An indirect criterion for the laminar to turbulent flow transition in shear-driven annular liquid films

• The near wall structure in shear-driven annular liquid films is resolved.
• The limit between the laminar sublayer and the buffer layer corresponds to ≈9 wall units.
• The limit between the buffer layer and the turbulent layer corresponds to ≈40 wall units.
• New laminar to turbulent flow transition criterion for annular liquid films.
• New prediction method for the average liquid film thickness.

An indirect method to identify the laminar to turbulent flow transition in shear-driven annular liquid films has been developed and used, together with literature measurements of the velocity profile, to approximately resolve the near wall structure in shear-driven annular liquid films. The limits between the laminar sublayer and the buffer layer and between the buffer layer and the turbulent layer have been found to correspond to about 9 and 40 wall units, respectively, which are higher than the corresponding limits of 5 and 30 wall units typical of single-phase boundary layers, thus indicating a weaker turbulence intensity in shear-driven annular liquid films with respect to single-phase wall-bounded flows. Additionally, a simple laminar to turbulent flow transition criterion and a prediction method for the average liquid film thickness have been developed for evaporation and condensation applications.

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