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.

我们使用直接数值模拟 (DNS) 在两个平行壁之间的封闭通道内表征湍流，下壁具有恒定面密度分布的顶篷。使用不同公式的 Forchheimer 阻力对冠层进行建模，并比较了湍流的特征特性。特别是，我们研究了附加阻力对流动平均剖面和湍动能平衡方程的影响。我们发现阻力的不同公式强烈影响靠近树冠的平均和湍流剖面。我们还观察了在树冠存在下湍流局部各向异性的变化。我们发现，通过压力和速度梯度相关性，能量从流向分量到冠层外的两个横向分量的转移是相等的；在冠层内部，这种相关性消除了流向和壁法向波动的能量，并注入了展向分量。因此，展向波动的能量含量与冠层内流向分量的能量含量相当。在冠层内部，我们观察到雷诺应力的湍流传输是湍流动能的重要来源。压力波动输运在靠近墙壁的冠层内起着重要作用，可与湍流输运相媲美。这种相关性消除了流向和壁法向波动的能量，并注入了展向分量。因此，展向波动的能量含量与冠层内流向分量的能量含量相当。在冠层内部，我们观察到雷诺应力的湍流传输是湍流动能的重要来源。压力波动输运在靠近墙壁的冠层内起着重要作用，可与湍流输运相媲美。这种相关性消除了流向和壁法向波动的能量，并注入了展向分量。因此，展向波动的能量含量与冠层内流向分量的能量含量相当。在冠层内部，我们观察到雷诺应力的湍流传输是湍流动能的重要来源。压力波动输运在靠近墙壁的冠层内起着重要作用，可与湍流输运相媲美。我们观察到雷诺应力的湍流传输是湍流动能的重要来源。压力波动输运在靠近墙壁的冠层内起着重要作用，可与湍流输运相媲美。我们观察到雷诺应力的湍流传输是湍流动能的重要来源。压力波动输运在靠近墙壁的冠层内起着重要作用，可与湍流输运相媲美。