A generalized Karman-like drag law for exotic vortex street equilibria

Th. von Karman showed that the time-averaged drag force on a submerged body producing a 2S vortex wake can be estimated by the features of a representative point vortex model. We generalize this approach, giving drag forces estimates for bluff bodies producing exotic wakes with N>2 vortices per period. The analysis consists primarily of a linear momentum balance applied to spatially periodic point vortex systems moving in relative equilibrium. Linear stability of some exotic vortex street equilibria help justify this approach. Drag force estimates are presented for 'P+S' (N=3) and '2P' (N=4) vortex wakes, and comparisons are made with the classic '2S' drag estimate.