Particle size effects in multiphase Rayleigh–Taylor instability

The Rayleigh–Taylor instability (RTI) is a fundamental fluid dynamic phenomenon that occurs when a denser fluid pushes against a lighter one under the influence of gravity, leading to complex interfacial instabilities. A similar phenomenon occurs when describing multiphase regions, where one fluid may be laden with a heavy particle phase that is accelerated into a lighter fluid. The rate of coupling between particles and carrier fluid, equilibration time, is finite and the particles can slip through the carrier fluid, altering the growth and evolution of the RTI. A multiphase RTI is studied for various particle equilibration times, using the Euler–Lagrange simulations. The dynamics of the particle and carrier phases are studied, and the growth rate of the multiphase interface is tracked and compared to models for the RTI for both the linear and nonlinear phases. Larger particles, with a long equilibration time, show strong decoupling effects, leading to a reduced vorticity deposition and amplitude growth length. In contrast, smaller particles equilibrate rapidly with the gas, allowing amplitude growth similar to an RTI. At intermediate particle sizes, we find a higher growth rate, in excess of the RTI, due to a concentration of the particle phase, leading to higher localized mixture densities. These findings emphasize the critical role of particle size in multiphase RTI.