Study Of Drag Reduction Research Articles

Drag reduction study based on boundary layer combustion on single expansion ramp nozzle

In hypersonic flight, frictional drag is an important factor affecting the overall engine performance. The wall frictional drag analysis and drag reduction technology of a unilateral expanding tail nozzle under typical working conditions are carried out by means of two-dimensional Reynolds-averaged N-S equations and SST k − ω turbulence model. The effects of hydrogen injection and combustion with different mass flow rates under different jet positions on the wall friction resistance are analyzed and compared, and the results show that, under the appropriate opening position, a better drag reduction effect can be obtained by injecting hydrogen with a mainstream flow rate of about 2.5%, which can achieve a reduction of 43.7%.

A Bio-Inspired Drag Reduction Method of Bionic Fish Skin Mucus Structure.

Efforts to enhance the speed and reduce the energy consumption of underwater vehicles have led to the proposal of a novel mucus release structure inspired by the secretion of mucus cells on fish skin. This structure features interconnected microgrooves with excellent flexibility for adjusting to different states, effectively reducing drag through mucus release. Numerical analysis of the drag reduction performance of the mucous-releasing micro-pore structure was conducted using ANSYS Fluent 19.2 software. This structure is capable of reducing the velocity gradient near the wall and, owing to the presence of micro-pore structures, decreasing the overall compressed area, thereby achieving drag reduction effects. The experimental results revealed a drag reduction effect of 20.56% when the structure was bent at an angle of 120°. The drag reduction varied under different attitudes such as tension and compression. This mucus release structure achieves reusability through a direct mucous injection process. This research provides valuable insights for the drag reduction study of underwater vehicles, such as ships and submarines, laying a foundation for advancing the development and applications of this field in the future.

Wall shear stress measurement of turbulent bubbly flows using laser Doppler displacement sensor

A novel wall shear stress meter is developed to promote studies of frictional drag reduction by injecting air bubbles into a turbulent boundary layer. Such studies require a tool having a time resolution sufficiently high to capture the unsteady effect of turbulent characteristics due to various bubble passage patterns. The present study adopts the principle of the heterodyne interferometer to capture of time variation of wall shear stress in turbulent flow up to 500 Hz in sampling frequency. We demonstrate the performance of the tool by applying it to bubbly flows beneath a flat-bottom model ship running at 3 m/s in a towing water reservoir, where bubbles experience wavy passage around a few Hz in frequency. The data obtained by the proposed shear stress meter agree well with Dean's formula for single-phase turbulent channel flow. The scattering of the data across three trials is sufficiently small, at approximately 3 %. This high reproducibility is a great advantage over conventional direct measurements, which have low reproducibility and a large scatter of the data of approximately 15 %. The obtained results represent reasonable drag reductions by injecting bubbles with different void fractions. We also evaluate histogram of the wall shear stress fluctuation to characterize the effect of drag reduction by unsteady passage of bubbles.

Laboratory study of drag reduction and heat transfer improvement in vertical pipe using crude oil/nanosilica/Polyisobutylene polynanofluids

Laboratory study of drag reduction and heat transfer improvement in vertical pipe using crude oil/nanosilica/Polyisobutylene polynanofluids

A Drag Reduction Study on the Aerodynamics of the Irish Taxi Sign

This comprehensive study focused on the standard taxi sign used in Ireland and its impact on drag production, fuel expenses, and CO2 emissions. Experimental analysis revealed that the conventional taxi sign significantly increased drag, especially when mounted on streamlined vehicles such as saloon cars, due to flow separation issues on the rear roof and rear windshield. Longitudinal reorientation of the sign offered a 14-fold reduction in drag increase compared to the traditional placement. It was found that positioning the sign in the middle of the roof offered the greatest fuel efficiency. Furthermore, the study estimated that implementing longitudinal repositioning on all Irish taxi signs could save drivers approximately EUR 832 per year and reduce national CO2 emissions by a substantial 22,464 tonnes annually. Comparative analyses with international taxi signs demonstrated that the Irish sign had significantly larger drag contributions, emphasizing the need for improved aerodynamics. To address the inherent drag issue, the study explored novel appendable devices and proposed alternative taxi sign designs. Among the tested solutions, a magnet-mounted front ramp proved the most effective, reducing total drag by nearly 30%. Additionally, a motorized flip-up taxi sign design demonstrated a remarkable 40% reduction in drag. Finally, a newly proposed taxi sign design, featuring longitudinal positioning and pointed triangular front and rear faces, resulted in a minimal 4.3% increase in vehicle drag compared to the baseline car.

