Numerical study of turbulent boundary layers over cubic roughness arrays

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

Graph reduction machine using activation record

학위논문(석사) - 한국과학기술원 : 전산학과, 1994.2, [ iii, 52 p. ]한국과학기술원 : 전산학과

재귀적 자료구조에 대한 함수형 프로그램의 병렬화를 위한 분석적 방법

학위논문(박사) - 한국과학기술원 : 전산학전공, 2000.8, [ vii, 135 p. ]한국과학기술원 : 전산학전공

Direct numerical simulation of a 30R long turbulent pipe flow at Re τ = 3008

A direct numerical simulation of a turbulent pipe  ow at a high Reynolds number of Reτ = 3008 over a long axial domain length (30R) was performed. The stream- wise mean velocity followed the power law in the overlap region (y+ = 90–300; y/R = 0.03–0.1) based on the power law indicator function. The scale separation of the Reynolds shear stresses into two components of small- and large-scale motions (LSMs) revealed that the LSMs in the outer region played an important role in constructing the constant-stress layer and the mean velocity. In the pre-multiplied energy spectra of the streamwise velocity  uctuations, the bimodal distribution was observed at both short and long wavelengths. The kx−1 region associated with the attached eddies appeared in λx/R = 2–5 and λx/y = 18–160 at y+ = 90–300, where the power law was established in the same region. The kz−1 region also appeared in λz/R = 0.3–0.6 at y+ = 3 and 150. Linear growth of small-scale energy to large-scale energy induced the kx−1 region at high Reynolds numbers, resulting in a large pop- ulation of the LSMs. This result supported the origin of very-large-scale motions in the pseudo-streamwise alignment of the LSMs. In the pre-multiplied energy spectra of the Reynolds shear stress, the bimodal distribution was observed without the kx−1 region