Heated strips can be used to mitigate turbulent flow

Reducing drag is one of the most effective ways to reduce turbulent flow. In what’s known as the targeted control method, specific drag structures are altered with the goal of impacting the overall turbulence. Hickey et al. explored the effectiveness of using heated strips to mitigate drag in fluid flow in a series of numerical simulations.

Heating a gas increases its viscosity, which would normally lead to an increase in drag. However, the group found that localized heating does not appear to impact the bulk flow. Instead, they discovered that carefully tuning the localized heating process can modify near-wall turbulent structures and locally overcome the expected disadvantages of increased drag. Its effects are modest, but optimally aligning heating strips within a flow can reduce local turbulence by up to 6% without impacting the bulk motion.

“The novelty of the work is using something that we know is detrimental, but getting a benefit out of it nonetheless,” said author Jean-Pierre Hickey. “It’s not a strategy that would typically be used.”

To observe this, the researchers conducted simulations of a turbulent channel flow and monitored the effects of heating strips of various sizes and at different temperature ratios.

Even though other mitigating approaches can reduce drag by larger amounts, Hickey noted this method has the unique ability to recycle energy waste in a process. “The thing about heating is you have excess heat or heat that’s not used that you need to evacuate in various engineering systems, so heating can be seen as energy-neutral,” he said.

In their future studies, the researchers plan to include other parameters such as the total number of strips and their spacing.

Source: “Targeted turbulent structure control in wall-bounded flows via localized heating,” by Jean-Pierre Hickey, Khaled Younes, Matthew X. Yao, Duosi Fan, and Joseph Mouallem, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/1.5144387 .