Why Velocity Overshoots in Accelerating Porous Media Flow

We analysed a high-fidelity DNS dataset of accelerating flow through a porous medium consisting of uniform spheres in hexagonal close-packed arrangement. The fluid was accelerated from rest by a constant pressure gradient until the superficial volume-averaged velocity attained its steady-state amplitude. Our focus is on the generation mechanism of the overshoot of the superficial streamwise velocity that appears just before the steady-state amplitude is reached. The relative magnitude of the velocity overshoot appears to be Reynolds number dependent, and can be larger than 5% of the steady-state value. The current study suggests that the velocity overshoot is a consequence of enhanced intercomponent energy transfer carried out by pressure, which redistributes streamwise energy into the orthogonal directions, and it mainly takes place in the wake regions behind the sphere contact points.     «

We analysed a high-fidelity DNS dataset of accelerating flow through a porous medium consisting of uniform spheres in hexagonal close-packed arrangement. The fluid was accelerated from rest by a constant pressure gradient until the superficial volume-averaged velocity attained its steady-state amplitude. Our focus is on the generation mechanism of the overshoot of the superficial streamwise velocity that appears just before the steady-state amplitude is reached. The relative magnitude of the vel...     »