The effect of compressibility on the primary global instability of unforced laminar separation bubbles

• Published in: Journal of the Brazilian Society of Mechanical Sciences and Engineering Vol. 41; no. 12; pp. 1 - 10
• Main Authors: Gennaro, E. M., Souza, B. D. P., Rodríguez, D.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.12.2019; Springer Nature B.V
• Subjects: Acceleration; Boundary layers; Bubbles; Compressibility effects; Computational fluid dynamics; Computer simulation; Deceleration; Dynamic stability; Engineering; Flow stability; Fluid flow; Incompressible flow; Mathematical models; Mechanical Engineering; Periodic structures; Plates (structural members); Review; Separation; Stability analysis; Global instability; Laminar separation bubbles; Compressible flow; Boundary layers
• ISSN: 1678-5878; 1806-3691
• DOI: 10.1007/s40430-019-2063-6

Laminar separation bubbles present a three-dimensional self-excited instability mechanism which leads to the appearance of spanwise-periodic structures. In incompressible flow, this mechanism was found to become active at conditions in which wave-like, two-dimensional perturbations are only convectively unstable. In the absence of continuous external excitation, the three-dimensional instability is expected to dominate the flow dynamics and initiate the laminar-turbulent transition. This work extends previous analyses by incorporating the effect of compressibility at subsonic conditions. Two-dimensional numerical simulations of a flat-plate boundary layer with a prescribed free-stream deceleration and acceleration are carried out to obtain a set of model laminar separation bubbles. A linear stability analysis is applied then, to study the influence of Reynolds and Mach numbers on the three-dimensional instability.