discrepancy in fvc::grad(U) -- CFD Online Discussion Forums

August 3, 2019, 19:26	discrepancy in fvc::grad(U)	#1
backscatter Member Anonymous Join Date: Aug 2016 Posts: 75 Rep Power: 9	HI all, Recently I noticed that in openfoam, gradient of a vector is computed as the outer product of the gradient operator and the vector. Page 25 (bottom) of the programmer's guide defines the gradient of velocity field as: Code: $\nabla_{i}a_{j}$ which is transpose of what we exactly mean by grad(U) as: Code: $\nabla_{j}a_{i}$ I checked the computed values of gradient of velocity field near the wall (where wall normal component is expected to be dominant) and I can confirm that it outputs the transpose of what we actually want. To my surprise, I have seen people use the grad(U) without taking its transpose in openfoam that would actually give the correct tensor. Has anybody encountered this issue before? OpenFOAM Version: 2.4.0 C. Okubo, Voulet, HPE and 2 others like this.

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