Inspection of the dynamic properties of laminar separation bubbles: free-stream turbulence intensity effects for different Reynolds numbers

Effects of free-stream turbulence intensity on laminar separation bubbles

“…These results indicate that changes in the location of mean separation in response to changes in bubble size may be dependent on the flow geometry as well as the level of FSTI. In the work of Simoni et al [38], a doubling of the Reynolds number (for constant FSTI) also results in no significant change in the location of mean separation, which is in contradiction to the well established upstream shift shown to exist over airfoils for increasing chord Reynolds numbers, e.g., Ref. [10].…”

“…At moderately increased levels of FSTI (less than approximately 1%), the transition process in the separated shear layer is promoted, with transition occuring further upstream [9,16,38,138,139]. The results from Lamballais et al [139] show that earlier shear layer breakdown and mean reattachment is observed for increases in the level of FSTI from 0% to 0.1% and 1%, but the transition process remains qualitatively similar.…”

“…Researchers have also studied the effects of FSTI on separation bubbles induced on flat plates [37,38]. Using planar PIV, Simoni et al [38] showed that the length of formed separation bubbles decreases with increasing FSTI as a result of an upstream shift in mean reattachment, with no significant change in the location of mean separation.…”

“…Using planar PIV, Simoni et al [38] showed that the length of formed separation bubbles decreases with increasing FSTI as a result of an upstream shift in mean reattachment, with no significant change in the location of mean separation. Using DNS, McAuliffe and Yaras [16] found that the location of mean separation shifted downstream slightly while there was a more significant upstream shift in the location of mean reattachment.…”

“…While some investigations have looked at the effects of free-stream turbulence intensity on separation bubble topology [9,34,38] and airfoil performance [28,39], its effects on the transition process in the separated shear layer remain to be fully addressed. In addition, studies measuring the effects of increased free-stream turbulence intensity on airfoil lift and formed laminar separation bubbles simultaneously are limited, and thus any relationship has yet to be fully addressed.…”