Characteristics of surface waves on the granular sheet of dense granular jet impingement

Abstract

Dense granular jet impingement widely exists in numerous natural flow phenomena and industrial processes. It is significant to investigate the influencing factors of the flow patterns of dense granular jet impingement and reveal the evolution rules of flow patterns. The dynamic behaviors of dense granular jets impinging on a flat target are experimentally studied by a high-speed camera and image processing software of NIH. The effects of the particle diameter（Dpar), the granular jet velocity（U0) and the solid content of the granular jet（X) on the flow patterns and surface waves of granular sheet are investigated. Two patterns, i.e., the liquid-like granular film and the scattering pattern are identified from the dense granular jet impingement. The results show that with the increase of the particle diameter, the solid content of the granular jet reduces, and the interparticle collision frequency decreases, which results in the granular sheet evolving into the scattering pattern. The opening angle of the granular sheet（) is bigger than that of the liquid sheet, and the granular jet velocity plays an insignificant role in the opening angle. The interesting behaviors of liquid-like surface waves are identified in the granular sheet. The frequency of surface wave of the granular sheet（f) is an order of magnitude smaller than that of the liquid sheet. The surface wave length（) increases and frequency decreases with the increase of radial position, as the surface waves merge during the granular sheet spreading radially. The surface wave spreading velocity normalized by the granular jet velocity is a constant of about 0.4. With the increase of the granular jet velocity, the pulsation of granular jet occurs due to the pressure fluctuation in the discharge process under the effect of gas-solid interaction. The frequencies of surface waves of both the granular sheet and the granular jet pulsation become the same generally. It is indicated that the surface wave is primarily caused by the granular jet pulsation. The results in this paper present the knowledge of the dense granular jet impingement and provide some principles for the steady operation of dense granular jet impingement in industrial process.