The structure of gravity currents flowing around a wall-mounted vertical circular cylinder

We analyze the structure of lock-release gravity currents as they approach and flow around a vertical obstacle. Two laboratory setups are used: an undisturbed horizontal channel and the same channel partially obstructed by a circular cylinder. Instantaneous two-dimensional velocity fields were acquired with Particle Image Velocimetry. The structure of the flow is discussed in terms of its instantaneous velocity components and by identifying its characteristic vortical coherent structures employing the Rortex/Liutex vector. The current is divided in three layers, characterized by different vortical structures. The lowermost layer features the hairpin-like vortical structures of smooth boundary layers while the shear layer features the growth of inflectional instabilities. Once the head has passed, the body of the current is upwelled, disrupting the shear layer and creating a region of intense mixing. A complex vortex system is formed with rotation compatible with returning the upwelled flow back to the current. The interaction of this region with the separated ambient flow requires the formation of a horizontal vortex that compatibilizes both flows. In the ambient fluid, the observed rotational structures may be the cores of Von K & aacute;rm & aacute;n vortices whose axis (vertical when shed) were rotated by the upwelling current.