Transitional Phenomena on an Elliptic Profile

Abstract

Intermittency and turbulent spots were experimentally studied on an elliptic profile with 16% relative thickness at two moderate chord Reynolds numbers. The measurements were performed on a two-dimensional model in the Large Water Tunnel Braunschweig. A temperature-sensitive paint enabled the global, non-intrusive, time-resolved determination of the surface temperature maps, and thus the study of the transitional phenomena. Two different adverse pressure gradients, as measured by pressure taps, were implemented by changing the profile angle-of-attack. With a weaker pressure gradient at a Reynolds number of 5.0 × 105 , large variations in the transition front were observed in space and time via temperature-sensitive paint; moreover, the spatial and temporal development of an isolated turbu- lent spot was evaluated from the temperature-sensitive paint data. A reduction of the spanwise, long-wavelength variations of the transition front was observed for a stronger adverse pressure gradient, but turbulent spots were still identified. In this pressure gradient case, marked intermittent events and streamwise oscillations were observed in the transition region at Reynolds numbers of 2.5 × 105 and 5.0 × 105 , respectively.