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We characterize the turbulent flow, using direct numerical simulations (DNS), within a closed channel between two parallel walls with a canopy of constant areal density profile on the lower wall. The canopy is modelled using different formulations of the Forchheimer drag, and the characteristic properties of the turbulent flows are compared. In particular, we examine the influence of the added drag on the mean profiles of the flow and the balance equations of the turbulent kinetic energy. We find that the different formulations of the drag strongly affect the mean and the turbulent profiles close to the canopy. We also observe the changes in the local anisotropy of the turbulent flow in the presence of the canopy. We find that there is an equal transfer of energy from the streamwise component to both the transverse components outside the canopy by the pressure and velocity-gradient correlation; inside the canopy, this correlation removes energy from both the streamwise and the wall-normal fluctuations and injects into the spanwise component. As a result, the energy content of the spanwise fluctuations is comparable to that of the streamwise components inside the canopy. Inside the canopy, we observe that the turbulent transport of Reynolds stresses acts as an important source of turbulent kinetic energy. The pressure-fluctuation transport plays a significant role inside the canopy close to the wall and is comparable to turbulent transport.

The energy- and flux-budget (EFB) theory developed previously for atmospheric stably stratified turbulence is extended to the surface layer in atmospheric convective turbulence. This theory is based on budget equations for turbulent energies and fluxes in the Boussinesq approximation. In the lower part of the surface layer in the atmospheric convective boundary layer, the rate of turbulence production of the turbulent kinetic energy (TKE) caused by the surface shear is much larger than that caused by the buoyancy, which results in three-dimensional turbulence of very complex nature. In the upper part of the surface layer, the rate of turbulence production of TKE due to the shear is much smaller than that caused by the buoyancy, which causes unusual strongly anisotropic buoyancy-driven turbulence. Considering the applications of the obtained results to the atmospheric convective boundary-layer turbulence, the theoretical relationships potentially useful in modeling applications have been derived. The developed EFB theory allows us to obtain a smooth transition between a stably stratified turbulence to a convective turbulence. The EFB theory for the surface layer in a convective turbulence provides an analytical expression for the entire surface layer including the transition range between the lower and upper parts of the surface layer, and it allows us to determine the vertical profiles for all turbulent characteristics, including TKE, the intensity of turbulent potential temperature fluctuations, the vertical turbulent fluxes of momentum and buoyancy (proportional to potential temperature), the integral turbulence scale, the turbulence anisotropy, the turbulent Prandtl number, and the flux Richardson number. (C) 2022 Author(s).

Rotating turbulence is ubiquitous in nature. Previous works suggest that such turbulence could be described as an ensemble of interacting inertial waves across a wide range of length scales. For turbulence in macroscopic quantum condensates, the nature of the transition between the quasiclassical dynamics at large scales and the corresponding dynamics at small scales, where the quantization of vorticity is essential, remains an outstanding unresolved question. Here we expand the paradigm of wave-driven turbulence to rotating quantum fluids where the spectrum of waves extends to microscopic scales as Kelvin waves on quantized vortices. We excite inertial waves at the largest scale by periodic modulation of the angular velocity and observe dissipation-independent transfer of energy to smaller scales and the eventual onset of the elusive Kelvin-wave cascade at the lowest temperatures. We further find that energy is pumped to the system through a boundary layer distinct from the classical Ekman layer and support our observations with numerical simulations. Our experiments demonstrate a new regime of turbulent motion in quantum fluids where the role of vortex reconnections can be neglected, thus stripping the transition between the classical and the quantum regimes of turbulence down to its bare bones., Comment: 21 pages, 11 figures

To date experimental data concerning the impact of internal gravity waves on the intensity of turbulence in a stably stratified atmospheric boundary layer are scarce. The paper presents the results of the analysis of the degree of influence on turbulence characteristics of wave-like motions of two classes: Kelvin-Helmholtz billows (KHBs) and horizontally propagating buoyancy waves (BWs). For this purpose the data of long-term sodar measurements carried out in the suburban area of Moscow were used. The passage of 30% of KHB trains and 90% of BW trains was accompanied with increase of turbulent kinetic energy and both heat and momentum fluxes. The relative increase in values of these characteristics was higher during BWs passage. Nevertheless the magnitude of turbulence characteristics were similar for both IGWs classes. In general the difference between characteristics calculated in the presence and in the absence of wavelike motions was smaller than between those in strongly and weakly stable boundary layers.

We present a boundary condition scheme for the lattice Boltzmann method that has significantly improved stability for modeling turbulent flows while maintaining excellent parallel scalability. Simulations of a three-dimensional lid-driven cavity flow are found to be stable up to the unprecedented Reynolds number $\mathrm{Re}=5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ for this setup. Excellent agreement with energy balance equations, computational and experimental results are shown. We quantify rises in the production of turbulence and turbulent drag, and determine peak locations of turbulent production.