Development of a Numerical Design Tool for SNS Cavitation Mitigation

The generation of a strong shock wave in the Spallation Neutron Source (SNS) can lead to cavitation and significant erosion on the vessel wall containing the liquid mercury target. Based on preliminary numerical and experimental work at various laboratories, it has been proposed that strategies such as inserting a cloud of small gas bubbles or a gas layer in the mercury target could absorb and deflect the shock waves and protect the walls from cavitation erosion. Another strategy involves the reduction of cavitation through new designs that take advantage of wall shaping and deformation, and energy absorption. In order to aid the design of such cavitation-mitigation schemes, this project will develop an advanced numerical software package, which couples multiscale, multiphase compressible fluid solvers with structure dynamics solvers. This code will be capable of simulating the relevant features of the flow, namely shock wave propagation through bubbly media, large liquid/gas interface deformations, shock wave induced cavitation, and deformation of structures due to shock wave and cavitation/structure interactions. In Phase I, multiphase codes adapted to study this problem were able to capture high pressure wave propagation in bubbly media, along with the interaction of the wave with the bubbles, free surface, and the wall structures. The potential success of different cavitation mitigation measures (including wall shape design, insertion of an air layer, and the generation of a bubbly medium) was demonstrated. Phase II will involve further improvements to the software package, including a generalization of interface capturing schemes for broader multiphase/material flows, a multiscale cavitation model for bubbly media, and a structure code for simulation of full fluid/structure interaction. The software package will then be validated by using existing and conducting benchmark experiments in SNS mercury test loops. Commercial Applications and Other Benefits as described by the awardee: In addition to the SNS application, the software package should have application to multiple fields: (1) naval applications, where the mitigation of shock wave impact is of keen interest to vessel protection and to propeller blade design; (2) chemical processes, to improve performance of bubble column reactors and multiphase slurries; and (3) minimally invasive medical procedures that use acoustic cavitation-based treatments such as shock wave lithotripsy.