History forces and the unsteady wake of a cylinder

History forces on a stationary cylinder in arbitrary unsteady rectilinear f low are calculated by means of a model based on the asymptotic properties o f the steady-state wake. The results capture many features found in numeric al solutions of the Navier-Stokes equation for the same flows, though quant itative agreement deteriorates as the Reynolds number increases over the ra nge 2 to 40. The cases studied are the impulsive start, stop, and reverse, and oscillatory flow.