How a successful rocket test unveiled a new era in hypersonics

The month of March will go down in history as a milestone in hypersonic technology research.

Humans have always pushed for more. To be faster, more advanced, and better than they were yesterday.

Now, thanks to an incredible partnership between The University of Queensland, Texas A&M University, CUBRC and T he United States Air Force, a new era in hypersonic flight testing has begun.

On 21 March, the Boundary Layer Turbulence Flight Experiment (BoLT II) rocket was launched from the NASA Wallops Flight Facility in Virginia.

The flight experiment successfully flew the planned flight path and acquired tremendous scientific data to further Australia and America's understanding of boundary layer transition, turbulent heating, and drag at hypersonic speed.

The successful launch of the two-stage suborbital sounding rocket paved the way for new discoveries in this field, according to those who led the testing.

Long distance travel at hypersonic speed has previously been unsustainable. This is due to the massive heat changes that vehicles endure at this speed.

Hypersonic speed is widely defined as any speed beyond Mach 5, meaning five times faster than the speed of sound.

It is therefore incredibly costly to develop materials that can sustain this for extended periods.

Associate Professor Anand Veeraragavan leads UQ’s effort in this field, along with Emeritus Professor David Mee and Dr Rowan Gollan from the School of Mechanical and Mining Engineering.

Associate Professor Veeraragavan said developing new technology to handle hypersonic speed is a significant engineering challenge. One that needs to be understood if sustained flight is ever going to be realised.

“Imprecise knowledge of boundary layer transition – which is where the air around the surface of a hypersonic vehicle is either smooth or swirls in circles – hinders the development of hypersonic vehicles,” he said.

“Often overly conservative design approaches are taken, because the heat loading due to turbulence cannot be estimated precisely.”

When the US Air Force approached UQ to be part of their hypersonic flight testing, Associate Professor Veeraragavan said the University was in a unique position to help.

This is due to the advanced testing capabilities developed in the Centre for Hypersonics.

Since the partnership was formed with the US Air Force, multiple test flights have been undertaken.

"UQ was in a unique position to contribute to BoLT II as we’ve been able to undertake heated model tests in the T4 shock tunnel, full-scale testing in X3R and demonstrate novel heat transfer gauges designed at UQ in collaboration with Oxford University,” Associate Professor Veeraragavan said.

"Heating the BOLT II model to a temperature profile similar to what it would have experienced in-flight and testing it at UQ’s shock tunnel T4 is a unique contribution made by us that no other ground test facility is undertaking."

“The insights gained and progress made via these flights have advanced our understanding of hypersonic physics in a way that cannot be facilitated in isolation by only undertaking computational simulations and ground test experiments.”

“BoLT II is now a scientific benchmark for hypersonic heating and will build a stronger understanding of heat loading to reduce design uncertainties in future applications.”

Unique to BoLT II, this project provided the first-ever full-scale ground testing of the flight geometry.

The impact of the successful test means new and more advanced testing can now take place, said Dr Sarah Popkin, who oversaw the BoLT II project for the Air Force Office of Scientific Research.

Post-processing of the flight data will be directly compared to previous results recorded by the CUBRC LENS II shock tunnel.

This facility replicated the Mach and Reynolds number conditions expected for the BOLT II trajectory but at higher, conventional disturbance air conditions.

“The results from these two data sources provide a one-of-a-kind direct comparison between ground and flight experiment conditions with identical hardware," Dr Popkin said.

"A second, full-scale wind tunnel test campaign, is being carried out by The University of Queensland, which is also matching flight conditions and simulating vehicle surface heating observed during flight.
 
“Words cannot express how grateful and happy I am that we have reached this moment. Absolutely, we would not be where we are without our amazing team and I’m excited to see what the data will teach us about high-speed turbulence."

The Air Force Office of Scientific Research said that BoLT II exemplifies just how it and The University of Queensland continue to discover, shape and champion bold, high risk, high reward basic research.