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Computational Thermal Sciences: An International Journal
ESCI SJR: 0.249 SNIP: 0.434 CiteScore™: 0.7

ISSN Imprimir: 1940-2503
ISSN On-line: 1940-2554

Computational Thermal Sciences: An International Journal

DOI: 10.1615/ComputThermalScien.2016016302
pages 135-146

IMPROVING ADIABATIC FILM-COOLING EFFECTIVENESS BY USING AN UPSTREAM PYRAMID

Zineb Hammami
Département ELM, Institut de Maintenance et de Sécurité Industrielle, Université Oran 2, Oran, Algeria
Zineddine Ahmed Dellil
Déepartement ELM, Institut de Maintenance et de Sécurité Industrielle, Universitée Oran 2, Oran, Algeria
Fadela Nemdili
Laboratoire Aero Hydrodynamique Navale, (LAHN) USTO-MB, Oran, Algeria, Faculté de Génie Mécanique, Université des Sciences et de la Technologie d'Oran, Mohamed Boudiaf, BP1505 El-Mnaouar, 31000, Oran, Algeria
Abbes Azzi
Laboratory of Naval Aero-Hydrodynamic, Faculty of Mechanical Engineering, Oran University of Sciences and Technology, PO Box 1505, El-Mnaouar Oran, Algeria

RESUMO

As film cooling is an important and critical process for gas turbine applications, designers are always looking to increase the adiabatic film-cooling effectiveness. One possible solution is to modify the approaching boundary layer flow and its interaction with the film-cooling jets. Inspired by published research where an upstream ramp is added just before the cooling jet rows, this study presents a new design of the ramp still showing good cooling performances and fewer aerodynamic losses. In the new design concept, the ramp looks like an upstream pyramid centered exactly in the space between the two adjacent holes. With this design, it is expected that space between adjacent holes, which is less cooled by the jet, will be protected by the upstream pyramid and more lateral jet spreading can be realized. For comparison purposes, three geometrical configurations are considered, which are the baseline case, the case with an upstream ramp, and finally the new case with an upstream pyramid. Computations, based on the ensemble-averaged Navier-Stokes equations solved by the realizable k−ε turbulence model and standard wall function, are used in the frame of the finite volume fluent computational fluid dynamic (CFD) code. For 12 computational cases, including the baseline case, centerline adiabatic film-cooling effectiveness as well as the laterally averaged adiabatic film-cooling effectiveness are presented and compared. Additionally, the surface distribution of the adiabatic film-cooling effectiveness is also presented. Lateral spreading is investigated by plotting lateral variation of the adiabatic film-cooling effectiveness at several longitudinal stations. Results obtained by the present computations show that the upstream ramp with a backward-facing step greatly increases surface adiabatic effectiveness. The laterally averaged adiabatic effectiveness with the ramp can be higher than without the ramp by increasing lateral spreading of the coolant. For the case with l/d = 2.8, the new proposed geometry (upstream pyramid) still improves the thermal performances by less lateral spreading but with better pressure distribution, while for the case of l/d = 1.75, the pyramid case outperforms other cases close to the hole injection area (x/d < 10). Therefore, as a conclusion, the proposed geometry presents a good compromise between increasing the adiabatic film-cooling effectiveness and keeping the pressure losses to smaller levels.


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