[ben_]

Hello all,

I am running a compressible flow with heat transfer in a small pipe of diameter 10mm. The simulation does not reach steady state, and it also does not seem to change in time steps. I am concerned with the results because they all have very small gradients (see attached) and according to my hand-calcs, the outlet temperature is currently ~200K colder than it should be. Has anyone had this problem, where the constant temperature wall condition does not seem to affect the fluid flow?

For this type of simulation, the Co number forces dt to be very small ~1e-7s. This makes the simulation computationally difficult. Does anyone know how many seconds we expect a pipe like this to converge behavior? It is possible that my two questions are related by the timescale of heat transfer between the wall and the fluid.

Thank you in advance, your help is greatly appreciated as I am currently stuck for how to proceed.

I used the following conditions (fixed):

---------------------------------
0, T
fluid_temp 600.0;
wall_temp 1374;
internalField uniform $fluid_temp; // My Sim
boundaryField
{
outlet_pipe
{
type zeroGradient;
}
bend
{
type fixedValue;
value uniform $wall_temp;
}
inlet_pipe
{
type fixedValue;
value uniform $wall_temp;
}
inlet
{
type fixedValue;
value uniform $fluid_temp; // My Sim
}
outlet
{
type inletOutlet;

value uniform 500; // My Sim
inletValue uniform $fluid_temp; // My Sim
}
}
-----------------------------------
0, p
inlet_pressure 15600000;
outlet_pressure 15000000;
internalField uniform $inlet_pressure; // My Settin
boundaryField
{
outlet_pipe
{
type zeroGradient;
}
bend
{
type zeroGradient;
}
inlet_pipe
{
type zeroGradient;
}
inlet
{
type fixedValue;
value uniform $inlet_pressure;
}
outlet
{
type inletOutlet; // MySim
inletValue uniform $inlet_pressure;
value uniform $outlet_pressure;
}
}
-----------------------------------

0, U
dimensions [0 1 -1 0 0 0 0];
mdot 0.804;
rho_guess 11.2;
ux_inlet_guess 918.3;
internalField uniform (0 0 0); // My Sim
boundaryField
{
bend
{
type noSlip;
}
inlet_pipe
{
type noSlip;
}
outlet_pipe
{
type noSlip;
}
inlet
{
type flowRateInletVelocity;
massFlowRate constant $mdot; // My Sim
rhoInlet $rho_guess;
}
outlet
{
type inletOutlet;
value uniform (0 $ux_inlet_guess 0); // My Sim
inletValue uniform ($ux_inlet_guess 0 0); // My Sim
}
}
-----------------------------------