Researchers seek to tackle challenges of hypersonic flight

The Stanford Predictive Science Academic Alliance Program (PSAAP) is using supercomputers 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. "The project focuses on what is known as the scramjet's 'unstart' problem," explained Parviz Moin, a professor at the university's 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. Essentially, the engine doesn't get enough oxygen and it dies. It's like trying to light a match in a hurricane." PSAAP's principal goal is to try and quantify the uncertainties associated with how the engines behave in the air, so that appropriate tolerances can be built into their designs. To do this, the university's departments of mechanical engineering, aeronautics and astronautics, computer science and mathematics have been pulled together. "Mechanical engineers and those of us in aeronautics and astronautics understand the flow and combustion physics of scramjet engines and the predictive tools. We need the computer scientists to help us figure out how to run these tests on these large computers," said Professor Moin. "That need will only increase over the next decade as supercomputers move toward the exascale – computers with a million or more processors able to execute a quintillion calculations in a single second." Thinking ahead to that day, the PSAAP team has created LISZT, an entirely new computer language for running complex simulations on massive processor sets. LISZT is said to be capable of directly expressing problems in engineering and science through code designed specifically for exascale architectures, making it equally accessible to experts working in fluid physics, combustion, turbulence and other mathematically intense applications, while still remaining computationally efficient. Beyond progress in the treatment of epistemic uncertainty in computer modelling and the creation of LISZT, the researchers have also made key advances in the specific disciplines that underpin scramjet engineering: combustion, turbulence and fluid flow in general. "We've had strong validation of our computational work against experiments," concluded Moin. "In particular, we've developed a number of new techniques to validate how we build physical models into our computer code. Collectively, these insights will enable the design of safer, more reliable hypersonic engines. These same technologies can also be used to quantify flow of air around wind farms, for example, or for complex global climate models."