Powered Stage Separation Aerodynamics of the Ares I Launch Vehicle

Overview

Computational fluid dynamics (CFD) experts at the NASA Advanced Supercomputing (NAS) facility at Ames Research Center have performed high-fidelity, time-accurate simulations of the Ares I Crew Launch Vehicle (CLV) stage separation process. The analyses were performed using the viscous, Navier-Stokes CFD code OVERFLOW and high-resolution computational meshes to resolve the complex, transient flow details needed for the design of the Ares I stage separation system. These simulations are the only means of characterizing the complex and highly nonlinear aerodynamics of the stage separation process.

Project Details

A database of steady-state stage separation simulations was initially developed, covering a wide range of vehicle flight angles, relative separation positions and angles between stages, off-nominal trajectories and thrust levels, and failures of isolated separation or ullage motors.

However, the stage separation occurs quite quickly and it is not apparent that steady-state methods are appropriate for these kinds of flows. For example, the flowfield in the interstage region can take longer to reach equilibrium than the time it takes for the two stages to separate. For this reason, a preliminary three-dimensional, six-degree-of-freedom (6DOF) analysis of the stage separation process was performed. This involved time-accurate simulation of the separating stages under the influence of time-varying thrusts from the separation motors and ullage settling motors.

Results and Impact

The results obtained from the steady-state aerodynamic database and the 6DOF analysis provided key insights into the complexities of the stage separation phase of flight. High-fidelity simulations are critical to developing effective, reliable stage separation systems because wind tunnel methods are unable to duplicate the flight conditions and full motor thrust levels needed to accurately characterize the stage separation flowfield. In addition to supporting the Ares CLV, the knowledge gained from this work will continue to aid in the development of stage separation systems for NASA's future launch vehicles.

Role of High-End Computing Resources

The NAS facility provided efficient supercomputing resources to complete these computationally demanding analyses in a timely fashion. Each database simulation required a thousand processors running for several weeks to complete. Over 200 simulation cases were completed to fulfill the database requirements, utilizing a tremendous amount of storage in addition to computational time.