Scour Features at Wood Bundles

Structures like blunt-nosed chevrons, log deflectors and double-winged log frames help in modifying the flow regime in the channel by concentrating the flow and increasing navigability. Moreover, they create scour pools in the downstream stilling basin, which can be used either as fish refuge or as an in-stream storage site for previously dredged material. In this respect, the use of wood debris in the channel in the form of wood bundles has gained attention for the ability of these structures to integrate into the surrounding fluvial habitat and to divert the flow partially towards the central part of the channel when placed in curves. Considering the absence of studies dealing with wood bundles as a restoration structure, the aim of this paper is to analyse the scour mechanism and equilibrium scour morphology of wood bundles in straight and curved channels. In doing so, a wide range of hydraulic conditions, structure positions and configurations were tested. Thereafter, dimensional analysis was carried out to derive useful empirical relationships to predict the maximum scour depth and length as well as the maximum dune height based on a novel, equivalent Froude number, which accounts for the effects of channel curvature and structure position. Moreover, the various resulting scour morphology types were classified, and conditions of their existence were determined depending on the abovementioned Froude number and other key hydraulic parameters.

Experiments on Longitudinal and Transverse Bedload Transport in Sine-Generated Meandering Channels

Bedload grains in consecutive meandering bends either move longitudinally or across the channel centerline. This study traces and quantifies the grains’ movement in two laboratorial sine-generated channels, i.e., one with deflection angle θ0 = 30° and the other 110°. The grains originally paved along the channels are uniform in size with D = 1 mm and are dyed in various colors, according to their initial location. The experiments recorded the changes in the flow patterns, bed deformation, and the gain-loss distribution of the colored grains in the pool-bar complexes. We observed the formation of two types of erosion zones during the process of the bed deformation, i.e., Zone 1 in the foreside of the point bars and Zone 2 near the concave bank downstream of the bend apexes. Most grains eroded from Zone 1 are observed moving longitudinally as opposed to crossing the channel centerline. Contrastingly, the dominant moving direction of the grains eroded from Zone 2 changes from the longitudinal direction to the transversal one as the bed topography evolves. Besides, most building material of the point bars comes from the upstream bends, although low- and highly curved channels behave differently.

Bed-Shear Velocity Measurement in Curved Open Channel

Generally, the condition of the rivers in Indonesia are alluvial rivers which had meanders, where the change in the river bed topography often occur. One of the parameters associated with changes in the river bed topography is bed-shear velocity, or Reynolds stress. The bed-shear velocity can be calculated by the Reynolds stress distribution method and the Clauser method which commonly used in straight channels. In fact, on natural channel there is a curve and even a meandering channel. With more complex flow conditions, the use of the Clauser method in curved channels can be questioned, is it still accurate or not. In this paper, both methods will be discussed by comparing the measurement data in the laboratory using 180 curved channel with flat bed. The results of data analysis show that the use of these two methods in curved channels produces an average difference of around 19.81%, where the Clauser method gives greater results and better tendencies. Apart from the differences in the results given, it can be said that the Clauser method as well as the Reynolds stress distribution method can still be used to calculate the bed-shear velocity in the curved channel

Numerical Study of Multivortex Regulation in Curved Microchannels with Ultra-Low-Aspect-Ratio

The field of inertial microfluidics has been significantly advanced in terms of application to fluid manipulation for biological analysis, materials synthesis, and chemical process control. Because of their superior benefits such as high-throughput, simplicity, and accurate manipulation, inertial microfluidics designs incorporating channel geometries generating Dean vortexes and helical vortexes have been studied extensively. However, existing technologies have not been studied by designing low-aspect-ratio microchannels to produce multi-vortexes. In this study, an inertial microfluidic device was developed, allowing the generation and regulation of the Dean vortex and helical vortex through the introduction of micro-obstacles in a semicircular microchannel with ultra-low aspect ratio. Multi-vortex formations in the vertical and horizontal planes of four dimension-confined curved channels were analyzed at different flow rates. Moreover, the regulation mechanisms of the multi-vortex were studied systematically by altering the micro-obstacle length and channel height. Through numerical simulation, the regulation of dimensional confinement in the microchannel is verified to induce the Dean vortex and helical vortex with different magnitudes and distributions. The results provide insights into the geometry-induced secondary flow mechanism, which can inspire simple and easily built planar 2D microchannel systems with low-aspect-ratio design with application in fluid manipulations for chemical engineering and bioengineering.

MHD dusty hybrid nanofluid peristaltic flow in curved channels

This paper presents numerical simulations for a magnetohydrodynamic convective process in curved channels. The worked suspension consists of water as a based hybrid nanofluid and two types of the nanoparticles, namely, Cu and Al2O3. Two systems of the governing equations are formulated for the hybrid nanofluid and dusty phases. The hybrid nanofluid system is modeled in view of lubrication approach. The governing equations are mapped to a regular computational domain then they solved numerically using the fourth order Runge-Kutta method. The obtained findings revealed that the growing in the Hartmann number causes a reduction in both of the hybrid nanofluid and dusty velocities while the mixture temperature is enhanced. Also, the temperature distributions are supported when either the Grashof number or the amplitude ratio is altered.

Determination of the Influence of Ventilation Device Geometry on Inertia of the Brake Disc

The variety of brake discs is determined by the presence of different geometries of the ventilation device. Modern brake discs are subdivided according to the geometry of the ventilation device by the presence of fins, which form channels and studs for heat transfer to the cooling air. In turn, ventilation channels can be radial and curved. Studs are subdivided by geometry into cylindrical, prismatic and complex configuration. The paper proposes the calculation of the power required to overcome the inertial forces of the brake disc for various variants of the ventilation device. The power expended to overcome the inertial forces of a brake disc with radial channels is 44 % less than that of a brake disc with curved channels. Brake discs with a ventilation device with prismatic studs have 1.22 times less power required to overcome inertial forces than with cylindrical studs and 1.31 times with DBA studs. When comparing the results of the method for determining the moments of inertia of brake discs with various ventilation devices and CFD models of similar brake discs created in the ANSYS Workbench Mechanical program, the discrepancy was 5.52 %. The study shows the dependence of the power of overcoming inertia forces on the number of ribs. With an increase in the number of ribs by 60, the power to overcome the inertial forces of the radial channels of the disk increased by 1.16 times, while the power of the curved channels of the disk increased by 1.07 times. With an increase in the number of studs by 50 pieces for a disc with cylindrical studs of the apparatus, the power expended to overcome inertial forces increases by 1.15 times, while for prismatic studs there is an increase of 1.05 times. With an increase in the number of studs by 50 pieces, the power to overcome the inertial forces of the ventilated brake disc from DBA increases by 1.17 times. When designing ventilation brake discs, in addition to the heat dissipation parameters, it is necessary to take into account the parameters of the power to overcome the inertial forces of the brake discs, which affect the operational parameters of the braking system as a whole.