Transient growth in the asymptotic suction boundary layer

Authors: Kurian, T., Fransson, J. H. M.
Document Type: Conference
Pubstate: Published
Journal: 60th Meeting of the APS Division of Fluid Dynamics, Nov 18–20, Salt Lake City (UT), USA. Abstract in Bull. Am. Phys. Soc.
Year: 2007


Recent experimental studies on roughness induced transient growth have shown that suboptimal perturbation theory may predict the evolution of energy in the streamwise direction. However there is a fundamental difference between the experimentally generated streaks using roughness elements and the ones arising from the theory. This is due to the complex interaction between the wake and the standing vortices, which depends on the ratio between the height of the roughness element (k) and the boundary layer thickness as well as the Reynolds number based on k. Knowledge in this area is sought after so that transition originating from transient growth may be predicted accurately. In the current experimental investigation we have performed a geometrical parameter analysis in order to study the transient energy growth behind a spanwise array of cylindrical roughness elements. We have chosen to work with the asymptotic suction boundary layer (ASBL), which has the advantage that we may change the boundary layer thickness and the Reynolds number independently. Five different heights of roughness elements were used along with three different free stream velocities. The applied pressure drop across the porous material gave a constant displacement thickness d = 1.45 mm. We will present the energy evolution of the individual modes triggered by the roughness array using spatial mode decomposition. Furthermore, the experimental results will be compared with suboptimal perturbation theory on the ASBL.