Drag Reduction Ratio Research Articles

Enhanced drag reduction of superhydrophobic coatings with femtosecond laser processing and TEOS/KH-SiO2/SA hybridization: CFD simulation and particle image velocimetry

Superhydrophobic surfaces have gained significant attention due to their potential applications in reducing frictional drag in various fluid flow systems. These surfaces mimic the lotus leaf's natural water-repellent properties, resulting in minimal contact between water droplets and the surface. The F-L@TEOS/KH-SiO2/SA coatings are developed using a combination of femtosecond laser ablation and chemical modification with tetraethyl orthosilicate (TEOS), KH550-modified SiO2 (KH-SiO2), and stearic acid (SA). The micro-nano structures formed on the surface enhanced its hydrophobicity, with a contact angle (CA) of 165.94°and sliding angle (SA) of 2.35°. The drag reduction performance is evaluated through experimental methods, including particle image velocimetry and gravity-driven motion analysis, as well as numerical simulations using computational fluid dynamics (CFD). Results showed that the superhydrophobic surface significantly reduced drag compared to untreated aluminum, with an average drag reduction ratio of 10.4 % in experiments and a calculated reduction rate of 9.86 % in simulations. The presence of micro-nano structures promoted the formation of an air layer at the solid-liquid interface, decreasing friction and enhancing slip flow. Additionally, the biomimetic surface generated turbulence at specific distances, aiding in energy dissipation and further reducing resistance. These findings demonstrate the potential of superhydrophobic coatings for applications requiring reduced fluid resistance, such as in marine vessels, pipelines, and fluid transport systems.

Numerical Study of the Influence of the Type of Gas on Drag Reduction by Microbubble Injection

In this work, a novel numerical method for studying the influence of gas types on drag reduction by microbubble injection is presented. Aimed at the microbubble drag reduction (MBDR) process for different types of gases, the mass transfer velocity of different types of gases in the gas–liquid phase is defined by writing a user-defined function (UDF), which reflected the influence of gas solubility on the drag reduction rate. An Eulerian multiphase flow model and the Realizable k−ε turbulence model are used for numerical calculation. The population balance model is used to describe the coalescence and breakup phenomena of the microbubble groups. Henry’s theorem is used to calculate the equilibrium concentration of the microbubble mixed flow. The interphase mass transfer rate of the microbubble injection process for different types of gases is studied by using permeation theory. The local mass fraction of the mixed flow is solved by the component transport equation. It is found that the larger the solubility of the gas, the lower the efficiency of MBDR. When the volume flow rate of the same type of gas is the same but the injection speed is different, the larger the solubility of the gas is, the greater the difference in the drag reduction ratio.

Study on Aerodynamic Drag Reduction by Plasma Jets for 600 km/h Vacuum Tube Train Sets

In order to break through the speed bottleneck, researchers envision using tubes to cover high-speed maglev trains and extract some of the air inside the tubes, creating a low-density environment on the ground, greatly reducing the aerodynamic drag of the trains, and in a relatively economical and feasible way, making high subsonic (600 km/h and above) and even supersonic ground transportation possible. The faster the running speed of high-speed trains, the greater the impact of aerodynamic drag on their energy consumption. Studying the aerodynamic characteristics of trains with a speed of 600 km/h can help optimize the aerodynamic shape of the train, reduce aerodynamic drag, and reduce energy consumption. This has positive implications for improving train energy efficiency, reducing energy consumption, and environmental impact. This paper adopts the numerical simulation method to study the drag reduction effect of the plasma arrangement and different excitation speeds on the train set in four positions when the incoming wind speed is 600 km/h, to analyze the mechanism of drag reduction, and then to analyze the combination of working conditions in order to investigate the drag reduction effect of plasma on the vacuum tube train set with an ambient pressure of 10,000 Pa. The findings demonstrate that the plasma induces the directional flow of the gas close to the wall to move the flow separation point backward and delay the separation of the flow, thereby reducing the front and rear differential pressure drag of the train set and lowering the aerodynamic drag coefficient of the entire train. The plasma arrangement is located at the rear of the flow separation point and in close proximity to the flow separation point. The pneumatic drag reduction effect peaks when the excitation speed reaches 0.2 times the train speed and the pneumatic drag reduction ratio is around 0.88%; the pneumatic drag reduction ratio of the rear car peaks when the excitation speed reaches 0.25 times the train speed and the pneumatic drag reduction ratio is 1.62%. The SDBD (Surface Dielectric Barrier Discharge) device is installed at the flow separation point around the nose tip of the rear car.

