arXiv subjects

C. Cabeza

Publications and source records attributed to C. Cabeza.

3 recordsLinked to original sources

arXiv2020

Spreading height and critical conditions for the collapse of turbulent fountains in stratified media

Axisymmetric fountains in stratified environments rise until reaching a maximum height, where the vertical momentum vanishes, and then falls and spread radially as an annular plume following a well-known top-hat profile. Here, firstly, we generalize the model of Morton et al. (Proc. R. Soc. Lond. A \textbf{234}, 1, 1956), in order to correctly determine the dependence of the maximum height and the spreading height with the parameters involved. We obtain the critical conditions for the collapse of the fountain, \textit i.e. when the jet falls up to the source level, and show that the spreading height must be expressed as a function of at least two parameters. To improve the quantitative agreement with the experiments we modify the criterion to take the mixing process in the down flow into account. Numerical simulations were implemented to estimate the parameter values that characterizes this merging. We show that our generalized model agrees very well with the experimental measurements.

physics.flu-dyn↗

arXiv2008

Nonlinear dynamics at the interface of two-layer stratified flows over pronounced obstacles

The flow of a two--layer stratified fluid over an abrupt topographic obstacle, simulating relevant situations in oceanographic problems, is investigated numerically and experimentally in a simplified two--dimensional situation. Experimental results and numerical simulations are presented at low Froude numbers in a two-layer stratified flow and for two abrupt obstacles, semi--cylindrical and prismatic. We find four different regimes of the flow immediately past the obstacles: sub-critical (I), internal hydraulic jump (II), Kelvin-Helmholtz at the interface (III) and shedding of billows (IV). The critical condition for delimiting the experiments is obtained using the hydraulic theory. Moreover, the dependence of the critical Froude number on the geometry of the obstacle are investigated. The transition from regime III to regime IV is explained with a theoretical stability analysis. The results from the stability analysis are confirmed with the DPIV measurements. In regime (IV), when the velocity upstream is large enough, we find that Kelvin-Helmhotz instability of the jet produces shedding of billows. Important differences with flows like Von Karman's street are explained. Remarkable agreement between the experimental results and numerical simulations are obtained.

physics.flu-dyn↗

arXiv2006

A simple mechanism for controlling vortex breakdown in a closed flow

This work is focused to study the development and control of the laminar vortex breakdown of a flow enclosed in a cylinder. We show that vortex breakdown can be controlled by the introduction of a small fixed rod in the axis of the cylinder. Our method to control the onset of vortex breakdown is simpler than those previously proposed, since it does not require any auxiliary device system. The effect of the fixed rods may be understood using a simple model based on the failure of the quasi-cylindrical approximation. We report experimental results of the critical Reynolds number for the appearance of vortex breakdown for different radius of the fixed rods and different aspect ratios of the system. Good agreement is found between the theoretical and experimental results.

physics.flu-dyn↗