Decrease In Drag Coefficient Research Articles

Enhancing Aerodynamic Performance of Double Rectangular Cylinders through Numerical Analysis at Varying Inclinations

In the present work, numerical simulations are conducted for external flow through a double rectangular cylinder with different inclinations at Reynolds number (Re) 50 to 200 based on free stream velocity. The cylinder aspect ratio is considered to be fixed at 0.25. During the numerical simulations, one cylinder is kept fixed, and the other cylinder is inclined at ‘θ = 20o’ first clockwise and then in an anticlockwise direction alternatively for both cylinders. Because of the inclined cylinder, the vortex dynamics lead to significant changes in flow-induced forces. In this article, the focus is given to how Re and inclination in the cylinder influence the flow structures and associated aerodynamic properties. It is shown that when any of the cylinders are inclined, a significant decrease in the average drag coefficient is noticed as compared to the parallel cylinder case. In a similar manner, the lift coefficient also decreases when any one of the cylinders is inclined at θ = 20o either clockwise or counterclockwise as compared to the parallel cylinder case.

Effect of wettability and surface roughness on flow and heat transfer characteristics in nanochannels

The flow and heat transfer processes of liquid argon within nanochannels with random roughness are investigated using the molecular dynamics method. This study explores the effects of surface roughness and wettability on flow and heat transfer performance. The results indicate that both surface roughness and wettability significantly influence temperature jumps, velocity slip, flow resistance, and temperature distribution. Specifically, hydrophilic surfaces can reduce temperature jumps and velocity slip due to their enhanced ability to adsorb liquid atoms, which effectively improves heat transfer while simultaneously increasing flow resistance. The fractal dimension D characterizes the surface roughness, which decreases as D increases. Additionally, both the Nusselt number and drag coefficient decrease with increasing D. In this study, we investigate cases where D ranges from 2.5 to 2.9, with D = 2.5 representing the highest roughness, and the smooth channel corresponding to the lowest roughness. For hydrophilic nanochannels at D = 2.5, the Nusselt number and drag coefficient increased by factor of 2.2 times and 5.2 times compared to smooth channels, respectively. For hydrophobic nanochannels at D = 2.5, the Nusselt number and drag coefficient increased by a factor of 4.5 times and 29.1 times compared to smooth surface channels, respectively. Considering both flow and heat transfer performances, the best comprehensive performance is achieved with D = 2.8 for channels with hydrophilic surfaces and D = 2.6 for channels with hydrophobic surfaces. This work systematically investigates the coupled effects of random roughness and wettability on the flow and heat transfer characteristics in nanochannels, providing new theoretical insights for optimizing nanochannel design.

Exploring Near-Wake Structures: Bio-Inspired Convergent-Divergent Riblets on Circular Bluff Bodies

Abstract Convergent-divergent (C-D) riblets represent a pioneering rough surface inspired by the skin of fast-swimming sharks and flight feathers of the birds. In this study, we applied convergent-divergent riblets to the outer surface of a circular cylinder to examine their influence on the near-wake flow structure behind the cylinder. Various experimental techniques, such as particle image velocimetry (PIV), hot-wire anemometer, and a load cell for force measurement, were employed for this study. The experimental measurements have been conducted at different Reynolds numbers ranging from (6–12) ×103. The findings from force measurement indicate a decrease in the mean drag coefficient of around 14%, 15%, 11%, and 12% obtained by riblets at Re = 6000, 7500, 10,000, and 12,000, respectively. The time-averaged flow field including streamlines, velocity field, Reynolds shear stress, vorticity, and turbulent kinetic energy were measured. The measurements suggest that the wake's size has decreased by using convergent-divergent riblets. Furthermore, data obtained from the hot-wire anemometer reveal that these riblets alter the vortex shedding frequency to a higher value and impact the amplitude peak of the power spectrum at various Re numbers.

