Fines erosion: Turbophoresis can be harmful

Abstract

Enabling turbulence dispersion in a computational fluid dynamics simulation of a developing liquid-solid pipe flow leads to a focus of low-Stokes number particles around the pipe axis. This phenomenon is found to concentrate their impacts on a centrally located target surface such that a local erosion spot develops. This result is counter-intuitive as low-Stokes particles are deemed to follow the carrier average streamlines going around the body, which diminishes their probability of impact. This is nevertheless a fact reported experimentally too. Analysis of the simulations reveals that turbulence tends to drive preferentially tiny particles from areas of high to low agitation. This phenomenon is sometimes named as turbophoresis. Long straight piping systems are typical candidates for turbulent pipe flows hosting an annular zone of turbulence that tends to disperse and concentrate fines towards the axis. At the approach of a body, like a cross-flow cylinder, particles may be somewhat re-scattered away by the carrier dragging them around. As such, this turbulence dispersion effect on fines concerns various industrial solid transport systems. Fine impacts concentration is likely to create unexpected, local wear zone.

Numerical Investigation of Erosion Wear in the Hydraulic Amplifier of the Deflector Jet Servo Valve

“…While jets in valves mean intense impacts, leading to severe erosion wear. Research on a cylinder blocking the jet has been performed, and the erosion caused by fluid impact was evaluated [12], which unveiled that the central region of the impact was not the most worn location, conforming to the impact angle dependence of erosion wear as already mentioned by Finne [5]. Another investigation of impact erosion came from Zhao [13], who conducted CFD-based simulations and experiments to discuss the erosion distribution on the target plate, with the conclusion that the farther away from the jet center, the greater the wear is.…”

“…Still based on the Edwards model, a description of DJV erosion rate distribution was given to explore the correlation between erosion and the valve performance [17]. However, the simulation showed that maximum erosion happened in the central region of the jet, not consistent with the conclusions of Boulanger [12] and Zhao [13].…”