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Aerospace 2018, 5(3), 97;

Discharge Coefficients of Ports with Stepped Inlets

Department Aeronautical and Automotive Engineering, Loughborough University, Loughborough LE11 3TU, UK
Received: 13 August 2018 / Revised: 14 September 2018 / Accepted: 16 September 2018 / Published: 19 September 2018
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Components of aeronautical gas turbines are increasingly being constructed from two layers, including a pressure containing skin, which is then protected by a thermal tile. Between them, pedestals and/or other heat transfer enhancing features are often employed. This results in air admission ports through the dual skin having a step feature at the inlet. Experimental data have been captured for stepped ports with a cross flow approach, which show a marked increase of 20% to 25% in discharge coefficient due to inlet step sizes typical of combustion chamber configurations. In this respect, the step behaves in a fashion comparable to ports with inlet chamfering or radiusing; the discharge coefficient is increased as a result of a reduction in the size of the vena contracta brought about by changes to the flow at inlet to the port. Radiused and chamfered ports have been the subject of previous studies, and empirical correlations exist to predict their discharge coefficient as used in many one-dimensional flow network tools. A method to predict the discharge coefficient change due to a step is suggested: converting the effect of the step into an equivalent radius to diameter ratio available in existing correlation approaches. An additional factor of eccentricity between the hole in the two skins is also considered. Eccentricity is shown to reduce discharge coefficient by up to 10% for some configurations, which is more pronounced at higher port mass flow ingestion fraction. View Full-Text
Keywords: discharge coefficient; air admission port; orifice; tolerance; eccentricity; step inlet; counterbore; crossflow discharge coefficient; air admission port; orifice; tolerance; eccentricity; step inlet; counterbore; crossflow

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Spencer, A. Discharge Coefficients of Ports with Stepped Inlets. Aerospace 2018, 5, 97.

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