Aerodynamic Drag Reduction Research Articles

Aerodynamic drag reduction of high-speed maglev train based on air blowing/suction

The significant increase in aerodynamic drag is still a key problem restricting the further speed increase of maglev trains. The Improved Detached Eddy Simulation (IDDES) turbulence model based on the Shear Stress Transport (SST) k-ω model was employed to explore the potential and effect of blowing/suction control on the aerodynamic drag reduction of the maglev train. In this study, the aerodynamic characteristics of the train's wake region, and the interference mechanism of blowing/suction on the flow field were studied. The results indicate that the best drag reduction rate ζd of 8.69% of the train and the lift reduction rate δl of 30.4% of the tail car are achieved when blowing along the normal direction of the surface at 0.5 times of the train speed at the separation region near the tail nose. In this case, the ζd and δl grow with the increase of blowing speed; however, the growth rate of ζd decreases when the blowing speed reaches 0.2 times to 0.5 times of the train speed. Studies in this paper propose an effective active flow control method to reduce the train aerodynamic drag, and provide theoretical guidance for the development of drag reduction technology for maglev trains.

Review on Flow Controls for Vehicles Aerodynamic Drag Reduction

Reducing aerodynamic drag in automobiles has been one of the focuses in automotive industry as it will increase vehicles performance and reduce power consumption which subsequently save the environment. Drag is a force that tend to pull the vehicle backwards. Pressure drag is the major contributor to drag of vehicle which caused by lower pressure in the rear area compared to front of vehicle. When vehicle moves forward, the stagnation point occurs in the front part of vehicle. The airflow then goes over the vehicle and separate at the back due to adverse pressure gradient. Thus, flow separation is created in the rear area of vehicle as indicated by the wake. Wake is a low-pressure region that need to be reduced so that the pressure between the front and rear could be reduced to minimize the drag. Flow control is introduced to delay this flow separation and it has been categorized as active and passive. Active flow controls require power input while passive flow controls do not need power input. This review article will explore those studies on flow controls applied in automobiles and investigate their working mechanisms along with research gaps detected. Relative comparison of effectiveness for each flow control is unfeasible as the parameters used differs but this problem can be resolved. Standard parameters need to be used in future researches in order address the discrepancy of results obtained from numerous studies around the globe. A current flow control technique is proposed to be conducted in UTM Aerolab to further investigate this interesting flow field.

The Truck Platooning Routing Optimization Model Based on Multicommodity Network Flow Theory

Truck platooning has been identified as an emerging and promising operational technology with the advantages of fuel consumption savings and carbon emissions reductions. We formulate the truck platooning routing optimization problem as a multi-commodity network flow problem from a transportation optimization and scheduling perspective. Based on fuel consumption savings generated through the reduction of aerodynamic drag by the formation of truck platooning, the route of each truck is also set to be a decision variable needing settlement to facilitate the formation of truck platooning to maximize fuel consumption savings. Considering fuel consumption and detour costs, we construct a truck platooning routing optimization model with minimum overall system fuel consumption as the optimization objective. The output of the routing optimization model could both reflect the composition of each truck platooning on each link and directly show the routings of each truck. To explore the impact of the restrictions on the number of trucks in truck platooning on overall fuel consumption savings, road networks are constructed and the truck platooning routing optimization model is solved by the commercial solver CPLEX. Compared to individual trucks, 8% or 12% fuel consumption savings are achieved, respectively, with the number of trucks being restricted or not restricted in truck platooning. Considering the different fuel reduction rates of the following trucks in platooning on the system performance in terms of the total fuel cost, a sensitivity analysis is also conducted. The results also show that the ideal truck platooning routing plan can be obtained by the proposed model, and the study provides a theoretical reference for the promotion and application of truck platooning.

Numerical study on aerodynamic resistance reduction of high-speed train using vortex generator

Vortex generator (VG) is one of the potential technical tools to reduce the aerodynamic resistance of high-speed trains. The passive control resistance reduction research of a high-speed train is carried out by using VG. Three typical installation locations, including flow separation point, boundary layer mutation and streamline transition location, and several nearby locations were selected to study the effect of VG location on the train aerodynamic characteristics. The results show that the tail car drag is significantly reduced when the VG is arranged at the boundary layer mutation, the tail car’s resistance can be reduced by 15.42%. The tail car reduces resistance by 3.87% when VG is set at the flow separation point. By analyzing the flow field structure, we found that the VG arranged in front of the separation point triggers the flow separation, which destroys the balance between the separation and longitudinal vortex. It effectively reduces the strength of the separation vortex, thereby reducing the tail car’s aerodynamic drag. The research provides a new thought for the aerodynamic resistance reduction of high-speed trains, and is of great significance to break the limitations of traditional aerodynamic drag reduction technology of trains.

