Coherent structures and secondary motions in open duct flow

This thesis investigates the turbulent secondary motions observed in the straight open and closed duct flow with a rectangular cross-section. The turbulent flow was simulated by means of direct numerical simulations, which resolve all the relevant spatio-temporal scales. Reynolds number and geometrical aspect ratio dependences of the mean secondary flow were investigated with a spacial emphasis upon coherent structure analysis

Direct numerical simulation of turbulent open channel flow: Streamwise turbulence intensity scaling and its relation to large-scale coherent motions

We conducted direct numerical simulations of turbulent open channel flow (OCF) and closed channel flow (CCF) of friction Reynolds numbers up to $\mathrm{Re}_\tau \approx 900$ in large computational domains up to $L_x\times L_z=12\pi h \times 4\pi h$ to analyse the Reynolds number scaling of turbulence intensities. Unlike CCF, our data suggests that the streamwise turbulence intensity in OCF scales with the bulk velocity for $\mathrm{Re}_\tau \gtrsim 400$. The additional streamwise kinetic energy in OCF with respect to CCF is provided by larger and more intense very-large-scale motions in the former type of flow. Therefore, compared to CCF, larger computational domains of $L_x\times L_z=12\pi h\times 4\pi h$ are required to faithfully capture very-large-scale motions in OCF -- and observe the reported scaling. OCF and CCF turbulence statistics data sets are available at https://doi.org/10.4121/88678f02-2a34-4452-8534-6361fc34d06b .Comment: Submitted to Progress in Turbulence X: Proceedings of the iTi Conference on Turbulence 2023. Data: https://doi.org/10.4121/88678f02-2a34-4452-8534-6361fc34d06

Coherent structures and secondary motions in open duct flow

This book addresses the turbulence-driven mean secondary motions in straight open duct flow with rectangular cross-section. Despite its weak intensity, the secondary flow influences the primary velocity distribution significantly. Coherent structure analysis showed that the secondary flow is the statistical footprint of quasi-streamwise vortices, and the unique mean flow pattern is a consequence of a vortex sorting mechanism that is only effective in the vicinity of free surface

A Scanning Tunneling Microscopy Study of Vanadium Oxide

Atomic resolution images of the (010) surface of a divanadiun pentoxide (V2O5) single crystal were successfully obtained by the use of a scanning tunneling microscope (STM). The images of the filled states at sample bias voltage, Vs = -2 V and the empty states at Vs = +2 V correspond to oxygen and vanadium ions, respectively. As for the vanadium ion sites, an additional peak of the electronic states at the conduction band edge due to the defects of vanadyl oxygen ions was found in the normalized conductance spectrum through the tunneling spectroscopy (TS) measurement

Spacial and temporal variations of water characteristics in the Japan Sea bottom layer

The Japan Sea is an almost landlocked marginal sea. We measured profiles of CTD potential temperature at 9 stations in the southeastern Japan Sea to clarify the characteristics of the abyssal circulation in the Sea. It was shown that the results were closely correlated with the topography of the Japan Sea which is characterized by a rise in the center of the Sea (Yamato Rise) and three basins (Japan, Yamato and Tsushima Basins) around the Yamato Rise.At each station in the Basins (6 stations), we observed the bottom layer, a layer of constant potential temperature (within ±0.0005°C) below 2,000–2,500 m depth to the bottom. Dissolved oxygen is also constant (within ±1 μmol kg−1) in the bottom layer. The bottom layer of the Japan Basin (northern basin) is shown to have lower potential temperature by 0.012°C and higher dissolved oxygen content by 5 μmol kg−1 than that of the Yamato Basin (southern basin). There is no bottom layer at the remaining 3 stations located in the passage between the Japan Basin and the Yamato Basin, possibly due to the topographic effect of the Yamato Rise which restricts the exchange and mixing of the two Basin bottom waters.By comparing the vertical profiles of dissolved oxygen in 1969, 1977, 1979 and 1984 in the Japan and the Yamato Basins, it was found that in both Basins the thickness of the bottom layer decreased by 400 m between 1969 and 1984, and the bottom oxygen concentration was also decreased by 5–7 μmol kg−1 between 1977 and 1984. These temporal variations were interpreted to be transient, probably caused by the recent reduction or cessation of new bottom water formation in the northern Japan Sea

Enhanced anti-HIV-1 activity of CC-chemokine LD78β, a non-allelic variant of MIP-1α/LD78α

AbstractWe compared the anti-HIV-1 activity of CC-chemokine LD78β with that of MIP-1α, another CC-chemokine which shows 94% sequence homology with LD78β. Despite its close similarity to MIP-1α, the anti-HIV-1 activity of LD78β appeared to be nearly 10 times higher than that of MIP-1α. Mutagenesis of MIP-1α showed that the N-terminal additional tetrapeptide, which was present in LD78β and absent in MIP-1α, is responsible for enhanced anti-HIV-1 activity. The N-terminal structure-function relationship of LD78β described here will be of value in understanding the chemokine-receptor interactions and designing anti-HIV-1 compounds based on LD78β