fluent 多相流计算设置outflow与pressure outlet提示不能计算？

做fluent多相流计算的时候（速度入口设置在另一个地方），顶部设置了pressure outlet，底部设置了outflow，结果fluent出现了下面提示：
Warning: Both outflow and pressure boundaries are present in the domain. This is an incompatibility and solution cannot proceed until this is fixed.
这个应该怎么解决啊