r. liu

The impeller of a double-suction centrifugal fan may be subject to axial offset due to assembly or operational failure. The internal flow is asymmetric about the central disc and deteriorates the fan’s performance. In this work, the characteristics of flow were numerically investigated for the baseline model (Model-BM) and the axially offset impeller model (Model-Offset). The objective and motivation are to provide a detailed assessment and quantification of the effect of offset impeller on the fan’s performance and transient physics of the asymmetric flow. The numerical data reveal that the offset impeller generates highly asymmetric flow. The difference in mean flow rate at the two inlets of Model-Offset is 25.02m³/h, accounting for 6.8% of the total flow rate. The static pressure rise reduces by 2.40% for Model-Offset, and the static pressure efficiency is reduced by 2.11%. The leakage flow gets pronounced in the enlarged clearance with the inward and outward motion of air, while the narrowed clearance blocks it. The reversed flow is significant in the NA-side blade passages, especially close to the impeller end ring, where the leakage flow and the volute tongue confinement dominate. The reversed flow persists throughout the impeller, is still evident as the air first enters the volute, and is significant on the NA-side of the fan outlet.

There is high flight efficiency of flapping wing aircraft, and its hovering ability, wind loading rating, maneuverability and concealment are better than that of multi-rotor and fixed-wing aircraft. In this paper, the bionic flapping wing is taken as the research subject, and a complete motion process of the flapping wing is divided into four stages by numerical method under the condition of incoming flow. It is found that there is delayed stall mechanism of leading-edge vortex, wake vortex capture mechanism and rotating circulation mechanism in flapping wing flight. On this basis, the impact of flapping wing kinematic parameters on flapping wing aerodynamic characteristics is explored. The effects of different flapping motion parameters on flapping aerodynamic parameters are investigated from three perspectives, including flapping frequency, direction of flapping wing motion and trajectory of flapping wing. It is demonstrated that increasing the flapping frequency can result in an improvement in the lift resistance characteristics. The phase difference of flapping wing motion can affect the angle of attack state for airfoil during flapping. When the flapping frequency, amplitude, and phase difference are identical, there is minimal disparity in the lift characteristics among different trajectories. However, a substantial discrepancy arises in the drag coefficient. The axisymmetric of motion trajectory will also cause significant differences in the lift characteristics.

As Rotating-sleeve Flow Distribution System (RFDS) running, the cavitation of the hydraulic pump may lead to the decreased volume efficiency, increment of vibration and noise, then affecting the operation of system. To deeply analyze the cavitation characteristics of RFDS, the Singhal cavitation model of RFDS was established, meanwhile corresponding experiments were carried out. Cavitation characteristics of RFDS were investigated under various revolving speed, inlet pressure and CAM groove profile. The results demonstrate that the variation trend of experimental volumetric efficiency is the same as that of simulation results. The maximum error is 2% and 3.2% at different rotating speeds and different inlet pressures respectively. Maximum gas volume fraction and cavitation time ratio increase monotonically as the rotating speed increases, and volumetric efficiency increases first and then decreases with the increase of rotating speed. Volumetric efficiency reaches up to 92.13% under the rotating speed of 500r/min. The increased inlet pressure can slow down the cavitation of RFDS and improve volumetric efficiency. Linear profile exhibits the best cavitation characteristic under both different rotating speed and inlet pressure.