A Study on the Validation for the Control Methodology on Outer Structures in a Laminar Boundary Layer

Kang, Y.D. and Koo, B., 2023. A study on the validation for the control methodology on outer structures in a laminar boundary layer. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 528-532. Charlotte (North Carolina), ISSN 0749-0208. In this paper, the effectiveness of flow control in the outer layer of the boundary layer destroying the hairpin vortices was visualized in a water channel. Here, hairpin vortices were generated beneath the test plate in a laminar boundary layer by a solenoid pinch valve controlled by a signal generator. The result of flow visualization demonstrated that a jet located outside of a boundary layer can destroy the neck of hairpin vortex, thereby disconnecting the link between the head and legs of the hairpin vortex. Detached from the head, the legs of the hairpin cannot be stretched in the streamwise direction anymore, leading to a reduction in the circulation of streamwise vortices and associated velocity fluctuations in the near-wall region. The data from hot-film were also reconstructed to confirm this procedure of real flow field. Both results showed that the legs of the control case were weakened compared to the uncontrolled case up to 15% in u-component velocity.