Analysis of the temperature-dependent plastic deformation of single crystals of quinary, quaternary and ternary equiatomic high- and medium-entropy alloys of the Cr-Mn-Fe-Co-Ni system

ABSTRACT Temperature-dependent plastic deformation behaviors of single crystals of quaternary and ternary equiatomic medium-entropy alloys (MEAs) belonging to the Cr-Mn-Fe-Co-Ni system were investigated in compression at temperatures in the range 9 K to 1373 K. Their critical resolved shear stresses (CRSSs) increase with decreasing temperature below room temperature. There is also a dulling of the temperature dependence of CRSS below 77 K due to dislocation inertial effects that we attribute to a decrease in the phonon drag coefficient. These behaviors were compared with those of previously investigated single crystals of the equiatomic Cr-Co-Ni and Cr-Fe-Co-Ni MEAs, and the equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy (HEA). The temperature dependence of CRSS and the apparent activation volumes below room temperature can be well described by conventional thermal activation theories of face-centered cubic (FCC) alloys. Above 673 K, there is a small increase in CRSS, which we believe is due to elastic interactions between solutes and mobile dislocations, the so-called Portevin-Le Chatelier (PL) effect. The CRSS at 0 K was obtained by extrapolation of fitted CRSS vs. temperature curves and compared with predictions from solid solution strengthening models of HEA and MEAs.

Water transport across the membrane of a direct toluene electro-hydrogenation electrolyzer: Experiments and modelling

Toluene/methylcyclohexane is a promising liquid organic hydride for hydrogen storage and transport under ambient conditions. Direct toluene electro-hydrogenation electrolyzers, utilizing proton exchange membrane technology, offer benefits in reducing the reversible decomposition voltage and eliminating theoretical heat losses associated with conventional hydrogenation methods. Nevertheless, water transport across the membrane can inhibit the supply of toluene to reaction sites at the cathode. This study investigates water transport across the Nafion™ 117 membrane of an in-house electrolyzer cell, employing sulfuric acid and toluene solutions as the anode and cathode reactant, respectively, and operating at current densities from 0.1 to 0.8 A/cm2. The experiments show that the cathode toluene concentration has a negligible effect on drag water, while water flux increases with electric current and decreases with higher anode sulfuric acid concentrations. The modelling approach assumes electro-osmosis and diffusion mechanisms govern water transport. Simulations predict a linear decrease in the electro-osmotic drag coefficient from 2.3 to 1.6 as the sulfuric acid concentration rises from 0.1 to 1.5 mol/L, while the back diffusion flux increases linearly up to 2 mg/(min·cm2). These findings closely align with experimental data and previous literature, despite the high complexity of water transport in polymer electrolyte membranes.

Two-phase numerical simulation of thermal and solutal transport exploration of a non-Newtonian nanomaterial flow past a stretching surface with chemical reaction

Abstract Non-uniform heat sources and sinks are used to control the temperature of the reaction and ensure that it proceeds at the desired rate. It is worldwide in nature and may be found in all engineering applications such as nuclear reactors, electronic devices, chemical reactors, etc. In food processing, heat is used to cook such as microwave ovens, pasteurize infrared heaters, and sterilize food products. Non-uniform heat sources are mainly used in biomedical applications, such as hyperthermia cancer treatment, to target and kill cancer cells. Because of its ubiquitous nature, the idea is taken as our subject of study. Heat and species transfer analysis of a non-Newtonian fluid flow model under magnetic effects past an extensible moving sheet is modelled and examined. Homogeneous chemical reaction inside the fluid medium is also investigated. This natural phenomenon is framed as a set of Prandtl boundary layer equations under the assumed convective surface boundary constraint. Self-similarity transformation is employed to convert framed boundary layer equations to ordinary differential equations. The resultant system is solved using the efficient finite difference utilized Keller box method with the help of MATLAB programming. The influence of various fluid-affecting parameters on fluid momentum, energy, species diffusion and wall drag, heat, and mass transfer coefficients is studied. Accelerating the Weissenberg number decelerates the fluid velocity. The temperature of the fluid rises due to variations in the non-uniform heat source and sink parameters. Ohmic dissipation affects the temperature profile significantly. Species diffusion reduces when thermophoresis parameter and non-uniform heat source and sink parameters vary. The Eckert number enhances the heat and diffusion transfer rate. Increasing the chemical reaction parameter decreases the shear wall stress and energy transmission rate while improving the diffusion rate. The wall drag coefficient and Sherwood number decrease as the thermophoretic parameter increases whereas the Nusselt number increases. We hope that this work will act as a reference for future scholars who will have to deal with urgent problems related to industrial and technical enclosures.

