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Vehicles can be easily swept away by floodwaters once the flow velocity and depth reach certain critical limits, with probabilities toward fatality reported to be nearly 50%. Therefore, understanding the response of the flooded vehicle is necessary in preparing safety guidelines and controlling the risks. In the present work, the hydrodynamic forces on an actual full-scale passenger vehicle being partially submerged and exposed to subcritical flows were investigated. This is one of the earliest works at the present time involving a full-scale vehicle being tested at two orientations, 90° and 0° and two situations, static and in movement. The drag coefficients were plotted against the Froude number among other hydrodynamic forces. The experimental outcomes revealed that the vehicle positioned at 90° orientation with respect to the incoming flows was the critical orientation for both vehicle situations. This is consistent with previous studies based on scale model cars. Besides, drag forces increased significantly with the increment of flow velocity, Froude number, and vehicle speed. Particularly, the flow depth had an accountable effect on the buoyancy, friction, rolling, and driving forces. Under hydrostatic conditions, the vehicle experienced floating instability at 0.40 m water depth when imposed to an approximate of 11 kN buoyancy force. Experimental outcomes originated from a full-scale vehicle such as this contribute to new knowledge in supplementing and validating results obtained from the most frequent scaled-model physical testing and numerical modeling. Outcomes obtained from this study will be beneficial in developing a proper safety guideline for vehicle safety.

Lateral intakes are used for water transmission and distribution on farms and irrigation networks. In present study, the flow field within a rectangular lateral intake in subcritical flow regime is numerically simulated in a three-dimensional. In this analysis of CFD, turbulence of flow field is simulated using standard k - ε , and RNG k - ε turbulence models, and changes of free surface is simulated by volume of fluid scheme. Comparison between CFD and experimental results showed that the numerical model simulated the free surface and velocity field with high accuracy. Root mean square error for longitudinal and transverse profiles of the flow free surface in the main channel is respectively calculated as 0.132% and 0.094%. Based on simulation results, with the flow progress towards the downstream diversion channel, the secondary circulation cell is developed. A relation is presented for calculating strength of the secondary flow with a nonlinear regression method and using Minitab software. Also, a relation is proposed for calculating the flow energy head within the downstream channel and lateral channel (E3, E2) compared to the flow energy head in the upstream intake (E1).

This study explores the formation of circular thin-film hydraulic jumps caused by the normal impact of a jet on an infinite planar surface. For more than a century, it has been believed that all hydraulic jumps are created due to gravity. However, we show that these thin-film hydraulic jumps result from energy loss due to surface tension and viscous forces alone. We show that, at the jump, surface tension and viscous forces balance the momentum in the liquid film and gravity plays no significant role. Experiments show no dependence on the orientation of the surface and a scaling relation balancing viscous forces and surface tension collapses the experimental data. A theoretical analysis shows that the downstream transport of surface energy is the previously neglected critical ingredient in these flows, and that capillary waves play the role of gravity waves in a traditional jump in demarcating the transition from the supercritical to subcritical flow associated with these jumps.

With the shift of oil and gas exploration to offshore environments, suppressing vortex-induced vibration (VIV) in riser systems—critical for drilling and fluid transport on floating platforms—has become imperative. Experimental studies on concave-to-convex fairings under subcritical flow conditions show that as cross-sectional profiles transition from concave to convex, near-wall vorticity decreases and wake vortices shed farther downstream. The convex fairing (0.35D protrusion) achieves the largest vortex shedding displacement, with a 2D separation from the riser wall, demonstrating progressively enhanced VIV suppression with convex geometrical dominance.

We study the use of small counter-rotating cylinders to control the streaming flow past a larger main cylinder for drag reduction. In a water tunnel experiment at a Reynolds number of 47 000 with a three-dimensional and turbulent wake, particle image velocimetry (PIV) measurements show that rotating cylinders narrow the mean wake and shorten the recirculation length. The drag of the main cylinder was measured to reduce by up to 45 %. To examine the physical mechanism of the flow control in detail, a series of two-dimensional numerical simulations at a Reynolds number equal to 500 were conducted. These simulations investigated a range of control cylinder diameters in addition to rotation rates and gaps to the main cylinder. Effectively controlled simulated flows present a streamline that separates from the main cylinder, passes around the control cylinder, and reattaches to the main cylinder at a higher pressure. The computed pressure recovery from the separation to reattachment points collapses with respect to a new scaling, which indicates that the control mechanism is viscous.

