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.
Highlights
For many years, the turbulence in the near-wall region of wall-bounded flows was considered to be characterized by a selfsustaining near-wall cycle in which turbulence structures propagate and are sustained without the need for external triggers.1,2 Hamilton et al.3 conducted a numerical simulation of plane Couette flow at low Reynolds number and concluded that there existed a process of cyclic regeneration of near-wall turbulence structures
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 details of the decoupling procedure based on this approach are documented in Mathis et al.,28 who used a one-point correlation coefficient to quantify the amplitude modulation imparted by the outer layer largescale motions on the near-wall small-scale motions
Summary
The turbulence in the near-wall region of wall-bounded flows was considered to be characterized by a selfsustaining near-wall cycle in which turbulence structures propagate and are sustained without the need for external triggers. Hamilton et al. conducted a numerical simulation of plane Couette flow at low Reynolds number and concluded that there existed a process of cyclic regeneration of near-wall turbulence structures. Scitation.org/journal/adv collected data from many previous studies and suggested that motions at each relevant scale can sustain themselves under some conditions This autonomous viewpoint is based largely on numerical simulations or experiments at low or moderate Reynolds number. Mathis et al. proposed a Hilbert transform method to quantify the degree of amplitude modulation that is exerted by the large-scale motions on the near-wall fluctuations Even this method is somewhat controversial, while at high Reynolds number other methods produce results that are consistent with it. The highest Reynolds numbers in the published papers were 1.01 × 105 in the laboratory and 2 × 105 in channel flow with large eddy simulation; data at higher Reynolds number were obtained from field measurements, but observations were lacking at lower and higher altitudes This makes it extremely difficult to study the amplitude modulation phenomenon.
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