Dynamic feature-based deep reinforcement learning for flow control of circular cylinder with sparse surface pressure sensing

This study proposes a self-learning algorithm for closed-loop cylinder wake control targeting lower drag and lower lift fluctuations with the additional challenge of sparse sensor information, taking deep reinforcement learning (DRL) as the starting point. The DRL performance is significantly improved by lifting the sensor signals to dynamic features (DFs), which predict future flow states. The resulting DF-based DRL (DF-DRL) automatically learns a feedback control in the plant without a dynamic model. Results show that the drag coefficient of the DF-DRL model is 25 % less than the vanilla model based on direct sensor feedback. More importantly, using only one surface pressure sensor, DF-DRL can reduce the drag coefficient to a state-of-the-art performance of approximately 8 % at Reynolds number $(Re) = 100$ and significantly mitigates lift coefficient fluctuations. Hence, DF-DRL allows the deployment of sparse sensing of the flow without degrading the control performance. This method also exhibits strong robustness in flow control under more complex flow scenarios, reducing the drag coefficient by 32.2 % and 46.55 % at $Re =500$ and 1000, respectively. Additionally, the drag coefficient decreases by 28.6 % in a three-dimensional turbulent flow at $Re =10\,000$ . Since surface pressure information is more straightforward to measure in realistic scenarios than flow velocity information, this study provides a valuable reference for experimentally designing the active flow control of a circular cylinder based on wall pressure signals, which is an essential step toward further developing intelligent control in a realistic multi-input multi-output system.

Parameterization scheme of the sea surface drag coefficient considering the influence of wave states and sea spray stress

The drag coefficient of the sea surface is crucial for the exchange of momentum between the ocean and atmosphere. The wave state significantly influences the variability of the drag coefficient. In the past, researchers commonly employed single-parameterization methods to describe this influence. However, the influence of wave conditions on drag coefficient is complex and variable, and it is difficult to accurately describe it with a single parameter alone. Wave age represents the ability of wind-induced waves to input energy, while wave steepness reflects the stability of the waves. By simultaneously considering wave age and wave steepness, a more accurate characterization of the dynamic nature of waves can be achieved. Additionally, the presence of sea spray profoundly impacts the distribution of the momentum flux between the ocean and atmosphere, thereby influencing the drag coefficient of the sea surface. In this study, we established a novel sea spray generation function that bases on both the wind speed and wave states (wave steepness and wave age). Considering this function, the momentum flux of sea spray droplets was analyzed under different wave states. Moreover, with increasing wave age or wave steepness, the effective sea surface drag coefficient is attenuated at low to moderate wind speeds. Considering the challenge of simultaneously obtaining wave age and wave steepness data, this paper proposes a relationship equation between the two wave state parameters. When the wave age is greater than 0.4, the correlation between the wave age and the wave steepness is strong. As the wind speed increases from low to high, there is a noticeable decrease in the effective sea surface drag coefficient with the corresponding increase in wave age. When the wave age is less than 0.4, the wave steepness reaches a maximum value, and the effective sea surface drag coefficient increases with the increase of the wave age at medium and low wind speed. With further increases in wind speed, the momentum flux derived from the air also increases. Simultaneously, the effective sea surface drag coefficient exhibits a decrease as wave age increases.

An Effect of Gap Ratios at Four Circular Cylinders in a Staggered Configuration Near a Plane Wall

The flow that crosses the arrangement of four circular cylinders will form a certain flow pattern according to the geometry of the body contour, the distance between the cylinders, and the flow orientation (α), and generated aerodynamic forces, such as lift force, drag force, as well as induced vibration on the body. The force coefficients on four circular cylinders in an equispaced arrangement with a staggered configuration located near a plane wall were calculated through the pressure distributions measurement. The pressure distributions on each cylinder surface and the plane wall were measured for various gap ratio values of G/D= 0.0 and 0.2 (G, the gap between cylinder to the plane wall; D, diameter) and L/D= 2.7 (L, gap spacing between cylinders) in a uniform flow at a Reynolds Number of 1.743 x 104. The results show that the drag and lift coefficients on the cylinders depend on the gap ratio value of G/D. The drag coefficient decreases, when the amount of G/D increases, especially on the upstream cylinders. The lift coefficient on the upper-downstream cylinders has a significant value more than other cylinders at a small spacing ratio.

