Reduction Of Drag Force Research Articles

Impact of annular nanosecond plasma actuators on drag reduction in transonic flow

During the last few decades, plasma actuators have emerged as promising devices for aerodynamic flow control. This study focuses on the use of nanosecond plasma actuators for such purposes. A thermal phenomenological model is employed to simulate the effects of these actuators. The propagation of shock waves and their interactions for two specific geometries of plasma actuators, linear and annular plasma synthetic jet actuators, are examined here. A comparative analysis of the performance of these two configurations is presented. Furthermore, the geometric characteristics and temperature model are analyzed to provide insights that can be applied to practical problems. The influence of the actuators on a projectile in the transonic flow is also investigated. The results of the present study show that actuators placed in the conical and cylindrical regions of the object do not contribute to drag reduction. Conversely, actuators positioned at the boat-tail and base of the object effectively reduce drag. This drag reduction is primarily attributed to thermal disturbances in the separation area. Additionally, it is observed that the effects of shock waves and their interaction with stationary waves around the projectile are negligible in terms of drag force reduction.

Stagnation point flow of hybrid nanofluid driven towards a sinusoidal-radius permeable circular cylinder

ABSTRACT Recent advancements in nanofluid technology have emphasized the potential of ternary hybrid nanofluids (THNFs) to significantly enhance thermal and hydrodynamic properties. The implementation of a wavy sinusoidal cylinder is proposed as a novel approach to optimize heat transfer in a variety of engineering applications. This study focuses on analysing the flow and thermal behaviour of TiO2-Al2O3-MoS2/Kerosene oil a THNF around a circular cylinder with a sinusoidal radius, demonstrating enhanced heat conduction capabilities compared to conventional hybrid nanofluids. The governing equations, formulated as partial differential equations, are solved using the bvp4c solver. The study reveals that the shape of nanoparticles plays a crucial role in heat transfer efficiency. Specifically, when the solid volume fraction increases from 1% to 3%, brick-shaped particles exhibit the lowest heat transfer enhancement of 25.80%, while blade-shaped particles achieve the highest enhancement of 68.24%. Additionally, the heat transfer coefficient improves from 1.5% to 1.8% across different nanoparticle shapes under varying dissipation parameters. Similar trends are observed in the reduction of drag force with changes in the velocity slip parameter. These findings underscore the significant impact of nanoparticle shape and volume fraction on the thermal performance of THNFs, offering valuable insights for optimizing heat transfer systems in engineering applications.

Parametric Optimization Study of Novel Winglets for Transonic Aircraft Wings

This paper deals with the topic of reducing drag force acting on aircraft wings by incorporating novel winglet designs, such as multi-tip, bird-type, and twisted. The high-speed NASA common research model (CRM) was selected as the baseline model, and winglet designs were retrofitted while keeping the projected wingspan constant. Computational analysis was performed using RANS coupled with the Spalart–Allmaras turbulence model to determine aerodynamic coefficients, such as CL and CD. It was observed that the multi-tip and bird-type designs performed exceptionally well at a low angle of attack (0°). A parametric study was conducted on multi-tip winglets by tweaking the parameters such as sweep angle (Λ), tip twist (Є), taper ratio (λ), and cant angle (Φ). The best combination of parameters for optimal aerodynamic performance while maintaining the wing root bending moment was determined using both the Taguchi method and Taguchi-based grey relational analysis (T-GRA) coupled with principal component analysis (PCA). Also, the percentage contribution of each parameter was determined by using the analysis of variance (ANOVA) method. At the design point, the optimized winglet design outperformed the baseline design by 18.29% in the Taguchi method and by 20.77% in the T-GRA coupled with the PCA method based on aerodynamic efficiency and wing root bending moment.

Buoyancy-driven micropolar ternary hybrid nano-suspension within an oblique incinerator-shaped chamber: Thermal and second law analyses

Since performance of thermal systems may depend on fluids’ thermal conductivities being utilized as coolants, improvement of thermal efficiencies of fluids having micro-structures and involving ternary hybrid nanomaterials may be highly valued. In fact, microrotation of ternary hybrid nanofluids (THNFs) in oblique incinerator-shaped chamber may find applications in industrial processes involving polymeric solutions and lubricants where they help in reduction of drag forces and act as better cooling agent. In view of this, the present study carries out thermal and second law dissection of micropolar THNF within an oblique incinerator-shaped chamber heated from bottom emplacing a roundish heater under a fixed heat flux. The THNF comprises of Al2O3, CNT and graphene as nanoparticles. The study reveals that streamlines and isotherms undergo prominent change due to inclination of the chamber. When Raleigh number and diameter of heater amplify streamlines, microrotations, and entropy generation intensify while average Bejan number whittles down. Average heat transfer rate ameliorates by 4.54 % and 2.17 % when total volume fraction augments from 1.5 % to 3 % and 3 %–4.5 %, respectively. Heat transfer rate reduces by 1.23 %, 0.48 %, 3.33 %, 5.24 %, 2.07 %, and 1.66 % when inclination angle increases from 0° to 90° with inclination angle step 15°.

