When could a computer simulation substitute for a wind tunnel or flight test?
It is the hot topic today in research and development circles. And there are many spirited opinions on the subject matter. If you speak with a flight test engineer, they might say never. The wind tunnel engineers could possibly agree. If you ask the same question of a modeling and simulation engineer, they could have a different answer for you.
To learn more, we went to Dr. David O’Brien, subject matter expert for aerodynamics in the Systems Readiness Directorate – Aeromechanics Division at the U.S. Army Combat Capabilities Development Command Aviation & Missile Center.
O’Brien has a unique perspective, coming up in the modeling and simulation world and getting his bona fides through the Vertical Lift Research Center of Excellence while matriculating at Georgia Institute of Technology. But at the DEVCOM Aviation & Missile Center his role is in airworthiness, as SRD is the delegated authority for the Army to measure its aircrafts’ suitability for safe flight. Which he said provided him a different perspective on the matter.
“In my field, we always want more information than we ever can truly get,” O’Brien said. “At the end of the day there's a cost and schedule associated with testing, so anywhere you can save a program cost and schedule there's an advantage to doing a virtual test. However, we need to complement it with enough physical testing to trust the models to make sure that they're giving us what we expect.”
One such information gathering simulation is DEVCOM AvMC’s revolutionary HELIOS, which models the coupled aerodynamic and structural dynamics response of a vehicle using computational fluid dynamics codes for aerodynamics, computational structural dynamics to model structural bending, and vehicle trim software with multi-body dynamics to set the controls to achieve vehicle trim. Not just a tool for the Army, in 2022, DEVCOM AvMC researchers applied its software to model the impact of recirculation on Navy aircraft performance for various static and dynamic flight conditions.
HELIOS and programs like it can influence early in the design process, reducing costly, time-consuming changes later in development. But even if modeling and simulation provides reliable data, researchers are still extrapolating unknown data and one key challenge will be convincing the stakeholders in the program that data is actionable. That is where verification, validation and accreditation comes into play. To build trust, computer simulations need to go through a rigorous VV&A process.
“In verification we're asking, ‘Did we build it right?’ And we can check that out. But then in validation, we are asking, ‘Did I build the right thing?’” O’Brien said.
Much has been said about the Army of 2030 and 2040 lately, and while that seems a long way off, the science for those transformations is happening now. Expanding the modeling and simulation infrastructure will benefit an aircraft in its design process, helping engineers test different ideas and theories. But replacing wind tunnel and/or flight testing?
“There's a big push to field faster,” O’Brien said. “But at the same time, we want to do it right. And we want to do it safely.”
The DEVCOM Aviation & Missile Center, headquartered at Redstone Arsenal, Alabama, is the Army’s research and development focal point for advanced technology in aviation and missile systems. It is part of the U.S. Army Combat Capabilities Development Command (DEVCOM), a major subordinate command of the U.S. Army Futures Command. AvMC is responsible for delivering collaborative and innovative aviation and missile capabilities for responsive and cost-effective research, development and life cycle engineering solutions, as required by the Army’s strategic priorities and support to its Cross-Functional Teams.