Wave propagation in stepped and joined shells Annual report, 1 Sep. 1968 - 1 Sep. 1969

Shell impact response and wave propagation in cylindrical and conical shells by experimental and analytical method

Particle concentration and stokes number effects in multi-phase turbulent channel flows

This investigation examines the effect that particle concentration has on the dynamics of two-phase turbulent channel flows at low and high density ratios. In the literature, little explanation is offered for the existence of high particle turbulence intensities in the buffer layer and viscous sublayer for particles with high Stokes number. The present study aims to explore particle dynamics in those regions. The spectral element method DNS solver, Nek5000, is used to model the fluid phase at a shear Reynolds number Re=, Particles are tracked using a Lagrangian approach with inter-phase momentum exchange (two-way coupling). Mean fluid and particle velocity statistics are gathered and analysed to determine the effect of increasing both Stokes number and concentration. Results indicate that the system with the greater Stokes number (air) has a much larger impact on the mean streamwise velocity and turbulence intensity profiles. As the concentration is increased, the mean flow velocity and turbulence intensity are reduced in the bulk and increased very close to the wall. For the low Stokes system, there is negligible effect on the flow statistics at low concentration. One-way coupled solid-phase statistics indicate that particles in water follow the flow very closely. At the higher densityratio, particles lag behind the flow in the bulk, but overtake the flow in the near-wall region, where the existence of increased streamwise turbulence intensities is also observed. To elucidate the dynamics, concentrations and fluxes are analysed. Particles are observed to be distributed more densely close to the wall in air, compared to a reasonably uniform distribution in water. Finally, contour plots indicate that particles in air tend to congregate in regions of low streamwise fluid velocity, and the extent to which this differs between the two systems is then quantitatively measured

Effect of Four-Way Coupling on the Turbulence Field in Multi-Phase Channel Flows

This paper investigates and compares the effect of a solid, spherical particle phase on surrounding carrier fluids (air and water) in a turbulent channel flow. The fluid phase properties are chosen to represent a flow typical of the nuclear waste industry, with the flow modelled using the direct numerical simulation (DNS) code, Nek5000, at a shear Reynolds number of 180. A Lagrangian particle tracker is developed and implemented to simulate the dispersed phase, capable of accommodating two-way coupling between the fluid and discrete phase and inter-particle collisions (four-way coupling). In order to investigate the effect that the four-way coupled particulate phase has on the turbulence field, mean fluid velocities and turbulence intensity statistics are recorded. The work demonstrates that the introduction of two-way coupling does indeed impact slightly on the turbulence field. Specifically, it reduces the mean velocity profile and increases the streamwise turbulence intensity in the near-wall region. Upon the introduction of inter-particle collisions, the flow statistics studied show a negligible response. Collision density distributions are studied and a temporal migration to the near-wall region is observed. Along-side this, to investigate particle density-ratio effects, water-based results are contrasted with simulations in air. The way in which the flow statistics are modified are shown to differ in air and water. Finally, a DLVO agglomeration model is demonstrated, whereby particles colliding with enough energy to overcome the potential barrier are considered bound. This is applied to the four-way coupled flow with temporal distributions of agglomerate counts presented