Numerical simulations of particle concentration and size effects in a slurry bubble column with a CFD‐PBM coupled model

AbstractThe combined effects of particle concentration (0–20 vol%) and particle size on the hydrodynamics of a slurry bubble column were studied by computational fluid dynamics coupled with population balance model (CFD‐PBM) in a wide range of superficial gas velocity (0.02–0.20 m/s). This CFD‐PBM coupled model included multiple effects of particles, namely increased slurry viscosity, reduced drag force, promoted bubble coalescence, and attenuated liquid turbulence, among which turbulence attenuation was crucial. To quantify liquid turbulence attenuation, a mechanistic model was established by equating the energy dissipated by particle motion to the attenuated liquid turbulence energy calculated from turbulent energy spectrum. The turbulent energy dissipation rate was reduced by over 60% at a solid concentration of 20%. Using this model, the effects of particle concentration and particle size on overall gas holdup were well predicted. This model advanced our understanding of how particles affect the gas holdup in a slurry bubble column.

Studi Pemodelan Numerik Penempatan Shark Fin Vortex Generator dengan Susunan Sebaris Pada Dindong Kiri dan Kanan Bus Penumpang

This study analyzes the impact of installing Shark Fin Vortex Generators (SFVG) in a row arrangement on the left and right sides of a passenger bus on the vehicle’s aerodynamic performance. A numerical modeling approach was used to visualize the airflow around the bus and measure key parameters such as drag coefficient (CD), lift coefficient (CL), and pressure coefficient (CP) distribution. Air velocity contour analysis shows that SFVG significantly optimizes airflow around the bus. The bus with SFVG achieved a higher airspeed of 50.23 km/h, while the bus without SFVG only reached 49.83 km/h, indicating a significant reduction in aerodynamic drag. Drag coefficient (CD) analysis shows that the bus with SFVG has a lower CD value of 0.63794782 compared to the bus without SFVG, which has an average value of around 0.70191103. Although the difference is small, it indicates that SFVG has the potential to reduce aerodynamic drag. A difference in lift coefficient (CL) values between the bus with SFVG (around 0.040190537) and the bus without SFVG (around 0.05368355) was also observed, suggesting that SFVG affects the lift force distribution on the bus. Pressure distribution analysis shows that SFVG alters the pressure distribution around the bus. Pressure contours on the bus with SFVG show concentrated pressure at the front of the bus with a peak pressure of about 213.22 Pa, whereas the bus without SFVG shows a higher peak pressure, reaching 465.17 Pa at the same location. This study also evaluates the potential of SFVG to reduce fuel consumption and the environmental impact of public transportation through reduced drag forces. The analysis results indicate that SFVG has the potential to improve energy efficiency and overall aerodynamic performance of the bus. Further research is needed to fully understand the impact of using SFVG in this context.

Improving the energy efficiency and carbon dioxide reduction of a long-haul bus through aerodynamic design optimization

<p>Exhaustion of fossil fuel resources, inconsistent fuel costs and the difficulty of adopting electric vehicle technology in commercial vehicles support the idea that there is an opportunity for research in public transit regarding the correlation between energy efficiency and aerodynamic drag. The turbulent external airflow over a bus at high speeds impacts acceleration, speed, and fuel economy. The fundamental bus's design is intended to carry enough passengers for a reasonable run. Envisaging the factors influencing aerodynamic drag is defiant due to the convoluted relationship between the moving bus and the air. Consequently, a comprehensive numerical and experimental exploration is executed on the bodywork of a bus to improve its aerodynamic efficiency. The aerodynamic drag is directly proportional to the variations in the air density, frontal area, freestream velocity and the drag coefficient. Minimal design reforms are performed on a distinctive long-haul bus. The exertion aims to minimize the drag coefficient, thereby improving the flow characteristics of the bus's bodywork. Through the shape optimization of the bus's bodywork, the modified design has attained a forty-five percent reduction in the drag coefficient. This substantial reduction in drag coefficient directly impacts the reduction of drag force, energy efficiency improvement, and carbon emissions reduction.</p>

