Drag Reduction Characteristics Research Articles

Research on the Flow and Drag Reduction Characteristics of Surfaces with Biomimetic Fitting Structure

Research on the Flow and Drag Reduction Characteristics of Surfaces with Biomimetic Fitting Structure

Drag reduction characteristics of the placoid scale array skin sup-ported by micro Stewart mechanism based on penalty immersed boundary method

Sharkskin performs an excellent flow drag reduction property, leading to numerous biomimetic research to obtain artificial drag reduction structures for underwater vehicles. The existing work mainly focused on replicating or simplifying the morphology of the placoid scale, however, such bionic structures cannot fully reproduce the drag reduction effects of sharks swimming in natural environments. This is because the existing research has not considered the influence of the multi-degree freedom motion characteristics of the placoid scale. Therefore, a new bionic drag reduction skin is proposed by combining micro Stewart mechanisms and placoid scales, where the micro Stewart mechanism is able to achieve the multi-degree freedom motion characteristics. The numerical results indicate that micro Stewart mechanisms inhibit the generation and development of the streamwise and spanwise vortex structures in the bionic placoid scale array, which can delay flow separation and improve the drag reduction effect of the placoid scale array. Compared with the bionic placoid scale skin and the blade groove skin without multi-degree freedom motion foundation, the new bionic skin achieves relative drag reduction efficiency of 15.78 % and 14.18 % at maximum, respectively, by reasonably adjusting the bionic skin parameters including the leg stiffness, leg damping, upper platform mass, upper platform center of mass height of the micro Stewart mechanism and the skin element distribution spacing. The research presents a novel sharkskin bionics design and reveals the mechanism of skin drag reduction to some extent.

Drag reducing performance and its influencing on natural yam mucilage

Yam mucilage is a novel environmentally friendly drag reducer. This study investigates drag reduction and degradation characteristics of Chinese yam mucilage, using an in-house rotor device. The effects of temperature, aging, and salts on the drag reduction rate (DR) of yam mucilage were also explored. Furthermore, the synergistic drag reduction properties of Chinese yam-polyethylene oxide (PEO) solution were investigated by blending Chinese yam mucilage with PEO. The rotational speed range of the rotor device was set at 200–700 r/min, corresponding to Reynolds numbers (Re) ranging from 30 396 to 106 385. The results demonstrated that the DR of yam mucilage initially increased, and then decreased at low concentrations, with increasing Re. Conversely, the DR of yam mucilage at high concentrations increased with increasing Re, albeit at a gradually slowing rate as concentration increased; however, the shear stability was gradually enhanced. Degradation testing revealed that yam slime exhibited semi-rigid, or rigid polymer characteristics, with notable shear stability. At a concentration of 2000 ppm and Re = 106 385, the maximum DR reached 44.1%. Prolonged heating and standing resulted in the reduced DR of yam mucilage. However, salt ions exerted dual effects on the DR of yam mucilage: Low concentrations of NaCl improved its effectiveness while Na2SO4 and high concentrations of NaCl diminished its efficacy. The addition of a small quantity of PEO was found to significantly enhance the drag reduction efficacy of yam mucilage, but no significant improvement in the shear stability of yam mucilage was observed. Yam mucilage exhibits promising potential as an environmentally friendly drag reducer with remarkable drag reduction capabilities.

Analysis of the Drag Reduction Performance and Rheological Properties of Drag-Reducing Additives.

In the practical application of hydraulic rotating machinery, it is essential to thoroughly explore drag reduction and rheological characteristics of drag-reducing additives to optimize machinery efficiency and reduce equipment consumption. This paper combines simulation and experimental approaches to investigate the drag-reduction performance and rheological properties of drag-reducing additives. Numerical simulations are initially conducted to investigate the shear-thinning properties of drag-reducing fluid and explore variations in drag-reduction rate. Turbulent phenomena characteristics are described by analyzing turbulent statistical quantities. Subsequently, the rheological behaviors of polyethylene oxide (PEO), cetyltrimethyl ammonium chloride (CTAC), and their mixed solutions under different conditions are scrutinized using a rotational rheometer. The findings indicate that the drag reduction effect amplifies as the rheological index n and characteristic time λ decrease. The numerical simulations show a maximum drag reduction rate of 20.18%. In rheological experiments, a three-stage viscosity variation is observed in single drag-reducing additives: shear thickening, shear thinning, and eventual stabilization. Composite drag-reducing additives significantly reduce the apparent viscosity at low shear rates, thereby strengthening the shear resistance of the system.

