Transonic Flight Regime

5.4.1 Main properties of physics of transonic flow

If the flow field contains parts with subsonic flow and other parts with supersonic flow, the prob­lem is called rransonic Properties in the flow Held strongly change:

• In the subsonic parts, the flow field balances all flow properties in the field and is described by elliptic balance equations.

• In the supersonic parts, the flow field cannot balance properties because flow speed is higher than information speed; it is described by hyperbolic radiation equations.

The supersonic parts usually are terminated by a strong shock. Whereas supersonic oblique shocks usually are kinematically fixed to the geometry, the strong normal shocks in transonic flow evolve in the flow field and are controlled by flow forces. Therefore they are prone to oscillations

5.4.2 Mathematics of transonic flow

Mathematical models describing gas dynamics of those different flow types arc strongly nonlin­ear. the equations are of mixed elliptic • hyperbolic type, even for the in vise id parts. Computa­tional analysis usually follows transient formulations to model type changes within the flow. These enable elliptic, hyperbolic and parabolic solution procedures. Some models may be used for design purposes to calculate flows with desirable aerodynamic properties, see book chapter 7.

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