Quantifying the scattering of sound in shear flow

Sound waves can become distorted when they propagate through shear flow, making it more difficult to reconstruct acoustic sources in aerospace engineering applications. For example, in open-jet wind tunnels, sound waves generated by wings, engines, or scaled full-aircraft models have to propagate through the shear layer of the jet to be measured by microphones outside the flow. Similarly, sound waves generated by turbofan jet engines also propagate through shear layers.

To better understand the interactions between sound waves and shear flows, Ma et al. developed and validated a 2D model based on modified linearized Euler equations, a numerical method that can more cleanly and reliably simulate sound scattering by shear flows. They used the model to study the spatial scattering of sound by a temporal mixing layer, an idealized type of shear flow.

“Unlike previous studies that often provided qualitative descriptions, we offer a quantitative characterization of how key parameters of the flow govern the scattered fields,” said author Ruixuan Ma.

The authors showed that as these key parameters changed, the sound scattering behavior transitioned from one distinct regime to another. They also found that the scattering behavior of the mixing layer is similar to that of a compact vortex due to the presence of large-scale vortical structures.

“Our work provides a foundational understanding of sound scattering mechanisms in shear flows,” Ma said. “This research can be applied to improve acoustic measurement accuracy in wind tunnels and to inform noise reduction strategies in aeronautical systems.”

Next, the authors plan to investigate 3D effects and extend the model to spatially developing mixing layers.

Source: “The spatial scattering of sound by a mixing layer: Case of short waves,” by Ruixuan Ma, Yimin Wang, Conghai Wu, Yong Luo, Hu Li, Shuaibin Han, and Zhouqin Fan, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0303749 .