查看更多>>摘要：Stabilised dense emulsions display a rich phenomenology connecting microstructure and rheology. In this work, we study how an emulsion with a finite yield stress can be built via large-scale stirring. By gradually increasing the volume fraction of the dispersed minority phase, under the constant action of a stirring force, we are able to achieve a volume fraction close to 80%. Despite the fact that our system is highly concentrated and not yet turbulent we observe a droplet size distribution consistent with the -10/3 scaling, often associated with inertial range droplets breakup. We report that the polydispersity of droplet sizes correlates with the dynamics of the emulsion formation process. Additionally, we quantify the visco-elastic properties of the dense emulsion finally obtained and we demonstrate the presence of a finite yield stress. The approach reported can pave the way to a quantitative understanding of the complex interplay between the dynamics of mesoscale constituents and the large-scale flow properties of yield stress fluids.
查看更多>>摘要：In this paper, the three-dimensional turbulent wall jet flow is investigated for three different developing initial velocity profiles. k- The developing initial velocity profiles at the nozzle exit are generated by three different lengths (l/h = 10, 50 and 90) of the square nozzle (20 +/- 0.5 mm x 20 +/- 0.5 mm). The velocity profiles at the nozzle exit are measured with the single probe hot-wire anemometer. The Reynolds number based on the bulk mean velocity and nozzle height is 25,000 for all the cases. The measured velocity profiles at the nozzle exit are used as the inlet conditions for the numerical simulations. The results show that the initial velocity profile affects the flow field of the wall jet in near and far-field regions. It is found that the contours of streamwise velocity and turbulent kinetic energy exhibit the effect of initial conditions in the near field. l/h = 50 l/h = 90 The Reynolds shear stress component (u'v') dominates in the vertical jet centreline plane, and it increases with a decrease in the nozzle length. The Reynolds shear stress component (u'w') dominates in the lateral plane, and also exhibit the dependency on initial conditions.
查看更多>>摘要：Experiments of particle image velocimetry (PlV) in the turbulent boundary layer at Re-tau- = 400 similar to 1000 have been conducted to investigate the convection characteristic of turbulent structure and the validity of Taylor's hypothesis. Views of 6(delta) x 1.26 (delta = delta 99, the boundary layer thickness) were captured by four streamwise-arranged cameras. Distributions of streamwise turbulent kinetic energy on a streamwise scale were investigated by continuous-wave transform, and scales were found where the portion of streamwise turbulent kinetic energy approaches maximum. Fluctuating velocities (instant velocity minus average velocity on time dimension) were divided into large-scale motion (LSM) and small-scale motion (SSM) portions, bounded by 1 delta. Convection velocities of LSM and SSM are determined by the spatiotemporal correlation method, and they are larger than local average velocities in near-wall regions, but smaller than local average velocities in wake regions. Statistical characteristics between velocity fields reconstructed by Taylor's hypothesis and original fields were compared by the autocorrelation method, and the reconstructed field's patterns are longer than original field's patterns, while their heights do not have clear distinction. The correlation of original velocity fields and reconstructed fields shows that LSM can hold on over 3 delta and SSM over 1 delta in streamwise convection separation for regions of gamma/delta > 0.2, given a threshold value (correlation coefficient C = 0.6).
NSTL
Taylor & Francis