A new simulation method developed by specialists in fluid dynamics is able to model flow dynamics around and through complex-geometry objects such as the complex aerodynamics around a moving car and its tires. The results can be seen in a video (see “Car and tire fluid dynamics simulation“) produced by Takashi Kuraishi, a research associate in the George R. Brown School of Engineering lab of Tayfun Tezduyar, the James F. Barbour Professor of Mechanical Engineering, and a student of alumnus Kenji Takizawa, a professor at Waseda and an adjunct professor at Rice.
“[Kuraishi] has been escalating the complexity of his calculations, starting with a stand-alone tire and now having the rest of the car,” says Tezduyar.
The video also demonstrates the efficacy of the NURBS Surface-to-Volume Guided Mesh Generation method, a technique developed by the Team for Advanced Flow Simulation and Modeling co-led by Tezduyar and Takizawa to model flow dynamics around and through complex-geometry objects. NURBS stands for Non-Uniform Rational Basis Splines, a mathematical technique to describe 3D shapes and provide computational analysis of fluid and structural mechanics problems involving such shapes.
The simulation shows what’s actually happening around a moving object, in this case the extraordinary activity around a common subject. Complicating the model is the fact that the tires are in contact with the road and deform as they roll.
“We’re dealing with near-actual car and tire geometries,” says Tezduyar.
“Knowing the airflow behavior around the car and its tires will lead to better understanding of their aerodynamic performance,” says Kuraishi, who earned undergraduate, master’s and Ph.D. degrees at Waseda and spent a year as a postdoctoral researcher there with Takizawa before coming to Houston. “Simulations this sophisticated are important to provide realistic solutions and reliable answers in design and performance evaluation.”
Tezduyar, whose lab has also modeled recovery parachutes for NASA’s Orion capsules, says NURBS use in computational analysis has grown dramatically in recent years, combining efficiency and accuracy by lowering the number of “mesh” points necessary to model a system. Think of the mesh as a net of fluid (like air) around an object, with the mesh points living in 3D “elements.” The points and elements move when the object moves.
In one model of a moving car, the computational flow analysis with NURBS was achieved with about 1.1 million points, a fraction of the number used in customary methods, while retaining its accuracy. That lowers the computational cost as well, say the researchers.
“We have a 3D mesh around the car and the tires, with more points near the tire surfaces for higher accuracy where it matters more,” says Tezduyar. “As the tire rotates, the points and elements rotate with it, but the problem is that as the tire rotates, the elements moving under the tire collapse – and this is what other methods cannot handle. Our method does, and it is key to getting an accurate simulation.”
The researchers say they are eager to collaborate with scientists and industry to model complex systems, including tires and vehicles.
“As time passes, naturally, new tire designs or improvements will be considered,” says Tezduyar. “It would be very beneficial for tire manufacturers to do this type of simulation before they invest in generating a prototype, because it would give them comprehensive and detailed numerical data about the aerodynamics around the tire that would be difficult to get in any other way.”