Learning Forum

[gelsonrhilgemberg]

Hi everyone

 

I need help with my DDPM simulation. I am Simulating a Pilot CFB BOILER using DDPM aproach, Species Transport (finite rate-eddy dissipation) with Air-wood-volatiles. The discret phase are sand (0,3mm diameter) and biomass (1 mm). My mesh have about 5 mm and minimum ortogonal quality 0,48, avg 0,95. I am using Gidaspow for drag force and non-spherical(biomass). I run the simulation in steps (cold flow, particles, energy-species equations). When simulating reactions, the continuity residuals shows higher value in beginner of each time step and  decrease over time, however, after a few time steps after (0,2-0,5s), the solver fails in one time step with Continuity, K-omega residuals. Temperature limited in all cells, turbulent viscosity ratio too. I reduced the loop-factor, I increased the lenght time factor, the number of iterations, I Reduced the URF but without sucess. If anyone knows what can be the problem, please help me.

Some parameters

First Order, transient, biomass and sand have same parameters in multiphase eulerian phase tab (Granular, gidaspow, lun, schaeffer, based ktgf)

DDPM - AIR-wood-volatiles - primary phase, sand and biomass discret phase

K-omega SST

Injections by surface and constant number parcell method (sand I tried 100, 50, 25 particles per parcell and biomass 1 particle per parcell)

Boundary conditions

air 4m/s in the bottom of riser 500k

sand in the y tube - 0,10kg/s (in begginer 0,15kg/s, expected around 0,3-0,5 kg in the system) 873k

air 0,5m/s in the y tube - 873k

biomass - 0,00055 kg/s in the bottom of riser - 323k

 

 

[Rob]

If you switch off the reactions how does it behave? For trouble shooting you need to reduce complexity and then build back up to identify the cause. 

[gelsonrhilgemberg]

Hi

When I Switch off the reactions the problem continues. I disabled the energy and species equation

.

 

My setup is this

 

Eulerian 

Lagrangean

 

For sand is 25 particles, Drag force -Huilin Gidaspow (Inert)

 

Species model

 

Material combusting particle

Methods are setting default.

When I started the simulation I put just cold fluid (the residuals were good), after I injected sand particles and biomass particles and the residuals started to oscilate but in the end of the time step reached 1E-3. With the reactions and energy enabled and URF for energy and species - 0,8, the simulation run  0.1 to 0.3s with time step 1e-4 and the simulation began to diverge. When I set smaller time steps, the residuals increasing more. Any tips or adjustments that can be made?