1. A method for simulating a fluid flow on a computer, the method comprising: for one or more locations on or near a boundary surface: performing a first calculation where a local boundary layer is taken to be a laminar boundary layer; performing a second calculation where the local boundary layer is taken to be a turbulent boundary layer; comparing a result from the first calculation where the local boundary layer is taken to be the laminar boundary layer to a result from the second calculation where the local boundary layer is taken to be the turbulent boundary layer; and based on the comparing, selecting the result of the first calculation where the local boundary layer is taken to be the laminar boundary layer or the result of the second calculation where the local boundary layer is taken to be the turbulent boundary layer; and inputting the selected result for the one or more locations into a simulation of activity of a fluid in a volume comprising the boundary surface.