Numerical investigation of effects of freestream turbulence on laminar-turbulent transition using an LES technique

*Vortex shedding from a circular cylinder; Spanwise vorticity contours of laminar flow around a circular cylinder.

*Number of Grid : 384*128

* Re (Reynolds Number) = 160

Sponsored by Korea Science and Engineering Foundation
Principal Investigator: Kyung-Soo Yang
Assistants: Jong-Yeon Hwang

In this study, effects of freestream turbulence on laminar-turbulent transition of separated shear layers are investigated by LES. The process in which freestream disturbances enter into shear layers and develop unstable waves is called 'receptivity',and it plays an important role in laminar-turbulent transition. With the advent of powerful supercomputers and numerical algorithms, the numerical solution of the full unsteady Navier-Stokes equations is becoming an integral tool for the study of the receptivity phenomena. One advantage of this technique is that one has complete control of the disturbance environment and is, therefore, able to isolate particular kinds of disturbances and study their individual effects. Until now, most research on receptivity has been devoted to boundary layers with simple types of disturbances, but little work has been done on receptivity problems of separated shear layers.In this investigation, two types of separated shear layers are considered. In one case, the location of a separation point is fixed by the geometry of a bluff body, and in the other case, determined by an adverse pressure gradient in the flow field such as a flow past a circular cylinder. In the latter case, the location of a separation point cannot be predicted apriori.