Numerical simulation of single-mode and multi-mode RTI regarding thixotropic effects by SPH

The Rayleigh-Taylor instability (RTI) between a heavier Newtonian liquid and a lighter thixotropic liquid is studied in this paper by weakly compressible smoothed particles (WC-SPH). It is assumed that the thixotropic liquid obeys the Moore rheological model. First, the developed code is verified against available Newtonian RTI cases. Then, it is applied to thixotropic RTI cases to investigate the effects of the different non-dimensional parameters, including the thixotropic number (destruction-to-rebuild ratio), Reynolds number, Bond number, and Deborah number. It is shown that Bo is the most paramount non-dimensional parameter (i.e., it determines whether the two-phase boundary is stable or unstable), while Re, De, and thixotropic numbers have secondary influences on RTI. Based on the obtained results, the behavior of the thixotropic case is similar to the Newtonian high viscous counterpart at initial times; however, it is different at long times. It is demonstrated that the value of the thixotropic number determines when the transition between the short-time and long-time phenomena occurs.