I make calculation of my model of finned heat exchangers by Ansys Fluent. Model is somewhat complicated and have abut 5 millions elements and 8 inflation's layers. I chose k-epsilon method for solving and choose pressure outlet and velocity inlet for air (1 m/s).
On outlet is appeared reversible flow on great amount (see atachment). What is reason?
How to eliminate this reversibilke flow?
Did i make some mistake in input data?
Hello Mr.Malden
Reverse flow happens whenever pressure increases in the flow direction. In numerical solution, say, for instance, in the positive x direction, i th node pressure is lesser than the (i+1)th node pressure during computation. The possible ways to avoid this are:
1. check BC as previous people suggested
2. check initialization pressure. For example ur outlet pressure BC is 1 atm and u initialize ur entire domain with less than 1 atm pressure, then, for sure, u will get reverse flow. If ur case is steady then no need to worry about initialization, provided u have given the proper BC.
Hi, Vigneshwaran
Here is BC. Because of different temperature profile on outlet there is different air density and probably ocuaring lifting efect. This lead to different pressure profile and reverse flow. But still I am suprised for amount of this reversed flow.
Hi Mr.Malden,
I am assuming ur operating pressure is 1 atm. Can u please answer these:
1. Ur case is steady or transient?
2. Wat initialization method u followed, either standard or hybrid or any other ?
3. If so, Wat is the pressure in ur domain before beginning the iteration?
4. Number of reverse flow cells increasing with increase in iterations?
steady, hybrid, operating pressure is 1 atm, number of cell total is about 1400 (as I remember started with less than 800 cell) ... right now I am not at computer
Since ur case is steady we cannot jump into any conclusion before the solution is converged. So wait for the converged solution eventhough u r getting reverse flow in some cells. Also if the number of reverse flow cells are decreasing with iterations then u need not have to worry about the solution.
Anyway if u r not satisfied with your converged solution u can try standard initialization with inlet pressure in your domain. If your inlet pressure is more than the outlet then u must not get reverse flow.
OK, thanks.
Additionaly I will try to improve mesh with controling mesh method.
reverse flow or reversible flow?
Is your 2nd figure the whole computational domain, i.r., the right-most boundary the computational boundary?
Did you check the streamline or velocity vector?
Mr. Shiuh-Hwa Shyu
Fig. is whole computional domain. Velocity is accordance with picture.
I thought the contour is for temperature. PLease look at the velocity vector as well as streamline to make sure that you see a reverse flow
I will bring my past experience. Reversible flow at the outlet in my example occurs in unstructuredmesh regardless of the size of the element.
When I changed the mesh in a structured form (HEX mesh on oulet part of HE) reversible flow at the outlet is disappeared, and the result in terms of temperature is different (which can not be ignored ?? !!).
Interesting. It seems to me that it has something to do with how fluent handle the outlet bc.
How can i calculate the hydraulic diameter of channel just like this to find the reynolds no. ?
See my question
How to calculate hydraulic diameter (for finned heat exchanger)-debate?
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