Experimental Determination of Reactions of Wind-Resistant Support of Circular Stacks in Various Configurations
Higher capacities of power plants together with increased awareness on environmental considerations have led to taller height of stacks. It is seen that strong wind can result in falling of stacks. So, aerodynamic consideration of stacks is very important in order to save the falling of stacks. One stack is not enough in industries and power sectors and two or three stacks are required for proper operation of the unit. It is very important to arrange the stacks in proper way to resist their downfall. The present experimental study concentrates on the mutual effect of three nearby stacks on each other at three different arrangements, viz. linear, side-by-side and triangular. The experiments find out the directions of resultant forces acting on the stacks in different configurations so that proper arrangement of supports can be made with respect to the wind directionality obtained from local meteorological data. One can also easily ascertain which stack is more vulnerable to wind in comparison to the others for a particular configuration. Thus, this study is important in studying the effect of wind force on three stacks in different arrangements and is very helpful in placing the supports in proper places in order to avoid failing of stack-like structures due to wind. Keywords—Stacks, relative positioning, drag and lift forces, resultant forces and supports.
Drag of circular cylinders in the atmospheric turbulence
A field experiment on the drag of circular cylinders was conducted during the approach of typhoon T9806 towards Kagoshima, Japan. A rotatable drag-measurement facility was developed which could orient itself perpendicular to the mean wind, and was deployed in an open field. Using this facility, we have successfully evaluated the drag coefficients Cd of circular cylinders. The results show that the Cd values of cylinders in a highly turbulent flow in the atmosphere are approximately equal to those in a smooth flow in wind tunnel experiments. This implies that the cylinder drags in a large-scale turbulence are close to the values in a smooth flow.
Interference between two circular cylinders; Series of unexpected discontinuities
When two cylinders face the flow one behind the other then they are in tandem arrangement. The systematic measurements of the front (gap) and base pressures of the downstream cylinder at various spacings showed a discontinuous ‘jump’ at some critical spacing. The drag force coefficients on the downstream cylinder showed a similar discontinuous change at the same critical spacing. This was attributed to two different flow patterns around the tandem cylinders. 
 
Following this, two cylinders arranged side-by-side to the approaching flow were considered. The inherently biased flow in the gap between the cylinders produced two different flow patterns around each cylinder. The biased flow was bistable causing a change over at irregular intervals of time. Thus each cylinder might be subjected to either of the two drag and lift forces. All the available data on measured forces were compiled together with the additional measurements in the range of spacings within which intermittent change-over of drag and lift took place. 
 
When two cylinders are neither in tandem nor in side-by-side arrangement then they are staggered. The systematic measurements of drag and lift forces on the downstream cylinder showed two unexpected features. Firstly, the position of the downstream cylinder at which the maximum lift force was exerted on it was plotted in transverse, (TD),-longitudinal, (LD), plane. Two different curves were obtained which overlapped one above the other within a range of staggered arrangments. This feature of the maximum lift force was considered as a sign that two entirely different flow patterns were the cause. 
 
The second feature found was that at some spacings the minimum drag force did not occur in the tandem arrangement but in adjacent staggered arrangements. A plausible explanation was offered for that peculiar CLmax and CDmin behaviour. 
 
Finally, a discontinuity in the lift force for some staggered arrangements was found and attributed to the bistable flow patterns in the gap.