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Renjing Cao,Zhouming Liu 한국유체기계학회 2021 International journal of fluid machinery and syste Vol.14 No.3
A computational model is formulated to investigate the unsteady flow characteristics of a circular cylinder behind an impinging airfoil near-wake at Re=200. The distance between the airfoil trailing edge and the downstream cylinder axis is fixed at 1.5D where D is the diameter of circular cylinder and the lateral spacing is varied from 5 to 5 so as to numerically investigate the effect of lateral spacing on the flow characteristics. The present work is concerned on the following aspects: the general flow patterns, the vortex shedding frequency, force fluctuations and spectra, as well as the effect of lateral spacing on the flow features at low Reynolds number and small axial spacing. The calculated flow pattern and its comparison with the visualization by Laser-Induced Fluorescence (LIF) technique are conducted. It is determined that three regimes can be defined in terms of H/D, where H is the distance between the cylinder center and the line extended from the airfoil leading edge to trailing edge. And four kinds of typical flow pattern associated with the three regimes can be identified accordingly. It is interesting to find that both the fluctuations of lift and drag forces on the circular cylinder exhibit symmetric features centered at H/D=0 and the dump distribution of C′D is found as well.
Performance Prediction and Flow Field Calculation for Airfoil Fan with Impeller Inlet Clearance
Kang, Shin-Hyoung,Cao, Renjing,Zhang, Yangjun The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.2
The performance prediction of an airfoil fan using a commerical code, STAR/CD, is verified by comparing the calculated results with measured performance data and velocity fields of an airfoil fan. The effects of inlet tip clearance on performance are investigated. The calculations overestimate the pressure rise performance by about 10-25 percent. However, the performance reduction due to tip clearance is well predicted by numerical simulations. Main source of performance decrease is not only the slip factor but also impeller efficiency. The reduction in performance is 12-16 percent for 1 percent gap of the diameter. The calculated reductions in impeller efficiency and slip factor are also linearly proportional to the gap size. The span-wise distributions of phase averaged velocity and pressure at the impeller exit are strongly influenced by the radial gap size. The radial component of velocity and the flow angle increase over the passsage as the gap increases. The slip factor decreases and the loss increases with the gap size. The high velocity of leakage jet affects the impeller inlet and passage flows. With a larger clearance, the main stream moves to the impeller hub side and high loss region extends from the shroud to the hub.