FLOW ABOUND TWO-DIMENSIONAL ROUGHNESS ELEMENTS

Flow around two-dimensional roughness elements in the form of rectangular blocks has been analyzed for reynolds number 0 ≤Re≤40 and blocks of aspect ratio 0.01 ≤W/h≤∞. A very good agreement exists between numerical and experimental results. The size of the upstream separation zone weakly depends on the length of the block but decreases rapidly with an increase of the Reynolds number. In contrast, the length of the downstream separation zone increases almost linearly as Re increases. While this length depends weakly on the aspect ratio of the block, the velocity magnitude inside the separation zone considerably increases with a decrease of the length of the block. The coupling between the upstream and downstream separation zones rapidly disappears when W/h increases and both zones can be considered independent and identical to those at the upstream and downstream facing steps with W/h≥6.