Higher Drag Coefficient Research Articles

Height Control System for Wind Turbines Based on Critical Wind Speed Calculation

The increasing frequency of wind turbine failures due to extreme weather conditions necessitates the implementation of new solutions to enhance their operational reliability. This paper presents an automatic rotor drop system specifically designed for wind turbines equipped with the Onipko rotor. The system aims to protect turbines from damage caused by critical wind speeds, reducing maintenance costs and extending the equipment’s lifespan. The unique design of the Onipko rotor allows it to operate at wind speeds as low as 0.1 m/s. However, its high drag coefficient and lack of aerodynamic optimization make it susceptible to mechanical stress and structural instability under strong gusts, requiring additional protective measures. The paper presents a calculation of the critical wind speed at which protective measures must be initiated. Through mathematical modeling, this study demonstrates the effectiveness of the rotor drop system in ensuring safe operation at wind speeds reaching 23.5 m/s. The optimization of the PI controller parameters provides a rapid response and stability, significantly enhancing the resilience of wind turbines to adverse weather conditions.

Influence of rotating wheels on Reynolds number sensitivity of passenger vehicle drag

Rotating wheels are essential to replicate realistic forces and flow fields during aerodynamic testing of passenger vehicles. Previous studies have found that the drag coefficient typically reduces with increased speed under rotating wheel conditions but is stable with stationary wheels. This paper investigates this velocity sensitivity for two vehicles, the aerodynamic research vehicle DrivAer and a production vehicle. Experiments with the DrivAer indicate that the drag reduction with increased speed cannot be explained by pressure changes on the vehicle body; instead, the effect is attributed to local flow changes around the wheels. Using numerical simulations, it is found that the separation at the front wheels' outer tire shoulder increases for lower velocities, thus resulting in higher drag coefficient and causing Reynolds number sensitivity. The degree of drag reduction is less for the DrivAer squareback than for the notchback due to the separation over the notchback's rear window. No direct difference is measured between various tires and rims. To assess the generality of the findings with the DrivAer, the results are compared to experiments with a production vehicle. It is observed that the drag sensitivity is less and only occurs if the rear wheels are rotating. Pressure measurements in the wheelhouses and around the wheel drive units confirm the front wheel separation's dependence on velocity and highlight the complex interaction between the front wheel wakes and rear wheel rotational state.

Study on the Hydrodynamic Performance of the Beam Used in the Antarctic Krill Beam Trawl

The beam trawl is one of the primary operational trawls for Antarctic krill, and its beam provides horizontal expansion support for the trawl net. The hydrodynamic performance of the beam significantly affects the vertical expansion and sinking performance of the trawl, as well as impacts the energy consumption of the fishing vessel. In this study, the beam of the Antarctic krill trawl used on the “Shen Lan” fishing vessel served as a prototype. Three types of beams, cylindrical, airfoil, and elliptical, were designed. The hydrodynamic performances of beams with different shapes at different angles of attack were studied using numerical simulation, and the accuracy of the numerical simulation was validated through the flume test. The results show that the cylindrical beam has a higher drag coefficient and a lower lift coefficient, compared to the airfoil beam and the elliptical beam. Under different angles of attack, the cylindrical beam’s drag coefficient is, on average, 49.54% higher than that of the airfoil beam and 59.74% higher than that of the elliptical beam. Its lift coefficient is 87.79% lower than that of the airfoil beam and 85.06% lower than that of the elliptical beam, respectively. At different angles of attack, the hydrodynamic coefficients of the airfoil beam and the elliptical beam are similar, and their trends, with respect to the angle of attack, are generally consistent. The drag coefficients increase with an increasing angle of attack, while the lift coefficients show a trend of initially increasing and then decreasing with an increasing angle of attack. The absolute values of the lift coefficients for the airfoil beam and the elliptical beam both reach their maximum values at an angle of attack of 45°, with values of 0.703 and 0.473, respectively. Compared to the cylindrical beam, the hydrodynamic performances of the airfoil beam and elliptical beam are superior.