Analyzing the Efficacy of Nickel Plating Coating in Hydraulic Pipeline Drag Reduction

This study delves into the drag-reducing properties of nickel plating coatings applied to hydraulic pipelines. To investigate the drag reduction characteristics of pipeline coatings, we designed a specialized experimental apparatus to conduct deceleration experiments. The primary objective was to systematically assess the drag reduction effect of varying coating thicknesses on liquid flow within the pipeline. Chemical nickel plating was employed for preparing drag reduction coatings with diverse thicknesses, achieved through precise adjustments in the composition and operating conditions of the plating solution. In the design of the experimental apparatus, careful consideration was given to crucial parameters such as the inner diameter of the pipeline, the inlet flow rate, and the control of experimental variables. It quantitatively assesses how varying coating thicknesses, flow velocities, and pipeline diameters impact the pipelines’ resistance to flow. By meticulously measuring the pressure differential across the pipeline, the research evaluates the extent of drag reduction afforded by the coatings and simultaneously elucidates the underlying mechanisms. Findings indicate a peak drag reduction rate of 5% under conditions of a 20 µm-thick nickel coating, 5 m/s flow velocity, and a 10 mm pipeline diameter. This study aims to comprehend how coatings affect linear losses along the pipeline, thereby establishing the groundwork for optimizing drag reduction technology. These outcomes highlight the coatings’ potential to mitigate linear losses due to shear stress during fluid transport, offering a viable solution to enhance hydraulic pipeline efficiency with significant industrial implications.

Flow evolution of mixed layer on convex curvature wall under hypersonic conditions

With the continuous upgrading of hypersonic vehicles, a new requirement for designing imaging window i.e. conformal window for improving aerodynamic characteristics, is put forward, in which the supersonic cooling film and optical window are required to maintain the same curvature shape as the aircraft body. In this work, the mixed-layer flow evolution on a convex wall (CV) is investigated. A nanoparticle-based planar laser scattering technique is used to design the flow field structure of the mixed layer in <i>Ma</i> = 6 hypersonic static wind tunnel, and the location of the mixed-layer instability is studied by combing fractal dimension. The results of pressure, and impulse of compression (<i>I</i><sub>p</sub>) evolution along the flow direction are obtained by numerical simulation, showing that the total incoming pressure (<i>P</i><sub>0</sub>) has a significant effect on the flow evolution of the mixed layer: as <i>P</i><sub>0</sub> increases, the ratio of static pressure (RSP) decreases, that the position of the mixed-layer instability is delayed, and that the flow velocity of the typical vortex structure increases. The favorable gradient existing at the CV wallleads the pressure to drop along the flow direction, and the pressure is enhanced when the supersonic air film along the tangential direction of the wall is under the operating condition. However, as <i>P</i><sub>0</sub> increases, the RSP decreases, and the lifting effect of the pressure on the CV decreases. The flow field is affected by the expansion effect of the CV, and <i>I</i><sub>p</sub> decreases along the flow direction. The supersonic air film can weaken the expansion effect on the CV and thus suppressing the decrease of <i>I</i><sub>p</sub>. The change rate of <i>I</i><sub>p</sub> (Δ<i>I</i><sub>p</sub>) is significantly affected by <i>P</i><sub>0</sub>, in a range of bending impulse |<i>I</i><sub><i>Φ</i></sub>| = 0.191–3.62, Δ<i>I</i><sub>p</sub> decreases from 178.67% to 12.02% when <i>P</i><sub>0</sub> = 0.5 MPa, and Δ<i>I</i><sub>p</sub> decreases from 40.38% to 5.64% when <i>P</i><sub>0</sub> = 1.0 MPa. Δ<i>I</i><sub>p</sub> decreases as |<i>I</i><sub><i>Φ</i></sub>| increases, but the decrease becomes less as <i>P</i><sub>0</sub> increases. The results reveal the flow evolution law of hypersonic mixed layer under the influence of convex curvature, and provide a certain reference for designing the shape of hypersonic vehicle to achieve aerodynamic drag reduction and thermal protection characteristics.

