Performance improvement in propulsion systems is essential towards achieving cost effective launch vehicles. Apart from propellant energetics, the nozzle plays a vital role in improving propulsion system performance. Therefore by improving performance of existing nozzles and by developing new nozzle concepts, which can operate at both low and high altitude regimes, it is possible to obtain significant gains in the delivered specific impulse of rockets. With these objectives, ISRO has established Nozzle Testing Laboratories (NTL) at Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram.

The NTL consists of a Nitrogen gas generation and storage system, a graphite cored induction heater (for heating nitrogen), a test chamber, a diffuser system and heat exchanger, coolant system and power supply systems. The facility utilizes the available 6600 m3 capacity vacuum vessel of the Hypersonic Wind Tunnel (HWT) for simulation of altitude pressure. For nozzle performance evaluation, heated nitrogen gas is allowed to expand in nozzles kept in the test chamber having simulated altitude pressure. Gaseous nitrogen admitted to the storage heater from the top exits the heater at the required temperature. The facility utilises fast response pressure transducers and instrumentation to study nozzle phenomena. Nozzles up to Area Ratio (AR) 300 and more can be tested in the facility.

The NTL has the capability to cater to a wide range of studies related to nozzles such as:

Contour optimization for large AR nozzles

Flow separation, techniques for flow separation control

Nozzle wall heat transfer

Regenerative cooling

Supersonic film cooling

Evaluation of new nozzle concepts

Experimental validation of flow separation control devices with minimal modifications in the existing contour nozzles enabling high AR operation can be carried out. Specific tests can be devised and carried out to validate Computational Fluid Dynamics (CFD) predictions. The facility can also be used to carry out open jet heat transfer studies.

The Nozzle Testing Laboratories was inaugurated recently by Chairman, ISRO which is a unique facility established for the first time in the country towards carrying out advanced R&D in the area of rocket nozzle.

Inside view of NTL

A typical 100 AR nozzle developed for tests in the facility

Nozzle Testing Laboratories (NTL) Building at VSSC