Microsatellites have been carried to space as secondary payloads aboard larger launchers for many years. However, this secondary payload method does not offer the specificity required for modern day demands of increasingly sophisticated small satellites which have unique orbital and launch-time requirements. Furthermore, to remain competitive the launch cost must be as low as $7000/kg. The question of paramount importance today is how to design both the liquid rocket engine turbopump and the entire engine to reduce the duration and cost of development.
The system design approach applied to rocket engine design is one of the potential ways for development duration reduction. The development of the design system which reduces the duration of development along with performance optimization is described herein.
The engineering system for preliminary engine design needs to integrate a variety of tools for design/simulation of each specific component or subsystem of the turbopump including thermodynamic simulation of the engine in a single iterative process.
The process flowchart, developed by SoftInWay, Inc., integrates all design and analysis processes and is presented in the picture below.
The preliminary layout of the turbopump was automatically generated in CAD tool (Block 11). The developed sketch was utilized in the algorithm for mass/inertia parameters determination, secondary flow system dimensions generations, and for the visualization of the turbopump configuration. The layout was automatically refined at every iteration.
The secondary flow system was modeled to determine the fluid mass flow rate that provides sufficient cooling for reliable operation of the bearings. The hydraulic network analysis tool was used for the secondary flow system calculation (Block 16). The calculation scheme of the secondary flow system is presented below
Heat amount produced by bearings friction (Block 15) is determined using turbopump axial load (Block 13) and bearings reaction in the radial direction. The radial reaction of bearing was determined using rotor dynamics simulation tool taking into account radial forces induced by circumferentially non-uniform flow admission on the turbine (Block 14). The rotor geometry was transferred from the turbopump parameterized CAD model (Block 11). The rotor model for bearing reaction determination is shown in the picture below
Preliminary FE stress analysis for the turbomachinery components (presented in Block 5 and Block 6) was also included in the algorithm. The stress analysis results for the pump is presented below. The results of this stress analysis were used for refinement of turbomachinery components geometry.
Overall seven different configurations of the turbopump were taken into account during the execution of the algorithm. The developed approach allows switching from a manual approach an automatic one, performing preliminary design steps described above for each configuration and recording crucial performance parameters for the selection of the best configuration. The configurations are presented in the picture below.
The preliminary design of the thrust nozzle for the engine was part of the algorithm as well. It can be seen in the picture below.
The configuration #1 was determined as the best option for the micro-launcher with 50 kg payload propelled by gas-generator cycle liquid rocket engine. The automatic search for optimum turbopump design took about 3.5 hours. The completion of the iterative process of turbopump preliminary design, including both pumps design, turbine design, turbopump preliminary layout development, secondary flows simulation, bearings simulation, rotor dynamics, and stress analysis would take 3 weeks at a minimum of experienced engineer labor time for a single configuration. Seven configuration would result in 21 weeks (840 hours) of labor time. Thus, the labor time for the preliminary design of the liquid rocket engine was reduced by 240 times utilizing the developed approach. This time reduction not only decreases labor time but also decrease the associated project cost and allows the engine to be supplied in a shorter period.
Off-The-Shelf Software Tools Utilized in this Study
The AxSTREAM® Platform was used in the design system, including:
- The AxSTREAM® Preliminary design for turbomachinery preliminary design
- The AxSTREAM NET™ 1D hydraulic networks analysis tool was used for leakage flows simulation
- The AxSTREAM Rotor Dynamics™ and AxSTREAM Bearings™ were used for rotor dynamics and bearings simulation
- The AxSTRESS™ was used for preliminary stress analysis of turbomachinery components
- The AxSTREAM ION™ was utilized for the development of the turbopump preliminary design system, including operation flowchart design, optimization, integration of the off-the-shelf and custom software tools, and execution.