An experimental study on the phenomenon of flow field around the limbs of cyclists

Reduction of aerodynamic drag is an important topic in the development of a bicycle racing, making it extremely vital to study the flow field phenomenon on the surface of a cyclist. As the wind flows over the human body, the flow separation phenomenon will appear on the surface. The purpose of this research is to study the aerodynamic characteristics of cyclists by utilizing flow visualization method in both water channel and wind tunnel. Cyclist models used in water channel and wind tunnel testing were based on a real male cyclist and printed using a 3D printer. Flow visualization technique was employed to observe the flow phenomenon around the arms, thighs and calves of the cyclist model. It is found that there are vortices meandering along the axial direction at the arms and thighs, double separation lines appear at the lower legs. Then, the surface pressure coefficient of the model was measured on a full-scale model in wind tunnel experiment to verify the flow condition in the vicinity of the model surface. These research methods help in getting a better understanding of the structure of the flow field around the cyclist, and further achieve the purpose of drag reduction.

Numerical Study on Reduction in Aerodynamic Drag and Noise of High-Speed Pantograph

Numerical Study on Reduction in Aerodynamic Drag and Noise of High-Speed Pantograph

A Numerical Analysis of Active Flow Control Techniques for Aerodynamic Drag Reduction in the Square-Back Ahmed Model

Aerodynamic drag reduction is required with new stringent constraints on pollutant emissions and fuel efficiency of ground vehicles. In this context, active flow control is a promising approach to achieve this target. This study focuses on applying different flow control strategies on the square-back Ahmed model to reduce aerodynamic drag. A steady blowing jet, a synthetic jet and an unsteady jet are located at the back edges of the model as flow control devices. A numerical study based on the 3D WMLES simulation was performed to evaluate the drag reduction capabilities of these devices at different operating conditions. The results showed that a maximum aerodynamic drag reduction of 26.51% was achieved when using a steady blowing jet, and 17.27% with an unsteady jet. In contrast, the effect of the synthetic jet on the aerodynamic drag of the model is solely at high control frequencies.

Aerodynamic Drag Reduction on Speed Skating Helmet by Surface Structures

The aerodynamic drag for speed skating helmets with surface structures was investigated in this work by using numerical and experimental methods. Computational fluid dynamic (CFD) research was performed to analyze the detail of the flow field around the helmets. The simplified helmet models, with riblet and bump surface structures, were analyzed using the CFD simulations. The pressure distribution and velocity field around the helmets were obtained through the CFD analysis. The CFD results showed that the boundary layer separation position was obviously delayed, and the pressure changed to a higher value at the back area for structured helmets. Therefore, the aerodynamic drag for the structured helmet was lower than that of the original model. According to the CFD results, three types of helmets, with the of riblet and bump surface structure printed on the helmets by using flexible film, were tested in a wind tunnel. A full-scaled skater mannequin of half a body was used in the experiment to simulate the actual skating process. Compared with the original helmet, a drag reduction rate of 7% was achieved for the helmet with the bump at the middle region in the wind tunnel experiment, at the average speed in competitions for skaters.

Aerodynamic drag analysis and reduction strategy for satellites in Very Low Earth Orbit

Research interest in operating satellites in Very Low Earth Orbit (VLEO) is growing due to their potential applications for high quality Earth observation and telecommunication. In VLEO, atmospheric drag is not only a critical issue affecting the attitude control and orbit prediction of satellites, but also a key factor limiting the operational life of satellites. In this work, we first employ the direct simulation Monte Carlo (DSMC) method to calculate the aerodynamic drag of elementary shapes including flat plate, cylinder, and sphere in the VLEO region, which are validated and compared with the free molecular flow (FMF) theory. Then, we calculate the aerodynamic drag of a conceptual VLEO satellite model, and the effects of the orbital altitude, accommodation coefficient of surfaces, and the molecular speed ratio on the aerodynamic drag coefficient are analyzed. Two drag reduction strategies, referred to as lateral side smoothing and shape optimization, are investigated in detail by DSMC calculations. We propose that combining these two drag reduction strategies can achieve better drag reduction effect. In addition, we modify the optimum aspect ratio theory by considering the rarefied gas effect to give a better prediction of the optimum aspect ratio for aerodynamic drag at lower orbital altitudes.