Vertical diffusion of bubbles injected beneath a flat-bottomed ship for frictional drag reduction

There has been concern about the short effective distance of frictional drag reduction achieved by air lubrication, but recent model ship experiments have shown over 30 m longer than our expectation. Also, the reduction ratio can be improved through the artificial generation of void waves appearing beneath the hull. These topics relate to the spatiotemporal bubble distribution and an understanding of them requires clarification of the distribution. In this study, optical probes were used to measure the distributions of bubble states beneath a 20-m long flat-bottomed ship towed with 6–8 m/s. The measurements explained the long effective distance of drag reduction and the process of void wave generation and development. The drag reduction ratio was about 7–25% and mainly depended on the void fraction within 10 mm of the hull. The vertical distribution of the void fraction remained unchanged over long downstream distances. The development of void waves was affected by the streamwise velocity difference between bubble clusters near the hull. The velocity was determined by the number density of the bubbles, decreasing to the half of ship speed until reaching a certain number density, 100 per meter in our experiments, and then becoming constant at higher density.

Mesoscopic analysis of drag reduction performance of bionic furrow opener based on the discrete element method.

In order to study the dynamic interface mechanical behavior between soil and agricultural machinery and reveal the causes of tillage resistance, three kinds of bionic furrow opener were designed according to the characteristics of earthworm head surface curve, using the discrete element method to simulate and analyze the process of the furrow openers. The results showed that the order of ditching resistance from large to small is traditional opener, bionic corrugated opener, bionic ridgeline opener, bionic composite opener. With the same ditching speed, the drag reduction effect of the three bionic openers increases with the increase of the ditching depth. During the process of increasing the depth from 30 mm to 60 mm and 90 mm, the ditching resistance of the traditional opener increased from 11.56 N to 28.32 N and 48.61 N as well as the maximum drag reduction ratio increased from 5.58% to 7.20% and 8.93% for the bionic composite opener. With the same ditching depth, the bionic composite opener reached the highest drag reduction rate of all bionic openers when the speed is 100 mm/s, the value is 9.08%. The width of the ditch of the three bionic openers is smaller than that of the traditional opener. Bionic corrugated opener can improve the ditch height and reduce the ditch width,the corrugated structure creates a gap between the surface of the core and the particles, reducing the number of contact and contact area of the particles. The number of contact particles of the three bionic openers is smaller than that of the traditional opener. The bionic composite opener has the smallest force field and the soil disturbance caused by the core share surface is small, the soil is evenly distributed along the core surface. The discrete element simulation shows that the bionic opener can effectively reduce the ditching resistance and improve the quality of ditching, which provides a theoretical basis for subsequent research and optimization.

Influence of fluorine incorporation into waterborne acrylic coatings on resulting hydrophobic, thermal stability and drag- reduction properties

Fluorinated polyacrylate copolymers containing various amounts of 1H,1H,2H,2H-perfluorooctyl methacrylate (FA) were synthesized via a miniemulsion polymerization process. The characteristics of latex particles and films were investigated using transmission electron microscopy, dynamic light scattering, attenuated total reflectance Fourier transform infrared spectroscopy, 1H and 19F nuclear magnetic resonance spectroscopy, atomic force microscopy, energy dispersive spectroscopy, water contact angle measurements, and thermogravimetric analysis. The results showed that particle size increased almost linearly with FA content, and the surface hydrophobicity of the films increased with FA content up to 14.6 wt% and then plateaued. As the FA content increased, the surface roughness of the films initially increased and then decreased. The thermal stability of fluorinated polyacrylate was significantly enhanced when a high amount of FA was incorporated into the polymer chains. The fluorinated acrylic copolymer coating also exhibited a significant drag reduction effect, with the maximum drag reduction ratio reaching 12% at a water flow velocity of 0.8 m/s.

Drag reduction using bionic groove surface for underwater vehicles.