Numerical investigation on effect of leading-edge deformation to alleviate dynamic stall of pitching airfoil in unsteady flow

Dynamic stall is a serious phenomenon that restricts aeronautical vehicles’ maneuverability. It happens on the blades as their angle of attack increase, especially on the blade of wind turbines. In this paper, two airfoils are investigated in actual conditions. To alleviate dynamic stall the geometries of the airfoils are modified by drooping and rounded leading-edge tip method and also combination of both. To study the effect of the modifications, the unsteady flow fields around the pitching airfoils, numerically simulated using URANS. Results illustrates, in addition to alleviate dynamic stall, the methods enhance aerodynamic characteristics by reducing drag force and preventing sudden jump of lift force, especially at the maximum angle of attack. Finally, a detailed investigation is conducted on the flow behavior around the airfoil to discover the supporting physics behind the improvements made by the present methods. Which revealed that these two passive methods, aim to prevent the formation of leading-edge vortex on the airfoil which finally delays the dynamic stall.

Suction and Lorentz force effects on MHD free convective transport of micropolar fluid passing a Unsteady analysis

A comprehensive study of the nature of micropolar fluid on an unsteady MHD-free convective transference through a perforated sheet is discussed considering the suction and Lorentz’s force effects. The corresponding similarity equations of temperature, momentum, concentration, and angular momentum equations have been modified into the non-dimensional similarity equations of the temperature, momentum, concentration, and angular momentum equations by utilizing the similarity technique. The modified equations have been resolved by exerting the shooting technique with the help of the finite difference method (FDM) through MATLAB. The fluid flow is inversely proportional to the changes in micro rotational effect (Δ). The concentration boundary layer gets thinner as the Schmidt number (Sc) advances and hence the concentration of the fluid decreases. Micropolar fluid helps reduce drag forces and also acts as a coolant. The heat transmission rate advances by around 391%, and 110% due to growing amounts of Pr from 0.71 to 7.0, and v0 from 0.6 to 3.0, respectively. The surface couple stress decays by about 33%, 45%, and 36% due to increasing values of M from 0.6 to 3.6, ∆ from 3.0 to 6.0, and λ from 0.1 to 1.2, respectively.

Experimental investigations on the effects of longitudinal groove fabric for drag reductions on a track cyclist

The previous study has shown that the longitudinal groove fabric can reduce drag forces on a circular cylinder by forcing a drag crisis (Zheng et al. 2021). In this study, the effects of the longitudinal groove fabric are investigated on a full-scale track cycling mannequin. The force measurement results show that the longitudinal groove fabric on the upper arms can achieve a maximum drag reduction of about 7% at a flow speed of 17 m/s, and its control effects depend on flow speeds. Large-scale particle image velocimetry measurements further show that the drag reductions on the upper arm are characterized by diminished streamwise velocity deficits. The control effects also vary on different spanwise locations of the arm, where the flow behaves distinctively. The measurements also reveal the distinct flow dynamics at different heights, i.e., wake interactions and swirling motions, showing the complexity of reducing drag forces from a track cyclist.

The aerodynamic performance of a platoon of lorries in close-proximity during an overtaking manoeuvre

For the first time, this paper examines the aerodynamic forces that arise in a platoon of Heavy Goods Vehicle lorries travelling in close proximity during an overtaking manoeuvre. Through an in-depth programme of wind tunnel experiments it is demonstrated that there is a complex relationship between the drag and side force coefficients, with a possible hysteresis-like behaviour shown. The influence of the overtaken lorry on the overtaking lorry is shown to be key in terms of the aerodynamic-induced forces experienced by the latter. Furthermore, the overtaking lorry is shown to benefit aerodynamically from the overtaken lorry, and this is attributed to the elliptical nature of the Navier-Stokes equations. In addition to examining the forces that arise during overtaking, the variation of the wind-induced forces with respect to yaw on a single lorry is compared to those on a middle lorry in a 3-lorry platoon. The aerodynamic benefits arising from platooning/vehicles travelling in close proximity are again demonstrated, although it is shown that these benefits may only exist over a limited range of yaw angles, raising questions about the real-world application of this approach. This has important implications for platooning in crosswinds and the drag force reduction that is assumed due to platooning.

