third verified at 4 different steam rates. In order to capture the unsteady nature of the flow and verify the fluid-dynamic forcing frequency, the Scale Adaptive Simulation principle, as implemented in Ansys CFX 14.5 code, has been employed. Computations were run with a computational time step of 0.0001 s and an effective simulation window of 0.2 s for time averaged values and pressure time signals. The unsteady response is monitored analyzing the frequency spectra of both integral variables (i.e. forces and moment on plug) and punctual pressure oscillations. Analysis of results showed that it is possible to correlate the principal frequency and amplitude with the operating conditions. Strouhal number based on plug diameter and bulk flow velocity remains in fact constant independently on operating conditions.

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1907394

https://www.researchgate.net/publication/288224206_Numerical_Analysis_of_the_Unsteady_Loads_on_a_Steam_Turbine_Double_Seat_Control_Valve

 

Journal of Engineering for Gas Turbines and Power 138(7) Nov 2015

Transaction of ASME Turbo Expo 2014 – GT2014-27078

Among the various type of seals used in gas turbine secondary air system to guarantee sufficient confinement of the main gas path, honeycomb seals well perform in terms of enhanced stability and reduced leakage flow. Due to the large amount of honeycomb cells typically employed in real seals, it is generally convenient to treat the sealing effect of the honeycomb pack as an increased distributed friction factor on the plain top surface. That is why this analysis is focused on a simple configuration composed by a honeycomb facing a flat plate. In order to evaluate the sealing performance of such honeycomb packs, an experimental campaign was carried out on a stationary test rig where the effects of shaft rotation are neglected. The test rig was designed to analyse different honeycomb geometries so that a large experimental database could be created to correlate the influence of each investigated parameter. Honeycomb seals were varied in terms of hexagonal cell dimension and depth in a range that well represents actual honeycomb packs employed in industrial compressors. For each geometry five different clearances were tested. This work reports the findings of such experimental campaign whose results were analysed in order to guide actual seals design and effective estimates of shaft loads. Static pressure measurements reveal that the effects of investigated geometrical parameters on friction factor well correlate with a corrected Mach number based on the cell depth.

The presence of acoustic effects in the seals was further investigated by means of hot wire anemometry. Acoustic forcing due to flow cavity interaction was found to be characterized by a constant Strouhal number based on cell width. Numerical simulations
helped in the identification of system eigenmodes and eigenfrequencies providing an explanation to the friction factor enhancement triggered at a certain flow speed.
Finally the generated dataset was tested comparing the predicted leakage flow with experimental data of actual seals (with high pressure and high rotational speed) provided by GE Oil & Gas showing a very good agreement.

http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2469758

https://www.researchgate.net/publication/283649049_Flat_Plate_Honeycomb_Seals_Friction_Factor_Analysis

 

Energy Procedia, Volume 45, 2014

Among the various type of seals used in gas turbine secondary air system to guarantee sufficient confinement of the main gas path, honeycomb seals well perform in terms of enhanced stability and reduced leakage flow. Reliable estimates of the sealing performance of honeycomb packs employed in industrial gas and steam turbines, are however missing in literature, thus, in order to evaluate the complete characteristic curve of the seals in the wide range of working conditions, an experimental campaign was planned. This work reports the findings of an experimental campaign aimed at evaluating aerodynamic losses within honeycomb seals.

Due to the generally large amount of honeycomb cells typically present in real seals, it would be convenient to treat the sealing effect of the honeycomb pack as an increased distributed friction factor on the plain top surface that is why the simplest config- uration, the honeycomb facing a flat plate, is employed in this paper. The geometry of the hexagonal cell and the investigated clearances were chosen to well represent actual honeycomb packs employed in industrial compressors. First the pressure distribu- tion within the seal was analysed verifying that downstream the first 5 rows of cells, where entrance effects are predominant, the relative pressure drop is almost constant thus the use of an equivalent friction factor is appropriate to characterize the seal. Subse- quent analysis focused on the characterization of the friction factor as function of the Reynolds number with the aim of establishing the proper geometrical scaling to achieve flow conditions similar to real turbine most critical ones.