Introduction: The reduction of drag is a crucial concern within the shipping industry as it directly influences energy consumption. This study addresses this issue by proposing a novel approach inspired by the unique ridge structure found on killer whale skin. The objective is to develop a non-smooth surface drag reduction method that can effectively decrease drag and improve energy efficiency for ships. Methods: The study introduces a technique involving the creation of transverse bionic groove surfaces modeled after the killer whale skin's ridge structure. These grooves are aligned perpendicular to the flow direction and are intended to modify the behavior of turbulent boundary layer flows that form around the ship's hull. Numerical simulations are employed using the Shear Stress Transport k-ω model to analyze the effects of the proposed groove surface across a wide range of flow conditions. The research investigates the impact of various parameters, such as the width-to-depth ratio (λ/A), groove depth, and inlet velocity, on the drag reduction performance of the bionic groove surface. Results: The study reveals several key findings. Optimal shape parameters for the bionic groove surface are determined, enabling the most effective drag reduction. The numerical simulations demonstrate that the proposed groove surface yields notable drag reduction benefits within the velocity range of 2∼12m/s. Specifically, the friction drag reduction ratio is measured at 26.91%, and the total drag reduction ratio at 9.63%. These reductions signify a substantial decrease in the forces opposing the ship's movement through water, leading to enhanced energy efficiency. Discussion: Comparative analysis is conducted between the performance of the bionic groove surface and that of a smooth surface. This investigation involves the examination of velocity gradient, streamwise mean velocity, and turbulent intensity. The results indicate that the bionic groove structure effectively mitigates viscous stress and Reynolds stress, which in turn reduces friction drag. This reduction in drag is attributed to the alteration in flow behavior induced by the non-smooth surface. Conclusion: The study proposes a novel approach for drag reduction in the shipping industry by emulating the ridge structure of killer whale skin. The transverse bionic groove surface, aligned perpendicular to flow direction, demonstrates promising drag reduction outcomes across diverse flow conditions. Through systematic numerical simulations and analysis of key parameters, the research provides insights into the drag reduction mechanism and identifies optimal design parameters for the groove surface. The potential for significant energy savings and improved fuel efficiency in maritime transportation underscores the practical significance of this research.

Effect of multi-channel shape design on dynamic behavior of liquid water in PEMFC

A well-designed flow channel is crucial for effective water management in proton exchange membrane fuel cell. This study presents novel simulation investigation of the dynamic behavior of liquid water in three-dimensional multi-channels with various shape designs, including straight channel (SC), blocked channel (BC), wave channel (WC), and tapered channel (TC). The first, second, and third single channels are arranged in order from gas inlet in multi-channel. The results indicate that drainage rate of first channel in multi-channel is slower than that of second and third channel. Among the four designs, BC and TC reduced water ejection time by 7 ms and 6.5 ms respectively compared to SC, and reduced the time by 39 ms and 38.5 ms respectively compared to WC. In base case, drag reduction rate of TC compared to BC and WC increased by 4.12% and 20.98% respectively. However, WC has the smallest water coverage and average drag reduction ratio, while SC has a lower average gas flow resistance coefficient. This research offers innovative perspectives and theoretical foundations for current flow field design.

Drag force on an oscillatory spherical bubble in shear‐thinning fluid

Power-law shear-thinning fluid motions induced by a translating spherical bubble with sinusoidal oscillation at a high frequency are numerically studied. We focus on reducing the time-averaged drag force $D$ on the bubble owing to the oscillation-enhanced shear-thinning effect. Under the assumption of negligible convection, the unsteady Stokes equation is directly solved in a finite-difference manner over a wide parameter space of the dimensionless oscillation amplitude $A$ (corresponding to the oscillatory-to-translational velocity ratio) and the power-law index $n$ of the viscosity. The results show that, for small amplitude ( $A\ll 1$ ), the drag reduction ratio $1-D/D_0$ (here, $D_0$ is $D$ with no oscillation) is proportional to $A^2$ . In contrast, for large amplitude ( $A \gg 1$ ), the drag ratio $D/D_0$ is proportional to $A^{n-1}$ , revealing a power-law behaviour. In the case of $A \gg 1$ for a strong shear-thinning fluid with small $n$ , the square of the vorticity over the entire domain is much smaller than that of the shear rate, and thus the bulk flow may be regarded as irrotational. To provide a fundamental perspective on the drag reduction mechanism, a theoretical model is proposed based on potential theory, and demonstrated to well capture the power-law relation between $D/D_0$ and $A$ .

