Comments on Some Recent Calculations Relating to the Laminar Boundary Layer with Discontinuously Distributed Suction

Abstract

In References (1), (2), Dr. Lachmann develops a method for calculating the growth of the laminar boundary layer over an aerofoil surface with spanwise suction slots placed at intervals along the chord. For this form of control, the laminar flow develops normally from the downstream edge of a slot until it attains the critical Reynolds number (expressed in terms of either the displacement or momentum thickness) at which transition is imminent. The layer then encounters another slot which so thins and stabilises the part not removed by suction, that it is able to continue downstream in the laminar state.A new feature of the above investigation is the establishment of a second critical Reynolds number which provides an initial condition on the downstream side of a slot. Essentially it defines the minimum value of the displacement or momentum thickness for which, in relation to the local surface roughness, there is no danger of transition due to this form of disturbance.