Generation of Gravity-Capillary Wind Waves by Instability of a Coupled Shear-Flow

The theory of surface wave generation, in viscous flows, is modified by replacing the linear-logarithmic shear velocity profile, in the air, with a model which links smoothly the linear and logarithmic layers through the buffer layer. This profile includes the effects of air flow turbulence using a damped mixing-length model. In the water, an exponential shear velocity profile is used. It is shown that this modified and coupled shear-velocity profile gives a better agreement with experimental data than the coupled linear-logarithmic, non smooth profile, (in the air)–exponential profile (in the water), widely used in the literature. We also give new insights on retrograde modes that are Doppler shifted by the surface velocity at the air-sea interface, namely on the threshold value of the surface current for the occurrence of a second unstable mode.

Experimental study of perturbations modeled by a membrane in 2D and 3D boundary layers

The work is devoted to experimental studies of the dynamics of the development of perturbations introduced by a membrane under various conditions. The studies were carried out under conditions of a low and moderate degree of free-flow turbulence. It is shown that the impulsive motion of the membrane generates a localized longitudinal structure in the boundary layer, as well as wave packets at its fronts. A circular membrane generates wave packets consisting of forward and oblique waves, while a rectangular membrane generates predominantly forward waves. A moderate degree of turbulence inhibits the development of wave packets at the linear stage and intensifies at the nonlinear stage. The separation of the boundary layer stimulates an increase in the amplitude of the wave packets.

Effects of Biochar Addition on Rill Flow Resistance

The development of rills on a hillslope whose soil is amended by biochar remains a topic to be developed. A theoretical rill flow resistance equation, obtained by the integration of a power velocity distribution, was assessed using available measurements at plot scale with a biochar added soil. The biochar was incorporated and mixed with the arable soil using a biochar content BC of 6 and 12 kg m−2. The developed analysis demonstrated that an accurate estimate of the velocity profile parameter Гv can be obtained by the proposed power equation using an exponent e of the Reynolds number which decreases for increasing BC values. This result pointed out that the increase of biochar content dumps flow turbulence. The agreement between the measured friction factor values and those calculated by the proposed flow resistance equation, with Гv values estimated by the power equation calibrated on the available measurements, is characterized by errors which are always less than or equal to ±10% and less than or equal to ±3% for 75.0% of cases. In conclusion, the available measurements and the developed analysis allowed for (i) the calibration of the relationship between Гv, the bed slope, the flow Froude number, and the Reynolds number, (ii) the assessment of the influence of biochar content on flow resistance and, (iii) stating that the theoretical flow resistance equation gives an accurate estimate of the Darcy–Weisbach friction factor for rill flows on biochar added soils.

Numerical Simulations of Heat Transfer Phenomena through a Baffled Rectangular Channel

In presence of baffle, the turbulent airflow phenomena as well as forced convective heat exchange characteristics in two-dimensional rectangular channel have been analyzed in this work. For variations in Reynolds number (Re), we have studied the variations in characteristics of thermal behavior due to the change in the shape of baffle. Computations have been done using finite volume method (FVM) and FLUENT software and the SIMPLE algorithm has been employed for solving the governing equations. Finally, the flow and thermal exchange characteristics viz., streamline flow, turbulence intensity (TE), axial velocity, turbulence kinetic energy (TKE), normalized friction factor (F), normalized average Nusselt number (Nuavg) and thermal enhancement factor (TEF) have been studied in details from numerical standpoint. It has been found that the triangular shaped baffle provides highest value of F at Re = 30,000 and at Re = 46, 000, the maximum value of the TEF is found for the same baffle implying that triangular shaped baffle is more suitable for overall purposes.

Hydrodynamic Performance of A-Jacks Concrete Armor Units in Riverbeds around Downstream in Flip Buckets

The jet flipped from flip buckets hits the dam’s downstream side as a free jet with an immense amount of energy, leading to bed erosion. Erosion of river bed materials downstream of dams could affect the performance of dams or power plants by altering the tailwater depth, rendering proper designs of controlling structures or erosion reduction methods highly indispensable in this regard. Hence, the hydrodynamic performance of A-Jacks concrete armor units in controlling scour was examined in this study. A-Jacks armors are applicable as a flexible protection without environmental risks often for bed erosion control. The desirable functionality of A-Jacks armors depends on the flow hydrodynamic parameters such as velocity profile variations ( U / U B ), the Reynolds stresses ( τ u ′ w ′ and τ v ′ w ′ ), and the skin friction coefficient ( C f ) created as a consequence of using A-Jacks armors on beds. The size of A-Jacks elements can have a role in increasing the flow turbulence to a certain depth so that after the impact of the flow with A-Jacks armor, the vortices’ intensity as well as the shear stress affecting the bed gradually decreases. The results of the numerical model suggest that the surge in the flow turbulence energy dissipation downstream of flip buckets significantly mitigates the underlying conditions of scouring phenomena, which is evidence of A-Jacks armors’ acceptable performance in scaling down scour depths.