A flow is called hypersonic if the Mach number is greater than 5. This means that the flow speed is more than five times the speed of sound. In air at room temperature, the speed of sound is around 340 m/s, so a Mach 5 flow would have a flow speed of 1.7 km/s or just over 6,000 km/h. When a rocket launches a satellite into earth orbit, when a probe enters the atmosphere of another planet or when an aircraft is propelled by a supersonic combustion ramjet engine (a scramjet), hypersonic flows are encountered. Hypersonics – from Shock Waves to Scramjets introduces the basic concepts associated with flight at speeds greater than Mach 5 and takes students to the stage where they can analyse the performance of a scramjet engine that might be used in a future access-to-space system.
Section 1. What is Hypersonics?
This section provides an introduction to the course. What we mean by “hypersonic speeds” is discussed and examples of vehicles that travel at such speeds are given. Shock waves and scramjets are also introduced. The rocket equation is introduced to show why staging of launch vehicles is used. The scramjet engine arrangement used throughout the course is outlined.
Section 2. Isentropic Flow
The times when a flow can be considered to be “isentropic” are introduced. This leads on to the fundamentals of compressible flow and steady adiabatic flows. We use the flow in a scramjet nozzle to demonstrate the principles.
Section 3. Shock Waves
Normal and oblique shock waves form when objects travel at close to, or in excess of, the speed of sound. In this section, methods for modelling the flow across shock waves are presented and discussed. Results from experiments are used to show the influence of flow deflection angle on the shock wave formed at hypersonic speeds. We use the flow in a scramjet intake to demonstrate the principles.
Section 4. Combustors in Scramjets
Flows with friction, heat addition and stoichiometry are important considerations for scramjet combustors. In this section example problems are worked through to show the importance of friction and heat addition to fluid flow at different Mach numbers. Stoichiometric concepts are developed so that the use of different fuels can be modelled.
Section 5. Hypersonics
This section looks at hypersonic flight, flight corridors and vehicle design. Hypersonics facilities, such as reflected shock tunnels and expansion tubes, are described since these are used to test scientific hypotheses related to hypersonic flight.
Section 6. Scramjets
This section describes the state of scramjet technology as it exists today, examines the history of scramjets and then looks at future possibilities of scramjet technology. The overall thrust of an air breathing engine is calculated.
Section 7. Project
In the final section, students are required to analyse the flow through an engine and determine the Specific Impulse for their own scramjet design.
Richard G. Morgan and David J. Mee