Another source of error is that ANSYS FLUENT assumes that the normal pressure gradient at the wall is zero. This is valid for boundary layers, but not in the presence of body forces or curvature. Again, the failure to correctly account for the wall pressure gradient is manifested in velocity vectors pointing in/out of walls.
Several alternate methods are available for cases in which the standard pressure interpolation scheme is not valid:
The linear scheme computes the face pressure as the average of the pressure values in the adjacent cells.
The second-order scheme reconstructs the face pressure in the manner used for second-order accurate convection terms (see Section 18.3.1). This scheme may provide some improvement over the standard and linear schemes, but it may have some trouble if it is used at the start of a calculation and/or with a bad mesh. The second-order scheme is not applicable for flows with discontinuous pressure gradients imposed by the presence of a porous medium in the domain or the use of the VOF or mixture model for multiphase flow.
The body-force-weighted scheme computes the face pressure by assuming that the normal gradient of the difference between pressure and body forces is constant. This works well if the body forces are known a priori in the momentum equations (e.g., buoyancy and axisymmetric swirl calculations).
When a case contains porous media, the body-force-weighted scheme is applied only for non-porous faces, where the scheme takes into account the discontinuity of explicit body forces (e.g., gravity, swirl, Coriolis) and the discontinuity of pressure gradients for flows with rapidly changing densities (e.g., natural convection, VOF). All interior and exterior porous faces are treated with a special scheme that preserves the continuity of the normal velocity across cell faces in spite of the discontinuity of the resistance.
The PRESTO! (PREssure STaggering Option) scheme uses the discrete continuity balance for a "staggered’’ control volume about the face to compute the "staggered’’ (i.e., face) pressure. This procedure is similar in spirit to the staggered-grid schemes used with structured meshes [ 264]. Note that for triangular, tetrahedral, hybrid, and polyhedral meshes, comparable accuracy is obtained using a similar algorithm. The PRESTO! scheme is available for all meshes.
For recommendations on when to use these alternate schemes, see this section in the separate User’s Guide.
目前现存的同为网格算法在存在较大体积力的情况下会产生震荡，ANSYS Fluent已经采用了相应的算法来改善，不过网上依然有人说对于多孔介质模拟ANSYS Fluent依然在界面产生颤裆，有人遇到过类似问题么？