[doug]

All,

I just ran a laminar 2D plane jet in fluent, but don't get the same as the similarity solution of Schlichting (1933). Any ideas why? My case is as follows:

Jet Reynolds number = 2.0
Jet half-width = .01
domain = 400x400 jet half-widths
I'm using a symmetry boundary condition along the centerline of the jet
The jet emerges from a wall boundary condition.
I use a wall boundary condition in the farfield transverse from the jet direction I use an outlet boundary condition in the farfield of the jet direction.

Is there an assumption that the similarity solution makes that must be enforced to match it?

Thanks.

Doug

[maryam]

helolo
if you solve your problem, please help me, guide me

[doug]

I changed my approach and it is working much better. From Schichting's study, you can get a velocity profile any distance, x, downstream of the virtual flow source. I'm using that velocity profile and reading it into Fluent and setting the inlet as a velocity inlet boundary condition with that velocity profile. Then you have to set the farstream boundary conditions in x and y to pressure boundary conditions. Then use the symmetry boundary condition through the centerline of the jet. This seems to be working great. Here are two pdf files that show my results. The f_center.pdf shows the centerline velocity as a function of x on a log-log plot vs. the analytical solution. The f_conv.pdf file shows the x-velocity profile at three locations along x. Hope that's helpful.

Doug

[maryam]

Hello, thank you for your help,
I want to simulate wall jet with Re=1000 and Velocity= 1m/s ,
now I generated mesh and imported to fluent,

I set all of data in fluent , I use a 2d box with 220mm hieght, 1000mm lenght and 10 mm slot width,

now I want to define boundary condition for it( inlet velocity for slot width, out let pressure for end of surface, no slip for bottom wall) and I don't know what can I do with top wall or free surface, I used pressure inlet and another time, wall specified shear but my simulation was wrong, please help me.

or if you know about jet tutorial please guide me.

thanks
maryam ( m_amiraftabi@yahoo.com)

[maryam]

how can I set velocity profile??
please help me, I will be crazyy.............
I use Define>profile>write>inlet velocity>velocity magnitude>write
then read>..
but it doesn't work

[maryam]

I think alot about your writing, but there is a problem that whether my mesh is true or not, I think your mesh should be different, so if it is possible help me, because it is very important to me
best
maryam

[maryam]

Thank you very much for your help, I finally could simulate turbulent wall jet and find data.
but if it is possible for you, please tell me how do you computed origin point (x.) at boundary layer theory book for laminar part??
because I should find origin point for turbulent and compare my data with analytical formulas. in chapter 22.8 boundary layer theory.

best
Maryam

[CaptainM1K]

Hi Doug

I am simulating a wall jet in Fluent and need to define the inlet velocity profile. I am then going to use validation data from experimental results by Karlson et al. Please help. Thanx

[doug]

Maryam,

it is difficult to compute an x-location for the turbulent jet. I haven't worked that out yet. However, for the laminar jet, it's pretty straight forward. I'm attaching a writeup for my laminar jet. Given the solution from fluent, you can calculate Eqs. 5.4.1 and 5.4.2 from the writeup, and then back out the x-location by rearranging 5.4.7 or 5.4.8. Like I said, I'm not sure how to do it with turbulent flow just yet.

[taw]

Hi Doug,

But why does the pressure boundary condition works. Fluent gives the solution, that is great. But here the channel is not a pump / turbine. But suppose you write your own code, how is this set up. Can someone explain. Or this equivalent to using SIMPLER other than SIMPLE solver.

Cheers,

taw

[samurai_01]

Hi everyone

You can use Pressure outlet BC for all top and outlet, as the domain is theoretically unbounded.

At inlet you can use velocity inlet.

at bottom= symmetry.

Iam attaching the results i have obtained for 300 inlet Re.
JET.jpg

Hop you find this useful!!!

[JiDo]

Hello guys, I am trying to simulate the same thing, 2D planar jet entering a quiescent atmosphere and I have a problem with reversed flow. Has anybody ever encountered this problem?

I am using velocity inlet for the orifice and then pressure outlet on each remaining edge, except the nozzle which is no slip wall. Fluent keeps announcing me that I have the reversed flow at the BC pressure outlet. I tried also put pressure inlet, instead of outlet, but that did not help at all - the same error just for pressure inlet.

Moreover when I plot velocity in x-axis I can see that the most of the domain has a negative velocity. I have no idea why. I would expect that the jet will be entraining the surrounding fluid and so move it to the same direction.

Thanks a lot for any advice.