Experimental and computational investigation of flow past two spinning cylinders in tandem.

摘要

Modeling of the flow about spinning cylindrical bodies in tandem is important in the design of smart submunitions for military applications. The objective of this study was to examine the flow about a pair of spinning cylinders, estimate the drag, and explore methodologies to control their relative position during flight. To accomplish this an experimental set up was designed and the Stevens Wind Tunnel utilized to perform the experiments on a pair of right circular cylinders mounted on a rotating sting.; Computations were performed in parallel to cover a wide range of velocities and the results were parameterized in terms of the flow Reynolds number, Rotation number and the separation distance between the cylinders. Reynolds numbers from 160,000 to 260,000, Rotation numbers from 0 to 1.2 and separation distances from 0 to 1 cylinder diameters were analyzed.; A plant model that relates the above parameters to drag coefficient was developed and tested to predict relative motion of the cylinders.; The flow field was found to have both an “open” and “closed” cavity mode. The switching and intensification of these modes and their resultant effect on drag has been shown to be periodic with respect to separation distance, attaining “open cavity” mode initially and intensifying to a maximum at a 3/4 diameter gap. Spinning tandem cylinders were found to retard the transition to an “open cavity” mode leading to a decrease in the drag on the downstream body. This retards separation of the two cylinders.; Combined drag was found to increase with spin at separation distances below 0.5 diameters while above 0.65 diameter separation, the drag decreased with increasing spin. For separation distances ranging from 0.5 to 0.65 diameters, the combined drag can either increase or decrease with spin. For all cases considered, the separation distance significantly affected the differential drag between the two cylinders.; The turbulence intensity near the forward cylinder increases with spin while the turbulence intensity near the aft cylinder is affected by both spin and gap, decreasing with distance from the leading edge.; Incorporation of these findings into a control algorithm would allow munitions to be optimally placed for greatest effectiveness.