Numerical simulation study on the drag reduction characteristics of grooves-microbubbles coupling surfaces

Surface drag reduction technologies can significantly reduce the resistance during ship navigation, enhancing speed, efficiency and adaptability under various operating conditions. This paper uses numerical simulation technology to analyze the drag reduction characteristics of grooved and grooves-microbubbles coupling surface, focusing on the effects of groove width, gas flow rate, and liquid flow velocity on the drag reduction performance. The research results indicate that the grooved surface is suitable for full surface drag reduction at velocity below 3 m/s with a maximum drag reduction rate of 4.02%. Microbubbles can greatly improve the drag reduction effect of the grooved surface, and the drag reduction effect of the coupling surface gradually increases with the gas flow rate increases. The maximum drag reduction rate can reach 89.86% at the gas inlet velocity of 1 m/s. The liquid flow velocity has a significant impact on the drag reduction. In both the groove model and the coupling model, the drag reduction rate initially rises and then declines with the liquid flow velocity increases.

Drag Reduction Analysis of Optimal Three-dimensional Bumps on the M6 Wing

Based on Isight optimization software and evolutionary strategy algorithm, this paper builds a bump optimization design platform by integrating the three-dimensional bump shape generator program, grid generation software Gridgen and flow field simulation software Fluent. This platform is successfully validated on the RAE2822 supercritical infinite straight wing, which reduces the drag coefficient by 11 counts and increases the lift-drag ratio by 11.48 percent. Through this platform, the drag reduction characteristics of optimal three-dimensional bumps on the M6 wing are numerical studied. The results show that the three-dimensional bumps can weaken shock waves and have spanwise characteristics, the stronger the shock waves, the more obvious the drag reduction effect of the three-dimensional bumps, and the wing with optimal three-dimensional bumps can improve flow field characteristics and prevent flow separations.

Co-effect of hydrophobicity and cavities on flow characteristics at microscale

Flowing characteristics of drag reduction are experimentally and numerically investigated with a combination of hydrophobic coating and various cavities in polydimethylsiloxane microchannels. Two typical types of cavities with different geometrical parameters, rectangular and triangular, are studied with a wide range of Reynolds numbers from 0 to 300. A promising hydrophobic processing method is proposed based on a comprehensive performance on surface morphology, water repellency, and structural distortion. In this method, hydrofluoric acid (40 wt. %) is adopted and the corrosion time is set to 5 min. The velocity field and streamlines are acquired by the micro-particle image velocimetry system and numerical models to explain the flow patterns in particular. The slip length is measured as 13.38 μm in the hydrophobic straight channel. For rectangular cavities, the drag reduction rate reaches nearly 14.1% under no-slip condition and 33.2% under slip condition. A critical turning point of the co-effect is found by numerical results when the slip length is about 15 μm, which is also determined by the cavities. The convergent and divergent angles of triangular cavities play a critical role in the pressure drop due to the competition of the vortex and flow impingement. A nonlinear model is developed based on the numerical results to predict Poiseuille number with the relevant important variables for a two-dimensional microchannel. Our results reveal the fundamental physics of flowing characteristics with the co-design of hydrophobicity and microstructures, predicting a composite design method for widespread applications in microfluids.

Drag reduction characteristics of recirculation flow at rocket base in an RBCC engine under ramjet/scramjet mode

To reduce the drag generated by the recirculation flow at the rocket base in a Rocket-Based Combined Cycle (RBCC) engine operating in the ramjet/scramjet mode, a novel annular rocket RBCC engine based on a central plug cone was proposed. The performance loss mechanism caused by the recirculation flow at the rocket base and the influence of the plug cone configuration on the thrust performance were studied. Results indicated that the recirculation flow at the rocket base extended through the entire combustor, which creates an extensive range of the “low-kinetic-energy zone” at the center and leads to an engine thrust loss. The plug cone serving as a surface structure had a restrictive effect on the internal flow of the engine, making it smoothly transit at the position of the large separation zone. The model RBCC engine could achieve a maximum thrust augmentation of 37.6% with a long plug cone that was twice diameter of the inner isolator. However, a shorter plug cone that was half diameter of the inner isolator proved less effective at reducing the recirculation flow for a supersonic flow and induced an undesirable flow fraction that diminished the thrust performance. Furthermore, the effectiveness of the plug cone increased with the flight Mach number, indicating that it could further broaden the operating speed range of the scramjet mode.

