The combined effects of viscoelasticity and shear-thinning on the flow characteristics of gel propellant in nozzle injectors

Gel propellants exhibit significant potential for aerospace propulsion systems due to their complex combined viscoelastic and shear-thinning properties, enabling mobility adjustments to suit diverse flow conditions. However, current research predominantly focuses on either their shear-thinning characteristics alone or isolates the study of their non-Newtonian flow behaviors. Here, we investigate the flow dynamics of gel propellants in converging–diverging nozzles, focusing on the synergistic mechanisms of viscoelasticity and shear-thinning behaviors. Using the White–Metzner constitutive model, we reveal that the drag reduction mechanism is governed by the concurrent modulation of the first normal stress difference (N1) and shear stress. Compared to purely elastic flows, our stress analysis demonstrates that shear stress reduction makes the primary contribution to the enhanced discharge coefficient (CD), while N1 plays a secondary yet non-negligible role. Viscoelasticity is found to actively suppress the shear stress magnitude, and this effect is more prominent in the low Reynolds number (low-inertia) regime, thereby exerting stronger flow control at low velocities. While the impacts of shear effect on CD dominates over a wider Reynolds number (Re) regime compared to the viscoelastic contribution, as the energy dissipation due to viscous losses dominate over elastic losses. These findings clarify the hierarchy of stress contributions in confined non-Newtonian flows, and fill the gap in understanding the combined effects of multiple rheological properties on the flow of gel propellants in nozzles.