Near-wall similarity between velocity and scalar fluctuations in a turbulent channel flow

The degree of near-wall similarity between velocity and scalar fields is examined with the use of direct numerical simulation databases for a smooth wall turbulent channel flow with passive scalar transport. Particular attention is given to correlations between velocity and scalar fluctuations as well as those between their derivatives. In the vicinity of the wall, the largest correlation is between the wall-normal vorticity fluctuation and the spanwise scalar derivative, mainly due to the significantly reduced effect of the fluctuating pressure gradient. Other correlations peak at locations where the effect of the pressure fluctuation is smallest. The near-wall similarity between momentum and thermal streaks is not perfect because momentum streaks are often intensified or weakened by the fluctuating pressure gradient.