  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 \cite{narasimha1973relaminarization} proposed a
quasi-laminar 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
$5\times 10^3$ 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.
