Relaminarization on Swept Leading Edges Under High-LiftConditions

Abstract

Detailed experiments were made to gain an improved understanding of relaminarization on swept wings under high-lift conditions. Two swept wings with different airfoil sections and flaps were tested, and measurements were made consisting of surface-pressure distributions13; and wall shear-stress fluctuations in the leading-edge zone. Measurements were made at a chord Reynolds number of 1.3 x 106 with wing-sweep angles of 45 and 60 deg and model incidence varied in the range of 3 to 18 deg in discrete steps. Following the attachment-line transition, the turbulent boundary layer relaminarized under certain13; conditions due to the acceleration around the wing's leading edge. Broad features of relaminarization and subsequent retransition are discussed based on wall shear-stressfluctuation data. The present dataset shows that relaminarization is likely if the maximum value of13; the acceleration parameter K, (evaluated along the external inviscid streamline) is greater than about 3 x 10-6, in agreement with earlier findings. Much higher maximum values of IC, result in significant reduction of intermittency during relaminarization. After relaminarization, the boundary layer retransitions across a separation bubble. Characteristics of the post relaminarization separation bubbles are shown to be similar to those of bubbles occurring in more pristine13; laminar boundary layers.