Numerical uncertainty is an important but sensitive subject in computa
tional fluid dynamics and there is a need for improved methods to quan
tify calculation accuracy. A known analytical solution, a Lamb-type vo
rtex unsteady movement in a free stream, is compared to the numerical
solutions obtained from different numerical schemes to assess their te
mporal accuracies. Solving the Navier-Stokes equations and using the s
tandard Linearized Block Implicit ADI scheme, with first order accurac
y in time second order in space, a vortex is convected and results sho
w the rapid diffusion of the vortex. These calculations were repeated
with the iterative implicit ADI scheme which has second-order time acc
uracy. A considerable improvement was noticed. The results of a simila
r calculation using an iterative fifth-order spatial upwind-biased sch
eme is also considered. The findings of the present paper demonstrate
the needs and provide a means for quantification of both distribution
and absolute values of numerical error.