FLAT SPIN OF A CIRCULAR-CYLINDER

Experimental results are analyzed to develop an understanding of the f low physics causing flat spin of circular cylinders in the critical Re ynolds number region. The analysis shows that the flow phenomenon play ing the key role in producing flat spin is a three-dimensional moving wall effect, which becomes especially powerful in the critical flow re gion by controlling how separation through its effect on boundary-laye r transition. Three-dimensional flow phenomena appear to establish the spanwise venting needed to sustain the asymmetric dow separation. It is also found that three-dimensional nonuniform roughness as well as b ody microasymmetry play important roles in initiating the flat-spin mo tion.