[rewol]

Hello everyone,

I am having a trouble initiating combustion in my case. I will try to give as much detail about the setup and mesh as possible.

Case Setup :
-Viscous, Laminar Flow
- DENSITY-BASED Solver !
- Species Transport Model, Methane-Air 1 step Mixture, (Non-premixed)
- Axisymmetric geometry, where fuel and Oxidizer enter the domain from different inlets @300K
- High Pressure Combustion Chamber ( Operating Pressure is 5 bar), so Real-Gas model is used for density.
- Both inlets are mass-flow-inlet, outlet is pressure outlet, a symetty axis and wall on top with no heat flux.

PROBLEM :

* First, i simulate a cold flow that converges relatively well, as instructed in User Manual. ( Steady State, Pseudo Transient, Second Order Upwind, NO REACTION)
* I patch the temperature in an area, as shown in third picture.
* I turn on volumetric reactions, use stiff chemistry solver, and start the simulation but it diverges after 100-200 iterations where resiuals go sky-up at first (understandable, due to high gradients and density change) but does not converge. (Again, second order upwind and ROE scheme, pseudo transient)

ATTEMPTS :
* I tried nearly all possible patching areas for temp even though it shouldnt matter in steady-state in theory. No luck there.

* I have used coarser mesh, more dense mesh, all uniform mesh but no luck there.

* Instead of patch, i stopped the solution in cold flow and turned on REACTIONS and change the OXIDEZER BC to blow hot air (2000K) in order to initiate combustion and slowly lowered it back to 300 K, no luck there.

* Tried with / without inlet / thermal diffusion, no luck there.

* First order upwind scheme does not yield any better results either.

* PATCHING TEPERATURE at inlets causes reversed flow because density and momentum balance goes crazy, making it really hard for velocity field to converge, in my opinion.

Basically at this point, i would take any suggestions since i ran out of opinions.

I would appriciate any tips / guides to achieve convergence.

Regards.


PIC_1_COLD_FLOW_SIMULATION_RESULTS.jpg

PIC_2_MESHING_AT_INLET.jpg

PIC_3_PATCHING_AREA_FOR_TEMPERATURE.PNG

PIC_4_RESIDUAL_BEHAVIOUR_AFTER_REACTIONS ARE ON.jpg

PIC_5_CASE_SETUP.PNG