Predicting Orion Launch Abort Acoustics

Speaker: François Cadieux, Computational Aerosciences Branch, NASA Ames Research Center
March 17, 2022

Presentation

Abstract

The Launch, Ascent & Vehicle aerodynamics (LAVA) team has been collaborating with the Orion Loads and Dynamics team at the Johnson Space Center (JSC) to assess the Orion launch abort system's (LAS) vibro-acoustic environment. The Orion LAS is an integral part of ensuring astronaut safety during the upcoming Artemis missions. It can pull the crew module away from the rocket in a split-second if an emergency arises during launch by firing its solid rocket motor. This abort motor produces four hot, turbulent, high-speed exhaust plumes that flow along the sides of Orion and can cause strong vibrations in the LAS structure. A campaign of computational fluid dynamics (CFD) scale-resolving simulations is undertaken to analyze and predict the strength and spatial distribution of vibrations for a wide range of abort scenarios to ensure that the system doesn’t shake itself apart in flight. The primary objectives are to establish best practices and to validate CFD predictions for surface fluctuating pressure across a wide range of frequencies with ground, wind tunnel, and flight test data. Secondary objectives are to predict acoustics for scenarios either too costly, too dangerous, or not planned to be tested, to elucidate trends, to reduce uncertainty and thus tighten safety margins for the vehicle design. Satisfactory agreement is obtained between CFD and ground, wind tunnel, and pad abort tests using the Cartesian adaptive mesh refinement (AMR) module of the LAVA solver. Simulation results for a supersonic ascent abort flight test are in reasonable agreement with the measurements but show larger excursions in regions where plume-shock interactions occur – likely due to CFD modeling assumptions. Overall, the database of CFD predictions provides valuable trending information to better understand the effects of altitude, Mach number, and vehicle acceleration on surface pressure spectra, as well as how to scale acoustics from wind tunnel to flight.

Funded by NASA's Orion Program

Biography

François Cadieux is a research aerospace engineer in fluid mechanics working in the Computational Aerosciences Branch of the NASA Advanced Supercomputing Division at NASA's Ames Research Center. He received the NASA Early Career Public Achievement Medal in 2018 for enhancing the safety and success of the Orion Launch Abort System through high-fidelity computational aero-acoustic predictions of the QM-1 test and launch abort scenarios. Cadieux joined the Launch, Ascent, and Vehicle Aerodynamics (LAVA) team in September 2016. He completed a postdoctoral fellowship at the Flow Physics and Computation Lab under the supervision of Prof. Rajat Mittal at Johns Hopkins University from 2015 to 2016. His research focused on developing and validating wall-modeled large-eddy simulation (LES) for separated flows. Cadieux also investigated the dynamics of active flow control to mitigate flow separation and delay stall. During his graduate work with Prof. Julian A. Domaradzki, Cadieux probed the limits of under-resolved LES for separated flows applicable to small unmanned aerial vehicles and low-pressure turbines and quantified the importance of numerical dissipation effects when performing LES on coarse grids. He obtained his Ph.D. in aerospace engineering from the University of Southern California in 2015.