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Aerodynamic Evaluation of Nacelles for Engines with Ultra High Bypass Ratio

Andreas Petrusson
Göteborg : Chalmers tekniska högskola, 2017. Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, ISSN 1652-8557; 2017:02, 2017.
[Examensarbete på avancerad nivå]

The aim in this project is to gain deeper understanding of nacelle drag for engines with ultra high bypass ratio. 2D axisymmetric nacelles with different fan cowl thickness and length are studied to investigate how these parameters affect the nacelle drag. Some different fan pressure ratios is also investigated. Furthermore, the drag for an aircraft fuselage with a fan and fan cowl at the rear that ingest the boundary layer of the fuselage is studied. This is the last part of the project and therefore this work still requires further study. First the geometries of the nacelles are designed. The fan cowl and inlet profiles of the nacelle are designed using a CST method, based on fourth order Bernstein polynomials. This allows for specifying the initial curvature radius of the profile, along with maximum radius and trailing edge position and slope. A core engine cowl and a bypass channel are also designed using these curves, but the internal parts of the core engine are not included in this project and the core nozzle is only considered as an outlet boundary. These geometries are simulated in an axisymmetric section using CFX, and the drag was computed from the flow state and pressure forces on the nacelle surfaces. The geometries of the boundary layer ingestion cases are constructed in a similar manner to the nacelles. For these cases, a whole aircraft fuselage is placed in front of a nacelle, with the rear of the fuselage going into the inlet of the nacelle. The fan diameter is varied to study the effect on drag, which means that different portions of the boundary layer are ingested by the fan. It is concluded that only shortening the fan cowl does not lower nacelle drag, since the aft core cowl should also be considered to contribute to the drag. Redesigning the aft core cowl could give a lower drag for the shorter and thinner cowl that are investigated, but the designs in this project does not take this into account. For the boundary layer ingestion cases, the drag is decreased more if a larger portion of the boundary layer is ingested. However, it could be more efficient if only some part of the boundary layer is ingested.

Nyckelord: Turbofan, Nacelle, Drag, Ultra-high bypass ratio, CFX, CST curve

Publikationen registrerades 2017-01-31. Den ändrades senast 2017-01-31

CPL ID: 247917

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