Abstract:

The current methods and data used by the aerospace industry to determine the excrescence drag due to surface imperfections are mainly based on ESDU Aerodynamic Data Items, limited to an excrescence height to boundary-layer thickness limit of 10.0%. Investigations have shown that, for cases where the excrescence height is greater than 10% of the turbulent boundary-layer thickness, applying a correction based on the change in effective kinetic pressure gives drag estimates in better agreement with experiment. Therefore it is possible to relax the current limitation on excrescence height by applying a correction factor based on an effective mean kinetic pressure derived from the local turbulent boundary-layer and velocity profiles.

This Data Item and the accompanying software provide a method that can be used to produce approximate power-law velocity (and the associated density and kinetic pressure) profiles from integral boundary-layer parameters such as shape parameter and momentum thickness.

The method is evaluated against experimental data up to separation. Examples are given, using VGK and VFP output, for typical cases where only integral boundary-layer data are available.