Localized drag modification in a laminar boundary layer subject to free-stream travelling waves via critical and Stokes layer interactions

• Published in: Journal of fluid mechanics Vol. 937
• Main Authors: Agarwal, T., Cukurel, B., Jacobi, I.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 25.04.2022
• Subjects: Boundary layer flow; Boundary layers; Experiments; Free flow; JFM Papers; Laminar boundary layer; Perturbation; Phase velocity; Reynolds number; Rivers; Skin friction; Streaming; Traveling waves; Velocity; Viscosity; Waves; boundary layer control; boundary layer structure; drag reduction
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2022.108

Perturbation of the laminar boundary layer by free-stream travelling waves was shown to produce highly-localized skin friction modification via steady streaming. The forced boundary layer flow was calculated numerically and studied as a function of the phase speed, frequency and amplitude of the perturbations. Upstream-travelling waves always produced negative streaming, whereas downstream-travelling waves produced positive or negative streaming that varied with forcing strength and streamwise location. The sign of the resultant streaming was explained in terms of the inclination of the induced velocity modes, which evolved spatially in response to the streamwise variation and overlap of the Stokes and critical layers.