Bionic gradient flexible fish skin acts as a passive dynamic micro-roughness to drag reduction

Fish skin has a unique biological feature that hard fish scales are embedded in a flexible dermis layer and covered by a viscoelasticity mucus or compliant epidermis layer. Therefore, the entire fish skin system can act as a dynamic resilient energy-absorbing coating with micro-roughness to absorb external turbulent pulsations. The microscopic morphology, arrangement of fish scales, and mechanical characteristics of tuna skin inspired the extraction and fabrication of the bionic gradient flexible fish skin (BGFFS) model. First, BGFFS was fabricated by the three-dimensional (3D) printing method, spraying and casting process. Then, the 3D morphology of the bionic fish skin was characterized. The results indicated that the BGFFS exhibited good morphology of fish scales and spatial gradient mechanical properties like fish skin. Moreover, the experimental results in a circulating water tunnel showed that the BGFFS had excellent drag reduction performance in a turbulent flow. When the Reynolds (Re) number was 6.8 × 104, the maximum drag reduction ratio could reach 13.8 %. The drag reduction mechanism was analyzed by the computational fluid dynamics (CFD) method, and the energy-absorbing effect of the BGFFS was measured by the polyvinylidene fluoride (PVDF) piezoelectric film. In this experiment, the maximum voltage signal reached 0.448 V. The drag reduction mechanism of the BGFFS was that the rolling friction caused by vortexes replaced sliding friction. In the meantime, the BGFFS could absorb the micro disturbances in a turbulent flow. These findings can serve as a foundation for an in-depth analysis of the hydrodynamic performance of fish as well as a new inspiration for drag reduction and antifouling.

Downstream persistence of frictional drag reduction with repetitive bubble injection

Frictional drag reduction using repetitive bubble injection is investigated in a turbulent boundary layer beneath a 36-m-long flat-bottom model ship towed at 8.0 m/s. Bubbles are injected with air flow rates periodically fluctuating at a repetition frequency of 0.5–2.0 Hz. The drag-reduction ratio reaches 24%, which is a 5% improvement relative to the conventional method of continuous bubble injection. Measurement of the local wall shear stress acting on the bottom plate and optical visualization of bubbly flow reveal that the transition of the status of bubble dispersion causes the streamwise decay of local drag reduction. The downstream persistence of the drag-reduction effect can be improved by a factor of 15 through the use of repetitive bubble injection. The estimation of the full-scale performance indicates that repetitive bubble injection provides approximately 7 times the frictional drag reduction provided by continuous bubble injection for long ship hulls exceeding 130 m.

Aerodynamic shape optimization of co-flow jet airfoil using a multi-island genetic algorithm

The co-flow jet is a zero-net-mass-flux active flow control strategy and presents great potential to improve the aerodynamic efficiency of future fuel-efficient aircrafts. The present work is to integrate the co-flow jet technology into aerodynamic shape optimization to further realize the potential of co-flow-jet technology and improve co-flow jet airfoil performance. The optimization results show that the maximum energy efficiency ratio of lift augmentation and drag reduction increased by 203.53% (α = 0°) and 10.25% (α = 10°) at the Power-1 condition (power coefficient of 0.3), respectively. A larger curvature is observed near the leading edge of the optimized aerodynamic shape, which leads to the early onset of flow separation and improves energy transfer efficiency from the jet to the free stream. In addition, the higher mid-chord of the optimized airfoil is characterized by accelerating the flow in the middle of the airfoil, increasing the strength of the negative pressure zone, thus improving the stall margin and enhancing the co-flow jet circulation.

Active control of flow past an elliptic cylinder using an artificial neural network trained by deep reinforcement learning

The active control of flow past an elliptical cylinder using the deep reinforcement learning (DRL) method is conducted. The axis ratio of the elliptical cylinder Γ varies from 1.2 to 2.0, and four angles of attack α = 0°, 15°, 30°, and 45° are taken into consideration for a fixed Reynolds number Re = 100. The mass flow rates of two synthetic jets imposed on different positions of the cylinder θ1 and θ2 are trained to control the flow. The optimal jet placement that achieves the highest drag reduction is determined for each case. For a low axis ratio ellipse, i.e., Γ = 1.2, the controlled results at α = 0° are similar to those for a circular cylinder with control jets applied at θ1 = 90° and θ2 = 270°. It is found that either applying the jets asymmetrically or increasing the angle of attack can achieve a higher drag reduction rate, which, however, is accompanied by increased fluctuation. The control jets elongate the vortex shedding, and reduce the pressure drop. Meanwhile, the flow topology is modified at a high angle of attack. For an ellipse with a relatively higher axis ratio, i.e., Γ ⩾ 1.6, the drag reduction is achieved for all the angles of attack studied. The larger the angle of attack is, the higher the drag reduction ratio is. The increased fluctuation in the drag coefficient under control is encountered, regardless of the position of the control jets. The control jets modify the flow topology by inducing an external vortex near the wall, causing the drag reduction. The results suggest that the DRL can learn an active control strategy for the present configuration.

