CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

SIMULATIONS OF AIRCRAFT WAKES AND ROCKET LAUNCH EMISSIONS
– Wroblewski, D. E., Coté, O. R., Hacker, J. M., and Dobosy, R. J. Velocity and Temperature
Structure Functions in the Upper Troposphere and Lower Stratosphere from High-Resolution Aircraft
Measurements J. Atmos. Sci., 67, 1157-1170, 2010.
2.3 Impact of rocket launches on atmospheric O 3 (D. Cariolle, A.
Poubeau, R. Paoli, O. Thouron)
2.3.1 Simulation of a rocket jet (A. Poubeau, R. Paoli)
The first objective of this study is to obtain large-eddy simulations using the AVBP code of the jet generated
by a rocket booster. The results of these simulations (at various altitudes) will then be used as an input to
the Meso-NH code to determine the influence of rocket emissions on the atmosphere at large scale.
Some two-dimensional simulations were run in order to set up all the parameters (boundary conditions,
artificial viscosities...) and have a first idea of the structure that should be observed at the exit of the nozzle.
The computational domain is composed of the nozzle, whose exit was connected to a box representing the
atmosphere. A tentative approach was to inject high pressure air at the entrance of the nozzle at a high
pressure. This configuration rapidly showed its limits, as a shock was formed right at the entrance of the
nozzle due to the high pressure imposed as a boundary condition. A solution to this problem was to add a
large tank that would discharge gas through the nozzle to the atmosphere. The following step was to run a
simulation that would correspond to the case of the rocket flying at an altitude of 20 km (where the ozone
concentration is maximum). The fact that the nozzle verifies the one-dimensional isentropic relations made
it possible to set the boundary conditions using the available data. The result presents all the characteristics
of an under-expanded jet. However, the turbulence in the mixing layer could not be observed in this 2D
configuration.
Following these results, some three-dimensional simulations were performed using the same parameters
(figure 2.4, left). To be closer to the actual case, the air injected in the nozzle was replaced by a gas
thermodynamically equivalent to the real gas (with the same C p , γ and R). Again, the results show a highly
supersonic, under-expanded jet, as it can be seen on figure 2.4 (right).
The next objective is to validate these simulations by the study of the spreading and the centerline property
decay rates of jets for which experimental data exist in the literature. Then the chemistry will be added to
represent fully the exhaust plume.
FIG. 2.4: Computational domain (left) and Mach number in a longitudinal cut (right)
184 Jan. 2010 – Dec. 2011