WHAT ARE SHOCKWAVES?
Shockwaves are strong compression waves caused by a sudden release of energy, such as an explosion, or by objects traveling at supersonic speed.
- Shockwaves are features exclusive to the supersonic regime and they always travel at a speed greater than Mach 1.
- They cause an instantaneous increase in properties such as pressure, temperature and density of the medium through which they propagate.
- Despite the destructive applications, shockwaves can also be used constructively in a wide variety of fields.
- Shock tubes are devices that help in the generation and study of shockwaves in a controlled manner.
- Shock tunnels are devices that help in aerodynamic testing of models.
SHOCK TUBE
Conventional high pressure driven shock tube shown schematically in the figure below consists of a constant area tube divided in to driver and driven sections separated by a diaphragm. On one side of the diaphragm, a gas is filled to a pressure high enough to rupture the metal diaphragm, and pressure in the other tube is reduced to a lower value than atmospheric pressure as required. The former is termed the driver side and the latter the driven side. When the diaphragm ruptures due to the high pressure gas in the driver tube, it generates a shock wave that moves along the length of the driven tube, thereby increasing the pressure, temperature and density of the driven gas. In a shock tube, the gas filled in the driven section is the test gas under consideration.
SHOCK TUNNEL
Hypersonic shock tunnel is essentially short duration hypersonic wind tunnel used for testing the hypersonic vehicles configuration like launch vehicles, missiles and space shuttles flying at Mach number higher than 5. Schematic diagram of a typical hypersonic shock tunnel is shown in the accompanying diagram. It consists of a shock tube connected to a convergent divergent hypersonic nozzle which is in turn connected to a test section and a dump tank. Driver and driven tubes of shock tube are separated by a metallic diaphragm and the nozzle and the shock tube are separated by a thin paper diaphragm. Test model is mounted in the test section which is evacuated to very high vacuum initially using vacuum pump. Operation of the hypersonic shock tunnel is very complex and the facility is more suitable to carry out research work and hence it is seldom used for teaching purpose at undergraduate level.
