Mass flow inlet boundary cond. dissappears!

Ema40 · July 29, 2015, 17:43

Hi members.

I am simulating a water turbine and this is not the first time, so I am not at the beginning, but now a very strange thing happens.

I impose a mass flow inlet as boundary condition at the inlet, initialize the solution and it is ok: at the inlet there is a water depth (as imposed) and a inlet flow rate. But after some time steps it disappears!! The water depth which I have imposed disappears and the inlet flux (computed by Report-fluxes-mass flow at the inlet) is become zero, despite I have imposed a mass flow rate of 60 Kg/s!!

I have also changed the direction of the mass flow but no changes.

Do you know why?

Thank you.

hwet · July 31, 2015, 03:05

If you mean you patch a water depth; it will go away as patching is only the initial condition.

Ema40 · July 31, 2015, 06:13

Thank you.

No no, I have imposed the water depth as boundary condition and, indeed, in the initial solution the water depth is ok, but after some time steps it disappears, despite it is a boundary condition!.

Thank you

hwet · July 31, 2015, 20:24

Hmm, probably give more details, add pictures of the setup so others can see better whats happening...

Ema40 · October 21, 2015, 12:19

Thank you.

Practically, when I start the simulation, all is ok. The water begins to flow from the inlet towards the outlet. Then , after some time steps, the inlet mass flow rate stops, so it happens as there is no mass flow which enters in the domain from the inlet, although I have imposed a mass flow inlet in the boundary conditions. The behavior is right in the first time step, but after some time steps, the water flow, which was provided by the inlet boundary condition, stops!

Very strange

July 29, 2015, 17:43	Mass flow inlet boundary cond. dissappears!	#1
Ema40 Senior Member Join Date: Oct 2014 Posts: 124 Rep Power: 12	Hi members. I am simulating a water turbine and this is not the first time, so I am not at the beginning, but now a very strange thing happens. I impose a mass flow inlet as boundary condition at the inlet, initialize the solution and it is ok: at the inlet there is a water depth (as imposed) and a inlet flow rate. But after some time steps it disappears!! The water depth which I have imposed disappears and the inlet flux (computed by Report-fluxes-mass flow at the inlet) is become zero, despite I have imposed a mass flow rate of 60 Kg/s!! I have also changed the direction of the mass flow but no changes. Do you know why? Thank you.

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July 31, 2015, 03:05		#2
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	If you mean you patch a water depth; it will go away as patching is only the initial condition.

July 31, 2015, 06:13		#3
Ema40 Senior Member Join Date: Oct 2014 Posts: 124 Rep Power: 12	Thank you. No no, I have imposed the water depth as boundary condition and, indeed, in the initial solution the water depth is ok, but after some time steps it disappears, despite it is a boundary condition!. Thank you

July 31, 2015, 20:24		#4
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	Hmm, probably give more details, add pictures of the setup so others can see better whats happening...

October 21, 2015, 12:19		#5
Ema40 Senior Member Join Date: Oct 2014 Posts: 124 Rep Power: 12	Thank you. Practically, when I start the simulation, all is ok. The water begins to flow from the inlet towards the outlet. Then , after some time steps, the inlet mass flow rate stops, so it happens as there is no mass flow which enters in the domain from the inlet, although I have imposed a mass flow inlet in the boundary conditions. The behavior is right in the first time step, but after some time steps, the water flow, which was provided by the inlet boundary condition, stops! Very strange