Numerical simulations of the flow of a kerosene gel: Effects of thixotropy and shear-thinning

The ability of a gel to act like a solid-like material at rest and flow like a liquid when sheared can be very useful in propulsion system. Numerical simulation of the flow of gel fuels can be used as a reference to assist experimental studies and applications of these materials. Non-linear rheological effects such as shear thinning, yield stress, thixotropy and viscoelasticity can create difficulties in the formulation and in the numerical investigations. This paper uses a thixotropic shear-thinning constitutive relationship while using a second-order kinetic equation for the structural parameter, where the Carreau-Yasuda model is used for a 5% organic kerosene gel. We study the simple shear flow to verify the accuracy of the numerical method, and the impact of the constitutive parameters on the apparent viscosity as a function of shear rate. To look at the thixotropic flow in more complex flows, we initially study the pipe flow of an organic kerosene gel for different pumping conditions. After performing a parametric study, we find that the thixotropy of the gel strongly affects the shear history, that is, the nonuniform aging distribution. The destruction of the microstructure can be accelerated by adjusting the flow intensity and the model parameters, but it seems that it is difficult to arrive at the equilibrium state within the time scale of the propulsion system; this poses a challenge to the design of the system.