Characteristics of drag due to streamwise inhomogeneous roughness
Characteristics of drag due to streamwise inhomogeneous roughness
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DOI：
10.1016/j.oceaneng.2021.108632
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发表时间：
2021-02-06
影响因子：
5
通讯作者：
Ganapathisubramani, B.
中科院分区：
文献类型：
--
作者：
Suastika, I. K.;Hakim, M. L.;Ganapathisubramani, B.
由于流向不均匀粗糙度引起的表面摩擦特性是通过以简化的方式利用等效砂粒粗糙度高度k（s）的阶跃变化（记为P（k（s）= 81.25 μ m）、Q（k（s）= 325.00 μ m）和R（k（s）= 568.75 μ m））模拟来研究的。所选的k（s）值表示普通船体粗糙度，即，从轻微的粘液到大约小的钙质污垢。对流向长度为30、60、120和240 m的平板上由P、Q和R三种粗糙度组合形成的各种粗糙表面的摩擦特性进行了RANS模拟研究。粗糙度的三种组合形成均匀（PPP、QQQ或RRR）或非均匀（PQR、PRQ、QPR等）。粗糙壁湍流边界层流动粗糙度高度的阶跃变化导致局部表面摩擦系数以过冲或下冲的形式突然变化，随后是松弛，其中不均匀的局部表面摩擦缓慢地返回到均匀的局部表面摩擦。粗糙度的排列顺序对总表面摩擦力起着关键作用，其值按以下顺序增加：PQR < PRQ < QPR < QRP < RPQ < RQP。相似律对均匀粗糙面和非均匀粗糙面都成立。
Characteristics of the skin friction due to streamwise inhomogeneous roughness are investigated by modeling it in a simplified manner using step changes in equivalent sand grain roughness height k(s) denoted as P (k(s) = 81.25 mu m), Q (k(s) = 325.00 mu m) and R (k(s) = 568.75 mu m). The selected k(s) values represent the common ship-hull roughness, i.e., from light slime to about small calcareous fouling. RANS simulations are performed to study the friction characteristics of various rough surfaces formed by a trio-combination of P, Q and R roughnesses on flat plates with streamwise lengths of 30, 60, 120 and 240 m. The three combinations of roughnesses form either homogeneous (PPP, QQQ or RRR) or inhomogeneous (PQR, PRQ, QPR, etc.) rough walled turbulent boundary layer flow. A step change in roughness height results in a sudden change of the local skin friction coefficient in the form of overshoot or undershoot, followed by a relaxation where the inhomogeneous local skin friction is slowly returning to the homogeneous local one. The sequence of roughness arrangement in a streamwise inhomogeneous roughness pattern plays a key role in the resulting overall skin friction with value increasing in the following order: PQR < PRQ < QPR < QRP < RPQ < RQP. The similarity laws hold for both homogeneous and inhomogeneous rough surfaces.