The different behaviour of the honeycomb sealing depending on the hexagonal cell arrangement and dimensions was evaluated in terms of friction factor.

Comparison with results coming from a previous CFD investigation is also presented and discussed in this paper.

https://www.sciencedirect.com/science/article/pii/S1876610214000551

https://www.researchgate.net/publication/275529656_Analysis_of_Flat_Plate_Honeycomb_Seals_Aerodynamic_Losses_Effects_of_Clearance

International Journal of Heat and Fluid Flow, Volume 44, December 2013

The accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of rotating machineries. The selection of a suitable model to account for the effects of turbulence on such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of different approaches available within commercial CFD solvers together with results obtained by means of in-house developed or open-source available research codes exploiting a suitable Reynolds Stress Model (RSM) closure, Large Eddy Simulation (LES) and a direct numerical simulation (DNS). The predictions are compared to the experimental data of Burin et al. (2010) in an original enclosed Couette–Taylor apparatus with endcap rings. The results are discussed in details for both the mean and turbulent fields. A particular attention has been turned to the scaling of the turbulent angular momentum G with the Reynolds number Re. By DNS, G is found to be proportional to Re^α, the exponent α = 1.9 being constant in our case for the whole range of Reynolds numbers. Most of the approaches predict quite well the good trends apart from the k–ω SST model, which provides relatively poor agreement with the experiments even for the mean tangential velocity profile. Among the RANS models, even though no approach appears to be fully satisfactory, the RSM closure offers the best overall agreement.

https://www.sciencedirect.com/science/article/pii/S0142727X13001252

https://www.researchgate.net/publication/258935419_Turbulent_Couette-Taylor_flows_with_endwall_effects_A_numerical_benchmark

International Journal of Heat and Fluid Flow, Elsevier, 2013

New calculations using an innovative Reynolds Stress Model are compared to velocity measurements performed by Particle Image Velocimetry technique and the predictions of a k–w SST model in the case of an impinging jet flow onto a rotating disk in a discoidal and unshrouded rotor–stator system. The cavity is characterized by a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Jet Reynolds numbers ranging from 1.72e4 to 4.3e4 and rotational Reynolds numbers between 0.33e5 and 5.32e5 are considered. Three flow regions have been identified: a jet-dominated flow area at low radii characterized by a zero tangential velocity, a mixed region at intermediate radii and rotation-dominated flow region outwards. For all parameters, turbulence, which tends to the isotropic limit in the core, is much intense in a region located after the impingement zone. A relative good agreement between the PIV measurements and the predictions of the RSM has been obtained in terms of the radial distributions of the core-swirl ratio and of the turbulence intensities. The k–w SST model over-estimates these flow characteristics in the jet dominated area. For the thermal field, the heat transfers are enhanced in the jet dominated region and decreases towards the periphery of the cavity. The jet Reynolds number appears to have a preponderant effect compared to the rotational one on the heat transfer distribution. The two RANS modelings compare quite well with the heat transfer measurements for these ranges of parameters.

https://www.sciencedirect.com/science/article/pii/S0142727X13001975

https://www.researchgate.net/publication/258935331_Turbulent_impinging_jet_flow_into_an_unshrouded_rotor-stator_system_Hydrodynamics_and_heat_transfer

Proceedings of ASME Turbo Expo 2013 – GT2013-94673

A numerical study of a state of the art leading edge cooling scheme was performed to analyze the heat transfer process within the leading edge cavity of a high pressure turbine airfoil. The investigated geometries account a trapezoidal supply channel with a large racetrack impingement holes. The coolant jets, confined among two consequent large fins, impact the leading edge internal surface and it is extracted from the leading edge cavity through both showerhead holes and film cooling holes. The CFD setup has been validated by means of the experimental measurements performed on a dedicated test rig developed and operated at University of Florence. The aim of this study is to investigate the combined effects of jet impingement, mass flow extraction and fins presence on the internal heat transfer of the leading edge cavity. More in details, the paper analyses the impact, in terms of blade metal temperature, of large fins presence and positioning. Jet’s Reynolds number is varied in order to cover the typical engine conditions of these cooling systems (Re_j = 20000 – 40000).

