Abnormal (?) Passive Scalar behaviour

cwl · August 26, 2014, 23:21

Simple case:
Rectangular axisymmetric 2D Porous Region 1.0x0.25m:
Inlet (short edge; any kind of boundary condition - just for velocity about 1 m/s),
Outlet (short edge; Pressure Outlet),
Wall,
Axis;

Ideal Gas;
Implicit Unsteady;
Coupled Energy;
Passive Scalar with "No Convection or Diffusion";
Region->Passive Scalar Source->Checked;
Passive Scalar Source = 0.0;

Initial: Temperature = 20 C, Passive Scalar = 20
Inlet: Temperature = 1800 C, Passive Scalar = 20 or 1800
Outlet: Temperature = 20 C, Passive Scalar = 20

Time Step = 0.025 s;

The problem is that though Passive Scalar should be constant across the Region - its value increases just with the Temperature if Passive Scalar Source is switched on (though it is set to zero) and does not if Passive Scalar Source is switched off.

I would be grateful for any suggestions or ideas - is it i am mistaken or it is a kind of program error.

cwl · October 3, 2014, 09:05

I am sorry to up the topic - but i still hope someone may clear the things out for me.

The problem remains the same:
Passive Scalar with No Convection/Diffusion and with Passive Scalar Source checked but value set to 0 - is affected by the flow, while it should not as it its equation is just dϕ/dt = 0, where d - is partial derivative. This happens regardless of Time Step, Maximum Inner Iterations, CFL - and regardless of Residuals.

August 26, 2014, 23:21	Abnormal (?) Passive Scalar behaviour	#1
cwl Senior Member Chaotic Water Join Date: Jul 2012 Location: Elgrin Fau Posts: 438 Rep Power: 18	Simple case: Rectangular axisymmetric 2D Porous Region 1.0x0.25m: Inlet (short edge; any kind of boundary condition - just for velocity about 1 m/s), Outlet (short edge; Pressure Outlet), Wall, Axis; Ideal Gas; Implicit Unsteady; Coupled Energy; Passive Scalar with "No Convection or Diffusion"; Region->Passive Scalar Source->Checked; Passive Scalar Source = 0.0; Initial: Temperature = 20 C, Passive Scalar = 20 Inlet: Temperature = 1800 C, Passive Scalar = 20 or 1800 Outlet: Temperature = 20 C, Passive Scalar = 20 Time Step = 0.025 s; The problem is that though Passive Scalar should be constant across the Region - its value increases just with the Temperature if Passive Scalar Source is switched on (though it is set to zero) and does not if Passive Scalar Source is switched off. I would be grateful for any suggestions or ideas - is it i am mistaken or it is a kind of program error.

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October 3, 2014, 09:05		#2
cwl Senior Member Chaotic Water Join Date: Jul 2012 Location: Elgrin Fau Posts: 438 Rep Power: 18	I am sorry to up the topic - but i still hope someone may clear the things out for me. The problem remains the same: Passive Scalar with No Convection/Diffusion and with Passive Scalar Source checked but value set to 0 - is affected by the flow, while it should not as it its equation is just dϕ/dt = 0, where d - is partial derivative. This happens regardless of Time Step, Maximum Inner Iterations, CFL - and regardless of Residuals.