Partner und Internationale Organisationen
(Englisch)
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Rolls-Royce, Snecma, Daimler-Benz Aerospace, Alfa Romeo Avio, Fiat Avio, ITP, DERA, Universität Karlsruhe, Università digli studi di Firenze, University of Limerick, EPFL, University of Oxford , VKI, ALSTOM, BMW-RR, Turbomeca, ABB
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Abstract
(Englisch)
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The overall objectives of the project are to understand the complex aero-thermal phenomena generated in cooled high pressure, intermediate pressure or low pressure turbines. This will lead to an improvement in the design of gas turbine reliability and safety and also lead to potential methods for increasing engine performance.
An experimental study is being conducted to investigate the adiabatic film cooling effectiveness and the heat transfer increase due to film injection on curved surfaces. Film cooling experiments have been performed for three basic curved wall configurations (two convex and one concave) that address a realistic range of wall curvature parameters representative of the first stage turbine airfoil design practice. Results from this experimental investigation will provide a database for the development of thermal design correlations, will improve the physical understanding of the film cooling process on curved surfaces and will enable a further improvement of gas turbine cycle efficiencies.
The current experimental results have been obtained with the concave test section for zero pressure gradient and accelerated free-stream conditions. Aerodynamic experiments without coolant injection were conducted for both free-stream boundary conditions to determine the main flow field quantities. Adiabatic film cooling effectiveness values were obtained with five injection configurations. Additionally heat transfer coefficients were derived for selected injection configurations. Air and CO2 were used as coolant fluids to achieve a variation of the density ratio.
Similar to previous experimental results obtained for convex surfaces, the film cooling effectiveness obtained on the concave surface with shaped injection holes achieved generally higher values than cylindrical injection holes for the same hole spacing. This is especially true at higher momentum flux ratios at those strong jet separation occurs for cylindrical hole injection. Results obtained with compound angle film injection indicate generally a low momentum flux ratio dependency. Film cooling effectiveness values obtained with compound angle injection achieved slightly higher levels compared to corresponding results from in-line film injection. This was attributed to an effectively increase coverage of the compound film holes. The results obtained with shaped injection configurations show an improved film cooling effectiveness at higher blowing rates due to the laid back angle of the shaped holes.
In contrast previous experimental results obtained for convex surfaces, the free-stream acceleration caused generally an increase in adiabatic film cooling effectiveness on the concave surface for the investigated injection configurations and boundary conditions. This increase was stronger for the results obtained with cylindrical holes.
The heat transfer results indicate in general small influences due to film injection on the concave test surface. The variation of the Stanton number ratios with the blowing rate is stronger for film injection with cylindrical holes than with shaped holes. The free-stream acceleration indicated no significant effects on corresponding Stanton number ratios determined during these heat transfer experiments. The results obtained with free-stream acceleration show a small increase in heat transfer levels. These findings are in agreement with the previous results obtained for convex surfaces.
A comparison of the film cooling results obtained with convex and concave surfaces reveal the following main conclusions:
· For zero pressure gradient flow the film cooling performance on convex surfaces is generally higher that on concave surfaces.
· If coolant separation occurs at high blowing rates, i.e. for cylindrical holes, film cooling performance on concave surfaces is similar or higher than values obtained on convex surfaces.
· For favorable pressure gradient flow film cooling performance is decreased on convex surfaces and increased on concave surfaces. Under those conditions film cooling performance might be better on concave surfaces than on convex surfaces.
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