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1776087

https://www.researchgate.net/publication/267504204_Numerical_Analysis_of_Heat_Transfer_in_a_Leading_Edge_Geometry_With_Racetrack_Holes_and_Film_Cooling_Extraction

International Journal of Rotating Machinery, Sep 2012

Heat transfer and pressure drop for a representative part of a turbine active cooling system were numerically investigated by means of an in-house code. This code has been developed in the framework of an internal research program and has been validated by experiments and CFD. The analysed system represents the classical open bird cage arrangement that consists of an air supply pipe with a control valve and the present system with a collector box and pipes, which distribute cooling air in circumferential direction of the casing. The cooling air leaves the ACC system through small holes at the bottom of the tubes. These tubes extend at about 180° around the casing and may involve a huge number of impinging holes; as a consequence, the impinging jets mass flow rate may vary considerably along the feeding manifold with a direct impact on the achievable heat transfer levels. This study focuses on the performance, in terms of heat transfer coefficient and pressure drop, of several impinging tube geometries. As a result of this analysis, several design solutions have been compared and discussed.

https://www.hindawi.com/journals/ijrm/2012/103583/

https://www.researchgate.net/publication/260246390_Aerothermal_analysis_of_a_turbine_casing_impingement_cooling_system

 

Proceedings of ASME Turbo Expo 2012 – GT2012-68592

Reliable means of predicting ingestion in cavities adjacent to the main gas path are increasingly being sought by engineers involved in the design of gas turbines. In this paper, analysis is to be presented that results from an extended research programme, MAGPI, sponsored by the EU and several leading gas turbine manufactures and universities. Extensive use is made of CFD modelling techniques to understand the aerodynamic behaviour of a turbine stator well cavity, focusing on the interaction of cooling air supply with the main annulus gas. The objective of the study has been to benchmark a number of CFD codes and numerical techniques covering RANS and URANS calculations with different turbulence models in order to assess the suitability of the standard settings used in the industry for calculating the mechanics of the flow travelling between cavities in a turbine through the main gas path.

The modelling methods employed have been compared making use of experimental data gathered from a dedicated two-stage turbine rig, running at engine representative conditions. Extensive measurements are available for a range of flow conditions and alternative cooling arrangements. The limitations of the numerical methods in calculating the interaction of the cooling flow egress and the main stream gas, and subsequent ingestion into downstream cavities in the engine (i.e. re-ingestion), have been exposed. This has been done without losing sight of the validation of the CFD for its use for predicting heat transfer, which was the main objective of the partners of the MAGPI Work-Package 1 consortium.

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1694463

https://www.researchgate.net/publication/267503304_An_Investigation_Into_Numerical_Analysis_Alternatives_for_Predicting_Re-Ingestion_in_Turbine_Disc_Rim_Cavities

1515

Heat transfer and discharge coefficient behaviour for a representative part of a turbine active cooling system were numerically investigated by means of an in-house code. This code has been developed in the framework of an internal research program and has been validated by experiments and CFD. The analysed system represents the classical open bird cage arrangement that consists of an air supply pipe with a control valve and the present system with a collector box and pipes, which distribute cooling air in circumferential direction of the casing. The cooling air leaves the ACC system through small holes at the bottom of the tubes. These tubes extend at about 180° around the casing and may involve a huge number of impinging holes; as a consequence, the impinging jets mass flow rate may vary considerably along the feeding manifold with a direct impact on the achievable heat transfer levels. This study focuses on the performance, in terms of heat transfer coefficient and pressure drop, of several impinging tube geometries. As a result of this analysis, several design solutions have been compared and discussed.

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1694498

https://www.researchgate.net/publication/267503620_Heat_Transfer_and_Pressure_Drop_Analysis_of_a_Turbine_Casing_Impingement_Cooling_System