Abstract: Virtual flow estimation is described that is suitable for use under steady-state and non-steady-state (i.e., transient) conditions. Examples of such an approach may not perform discretization of the underlying model described by partial differential equations, but may instead perform discretization in a derived estimator separate and distinct from the underlying model. In this manner, a non-executable continuous time-estimator may be transformed to an executable discrete time-estimator suitable for use in under non-steady state (i.e., transient) conditions.