Turbulent Jet
1 Attachment(s)
I am interested in simulating turbulent jets with a 3D solver I've been working on. I was curious if anyone has suggestions on what I should use as an inlet condition. So far I'm using Gaussian noise where my standard deviation is equal to the maximum velocity. I am also setting u, v, w, p = 0 for my initial condition. I am using no-slip everywhere except the inlet and outlet. Does anyone have suggestions on some an inlet condition?
|
I suppose you are working with an incompressible formulation, therefore you cannot simulate the pysical transient from the rest.
At the first time step the flow immediately accomodate for the balance between inflow and outflow and the divergence-free constraint in the interior. That means you have to wait that the solution forgets the initial condition to get a physically correlated flow condition. Therefore, don't worry too much about the initial condition. |
What type of simulation are you doing, LES or RANS? Is the incoming flow turbulent or laminar?
Sent from my iPhone using CFD Online Forum mobile app |
Jet parameters
So far I have not implemented any turbulence models (RANS or LES). I want to start with a simple jet. Should I expect it to take awhile for the jet to form given my initial condition for my velocities are 0 however my inlet is just noise. Just to confirm, u, v, w = 0 except the outlet, is that the correct set of BCs?
|
If you have a good fine grid, you can work in a DNS formulation just setting a parabolic inlet profile (laminar inflow) and let the transition of the jet along x (that is for increasing Re_x). You need a sufficient lenght of the domain and have to wait a physical correlation of the velocity.
|
Inlet condition
|
You need the inlet solution coming from a pipe flow, not a 2D channel
|
Inlet BC (correction)
Much apologies about that, what I meant to say was
Code:
for (int i=60; i < 80; i++) |
Quote:
if the inlet is a duct with squared section, the solution is not that of circular pipe or plane channel... you have to solve the equation Lap u = Re*dp/dx u= 0 on the boundaries of the duct |
Inlet BC
|
But you do not have a circular pipe...the 2d profile in a squared section is quite different.
Here you can find the solution https://books.google.it/books?hl=it&...20duct&f=false |
Strange problem
2 Attachment(s)
So, I decided to change my test for the round jet as its more related to what I need to do. As such,
Code:
for (int i=0; i < nx; i++) |
I don't understand what are you plotting....
Start debugging the first time step, check if the flow rate in inlet is equal to that at the outlet, check the continuity in the interior. Plot the 1D sections of the inlet profile. |
Clarification
The plots I attached are that of the u-velocity from a top perspective and a rotated perspective. I will double check the inlet and outlet. On a side note, for visualization, should I be plotting the magnitude of the velocities? Thanks!
|
Quote:
|
Jet formulation
5 Attachment(s)
So after a few days of working on this problem. I have the following findings. With a parabolic inlet profile I have a problem where the jet does not fully form. What I mean is it starts expanding in terms of the radius of the jet, but not the length of the jet. I have been checking my conservation of mass and it is on the order of 1e-7.
|
And do you get a steady state solution with the jet not entering in the domain?
|
Jet formation
I am of the understanding I should change the inlet to u = 0 so the solution is appropriately contained in the domain?
|
Quote:
No, I wonder what happens just after 1 time step and if you have a flow rate in outlet. Then plot in the plane yz the contour of the u velocity to understand if the inlet profile is correct. |
Jet
1 Attachment(s)
Dr. Denaro, my jet profile at t = 1.0 is attached. My inlet profile is
Code:
for (int i=0; i < nx; i++) |
All times are GMT -4. The time now is 15:29. |