The temperature drops unusually at first few interactions...

tjushang · September 19, 2014, 05:47

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, 09:24

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, 05:47	The temperature drops unusually at first few interactions...	#1
tjushang New Member Yibao Shang Join Date: Jun 2014 Location: China Posts: 15 Rep Power: 12	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.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
whats the cause of error?	immortality	OpenFOAM Running, Solving & CFD	13	March 24, 2021 08:15
Calculation of the Governing Equations	Mihail	CFX	7	September 7, 2014 07:27
is internalField(U) equivalent to zeroGradient?	immortality	OpenFOAM Running, Solving & CFD	7	March 29, 2013 02:27
reactingFoam temperature drops below bc	pit	OpenFOAM Running, Solving & CFD	0	August 5, 2011 06:59
Temperature drops in Methane combustion	CPRL	Siemens	0	July 24, 2007 13:56

October 9, 2015, 09:24		#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.