A multiyear collaboration among Stanford engineering departments uses some of the world's fastest supercomputers to model the complexities of hypersonic flight. Someday, their work may lead to planes that fly at many times the speed of sound.
Aeronautical engineers believe hypersonic planes flying at seven to 15 times the speed of sound will someday change the face of air and space travel. That is, if they can master such flight's known unknowns.
Hypersonic flight is a particularly intense engineering challenge both in the mechanical forces placed on the structure of the plane and in the physics of the sophisticated engines that must operate in the extremes of the upper atmosphere where the planes would fly.
The Stanford Predictive Science Academic Alliance Program (PSAAP) is using computers to model the physical complexities of the hypersonic environment – specifically, how fuel and air flow through a hypersonic aircraft engine, known as a scramjet engine.
In particular, the program focuses on what is known as the scramjet's “unstart” problem, said Parviz Moin, the Franklin P. and Caroline M. Johnson Professor in the School of Engineering. "If you put too much fuel in the engine when you try to start it, you get a phenomenon called 'thermal choking,' where shock waves propagate back through the engine," he explained. "Essentially, the engine doesn't get enough oxygen and it dies. It's like trying to light a match in a hurricane."
Modeling the unstart phenomenon requires a clear understanding of the physics and then reproducing mathematically the immensely complex interactions that occur at hypersonic speeds. It is impossible to model the physical world exactly. As a result, PSAAP's principal goal is to try to quantify uncertainties – the known unknowns – so that scramjet engineers can build the appropriate tolerances into their designs to allow the engines to function in extraordinary environments.
One reason computational uncertainty quantification is a relatively new science is that, until recently, the necessary computer resources simply didn't exist. Thanks to its close relationship with the Department of Energy, the Stanford team enjoys access to the massive computer facilities at the Lawrence Livermore, Los Alamos, and Sandia national laboratories, where their largest and most complex simulations can be run.