Research on the impact of air-blowing on aerodynamic drag reduction and wake characteristics of a high-speed maglev train

The maglev train fills the speed gap between ground transportation and airplanes. However, the increasing train speed results in greater energy losses due to increased aerodynamic drag, impeding the green and sustainable development of high-speed railways. This study employs the numerical simulation method to explore the effects of installing air-blowing slots on the surface of the TR08 maglev train's tail car and blowing air along three different directions at two different speeds on drag reduction and the characteristics of the wake flow field. Among them, only blowing air along the streamwise direction at speeds of 12 m/s (X12) and 24 m/s (X24) shows drag reduction effects of 2.06% and 6.53%, respectively. However, considering the energy efficiency, only X12 achieves a net energy saving of 58.96%, while the energy consumption by blowing air and saving by reducing drag in X24 are roughly balanced. Air-blowing reduces the aerodynamic lift of the tail car (Cl), with blowing air along the perpendicular direction at 24 m/s (Z24) reducing the Cl by 99.57%. Additionally, Z24 reduces the maximum velocity value of the train-induced air flow (Usmax¯) by 61.91%. The research findings provide new insight and data support for the development of blowing/suction drag reduction techniques.

Effects of ammonia combustion on skin friction characteristics for supersonic flow

Boundary layer combustion is an effective method to reduce friction in scramjet combustors. In existing research on drag-reducing fuels, hydrocarbons pose challenges related to carbon deposition and emissions. Meanwhile, hydrogen presents significant difficulties in storage and transportation. For the first time, this paper explores ammonia as a drag-reducing alternative. We employed the Reynolds-averaged Navier-Stokes (RANS) method to investigate the characteristics of drag reduction by ammonia combustion in supersonic flow. Numerical results indicate that the local drag reduction by ammonia combustion is better than hydrocarbon and worse than hydrogen compared to existing research. Ammonia exhibits superior potential for drag reduction. However, the overall drag reduction at room ammonia injection temperature is limited due to the significant distance between the ammonia self-ignition point and the injection port. To address this challenge, we proposed two optimization strategies: increasing the ammonia injection temperature and increasing the inlet ammonia decomposition ratio. As the ammonia injection temperature increases, the self-ignition position moves towards the inlet, and the combustion drag reduction region expands upstream. Interestingly, a higher ammonia inlet decomposition ratio does not necessarily lead to a better drag reduction effect. In fact, an excessively high decomposition ratio can inhibit the combustion drag reduction effect. The most effective drag reduction occurs when the ammonia inlet mass fraction is 50%, resulting in a 42.8% reduction in integrated drag compared to the case without NH3 injection. Overall, this paper offers critical insights into the utilization of ammonia combustion in scramjets to reduce drag.

Study on the cooling and drag reduction characteristics of multi-port injector array film cooling using gaseous hydrocarbon fuel as coolant

Supersonic film cooling utilizing gaseous hydrocarbon fuel is an effective method to meet the thermal protection and drag reduction requirements inside a scramjet engine. The film injection scheme for film cooling using gaseous hydrocarbon fuel is crucial in determining the thermal protection and drag reduction performance of the film with oxidative cracking reaction. In this paper, a numerical study is conducted to compare the thermal protection and drag reduction performance of gaseous hydrocarbon fuel film under the slot injector film cooling structure and the multi-port injector array film cooling structure. The results show that the multi-port injector array film cooling utilizing gaseous hydrocarbon fuel as a coolant improves both thermal protection and drag reduction performance compared to the slot injector film cooling structure. The chemical reaction of hydrocarbon fuel expands the cooling range and low resistance area of a single discrete hole. The reason is that the multi-port injector array film cooling intermittently interrupts the oxidation and heat release process of the hydrocarbon fuel in the boundary layer, resulting in higher cooling efficiency in the film cooling injection area. It also improves the spatial distribution of the hydrocarbon fuel film, allowing for effective utilization of the chemical heat sink of the hydrocarbon fuel, which improves the thermal protection performance and expands the effective cooling area. Furthermore, the enhanced mixing of the multi-port injector array film cooling in the film injection area improves drag reduction performance through combustion inside the boundary layer, resulting in a significant drag reduction of 36.6%. The multi-port injector array film cooling also effectively distributes the low skin-friction resistance region due to the low molecular viscosity after the secondary cooling flow injection. Moreover, under supersonic mainstream conditions, the mixing efficiency of the multi-port injector array film cooling structure and the slot injector film cooling structure both decreases, and the difference gradually decreases.

