Building CFD-Based Aerodynamic Databases for the Space Launch System

Overview

NASA's new Space Launch System (SLS) will be the first rocket since the Saturn V to carry astronauts beyond low-earth orbit, carrying 10% more payload than Saturn V and three times the payload of the space shuttle. The SLS configuration consists of a center core and two solid rocket boosters, which separate from the core as their fuel is exhausted two minutes from lift-off. During these first two minutes of flight, the vehicle powers its way through strong shock waves as it accelerates past the speed of sound. It then pushes its way beyond strong aerodynamic loads at the maximum dynamic pressure, and is enveloped by gaseous plumes from the booster-separation motors. The SLS program relies on computational fluid dynamic (CFD) simulations to provide much of the data needed to build ascent aerodynamic databases describing the structural load distribution, the surface pressures, and aerodynamic forces on the vehicle.

Project Details

The goal of this project is to quantify the aerodynamic forces during the ascent of the SLS vehicle through computational simulations, and provide data to build numerous aerodynamic databases. Previous launch systems relied almost entirely on data from wind tunnel testing for these databases. Fortunately, with the continued growth of computational resources and capabilities, it is feasible to use more CFD and rely less on expensive wind tunnel tests. Over the life of this project, NASA has continually analyzed several different SLS vehicle designs, including: multiple design iterations of the first flight vehicle, which will launch in the Exploration Mission-1 (EM-1); multiple designs of the second SLS vehicle, which will be the first to carry astronauts during the EM-2 mission; and the cargo version of the SLS rocket. The project utilizes multiple CFD tools to perform the analysis, including the NASA-developed flow solvers Cart3D, OVERFLOW, and FUN3D.

Results and Impact

The project has created several different aerodynamic databases for the SLS designs, including distributed line loads used in structural analysis; surface pressures used in venting and other dynamic analysis; protuberance aerodynamic loads used in the design of the vehicle; and forces and moments on the vehicle during booster separation used to verify the booster-separation system.

Recent highlights include a moving-body dynamic simulation of a nominal booster-separation event using the OVERFLOW solver. The simulation of the 22 different plumes that fire during the separation includes the 16 booster-separation motor plumes, plumes from the four core-stage main engines, and two plumes from the boosters.

Why HPC Matters

All of our CFD simulations of the SLS vehicles were run on the Pleiades supercomputer at the NASA Advanced Supercomputing (NAS) facility. In each of the past two years, the project has used over 20 million core hours on Pleiades. Depending on the configuration and flow conditions, each Cart3D simulation requires approximately 100 to 200 core hours, and the OVERFLOW runs require 10,000 to 30,000 core hours. A total of 12.7 million core hours were used to build the booster separation database, and over 2 million core hours were used to compute the single moving-body dynamic simulation of the booster-separation event. The project typically uses 50 to 100 terabytes of short-term disk storage at any given time.

More Media

See additional images/videos related to this demo in our media gallery.