Inviscid Flow

In real-world applications, there’s no fluid completely free from the effects of viscosity. However, the transition from inviscid to viscous modeling in numerical CFD modeling entails significantly different computational efforts. Inviscid models are mathematically straightforward, resulting in much faster computational times.

Cases that can be modeled using inviscid approaches involve very high Reynolds numbers, where the inertia effects in the flow dominate significantly over external forces (friction) indicated by a very thin boundary layer (BL). Examples include flow-around projectiles or high-speed aircraft.

Figure 2.5. Low vs High Reynold Number Boundary Layer (Exagerated)

While unable to accurately predict lift and drag, inviscid modeling allows for quick trend analysis to find the most optimal designs. After obtaining such designs, one can analyze them using viscous models to gather detailed data.

The mathematical form of the inviscid equations for continuity is the same as equation 2.9. Then, the momentum equation is equation (2.10) with shear stress tensor = 0, while the conservation of energy equation is defined as follows:

(2.15)

With Sh is the source term for energy. The governing equations for inviscid flow mentioned above are also known as the Euler equations