Heat transfer improvement and drag force reduction around three heated square cylinders controlled by partitions

Investigating the subject offers a pioneering approach to enhancing thermal performance and aerodynamic efficiency, unlocking novel strategies for optimizing energy utilization and air dynamics in engineering applications. In this research, a numerical study of airflow control coupled to heat transfer around several heated square cylinders is carried out at a fixed Reynolds number (Re=100). The effect of the positioning and length of the control partitions is examined. Numerical simulations are carried out using the lattice Boltzmann method with multiple relaxation times model. The obtained results reveal the existence of a critical position g=0 where a significant improvement in the Nusselt number is observed. This improvement amounts to 31.1% for the rear face of the top obstacle, 30.2% for the rear face of the central obstacle, and 36.65% for the rear face of the bottom obstacle compared to the uncontrolled case. Thus, a complete suppression of the vortex shedding is observed when the length of the partitions reaches a critical value (Lp=4D). Furthermore, a maximum percentage of drag reduction is achieved by around 6.03% for the central block and 16.67% for the two end blocks when the length of the control partitions reaches this critical value.

DESIGN, EXPERIMENTAL STUDIES, AND CFD INVESTIGATIONS OF BIO-INSPIRED SLOTTED REAR DIFFUSER ATTACHMENT ON CAR MODEL FOR ENHANCING AERODYNAMIC PERFORMANCE

The performance enhancement of vehicle design is still a challenging phenomenon for technologists. A suitable pathway for performance enrichment is naturally available in living species. One adaptable design solution arrived through the penguin microbubble concept, which was used to reduce drag. The present work attempts to design rear-slotted diffuser attachments on car models to reduce drag force through the diversion of air. The drag reduction enhances the vehicle’s aerodynamic performance and reduces lift force to increase stability. Normally, high-speed vehicle performance and stability are determined by aerodynamic forces exerted on the body surface. The higher level of drag and lift forces leads to more fuel utilization and, in the case of electric vehicles, more power consumption. The drag force on the vehicle is mainly due to the formation of the wake region behind the body in the downstream region. The above forces are reduced using a rearward-slotted diffuser at the rear end underneath the vehicle. The aerodynamic performance of the vehicle models was estimated through wind tunnel experiments and numerical simulation for various wind speeds. The experimental work was conducted on selected car models with and without rearward slotted diffusers to compare the forces and performances of vehicle models. Interestingly, increased pressure was observed downstream of the vehicle while providing a slotted diffuser, consequently diminishing the wake area behind the vehicle. The drag and lift coefficient reduction were attained as 4.74% and 11.02% at 50 m/s (180 km/hr) on the chosen vehicle model. Also, a significant reduction in fuel consumption was calculated at higher speeds while attaching a slotted diffuser at the rear end of the car.

Deep reinforcement learning-based active control for drag reduction of three equilateral-triangular circular cylinders

Deep reinforcement learning (DRL) is gaining attention as a machine learning tool for effective active control strategy development. This study focuses on employing DRL to develop an efficient active control strategy for flow around three circular cylinders arranged in an equilateral-triangular configuration in a two-dimensional channel. The analysis of control outcomes reveals that DRL induces vortices of varying sizes between the cylinders, resulting in large elliptical vortices at the rear. This enhancement in flow stability leads to a significant 40.40% reduction in cylinder drag force and an approximate 8.23% decrease in overall drag oscillations. Our research represents a pioneering application of DRL for stabilizing complex flow around multiple cylinders, yielding remarkable control effectiveness. The noteworthy outcomes in controlling the stability of complex flows highlight the capability of DRL to grasp intricate nonlinear flow dynamics, showcasing its potential for investigating active control strategies within complex nonlinear systems.

Dynamics of the flip long jump

The long jump is a track and field event in which athletes attempt to jump as far as possible from a take-off point into a sandpit. In the 1970s, an athlete called Tuariki Delamere tried to introduce a ‘front flip’ technique where one goes into a front tuck instead of using a regular technique like the hitch kick and argued that it would allow for a longer horizontal distance. Several reasons have been proposed for the superiority of this technique, including the reduction of drag force during flight and increased angular momentum at take-off. We show that the air resistance makes a negligible contribution to the horizontal distance covered whereas a larger angular momentum can increase the distance of a jump. We explain why the technique was banned and discuss whether our argument implies that the technique can be deemed to be superior in practice.

Large eddy simulations of cavitation around a pitching–plunging hydrofoil

In this study, we numerically examine the behavior of the NACA (National Advisory Committee for Aeronautics) 66 hydrofoil under combined oscillatory motion, considering different cavitation numbers. The large eddy simulation method is used for the turbulence modeling. The vertical oscillation (combined oscillation) creates an effective angle of attack, leading to reduced drag force. Our findings indicate that increasing the speed of hydrofoil oscillation leads to a delayed onset and increased production of cavity clouds. Moreover, an increase in the angle of attack during combined oscillatory motion decreases the detachment length of cavitation bubbles. Further investigations show that cavitation on the hydrofoil's surface can accelerate the shift from a laminar to turbulent boundary layer, reinforcing the turbulent boundary layer's strength and thereby delaying the onset of flow separation. Additionally, we accurately examine the terms of the vorticity transport equation in this research. It is evident that the vorticity dilatation term forms near the boundary layers close to the hydrofoil surface and correlates well with the vapor volume fraction. This term plays a vital role in the cavitation inception process.

