The Exhaust Nozzle

A gas turbine can be used to generate thrust or shaft power. At this stage in the development of this rig, I am only attempting to get thrust. It is possible to use another turbocharger turbine connected to the exhaust of the rig to generate shaft power, but there are serious obstacles due to the high rotational speed and the ability of the bearings to take radial loads. Thrust is generated by a nozzle connected to the turbine. The exhaust gas is expanded in the nozzle and accelerates. The thrust is the massflow times the exhaust velocity.

This nozzle has an adjustable outlet area, so that the effect of changing the nozzle expansion ratio can be investigated. As the nozzle is reduced in area, the turbine inlet temperature increases, and the exhaust velocity and thrust increases. The nozzle is adjusted by the worm drive hose clip around it. Cheesy, but effective! Fighter aircraft use a similar arrangement to allow the afterburner nozzle to be adjusted.

adjustable exhaust nozzleclose-up, adjustable exhaust nozzle

You can see the Exhuast Gas Temperature (EGT) thermocouple mounted on the nozzle.

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