科研之友
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摘要
A numerical study is made of the shear flow past a square cylinder (of height A*) near a wall (at a gap height 0.5A*) in presence of a vortex generating upstream rectangular cylinder (of different heights a* and widths b*) placed at a fixed height 1.25A* in an offset tandem arrangement. Influence of fluctuating aerodynamic forces of the vortex generator (VG) on the downstream cylinder (DSC) is investigated based on parameters : spacing between the cylinders S(=DA*), ratio of heights r(2) = aA* (<= 1), aspect ratio r(1) = ba* (<= 1) and Reynolds number Re (based on A*). A formula is derived for local Re-i = Re x (L+r(2)/2-) x r(2) to calculate the effective Re for the VG placed at height L. The critical Reynolds number Re-r1-1.25 (at which the VG of r(1) = 0.1, 0.5 and 1.0 starts to shed the vortices) is predicted (using the formula for Re' and the Lagrange interpolation based on the previous data for single cylinder) and validated in the present study of tandem arrangement. A linear relation between Re-r1-1.25 and r(1) is established to predict Re-r1-1.25 and finally a region of finite volume in the r(1)ReS-space (for the values of r(1), Re-r1-1.25 and critical spacing S-cr for fixed value of r(2)) is proposed in order to generate the unsteadiness in the steady flow of the DSC at lower Re. The governing unsteady Navier-Stokes equations are solved numerically through a finite volume method on a staggered grid system using QUICK scheme for convective terms. The results for the present case of offset arrangement are compared with that for the case of inline arrangement highlighting some of the major issues : generating the vortices by the VG, the appearance of multiple peaks in the spectra of fluctuating lift coefficient, and the deviation of the aerodynamic characteristics of the DSC from that of the isolated square cylinder.
- 出版日期2016-8-1
- 单位哈尔滨工业大学深圳研究生院