Influence of Nose Cone Fairing and Spike on Supersonic Blunt Body Flows

Experiments and computations were performed at Mach number 2.0 for various nose cone fairing bodies with a sharp spike and conical spike of L/D ratio=1.0 and with a sharp spike having a fixed tip location of different L/D ratios. Attempts were made to alter the flowfield of various nose cone fairing bodies with the adoption of the spike. Qualitative and quantitative measurement studies indicate the changes that support the reduction of drag forces, not only on hemispherical blunt bodies but also on various nose cone fairings. This drag reduction with the configurations tested in this study indicates the importance of the region between the spike and the blunt-body face. The results presented here justify the quality and quantity of recirculating flow and its implication for drag reduction.

Effects of different working parameters on the turbulent drag reduction regulated by annular plasma synthetic jet actuators

Reduction of turbulent drag force is one of important works in the design of airplanes and hypersonic aircrafts. The annular plasma synthetic jet (APSJ) has become an interesting and popular flow control method in reducing the drag of turbulent boundary layers. In this paper, a comprehensive experimental study is carried out on the turbulent drag reduction regulated by an array of annular plasma synthetic jet actuators. The effects of the operating parameters such as the actuation voltage, the pulse frequency and the incoming wind speed on the drag reduction rate are studied and discussed in detail. The performances of the plasma actuator array are evaluated and summarized at multiple working conditions. Finally, the coherent structures of turbulence and the hairpin-like vortices are depicted and discussed. The results show that the optimal drag reduction rate is achieved, as the actuation voltage, pulse frequency and incoming wind speed are Vpp = 7 kV, fp= 50 Hz, and U∞ = 7 m/s, respectively. A resonant coupling phenomenon is observed when the pulse frequency of the actuators approaches the characteristic frequency of the coherent structure. The upward sweep flow induced by APSJ actuators may lead to a reduction of the turbulent drag force, but the downward wash flow leads to an increase in the drag. Present study could provide solid experimental data and a helpful guidance for the drag reduction of an airplane.

Machine learning-based optimization of a pitching airfoil performance in dynamic stall conditions using a suction controller

Flow separation control on oscillating airfoils is crucial for enhancing the efficiency of turbine blades. In this study, a genetic algorithm was employed to optimize the configuration of a pure suction jet actuator on an oscillating airfoil at a Reynolds number of 1.35×105. Neural networks based on multilayer perceptrons were used to train the aerodynamic coefficients as functions of the control parameters and reduce the number of simulations. The objective function was the mean performance coefficient, defined as the ratio of the average lift to the average drag during an oscillation period. The control parameters were location, velocity, opening length, and suction jet angle relative to the airfoil surface. The optimal jet had the maximum velocity and opening length and was normal to the airfoil surface. The optimal jet location was near the leading edge vortex (LEV) (between 3% and 6% of the chord). The optimum jet can increase the average performance coefficient (average ratio of lift to drag during a period) by about 24 times. The major part of this improvement is related to reducing drag force. The average lift coefficient increases from about 0.58 to about 0.92 using this jet, while the average drag coefficient decreases from about 0.23 to about 0.02. The optimal jet suppressed the dynamic stall vortex, which resulted from the combination of two clockwise vortices: LEV and turbulent separation vortex. Suppressing this vortex prevented the counterclockwise trailing edge vortex from growing at the end of the airfoil.

Wind tunnel evaluation of novel drafting formations for an elite marathon runner

Drafting is a strategy in marathon running races that reduces the drag force acting on a designated runner. Drafting involves a formation of athletes, called pacers, running in front of (and sometimes behind) the designated runner. The present experiments evaluated complex formations involving up to seven pacers with the aim of enhancing the performances of an elite marathoner. Wind tunnel measurements with 1/10 scale articulated runner manikins were carried out. First, simple formations with one or two pacers were examined and the results were compared with previous investigations. Second, the runner formations of the Nike Breaking2 and INEOS 1:59 Challenge events whose goal was to break the 2 h marathon barrier were studied. The main finding was the identification of three complex formations of six and seven pacers that allow a drag-force reduction of about 60% with respect to a solo runner and an estimated time saving of 262 s. These results point to how it may be possible to run the fastest marathon ever.