Shock Wave Types of booms Mach wave.pptx

Shock wave, strong pressure wave in any elastic medium such as air, water, or a solid substance, produced by supersonic aircraft, explosions, lightning, or other phenomena that create violent changes in pressure. Shock waves differ from sound waves in that the wave front, in which compression takes place, is a region of sudden and violent change in stress, density, and temperature. Because of this, shock waves propagate in a manner different from that of ordinary acoustic waves. In particular, shock waves travel faster than sound, and their speed increases as the amplitude is raised; but the intensity of a shock wave also decreases faster than does that of a sound wave, because some of the energy of the shock wave is expended to heat the medium in which it travels.

1. Shock Wave

2. Shock Wave Shock wave, strong pressure wave in any elastic medium such as air, water, or a solid substance, produced by supersonic aircraft, explosions, lightning, or other phenomena that create violent changes in pressure . Shock waves differ from sound waves in that the wave front, in which compression takes place, is a region of sudden and violent change in stress, density, and temperature. Because of this, shock waves propagate in a manner different from that of ordinary acoustic waves. In particular, shock waves travel faster than sound, and their speed increases as the amplitude is raised; but the intensity of a shock wave also decreases faster than does that of a sound wave, because some of the energy of the shock wave is expended to heat the medium in which it travels.

3. What is the name of the shock wave at the front of the aircraft? Sonic boom is an impulsive noise similar to thunder. It is caused by an object moving faster than sound which is about 750 miles per hour at sea level. An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the water waves caused by a ship's bow. When the aircraft exceeds the speed of sound, these pressure waves combine and form shock waves which travel forward from the generation or "release" point.

4. Types of booms There are two types of booms: N-waves and, U-waves. The N-wave is generated from steady flight conditions, and its pressure wave is shaped like the letter "N." N-waves have a front shock to a positive peak overpressure which is followed by a linear decrease in the pressure until the rear shock returns to ambient pressure. The U-wave, or focused boom , is generated from maneuvering flights, and its pressure wave is shaped like the letter "U." U-waves have positive shocks at the front and rear of the boom in which the peak overpressures are increased compared to the N-wave.

5. N-waves sonic boom

6. U-waves sonic boom

7. Mach Wave A Mach wave is a pressure wave in fluid dynamics. It travels with the speed of sound by a slight change of pressure added to a compressible flow. Mach Angle: ‘Mu’ is an angle which depends only on the Mach number and is therefore called the Mach angle of the flow.

8. What causes Mach cones? When the object moves at supersonic speeds (Ma > 1), the object "out runs" the pressure pulses it generates. The locus of wave fronts forms a cone which is termed a Mach Cone. when v>c (i.e. when the airplane is faster than sound),

9. You see, when v>c (i.e. when the airplane is faster than sound), then the sound waves form to a cone with the airplane at the tip of the cone. During a time interval t the airplane flies a distance vt. In the same time a spherical sound wave grows to radius ct. To calculate the cone angle θ consider the red right-angled triangle.

10. What is a Mach stem? A shock wave formed by the fusion of incident and reflected shock waves from an explosion. Or What happens when two shock waves meet? When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet .

11. Explanation with Example Shock wave : Imagine you are a *rigid* heavy fat person in a fish market full of people like you (in the pre corona world). Now suddenly a bus is traveling at a great speed (you cannot run with that speed). Now, you will try to run as fast as you can but you have a limit to it. The bus will collide with you and everyone will have to forcefully (compressively) cling on the front of the bus. That phenomenon is called a shock disturbance or a shock wave. Consider people as air particles and bus as a blunt body. Mach wave : In the above example, the bus is a big blunt body. Imagine one of you is capable to run at that high speed. The disturbance created by that person will be weak but that will also give you a shock (the weakest shock). Now such a disturbance is called a Mach wave. Technically, in supersonic flows size of gas are capable enough to cause Mach wave generation. So, Mach waves are weakest isentropic waves in a supersonic flow field and the flow through them will experience only negligible changes of flow properties.

12. Why do Shock Waves travel faster than Sound waves? When you compress a gas it gets hotter and when you expand it, it gets colder------(adiabatic processes) With normal sound waves the increases and decreases in pressure compared with the absolute pressure in the atmosphere as so tiny, that there is very little change in the temperature of the air. However, if you create a large enough increase in pressure, that will raise the temperature of the air enough to increase the speed of sound in the air. That's what happens with a shock wave. It compresses the air significantly enough compared with the absolute pressure that the temperature goes up so the speed of sound goes up and the wave moves faster than the normal speed of sound.