Turbulent Structure in Steep Open-Channel Flows

Velocity measurement with a fiber-optic laser-Doppler anemometer were conducted in steep open-channel flows over smooth and incompletely rough beds. The channel slopes were changed between 1/500 and 1/25 by steps, and as a result, the Froude number changed from 0.5 to 3. The law of the wall and the distributions of turbulence intensity were examined in more detail. The von Kármán constant κ in the log law was verified to be unversally equal to 0.41. On the other hand, the integral constant A in the log law coincided with the usual value of 5.29 in subcritical flows, whereas it decreased with an increase of the bed slope in supercritical flows. This decrease of A was explained by a decrease of the damping factor B in the van Driest's mixing-length formula. The decrease of B was well correlated with an increase of the friction velocity and the roughness. The streamwise turbulence intensity became smaller in the near-wall region than the semi-empirical universal formula, as the friction velocity became larger

Evaluation of bed shear stress from velocity measurements in gravel-bed river with local non-uniformity

River hydrodynamicsTurbulent open channel flow and transport phenomen

Flow Structure and Sediment Trasport around Groynes in Compound Open Channels

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Turbulence Measurements in Compound Open Channels

An investigation on a three-dimensional ( 3 -D) turbulent structure including turbulence-driven secondary currents in compound open-channel flows is a very important topic in hydraulic and river engineerings, as well as in fluid mechanics. In this study, accurate measurements in fully-developed compound open-channel flows were conducted by making use of a filder-optic laser Doppler anemometer (FLDA). Secondary velocities could be measured very accurately with the present 3-D measurement system. The characteristics peculiar to compound open channel flows are recognized in a junction region between the main channel and the flood plain, whereas the characteristics in rectangular open channel flows are observed in a region near the side wall of the main channel. Strong inclined secondary currents, which are associated with a pair of longitudinal vortices, are generated in a junction region between the main channel and the flood plain. The primary mean velocity filed is directly influenced by these secondary currents. Turbulence intensisies and the Reynolds stresses are also reveald in detail. Moreover, the effects of channel gemetry and bed roughness on turbulent structures are examined

Experimental Study on Three-Dimensional Flow Structures in Straight River Channel with a Pool

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Spanwise Streaky Structure and Macroturbulence in Open-channel Flows

In order to reveal the interrelation between the bursting phenomenon occurring originally in the wall region and the macroturbulence such as kolk-boils and the cellular secondary current, which are observed in the outer region of an actual river, the present study has examined the spanwise spatial structures of open-channel flows with and without the cellular secondary current which was created artificially. A new conditional averaging technique, whereby the signals of a sampling probe are weight-averaged by the sorted instantaneous Reynolds-stress signals of a detection probe, has been used to evaluate the mean spanwise streaky spacings throughout the flow depth. The direct effect of the cellular secondary current on the bursting motion was not recognized. It was suggested that the coherent structures of an open-channel flow would indicate the doublestructure of turbulence, in which both the bursting and macroturbulence coexist self- consistently

Three-Dimensional Turbulent Structure and Associated Secondary Currents in Straight Rivers : Field Measurements of River Turbulence

Fundamental structures of turbulence in two-dimensional (2-D) and further three-dimensional (3-D) open-channel flows have recently been almost clarified theoretically and experimentally through accurate experimental data which were obtained using a laser-Doppler anemometer system in laboratory flumes ; this detailed knowledge is now available in an IAHR monograph written by Nezu & Nakagawa (1992). Many of these experiments have, however, been conducted at moderate Reynolds numbers, say Re 記号 10⁴. Therefore, it is not yet clear whether such laboratory data of open-channel turbulence can be applied to river turbulence at high Reynolds numbers. In this study, velocity measurements of the Biwako-Sosui River (Re = 8 × 10⁵) in Kyoto and the Aichi Irrigation Channel (Re = 6 × 10⁵) in Nagoya have been conducted, using three-component electromagnetic flow meters. It was first found that multi-cellular secondary currents and free-surface secondary currents were evident in actual rivers. The features of such secondary currents in rivers were in a good agreement with those in laboratory flumes. Key Words : turbulence-driven secondary currents ; river turbulence ; field measurements ; velocity-dip phenomenon ; effects of aspect ratio

Study on the Transport Characteristics of Floating Garbage in Hori River

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Non-thermal photon production via bulk comptonization at supernova shock breakout

We investigate roles of the bulk comptonization process in the propagation of thermal photons emitted at the shock breakout of a supernova explosion. We use a hydrodynamical model based on a self-similar solution for the shock breakout. The propagation of photons is treated by a Monte-Carlo technique. Results of the simulations successfully reproduce the power-law spectrum observed by X-ray observations for XRF 080109/SN 2008D, if a mildly relativistic shock velocity is assumed. Effects of some radiative processes, photoionization, radiative recombination, and free-free absorption on the propagation of emitted photons are also investigated. It is found that none of them hardly changes the spectrum regarding the progenitor stars of type Ib or Ic supernovae. Light curves calculated under the assumption of a spherical explosion indicate that the progenitor radius is required to be $/sim 10^{13}$ cm.Comment: 10pages, 6 figures, to appear in Ap

Acute optogenetic silencing of orexin/hypocretin neurons induces slow wave sleep in mice

Orexin/hypocretin neurons have a crucial role in the regulation of sleep and wakefulness. To help determine how these neurons promote wakefulness, we generated transgenic mice in which orexin neurons expressed halorhodopsin (orexin/Halo mice), an orange light-activated neuronal silencer. Slice patch-clamp recordings of orexin neurons that expressed halorhodopsin demonstrated that orange light photic illumination immediately hyperpolarized membrane potential and inhibited orexin neuron discharge in proportion to illumination intensity. Acute silencing of orexin neurons in vivo during the day (the inactive period) induced synchronization of the electroencephalogram and a reduction in amplitude of the electromyogram that is characteristic of slow-wave sleep (SWS). In contrast, orexin neuron photoinhibition was ineffective during the night (active period). Acute photoinhibition of orexin neurons during the day in orexin/Halo mice also reduced discharge of neurons in an orexin terminal field, the dorsal raphe (DR) nucleus. However, serotonergic DR neurons exhibited normal discharge rates in mice lacking orexin neurons. Thus, although usually highly dependent on orexin neuronal activity, serotonergic DR neuronal activity can be regulated appropriately in the chronic absence of orexin input. Together, these results demonstrate that acute inhibition of orexin neurons results in time-of-day-dependent induction of SWS and in reduced firing rate of neurons in an efferent projection site thought to be involved in arousal state regulation. The results presented here advance our understanding of the role of orexin neurons in the regulation of sleep/wakefulness and may be relevant to the mechanisms that underlie symptom progression in narcolepsy.National Institutes of Health (U.S.) (Grant R01NS057464