Aerofoil profile drag for Mach numbers below the drag rise condition.
Abstract:ESDU 00027 provides simple equations and graphs for predicting the minimum profile drag coefficient for an aerofoil with fixed transition position on both the upper and lower surfaces. The method is based on correlating results of calculations made with the VGK Computational Fluid Dynamics program which iteratively allows for the effect of boundary layer thickness in deriving the pressure distribution around the aerofoil at subsonic Mach numbers. ESDU 96028 indicates that VGK calculations model very closely the best experimental data. The behaviour of lift-drag polars for aerofoils with free transition and fixed transition is illustrated and discussed and it is explained that with fixed transition the polar is relatively flat over a range of lift coefficient. It is the drag coefficient corresponding to that flat region that is predicted by the method. The method provides an equation for the drag coefficient due to thickness distribution as a function of transition position and Reynolds number. Graphs give two factors to be applied to that prediction, one to allow for the effect of compressibility at higher Mach numbers and one to allow for camber effects and, in particular, the effect of rear loading on supercritical aerofoils. The accuracy of the method is discussed and the ranges of the parameters for which it was developed are tabulated. Plots of predictions by the method against the VGK data show a correlation to within two drag counts at low Reynolds number over the full range of Mach number but within one drag count at high Reynolds number combined with low Mach number. Two fully worked examples illustrate the use of the method.
|Data Item ESDU 00027|