Effects of the Yaw Angle on Air Drag Reduction for Various Riblet Surfaces.

Biomimetic riblet surfaces, such as blade, wavy, sinusoidal, and herringbone riblet surfaces, have widespread applications for drag reduction in the energy, transportation, and biomedicine industries. The drag reduction ability of a blade riblet surface is sensitive to the yaw angle, which is the angle between the design direction of the riblet surface and the average flow direction. In practical applications, the average flow direction is often misaligned with the design direction of riblet surfaces with different morphologies and arrangements. However, previous studies have not reported on the drag reduction characteristics and regularities related to the yaw angle for surfaces with complex riblet microstructures. For the first time, we systematically investigated the aerodynamic drag reduction characteristics of blade, wavy, sinusoidal, and herringbone riblet surfaces affected by different yaw angles. A precisely adjustable yaw angle measurement method was proposed based on a closed air channel. Our results revealed the aerodynamic behavior regularities of various riblet surfaces as affected by yaw angles and Reynolds numbers. Riblet surfaces with optimal air drag reduction were obtained in yaw angles ranging from 0 to 60° and Reynolds numbers ranging from 4000 to 7000. To evaluate the effects of the yaw angle, we proposed a criterion based on the actual spanwise spacing (d+) of microstructure surfaces with the same phase in a near-wall airflow field. Finally, we established conceptual models of aerodynamic behaviors for different riblet surfaces in response to changes in the airflow direction. Our research lays a foundation for practical various riblet surface applications influenced by yaw angles to reduce air drag.

Aerodynamic Drag Reduction of Commercial Ground Vehicles Using Numerical Techniques

Automobiles of today warrants improved aerodynamic behaviour that results in low drag producing vehicles. Such optimally designed vehicles offer advantages such as better overall performance, desirable driveability, rapid response, improved stability and added fuel economy. In this paper, an attempt is made to accomplish lower drag coefficient by incorporating the dimples shape on the vehicle roof surface. Aerodynamic flow analysis was conducted with and without dimple shape effect on a bus truck trailer and commercial vehicles, using ANSYS Fluent software tool. Effect of different sized and shaped dimples on aerodynamic performance was analysed as well. Results obtained were validated with available literature and it is found that coefficient of drag obtained showed less than 10 % error. It was found that drag values were significantly reduced with dimple effect on both the commercial vehicles. Both models demonstrated that the fluid flowing on the surface did not separate from the vehicle roof, and the vortex size at the back was reduced. Further paper gives a detailed study of various parameters like turbulence model effect, pressure distribution on the vehicles, temperature and mach number variations. This study is proposed to enhance energy efficiency of the automobiles as better aerodynamics improves their mileage and fuel economy.

Effect of a Detached Bi-Partition on the Drag Reduction for Flow Past a Square Cylinder

The objective of this research is to study the fluid flow control allowing the reduction of aerodynamic drag around a square cylinder using two parallel partitions placed downstream of the cylinder using the lattice Boltzmann method with multiple relaxation times (MRT-LBM). In contrast to several existing investigations in the literature that study either the effect of position or the effect of length of a single horizontal or vertical plate, this work presents a numerical study on the effect of Reynolds number (Re), horizontal position (g), vertical position (a), and length (Lp) of the two control partitions. Therefore, this work will be considered as an assembly of several results presented in a single work. Indeed, the Reynolds numbers are selected from 20 to 300, the gap spacing (0 ≤ g ≤ 13), the vertical positions (0 ≤ a ≤ 0.8d), and the lengths of partitions (1d ≤ Lp ≤ 5d). To identify the different changes appearing in the flow and forces, we have conducted in this study a detailed analysis of velocity contours, lift and drag coefficients, and the root-mean-square value of the lift coefficient. The obtained results revealed three different flow regimes as the gap spacing was varied. Namely, the extended body regime for 0 ≤ g ≤ 3.9, the attachment flow regime for 4 ≤ g ≤ 5.5, and the completely developed flow regime for 6 ≤ g ≤ 13. A maximal percentage reduction in drag coefficient equal to 12.5%, is given at the critical gap spacing (gcr = 3.9). Also, at the length of the critical partition (Lpcr = 3d), a Cd reduction percentage of 12.95% was found in comparison with the case without control. