Research On Reducing Turbine Flowmeter's Sensitivity To Viscosity Change

As an important flow meter, turbine meter is widely used in many fields for its sole merits. The change of fluid viscosity is one of the main factors that affect the performance of turbine flow meter. It is significant for improving the accuracy and extending application fields to reduce the effect of viscosity change on turbine meter. This thesis reduces the sensitivity of turbine flow meter to viscosity change by optimize the structure and the geometric parameters of its design. The mainly research works of this thesis are as following. 1. The effect of viscosity change on the performance of turbine meter, the correctness of it, the mechanism of it and the means of reducing it are further analyzed. 2. Based on the analysis of previous mathematic model's shortages, a viscous mathematic model of turbine flow meter is developed, by the combination of the boundary layer theory and the Kutta-Joukowsky airfoil theory considering the effect of the viscous boundary layer on the torques calculation. When the turbine meter measures the high viscosity fluid, this model has good accuracy of meter factor prediction. The characteristics curves predicted by the viscous model, adopting different velocity profile at the inlet of rotor blades, are analyzed. The validity of this model is verified by comparing the characteristics curves with those obtained from water flow and high viscosity fluid experiments. 3. The method for optimization the geometric parameters of turbine meter rotor is put forward on the base of the viscous mathematic model of turbine meter. And a team of geometric parameters of turbine flow meter, which is non-sensitive to viscosity change, is obtained in theory. A novel structure of rotor hub is put forward by the analysis of turbine meter rotor hub, is that hollow hub. It is confirmed by the experimental data that the sensitivity of the turbine meter to the viscosity change is reduced by this hollow hub rotor. Five mathematic models of permanent magnet bearings are compared with each other. As a result of it, the accuracy of performance parameters calculation is improved. Based on the analysis of previous turbine flow meters with magnetic bearings, a novel structure is put forward, namely, turbine meter rotor is supported by two axially magnetized radial magnetic bearings and two pivot bearings. The theoretical analysis of the novel structure and the computation of performance parameters are shown also. 4. The variation of the velocity profile at the inlet of turbine rotor blades is studied by the numerical simulation of the two-dimensions flow field inside the annulus pipe when the fluid viscosity or the velocity profile at the inlet of the meter change. The structure of the upstream flow conditioner is analyzed. The effects of cylinders with different shape front ends on flow regime are compared with each other. The variation of velocity profile, induced by the change of fluid viscosity, at the inlet of rotor blades is controlled by the sharp change of the hub shape of the upstream flow conditioner, at the rear end of it. The method for prediction the meter factor of the turbine flow meter by the computational fluid dynamics (CFD) software package (FLUENT) is put forward. The law of the fluid flow inside the turbine meter is gotten through the three-dimensions numerical simulation of the flow field. The advices for optimization the turbine meter design are given.