Aerodynamic Performance Enhancement of Low Aspect Ratio Military Drone Aircraft Wing through Employing Leading Edge Tubercles

Present study aim to improve the aerodynamic performance of low Aspect Ratio (AR) military drone aircraft wing, through employing leading edge tubercle. For that purpose two wing model were design one with smooth leading edge and second with tubercle leading edge. The wing models were developed by using NACA0012 airfoil profile, whereas tubercles of amplitude 5% of chord (c) and wavelength of 11% of c is employed. The numerical simulation as performed at chord based Reynolds number of 140000 in pre-stall and post stall regime. The computational fluid dynamic simulation is performed at different angle of attack ranging from 0 degree to 25 degree with the interval of 5 degree. Computational Fluid Dynamics (CFD) results reveal that tubercle at the leading edge of the low AR wing has favorable effect on the wing performance. Aerodynamic performance of both smooth leading edge and tubercle leading edge wing is similar up to 15o angle of attack, whereas at 20 degree and 25 degree significant improvement in Lift-to-Drag L/D ratio is observed. It is estimated that at maximum increment of 53% in lift coefficient ii achieved at 25 degree angle of attack for as compared to smooth LE wing model. Moreover, maximum 20.5% decrease in drag coefficient is estimated in case of tubercle leading edge as compared to baseline model at 20 degree angle of attack. The critical observation of field around the tubercle leading edge wing is found that tubercles restrict flow separation through generation of low strength vortices; these vortices enhance momentum exchange within the boundary layer.

Influence of cylinder rotation in close to a free surface on flow characteristics

This study investigates the numerical simulation of unsteady flow over a rotating circular cylinder near a free surface using the Volume of Fluid (VOF) method. The hydrodynamic characteristics and flow pattern are analyzed for various Froude numbers (0.3, 0.55, and 1), submergence depths (0.4, 0.6, and 1), and rotation rates (±0.5, ±1, and ±2). The results indicate that both the rotation direction and rate significantly influence flow instability. Counterclockwise rotation reduces free surface instability and drag coefficient. At a rotation rate of 2, the average drag coefficient decreases by 93% compared to a stationary cylinder at Froude number 0.3. Clockwise rotation induces free surface instability and increases the lift and drag coefficients. Higher Froude numbers result in more significant free surface variations, and increased submergence depth leads to stretched vortices.

Numerical Simulation of Aerodynamic Characteristics of Electric Vehicles with Battery Packs Mounted on Chassis

Aerodynamic characteristics are of great significance to the fuel economy and handling the stability of electric vehicles. The battery pack of electric vehicles has a huge structure and is usually arranged in the chassis area of the vehicle, which inevitably occupies the space at the bottom of the vehicle and affects the aerodynamic characteristics of the vehicle. To study the effect of the power battery pack installed in the chassis on the aerodynamics characteristics of the electric vehicle, the Computational Fluid Dynamics (CFD) method is used to study the flow and pressure fields of the SAE (Society of Automotive Engineers) hierarchical car model with battery packs mounted on chassis. The influence of the structure parameters of the battery pack on the automobile’s aerodynamics are also analyzed in detail. Based on the simulation results, it can be seen that the battery pack installed on the chassis has a great impact on the flow and pressure field at the bottom and tail of the vehicle, causing the drag coefficient and lift coefficient to increase. The structural parameters of the battery pack have contradictory effects on the drag and lift coefficients. As the length of the battery pack increases, the drag coefficient decreases, and the lift coefficient increases. As the battery pack width and height increase, the drag coefficient increases, and the lift coefficient decreases. The research results provide a reference for the optimization of the aerodynamic characteristics of electric vehicles with battery packs mounted on chassis.