CFD simulations for layout optimal design for ground-mounted photovoltaic panel arrays

Photovoltaic (PV) power plants play an important role in regulating regional energy structures and reducing carbon emissions. The existence of PV power plants also alters the microclimate in surrounding environments, which requires an optimal design of their layout and structural parameters. PV power plants consist of arrays of ground-mounted PV panels. In this study, 3D computational fluid dynamics (CFD) simulations based on the shear-stress transport k–ω turbulence model were performed to study airflow around ground-mounted PV panel arrays. The accuracy of the CFD model was validated by comparing the simulated results with field data. Different scenarios were established by changing the wind velocity, arrangement of PV panel arrays (i.e., row and column spacing), and key structural parameters (i.e., panel inclination angle). The results showed that the highest drag coefficient (CD) and lift coefficients (CL) were found behind the first row of the arrays for straight winds (0° and 180°), while the minimum wind loads (lift and drag) are encountered by the middle of the array for oblique winds (45° and 135°). According to the wind resistance effect, the PV panel array with an inclination angle of 35°, a column spacing of 0 m, and a row spacing of 3 m had the best efficiency of wind block. As the increase of ambient wind velocity, the inclination angle should be reduced to rise the resistance efficiency and avoid possible damage to PV panels. This study provides scientific reference for an optimal design and construction of PV power plants in terms of wind resistance.

Tuning and Coupling Irreversible Electroosmotic Water Flow in Ionic Diodes: Methylation of an Intrinsically Microporous Polyamine (PIM-EA-TB).

Molecularly rigid polymers with internal charges (positive charges induced by amine methylation) allow electroosmotic water flow to be tuned by adjusting the charge density (the degree of methylation). Here, a microporous polyamine (PIM-EA-TB) is methylated to give a molecularly rigid anion conductor. The electroosmotic drag coefficient (the number of water molecules transported per anion) is shown to increase with a lower degree of methylation. Net water transport (without charge flow) in a coupled anionic diode circuit is demonstrated based on combining low and high electroosmotic drag coefficient materials. The AC-electricity-driven net process offers water transport (or transport of other neutral species, e.g., drugs) with net zero ion transport and without driver electrode side reactions.

Airborne dust-induced performance degradation in NREL phase VI wind turbine: a numerical study

ABSTRACT The meteorological conditions markedly affect the energy efficiencies and cost/power rate of the wind turbines. The dusty environment is common in arid windy areas and airborne particles generally degrade wind turbine performance. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine has been designed to be insusceptible to surface roughness, a consequence of facing dusty winds. This study numerically investigates the wake flow topology and analyses the performance of this turbine for either clean or dusty air. First, the numerical approach is validated against the available experimental data for clean air. Following this, the model is developed into a Lagrangian-Eulerian multiphase approach to comprehensively analyze the effects of the dusty air. The dependence of aerodynamic performance on the wind speed (U ∞ = 5–25 m/s), particle diameter (d p = 0.025–0.9 mm), and angle of attack (AoA = 0°–44°) is investigated. The turbine performance deteriorates acutely for d p ≥ 0.1 mm and post-stall state. As such, the generated power is reduced by 4.3% and 13.3% on average for the air with the d p = 0.05 and 0.9 mm, respectively. The particles change the flow field profoundly, declining the pressure difference between the suction/pressure sides of the blade-airfoil, advancing the boundary layer separation, and strengthening the recirculation zones. The above changes account for a lower lift coefficient and a higher drag coefficient.

Enhancing the Dynamic Stability of Pylons via Their Drag and Lift Coefficients by Finite Volume Method

