이재화 교수

Direct numerical simulation of a turbulent boundary layer was performed to investigate the spatially coherent structures associated with very-large-scale motions (VLSMs). The Reynolds number was varied in the range Re θ = 570–2560. The main simulation was conducted by using a computational box greater than 50δ o in the streamwise domain, where δ o is the boundary layer thickness at the inlet, and inflow data was obtained from a separate inflow simulation based on Lund's method. Inspection of the

Direct numerical simulation (DNS) of a spatially developing turbulent boundary layer (TBL) over a wall roughened with regularly arrayed cubes was performed to investigate the effects of three-dimensional (3-D) surface elements on the properties of the TBL. The cubes were staggered in the downstream direction and periodically arranged in the streamwise and spanwise directions with pitches of p x / k = 8 and p z / k = 2, where p x and p z are the streamwise and spanwise spacings of the cubes and k

It is known that large-scale streamwise velocity-fluctuating structures ( $u^{\prime }$ ) are frequently observed in the log region of a zero pressure gradient turbulent boundary layer, and that these motions significantly influence near-wall small-scale $u^{\prime }$ -structures by modulating the amplitude (Hutchins & Marusic, J. Fluid Mech. , vol. 579, 2007, pp. 1–28; Mathis et al. , J. Fluid Mech. , vol. 628, 2009, pp. 311–337). In the present study, we provide evidence that the spatial o

A direct numerical simulation of a fully developed turbulent pipe flow was performed to investigate the similarities and differences of very-large-scale motions (VLSMs) to those of turbulent boundary layer (TBL) flows. The Reynolds number was set to ReD = 35 000, and the computational domain was 30 pipe radii in length. Inspection of instantaneous fields, streamwise two-point correlations, and population trends of the momentum regions showed that the streamwise length of the structures in the pi

Direct numerical simulations (DNSs) of spatially developing turbulent boundary layers (TBLs) over two-dimensional (2D) rod-roughened walls and three-dimensional (3D) cube-roughened walls were performed to investigate the effects of the streamwise spacing of roughness elements on the properties of the TBLs. The inspection of the Reynolds stresses showed that except for the 2D rough walls with px /k = 2 and 3, the effects of the roughness on the 2D and 3D rough walls extend to the outer layer and

We examine the origin of very-large-scale motions (VLSMs) in fully developed turbulent pipe flow at friction Reynolds number, $\mathit{Re}_{\unicode[STIX]{x1D70F}}=934$ , using data from a direct numerical simulation. The VLSMs and the packet-like large-scale motions (LSMs) found in this study are very similar to those found in earlier studies. Three-dimensional time-evolving instantaneous fields show that one component of the process leading to the large streamwise length of VLSMs is the concat

Numerical simulations using the immersed boundary method were performed to investigate the flapping dynamics of a flexible flag in a uniform flow. The relevant parameters related to the problem are the mass ratio , the bending rigidity of the flag and the Reynolds number , where ρ1 denotes the line density difference between the flag and the surrounding fluid. By varying the parameters over the ranges 0 ≦̸ ρ ≦̸ 10 and 10−4 ≦̸ KB ≦̸ 10–1 for Re = 200, we identified three dynamical states: the str

Abstract