Field observations showed that in many gravel-bed rivers, rice stems and gravel interact with each other and affect the flow structure. This calls to conduct research in more details in laboratory to better understand impacts of interaction between rice stems and gravel bed rivers on the flow structure. The outcome of such investigations can improve the estimation of drag coefficient in hydrodynamic models. Experiments were carried out in a flume with gravel bed and the vegetated vertical flume walls to investigate turbulence characteristics under favorable pressure gradient flows. Results showed that the stress fraction involves both the sweep and ejection dominance near the vegetated flume walls, showing no negative Reynolds shear stress near water surface. The values of exuberance ratio play a significant role on the magnitude of the Reynolds shear stress which varies with the distance from the vegetation. Quadrant analysis reveals that a major part of the momentum flux is transported during a short period of strong turbulence activity near the bed at the central axis. Augmentation of the hole size makes difference between contributions of sweep and ejection with those of the outward and inward interactions near the bed, however, the hole size doesn’t play any role near the water surface.
Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of naturally formed mobile bedforms on velocities, turbulent intensities and turbulent stresses. Instantaneous velocities are measured using a two-dimensional particle image velocimetry (PIV) to evaluate the turbulence structure of free surface flow over a fixed (immobile) bed, a weakly mobile bed and a temporally varying mobile bed with different stages of bedform development. This paper documents the vertical distribution of velocity, turbulence intensities, Reynolds shear stress and higher-order moments including skewness and turbulent diffusion factors. Analysis of the velocity distributions shows a substantial decrease of velocity near the bed with increasing bedform mobility due to increased friction. A modified logarithmic law with a reduced von Kármán constant and increased velocity shift is proposed for the case of the mobile bedforms. A significant increase in the Reynolds shear stress is observed in the mobile bedforms experiments accompanied by changes over the entire flow depth compared to an immobile bed. The skewness factor distribution was found to be different in the case of the flow over the mobile bedforms. All higher-order turbulence descriptors are found to be significantly affected by the formation of temporally varying and non-equilibrium mobile bedforms. Quadrant analysis indicates that sweep and outward events are found to be dominant in strongly mobile bedforms and govern the bedform mobility.
The study presents experimental investigations of spatial turbulence intensity and scales of turbulent eddies (macroeddies) in a rectangular channel and the impact of the hydraulic jump on their vertical and streamwise distributions over a flat and scoured bed. The results of four tests and two different discharge rates are presented. Intensive mixing caused by the hydraulic jump has an impact on the instantaneous velocity, turbulence intensity and sizes of macroeddies, as well as their vertical and longitudinal distributions along the channel. The largest differences in turbulence characteristics were reported directly after the hydraulic jump, above the eroded bed. The interaction between the stream of the increased turbulence and the bed is a direct cause of formation of scour downstream water structures, which has a great effect on overall flow characteristics. The scour hole that arose downstream the jump moderated, in a small degree, the turbulence intensity at its end. Just next to the hydraulic jump only the small longitudinal relative sizes of macroeddies were present, while at the end of the analyzed reach, downstream of the scour, the relative scale reached around 1.5 depth of the stream.
This work describes Large Eddy Simulation of backward-facing step flow laden with particles. The concentration of the particles in the flow is high enough for consideration of two-way coupling. This means that the particles are influenced by fluid and vice versa. The inter-particle collisions are neglected. The Euler-Lagrange method is adopted which means that the fluid is considered to be continuum (Euler approach) and for each individual particle is solved Lagrangian equation of motion. Particles are considered to be spherical. The simulations are performed for different volume fractions. The results are compared to the single-phase flow in order to investigate the effect of the particles on the turbulence statistics of the carrier phase. and Obsahuje seznam literatury
Summary: In the present paper indications have been presented that:
(1) Kernels with tangled magnetic lines of force occur in solar flares.
(2) Random (turbulent) motions occur in hot flare plasma.
(3) A MHD turbulence can explain huge flare energy release (plasma heating. electron and proton acceleration).
(4) It has been also shown that a MHD turbulence can efficiently develop in a strong magnetic field in the solar corona.
On this basis it is suggested that the MHD turbulence is Ihe basic mechanism of the flare energy release.
In May and June 2013 Turkey witnessed one of the longest and biggest social unrests in its modern history. Protesters all around the country rebelled against the government's authoritarian tendencies and police violence, exemplified by the hars treatment of activists resisting the reshaping of Istanbul's favorite Taksim Square and the adjacent Gezi Park. This essay address the origins, development and outcomes of the Turkish "Occupy Gezi" movement. It seeks the roots of the movement on three interdependent levels centered around the uses and misuses of public space and the instrumentalization of civil society in the hegemonical political discourse. Accordingly, the demonstrations are analyzed as (1) a critique of neoliberal developmentarism in Turkey, reflected in the marketization/commodification of public space and the destruction of the envoronment; (2) as a critique of the majoritarian, non-inclusive concept of democracy that accompanies neoliberal economic policies in Turkey and has manifested itself in the attempt to appropriate public space and to gain effective control over "disloyal" elements of society; and (3) finally as a critique of state paternalism, its most palpable effect being the imposition of conservative values, the distaste for alternative life-styles and the construction of a homogeneous mass of "Turkish citizens" adhering to similar values. We argue that the alleged Islamism of the ruling AKP played only an accessory role in the outbreak and development of the protests. What was an ecological protest and outcry at non-participative urban transformation in the beginning turned into a widespread popular happening whose participants tried to create an alternative to the bureaucratic machinery of the neoliberal state and the increasingly authoritarian behavior of its representatives who are unresponsive and unsensitive to the frustrations of oppositional voices, non-religious classes and different life-styles., Petr Kučera., and Obsahuje bibliografii