Drag Reduction Characteristics of Microstructure Inspired by the Cross Section of Barchan Dunes under High Speed Flow Condition

Abstract

A new type of microstructure inspired by the cross section of barchan dunes was proposed to reduce windage, which was considered as a passive drag reduction technology in aerospace manufacturing field. Computational fluid dynamics method was carried out to discuss the effect of the microstructure on the skin friction reduction under high velocity flow condition. Different microstructure heights were employed to survey the reduction of drag. The results illustrated that the appearance of microstructure led to a generation of pressure drag in nonsmooth model (with microstructures inspired by cross section of barchan dune) in contrast to smooth model. However, the microstructure significantly increased the thickness of the low-speed fluid by 11.4% in the near-wall flow field, causing the low-speed fluid to rise and decreasing the velocity gradient near the wall, thereby reducing viscous resistance. In addition, high-speed fluid flowed above the microstructure units instead of along the inner side of the units due to the influence of micro-vortex, resulting in a reduction of friction near the surface. Furthermore, micro-vortex was considered to be the significant internal factor to achieve turbulent drag reduction since it could not only reduce the viscous resistance by promoting the fluid flow above the microstructure but also provide a reverse thrust force. The understanding of the mechanism of drag reduction provides theoretical guidance for further fabrication of drag reduction coatings using renewable materials.

Rational Analysis of Drag Reduction Variation Induced by Surface Microstructures Inspired by the Middle Section of Barchan Dunes at High Flow Velocity

“…More governing equations could be referred to previous studies [29,31]. Furthermore, the reliability of the calculation model is also verified in the previous work [27]. In addition, the large eddy simulation (LES) method is adopted for simulation in order to acquire the subtle flow characteristics and variation in the flow field.…”

“…Otherwise, simulation results demonstrate the same tendency with theoretical values. The maximum relative error The previous solver parameters and grid construction methods were followed in this work [27]. Moreover, the independence of the computational grid was also verified to ensure the accuracy of the calculation, as shown in Figure S3.…”

“…In contrast, the pressure far field boundary was adopted to inlet and outlet under compressible flow conditions. The previous solver parameters and grid construction methods were followed in this work [27]. Moreover, the independence of the computational grid was also verified to ensure the accuracy of the calculation, as shown in Figure S3.…”

“…The microstructural unit of the barchan dune was inspired by the regularly arranged natural barchan dune, which consisted of unique windward and slip surfaces, indicating a strong ability to maintain shapes [21][22][23][24][25][26]. In this work, a symmetrical geometric shape was extracted from the cross-section of barchan dune in order to construct the microstructure unit, as proposed in our previous work and shown in Figure S1 [27].…”

“…The computational domain used in this work is the same as that used in the previous work [27]. Considering the aeronautical applications, the flow velocity (U ∞ ) was broadly defined as 69.4, 83.3, 97.2, 111.1, 138.9, and 250 m/s, respectively.…”