Hi Yong Cao, I suspect you might be using linear elements? (meaning that the edges of the elements are straight and not curved). If that's the case, the pressure "oscillation" is physical, to remove it you should use curved elements at the cylinder boundary. Cheers, Giacomo On Thu, May 5, 2022 at 10:09 AM 曹勇 <yongcao@sjtu.edu.cn> wrote:
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Hi all,
I recently started to use Nektar++ v5.0.3. I would like to simulate the incompressible flow past a smooth circular cylinder at Re=3900. The case is classic and widely studied.
The test case used 3345 macro-elements in 2D plane (x-y plane). 70 edges are distributed on the cylinder boundary. The other direction (z direction) is solved by Fourier mode. For the purpose of test, a short spanwise length is set, like Lz=0.2. The results of instantaneous velocity field seems smooth near the boundary of circular cylinder. However, the instantaneous pressure field showed overshoot (or numerical oscillation?) between two neighboring macro-elements. I attached an example in the email. In order to manifest the overshoot, the visualization uses the magnitude of pressure gradient.
For solving this problem, I conducted some additional tests by either adding macro-elements along the cylinder boundary or increasing the number of points of Gauss quadrature. Both methods smoothened the instantaneous pressure field around the cylinder boundary. However, neither removed the overshoot completely.
It will be appreciated if anyone could give suggestions.
Thank you very much in advance. Yong Cao
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