Influence of Particles on Fluid Turbulence in Pipe and Diffuser Gas-Solids Flow

The influence of glass particles with different Reynolds numbers Rep = |u-u P |d P ρ/η on axial and radial gas fluctuations as well as on Reynolds stresses was investigated for pipe and diffuser (continuous pipe expansion) gas-solids flow. Measurements were carried out using phase-Doppler anemometry distinguishing between velocity signals of the solid and fluid phase due to particle or tracer size. In fully developed pipe flow small particles (Rep = 60) damp turbulence but with increasing Rep vortex shedding behind the particles reduces attenuation and finally leads to turbulence enhancement. Behind the diffuser particles are decelerated and cause a steeper velocity gradient and, thus, an increase in turbulence. The measured data are compared to CFD calculations investigating Reynolds stress model and k-e model for the description of turbulence. Using small particles good agreement is achieved considering the momentum transfer between the phases. For larger particles the modeling of vortex shedding by turbulent particle source terms is needed for a satisfactory prediction.