A novel LES method for predicting drag reduction in viscoelastic fluid based on the time period of turbulence structures

Direct numerical simulations (DNS) of turbulent channel flow of viscoelastic fluid were performed with the Oldroyd-B model as a constitutive equation to identify the temporal characteristics of turbulence structures. First, using the results of the DNS in a minimal flow unit (MFU), temporal variations in the energy input and dissipation rates in fully developed wall turbulence of viscoelastic fluid were observed and compared with those of Newtonian fluid. Then, a modified time scale reflecting the local turbulence state was proposed by considering the temporal variation in the viscous stretching stress intensity. It was also found that the idea of the modified time scale could be extended and applied locally to viscoelastic fluid turbulence in a more significant computational domain than MFU to investigate the temporal characteristics of the turbulence structures. Finally, using the local modified time scale, a prediction method employing large eddy simulation for Newtonian fluid turbulence was extended for viscoelastic fluid turbulence. We proved that the drag reduction of viscoelastic fluid turbulence could be accurately predicted with a drag reduction ratio of approximately 40% by using the local modified time scale and the model in the constitutive equation. • The characteristics of viscoelastic fluid turbulence were observed from DNS results. • Active and hibernating turbulence states were compared with those in Newtonian fluid. • A local modified time scale which reflected the local turbulence state was proposed. • LES was extended using the modified time scale for viscoelastic fluid turbulence. • The proposed LES could predict the drag reduction of viscoelastic fluid turbulence.

Drag reduction due to nonionic-type surfactants in turbulent pipe flow of ethylene glycol aqueous solution

The drag-reducing effects of two nonionic-type surfactants, oleyl-N, N-dimethylamine N-oxide (ODMAO) and octadecyl-N, N-bis(2-hydroxyethyl)amine N-oxide (C18BAO), in ethylene glycol (EG) aqueous solution were comprehensively investigated at various surfactant concentrations of up to 2000 ppm by weight at various solution temperatures ranging from −5 to 80 °C in turbulent pipe flows. In EG aqueous solution (30% by weight), the mixture of ODMAO with salicylic acid with a molar ratio of 0.2 could effectively reduce the turbulent drag in the low-temperature range (up to 40 °C), whereas the effect of C18BAO was more notable at a temperature higher than 40 °C. Furthermore, the mixture of ODMAO and C18BAO in EG aqueous solution exhibited a high drag reduction ratio of more than 60% in a considerably wider range of solution temperatures (from 20 to 60 °C), while the drag reduction performance deteriorated below 0 °C and beyond 60 °C.

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

Aerodynamic drag reduction is a key element for the design of aircrafts, and it is also considered to be affected by the flow velocity. Herein, the influence of high flow velocity on the drag reduction induced by the surface microstructure inspired by a cross-section of barchan dune was investigated by the computational fluid dynamics method in this work. Overall, the drag reduction ratio was decreased while the pressure drag and viscous resistance enhanced simultaneously with the augmentation of flow velocity. Otherwise, drag analysis revealed that the total drag was a power function of flow velocity, which meant that the effect of flow velocity on drag was extremely fierce. Additionally, the microstructure improved the thickness of the boundary layer with a growth rate of 14.2%, and then reduced the viscosity resistance with limits during the development process of flow velocity. Furthermore, the micro-vortex caused by the surface microstructure provided the reverse wall shear stress, with the maximum value ranging from −4.77 Pa to −51.27 Pa, and then reduced the velocity gradient above the microstructure, thereby improving the drag reduction. However, both Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) calculations showed that the excessive velocity could lead to the dissipation of micro-vortex, which augmented the contact area between the fluid and the surface, resulting in the enlargement of viscous resistance. Finally, it was confirmed that the variation of surface microstructure height had a significant influence on drag reduction at high flow velocity. The underlying mechanism of drag reduction could also provide theoretical guidance for the design and optimization of drag reduction coatings in aeronautical applications.

Frictional drag reduction caused by bubble injection in a turbulent boundary layer beneath a 36-m-long flat-bottom model ship

The reduction of frictional drag caused by bubble injection was experimentally investigated in a turbulent boundary layer beneath a 36-m-long flat-bottom model ship. For this model ship towed at 8 m/s, the drag reduction increased exponentially (with a power index of 1.2) with the air flow rate, and the drag-reduction ratio reached 28% at the maximum air flow rate. The local wall shear stress measured at 23 locations on the flat-bottom surface revealed a reduction in the local friction coefficient of 50% immediately downstream of the bubble injector and 20% at the stern. This downstream decay proceeded nonlinearly, inferring that the spatial transition of local drag-reduction characteristics depends on the status of bubble dispersion. We established a formula characterizing the streamwise decay from measurements of the transition of drag-reduction characteristics along the 36 m length of the model. This formula can be used to evaluate the downstream persistence of bubbly drag reduction and estimate the full-scale performance of air lubrication technology.

