Computer Simulation Enabling Next Generation Of Airplanes, Spaceplanes

By James Schultz

Methodically testing and evaluating miniature airplane components in a wooden contraption the size of a large packing crate, the Wright brothers gathered invaluable information on aerodynamic shapes and performance that made their historic December 1903 flight possible. A little more than two decades later, aeronautical researchers were building much larger and far more sophisticated successors to the Wrights’ relatively primitive wind tunnel.

But just like the Wrights, engineers needed wind tunnels to certify that aircraft parts would hold up to the rigors of flight. The movement of air over components would verify whether airplanes could endure extremes of wind, temperature, pressure, buffeting from heavy weather and the routine structural abuse of takeoffs and landings. So it was that newly designed aircraft segments would literally be cut, sculpted and then tested: first wood, then metals and, most recently, advanced Space Age materials lighter than aluminum and stronger than steel.

Wind tunnel testing continues to this day. Yet what the Wrights didn’t have access to, an entirely new generation of aeronautical engineers does. Computers are allowing designers to evaluate blueprints before the first aerospace component takes physical form. Given the increasingly stringent requirements for air and space travel — superlightweight but durable materials that must withstand high speeds and even higher temperatures, all the while propelled by fuel-efficient, sound-dampening engines — computer-based modeling has become an essential conceptual tool. Even before the first piece of spar or wing is fashioned, the techniques of computational fluid dynamics, CFD, are revolutionizing the ways in which aircraft are conceived and evaluated.

“Using computers is the safest, fastest, cheapest way to optimize design,” says Oktay Baysal, associate dean of the Old Dominion College of Engineering and Technology and a professor and eminent scholar of aerospace and mechanical engineering. “Your ‘tools’ are the computer codes, the software. You can evaluate components without first building and testing them before finding the right one.”

Computers’ Essential Role

Before designing aircraft components, engineers must take into account the physical principles that govern the complex, turbulent flows of air over surfaces and the way air movement creates friction, causing drag or heating at leading surfaces and pressure points. Computers are “taught” these physical laws through elaborate mathematical models which, in turn, are translated into computer programs. “Advances in numerical algorithms and computer technology in the past two decades allowed us to essentially ‘stuff’ the wind tunnel into the computers,” says Baysal. The resultant CFD techniques thus enable designers to quickly and more accurately represent physical reality. Designs can then be modified to identify and compensate for natural points of aerodynamic weakness, reshaping structures to bolster performance.

“Humans remain in the loop. But we are trying to automate the design process as much as possible,” Baysal says. “A computer isn’t smart like a human, but it can handle many, many variables and calculate interactions. A computer can track millions, even billions of parameters that humans cannot.”

Baysal has participated in a number of projects in which computer modeling has figured prominently. Within the last several years, he has worked as a principle investigator in efforts to mathematically represent and improve proposed weapons-bay designs for military fighters. Baysal has also devised aerodynamic enhancements to proposed next-generation supersonic and hypersonic commercial airliners, including engine nozzle and engines-integration studies, and developed computational methods to reduce noise and vibration from the deployment of commercial aircraft landing gear. Baysal says that one of his most intriguing projects was to ascertain the most efficient means of separating missiles from warcraft flying at speeds faster than sound.

“The question is, when you’re flying at that speed, how do you safely separate the rocket from the aircraft while maintaining the rocket’s correct [spatial] attitude?” Baysal posits. “You can’t simulate that process with just a cut-and-try approach.”
Not all of the work has been high in the sky. One recent project involved verifying the sound-abating qualities of barricades for a light rail system from New York City to John F. Kennedy International Airport. The barriers were required to absorb and diffuse the noise generated by the trains’ wheels. Baysal’s detailed vibrational and acoustic analyses verified that the design would perform as advertised.

All of the aforementioned accomplishments have been made possible by the growing sophistication of computers. Without the continual increase in computing capability, CFD progress would come to an abrupt and unwelcome halt.

“When I was a student in the late 1970s, I was literally using punch cards. A box held 2,000 lines of software code, and I’d carry around four to five boxes to write 8,000-line programs,” Baysal recalls. “Wrinkle one of those cards and you’d have to start all over again. Running one job took up to four weeks. Now we’re able to conduct a trillion or more calculations per second. I can finish a single study in 30 minutes.”

Down-To-Earth Application

Especially when considering ultra-high-performance aircraft, computer modeling is no longer an option but a necessity. In particular, computational fluid dynamics is being employed for the aerospace industry’s most challenging projects, such as a series of planned experimental vehicles that NASA is planning to deploy.

One such program is known as Hyper-X, a multi-year experimental ground and flight test program. The project seeks to demonstrate “air-breathing” engine technologies that promise to increase payload capacity or reduce vehicle size for the same payload for aircraft and/or reusable space launch vehicles. The craft will travel through the atmosphere at up to 10 times the speed of sound, or approximately 6,600 mph at an altitude of 100,000 feet. Payload capacity will be increased by discarding the heavy oxygen tanks that rockets must carry and by using the oxygen in the atmosphere as a key propellent.

Such speeds generate enormous aerodynamic stresses and require advanced heat-dissipating techniques to insure that fast-traveling craft won’t incinerate from friction. Unique power plants, such as supersonic-combustion, rapid-air movement engines, or scramjets, are also required. Baysal, who has just concluded a Hyper-X-related CFD research project, says that computer modeling of such complex equipment is especially helpful prior to high-speed wind tunnel studies and test flights.

CFD is also being applied to ground vehicles, which encounter many of the same aerodynamic obstacles as do aircraft. Mathematical modeling is enabling designers to suggest different kinds of structural materials, saving on weight and manufacturing costs. New kinds of hybrid engines — including electric/gasoline and those running on compressed gas or hydrogen fuel cells — can also be evaluated. In addition, through modeling, engineers are making trucks, cars and trains more streamlined, cutting air resistance and thus saving substantially on fuel costs.

“What NASA has been saying all along is true: What is developed for aerospace can be applied to down-to-earth things like cars, trucks and trains,” Baysal says. “These aren’t dream machines. They’re real projects, with outcomes that will benefit consumers directly.”