Abstract:

ESDU 94013 presents the coordinates for the cowl external profile as originally defined and now taken as a 'standard', together with the lip radius. When second divided differences of the coordinates are taken they are found to lack smoothness which means that the curvatures are not smooth. As a result computed pressure distributions also contain irregularities. A simple curve fit to the profile is given but is not felt to model the profile closely enough for flow computations (it fits the profile to about 0.6 per cent of Y, where Y is half the difference of the maximum and the highlight diameters). A more complex fitting equation is also provided that fits the profile to 0.15Y and is felt to meet the requirements for flow calculations; a comparison of pressure distribution results using the original profile and the fitted one illustrates the improvement found.