What happens when an object moves faster than the speed of sound? Imagine an airplane, or a space capsule returning from the International Space Station; or even natural occurrences like lightning and earthquakes. At speeds below that of sound, the air in front of the object moves away, allowing the object to move forward smoothly. As you keep increasing the speed – when it surpasses the speed of sound – a 'disturbance' is formed in the area around the object.
The air in front of the object begins to change, increasing in pressure, density and temperature, sharply and abruptly. Such a disturbance is called a 'shock wave'.
Studying shock waves that are created at speeds many times faster than that of sound – Mach speeds, where Mach 1 equals the speed of sound – has obvious applications in aerospace engineering. Imagine a space capsule containing astronauts returning from the International Space Station. Shock waves around the capsule create extremely high pressures and temperatures when they are generated. But for vehicles flying at Mach 5 speeds, shock waves also increase resistance while flying. Obviously, such speeds are not conducive to life. However, the astronauts need to get back home.
Most rockets, satellites or manned capsules that need to enter the Earth’s atmosphere from space move at speeds faster than sound. When a vehicle is reentering the earth’s atmosphere, the space between the object and the shock wave created has very high temperatures between 1700 and 5700 Centigrade.
“In this lab, we recreate the same conditions as a capsule reentering the Earth’s atmosphere. We generate these conditions in the lab for not more than one or two milliseconds. The data from these tests are used to design better space crafts and fundamentally study the shock wave’s structure and characteristics,” explains Dr. Jagadeesh, a senior researcher and professor at the Laboratory for Hypersonic and Shock Wave Research (LHSR), IISc Bangalore.
The lab has been studying the fascinating world of shock waves and their applications for up to 30 years now. What began as a laboratory for aerospace science has now become an interdisciplinary research field due to the multiple applications of shock waves, with more than 20 faculty members across departments at IISc using the facilities in their research programme.
The LHSR is one of the largest engineering science labs on the IISc campus and one of the largest shock wave labs in the world, with most of the equipment having been built by the researchers themselves. The findings of this lab, both fundamental and applied, have been used by ISRO, DRDO and several corporate agencies to develop futuristic equipment for military, aerospace and corporate needs.
Dr. Jagadeesh believes that “while the lab does research on fundamental areas of shock waves that are generated at hypersonic speeds, it is important to take the application and usefulness of these ideas to the common man through commercialization of the products that we develop. After all, good technology can only come out of good science.”
When shock waves are generated in laboratory conditions, the amount of energy can be controlled to generate shock waves that are not as harmful as ones created in nature. By controlling this factor, shock waves can be used in several other areas of research such as chemical engineering, biomedical engineering, manufacturing processes and even animal husbandry and agriculture. Apart from Prof Jagadeesh, Prof KPJ Reddy from Aerospace Engineering and Prof Arunan from the Department of Inorganic and Physical Chemistry, IISc, have been involved in these application oriented research programmes.
The LHSR lab has conducted several successful experiments using shock waves to deliver drugs to target tissues inside the body, to insert DNA inside cells within a living body, extract oil, help treat several lung and skin infections caused by bacteria along with antibiotics, and design better solar cells using shock waves.
About the lab
Dr. Jagadeesh is a Professor in the Department of Aerospace Engineering at IISc, Bangalore.