TWO PHASE FLOW ANALYSES OF A CONVERGENT DIVERGENT JET NOZZLE

Abstract

In this study, Jet Propulsion Lab (JPL) Nozzle is taken to simulate the effects of particulates on gas phase, which is a two-phase flow. Nozzle is a thrust producing component of a rocket. When the flow inside a nozzle domain becomes two phase, then it affects in reduction of thrust as compared to the single phase gas flow. Thrust and exit mach no. of a nozzle are the two major parameters, through which performance of a rocket is measured. Two-phase flow inside the nozzle domain is due to the burning of aluminium fuel in the combustion chamber of Solid Rocket Motor (SRM). The burning results into formation of gases and alumina (a solid particulate). The presence of these particulates affects the mach no. of the gas. These particles are also likely to agglomerate on throat area of the nozzle which can reduce the thrust. These adverse effects on the flow due to the presence of two phase flow, makes this study significant for Computational Fluid Dynamics (CFD) practitioners as well as for rocket propulsion engineers. There are mainly two models to analyse two-phase flows in CFD; one is Eulerian-Eulerian model and the other is Eulerian-Lagrangian model. To study both of them is difficult and complicated. That is why there is an acute scarcity of literature which deals with both of these models in a supersonic convergent divergent nozzle channel. For simulations in FLUENT Eulerian-Eulerian model is taken as Two-Fluid Mixture model and Eulerian-Lagrangian model is Dispersed Phase Model (DPM). Unsteady and non-reacting flow patterns for two-phase (gas-solid) flows have been analysed computationally. Particles of 10 micro-meter (µm) size are added -to investigate the simulation of the two-phase flow- with 20% volume fraction. The ix presence of particles inside the gas has been investigated by using both of the computational models (Eulerian-Eulerian and Eulerian-Lagrangian) to see the effects on thrusts and mach nos. Both laminar and turbulent types of flows are taken under study for simulations. Firstly, the single gaseous phase is simulated inside the JPL nozzle, thrust and mach no. are computed. Then the same was conducted for the two phase flow with both models (Eulerian-Eulerian and Eulerian-Lagrangian). For two phase flow in the Lagrangian-Eulerian Model, particles are uniformly injected from the nozzle inlet. Particle trajectories are tracked. This method shows that particles sustain their identity means one can track them. In Eulerian-Eulerian model, aggregated properties of particles and gas are taken. It is actually the homogeneous mixture in which particle tracking is not possible. For all the turbulent mathematical models Spalart Allmaras, k-ε and k-ω models it is found that -unlike laminar flows- thrust and mach no. distribution are changed with respect to the both afore-mentioned models (Eulerian-Eulerian and Eulerian-Lagrangian). Thus it changes the mach no. and thrust. k-ω and laminar flows produced better results it is suggested to use in both of these models (Eulerian-Eulerian and Eulerian-Lagrangian) with respect to the type of flow considered.