3 차원 입방형 표면조도를 갖는 난류경계층에 대한 수치적 연구

Abstract

Direct numerical simulations of turbulent boundary layers over the cube-roughened walls were performed with varying spanwise extent. Recent work by Lee et al. (2011) showed that the inner layer statistics are influenced by the streamwise pitch over the 3-D square-edged roughness and these have the maximum at px/k=4 with pz/k=2. However, the present simulations showed that the surface drag, including form drag and roughness function, etc., is also affected by spanwise spacing and the maximum contribution occurs at pz/k=3 with px/k=3 which has the roughness density, 0.111. This result might indicate that the main parameter for the wall friction is roughness density rather than roughness configurations. In addition, it was shown that outer peaks of the Reynolds stresses are increased with increasing spanwise length, implying stronger inner and outer layer interactions at larger pz/k, which is consistent with those of streamwise spacing. This signifies streamwise and spanwise spacing as the principal variable in the outer layer.