A numerical study on the benefits of passive-arc plates on drag and noise reductions of a cylinder in turbulent flow

In this study, we introduce a novel arrangement consisting of two arc plates around a cylinder with the privilege of improved fluid flow and noise control. The arc plates are placed symmetrically and concentrically at the rear portion of a circular cylinder. The coverage angle (30 °≤β≤75°) of the plates and the normalized radius of arc plates (1.125≤Rd≤1.625) are varied to find the optimum case in terms of drag and noise reductions. The simulations are performed for a turbulent flow with a Reynolds number of 22 000. The numerical analysis is based on an unsteady Reynolds-averaged Navier–Stokes (URANS) solver and Ffowcs Williams and Hawkings (FW–H) acoustic analogy. It is found that by implementing the arc plates, the noise level and drag coefficient decrease dramatically. The results also reveal a strong correlation between the vortex shedding suppression and the noise reduction. It is shown that as the fluctuation of lift force decreases, the performance of flow and noise control enhances simultaneously. Furthermore, the noise assessment indicates that in a specific configuration of the arc plates, the overall sound pressure level decreases by around 51 dB compared to the uncontrolled case with no arc plates. Also, a maximum noise reduction of 27 dB is achieved, in which the drag coefficient reduces by 39% compared to the case with no arc plates. In conclusion, the results provide strong support for the proposed passive method as a beneficial strategy for noise reduction and wake control of cylindrical structures, which have wide applications in industry.

Interaction of Two Rigid Spheres Oscillating in an Infinite Liquid under the Control of a Magnetic Field

The transient creeping motion of two rigid spheres oscillating in a boundless viscous fluid beneath the impact of the magnetic field is investigated. There is no slippage associated with a Stokes flow on the two rigid spherical surfaces with different sizes and radii. The solutions can be obtained using the boundary collocation scheme at low Reynolds numbers. The unsteady real and imaginary drag coefficients are estimated on the hard spherical particles. These coefficients are computed in tables for various parameters and illustrated graphically. The frequency parameter and Hartmann number also play a significant role in this study where the drag coefficients decrease or increase by 100 percent after the value of κ = 5.0 . Using available literature data, we tested the accuracy and reliability of our results.

Numerical investigation of aerodynamic performance of an axial fan blade equipped with vortex generators

Delay in the onset of static stall via passive vortex generators (VGs) results in more efficient equipment. Nevertheless, most studies of VGs are conducted on wind turbine blades rather than other turbomachinery devices like axial fan blades. This study is feasibility research to see whether the aerodynamic performance of axial fan blades improves in the presence of VGs. Therefore, the VGs' effect of a static blade with an elliptical profile having a maximum thickness of 8% chord length and without a twist angle is investigated. Fully resolved RANS (Reynolds-averaged Navier–Stokes) simulation with the shear stress transport k–ω turbulence model at Re = 1 × 105 is used to discover the blade flow characteristics with VGs for two types of fan, eight and twelve blades. It is shown that, in both fans, not only can implementing VGs improve the aerodynamic performance of the blade effectively but also the separation phenomenon is delayed. Furthermore, it is concluded that installing VGs performed better in the 8-blade fan, with up to a 3° separation delay, a 9.88% increase in the maximum lift coefficient, and a 48.15% decrease in the maximum drag coefficient with respect to the clean blade. Analyzing the aerodynamic performance of real axial fans considering rotary blades with twist angles equipped with VGs will be feasible in future research.

Experimental and Artificial Neural Network (ANN) Modeling of Instream Vegetation Hydrodynamic Resistance

This study examines the impact of upstream structures on the bulk drag coefficient of vegetation through experimental means, which has not been previously conducted. An embankment model was placed upstream of the vegetation, both with and without a moat/depression. The results showed that the presence of an upstream structure reduced the bulk drag coefficient of vegetation as the structure shared the drag. When only the embankment was placed upstream, a maximum decrease of 11% in the bulk drag coefficient was observed. However, when both the embankment and moat models were placed upstream, a 20% decrease in the bulk drag coefficient was observed. Regression models and artificial neural network (ANN) models were developed to predict the bulk drag coefficient based on the variables affecting it. Five ANN models with different training functions were compared to find the best possible training function, with performance indicators such as coefficient of determination (R2), root mean square error (RMSE), Nash–Sutcliffe efficiency (NSE), sum of square error (SSE), mean absolute error (MAE), and Taylor’s diagrams used to evaluate the model performance. The ANN model with nine neurons in each hidden layer performed the best, achieving the highest R2 and NSE values and the lowest RMSE, SSE, and MAE values. Finally, the comparison between the regression model and the ANN model showed that the best ANN model outperformed the regression models, achieving R2 values of 0.99 and 0.98 for the training and validation subsets, respectively.

