But has the GUI been an overall "win" for the CFD industry? Certainly the GUI has lowered the intellectual barrier required to start using CFD and that has opened CFD analysis to more markets -- markets which can't afford to support an in-house CFD expert. By pressing just a few buttons, a novice user can now generate a complete CFD solution without knowing any of the myriad details which lie below the surface. Questions of appropriate boundary conditions, turbulence closure, etc. never arise because all is hidden behind the powerful user interface.

Is using a GUI too easy? One argument is that the GUI, because of its high accessability, promotes uncritical use of CFD modeling. If we don't understand what the GUI is doing, then how can we ever hope to command it successfully? It is at this point that the GUI becomes a hinderance to the CFD process. The user errors it helps correct (the improper location of a boundary condition, for example), only serve to perfect an incorrect model.

There is also the issue, raised by Tom Christiansen in a Usenet article in 1992 (viewable here), that GUIs make simple things simple and complex ones impossible. A program designed to work solely from the GUI isolates the program from all others. Scripts can not be written to control graphical applications and combine them with other programs to solve a larger more complex problem. Graphical programs are also difficult to run remotely -- something we find ourselves doing more often now that large parallel processing machines are used for flow solutions.

Lastly, graphical programs tend to slow down experienced users. Even a moderate typist can enter commands faster from the keyboard than from a GUI -- and usually with less error.

Like all of engineering, the answer lies in a balance. CFD applications should first and foremost be command-driven "batch" programs able to be controlled through simple keyboard actions (or scripts). Only then should a well-designed graphical interface (one which makes liberal use of keyboard shortcuts) be placed on top of the application.