[kadams2]

I am currently working on a project to analyze the acoustic properties of a rocket engine and am using the ANSYS FLUENT and Modal Acoustics toolkits to perform the simulations. I am trying to understand how the acoustics in the chamber impact the combustion, and I am not interested in the acoustics of the structure of the chamber. For my geometry I created a structural steel shell and an air cavity inside of it and attempted to specify the air cavity as the acoustics region and the shell as the structural region in Modal Acoustics, but when attempting to solve, I get the warning messege:
One or more acoustic physics region objects are scoped to bodies with acoustic damping material properties like Viscosity and/or Thermal Conductivity defined on them. These damping inputs may result in a solver error when an undamped solver is used to solve the analysis. Suppress these material properties if you wish to use undamped solver.
And when I suppress the shell and just try to simulate the air cavity, I get the error messege:
Air contains invalid property data.
These problems are:

Elasticity is required, but is currently undefined.

These problems must be corrected before you can continue.
Please switch to Engineering Data and correct the invalid property data.

My mentor seems to interpret this as the air cavity being interpreted as a solid even while it is specified as a fluid in the geometry and as air in setup. Thank you!