科创中国

Currently, relatively large errors are found in numerical results in some low-specific-speed centrifugal pumps with unshrouded impeller because the effect of clearances and holes are not accurately modeled. Establishing an accurate analytical model to improve performance prediction accuracy is therefore necessary. In this paper, a three-dimensional numerical simulation is conducted to predict the performance of a low-specific-speed centrifugal pump, and the modeling, numerical scheme, and turbulent selection methods are discussed. The pump performance is tested in a model pump test bench, and flow rate, head, power and efficiency of the pump are obtained. The effect of taking into consideration the back-out vane passage, clearance, and balance holes is analyzed by comparing it with experimental results, and the performance prediction methods are validated by experiments. The analysis results show that the pump performance can be accurately predicted by the improved method. Ignoring the back-out vane passage in the calculation model of unshrouded impeller is found to generate better numerical results. Further, the calculation model with the clearances and balance holes can obviously enhance the numerical accuracy. The application of disconnect interface can reduce meshing difficulty but increase the calculation error at the off-design operating point at the same time. Compared with the standard k–ε, renormalization group k–ε, and Spalart–Allmars models, the Realizable k–ε model demonstrates the fastest convergent speed and the highest precision for the unshrouded impeller flow simulation. The proposed modeling and numerical simulation methods can improve the performance prediction accuracy of the low-specific-speed centrifugal pumps, and the modeling method is especially suitable for the centrifugal pump with unshrouded impeller.

Majority of non-Newtonian fluids are pseudoplastic with shear-thinning property,which means that the viscosity will be different in different parts of the stirred tank.In such mixing process,it is difficult to predict accurately the power consumption and mean shear rate for designing novel impeller.Metzner-Otto method is a widely accepted method to solve these questions in mixing non-Newtonian fluids.As a result,Metzner-Otto constant will become a key factor to achieve an optimum way of economical mixing.In this paper,taking glycerine and xanthan gum solutions as research system,the power consumption,stirred by the impeller composed of perturbed six-bent-bladed turbine(6PBT)with differently geometrical characteristics in a cylindrical vessel,is studied by means of computational fluid dynamics(CFD).The flow is modeled as laminar and a multiple reference frame(MRF)approach is used to solve the discretized equations of motion.In order to determine the capability of CFD to forecast the flow process,the torque test experiment is used to measure the glycerine solution power consumption.The rheological properties of the xanthan gum solutions are determined by a Brookfield rheometer.It is observed that the power consumption predicted by numerical simulation agrees well with those measured using torque experiment method in stirring glycerine solution,which validate the numerical model.Metzner-Otto constant is almost not correlated with the flow behavior index of pseudoplastic fluids.This paper establishes the complete correlations of power constant and Metzner-Otto constant with impeller geometrical characteristics through linear regression analysis,which provides the valuable instructions and references for accurately predicting the power consumption and mean shear rate of pseudoplastic fluids in laminar flow,comparatively.