Inviscid flow analysis neglect the effect of viscosity on the flow and are appropriate for high-Reynolds-number applications where inertial forces tend to dominate viscous forces. One example for which an inviscid flow calculation is appropriate is an aerodynamic analysis of some high-speed projectile. In a case like this, the pressure forces on the body will dominate the viscous forces. Hence, an inviscid analysis will give you a quick estimate of the primary forces acting on the body. After the body shape has been modified to maximize the lift forces and minimize the drag forces, you can perform a viscous analysis to include the effects of the fluid viscosity and turbulent viscosity on the lift and drag forces.
Another area where inviscid flow analysis are routinely used is to provide a good initial solution for problems involving complicated flow physics and/or complicated flow geometry. In a case like this, the viscous forces are important, but in the early stages of the calculation the viscous terms in the momentum equations will be ignored. Once the calculation has been started and the residuals are decreasing, you can turn on the viscous terms (by enabling laminar or turbulent flow) and continue the solution to convergence. For some very complicated flows, this is the only way to get the calculation started.
Information about inviscid flows is provided in the following subsections:
For more information about the theoretical background of inviscid flows, see Inviscid Flows in the Theory Guide.
For inviscid flow problems, you must perform the following steps during the problem setup procedure. (Only those steps relevant specifically to the setup of inviscid flow are listed here. You must set up the rest of the problem as usual.)
Enable the calculation of inviscid flow by selecting Inviscid in the Viscous Model Dialog Box.
Setup → Models → Viscous
→ Model → Inviscid
Set boundary conditions and flow properties.
Setup → 
Boundary Conditions
Note: Walls are assumed to be slip surfaces (the velocity is not equal to zero, unlike viscous flows) and therefore have a tangential velocity computed based on the solution of the governing equations.
Setup → Materials
Solve the problem and examine the results.
Since inviscid flow problems will usually involve high-speed flow, you may have to reduce the under-relaxation factors for momentum (if you are using the pressure-based solver) or reduce the Courant number (if you are using the density-based solver), in order to get the solution started. Once the flow is started and the residuals are monotonically decreasing, you can start increasing the under-relaxation factors or Courant number back up to the default values.
Modifications to the under-relaxation factors and the Courant number can be made in the Solution Controls Task Page.
Solution → Controls
The solution strategies for compressible flows apply also to inviscid flows. See Solution Strategies for Compressible Flows for details.
If you are interested in the lift and drag forces acting on your model, you can use the Force Reports Dialog Box to compute them.
Results → Reports → Forces Edit...
See Forces on Boundaries for details.