# Vertical 2D, Variable density flow with hydrostatic pressure assumption

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 11, 2014, 03:51 Vertical 2D, Variable density flow with hydrostatic pressure assumption #1 New Member   Ehsan Join Date: Nov 2013 Posts: 5 Rep Power: 8 hi everybody i'm trying to model a 2D vertical flow with variable density and hydrostatic pressure assumption. would anybody help me know which one of cfd simulation softwares can model this type of flow ?? as far as i know, flow3d is unable to model this flow and i don't know about other softwares. thank U

 May 14, 2014, 09:53 #2 New Member     Vijay Mali Join Date: Apr 2014 Location: India Posts: 18 Rep Power: 8 Hi Ehsan, I think this should be possible to do this in ANSYS FLUENT. But I would like to know more about your problem to confirm this. Could you please share more details about the problem? ehsansh89 likes this.

 May 15, 2014, 06:14 #3 New Member   Ehsan Join Date: Nov 2013 Posts: 5 Rep Power: 8 Hi vijay. thank U for your reply I'm trying to model a 2D vertical (in X and Z directions) free surface flow and apply it to some test cases. but this model should have some specs. first, the water density is variable over the flow field (because of a temperature gradient or salinity gradient). second, the pressure is assumed to be hydrostatic (p=gamma*h). in other words, in the vertical momentum equation (momentum equilibrium in Z direction), we neglect the terms including w (velocity in Z direction). and i'm trying to find a cfd software that is able to model this flow. I would appreciate it if you could let me know if my explanation about problem is enough detailed. thank U

 May 16, 2014, 07:15 #4 New Member     Vijay Mali Join Date: Apr 2014 Location: India Posts: 18 Rep Power: 8 Hi Ehsan, What I understood from your explanation is this : You have 2D vertical duct in which you want to model the flow. You want to make density as a function of either temperature or salinity. This should be possible using ANSYS FLUENT. There are inbuilt density vs temperature functions you can use. For salinity, you may need to write UDF but its possible to do (with some hard work ) Please explain more on: 1) What do you mean by free surface flow. Do you mean that you want to model free surface between water and air 2) What do you mean by the pressure is assumed to be hydrostatic 3) What do you mean by we neglect the terms including w Thanks Vijay ehsansh89 likes this.

 May 18, 2014, 07:39 #5 New Member   Ehsan Join Date: Nov 2013 Posts: 5 Rep Power: 8 Hi vijay free surface flows are a category of flows that have a suface in touch with air, for example flow in channels, rivers, lakes, oceans ,etc. in this flows relative pressure in the free surface is equal to zero. in contrast, for example flow in pressure pipe is not a free surface flow. let me explain more about hydrostatic pressure assumption: suppose a still lake with no flow in it. in every point under the water, pressure is equal to gamma*h. this is a hydrostatic pressure. now suppose that the wind blows and causes a flow in the lake. now every point of the water has a u(horizontal velocity) and a w(vertical velocity). now the pressure in a point is not equal to gamma*h. because presence of w produces an additional pressure and in this situation pressure is equal to (gamma*h)+(additional pressure produced by w). this is a hydrodynamic pressure. now i want to modell a flow (that has u and w), but i want to assume that pressure is hydrostatic (because in my test cases the additional pressure produced by w is small and negligible) and study the flow with the hydrostatic pressure assumption. thanks a lot for your help vijay. ehsan

 May 19, 2014, 11:20 #6 New Member     Vijay Mali Join Date: Apr 2014 Location: India Posts: 18 Rep Power: 8 Hi Ehsan, Do you mean to say that you want to model a following 2D section flow : 1) The direction is X (horizontal) and Z (vertical) 2) X velocity (u) is considerable, Z velocity (w) is negligible 3) Hydrostatic pressure variation in Z direction (due to change in density or other stuff) In your initial post, you said 2D vertical flow, but later replies you said u is considerable but w is negligible. It means its a horizontal flow If above problem understanding is correct, I feel its pretty straight to model that. Let me know if I am missing something. Thanks Vijay ehsansh89 likes this.

 May 24, 2014, 13:09 #7 New Member   Ehsan Join Date: Nov 2013 Posts: 5 Rep Power: 8 Hi no, no, w is not negligible. the pressure produced by w is negligible. the model is 2d vertical and has u and w. Thanks a lot dear Vijay