In order to analyze the influence of the number of blades on the radial force characteristics of pump as turbine during the variable flow rate transition process, six impellers with different number of blades are designed. On the basis of verifying the correctness of the numerical calculation method by the external characteristic experiment, the steady and unsteady numerical simulation of each scheme is carried out by ANSYS-CFX software, the radial force characteristics on impellers with different schemes are compared and analyzed. The results show that during the transition process of variable flow rate, the radial force vector and its fluctuation range on the impeller gradually decreases with the increase of the number of blades. The radial resultant force obviously increases with the increase of time in the transition to large flow rate, and obviously decreases with the increase of time in the transition to small flow rate. The dominant frequency of the radial force is equal to leaf frequency, and the pulsation amplitude of the radial force of Z9 is the minimum in both transition processes. In the transition process of variable flow rate, when the number of blades is Z9, the efficiency is the highest, the radial force on the impeller is the minimum, and the pulsation amplitude of the radial force is also the smallest, so for this pump as turbine, the value of blade number equals 9 is the optimal.
In this study, we analyze the flow characteristics of pulp suspensions in a sudden expansion channel, which is used as a tube bank in papermaking machines. Flow visualization using a light section method and measurements of time-averaged and fluctuating fiber concentrations, Ca and C’, and pressure, were performed. The experiments were carried out on pulp suspensions with a bulk fiber concentration (Cs) of 0–2.0 wt% in a channel with an expansion ratio of 2 at varied average velocities (Ua) of 0.046.6 m/s. We examined the effect of flow velocity on the changes in concentration and pressure distributions along the channel axis. The distribution of the pulp fiber concentration behind the sudden expansion significantly changes depending on the flow state in the upstream channel before the expansion. In particular, for low and moderate velocities, the flow field is characterized in the main flow region consisting of flocculated plug fibers and a recirculation region with a low concentration near the expansion corner by a type of streamline originated from the thin water-layer in the upstream channel. The distribution of Ca shows a tongue-shaped structure in the central part of the cross section, and C’ is large near the annulus streamline. As the velocity is further increased, the flocculated fibers gradually disperse, and the distributions of Ca and C’ become almost uniform. In addition, the uniformity of fiber concentration does not change much in the section downstream from a distance 10 times the step height from the sudden expansion plane.