This study aimed to estimate the drag and lift coefficients of the long-span bridge pylon using the finite volume method (FVM). The k-ω turbulence model was applied to analyze the behavior of wind flow around the pylon, yielding drag and lift coefficient values with an error of 0.98% compared to a previous tunnel experiment. Four recommended cross-sections were proposed to reduce drag and lift forces acting on the pylon, including concave, convex, crossing, and chamfering cross-sections. The finding indicated that drag and lift coefficient decreased for all cross-sections. Cutting edges of concave, convex, and chamfering cross-sections with a ratio ranging from 0.2 to 0.3 has the greatest impact on reducing drag coefficient, while the crossing cross-section with a cutting ratio ranging from 0.2 to 0.25 has the lowest drag coefficient. The maximum reduction in drag and lift coefficients were 23.69% and 13.14% for concave and chamfering cross-sections. Thus, cutting edges of cross-sections is an effective method to enhance the aerodynamic stability of the pylon. Additionally, we evaluated drag and lift coefficients for different wind direction angles. The angles of 0, 30, and 90 degrees resulted in the highest drag coefficient, while the angle of 0 degrees and the angle of 90 degrees resulted in the lowest and highest lift coefficient, respectively. This study not only provides recommendations for cross-sections that reduce forces acting on the pylon but also provides the intensity of this reduction through corresponding estimation equations. In conclusion, concave and chamfering cross-sections are the most effective in reducing drag and lift coefficients, or, in other words, increasing the aerodynamic stability of the pylon.

Confined flow past heated square cylinder for various inclination of lateral sides

In the present study, the effect of taper on the lateral sides on fluid flow and heat transfer characteristics on a square cylinder has been analyzed numerically. Two-dimensional simulations have been carried out in the laminar flow regime (Re 100–800) for divergent blockage ratios (ϵ = H/D) and taper angles on the forward and backward sides of the lateral cylinder. Compared to the square cylinder, the forward tapered modification cylinders led to significant total drag reductions, pressure drop, and higher heat dissipation for low Re. The backward taper cylinder illustrates a minor increase in heat dissipation; however, the high drag coefficient and pressure drop penalty cannot be neglected. Moreover, an optimized geometry has been identified as a function of all the parameters. The reduction in blockage ratio has been determined to suppress the vortex shedding for higher Re completely. Results also indicate that the decrease in blockage ratio reduces the critical Re of the domain. The slightly tapered surfaces on either side of the square geometry significantly influence heat transfer and apply to modern industrial electronics and their cooling.

In-situ pressure-preserved coring for deep exploration: Insight into the rotation behavior of the valve cover of a pressure controller

In-situ pressure-preserved coring (IPP-Coring) is considered to be the most reliable and efficient method for the identification of the scale of oil and gas resources. During IPP-Coring, because the rotation behavior of the pressure controller valve cover in different medium environments is unclear, interference between the valve cover and inner pipe may occur and negatively affect the IPP-Coring success rate. To address this issue, we conducted a series of indoor experiments employing a high-speed camera to gain greater insights into the valve cover rotation behavior in different medium environments, e.g., air, water, and simulated drilling fluids. The results indicated that the variation in the valve cover rotation angle in the air and fluid environments can be described by a one-phase exponential decay function with a constant time parameter and by biphasic dose response function, respectively. The rotation behavior in the fluid environments exhibited distinct elastic and gravitational acceleration zones. In the fluid environments, the density clearly impacted the valve cover closing time and rotation behavior, whereas the effect of viscosity was very slight. This can be attributed to the negligible influence of the fluid viscosity on the drag coefficient found in this study; meanwhile, the density can increase the buoyancy and the time period during which the valve cover experienced a high drag coefficient. Considering these results, control schemes for the valve cover rotation behavior during IPP-Coring were proposed for different layers and geological conditions in which the different drilling fluids should be used, e.g., the use of a high-density valve cover in high-pore pressure layers.

Nanostructure-dependent nanobubble drag reduction on NiTi self-adaption surface

Under the inspiration of visualized nanobubbles associated with rugged interface, molecular simulations are performed to study thermally induced phase transition in NiTi shape-memory alloys. The perfect reversibility between the cubic austenite B2 and monoclinic martensitic B19′ phases showed two types of morphological structures in the nanoscale. The nanostructures were established as the wall of the nanochannel, which was used to predict the nanobubble flow behavior in the ternary system. Results indicated that the interface with low-temperature B19′ exhibited attractiveness to trap the nanobubble, resulting in low drag coefficient. Conversely, the interface with high-temperature B2 repulsed the nanobubbles as the bulk one, resulting in high drag coefficient. This study provides foresight to invest in shape memories for nanostructure temperature response, which helps realize nanobubble drag reduction.

