Breaking the Sound Barrier
Using wind tunnels to research supersonic flight
What do a fighter jet, a space rocket, and a shooting star have in common? They all travel faster than the speed of sound! But how do scientists study what happens at supersonic speeds? They simulate the extreme conditions of high-speed flight in experiments. Vacuum technology from the Busch Group is an indispensable part of them.
As a rocket travels into space, it reaches supersonic speeds because it accelerates rapidly. This acceleration exerts a tremendous force on the spacecraft. Every component and material that makes up the rocket must therefore be tested beforehand to ensure that it can withstand these forces. These tests not only ensure that astronauts are able to travel in space safely but also make future aerospace more efficient and environmentally friendly. But how can you simulate these conditions on the ground? The answer is a high-speed wind tunnel. It uses the interaction of pressure and vacuum to mimic the extreme flight conditions in space. On one end of the tunnel are one or more large accumulator tubes in which air is compressed. At the other end is a vacuum vessel, evacuated by a vacuum pump. The experiment itself is carried out in the measuring section in between.
Bringing hypersonic speeds down to Earth
Inside the measuring section, researchers position aircraft models, sensors, or material samples to observe how they interact with ultrasonic flow. The data they collect helps engineers improve designs, enhancing the safety, efficiency, and sustainability of future aircraft and spacecraft. To perform a test, the valve to the accumulator tube is opened, creating a dilution wave that flows into the accumulator tube and accelerates the accumulator air towards the nozzle. Due to the differential pressure between the accumulator tube and the vacuum vessel, and thanks to the specially shaped ultrasonic nozzle, an ultrasonic flow is created in the measuring section. This airflow achieves up to seven times the speed of sound – over 8,600 km/h or twenty times faster than a Formula 1 car!
The secret behind ultrasonic flow: vacuum
Vacuum pumps from the Busch Group are key to accelerating, but also to slowing down the high flow velocity. These vacuum pumps generate the necessary vacuum conditions in the vacuum vessel positioned at the end of the measuring station to efficiently create the necessary differential pressure. Without the vacuum pump, a lot more technical effort would be necessary to achieve the required pressure ratio. The air from the accumulator is collected in the vacuum vessel during the test and then discharged as normal ambient air.
Bringing hypersonic speeds down to Earth
Inside the measuring section, researchers position aircraft models, sensors, or material samples to observe how they interact with ultrasonic flow. The data they collect helps engineers improve designs, enhancing the safety, efficiency, and sustainability of future aircraft and spacecraft. To perform a test, the valve to the accumulator tube is opened, creating a dilution wave that flows into the accumulator tube and accelerates the accumulator air towards the nozzle. Due to the differential pressure between the accumulator tube and the vacuum vessel, and thanks to the specially shaped ultrasonic nozzle, an ultrasonic flow is created in the measuring section. This airflow achieves up to seven times the speed of sound – over 8,600 km/h or twenty times faster than a Formula 1 car!
The secret behind ultrasonic flow: vacuum
Vacuum pumps from the Busch Group are key to accelerating, but also to slowing down the high flow velocity. These vacuum pumps generate the necessary vacuum conditions in the vacuum vessel positioned at the end of the measuring station to efficiently create the necessary differential pressure. Without the vacuum pump, a lot more technical effort would be necessary to achieve the required pressure ratio. The air from the accumulator is collected in the vacuum vessel during the test and then discharged as normal ambient air.
Read more – Why spacecraft heat up when re-entering Earth’s atmosphere
When a spacecraft re-enters the atmosphere from a low Earth orbit, it is moving at about 28,160 km/h – around 25 times the speed of sound. While doing so, it faces temperatures hotter than molten lava – sometimes exceeding 1,600 °C. This happens due to a process called compression heating.
At such high speeds, the air molecules directly in front of the spacecraft do not have time to flow around it because they can only move as fast as the speed of sound (1,235 km/h). Instead, the air molecules quickly compress into a shockwave, creating a region of high temperature and pressure that heats up the surface of the spacecraft. For this reason, rockets and capsules are equipped with heat shields designed to absorb and dissipate this energy safely. Without them, re-entry into the atmosphere would be impossible as the metal that makes up the rocket would melt. Understanding these effects is crucial for designing next-generation space vehicles. The same wind tunnels used to test supersonic aircraft also help scientists simulate re-entry conditions, ensuring that future spacecraft can return to Earth safely.
When a spacecraft re-enters the atmosphere from a low Earth orbit, it is moving at about 28,160 km/h – around 25 times the speed of sound. While doing so, it faces temperatures hotter than molten lava – sometimes exceeding 1,600 °C. This happens due to a process called compression heating.
At such high speeds, the air molecules directly in front of the spacecraft do not have time to flow around it because they can only move as fast as the speed of sound (1,235 km/h). Instead, the air molecules quickly compress into a shockwave, creating a region of high temperature and pressure that heats up the surface of the spacecraft. For this reason, rockets and capsules are equipped with heat shields designed to absorb and dissipate this energy safely. Without them, re-entry into the atmosphere would be impossible as the metal that makes up the rocket would melt. Understanding these effects is crucial for designing next-generation space vehicles. The same wind tunnels used to test supersonic aircraft also help scientists simulate re-entry conditions, ensuring that future spacecraft can return to Earth safely.