
Since inviscid flow problems will usually involve highspeed flow, you may have to reduce the underrelaxation factors for momentum (if you are using the pressurebased solver) or reduce the Courant number (if you are using the densitybased solver), in order to get the solution started. Once the flow is started and the residuals are monotonically decreasing, you can start increasing the underrelaxation factors or Courant number back up to the default values.
Modifications to the underrelaxation factors and the Courant number can be made in the Solution Controls panel.
Solve Controls Solution...
The solution strategies for compressible flows apply also to inviscid flows. See Section 9.6.5 for details.