RIBLET DRAG REDUCTION AND THE EFFECT OF BULK FLUID ROTATION IN A FULLY TURBULENT TAYLOR-COUETTE FLOW

Low drag surfaces are often desired in many industries with applications in open and closed channel flows, such as ship hulls and pipe flows. Drag reduction is a phenomenon that can have substantial energy savings, resulting in ecological and economical benefits. We use a Taylor-Couette facility as experimental instrument to measure the drag change of turbulent wall-bounded flows above modified surfaces [2, 4]. In this manuscript, we apply a riblet surface to observe the drag change compared to a smooth reference surface. Riblets are small surface protrusions which are aligned in the flow direction. They reduce drag by disturbing the spanwise motion of the flow at the surface and thereby moving turbulent vortices further away from the wall [1]. The turbulent flow is investigated via tomo-PIV measurements, which identify the change in flow structures and velocity profile of the flow between two counter-rotating cylinders.