Experimental And Numerical Study Of Dense Granular Impinging Jets

The dense granular jets impinging are the significant process of the opposed multi-burner gasification.It is important to investigate the different regimes of the dense granular impinging jets and reveal the evolution rules of the flow regimes.The dynamic behaviors of dense granular impinging jets were studied by a high-speed camera,image processing software of Image J and Discrete Element Method(DEM),etc.The formation and instability of the liquid-like granular sheet had been researched.The main contents and results are summarized as follows:1.The regimes of dense granular impinging jets and the effects of the particle diameter(Dp),the granular jet velocity(u0),the impact angle(2θ)and solid fraction(xp)on the flow regimes of the granular impinging jets were investigated.With the increase of particle diameter,granular jet velocity and the decreasing of solid fraction of the granular jet,the regime of granular impinging jets transition from granular film to scattering pattern.And as the impact angle increases,some particle move upward toward the impinging point after impact,and the height and width of the granular sheet increases.2.The non-asymmetric oscillation and wave structures of the granular sheet from dense granular impinging jets were investigated,and the instability of the granular sheet and regulation mechanism were revealed.Results show that with the increase of granular jet velocity and decrease of solid fraction,the liquid-like granular sheet becomes unstable and a non-axisymmetric oscillation appears.And the amplitude and frequency of the granular sheet increase with granular jet velocity,and the wave structures become apparent.The interesting merging behaviors of the surface waves were observed on the granular sheet.The propagating velocity of surface waves normalized by the granular jet velocity varies from 0.7 to 0.9.The merging behaviors will reduce the frequency of the surface waves and increase the surface wavelength.The results also show that the oscillation frequency of the granular film nearly equals to the pulsation frequency of the granular jet.It is indicated that the gas-solid interaction inside the nozzle increase with increasing granular jet velocity,and causes the instability of the granular jet,and result in the non-axisymmetric oscillation on the granular sheet consequently.3.The numerical simulation of dense granular impinging jets had been taken by the DEM.The simulation results were in good agreement with those of the experiment at different solid fraction and impinging angle.The propagating velocity of particles increases with the increasing of-z/D.Based on the particle time-mean velocity,collision frequency and normal stress distribution in the computational domain,it is concluded that with the increase of the solid fraction,the particle time-mean velocity and energy become more uniform,and then the granular sheet of the dense granular impinging jets easily forms.