Iterated Inducer Design using Cavitation Modelling and Testing using a Hot Water Cavitation Tunnel

Abstract

High power to weight turbo-pumps enable the creation of powerful compact rocket engines capable of launching payload to space. The desire to reduce cost of payload to space requires engineers to push the limits on hardware. Cavitation in turbo-pumps is a phenomenon requiring mitigation when pushing pump rotational speeds and reducing vehicle tank pressures. Design and optimization of turbo-pump inducers is essential for the further improvement of pump suction performance. Experimental evaluation of performance while more accurate compared to numerical models come with material cost and slower iteration time. Numerical models excel in these areas while compromising
on accuracy. Accurate modelling of cavitation is key to accurately model the suction performance of turbo-pump inducers. This work focuses on the design and optimization of an existing turbo-pump inducer to further improve the suction performance. The main questions in this work focus on the effect on cavitation performance by modifying multiple geometric features present in inducer design. The application of an enhanced Rayleigh-Plesset cavitation model capable of modelling cryogenic thermal suppression effect is investigated using a hydrofoil verification case. Numerical stability prevented the application of this enhanced model on the full-pump and further work is performed using the Zwart-Gerber-Belamri Rayleigh-Plesset cavitation model. A parameter design
study is performed to identify the sensitivity of key turbo-pump inducer design parameters on the suction performance of an excising inducer-impeller pair. Outcome of this study is used to establish an iterated inducer design from the baseline with a predicted ≈ 15% performance increase in pump suction performance. The outcome of this parameter study adds to the current body of literature available on the design of cavitating turbo-pump inducers. The iterated inducer design is materialized for experimental evaluation using a cavitation tunnel developed by Rocket Factory Augsburg (RFA). Suction performance of both the baseline and iterated inducer design are experimentally
evaluated to allow for comparison between numerical prediction. In this work both the numerical prediction results show agreement in predicting the relative improvement in suction performance measured in experiment. Performance increase in suction performance is measured experimentally to be ≈ 14% compared to the ≈ 15% predicted numerically. Yet, the absolute performance prediction of suction performance shows deviations from the observed value of ≈ 13 − 15%. A set of considerations are provided on the implementation of numerical cavitation models and testing of cavitating inducers. These considerations can help improve the accuracy of these numerical models
and increase usability of cavitation testing facilities.