Definition of "wakeless"

Here, γ0(ξ, t) is the vortex bound to Sb in the wakeless ”quasi-steady” flow past Sb which can be determined by steady airfoil theory for the original prescribed Un(ξ, t), with time t frozen to serve merely as a parameter for the moment.

2010 Theodore Yaotsu Wu, "A Review on Fish Swimming and Bird/Insect Flight" arxiv