Wavy residuals

Subha

<U>Problem:</U>

I am doing a CHT simulation of the cooling system of a pump. My model consists of a Motor covering (whose inner wall is the source of heat), outer Outer covering and inbetween them is the fluid. The fluid is cooled in a flange. I am simulating this full setup with flange.

In order to finalise with the boudary layer, I am doing a simulation only with the fluid region, which travels from the flange to the region between Motor covering and Outer covering. The fluid domain has 3.3 M hexa cells. I am doing with a SST turbulence and gamma model 260 transitional turbulence. The model has a Inlet with mass flow rate and opening with open pres. and dirn and both inlet and opening with a fixed temperature. I had set up a Conservation target of 0.01 and Max residual target of 1e-5

I did the simulation with a autotimescale (0.1s) and after about 100 iterations the Momentum, Mass and Heat transfer residual graphs keeps oscillating. I re-tried the simulation with a physical timescale of 0.4s and I found no improvement. For both the simulations I did until 500 iterations.

<U>Results:</U>

The max. RMS residual is 1.2e-04

My domain imbalances are:
Domain 1 Domain 2
U-Mom 0.0642 % -0.0879 %
V-Mom 0.0258 % -0.0103 %
W-Mom 0.0266 % -0.0162 %
P-Mass 0.0659 % -0.0667 %
H-Energy 0.0721 % -0.0661 %

The monitor points of Temperature on both the domains are stable (horizontal graph).
The monitor point of Velocity on Domain 2 is stable and the one in Domain 1 is not.

<U>Questions:</U>

1. Has my simulation converged?
2. What does the wavy nature of the residuals imply?
3. What does the monitor point velocity on domain 1 imply while the velocity on domain 2 is stable?


Any sort of help is really appreciated.
Regards,
Subha.