Drag reduction study of naturally occurring oscillating axial flow induced by helical corrugated surface in Taylor–Couette flow

This study investigates drag reduction capability of naturally occurring-oscillating axial secondary flow (ASF) induced by helical-corrugated surface in Taylor–Couette flow (TCFHelical) for three values of pitch to wavelength ratios (P* = 1, 2, and 3) and amplitude to wavelength ratio(A*) of 0.25. As reported in Razzak et al. [“Numerical study of Taylor Couette flow with longitudinal corrugated surface,” Phys. Fluids 32(5), 053606 (2020)], emergence of naturally occurring-oscillating ASF induced by longitudinal-corrugated surface in TCF (TCFLongitudinal) and increasing trend on its magnitude with Reynolds number (Re) results in the occurrence of drag reduction. This has motivated us to study the possibility of enhancing drag reduction by maintaining a consistently increasing trend with Re in the magnitude of naturally occurring-oscillating ASF induced by the helical-corrugated surface on the stationary outer cylinder in TCF. From flow structures, steady ASF with non-zero mean is observed at Re = 60, which suppresses the strength of azimuthal vorticities for Re > 85, and contributed to the occurrence of drag reduction. As Re is increased to 100, 90, and 85 for P* = 1, 2, and 3, respectively, the formation of periodic oscillating ASF with non-zero mean and its increasing trend in magnitude with Re suppresses azimuthal vorticities further, which contributes to the maximum drag reduction of 13%. For Re > 165, 145, and 140 for P* = 1, 2, and 3, respectively, non-periodic oscillating ASF is observed, and its magnitude remains nearly unchanged or decreases slightly with Re, which results in the suppression effect of azimuthal vortices to be weaker. This results in the decrease in the drag reduction. Oscillating ASF observed in TCFHelical is found to occur at earlier Re, and it is stronger than that of TCFLongitudinal, which contributes to the occurrence of higher drag reduction in TCFHelical.

Aerodynamic Optimization Design of Supersonic Wing Based on Discrete Adjoint

Reducing fuel consumption and improving the economy by effectively reducing cruising drag is the main objective of the aerodynamic design of supersonic civil aircraft. In this paper, the aerodynamic optimization design system based on the Reynolds-Averaged Navier–Stokes (RANS) equation and discrete adjoint theory is applied to supersonic wing design. Based on this system, a single-point optimization design study of aerodynamic drag reduction in cruise conditions was carried out for two typical supersonic wing layouts, subsonic leading edge and supersonic leading edge, and the drag reduction reached 3.78% and 4.53%, respectively. The aerodynamic design characteristics of different types of supersonic wings were explored from the perspectives of wing load, twist angle distribution, pressure distribution, airfoil shape characteristics, and flow field characteristics. The optimization results show that the drag reduction of the subsonic leading edge configuration is dominated by the induced drag, while the optimizer mainly focuses on reducing the shock wave drag for the supersonic leading edge configuration. By comparing the sensitivity analysis of lift and drag coefficients to airfoil deformation with the optimization results, the optimized dominant directions of two types of supersonic wings are qualitatively analyzed. The derivatives obtained from discrete adjoint equations are useful to elaborate the design tendency and the reason for the trade-off generation of supersonic wings under specific layouts and engineering constraints, which provides a reference for the design of supersonic wings in the future.

Experimental and numerical study of drag reduction and heat transfer enhancement in a vertical pipe using water/polyisobutylene/nano-SiO2 polynanofluids

Poly-nanofluids (PNFs) are a new type of material that is manufactured by dispersing nanoparticles in dilute polymer solutions. This study looked at heat transfer and drag reduction using a water/polyisobutylene/nano-SiO2 PNF through a vertical copper pipe under conditions of constant heat flux. The effects of ploy-isobutylene (PIB) polymer solution, water/nano-SiO2 nanofluid, and aqueous PNF on heat transfer and drag reduction in a vertical pipe have been studied, separately. All prepared solutions had Reynolds numbers ranging from 7000 to 22000. Nano-SiO2 particles with an average size 20 nm and concentration ranges of 0.1–1 wt.% have been dispersed in aqueous PIB solutions as base fluids with 10–50 ppm concentration of the polymer. The optimal nanoparticle and polymer concentrations for the prepared nanofluid, polymer solution, and PNFs were 0.75 wt.% and 50 ppm, respectively. The friction factor of PNFs at optimal concentrations was 75% less than pure water. Ansys Fluent software was employed to verify the findings of the experiment and simulate the heat transfer and drag reduction phenomena at optimal conditions. Based on the results, the experimental and numerical data were in reasonable agreement, with a deviation of less than 5%.

