Robust Cryogenic Cavitation Modeling for Propulsion Systems Ground Test Facilities

Rigorous ground testing mitigates space propulsion system risk by enabling advanced component and system level rocket propulsion development and by demonstrating that designs reliably meet the specified requirements over the operational envelope before the first flight. The development of advanced ground test technology components and systems that are capable of enhancing environment simulation, minimizing program test time, cost and risk and meeting environmental and safety regulations is focused on near-term products that augment existing state-of-the-art propulsion system test facilities. Thus improved capabilities to model and predict component behavior in harsh ground test environments are needed for enhanced facility design. In particular, components such as pumps, turbines, valves and chokes may experience vibration and damage due to cavitation in the flowing liquid, and any reduction in the severity of the operating conditions would provide expanded test and performance benefits. The proposed innovation is to develop an unsteady cavitation model based on a tabular equation of state and a representation of cavitation bubble dynamics that together describe the growth and collapse of nucleated bubbles in a liquid cryogen. Important nonequilibrium mechanical and thermal effects will be considered by using a drift-flux model and adding an additional energy equation for the liquid temperature. Validation of the advanced cavitation models will be accomplished for both steady and unsteady flows by comparing surface pressure and temperature data and computing power spectra from frequency domain analyses. The final analysis tool will be used to demonstrate the significant nonequilibrium flow behavior for both the validation cases and actual production analysis problems of interest to NASA.

This technology will provide NASA with an efficient, robust cryogenic cavitation simulation tool suitable for use in propulsion systems ground test facility component design and analysis as well as other in advanced applications. The research product will provide enabling engineering and scientific technologies to predict complex cryogenic flow problems with nonequilibrium cavitation, resulting in reduced ground test facility costs and system risk by increasing test productivity. Potential enhancements include modified treatment of evaporation and condensation rates, turbulence/cavitation interaction modeling, detailed liquid/vapor thermal interface effects, variable transport properties, expanded thermodynamic databases and extended model validation. The proposed cavitation modeling tool is also applicable to hydrogen inducers, impellers and pumps operating at high vapor fraction.

The growing trend toward coupled multi-physics analyses is opening significant new markets as more difficult problems can be addressed using advanced computational techniques. The ability to robustly model complex cryogenic flows with cavitation will allow the commercial aerospace and defense industries to improve design and development of new products and streamline ground testing. Our analysis software can also be applied in the fields of medicine (magnetic resonance imaging), food processing (ultrasonic freezing) and semiconductor processing (plasma etching and vacuum pumping of gas contaminants). The basic architecture of the modeling framework can remain the same while new plug-in modules are developed to address different physics and design requirements.

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