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Polly February 11, 2003 03:48

Free convection flow over vertical flat plate
Hi all,

I'm simulating a free convection flow over vertical flat plate in 2 dimentional coordinate by using CFX program. And I have a problem in CFD which need some suggestion about boundary condition now.

My domain is air at 300 K. I perform a geometry as a rectangular that has one grid thick . One side ( vertical left side)of the regtangular is a hot plate, temperature = 323 K. I set boundary condition at the bottom side to inlet boundary by given an entrance velocity = 0.0 m/s and the top one to outlet boundary condition by specify reference static pressure to 0.0(reference pressure = 101325 Pa). And then set the symmetry plane at an opposite side of hot plate.

After solving process, the result is not resonable. Could anybody give me some suggestion about this please.

Thank you in advance, Polly

Jim Park February 11, 2003 14:25

Re: Free convection flow over vertical flat plate
Not sure I understand the details you state?

Would CFX do a 2-dimensional problem as a 3-d problem with the third dimension (horizontal along the plate?) only one cell thick? Is that what you mean by "one grid thick"?

I can quickly imagine 2 free convection problems that might apply:

1. One vertical wall of a closed box is heated. In that case, the v = 0 at the bottom is OK. I don't understand how how fluid leaves the box. If the top is open, you should specify a temperature for the fluid entering along part of the top. This is bit of a tricky boundary condition to apply along that top boundary.

2. Your heated plate is part of a longer vertical wall; think about a light fixture mounted flush in a wall several feet (or meters) above the floor in a closed room. In this case, the air rises due to heat-induced buoyancy and the vertical velocity just below the plate cannot be zero. The BC there should be (perhaps) dv/dz = 0 where v is the vertical velocity and z is the vertical dimension. You will need to specify the temperature of the air at that point for your energy balance as well.

So, two different problems with different boundary conditions. And you may actually want to solve something other than either of these ...

Good luck.

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