[dreamz]

I am modeling flow of jet of water that strikes a fixed plate. The plate is kept
normal to the direction of flow of water. The water after striking the plate escapes
along the length of the plate. What boundary conditions should I put for this problem?

I have created the following geometry and have tried the boundary conditions but the results are not correct.

Kindly help.

Please find the image of the geometry here:

[`e`]

Are you modelling 2D, 3D, axisymmetric? The inlet arrow should be pointing towards the fluid domain instead of outwards. What results are you getting and how exactly are they wrong?

[LuckyTran]

What type of inlet are you using.

And there shouldn't be symmetry planes.

[dreamz]

I am modeling in 2d and have not modeled it as an axisymmetric problem. I apologize for the lack of clarity in the figure. The arrows are meant only for representation. The inlet I have specified as velocity inlet with velocity of flow inlet in positive direction of x-axis.
About results:
1. I am not able to achieve convergence.
2. The pressure force normal to the plate is doesn't match with the calculated value. I have used the reports option from fluent to get the pressure force.
3. Reversed flow is occurring and the residuals oscillate during iterations.

[dreamz]

@LuckyTran

I have specified velocity inlet. I am confused about the boundary conditions. If symmetry is incorrect then what should I specify there?

[`e`]

Let's start with two things:
1) set your symmetry boundary conditions to wall. Should the perpendicular pressure outlets also be walls instead, or did you want to allow flow to bounce back (requires a larger domain)?
2) if you're intending to model jet flow (pipe) and using 2D planar, then don't. 2D planar flow is as if you're modelling an infinitely deep flow (more of a T-intersection than a pipe jet). Either model the entire pipe (3D) or use 2D axisymmetric conditions (mesh a small wedge of the full geometry).

[dreamz]

@'e'
Actually, if we specify the symmetry boundary conditions as wall then it becomes a flow through a pipe. Which is not the case here. The edges that are given symmetry boundary condition are part of the water jet. Hence, I don't know whether wall will be an appropriate boundary condition or not. Hence I mentioned that I am confused about the boundary condition to be used.

Also the reason I specified perpendicular walls as pressure outlet because they are open to the atmosphere. So, I felt that it should be pressure outlet. I do not want the flow to bounce back that much is clear for me.

I also feel that the small horizontal edges through which the fluid comes out should be modeled as outflow. But is outflow boundary condition suitable or not that I don't know.

Further, I can surely try to model 2d axisymmetric or full 3d flow. But again, I need to be clear about the boundary conditions to be used.

I will try to model according to your suggested boundary conditions and methodology and then see the results, but I want to know the reasoning behind them. Kindly guide me.

[`e`]

If you're simulating water jet flow through air and not within a pipe then you'll need to include the surrounding air (larger computation domain, and you must use a multiphase model). Here are a couple of threads on this topic: 1 and 2; search the forum/internet for further information first if you need some background knowledge.

[dreamz]

@'e'
You are right. I overlooked this fact. The situation which I am trying to model is the one where water jet is through air. I don't know why but the thought of multiphase flow didn't even cross my mind. I will look into that. This is relatively new field for me, multiphase model. I will delve into it deeper and then tackle this problem. But a million thanks 'e' for the eye opener. Now I need to find how to model my problem through this angle. I will get back soon once I find something new..

[`e`]

No worries, I'm glad it's making sense for you now and good luck!