ESDU 90029:2012

ESDU 90029 provides information to assist in the application of
the group of ESDU data on the prediction of the drag due to such
excrescences as grooves, ridges and steps, rivets, and cylinders
and stub wings immersed in the boundary layer. Those data were
obtained from wind-tunnel tests of an idealised condition in which
the excrescence was mounted on a flat plate with no pressure
gradient, and the application of such data to the real aircraft
situation is considered. Corrections are required for the effect of
pressure gradient and flow orientation. The pressure gradient
correction on a lifting surface is a magnification factor (although
it can be less than unity) and its estimation in incompressible
two-dimensional flow is discussed; its variation with the
boundary-layer parameters on an aerofoil is illustrated
graphically. The analysis is extended to compressible flow and
reference is made to the prediction methods of ESDU 87004, 91028
and 91029. The treatment of an excrescence only partially immersed
in the boundary layer is also considered, and recommendations are
made for the case of excrescences on non-lifting components. The
effect of flow orientation is more briefly discussed, and
suggestions are made for some situations, while the treatment of an
excrescence for which no specific data are available is also
considered. The significance of the excrescence drag penalty on
aircraft performance is discussed, and acceptable levels in current
good design practice are suggested. Reference is made to ESDU 93032
in which the excrescence drag of the wing of a subsonic transport
aircraft at the cruise condition is considered as a detailed set of
examples in which the data from a number of Data Items are
utilised.