By Pralhad Pawar
In the nineteen century, man dreamt about flying and began building flying machines patterned on the flight of birds. These bird-like crafts failed and man realised that deeper understanding is required, especially on the lift and drag forces acting on the object’s surfaces during flight.
Wind tunnels are used to copy the actions of an object inflight and have been an indispensable tool since the development of aircraft and subsequently for the advancement of supersonic aircraft and spacecraft.
Akin to an object flying at high speeds in stationary air, in the wind tunnel this condition is simulated by keeping the object stationary and moving air at high speeds across it - thereby making it seem that the object is actually flying.
In a wind tunnel facility, miniature models or exact same small-sized replicas of rockets or space vehicles are tested for its aerodynamic condition. With this, the lift and drag forces acting on the objects are measured for its aerodynamic stability under controlled conditions.
Hence, wind tunnel testing is indispensable before committing an advanced aircraft/spacecraft design for actual flying.
As India embarks on its ambitious space missions, it needs to properly test newly-built spacecraft for aerodynamic stability at high speeds and angles during the development stage. ISRO’s Vikram Sarabhai Space Centre has therefore entrusted Tata Projects Ltd to design and build a grassroot 1.2m Trisonic wind tunnel facility on turnkey basis. Tata Projects has entered into a tie-up for knowhow and technology with a Canadian firm named Aiolos Engineering Corporation.
This trisonic blowdown facility will be a state-of-the-art project which will enable ISRO to develop upcoming space vehicle and rocket launch events that are being lined up in future.
This facility can simulate flow conditions ranging from 0.2 Mach up to 4 Mach (Mach 4 means four times the speed of sound or about 4780 Kmph).
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The wind tunnel is designed to carry out a wide variety of high-speed tests besides diagnostic studies of airflow around the model surface, including aerodynamic forces and moments measurements, drop trajectories, performance evaluation, jet engine base-flow simulation and dynamic stability. The entire sequence of operation shall be controlled by a sophisticated fast response tunnel automation system. All these tests ensure the integrity of the shape for functional reliability and also optimise the performance of the object in flight.
This is India’s first such facility to be built with an ejector system which aims to reduce the tunnel start or stop loads from acting on the model. In addition, an ejector system shall be used at subsonic mach numbers.
A huge mass of air amounting to around 30,000 kgs per test of duration less than a minute is consumed during the testing operations. The flow of air in the wind tunnel ranges from 240 km/h to 4938 km/h based on the required Mach number. The air is supplied by two larger air compressor systems consuming 10MW power and stored at pressures of 20 times atmospheric pressure in large air storage vessels of about 4500 m3 volume.
The Mach number range is precisely controlled by a specially designed component called Flexible Nozzle. Within this, the flow area contour is controlled by a combination of hydraulic actuators and electro-mechanical actuators/screw stops which can be set precisely for the desired Mach number.
In addition, the services of the high-speed wind tunnel will also be available to the commercial aircraft industry, educational institutions, and other government agencies requiring controlled high-speed conditions up to Mach 4, for wind tunnel testing.
From sending India’s first satellite into space (Aryabhata) to successfully launching some of the most historic missions like Chandrayaan-1 (2008) and Mangalyaan (2013), ISRO has successfully done it all and with a success rate that is the envy of all its competitors. Today, India through ISRO has built an unrivalled reputation for launching rockets into space at very competitive prices.
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In conclusion, the upcoming Trisonic blowdown wind tunnel facility will further win widespread acclaim for the nation by providing a cutting-edge real-time testing facility. It will enable ISRO and its divisions such as Vikram Sarabhai Space Centre to successfully attain the next level of space technology prowess for forthcoming prestigious launches such as Chandrayaan 2 - Lunar Mission and RLV-TD - Reusable Launch Vehicle. Furthermore, such testing facilities will be crucial for Gaganyaan - India’s maiden human space mission wherein the precious lives of our astronauts shall be at stake.
(This article has been authored by Mr Pralhad Pawar, Chief Technology & Engineering Officer – Tata Projects Limited. Views expressed are personal.)