A blunt obstacle in the path of a rapid granular avalanche generates a bow shock (a jump in the avalanche thickness and velocity), a region of static grains upstream of the obstacle, and a grain-free region downstream. Here, it is shown that this interaction is qualitatively altered if the incline on which the avalanche is flowing is changed from smooth to rough. On a rough incline, the friction between the grains and the incline depends on the flow thickness and speed, which allows both rapid (supercritical) and slow (subcritical) steady uniform avalanches. For supercritical experimental flows, the material is diverted around a blunt obstacle by the formation of a bow shock and a static dead zone upstream of the obstacle. Downslope, a grain-free vacuum region forms, but, in contrast to flows on smooth beds, static levees form at the boundary between the vacuum region and the flow. In slower, subcritical, flows the flow is diverted smoothly around the dead zone and the obstacle without forming a bow shock. After the avalanche stops, signatures of the dead zone, levees and (in subcritical flows) a deeper region upslope of the obstacle are frozen into the deposit. To capture this behaviour, numerical simulations are performed with a depth-averaged avalanche model that includes frictional hysteresis and depth-averaged viscous terms, which are needed to accurately model the flowing and deposited regions. These results may be directly relevant to geophysical mass flows and snow avalanches, which flow over rough terrain and may impact barriers or other infrastructure.

When an acoustic wave travels in a lossy medium such as a liquid, it progressively transfers its pseudo-momentum to the fluid, which results in a steady flow called acoustic streaming. This phenomenon involves a balance between sound attenuation and shear, such that the streaming flow does not vanish in the limit of vanishing viscosity. Hence, the effect of viscosity has long been ignored in acoustic streaming experiments. Here, we investigate the acoustic streaming in sessile droplets exposed to surface acoustic waves. According to experimental data, the flow structure and velocity magnitude are both strongly influenced by the fluid viscosity. We compute the sound wave propagation and hydrodynamic flow motion using a numerical method that reduces memory requirements via a spatial filtering of the acoustic streaming momentum source terms. These calculations agree qualitatively well with experiments and reveal how the acoustic field in the droplet, which is dominated by a few caustics, controls the flow pattern. We evidence that chaotic acoustic fields in droplets are dominated by a few caustics. It appears that the caustics drive the flow, which allows for qualitative prediction of the flow structure. Finally, we apply our numerical method to a broader span of fluids and frequencies. We show that the canonical case of the acoustic streaming in a hemispherical sessile droplet resting on a lithium niobate substrate only depends on two dimensionless numbers related to the surface and bulk wave attenuation. Even in such a baseline configuration, we observe and characterize four distinct flow regimes.

We reformulate shallow water theory to understand viscous shear induced natural hydraulic jumps in channels slightly deviated from the horizontal. One of the interesting contributions of the study is a modified expression for Froude number to predict jumps in inclined channels. The proposed Froude number is different from the conventional expression which incorporates channel inclination as a straight forward component of gravity. This highlights the complexity that a jump can generate even in single phase laminar flow. We also obtain an analytical expression for predicting jump strength and show that the scaling relationship originally proposed for jump location in horizontal channels is applicable for both upslope and downslope flows. As expected, upslope flow aids jump formation and beyond a critical adverse tilt, a submerged jump results in subcritical flow right from the entry. On the other hand, both Reynolds number and channel tilt suppress the tendency to jump in downslope flows and below a critical downslope inclination, the flow remains supercritical throughout the channel length. The film thickness for fully developed flow can be predicted from the exact solution of the Navier–Stokes equations. As the theory encounters a singularity in the jump region, numerical simulations and experimental results have been used to obtain additional insights into the physics of jump formation. They have revealed the existence of submerged jump, wavy jump, smooth jump and no jump conditions as a function of liquid Reynolds number, scaled channel length and channel inclination. Such a variety of jump geometries in planar laminar flow has not been reported earlier. Both theory and simulations also reveal that the linear free surface profile upstream of the jump is a function of Reynolds number only, while the downstream profiles can be tuned by changing both Reynolds number as well as the channel length and tilt over the range of parameters studied. We thus demonstrate that, despite the simplicity and the approximations involved, shallow water equations formulated assuming self-similar velocity profiles can elucidate the physics of planar laminar jumps over slight inclinations, difficult to avoid in practice. The analytical and simulated results have been extensively validated with experimental data obtained from a specially designed test rig which ensures laminar flow before and after the jump. To the authors’ knowledge, almost no experimental study has to date been reported on films ‘thin enough’ to remain laminar even after the planar jump.

This study conducted a numerical investigation of the flow past a linearly tapered cylinder in the subcritical flow regime. This study concentrated on the influence of this geometric perturbation on the flow and heat transfer characteristics by comparing them with those of a uniform circular cylinder. It is revealed that the linearly tapered cylinder effectively reduced the mean drag and fluctuating lift coefficients. The tapered cylinder presented different separation angle locations at different spans, gradually moving backward as the diameter increased. The linearly tapered cylinder provided a higher mean Nu than a uniform cylinder at the same Re of 3000, resulting in an increase of about 25.48% of that for a uniform cylinder. Furthermore, the variation in the Nu over time was correlated with the force coefficients. Different views of the 3D contours depicting the Nu made it evident that the Nu had a maximum at both ends of the cylinder. Characterized by high-speed velocities, the Nusselt number was notably higher in the wake region.