Influence of a groove-structured vortex generator on the drag reduction characteristics of a multiphase pump

The oil–gas mixture pump significantly contributes to marginal oil field extraction and remote transportation of deep-sea oil. Nevertheless, during the operation of the mixture pump, it is inevitable to encounter problems like the separation of the mixed media from the hydraulic components as well as the gas phase from the liquid phase, which leads to enhancing the flow resistance of the mixed media. Therefore, this study investigates the influence of a groove-structure vortex generator on the drag reduction characteristics of a helical axial-flow gas–liquid multiphase pump under the design flow rate condition and various inlet gas content rates. The findings show that the vortex generator with diverse groove depths can prevent the separation of the mixed media from the blade suction surface effectively and minimize the flow resistance of the media in the 1/10 of the blade inlet. In particular, excellent drag reduction results were gained with a maximum drag reduction rate of 36.7% when the relative depth was 3/40. In addition, the efficiency of the mixture pump increased by a maximum of 2.1%, and the head increased by a maximum of 4.3%. The significance of this study lies in its potential to further optimize the design and performance of gas–liquid multiphase pumps. It provides new insights into the design and application of vortex generators. It offers robust support for the optimization and enhancement of gas–liquid multiphase pumps.

Microbubbles drag reduction characteristics of underwater vehicle during pitching movement

In this study, we investigate the effects of ventilation parameters and motion characteristics on the drag reduction characteristics of microbubbles during the pitching motion of underwater vehicle. Based on the Population Balance Model (PBM), a numerical method is established that takes into account the phenomenon of microbubbles aggregation and breakage. The effects of the pitching frequency and ventilation volume coefficient on drag and lift are conducted in this study. The results show that the numerical method can accurately predict the distribution and force characteristics of microbubbles for the vehicle in pitching motion. Added mass force of the water phase is weakened when the vehicle is surrounded by microbubbles during the pitching motion. This causes a gradual decrease in the phase difference between the drag and lift coefficients under different pitching frequencies. Moreover, the drag rate of the microbubble is inversely related to the pitch angle. Namely, the drag reduction rate of microbubbles decreases with an increase in pitch angle. The drag coefficient decreases significantly when the vehicle is covered by the microbubbles. This leads to the phase of the drag coefficient slightly lagging behind the pitch angle. Furthermore, the lift coefficients of vehicle are similar for different ventilation flow rates.

Numerical research on drag-reduction characteristics of a body of revolution based on periodic forcing

Effective drag-reduction technology is important for enhancing navigation speed, extending endurance, and enabling efficient energy usage of underwater vehicles. In this study, we investigated the effectiveness of a body of revolution to influence the turbulent boundary-layer properties by performing numerical simulations and varying a periodic sinusoidal force in a series of annular slots. The selected control parameters included the normalized periodic force amplitude and periodic force frequency; the effects of these parameters on drag reduction have not been demonstrated in previous studies. The surface pressure and velocity analyses revealed that frictional drag accounted for 71.7% of the total drag reduction, and it was the dominant contributor to the drag-reduction effect. Unsteady vortices were generated in the boundary layer, and a retarded fluid region was created on the surface. A clockwise vortex was generated downstream of the annular slots during blowing, reducing the pressure drag on the surface of the revolution body. The clockwise vortex weakened when suction was applied. The results of this research might provide ideas for solving the drag-reduction problem in the design of revolving-body-type underwater vehicles.

