  The multiscale gap-tooth scheme uses a given microscale simulator of
complicated physical processes to enable macroscale simulations by computing
only only small sparse patches. This article develops the gap-tooth scheme to
the case of nonlinear microscale simulations of thin fluid flow. The microscale
simulator is derived by artificially assuming the fluid film flow having two
artificial layers but no distinguishing physical feature. Centre manifold
theory assures that there exists a slow manifold in the two-layer fluid film
flow. Eigenvalue analysis confirms the stability of the microscale simulator.
This article uses the gap-tooth scheme to simulate the two-layer fluid film
flow. Coupling conditions are developed by approximating the values at the
edges of patches by neighbouring macroscale values. Numerical eigenvalue
analysis suggests that the gap-tooth scheme with the developed two-layer
microscale simulator empowers feasible computation of large scale simulations
of fluid film flows. We also implement numerical simulations of the fluid film
flow by the gap-tooth scheme. Comparison between a gap-tooth simulation and a
microscale simulation over the whole domain demonstrates that the gap-tooth
scheme feasibly computes fluid film flow dynamics with computational savings.
