Hi Paolo,
Some aircraft include these effects such as the Project Airbus A320 but I believe you can add them to others. If you search in the Avsim library for 'vortex' or 'vortices' you will see about 100 hits.
These include a file called 'ntdfx_174164.zip' which allows you to add touchdown and vortex effects to your aircraft in FS2004/FS2002 - I haven't tried it but it could be what you're looking for...

EDIT: There's an interesting thread in the Avsim Forum on this issue that explains how to add effects of this type - look
here...