Abstract:

ESDU 00022 illustrates the use of constrained multivariate optimisation techniques in the minimisation of drag by the use of leading- and trailing-edge flap deflections, at a single design point (Mach number, lift coefficient). It demonstrates the effect of problems within the Computational Fluid Dynamics method on the operation of the optimisation process. The optimisation objective in this example is to minimise the drag coefficient at a single design point - Mach number 0.79, lift coefficient 0.75, Reynolds number 20 million and transition fixed at 5 per cent of chord on both surfaces. The flow calculation method used is BVGK for viscous flow, set up to calculate the drag coefficient at the required lift coefficient. The basic section was designed to meet various design points applicable to a modern combat aircraft by deflection of plain leading- and trailing-edge flaps. The thickness distribution of the section (5.821 per cent thickness/chord at 42.39 per cent chord, 0.2552 per cent leading-edge radius/chord ratio, trailing-edge thickness 0.7335 per cent chord) was designed to ensure a good supersonic capability. The section is highly cambered to provide a very high manoeuvre performance at a Mach number of 0.79. Reduction of the drag of this aerofoil section at the selected flight condition is to be sought by the changes in effective camber available from the deflection of leading- and trailing-edge plain flaps, hinged (in this case) at 15 per cent and 75 per cent of chord, respectively. ESDU 00022 is one of a series illustrating the process of using such optimisation techniques, indicating their advantages and revealing the kinds of problems that can arise. An introduction to the application of constrained multivariate optimisation techniques to the design of aerofoil section shapes is given in ESDU 99019.