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Bengaluru: On the afternoon of 20 May, a very loud, crack was heard throughout the city, with local reports that confirm people had heard near the airport in the north and around Electronic City in the south. Despite the fact that the sound resembled a loud explosion, it would be a very intense explosion was heard across a large geographic area, but the residents of the city could not see any smoke or a fire that could have accompanied such a blast.
Some people this author spoke to speculated that it could have been a leak of hydrogen: hydrogen reacts explosively with the oxygen in the air and no flame. The idea is not so far-fetched taking into account that there are many research centres including the ISRO, in the city that could be experiencing with hydrogen. While others wondered if it could be an earthquake, an idea that was quickly disadvantaged after the seismic data is indicating no activity, and also because earthquakes do not release enough acoustic energy to be heard around a city.
However, by the morning of 21 May, the Indian Air Force (IAF) said in a press release that the sound associated with a jet to go supersonic outside of the city limits in a test flight. When any object flies through the atmosphere, continually pushes the air in front of it, creating waves of pressure that are transmitted out at the speed of sound. When the object goes supersonic – that is to say, it crosses the speed of sound in the medium in which it is flying, in this case the atmosphere – these pressure waves are inserted at faster than the speed of sound. But since it can only be move look at the speed of sound, they begin to build up in the front of the object. At some point they merge into a single high-pressure wave is known as a shock wave.
When this shock wave reaches your ear, and hear the sonic boom: a loud noise, the noise of the signaling is not a supersonic object in its wider neighbourhood. The air force jet have also been supersonic for a while, and at this time, it constantly produces the shock waves. But hey only once because the waves flow out of the front tip of the jet in the form of a cone, and the boom that is audible only when the waves get you, not when they pass over you. That is to say, the rise of the brands is the time to experience a sudden and transient change in the pressure of the surrounding air.
In the second place, you can hear a second boom associated with the same object due to the differences in pressure around the mouthpiece. Whatever the speed of the jet flying, there is a negative pressure behind the tail for the same reason that there is an excess pressure or overpressure in the front: the jet of the passage pushes the air in the front and pulls the air towards itself in the back. So for a stationary observer, a passing jet would create an N-shaped pressure profile: in the first place, the observer will note the pressure, then a constant decrease as the jet moves ahead, culminating with a negative pressure in the end, quickly followed by the normal atmospheric pressure.
The two expansions are associated with the two drastic changes in the pressure in the first place, when the overpressure is created and the second when the negative pressure moves quickly to normal. This is the reason that a sonic boom can also be heard when, for example, the stages of the SpaceX Falcon Heavy rocket returned to earth after his release (audible to 1:39 in the video below), the slowdown using retrograde thrusters, or when a plane slows down from supersonic to subsonic speeds – as the ministry of defence said in a statement to ANI.
Although there is no way to keep the jets supersonic flow of the production of sound waves when you accelerate or decelerate, those with the smoothest of aerodynamic profiles may produce less noise in these phases. This is desirable considering this type of aircraft are generally used in war and it is important for them to be as unnoticeable as possible. According to the ministry of defence, “sonic boom was heard probably while the aircraft is decelerated from supersonic to subsonic speed between 36,000 and 40,000 feet in height.”
Note that the speed of sound in a medium depends on the average density, which in turn affects your blood pressure. At 30,000 feet, for example, the atmospheric pressure is 30.1 kPa and at sea level is 101.3 kPa (this is why aircraft cabins are pressurized). So that the speed of sound through the air at 30,000 feet of altitude is 303 m/s, while that is 340 m/s at the level of the sea. A jet of the transition from supersonic to subsonic speeds at 35,000-40,000 feet probably slowed from above 294.9-295.4 m/s down.
The Sukhoi Su-30, Mirage 2000 and the Rafale – all three of which the IAF operates top speeds in excess of this limit. (The last batch of planes Rafale was, at the beginning of this year, is expected to be delivered in May.) The News Minute he quoted an anonymous police official, speculating that the boom could have been associated with a Sukhoi Su-30.
All this said, there are some doubts about the IAF of the statement that contains the word “routine”. Specifically, the IAF refused his command training was involved, but suggested that “the Aircraft and Systems Testing Establishment [ASTE]”– a part of the IAF and the Hindustan Aeronautics Limited [HAL] could have carried out its routine test flight, making it necessary to go supersonic at times” (source). HAL since denied its involvement, which leaves us with the ASTE.
In fact, at 9:35 pm on May 20, a Ministry of Defense in PRO of the twitter account, “it was a routine IAF Flight Test involving a supersonic profile that took off from [Bengaluru] Airport and flew in the air space assigned outside of the city limits. The aircraft was from the Aircraft Systems and Testing Establishment (ASTE).”
Despite the fact that the MoD described the flight as “routine”, the explosions are not ‘normally’ heard throughout the city. But city officials are brushing this concern aside because the city is also quieter these days because of the blockade, and that the boom just stuck out like a sore thumb.
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