Comparative Study of Drag Reduction of Square-back Vehicle Geometry using Steady blowing and Fluidic Oscillators Method

Comparative Study of Drag Reduction of Square-back Vehicle Geometry using Steady blowing and Fluidic Oscillators Method

Drag reduction study of a microfiber-coated cylinder

Drag reduction for a bluff body is imperative in a time of increasing awareness of the environmental impact and sustainability of air travel. Microfiber coating has demonstrated its ability to reduce drag on a bluff body. This was done by applying strips of the coating to a cylinder. To widen the application range of the microfiber coating, a fully microfiber-coated cylinder is studied as it has no directionality relative to incoming flow. It is hypothesized that a large coating coverage will cause a reduction in drag dependent on the Reynolds number Re. The fully microfiber-coated cylinder is studied in a wind tunnel and the drag coefficient is determined at a range of Re in the subcritical-flow regime. It is found that the drag coefficient of the microfiber-coated cylinder is a function of Re, and the critical Reynolds number, where the maximum drag reduction occurs, is lower for a microfiber-coated cylinder compared to that of a conventional smooth-surface cylinder.

Ultrafast Self-Healing Superhydrophobic Surface for Underwater Drag Reduction.

The self-healing superhydrophobic surfaces have attracted great interest owing to restoring superhydrophobicity without preparation crafts. However, the self-healing superhydrophobic surface still faces the dilemma of long repairing time. Especially in aqueous environments, superhydrophobic surfaces are highly susceptible to contamination and damage. In the current study, a superhydrophobic surface with ultrafast repairability was developed, which apply for drag reduction in aqueous medium. The prepared superhydrophobic surface can recover superhydrophobicity in only 30 s after severe physical and chemical damage. In addition, this research pioneered the combination of superhydrophobicity and porous structures for underwater drag reduction. The study of drag reduction confirms that the superhydrophobic surface can reduce the frictional drag by about 43% in the water. However, the drag reduction rate of the superhydrophobic surface with the porous structure can be improved to 76% due to increased stability of the air layer. More importantly, the porous structure with the average pore size of 50 μm has the most excellent stability through further experiments on the underwater air layer. This is attributed to the proper size of the pore to effectively balance the capillary force and resist wetting in the marginal region. This study will bring inspiration for the large-scale application of superhydrophobic surfaces and long-term drag reduction.

Calculation Model of the Effect of Periodic Change of Normal Force on Sliding Friction Characteristics between the Planes

How to reduce the friction resistance between two planes is a difficult problem that has been studied in the field of tribology. Aiming at this problem, the concept of reducing the friction resistance by exciting the periodic change of normal force between the planes is proposed. A calculation model of the displacement amplitude distribution of the plate is established based on the principle of reciprocity of work, and the influence of the periodic change of normal force on sliding friction between the planes is studied. Additionally, an experimental device for analysis of friction between the planes under the periodic change of normal force is established. The calculation model of the plate’s displacement amplitude distribution considering the change frequency of normal force is verified and modified by experiments. The research results mainly show two aspects. On the one hand, the calculation model of the displacement amplitude distribution of the plate is in good agreement with the experimental results, which can effectively help to study the effect of periodic change of normal force on sliding friction between the planes. On the other hand, the change of amplitude and frequency of the normal force have an influence on the sliding friction between the planes. That is, the latter decreases with the increase of the former. The above conclusions have great reference significance for the study of vibration drag reduction in engineering production.

