[Gape]

Hello,

I have convergence issues with the steady stade centrifugal Pump. The Momentum do not go under 10^-3. And the max. Residuals bouncy.

Measurement data of the pump at 1791 rev/min:

P_in: -19886Pa
P_out: 78775Pa

Model:
-Intake tube (length 150mm)
-Impeller (without gaps in front and behind the Impeller-->reduce Mesh elements)
-Volute

current Mesh:
-ca. 8 Mio Elements
-Assembly so I have a uniform Mesh
-10 Inflation Layer (total thickness 0,6mm, layer compression) (not automatic inflation, each Domain severel,also Interface e.g. from Impeller to volute inflated)
-curvature and wall distance
- elements in gap=8
-max element size=5mm
-min element size=0,1mm
max. skewness=0,91

Solver Settings:
operation Conditions 100344Pa
inlet: -19886Pa
outlet: mass Flow=3.86kg/s

Monitor Point:
Pressure Inlet: -19886Pa and Total Pressure= st. Pressure + Operating Pressure, so that is correct

no slip wall
SST-->with curvature correcction (recommanded for Centrifugal Pumps)
Time-Scale: I have try out: Auto-Time-Scale (0,0038s), pysical Time-Scale (1/omega) omega in rad/s or (1/(pi*rev/min)) or smaler (smalest Mesh Element/ (Tip speed r*omega) =0.000019s-->than it solves transient behavior, but small time-Scale give a more accurate Flow fild, this is required for turbulance equations....and so on.
Turbulance: 1. Order better for Tetraeder Mesh 2. Order

Solution:
-a higher Delta p -->Ansys calculatet an P_out: 1.2bar -->comparison Measurements 0.89bar.

but that is correct because I negligible friction losses for the rotating disc an gap losses too.

I have try out Velocity Inlet and Mass Flow outlet, that gives the same Delta p.

But the Residuals for the Momentum do not come down under 10^-4 after 300 til 600 iterations. And and the pressure distribution in the impeller is uneven for comparison to a Simulation only with the impeller.



I have tried so much, even with the model and smaller speed it will not get better. I need some help.