Particle trajectories in swirling flows (coal combustion gas turbine technology)

Abstract

The ability to utilize fuels which form participate matter upon combustion (e.g., coal) in a gas turbine depends in part upon an understanding of the nature of particle trajectories in swirling flows. Although a number of investigators have studied specific flows or developed specific computational methods for particle trajectories in swirling flows, none have obtained solutions which are general in nature. In this paper a series of exact general solutions for trajectories of spherical particles in free-vortex swirling flow have been obtained in the absence of aerodynamic lift phenomena. As would be expected from related works, it has been found that for low particle Reynolds numbers (Stokes flow) the degree to which a particle either follows the flow streamlines or is centrifuged out across them is essentially described by a single dimensionless parameter, the Stokes number. For higher particle Reynolds numbers the results can be presented in terms of two relevant parameters, one of which may be the Stokes number. Furthermore, even in this latter case the results indicate that the Stokes number is the dominant parameter. Based on these results a number of conclusions have been drawn on the nature of particle trajectories in turbine airfoil passages, and in centrifugal separators.