Qin, Y. & Sun, R. Acta Mech. Sin. (2017) 33: 62. doi:10.1007/s10409-016-0622-y
In a recent paper (Li et al., Acta Mech. Sin. 31, 32–44, 2015), the authors claimed that the general solution of steady Stokes flows can be compactly expressed using only two harmonic functions. They present two cases of a flat plate translating through a viscous fluid. The present paper shows that such a two-harmonic solution does not describe the rotation of a circular plate in an unbounded fluid and thus confirms that at least three independent harmonics are required to express the general solution of Stokes equations.