| Since the lead-based alloy has excellent thermal hydraulics and neutronics performance,it is used as the coolant material in the advanced nuclear systems such as the Generation-IV reactors and fusion reactors.The flow field of liquid lead-based alloy is one of the important parameters for the design of thermal hydraulics and key components,as well as the experiments of material corrosion for advanced reactor.At present,the ultrasonic Doppler velocimetry(UDV)is considered as one of the most potential methods for the flow field measurement of high temperature liquid metal.According to the propagation characteristics of ultrasonic wave and the experiments of flow field measurement,the acoustic pressure causes disturbances on fluid,the flow tracking capability,ultrasonic scattering and concentration performance of tracer particles will greatly affect the flow field measurement.In this paper,the studies of theories and experiments are performed to study the above mentioned factors systematically,and the main conclusions are made as follows:(1)It is analyzed with multi-fields coupling method for the distribution characteristic of fluid disturbances induced by acoustic pressure.The disturbances have great fluctuations in the near ultrasonic field(3?28 mm/s),and it decreases with the increase of propagation distance in the far ultrasonic field.In addition,the disturbance effect is increased with the excitation voltages,while it decreases with acoustic impedance,and the influences caused by the backing layer is small.When the backing layer thickness is 8 mm and the excitation voltages achieves 36 V,the disturbance of 28 mm/s is generated in the lead bismuth fluid,which will greatly disturb the measurement of transient flow fields and turbulence fluctuations.(2)It is studied for the influencing of the flow tracking capability,the ultrasonic scattering performance and the concentration of tracer particles on velocity measurement through theoretical analysis and experiments.The flow tracking capability ? decreases with the density ratio pp/pfbetween particle and fluid,and the particle diameter dp,which will lead to the great difference between the motion velocity of tracer particle and the flow velocity.While the ultrasonic scattering performance ?s increases with dp,and pp/pf,which will improve the echo strength and measuring signal-to-noise ratio.In this paper,Polyamide tracer particle with dp=40?m is selected,and its concentration performance is studied by experiments.The results indicate that the concentration n is coupled with Reynolds number which affect the measuring accuracy when n<12/mm3,while no effect on measuring results when n?12/mm3,and the threshold of the ultrasonic scattering characteristic parameter?0=?sn=4.8×10-3 for the velocimetry is determined.Therefore,the selection of tracer particles should commonly meet 0.99???1.01 and scattering characteristic parameter?=?sn?4.8×10-3.(3)Both measuring experiments and numerical analysis for complex one-dimensional and two-dimensional vortex flow field are performed,and the results indicate that the one-dimensional flow field in the radial direction presents well central symmetry distribution.The experimental results and numerical simulation results are in good agreement,and the relative deviation between them is better than 15%.In addition,according to the comparison for the vector and contour graph of the vortex flow field which obtained by experiments and simulations,respectively,it is found that the positions of the domains with high flow velocity and the domains with low flow velocity are corresponding the same,the vortex centers for the fluid domains above the impeller are near the position of(r=95 mm,h=l50 mm),and the vortex direction above the impeller is counterclockwise while the below vortex is the clockwise,which indicate that the experimental measurement results agree well with the numerical simulation results.Based on the surveys of the acoustic pressure and tracer particles,it provides important foundation for the error analysis and experimental condition optimization of the UDV measurement,which ensures the measuring reliability from the sources.And according to the verifications of flow field measurements in the complex flow states,it lays a solid foundation for the engineering applications such as thermal hydraulics studies. |
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