On the streamwise and normal vortices forming on plates with spanwise periodic cambering

Abstract

Three-dimensional measurements of the flow field over rigid plates with periodic cambering in the spanwise direction were performed. Two plates of an aspect ratio of 5 with 5 and 9 periodic cells were used, and measurements were performed at a Reynolds number of 28,000 and three angles of attack. Previous research showed that organized vortices form in the valleys between the periodic cells, and that these vortices contribute to slight enhancement of lift and reduction in drag. In this investigation, the details of these vortices are examined and compared at three different flow fields including: 1) short separation bubble, 2) long separation bubble and 3) fully separated flow. The formation of these primary vortices is observed in all cases. The formation of these vortices is influenced by the interaction between the periodic cambering, and the thickness and strength of the backflow. This interaction becomes strongest when a long separation bubble forms resulting in larger vortices in size and magnitude. The instantaneous flow field shows that the primary vortices form most of the time, while they move in the spanwise direction and breakdown in the streamwise direction at other instances of time. In addition to the primary vortices, smaller vortices also form in the vicinity of the primary vortices. Proper Orthogonal Decomposition results indicate that reconstructing the flow field with different number of modes isolates the primary vortices from the smaller scale vortices.