High Altitude Rocket Reactive Jet Flow Simulations with a Hybrid NS-DSMC Methodology
Creators: name:  V. CHARTON 
name:   J. LABAUNE 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: PROPULSION PHYSICS
NOZZLE
TURBOPUMPS

description: The design of several aerospace systems involves studying multiscale physical quantities such as pressure, temperature and velocity. For example, high altitude rocket propulsion, vehicle re-entry, atmospheric deceleration, landing or satellite propulsion typically encounter both high density and rarefied flows. Numerical simulation of such flows is a challenge regarding the great variation of density it involves. The present work uses a hybrid methodology to accurately simulate rarefied flow physics as well as highdensity areas. This methodology couples Navier-Stokes (NS) resolution and Direct Simulation Monte Carlo (DSMC) in a one-way approach that enables the simulation of steady-state and quasi-steady-state problems. The idea is to split the calculation into zones where the flow is either computed by Computational Fluid Dynamics (CFD) resolving NS equations or by DSMC according to specific criteria based on the rarefaction level. Such methodology was experienced in the context of micro-thrusters by Grabe et al. [1] or La Torre et al. [3]. However, it has some limitations regarding the computational cost. The present work aims to optimise the methodology to enable more complex simulations with reactive flows and metric-sized nozzles. To this end, Grabe et al. [1] experimental work realised at the German Aerospace Centre (DLR) is used to validate the simulation results. Two main improvements are made. First, the area close to the inner nozzle wall is often defined as a rarefied region due to strong gradients. However, this study shows that this area can be removed from DSMC simulation, allowing significant computational cost decrease without degrading the final results. In order to remain as close as possible to the rarefied physics in this quasi-continuous area, a Maxwell wall condition is used during the NS calculation to reproduce the wall bounce on velocity and temperature that might be yielded by rarefied effects. Second, the influence of the continuous to rarefied flow interface definition, governed by a rarefaction criterion, is evaluated through a parametric study. This improves the understanding of the criterion influence, as there is little literature knowledge, to identify the best criterion value regarding accuracy and computation cost. It is shown that the optimisation of the hybrid methodology allows a computational cost decrease up to 5 times. Thanks to this optimisation work, it is possible to consider a more complex configuration in the second part of the present study. Thus, the simulation of a metric sized nozzle with reactive multi-species flow and in-flight co-flow is realised. The goal is to evaluate and demonstrate the capacity of the methodology to handle the simulation of such rocket flow. A particular interest is the electron density resulting from ionisation of the flow, answering a need in the anticipation of radio communication attenuation between the ground station and the rocket. The rocket geometry and the flow characteristics such as the combustion chamber pressure and temperature, the flight altitude and Mach and the considered species and chemical reactions are taken as close as possible to an actual configuration as the one seen in Kinefuchi et al. [2] work on the third stage of MV rocket.