SIMULATING THE DRAG REDUCTION MODEL FOR A VEHICLE BY USING VORTEX GENERATOR

Petroleum fuel consign has been lessening at a very high proportion. Almost all automobiles depend upon an IC engine driven by petroleum fuels. As much as the number of automobiles is developing in this modern world, it is obligated to reduce fuel expenditure. One of the ways to do this is to diminish the car's drag. Among a manifold process of reducing drag, using Vortex Generators is one. Delta-shaped vortex generators are used at the rear trunk of the range rover, where the flow separates. K-epsilon turbulent model in ANSYS-Fluent 19.2 software is used to imitate the airflows. This work observed the number and spacing between successive vortex generators based on comparing drag coefficient values. The contours of static pressure and velocity magnitude were also observed for each model. When the vortex generators were attached, the pressure coefficients at the rear trunk began to increase, confirming the increment in back pressure. Hence, the increase in back pressure indicates a reduction in the drag coefficient. It has been found that a combination of 7 vortex generators is the optimum solution. The devices work better at a higher velocity than the lower velocity without affecting vehicle stability. The vortex - 4 model's drag coefficient was found to be significantly lower than that of the standard model vehicle, which is 0.42877. The Base Model of Range Rover (2020) is my sense of humor, the highest drag coefficient. So vortex generators are commonly used on automobile vehicles to prevent downstream flow separation and improve their overall performance by reducing drag.

Numerical Analysis of Slotted Wings Using Fluid-Structure Interaction

For shorter landing and take-off path in airports, the aircrafts should reduce their speed with keeping high lifting force. This paper is to identify solutions to increase the lift force of the wing significantly under several flight scenarios (such as takeoff and landing) using leading-edge slats and their relationship with the dynamic parameters of the aerodynamic wing. The study is performed by the use of ABAQUS 2016 software. The problem is solved for turbulent flow and 2-dimensional composite wing at constant Reynolds’s number of (6.49 × 105) and constant boundary conditions. Various depths have been used for the auxiliary airfoil at constant width and gap. All stresses at the wing base were obtained. The pressure distribution on the airfoil surface was determined, air velocity distribution was tracked over the surface, lift and drag forces and their coefficients were computed. The results show that the highest value of the lift coefficient is 0.489 at the depth (-3 %) of the wing chord, it decreases when the depth of the slat becomes zero %, and the rise returns with increasing depth to (4 %), but it does not reach the maximum value, while the highest drag coefficient was (1.89) at depth (4 %) of the wing chord. The maximum value of Von Mises stress was found at depth of 4 % with value of 1.605 × 105 Pa.

Examination of Twisted Elliptical Tube Heat Enhancement Within the Mixed Convective Zone

Previously, the investigation of the heat transfer performance of twisted elliptical tubes has been restricted to the effects of forced convective conditions without considering the impact of buoyancy conditions. Therefore, this work investigates heat transfer enhancement of twisted elliptical tubes of different pitch lengths at different mixed convective regimes. The model continuity, momentum, and energy equations were solved using the finite volume technique and validated using both analytical and experimental results. Under the variation of Gr and Re, the results show that twisted elliptical tubes are better than smooth elliptical tubes for heat transfer but with a corresponding high drag coefficient. The heat enhancement of 48% was obtained at a twisted pitch length of 200 mm and Re of 2000 as compared to the plain tube. In addition, on the effect of twist pitch length, the results show that the more twisted a tube is the more its Nu and F. This indicates that induced secondary flow by the twist has a high impact on the Nu and F. The results show that heat enhancement of the elliptical tube depends on P, Gr, and Re. Similarly, there is a fluid-thermal-structure interaction interplay in the hydrothermal behavior of elliptical tubes.

Boundary layer hydrodynamics of patchy biofilms

Algal biofilms, ubiquitous in aquatic systems, reduce the performance of engineered systems and alter ecosystem processes. Biofilm morphology is dynamic throughout community development, with patchiness occurring due to periodic sloughing, but little is known about how community level physical structure affects hydrodynamics. This study uses high resolution particle image velocimetry (PIV) to examine spatially explicit turbulence over sparse, uniform and patchy biofilm at turbulent Reynolds numbers. All biofilms increase the near-bed turbulence production, Reynolds shear stress, and rotational flow compared to a smooth wall, and non-uniform biofilms have the greatest increase in these parameters, compared with a uniform or sparse biofilm. However, a higher drag coefficient over uniform biofilm compared with non-uniform biofilm indicates that percent coverage (the amount of area covered by the biofilm) is a useful predictor of a biofilm’s relative effect on the total drag along surfaces, and in particular the effect on ship performance.