Drag Reduction Performance of Triangular (V-groove) Riblets with Different Adjacent Height Ratios

Surface structure is used to interfere with the turbulent boundary layer in the groove drag reduction, which is important to the endurance and stability of high-speed and ultrahigh-speed aircraft. The size of the groove structure directly affects the flow in the turbulent boundary layer and changes the drag reduction effect. The drag reduction characteristics of bionic triangular (V-groove) riblets were studied through Particle Image Velocimetry (PIV) experiment and Finite Volume Method (FVM) simulation. Triangular riblets with adjacent height ratios (AHR) of 1.00, 1.74, and 3.02 were considered in this research, and the influence of these groove structures on the flow characteristics of turbulence near the wall is compared with those of the smooth plates. The distribution of time-averaged velocity, turbulence intensity, and coherent structures of turbulent boundary layer on the riblet surface is analyzed to document the effects of the geometric parameters of various groove structures on drag reduction rates. Results showed that the best drag reduction is obtained using the V-groove riblets with adjacent height ratio of 1:1 under the low free-stream velocity. The results can be used as a reference for further optimization of drag reduction structures with surface grooves.

Effect of V-Shaped Groove Microstructure on Blood Flow Resistance in Bionic Artificial Blood Vessels

This study aims to investigate the blood flow in bionic artificial blood vessels and to reduce the resistance to blood flow, the drag reduction characteristics of V-shaped groove drag reduction microstructures in artificial blood vessel structures were investigated in depth. By varying the parameters of incoming flow velocity, groove width, and groove depth, the effect of various variable conditions on the drag reduction effect of the grooves was investigated, and the flow field characteristics and drag reduction effect of the V-shaped groove microstructure in the artificial blood vessel were obtained. A detailed analysis of the effect of velocity and groove size on the drag reduction effect of the groove was also carried out to demonstrate the drag reduction mechanism of the V-shaped groove microstructure and to summarize the variation law of the drag reduction rate of the V-shaped groove. The results show that the resistance reduction rate of the V-shaped groove microstructure decreases with the increase of blood flow velocity, increases with the increase of groove width, and increases and then decreases with the increase of groove depth. The velocity range used in this paper is 0.3–0.6 m/s, the groove width varies from 0 to 0.3 mm, and the groove depth varies from 0 to 0.3 mm.

Research on the drag reduction characteristics and mechanism of a cylinder covered with porous media

As an effective drag reduction control method, porous media have attracted extensive attention in various engineering fields. In this paper, the large eddy simulation method is used to study the flow problem around a cylinder with and without porous media covering at subcritical Reynolds numbers. The drag reduction characteristics and the mechanism of a cylinder covered with porous media were studied. The results of the aerodynamic drag coefficient show that when the Reynolds number is 5.6 × 104 and when the porous media are arranged on the leeward side of the cylinder at an azimuth angle of 270°, the drag reduction rate is the largest, reaching 8.53%. The flow field results indicate that after porous media covering, the large-scale wake vortex shedding was effectively suppressed, the vortex shedding frequency was reduced, the vortexes in the wake area became thinner and longer, and the vorticity decreased. It is confirmed that porous media can stabilize the wake shear layer and suppress the unsteady vortex motion in the wake. Meanwhile, airflow can penetrate the porous media, leading to velocity slip at the interface between the porous media and the airflow, making the free shear layer more stable, and strengthen the wake vortex.

Effects of inflow parameters on thermal protection and drag reduction characteristics for hydrocarbon fueled supersonic film with combustion

Hydrocarbon fueled supersonic film is considered to be one of the most effective methods for achieving thermal protection and drag reduction meanwhile in scramjet combustors. In this paper, the effects of film and mainstream inflow parameters on thermal protection and drag reduction characteristics for hydrocarbon fueled supersonic film with combustion are numerically investigated. The results indicate that, based on the traditional supersonic film without chemical reaction, combustion brings beneficial effects on thermal protection and drag reduction characteristics mainly depend on the relative proportion and location of exothermic chemical reactions in the boundary layer. It is found that, film inflow parameters only change the reaction energy spatial distribution through changing mainstream energy addition by mixing. However, mainstream inflow parameters directly change reaction conditions, therefore influencing the reaction path, and bringing greater effects on the characteristics. It is worth mentioning that, with film inlet height increases under a constant film equivalence ratio, combustion brings more benefits for both thermal protection and drag reduction characteristics based on the traditional film. Moreover, mainstream Mach number increasing or total temperature decreasing can even inhibit the exothermic reactions, which only brings beneficial effects on thermal protection characteristics, however, barely has effects on drag reduction characteristics.