Now one question about gravity effect comes to me. i'd like to simulate a channel flow in cfx considering the effect of gravity. The fluid material is constant density water. How can i simulate it? In my testing, the option of buoyancy is not usefull for constant density. How should i do? any suggestion from you?

Two phase homogenous model.

Free Surface Flow - Tutorial 7

If I only want to simulate single phase flow,and the material is constant density(not related by temperature or pressure),how should i do?

If Buoyancy doesn't help you could program yourself a hydrostatic pressure - see also tutorial 7. Actually I don't understand your problem. Maybe you should be more precise.

Thanks, For example, i 'd like to simulate a water siphon tunnel.you know the gravity is very important for this case. But as the explaination of CFX documents, the buoyancy is only affected by density change. in my case,the fluid material is constant density water.

If you do not have two different phases in your model, then there is no need to include buoyancy. You have include the hydrostatic pressure differences in your pressure boundaries.

Astrid

There is the full buoyancy model and the Boussinesq approximation available in CFX. This info might be useful. Read CFX manual for this. TobiasZ