Drag reduction in cylindrical wake flow using porous material

Due to its unique pore structure, porous materials have the potential to be used in the fields of acoustic noise reduction and flow drag reduction control. In order to study their effects and mechanism of drag reduction on the flow around a circular cylinder, experiments are conducted in a low-speed wind tunnel with low turbulence intensity. The drag forces acting on a circular cylinder model are measured using wind tunnel balance when porous materials with different permeability are applied within different intersection angles on the trailing-edge and leading edge, and the flow fields are visualized with a particle image velocimetry system with high time resolution. The method of dynamic mode decomposition (DMD) is also used for reduced-order analysis of the vorticity field in the wake of the cylinder. The measured drag forces and wake flow fields are then compared with those of a smooth cylinder, and the results show that porous materials laid on the trailing-edge can reduce drag, when a porous material with 20 pores per inch is laid within 270° on the leeward side, the best effect of the drag reduction ratio of 10.21% is reached. The results of flow visualization indicate that after the porous material is applied, the vortex region in the wake of the cylinder is expanded; both the frequency of vortex shedding and the magnitude of vorticity fluctuation decrease; the Reynolds-shear-stress decreases significantly, and both indicate that vorticity is dissipated earlier. The results of DMD analysis show that porous materials can effectively relax the energy of vortices in different modes.

Investigation on drag reduction of aqueous foam for transporting thermally produced high viscosity oil

An innovative idea is proposed for facilitating the transportation of thermally produced high-viscosity oil by injecting temperature tolerant aqueous foam. To this aim, experimental investigations of the flow characteristics of heated highly viscous oil flowing through a 25 mm i.d. horizontal rough-wall tempered borosilicate glass pipe were conducted. Measurements were made for the superficial oil and foam velocities in the range of 0.05–0.40 m/s and 0.04–0.39 m/s, respectively. Eccentric core annular flow configurations detected by a high-speed camera were found to be particularly dominant throughout the entire tested range. A two-fluid, three-zone mechanistic model for horizontal foam-oil flows was implemented for the case of shear thinning power-law fluid in the annulus, which is in accordance with the foam rheological behavior at the tested elevated temperature. Good agreement was achieved between the predicted and measured data over a wide range of operational conditions. When a complete foam annulus encapsulating the oil core is formed, a critical value of input foam volume fraction can be determined for the maximum drag reduction ratio. An optimal oil core-to-pipe radius ratio range was determined for the highest oil-transport operational coefficient. The drag reduction performance of the tested hot oil-foam system is better than that obtained with the oil-foam system employed at room temperature.

Improved Stable Drag Reduction of Controllable Laser-Patterned Superwetting Surfaces Containing Bioinspired Micro/Nanostructured Arrays.

Superwetting surfaces are widely used in many engineering fields for reducing energy and resistance loss. A facile and efficient method using laser etching has been used to fabricate and control superwettable drag reduction surfaces. Inspired by the self-cleaning theory of lotus leaves, we propose controllable patterned bionic superhydrophobic surfaces (BSSs) simulating the uneven micro/nanostructures of lotus leaves. The superhydrophobicity and drag reduction ratios at low velocities are highly improved using a laser ablation method on metal substrates. However, unstable air layers trapped on superhydrophobic surfaces are usually cut away by a high-velocity flow, which greatly reduces the drag reduction performance. The fabricated bionic superhydrophobic/hydrophilic surfaces (BSHSs) with alternated hydrophilic strips can build a large surface energy barrier to bind the three-phase contact line. It maintains the stable drag reduction by capturing the air bubbles attached to the hydrophilic strips at a high velocity. Three-dimensional simulation analysis and equipment to measure the weak friction of a self-assembled solid–liquid interface are used to explain the drag reduction mechanism and measure the drag reduction ratios at different flow speeds. BSSs achieve an improved drag reduction effect (maximum 52.76%) at a low velocity (maximum 1.5568 m/s). BSHSs maintain an improved and steady drag reduction effect at high speed. The drag reduction ratios can be maintained at about 30% at high speed, with a maximum value of 4.448 m/s. This research has broad application prospects in energy saving, liquid directional transportation, and shipping due to their robust superhydrophobic properties and stable drag reduction effect.