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Absurd velocty magnitude value

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Old   May 10, 2018, 12:20
Default Absurd velocty magnitude value
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Hi everyone,

I am simulating a Spinning Disk Reactor on Fluent.
I created a cylinder because I need to value the height of the liquid film once it touches the base of the structure. So I draw:

- big cylinder (0,1 cm height and 10 cm diameter);
- 2 inlet (cylinders much smaller than the big one) placed on the "superior" face;
- the whole body set as fluid body.

The bc are these:
- 2 inlets: mass-flow-inlet where I set constant flow (kg/s and species in mass fraction);
- 2 channels: The heights of inlets (almost 0, created just to let the liquid go in). Stationary walls and no slip;
- outlet: the lateral surface of the big cylinder. I need the flow leaving from there for centrifugal force. Pressure-flow-outlet condition;
- inferior disc: the "base" of the big cylinder. This rotates, so I set moving wall, rotational on z-axis (with 14 rad/s value of velocity) and no slip.

The problem is that during my simulation I get a value of almost 700 m/s for magnitude velocity!
It's not possible of course...
I have flow values like 10^-3 kg/s (more or less) and that value of 700 m/s has no sense... It's definitely too high!
The mixture is composed of 5 components:
water and species A, B, C and D.
Phases: 1 air and 2 is the mixture.
To insert the mixture:
I set on inlet 2 the mass fraction of A and Fluent gets water mass fraction (by itself, I set water as last component of mixture) as 1-A. The others are 0.
Inlet 1: Mass fraction of B, C, D and Fluent does water = 1 - (B+C+D).

model: transient, VOF, Energy equation On, viscous k-epsilon and species equation (but no chemical reaction included).

How is it possible????

Another strange thing is when I initialize: z velocity already has an incredible value (almost 400 m/s for every species).
I tried also to test the system with just one component (first time A + water, then only B+water and finally C+water) and one inlet (inlet2 set as wall):
the system runs same results (slightly lower velocity than 700) for C and D, while for B it diverges on y momentum after few time steps (I set a
really small size, 10^-5).

The only explanation I have is that B properties of material are wrong, but the speed of other components are absurd anyway...

Kind Regards
Bilbo is offline   Reply With Quote


boundaries condition, initialization, rotating disc, rotating disk, velocity magnitude

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