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Particle-turbulence interaction of high Stokes number irregular shape particles in accelerating flow: a rocket-engine model
Keywords:Particle laden turbulent flow, Rocket engine, Spatial acceleration, Turbulence modulation
AbstractMetal particles in solid propellants enhance rocket engines performance. An interaction of particles with a high Reynolds number turbulent gas flow accelerating to a nozzle, has not been characterized thoroughly. We study the particle-turbulence interactions in a two-dimensional model of a rocket engine. Two-phase particle image/tracking velocimetry provides the flow velocity simultaneously with the velocities of irregularly shaped inertial particles ($d_p \sim 350 \mu$m, Stokes $St \sim 70$, particle Reynolds number $Re_p \sim 300$). We reveal the local augmentation of turbulent fluctuations in the particle wakes (up to 5 particle diameters downstream the particle). Despite the low mass fraction, the large response time of the particles leads to an increase of turbulent kinetic energy (TKE) everywhere in the chamber. The increase of local particle mass fraction near the nozzle, due to the mass conservation and converging streamlines, compensates for the dampening effect of the strong mean flow acceleration and further augments TKE at the nozzle inlet. Furthermore, this is accompanied by unexpectedly isotropic fluctuations in the proximity of the nozzle. The phenomenon of the isotropic, strongly enhanced turbulence in the proximity of the engine nozzle achievable with the low mass fraction of high $St,Re_p$ particles, can be used to improve the design of solid propellant rocket engines.
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