Numerical study of amplitude modulation in the atmospheric boundary layer at very high Reynolds number

Abstract

Wall model large eddy simulations (WMLES) are carried out to investigate the amplitude modulation exerted on near-wall small-scale motions by outer layer large-scale motions in the atmospheric boundary layer at high Reynolds number O(106-107). The properties of the mean and fluctuating velocities show good agreement with those found in previous studies. Furthermore, the positions at which there is no amplitude modulation found in the present study are consistent with those found in previous studies. A new phenomenon is observed, namely, that the value of the negative maximum correlation at high Reynolds number is smaller than that at low and moderate Reynolds number. Further investigation shows that the negative maximum correlation decreases with increasing Reynolds number, which could be explained by intermittency effects. There is good agreement of the correlation for different values of the Reynolds number when scaled with outer variables, which confirms that the large boundary-layer-height-scaled events that inhabit the logarithmic region are the source of amplitude modulation. This is confirmed by the locations of other characteristic points, which are independent of Reynolds number. In contrast, when scaled with inner variables, these characteristic points have a strong linear dependence on Reynolds number. Furthermore, the reversal in sign of the correlation corresponds to the crossover points of small-scale turbulent intensity and the local peak in the energy distribution, which gives the first and secondary crossover points a specific physical meaning. Finally, we provide an overview of the energy distribution, which gives an intuitive view of the outer peak energy site.