The temperature drops unusually at first few interactions...

tjushang · September 19, 2014, 04:47

Hi everyone! I modeled a 3D chamber to simulate transient combustion in engine. I initialized temperature field as a value of 750K, then I patched a 2000K hot core with radius of 2mm. My numerical scheme are listed as follows:
Density-Based Solver
Turbulence: LES-Smagorinsky Lilly
Species: Species transport-EDC model coupled with detailed H2 mechanism Ideal gas
Formation: Explicit (cuz it's time saving)
Flux type: Roe-FDS
Spatial Discretization: Gradient-Last squares cells based Flow-Third-order MUSCL (cuz I intend to study the pressure wave formed by flame, which may have obvious discontinuity)
Transient Formulation: Second-order implicit
Time step: 1e-8s

When I started calculation, the TUI showed:" Time step reduced in xxx cells due to excessive temperature change." This message disappeared after several interaction. But the hot core I patched drops unusually to nearly 750K, which is obviously a unreal process. There must be something wrong with my settings but I don't where's the problem.

By the way, I use ISAT to accelerate the calculation, at first it said:"DASAC failure...", so I rise memory for ISAT from 100mb to 400mb, after which I could carry on my calculation.

I'd be quite appreciated if anyone could give some guidance to this problem. Please help me.

bobinson · October 9, 2015, 08:24

Hi tjushang,

I had the same problem as you did but in my case I was simulating open atmosphere hydrogen combustion. As you mentioned you used LES-SL. I tried you case and fail. But when I switched to LES RNG it start working. To activate RNG for LES type (allow-rng-subgrid-model).

Hope this helps.

September 19, 2014, 04:47	The temperature drops unusually at first few interactions...	#1
tjushang New Member Yibao Shang Join Date: Jun 2014 Location: China Posts: 15 Rep Power: 11	Hi everyone! I modeled a 3D chamber to simulate transient combustion in engine. I initialized temperature field as a value of 750K, then I patched a 2000K hot core with radius of 2mm. My numerical scheme are listed as follows: Density-Based Solver Turbulence: LES-Smagorinsky Lilly Species: Species transport-EDC model coupled with detailed H2 mechanism Ideal gas Formation: Explicit (cuz it's time saving) Flux type: Roe-FDS Spatial Discretization: Gradient-Last squares cells based Flow-Third-order MUSCL (cuz I intend to study the pressure wave formed by flame, which may have obvious discontinuity) Transient Formulation: Second-order implicit Time step: 1e-8s When I started calculation, the TUI showed:" Time step reduced in xxx cells due to excessive temperature change." This message disappeared after several interaction. But the hot core I patched drops unusually to nearly 750K, which is obviously a unreal process. There must be something wrong with my settings but I don't where's the problem. By the way, I use ISAT to accelerate the calculation, at first it said:"DASAC failure...", so I rise memory for ISAT from 100mb to 400mb, after which I could carry on my calculation. I'd be quite appreciated if anyone could give some guidance to this problem. Please help me.

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October 9, 2015, 08:24		#2
bobinson New Member SV Join Date: Apr 2012 Posts: 15 Rep Power: 14	Hi tjushang, I had the same problem as you did but in my case I was simulating open atmosphere hydrogen combustion. As you mentioned you used LES-SL. I tried you case and fail. But when I switched to LES RNG it start working. To activate RNG for LES type (allow-rng-subgrid-model). Hope this helps.