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    ANSYS Fluent较大体积力模拟问题

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    • 李东岳
      李东岳 管理员 最后由 编辑

      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).
      figure
      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.

      以上内容选自ANSYS Fluent理论指南。

      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?

      或者有人使用Fluent模拟较大体积力问题产生过震荡?

      CFD高性能服务器 http://dyfluid.com/servers.html

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      • I
        ibelief 最后由 编辑

        没有做过这方面....

        努力收敛

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        • G
          G8S7 @李东岳 最后由 编辑

          @东岳 在 ANSYS Fluent较大体积力模拟问题 中说:

          PRESTO!

          Fluent中的PRESTO!压力插值格式就是用交错网格吗?把压力存储在网格中心,把速度分量存储在网格界面上?这种PRESTO!插值格式FLUENT理论指导也不说清楚,就一段话就解释完了,真是操蛋。

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          • Z
            zhangzh 最后由 编辑

            话说什么叫较大体积力?考虑重力的气液两相流动算吗?反正我看到文献力一般处理这种都是PRESTO!

            沉 1 条回复 最后回复 回复 引用
            • 沉
              沉剑 @zhangzh 最后由 编辑

              @zhangzh fluent员工在ansys论坛里面明确过,不能任何透露关于presto!以及BFW信息。不止压力,transient的rhie-chow插值也写很烂,更不要在多相流条件下。

              李东岳 1 条回复 最后回复 回复 引用
              • 李东岳
                李东岳 管理员 @沉剑 最后由 编辑

                @沉剑 Fluent这搞得挺狠啊

                CFD高性能服务器 http://dyfluid.com/servers.html

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