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

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