Laminar-Turbulent-Laminar Transition Cycles

摘要

Recent experimental work in the leading edge region of a 60 deg-swept wing at an angle of attack of 18 deg shows three distinct minima within the first 10 percent of the chord in the rms value of the signal from surface hot film gauges and in an intermittency coefficient. Qualitatively similar but weaker variations are seen at other high angles of attack and on other wings tested in the experiments. Based on an analysis of the variation of pressure gradient, curvature and Reynolds number in these flows, it is proposed that the most direct interpretation of the observations is that there is a sequence of transitions in the flow, from laminar to turbulent, reverting towards laminar, back again towards turbulent etc. In the case mentioned six such transitions, not all of them complete, can be identified. Such 'transition cycles* may account for the problems encountered in scaling maximum lift coefficient from tunnel to flight Reynolds number.