Hypersonic Waveriders

Hypersonic Flow
Vehicle Design
Based on a paper originally written
by Jeff Scott
Spring 2000


Since the beginning of aviation, the trend in aircraft design has been towards greater speed, and engineers have constantly pushed the limits of current propulsion technology. The turbojet marked a revolutionary advance over the piston engine and ushered in an era of supersonic aircraft traveling at 2 to 3 times the speed of sound. Many are now working to push the speed envelope to its next great frontier, that of hypersonic travel at 5 to 25 times the speed of sound. One of the most practical and efficient approaches to travel at these high speeds is known as the waverider. In the following pages, this type of vehicle will be explored and compared with subsonic and supersonic designs. In addition, the nature of hypersonic flow will be discussed to better understand how the characteristics of the flow dictate the shapes and performance of optimum waverider designs. Finally, several concept vehicles and potential applications for hypersonic flight will be presented.

What is a Waverider?

Simply put, a waverider is any vehicle that uses its own shock wave to improve its overall performance. The concept is probably most familiar from the world of water sports-motorboats ride the bow wave they create to reduce friction drag and surfers similarly ride the crests of waves. An aircraft traveling at Mach 1 or higher also produces a wave, a shock wave of air. If the aircraft is tailored correctly, it can be designed to ride this wave to produce greater lift, less drag, greater range, and overall improved performance. The reason waveriders are only practical at higher Mach numbers is due to the fact that the shock wave must remain close to the surface, a quality of hypersonic flow. A shock creates greater pressures in its wake, and the shock lying close the lower surface of the aircraft results in a large pressure force increasing the lift on the vehicle. This idea, which will be explored further in later sections, is known as compression lift and is the primary benefit of the waverider concept.

What is Hypersonic Flow?

The general rule of thumb is that the hypersonic regime begins at about Mach 5. There is no sudden change in flow properties at this speed, such as a sonic boom when crossing from subsonic to supersonic speed, but flow phenomena generally of little or no importance at lower speeds begin to take on greater significance at about Mach 5. Some phenomena, such as increasing temperature and the formation of a shock layer, begin to impact vehicle design at about Mach 3. Others, such as chemically reacting flow, don't begin to have a significant effect until about Mach 7 or more. Nonetheless, Mach 5 is a convenient definition for the speed at which these effects become progressively more important as Mach number increases. Since most waverider concepts are intended to operate at speeds in this range, the characteristics of hypersonic flows need to be understood to see how they influence waverider design.

Last modified 11 March 2012

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