High Drag States in Tidally Modulated Stratified Wakes

Abstract Large-eddy simulations (LES) are employed to investigate the role of time-varying currents on the form drag and vortex dynamics of submerged 3D topography in a stratified rotating environment. The current is of the form Uc + Utsin(2πftt), where Uc is the mean, Ut is the tidal component, and ft is its frequency. A conical obstacle is considered in the regime of low Froude number. When tides are absent, eddies are shed at the natural shedding frequency fs,c. The relative frequency is varied in a parametric study, which reveals states of high time-averaged form drag coefficient. There is a twofold amplification of the form drag coefficient relative to the no-tide (Ut = 0) case when lies between 0.5 and 1. The spatial organization of the near-wake vortices in the high drag states is different from a Kármán vortex street. For instance, the vortex shedding from the obstacle is symmetric when and strongly asymmetric when . The increase in form drag with increasing stems from bottom intensification of the pressure in the obstacle lee which we link to changes in flow separation and near-wake vortices.

Bioconvective electromagnetohydrodynamic hybrid nanoliquid flow over a stretching sheet with stratification effects: a four-factor response surface optimized model

The current work presents a theoretical investigation on the bioconvective electromagnetohydrodynamic (EMHD) hybrid nanofluid flow over a stretching surface considering viscous dissipation, chemical reaction, and stratification effects. The highly nonlinear system of partial differential equations (PDEs) is reduced to a system of ordinary differential equations (ODEs) with the aid of effectual similarity transformations. The transmuted ODEs are then treated numerically using bvp4c (a finite difference-based built-in numerical procedure) in MATLAB. It is observed that an increase in the electric field parameter augments the velocity profile. It is also noted that the Nusselt number is a decreasing function of the thermal stratification parameter. Further, the influence of nanoparticle volume fraction of carbon nanotubes , the nanoparticle volume fraction of magnetite nanoparticles , Hartmann number , and electric field parameter on the drag coefficient has been statistically scrutinized utilizing the four-factor response surface methodology. The highest drag coefficient is experienced for smaller values of Hartmann number and larger values of electric field parameter. The current work finds application in cancer therapy, bio-microsystems, biomedical imaging, and therapeutic drug delivery.

Comprehensive experimental study on bluff body shapes for vortex-induced vibration piezoelectric energy harvesting mechanisms

• Both bluff body shape and flag configuration are two crucial factors. • The bluff body shapes with higher drag coefficients can harvest more energy. • Short full active flags generate more energy in higher wind speed. • A new experimental approach in flexible VIV piezoelectric energy harvester. • Electrode pattern are as important as upstream bluff body shapes. Vortex-induced vibration (VIV) is an appropriate mechanism to harvest energy from the low-speed wind energy by flexible piezoelectric flags as transducers. To enhance the low-speed wind energy harvesting, this work proposes a novel study on finding the best possible combination of bluff body shape and flag configuration. This study considered several bluff body shapes in different cross sections and flag configurations as two crucial parameters for finding an appropriate combination. In high flexible piezoelectric flag, zero strain or electrical canceling point along the length of the flag is an important parameter that could be considered in energy harvester design. To this purpose, wind tunnel experiments were conducted to investigate the combination of proper bluff body shape and flag configuration to improve the harvester performance. The proposed bluff body shapes are classified by drag and lift coefficients which are calculated by a computational fluid dynamics (CFD) analysis. Then, several flag configurations in different active area length were clamped to these bluff bodies and tested in the wind tunnel in low wind speed range. The analysis in time and frequency domain of the acquired voltage lead to the conclusion that in low wind speed the bluff body with higher drag coefficients can excite more the longer full active piezoelectric flags, consequently generating more energy. However, for the same bluff body shapes, short full active flags generate more energy in higher wind speed. This study could develop a new experimental approach on finding the most favorable combination of bluff body shape and flag configuration which is as important as just considering bluff body shape to improve the efficiency of the low-speed wind piezoelectric energy harvesting system.

