There are many excellent texts on fluid mechanics, computational and analytical. Please learn the science (theory) before the calculations (software). Don't just run some case with Fluent and think that you understand the subject matter—even if some university will let you get away with this easy path. While it may seem tough now, expectations for graduate students have plummeted over the past half-century. You must climb the mountain in order to see the view. Trust me, it's worth the extra time and effort.

See these books:

1- Small Book By Randy Leveque: "Numerical Methods for Conservation Laws"

2- Large Book by Randy Leveque: " Finite Volume Methods for Hyperbolic Problems"

3- This is very good book dedicated to Convection-Diffusion numerical methods: Numerical Solution of Time-Dependent Advection-Diffusion-Reaction Equations

Those are more from math angle but if you want to look at the same problem from Mechanical Engineering angle see these books:

4- Computational Fluid Dynamics - 2nd edition, By T. J. Chung

5- An Introduction to Computational Fluid Dynamics: The Finite Volume Method by H. Versteeg and W. Malalasekera

6- Computational methods for fluid dynamics, Book by Joel H. Ferziger

These are cover most of the needs you have for your question.

Thank you very much Kaveh Zamani !!

There are many excellent texts on fluid mechanics, computational and analytical. Please learn the science (theory) before the calculations (software). Don't just run some case with Fluent and think that you understand the subject matter—even if some university will let you get away with this easy path. While it may seem tough now, expectations for graduate students have plummeted over the past half-century. You must climb the mountain in order to see the view. Trust me, it's worth the extra time and effort.

Dudley J Benton That is exactly what i am planning to do.Thanks for the advice btw.

Here are some papers:

Article Effect of Vent Aspect Ratio on Unsteady Laminar Buoyant Flow...

Article Unsteady Laminar Buoyant Flow Through Rectangular Vents in L...

Article Effect of Vent Aspect Ratio on Unsteady Laminar Buoyant Flow...