Aero‐mechanical optimisation of a structural fan outlet guide vane

The aero‐mechanical optimisation of a fan outlet guide vane (OGV) in the bypass duct of a modern turbofan engine is presented. The purpose of the described outlet guide vane arrangement is to remove the swirl from the flow coming from the fan and to connect the engine core structurally with the bypass duct and the engine mounts respectively. For that reason the outlet guide vanes have to fulfill aerodynamic requirements–such as low pressure loss and large working range and turning of the absolute flow to 0 degree–as well as the structural requirement to withstand the engine loads in all operating conditions. Such an arrangement has the advantage, that additional struts downstream of the fan outlet guide vane become obsolete, which is beneficial for the engine length and weight and hence the engine specific fuel consumption. At the same time the structural and aerodynamic requirements on such an outlet guide vane are intuitively contradictory. Therefore the design is more complex than for a conventional purely aerodynamic guide vane. To achieve the different requirements the conventional iterative design process has been replaced by a multi‐disciplinary approach, which delivers an aero‐mechanically optimised fan outlet guide vane geometry based on aerodynamic and mechanical boundary conditions and constraints. The prescribed boundary conditions are the structural load cases (flight conditions) and the aerodynamic inlet and outlet conditions for the fan design point. In addition an existing bypass duct geometry is used to get a valid comparison with a conventionally designed outlet guide vane/strut arrangement. In the structural optimisation, carried out as a parameter study, the effect of several geometrical parameters is investigated using the software ABAQUS. The aerodynamic optimisation is performed using the 2D‐CFD‐solver MISES on individual profile sections such that a minimum pressure loss and a maximum working range is achieved. For that purpose the profile shape is modified freely taking into account the constraints from the structural optimisation. A 3D‐RANS‐CFD analysis of the optimised vane and the comparison with the conventional vane/strut arrangement confirmed the improved performance of the chosen design approach and showed a significant reduction in pressure loss (ΔP/D) of nearly 20% compared to the conventional OGV/strut arrangement, leading to an SFC reduction of about 0.5%.