Experimental Characterization of Drag Coefficient of an UAV Recovery Parachute

Parachute recovery systems are proved to be an efficient method to recovery and rescue unmanned aerial vehicles (UAV) as it follows most requirements of reliability and airworthiness in flights. Parachutes are key components of the recovery systems and the drag coefficient of parachutes plays a crucial role in evaluating parachute’s performance. The purpose of the research is to determine and compare the impact of some factors on aerodynamic drag force during the inflation of a parachute. The canopy’s shape (flat circular type and extended skirt 10% flat type), of the length of suspension lines (be in proportion to nominal diameter from 0.6 to 1.5) are considered. Measurement of the drag force of the parachute models is carried out in an open return wind tunnel. Experimental results show that flat circular canopy has a higher drag coefficient than extended skirt 10% flat model in the range of low speed from 3 to 6 m/s. However, when wind speed is greater than 6 m/s, the drag coefficients of both two parachute types are nearly 0.85. In terms of the suspension line, the longer length would significantly raise the coefficient of drag force.

Effective electroosmotic transport of water in an intrinsically microporous polyamine (PIM-EA-TB)

Tertiary-amine-based Polymers of Intrinsic Microporosity (PIMs) provide a class of highly porous molecularly rigid materials for the electrochemical transport of both ionic and neutral species. Here, the transport of water molecules together with chloride anions (i.e. the electroosmotic drag coefficient) is studied for the intrinsically microporous polyamine PIM-EA-TB immersed in aqueous 0.01 M NaCl (i) when protonated for pH < 4 or (ii) when not protonated for pH > 4. Preliminary data suggest that in both cases a high electroosmotic drag coefficient is observed based on direct H2O transport into a D2O-filled compartment (quantified by 1H-NMR). For PIM-EA-TB there is a strong pH dependence with a higher electroosmotic drag coefficient in less acidic solutions (going from approx. 400 H2O per anion at pH 3 to approx. 4000 H2O per anion at pH 7), although the underlying absolute rate of water transport at a fixed voltage of −1 V appears to be essentially pH independent. Water transport through the PIM-EA-TB microchannels is rationalised based on the relative populations of chloride anions and of water in the micropores (essentially a ‘piston’ mechanism).

Strong and Stable Magnetorheological Fluids Based on Flaky Sendust-Co0.4Fe0.4Ni0.2 Nanocomposite Particles.

The magnetorheological (MR) performance of suspensions based on magnetic (flaky Sendust (FS))-magnetic (Co0.4Fe0.4Ni0.2) nanocomposite particles was investigated by using a vibrating sample magnetometer and a rotational rheometer. Flaky Sendust@Co0.4Fe0.4Ni0.2 nanocomposite particles were fabricated through wet chemical synthesis of Co0.4Fe0.4Ni0.2 on the surface of FS. The density of the resultant FS@Co0.4Fe0.4Ni0.2 was less than that of FS due to the pore/void formation in the composite particles. Because of the high saturation magnetization of Co0.4Fe0.4Ni0.2 (165 emu/g), FS@Co0.4Fe0.4Ni0.2 (145 emu/g) exhibited greater magnetization than bare FS (130 emu/g), which resulted in the good performance of FS@Co0.4Fe0.4Ni0.2-based MR fluids: the suspension exhibited a remarkably high yield stress, almost one order greater than that of MR fluids based on hierarchically structured (HS) Fe3O4 particles. In addition, the high drag coefficient of FS@Co0.4Fe0.4Ni0.2 in the liquid medium, in conjunction with its lower density, resulted in a substantially improved long-term stability, better than that of Co0.4Fe0.4Ni0.2- or FS-based suspensions. Although the density of the FS@Co0.4Fe0.4Ni0.2 nanoparticles is higher than that of HS-Fe3O4 particles, their stability is much better than the stability of HS-Fe3O4 particle's suspension. Manufactured magnetic-magnetic nanocomposite particles provide a feasible MR suspension of high MR performance and long-term stability.