Error MessageDissimilar Contacting Fluids Detected

Mar 3, 2012


After assigning materials, and selecting the next set up task, one of the following warnings is given:

Dissimilar adjacent fluids detected

Dissimilar contacting fluids detected



This warning means that two or more different fluid materials contact one another. Autodesk® Simulation CFD does not support direct mixing of different fluids, and provides this warning to indicate that adjacent parts should have the same fluid material.


The solution is to check material assignments, and ensure that all contacting parts are either assigned the same fluid material or a solid material.


A common reason for this situation is that a unique fluid material is assigned to a part, and other parts (that touch the first) are not assigned any material. Often the intent is that these parts should be solids, so changing their material assignments to solid solves the problem.


A number of users have seen this warning as a result of setting up mixing, nozzle spray, or surface tension analyses that use different fluid materials. A common example is to have air and water touching. Autodesk® Simulation CFD does not directly support these types of analyses through the use of contacting fluids.

  • For mixing, an alternative (approximate) strategy is to use a general scalar boundary condition, and vary the fluid properties (density and viscosity) with the scalar concentration.
  • For nozzle spray analyses, the general idea of the spray can be obtained by exhausting the nozzle into a larger fluid volume (with the same fluid passing through the nozzle). Often the mixing with air is not critical to learn what the velocity will be. Quantities such as pressure and velocity can be extracted from such an analysis.
  • Autodesk® Simulation CFD doesn't support surface tension, but modeling the water domain can often provide some insight into the flow.


Simulation CFD