Direct Determination of the Onset of Transition to Turbulence in Flow Passages

Abstract

Easily applied methods are proposed, based on tests with air and water, for direct determination of the onset of transition in flow passages using static and dynamic wall pressure data. With increasing Reynolds number from laminar flow, the characteristic feature of transition is the change from steady to oscillating pressure readings. It is established that the power spectral density (psd) representations exhibit a distinctive change in profile at transition. Further, it is shown that the root-mean-square (rms) values of the wall pressure fluctuations rise sharply at transition. The critical Reynolds numbers recorded via the change from steady to unsteady pressure readings are almost the same as those deduced from the psd and rms pressure data or from the familiar friction factor-Reynolds number plots.