Experimental, comparative and statistical study of heat transfer and drag reduction of Water/Polyisobutylene/nanoSiO2 poly-nanofluid through a horizontal pipe

Turbulent flow of fluid samples (polymeric solution, nanofluid and Poly-nanofluid (PNF)), into a horizontal pipeline was investigated to achieve heat transfer properties and drag reduction. Water, Polyisobutylene (PIB) and nanoSiO2 were the materials used in this study. PNFs prepared by dispersing SiO2 nanoparticles (with concentration range of 0.1–1 wt.%) into dilute Water/PIB solution (with concentration range of 10–50 ppm). The effect of polymer and nanoSiO2 presence on heat transfer properties such as convective heat transfer coefficient and Nusselt number were evaluated and Reynolds number changes were studied in this research. At the same time the effect of concentration and Reynolds number on the Nusselt number and drag reduction evaluated by utilizing a statistical method called analysis of variance (ANOVA).

Numerical study of frictional drag reduction using micro-bubbles in a vertical Couette-Taylor system

In this work, we numerically study the reduction of frictional drag in a vertical Couette-Taylor system by using micro-bubbles. The silicon flow is in the annular gap between two concentric cylinders as the internal cylinder is rotating while the outer cylinder is stationary. Taylor vortices are formed between the cylinders and the rotational Reynolds number also varies from 700 to 4500. The carrier flow is silicone while air bubbles are constantly injected into the carrier phase at the bottom of cylinders and rise through the flow. By employing a discrete phase model and Euler-Lagrange approach, we investigate a two-phase turbulent flow. In this way, we study the distribution of the bubbles through the flow, which is acquired using numerical modeling. Our numerical results are in good agreement with the experimentally reported data for different values of Reynolds numbers. We also investigate the effect of injected air with a constant flow rate on the skin friction drag and on the drag coefficient ratio. Our numerical results illustrate a reduction of drag about 36% when microbubbles are injected into the system. This reduction can be achieved by the effect of the bubbles on the density of the fluid and transformed momentum.

Trailing-edge noise reduction potential of a locally applied shallow dimpled surface

There is a strong need for airframe noise reduction methods that preserve the aerodynamic performance of lift-generating airframe components. Inspired by the drag reduction studies of van Nesselrooij et al. (2016) and Spalart et al. (2019), the current study explored the trailing-edge noise reduction potential of shallow dimples applied near the trailing edge of a NACA0012 airfoil (approximately the latter 18% of the chord). The effect of shallow dimples on the aerodynamic coefficients is studied by Reynolds Averaged Navier–Stokes (RANS). To investigate the noise reduction credentials of dimples, high-fidelity Overset-Large Eddy Simulations are carried out for a chord based Reynolds number Rec of 4.2 ×105 at zero angle of attack. Near-field analysis revealed that this local application of dimples eliminated the tonal vortex shedding noise, which is otherwise present in the reference configuration without dimples. Furthermore, the application of shallow dimples resulted in the breakdown of the span-wise coherence in the low-to-mid frequency range and a reduction in the convective velocity of the stream-wise convecting eddies. These effects have a favourable impact on the trailing edge noise reduction with a modest 1.8% increase in the overall drag (less than 1 drag count). The far-field sound characteristics revealed that the dimple treatment resulted in the reduction of overall sound pressure levels in the downstream radiation direction (≈ 5.5 dB) and an increase in the upstream radiation direction (≈ 3.5 dB). In a nutshell, this manuscript argues for the inclusion of shallow dimples to the list of potential candidates for passive noise reduction methods, such as serrations, porous materials, and finlets.

Development of eddy viscosity measurement system utilizing velocity profiler

We propose a novel turbulent eddy viscosity profiler to evaluate the influence of interactions between turbulent eddies and dispersed materials as an effective eddy viscosity in Taylor-Couette geometry for frictional drag reduction studies. This method was conceived from the ultrasonic spinning rheometry which evaluates rheological properties by substituting experimentally obtained velocity profiles into the equation of motion. The eddy viscosity is calculated using a model derived from Reynolds-averaged Navier-Stokes equation. By modeling the Reynolds shear stress using the concept of the eddy viscosity, only the spatial distribution of the eddy viscosity remains to be estimated from the mean velocity distribution. We can extract the contributions of eddies with different time and spatial scales depending on the definition of the averaging operation, since mean velocity profiles include the information of momentum transfer by eddies which have the specific time and spatial scales. In this paper we derive the analytical model equation where velocity profile is averaged in temporal and axial directions and the molecular viscosity term balances with the eddy viscosity term. In this case, we can separate the original flow field into Couette-like mean velocity and fluctuation components corresponding to Taylor vortices and smaller fluctuations. Additionally, we show the experimental apparatus and the result for a glycerin aqueous solution using the equation with the above averaging operation. The distribution of eddy viscosity is obtained as a function of radial position.

