Reynold's Experiment

REYNOLD’S EXPERIMENT

It was introduced by Osborne Reynolds (1842–1912), who popularized it’s use in 1883. In his 1883 paper Reynolds described the transition from laminar to turbulent flow in a classic experiment, in which he examined the behavior of water flow under different flow velocities using a small stream of dyed water introduced into the center of clear water flow in a larger pipe. The larger pipe was glass so the behavior of the layer of the dyed stream could be observed, and at the end of this pipe there was a flow control valve used to vary the water velocity inside the tube. When the velocity was low, the dyed layer remained distinct through the entire length of the large tube. When the velocity was increased, the layer broke up at a given point and diffused throughout the flu-id's area cross-section. The point which this happened was the transition point from laminar to turbulent flow. The ratio of inertia forces to viscous forces, the parameter obtained is called the Reynolds number (Re), in honor of Osborne Reynolds

where,
Re = Reynold’s number
V = velocity of fluid
D = diameter of pipe
μ = dynamic viscosity of fluid
ρ = density
With respect to Reynolds number: Re = 2300 transitional flow.

Laminar Flow (Re < 2300, only in pipe): Laminar flow may be described as an orderly pattern , i.e. in laminar flow the fluid moves in layer, or laminas, one layer sliding over an adjacent layer with only a molecular interchange of momentum. Such that the transverse exchange of momentum is insignificant.

Turbulent Flow (Re > 2300, only in pipe): The turbulent flow is a three-dimensional random phenomenon, exhibiting multiplicity of scales, possessing

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

SOUND BARRIER

Sound Barrier

Sound barrier means the increase in aerodynamic drag as an airplane approaches the speed of sound. In the air, the speed that the waves travel is determined by atmospheric conditions, so the speed of sound can vary depending on temperature. The sound barrier is a concept developed in the early 20th century, when many scientists believed that the drag on aircraft caused by approaching the speed of sound made it impossible for any aircraft to reach or exceed the speed of sound without being destroyed. Most of the time, it isn't even noticeable. Breaking the sound barrier is usually something for military aircraft, as few commercial aircraft have top speeds over the speed of sound. Flying faster than sound produces a sonic boom.

In 1942, the United Kingdom's Ministry of Aviation began a top-secret project to develop the world's first aircraft capable of breaking the sound barrier. The project resulted in the development of the prototype Miles M.52 turbojet-powered aircraft, which was designed to reach 1,000 mph (417 m/s; 1,600 km/h) (over twice the existing speed record) in level flight, and to climb to an altitude of 36,000 ft (11 km) in 1 minute 30 seconds.