[Kostas_K]

Hello all,

Im a beginner in Fluent and CFD so please bear with me.

Im trying to run a DES simulation for a 3d turbulent jet. I want to visualize the velocities (x,y,z), vorticities (x,y,z) etc.

I am trying to simulate a duct (0.35mx0.35mx0.25m). The duct is seperated by a wall which has a sharp-edged rectangular orifice configuration(70 mm x 7 mm). My inlet is 0.1 m before the wall that has the orifice and my outlet 0.15m after the wall. My mesh consists of tetrahedrons everywhere exccept where i used inflation. There are 1.6 million elements total.

Given data was ony the Reynolds number at the orifice (Re=23000 or Re hydrolic diamaterer=42000). It is calculated that the velocity at the orifice is v2=50m/s and so the velocity at the inlet has to be v1=0.133m/s. Also the simulation is done as incompressible.

In Fluent my inputs are:
Pressure-based solver
Transient
Energy off
Delayed Detached Eddy Simulation (DES) with the Spalart-Allmaras model

Boundary Conditions:
for walls i used default options
for outlet i used default options
for interior i used default options
for inlet i used mass-flow inlet
-mass flow rate = 0.19958 kg/s
-z component of flow direction = 0.133m/s
-turbulence specification method = turbulent viscosity ratio
-turbulence viscosity ratio=10

SIMPLE scheme was selected.
Gradient: Least square cell based
Pressure: Second Order
Momentum: Second Order Upwind
Modified Turbulent viscosity: Second Order Upwind
Transient Formulation: Bounded Second Order Implicit

Under-Relaxation factors were left default except for:
pressure: from 0.3 (default) --> 0.4
momentum: from 0.7(default) --> 0.8

All Residuals were changed to 1e-05

Using Standard Initialization, the solution was initialized as zeros (0) everywhere

For time step i choose Dt=5e-04 and max iterations/time step= 10

I use solution animations to check the results while running the simulation and the results are very close to what was expected...but the residuals are not willing to go down and converge

Do you have any changes to propose for all the above settings ?
Did i make a mistake somewhere ?

Sorry for the long thread.

Any help will be greatly appreciated

Thank you.
Kostas