A Study of Drag Reduction on Cylinders with Different V-Groove Depths on the Surface

In this study, the drag reduction effect is studied for a cylinder with different V-groove depths on its surface using a k-ω/SST (Shear Stress Transport) turbulence model of computational fluid dynamics (CFD), while a particle image velocimetry (PIV) system is employed to analyze the wake characteristics for a smooth cylinder and a cylinder with different V-groove depths on its surface at different Reynolds numbers. The study focuses on the characteristics of the different V-groove depths on lift coefficient, drag coefficient, the velocity distribution of flow field, pressure coefficient, vortex shedding, and vortex structure. In comparison with a smooth cylinder, the lift coefficient and drag coefficient can be reduced for a cylinder with different V-groove depths on its surface, and the maximum reduction rates of lift coefficient and drag coefficient are about 34.4% and 16%, respectively. Otherwise, the vortex structure presents a complete symmetry for the smooth cylinder, however, the symmetry of the vortex structure becomes insignificant for the V-shaped groove structure with different depths. This is also an important reason for the drag reduction effect of a cylinder with a V-groove surface.

Numerical study of air layer drag reduction of an axisymmetric body in oscillatory motions

Numerical study of air layer drag reduction of an axisymmetric body in oscillatory motions

A study of drag reduction with textile roughness on a cyclist model

Efforts were made to examine the effect of textile roughness for the reduction of aerodynamic drag experienced on a cyclist model. First of all, flow visualization experiments were conducted in a water channel with a 1/5 scale cyclist model to identify the flow separation lines on the contoured surface. Subsequently, based on the information learned, the idea of delaying flow separation on the model surface was implemented by means of sport suits. Seven sport suits featuring different textile materials and local roughness patterns were tested on a full-scale cyclist model in wind tunnel experiments, in addition to a reference case without a sport suit. From the CD data deduced, we identified a critical condition in most of the cases studied, featuring a least drag coefficient occurred at a Reynolds number within the flow speed range studied. For the best case found, the drag coefficient is amounted 7.5% less than that of the reference case at the same Reynolds number. Furthermore, the Cp and Cprms values reduced from the pressure measurements on the cyclist model with the sport suits unveil a trend that the reduction of drag actually infers the retreat of the local flow separation lines toward the rear side of the body accompanied with less severe the flow unsteadiness.

Thriving artificial underwater drag-reduction materials inspired from aquatic animals: progresses and challenges.

In the past decades, drag-reduction surfaces have attracted more and more attention due to their potentiality and wide applications in various fields such as traffic, energy transportation, agriculture, textile industry, and military. However, there are still some drag-reduction materials that need to be deeply explored. Fortunately, natural creatures always have the best properties after long-term evolution; aquatic organisms have diversified surface microstructures and drag-reducing materials, which provide design templates for the development of thriving artificial underwater drag-reduction materials. Aquatic animals are tamed by the current while fighting against the water, and thus have excellent drag reduction that is unparalleled in water. Inspired by biological principles, using aquatic animals as a bionic object to develop and reduce frictional resistance in fluids has attracted more attention in the past few years. More and more aquatic animals bring new inspiration for drag-reduction surfaces and a tremendous amount of research effort has been put into the study of surface drag-reduction, with an aim to seek the surface structure with the best drag-reduction effect and explore the drag-reduction mechanism. This present paper reviews the research on drag-reduction surfaces inspired by aquatic animals, including sharks, dolphins, and other aquatic animals. Aquatic animals as bionic objects are described in detail, with a discussion on the drag-reduction mechanism and drag-reduction effect to understand the development of underwater drag-reduction fully. In bionic manufacturing, the effective combination of various preparation methods is summarized. Moreover, bionic surfaces are briefly explained in terms of traffic, energy sources, sports, and agriculture. In the end, both existing problems in bionic research and future research prospects are proposed. This paper may provide a better and more comprehensive understanding of the current research status of aquatic animals-inspired drag reduction.