Numerical Analysis of Fluid Forces for Flow Past a Square Rod with Detached Dual Control Rods at Various Gap Spacing A twodimensional numerical study was conducted for flow past a square rod in the presence of two control rods. One is placed vertically in the upstream direction and the second one is placed horizontally in the downstream direction of the square rod. The influence of gap spacing was studied by taking g1  1xe2x80x935 and g2  0.5xe2x80x935 (where g1 is the gap between the upstream control rod and the main rod, and g2 is the space between the main rod and the downstream control rod) at Re  160. The simulation results were obtained in the form of vorticity contour, drag and lift coefficients, Strouhal number, and force statistics. Under the effect of gap spacing, three different flow modes were found and named according to their behavior. It was found that the mean drag coefficient showed decreasing behavior by increasing the value of g2 continually at a fixed value of g1. The largest value of     C d m e a n     was found at (g1, g2)  (1, 1) and the greatest percentage reduction in     C d m e a n     was obtained at (g1, g2)  (1, 3), which is 139.72%. The effect of thrust was also noticed for all selected values of g1 and g2. Furthermore, it was noticed that the Strouhal number and the root mean square values of the drag and lift coefficients smaller values than the single rod values, except for the Clrms value of (g1, g2)  (1, 3) and (1, 4).

Research on Finite Ground Effect of a Rotor The enrichment of the application scenarios of rotorcrafts presents new challenges for the study of their aerodynamic characteristics, such as operating above a building surface of finite size. In this paper, the ground effect is divided into infinite ground effect and finite ground effect, and three types of finite ground effects with different blocked area are studied. Through numerical simulations, the rotor thrust data and flow field figures in ground effect are obtained. Based on the rotor thrust data, mathematical models are established to describe the rotor thrust alteration caused by infinite and finite ground effect. The analysis of the flow field reveals the mechanism of the finite ground effect.