An Assessment of the Two-Layer Quasi-Laminar Theory of Relaminarization Through Recent High-Re Accelerated Turbulent Boundary Layer Experiments

Abstract

The phenomenon of relaminarization is observed in many flow situations, including that of an initially turbulent boundary layer subjected to strong favourable pressure gradients. Available turbulence models have hitherto been unsuccessful in correctly predicting boundary layer parameters for such flows. Narasimha and Sreenivasan [1] proposed a quasilaminar theory (QLT) based on a two-layer model to explain the later stages of relaminarization. This theory showed good agreement with the experimental data available, which at the time was at relatively low Re. QLT, therefore, could not be validated at high Re.Some of the more recent experiments report for the first time comprehensive studies of a relaminarizing flow at relatively high Reynolds numbers (of order 5 × 10 3 in momentum thickness), where all the boundary layer quantities of interest are measured. In the present work, the two-layer model is revisited for these relaminarizing flows with an improved code in which the inner-layer equations for quasi-laminar theory have been solved exactly. It is shown that even for high-Re flows with high acceleration, QLT provides a much superior match with the experimental results than the standard turbulent boundary layer codes. This agreement can be seen as strong support for QLT, which therefore has the potential to be used in RANS simulations along with turbulence models.

Local gas transfer rate through the free surface in spatially accelerated open-channel turbulence

“…They provided the mean velocity profile and turbulent statistics and obtained universal properties via a proper scaling without a Reynolds number dependency. Ranjan and Narasimha 40 Figure 6 shows the streamwise variations in the mean surface velocity normalized by the entrance velocity, Us/Us(x = 0). The present results were obtained from the PIV measurements.…”

“…This physical phenomenon is called relaminarization. Relaminarization in duct flow is observed due to several physical causes, 40,49 including turbulent dissipation due to viscosity and turbulent energy consumption due to the external forces.…”

Relaminarization effects in hypersonic flow on a three-dimensional expansion–compression geometry

“…A boundary layer encountering a stronger expansion is expected to recover over an even longer streamwise distance. The two-layered structure of such relaminarizing boundary layers poses modelling challenges to the typical design tools that employ equilibrium turbulence models (Rumsey & Spalart 2009;Ranjan & Narasimha 2017;Nicholson et al 2021).…”