There are various reasons why CFD is becoming popular, some of which are:

• CFD allows numerical simulation of fluid flows, results for which are available for study even after the anaylsis is over. This is a big advantage over, say, wind tunnel testing where analysts have a shorter duration to perform flow measurements.
• CFD allows observation of flow properties without disturbing the flow itself, which is not always possible with conventional measuring instruments.
• CFD allows observation of flow properties at locations which may not be accessible to (or harmful for) measuring instruments. For example, inside a combustion chamber, or between turbine blades.
• CFD can be used as a qualitative tool for discarding (or narrowing down the choices between), various designs. Designers and analysts can study prototypes numerically, and then test by experimentation only those which show promise.
  

Source : CFD -wiki