Through the application of thermal imprint manufacturing technology, the work aims to systematically investigate the impact of the coupling effect between micro-groove morphological deviations and flow velocity on drag-reduction mechanisms. The software ANSYS was employed to construct a computational model of micro-grooves with different straightness and symmetry deviations, focusing on the drag-reduction behavior under three flow velocity conditions of 102, 136, and 170 m/s (corresponding to Reynolds numbers Re=1.04×104, 1.38×104 and 1.73×104). Furthermore, by comparing key parameters such as drag reduction, pressure field, velocity field, turbulence characteristics, vortex structure, and wall shear stress under two types of morphological deviation conditions, the relationship between error types and flow field responses was revealed. The results of the study showed that: (1) The effect of morphology error on drag-reduction performance increased significantly with the increasing flow velocity. The variation rates of drag reduction for straightness deviation were -0.004 4%/μm, -0.005 5%/μm and -0.006 3 %/μm at flow rates range of 102-170 m/s, whereas the variation rates of drag reduction for symmetry deviation for the same Mach number operating conditions were -0.001 0%/μm, -0.001 8%/μm and -0.002 5%/μm. From the above, this showed that straightness deviation was more sensitive to drag-reduction performance under high flow velocity conditions. (2) With the increase of the flow rate, the morphological accuracy of the micro-grooves showed a significant increase in nonlinearity. To maintain the drag-reduction effect of the micro-grooves, at flow velocities of 102, 136, and 170 m/s, the allowable error in straightness was strictly controlled to within ±16, ±10 and ±2 μm respectively, while the allowable error in symmetry was controlled within ±70, ±20, and ±10 μm respectively. (3) There was a significant difference in the effect mechanism of the two morphological deviations on the drag-reduction characteristics: the straightness deviation increased both differential pressure resistance and friction resistance in the groove, and significantly intensified the velocity gradient, inducing localized reflux and flow vortices, whereas the symmetry deviation mainly destroyed the symmetry of the flow, leading to localized turbulence enhancement and flow instability. Therefore, when the hot embossing technology is used to fabricate the micro-groove drag-reduction structure, it is necessary to meet the strict precision requirements of array straightness error ≤±2 μm and symmetry error ≤±10 μm. Only then can the drag-reduction effect be maintained within the Reynolds number range of Re=1.04×104-1.73×104. Exceeding these precision thresholds may cause micro-grooves to degrade in functionality or even induce drag-increasing effects due to flow instability. This study reveals the quantitative relationship between morphological accuracy and drag-reduction performance, and proposes corresponding process optimization schemes, providing theoretical support for precision control in micro-groove manufacturing. In the future, the accuracy and consistency of morphology control can be further improved through technical measures such as optimizing mould processing and improving hot stamping process parameters. Looking ahead, advances in micro-nano manufacturing technologies (such as ultra-precision machining and nanoimprinting) are expected to break through existing precision limitations, thereby expanding the applicability of micro-groove drag-reduction technology across a wider range of Reynolds numbers. At the same time, it can also promote the large-scale application of this technology in fields such as aerospace, providing innovative solutions for energy conservation and emission reduction.
Key words
thermal embossing technology /
spreading micro-groove /
drag-reduction performance /
straightness deviation /
asymmetry deviation /
flow field characteristics /
allowable error
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Funding
Organised Research at North China University of Technology (110051360024XN148-38)
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