Flow Stability in a Miniature Centrifugal Pump under the Periodic Pulse Flow

The flow behavior inside a miniature centrifugal pump, under a periodic pulse flow rate, was studied by means of numerical simulation. For a given incoming periodic pulse flow with a sine wave, the performance of the centrifugal pump was investigated in the section with increasing flow and the section with decreasing flow, and the special points of the flow rate and the periodic flow were identified. Further, the energy gradient method and the Q-criterion were adopted to analyze the internal vertical structure and flow stability. It was found that the regions with large variations in velocity and total pressure were mainly located at the leading edge of the suction surface and the middle area of the pressure surface of the blades. Irregular pressure fluctuation frequency under the periodic pulse flow was shown; this was mainly concentrated in the low-frequency zones close to the impeller’s rotational frequency. In addition, for the same flow rate in the periodic pulse flow, the pressure frequency fluctuation for the increasing flow rate section was higher than that observed for the decreasing flow rate section. It was found that the most unstable sections appeared in the first half-period of the flow rate variation (large flow rate), according to the distributions of the Q criteria of the vortex and the energy gradient function K. In this section, motions of strong vortices led to large gradients of the mechanical energy.

Unusual Emission Variations Near the Eclipse of Black Widow Pulsar PSR J1720−0533

We report on an unusually bright observation of PSR J1720−0533 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar is in a black widow system that was discovered by the Commensal Radio Astronomy FAST Survey (CRAFTS). By coincidence, a bright scintillation maximum was simultaneous with the eclipse in our observation, which allowed for precise measurements of flux density variations, as well as dispersion measure (DM) and polarization. We found that there are quasi-periodic pulse emission variations with a modulation period of ∼22 s during the ingress of the eclipse, which could be caused by plasma lensing. No such periodic modulation was found during the egress of the eclipse. The linear polarization of the pulsar disappears before the eclipse, even before there is a visually obvious change in DM. We also found that the pulse scattering may play an important role in the eclipse of PSR J1720−0533.