Experimental investigation of a turbofan nacelle at different mass flow ratios and angles of attack

Examensarbete för masterexamen
Dwalibi, Johannes
The air travel sector is rapidly increasing worldwide motivated by the push for greater connectivity in an increasingly globalised economy. The turbofan engine is widely used for aircraft propulsion and it is designed to satisfy the increasing demand for fuel efficiency. As bypass ratio (BPR) increases, the overall efficiency of the engine increases which is a main factor that yields lower specific fuel consumption (SFC). However, high-bypass ratios are accompanied by increased weight and nacelle drag. Therefore, turbofan nacelles require careful design to balance performance benefits of the higher propulsive efficiency against weight and drag penalties. In order to reduce the drag it is necessary to understand how the flow-field around it behaves at different flight conditions. Therefore, a scale model of a powered turbofan nacelle was built and tested at the Chalmers low speed wind tunnel. A 3D axisymmetric nacelle geometry was generated using the class shaped transformation (CST) method which allows for parametric aerodynamic geometry definitions. Furthermore, the geometry is imported to a CAD software, where the mechanical design and assembly modelling were conducted. The model was manufactured, build and tested in the wind tunnel. Measurements of force, fan speed and static pressure were carried out for different angles of attack (AoA) and mass flow ratios (MFR). In addition, surface tufts were used in order to visualise the flow-field, changing angles of attack (AoA) has been conducted using rotary table and mass flow ratios (MFR) have been controlled by varying (EDF) rotational speed in accordance with the wind tunnel air velocity. Results show that the flow around the nacelle body differs substantially depending on whether the fan is turned on or off, suggesting that experiments using flow-through nacelles would not be enough for thoroughly assessing the aerodynamic behaviour of this component. It was also observed that the higher the (MFR) is, the larger the backward forces are.
CST, Drag, Axisymmetric nacelle, Axisymmetric nacelle, Mass flow ratio, Wind tunnel, Load cell, Measurement, Flow visualisation
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