creating mesh from scratch
 

Can anyone guide me how to create a mesh for air duct with reducers and elbows, to be used in fluent 3D.

Tutorials?
 

That is a broad question...

What software are you using? Have you tried any of its related tutorials?

If you are looking for a software, you could try ANSYS Meshing if the geometry is straight forward enough.

Try ICEM CFD if you think it is more complicated or you are starting with poor or faceted geometry.

Simon

thanks simon,

we are using ansys workstation. can i use turbo grid for that purpose?

U can start by seeing the modeling guide of gambit (assuming u are using Gambit) - 'meshing the geometry' section. This is a part of gambit documentation. Then u can try various schemes like :-
(i) Cooper for the duct volume or
(ii) Generate a face mesh followed by volume mesh.

All depends on ur PC viability and memory requirements.