Fundamental aspects of solids-gas flow: Part V: The effects of fluid turbulence on the particle drag coefficient



This article presents an analysis of the experimental evidence presently available on the effects of the free-stream turbulence on particulate momentum transfer, obtained from both wind-tunnel tests with stationary bodies and from single-particle systems in which the solid is moving freely with the stream. Original experimental measurements recently obtained with a radio-tracer technique are also included. The drag coefficient appears to depend primarily on the magnitude of the relative turbulence intensity and on the particle Reynolds Number, while acceleration has negligible effects. Increasing intensities cause a systematic regression of the transition region of the drag coefficient curve towards lower Reynolds Numbers, together with a moderate increase of the drag coefficients for both the subcritical and supercritical Reynolds Numbers. The momentum transfer behavior suggests the occurrence of a laminar-turbulent transition in the attached boundary layer at a critical value of the Reynolds Number for a given relative intensity. Indirect evidence involving heat and mass transfer phenomena appears to support this hypothesis.