论文标题
粗糙度子层中的湍流特征在跨度均匀的横杆上
Turbulent characteristics within roughness sublayer over spanwise homogeneous transversal bars
论文作者
论文摘要
最近，已经研究了剪切层内的湍流特征，建筑物，沙丘中。 Kevin-Helmholtz不稳定性触发了发夹涡流脱落，已被广泛结论为混合层类比的“签名”。但是，复杂的粗糙度类型使观察到的湍流发展进步的实践变得复杂。为了简化这一点，在这项工作中采用了Spanwise均匀的粗糙度，以捕获不同流的粗糙度元件距离下的流流相位。流式连续的对象距离$λ_x$用于显示粗糙度元素距离。从情况1到案例4观察到了从动荡的通道流到树冠流的过渡趋势。但是，当$λ_x/h <1.0 $（随着连续的距离降低）的降低时，证据表明湍流从canopy流动从案例4到案例4到案例6。瞬时结果验证了湍流混合的湍流混合和减少的湍流式湍流和减少的湍流。附件的假设（aeh）在$λ_x/h <1.0 $案例中有效。同时，雷诺平均流量结果表明，当$λ_x$ $λ_x/h <1.0 $ $λ_x$继续减少时，粗糙度剪切“曲线”的有效性将降低。在元素上取样点上三个波动变量的概率密度函数（PDF）表明，“增加”趋势降低了间距对上部区域的趋势，其中2和3中最大效应在旋转的结构可视化中出现，也表明了在粗糙的siplysective directive directive directive directive directive directive directive directive syromblesive systective distrance systective systrys systry syst ryst ryst ryst rystective。最后，瞬时结果表明壁法线动量通量转运和湍流旋转结构与元素间距相关。
Turbulent characteristics within shear layer have been studied, recently, within vegetative canopy, buildings, dunes. Kevin-Helmholtz instability triggered hairpin vortex shedding has been widely concluded as the "signature" of mixing layer analogy. However, convoluted roughness types complicate the observing practice of turbulent evolving progress. To simplify that, spanwise homogeneous roughness has been adopted in this work to capture the streamwise flow alternations under different streamwise roughness element distances. Streamwise successive object distance $λ_x$ is used to show the roughness element distance. The transitional trends from turbulent channel flow to canopy flow have been observed from Case 1 to Case 4. However, when $λ_x/h<1.0$, as successive distance decreases, the evidences indicate turbulent flow is transferring from canopy flow into channel flow from Case 4 to Case 6. Instantaneous results verifies the enhancement of turbulent mixing and decreasing turbulent coherency. The attached-eddy hypothesis (AEH) becomes valid in $λ_x/h<1.0$ Cases. Meanwhile, Reynolds-averaged flow results show the roughness shear "curve" effectiveness will decrease when $λ_x$ keeps decreasing after $λ_x/h<1.0$. The probability density function (PDF) of three fluctuating variables on a sampling point over element display the "increasing-decreasing" trend of decreasing spacing effect on upper region, wherein the maximal effect emerges in Case 2 and 3. And the swirling structural visualizations also demonstrate the progress of turbulent structure changing in roughness sublayer at different streamwise successive object distances. Finally, the instantaneous results show wall-normal momentum flux transports and turbulence swirling structures are correlated to the element spacing.
