No abstract

Aerodynamic characteristics of two tandem square cylinders are investigated in horizontal and diagonal arrangement respectively, with the variation of the spacing ratio (i.e. the center-to-center space P versus the width B of the square cylinder) P/B=1.75-5 at Re=8×10 4 in the present study. The study focuses on the aerodynamic characteristics of diagonal tandem cylinders and the comparison with those of horizontal tandem cylinders. The results show that the aerodynamic characteristics of two diagonal square cylinders are distinctly different from those in the horizontal arrangement. At the small spacing, the mean and fluctuating aerodynamic coefficients, the maximum of mean negative pressures and the fluctuating pressures for diagonal tandem cylinders are noticeably larger than those of horizontal tandem cylinders due to a pair of recirculation flows. It is interesting that there are multiple peaks in the power spectra of diagonal tandem cylinders. The Strouhal numbers corresponding to the predominate peak of diagonal tandem cylinders are clearly smaller than those of horizontal tandem cylinders at the same spacing ratio. Additionally, the inter-and intra-cylinder correlations of aerodynamic forces for two types of arrangements change diversely with the variation of the spacing ratio. Moreover, the flow modes should be different from those of two horizontal tandem cylinders, which could be concluded to three regions in the investigated spacing ratio.

To study the gas and liquid flow characteristics inside the diaphragm compressor and optimize the structure of the gas and oil chambers to improve the overall reliability of the machine, the CFD method was used to establish fluid models for the gas and oil chambers separately. The velocity and turbulence energy distribution of the gas chamber, as well as the pressure and flow velocity distribution of the oil chamber, were obtained. Various layout schemes for the gas and oil holes were optimized and compared. The results showed that the maximum flow velocity and turbulence energy of the gas chamber for scheme 1 were greater than those of the original design, but both decreased gradually for schemes 1-4. The centering of the distribution hole in the oil chamber had a significant effect on fluid characteristics, and the results from schemes 1-4 indicated that as the hole diameter increased, the maximum flow velocity and pressure gradually decreased. Additionally, under the condition of ensuring that local stresses were not too high, the fourth scheme was the optimal solution for both the gas and oil chambers. The maximum turbulence energy of the gas chamber decreased by 29.1% compared to the initial structure, and the maximum pressure and velocity of the oil chamber decreased by 35.5% and 71.5%, respectively.