Abstract
Obstacles within fluids have been widely used in engineering and in physics to study hydrodynamic interactions. In granular matter, objects within a granular flow have helped to understand fundamental features of drag and lift forces. In our group, we have studied numerically the flow mediated interaction between two static disks within a vertical granular flow in a two-dimensional container where the flow velocity and the distance between obstacles were varied. Attractive and repulsive forces were found depending on flow velocity and separation between intruders. The simulations evidenced a relationship between the average flow velocity in a specific section ahead of the obstacles and the attractive-repulsive lift. On the other hand, it was showed that the lift force on an object dragged within a granular medium depends on the shape of the intruder. Here we present experimental results of the interaction between two side-by-side intruders of different shapes within a vertical granular flow. We built a quasi-two-dimensional container in which we placed the intruders and using load cells we measured lift and drag forces during the discharge process for different flow velocities.
Highlights
The interaction of obstacles within a flow is widely studied for theory and applications in fluid mechanics
In the present work we show the experimental results for drag and lift forces on obstacles of different shapes placed into a gravitational granular flow
Our Particle Image Velocimetry (PIV) analysis could be tested by plotting the velocity measured by this method and the mass flow directly measured with the scale at the outlet
Summary
The interaction of obstacles within a flow is widely studied for theory and applications in fluid mechanics. Granular matter community has thoroughly studied forces on objects immersed in granular flows [3,4,5,6]. Flow velocity and its fluctuations have shown to play an important role in attractive and repulsive regimes in flow mediated interactions between obstacles, and lift forces have been associated with a Bernoulli-like phenomenon: a pressure drop associated to flow velocity. Lift forces have been shown to depend on the shape of the immersed object which is due to the “asymmetry in pressure caused by gravity between the lower and the upper parts of the object” [2]. It was shown numerically that in a static pair of obstacles within a granular flow exists attractive and repulsive lift forces depending of the flow velocity and the separation between them [1]. In the present work we show the experimental results for drag and lift forces on obstacles of different shapes placed into a gravitational granular flow
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