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

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