Liquid propellant rocket is known as the most common traditional rocket design. Although the first design was launched back in 1926, liquid propellant rocket remains a popular technology which space exploration companies and institutions study for further improvement.
The implementation of this particular technology is based on a simple idea: fuel and oxidizer are fed through a combustion chamber where both liquids will met and burned to produce launching energy. In order to inject propellant to combustion chamber, a turbo-pump is used to create required pressure . The turbo-pump design and operating parameters contribute to the optimization of both turbo-pump and engine system performance. The pump needs to be designed to avoid cavitation while operates pushing the liquid to combustion chamber.
There are three different cycles which are often used in liquid propellant rocket: the staged combustion, expander and gas generator cycle. Configuration of the turbo-pump strongly relies on the cycle and engine requirements –thus the best design must be selected from options available for the particular cycle’s optimal parameters. For example for staged combustion cycle, where turbine flows is in series with thrust chamber, the application allows high power turbo-pumps; which means high expansion ratio nozzles can be used at low altitude for better performance. Whereas, for implementation of gas-generator cycle, turbine flows are linked in parallel to thrust chamber, consequently, gas generator cycle turbine does not have to work the injection process from exhaust to combustion chamber, thus simplified the design and allows lighter weight to be implemented.
Some parameters are interdependent when it comes to designing a turbo-pump, i.e: turbo-pump cycle efficiency, pump specific needs, pump efficiencies, NPSH, overall performance, etc. Often in practice, pump characteristics will determine the maximum shaft speed at which a unit can operate. Once it’s determined turbine type, arrangements, and else can be selected. Another thing that must be taken into consideration while designing a turbo-pump is how it affect the overall payloads.
Turbo-pump design affect payload in different ways:
- Component weight
- Inlet suction pressure. As suction pressure goes up, the tank and pressurization system weight increased and reduce the payload.
- Gas flowrate, since increase in flowrate decrease the allowable-stage burnout weight, which would decrease payload weight.
All those has to be taken into consideration while trying to select an optimal design of turbo-pump, since it crucially affects overall performance of the engine.
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