An Analysis of Buoyancy-Driven Heat Behaviour and Flow Pattern of a Water-Copper Nanofluid in a Cylindrical Conduit

The flow of fluids and heat characteristics through free convection within an enclosed space has gained substantial study due to the various applications in manufacturing industries. This work examined the influence of buoyancy factors on normal convection in a heated tube filled with Copper (Cu) nanofluid. The method of finite difference was employed to characterize the regulating fluid formulae, and C++ programming language was employed to evaluate the Navier Stoke and continuity fields. This study examined Cu nanoparticles with particle sizes ranging from 1% to 10% and buoyancy values between 2.6 x 103 and 2.8 x 103 N. Cu nanofluid was used as the working fluid and the findings are presented as temperature gradient, Nusselt number, stream function, and vorticity curves. The findings revealed that an increase in the weight proportions of nanoparticles to 0.04 amplifies the buoyancy parameters to the highest value of 2.75 x 103 N; it yields a substantial enhancement in the heat transport rate by convection. Also, as the buoyancy factor increases, the temperature gradient, vorticity, and stream function of the nanofluid improve, while the local drag coefficient decreases. This study advances the understanding of buoyancy-driven convective flow and heat behavior in the technical design of floating vessels for safety and effectiveness.

A New Flow Control Method of Slat-Grid Channel-Coupled Configuration on High-Lift Device

A slot formed between the slat and the main wing of the 2D high-lift device is used to accelerate the convergence of the flow to the upper surface of the main wing to improve the flow field quality. In order to further enhance flow characteristics, this paper proposes a design method for multi-channel leading-edge slats based on grid flow channels. On the one hand, a specific shape of a shrinking expansion tube is formed to improve the lift characteristics of the leading slat. On the other hand, the newly formed slot plays a similar role to that of the jet stream, delaying the separation on the upper surface of the main wing, making the separation point move back and helping to improve the lift characteristics of the main wing. The optimization of coupled slat-grid channel configuration is developed by using the DOE algorithm. The geometric parameters, such as coordinates and curve slope, are considered as design variables, and the maximum lift–drag ratio is taken as the optimization objective required to obtain the optimal configuration. The simulation and optimization results show that the lift coefficient increases by 3.3%, the drag coefficient decreases by 12.7%, and the lift–drag ratio increases by 18.4% of the optimal configuration compared with the original airfoil at an angle of attack of 16.3°.

EXPERIMENTAL OPTIMIZATION OF AERODYNAMIC DRAG COEFFICIENT OF A MINIBUS MODEL WITH NON-SMOOTH SURFACE PLATE APPLICATION

In this study non-smooth surface plate application was experimentally investigated to flow control around a scaled minibus model in a wind tunnel. 1/15 scaled minibus model and non-smooth surface plate were designed in SolidWorks® Cad program and produced in 3-D printer. It was focused on decrease of drag coefficient of vehicle with non-smooth surface plate by reducing flow separation. The experimental tests carried out 4 free stream velocities between the speed of 13.90-27.40 m/s and 2.62x105-5.18x105 Reynolds numbers. In wind tunnel tests Reynolds number independence was used to ensure dynamic similarity. The blockage rate was 10.68 %. It was determined that the using of non-smooth surface plate e on the front roof area of minibus model decreased to drag coefficient by an average of 1.03%. This reduction rate can decrease fuel consumption of vehicle about 0.5% at high speeds.

UTCartによる民間航空機巡航形態の実機レイノルズ数定常流れ場解析

To verify the applicability of UTCart (a compressible flow solver based on the hierarchical Cartesian grid method) to high Reynolds number flows, a flow field analysis around a commercial airliner at cruise was conducted. The analysis is performed in the range of Reynolds number from that in general wind tunnel tests to the flight Reynolds number, and the reproducibility of the Reynolds number effect is verified through comparison with the results in the high Reynolds number wind tunnel tests. The simulations were able to reproduce the Reynolds number effects (lift coefficient increase and drag coefficient decrease, etc.) observed in the wind tunnel tests.