Hypersonic Flow

There exist various criteria to be satisfied by the free stream Mach number M?, which makes the flow to be classified hypersonic when it is very high supersonic. Depending on the value of the Mach number, we have hypersonic aerodynamics determined by a predominant parameter with which the flow physics does not change. That is according to some flow parameters the flow is considered to be hypersonic for M? > 3, and with respect to some other parameter the flow is regarded as hypersonic for M? > 5 (Anderson 1989). Moreover, the dependence on the Mach number may vary for the same parameter with the body shape. An important parameter of hypersonic flow is the temperature. In the stagnation flow, the temperature may reach some high values which can exceed the durability limits of the materials. For this reason in hypersonic flows heat transfer and thermodynamics play an important role, which forces us to add the concept of aerothermodynamics to aerodynamics (Bertin 1994). In addition, at high temper­atures there are considerable changes in the viscosity and specific heats of the air to be accounted in hypersonic flows. The classical approach gives us the ther­modynamic properties of the air either in normal temperatures or in very high temperatures approaching infinity. In the temperature ranges which are of interest to us the composition and the properties of the air can be determined by the aid of statistical thermodynamics (Lee et al. 1973). In higher speeds, temperatures and altitudes the chemical composition of the air changes. During the chemical reac­tions the energy needed is provided by the medium of the air for which the formation energy of each species must be included in the energy equation. This in turn affects the flow domain about the body and the shock location. The concept of aerothermochemistry is needed to be introduced at this stage. Furthermore, for a ballistic re-entry problem the speeds become so high that ionized flow around the capsule occurs. The ionized flow regions can be studied by plasma flow.

First studies on hypersonic aerodynamics started after WWII by the design work performed on intercontinental ballistic missiles. The first historic manned hypersonic flight and safe re-entry was made in 1961. Since then, based on the data recorded during re-entry, experiments performed in specially designed hypersonic

U. Gulfat, Fundamentals of Modern Unsteady Aerodynamics, 193

DOI: 10.1007/978-3-642-14761-6_7, © Springer-Verlag Berlin Heidelberg 2010

wind tunnels and the advances made in computational methods considerable progress is achieved in the multi disciplinary field of hypersonic aerodynamics. Naturally, the progress made in this field was not only applicable to re-entry problems and to the flight of intercontinental ballistic missiles but also useful for the design of intercontinental planes with sustainable hypersonic flight in the future.

In this chapter, starting by the Newton’s impact theory which predicts the surface pressure coefficient with a simple formula for blunt bodies, various order piston theory to be used for slender bodies, hypersonic similarity based on the Euler equation, viscous hypersonic flow and high temperature gas dynamics knowledge will be provided.