HYPERSONIC FLOW

hypersonic flow

Flow streams with Mach number about 5 are generally termed HYPERSONIC. What is scared about Mach number 5? Is the upper limit for hypersonic flow finite or infinite?. The Mach number 5 is treated as the lower limit of Hypersonic flow. This is because up to Mach number 5, any change in flow velocity is dictated by the change in flow velocity as well as the change in the speed of sound. In the accel-erating supersonic flow, the change in magnitude of absolute velocity is more than the change in speed of sound. But for accelerating Hypersonic flow, the change in flow Mach number is dominated by the change in speed of sound and the flow ve-locity is not dominant. For example, for increase of Mach number from 5 to 7, the decrease of speed of sound is predominant compared to increase of flow velocity. In other words, it may be stated that for Mach numbers above 5 the effect of change in speed of sound Hypes the change in flow Mach number (the sonic effect dictates the Mach number change or the sonic effect Hype the Mach number change) and hence the flow is referred to as HYPERSONIC. The upper limit for Mach number of hypersonic flow is around 40. Flow with Mach number above 40 would experience very strong tempera-ture effects, leading to dissociation and ionization and field is referred to as high enthalpy gas dynamics, which encom-passes high-temperature and plasma flows.

Reference: Rathakrishnan. E, Gas Dynamics, Seventh Edition, Prentice Hall of India Pvt. Ltd, New Delhi, 2020