A historical review of work at TU Delft on the e N method for transition prediction is presented. The method is shown to be applicable to boundary layers with pressure gradient, suction and separation. Some applications to airfoil design will be discussed. An explanation will be given of the reason for the success of this linear theory to "predict" the position of transition which itself is a highly non-linear phenomenon. It will also be explained why the velocity profile shape factor H is a suitable parameter to characterize stability diagrams for flows with and without suction. Finally a new database method will be presented that is based on the observation that many stability diagrams show a remarkable similarity when properly scaled and shifted. The discussion will be restricted to two-dimensional incompressible flow.

SI.l!l'ID'illY'!his paper gives a review of research at Delft Uni versi ty of Technology on laminar separation b.Il±>les. Results of flow visualisation studies are used to define an empirical relation for the angle ~ at which the se~ation streamline leaves the wall. The "e-to-the-n" transition predictIon method is extended to separated flows. A universal description of the laminar part of the b.Il±>le is proposed, resulting in a simple b.Il±>le prediction method.

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This paper presents a holographic interferometer technique for measuring transparent (2-D or quasi 2-D) density fields. To be able to study the realization of such a field at a certain moment of time, the field is "frozen" on a holographic plate. During the reconstruction of the density field from the hologram the length of the path traversed by the reconstruction beam is diminished in equal steps by applying a computer controlled voltage to a piezo-electric crystal that translates a mirror. Four phase-stepped interferograms resulting from this pathlength variation are digitized and serve as input to an algorithm for computing the phase surface. The method is illustrated by measuring the basically 2-D density field existing around a heated horizontal cylinder in free convection.