Proceedings of ASME Turbo Expo 2014 – GT2014-25460

Film cooling represents one the most widely-used cooling techniques for hot gas path components. In particular, effusion cooling has recently become an important focus of attention in the context of aero-engine design due to its high cooling performance. Notwithstanding the huge amount of work dedicated to the heat transfer on the hot side of effusion cooling plates, it has been demonstrated that up to 30 % of the total cooling effectiveness of a typical effusion cooling configuration can be ascribed to cold side convective cooling. Nevertheless, in open literature it is possible to notice a lack of knowledge as far as this topic is concerned.

This paper describes a numerical activity aimed at investigating the phenomenology of the heat transfer at the entrance of film cooling holes. First of all the accuracy of the numerical approach has been validated through a comparison of enhancement factor measurements on a test case available in literature. Steady state RANS simulations have been performed, modeling turbulence by means of the k–ω SST model. The use of a transition model has been taken into account, since in these configurations the transitional behavior of the boundary layer has been highlighted in literature. Subsequently, the attention has been turned to the comprehension of the phenomena involved in the heat transfer augmentation, focusing the attention to the influence of fluid dynamic parameters such as suction ratio and Reynolds number. A good agreement has been highlighted with experimental data, therefore this work provides a starting point for future investigations on more representative configurations.

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1908139

https://www.researchgate.net/publication/263277738_Numerical_Investigation_on_the_Heat_Transfer_Enhancement_Due_to_Coolant_Extraction_on_the_Cold_Side_of_Film_Cooling_Holes

Journal of Engineering for Gas Turbines and Power 137(12), Jul 2015

Transaction of ASME Turbo Expo 2014 – GT2014-25393

Effusion cooling represents one of the most innovative techniques to limit and control the metal temperature of combustors liner, and recently, attention has been paid by the scientific community on the characterization and the definition of design practices of such devices. Most of these studies were focused on the heat transfer on the hot side of effusion cooling plates, while just few contributions deal with the effusion plates cold side convective cooling. This paper reports a numerical survey aimed at the characterization of the convective cooling at the effusion plates cold side. Several effusion holes spacing is accounted for in conjunction with representative operating conditions. The study led to the development of an empirical correlation for the prediction of the cold side heat transfer coefficient enhancement factor, EF: it expresses the EF related to each extraction hole as a function of the pressure ratio β and the effusion plate porosity factor σ.

http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2469160

https://www.researchgate.net/publication/263277814_Heat_Transfer_Enhancement_Due_to_Coolant_Extraction_on_the_Cold_Side_of_Effusion_Cooling_Plates

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