implicit div(k*grad(a*u)) -- CFD Online Discussion Forums

August 8, 2011, 13:45	*implicit div(kgrad(au))*	#1
gunnar2 New Member Join Date: Aug 2011 Posts: 6 Rep Power: 14	Hello, I have asked in "Running / Solving / CFD (http://www.cfd-online.com/Forums/ope...-k-grad-u.html)" before, but now this seems to be a programming question. How can I treat $\nabla\cdot k \nabla \alpha u$ implicitly? - scalar field (known diffusivity) $\alpha$ - scalar field (known mass fraction) - scalar field (unknown) fvm::laplacian(k,alpha*u) generates a compiler error. I think a possible solution is to right-multiply the fvMatrix fvm::laplacian(k,u) with a diagonal matrix $D_\alpha$ made up of the values of $\alpha$ on it's diagonal. But how do I write this in C++? Thank you Gunnar

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