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source terms-convergence problem

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Old   March 28, 2010, 07:47
Default source terms-convergence problem
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qiang xia
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I am modeling the hybrid rocket motor combustion chamber, so there is an oxidizer flow perpendicular to the fuel flow. A diffusion flame exists over a solid fuel. The heat transfer between the diffusion flame and solid fuel should be considered.
I define a thin fluid zone adjacent to the fuel surface, then mass source term, radial momentum source term, species source term and energy source term can be defined relative to the specified mass flux. Consequently, pyrolysis species to enter the domain whilst being able to calculate heat transfer at the fuel surface by setting it as a wall BC.
My source terms are as followings:
mass source term: m/V=rhoS*A*r/V
radial momentum source: mv/V
species source term: m/V=rhoS*A*r/V (when the fuel pyrolysising, only one species was considered, in my opinion, the species source term is equal to mass source term )
energy source term: m*S_e/V
which V is the cell volume, rhoS is the solid fuel density, A is the cell area,v is the pyrolysising velocity, S_e is the formation enthalpy and r is the regression rate of solid fuel, and can be expressed as arrhenius equation: r=A*exp(-E/RT), which all coefficients have been obtained from literature. my problem is :
when I compiled my UDF and loaded successfully, After more than 20,000 iterations , I can not get a convergent solution. by the way , all ds[eqn] in DEFINE_SOURCE are set to zero. can anyone help me ? it is urgent, Big thanks,
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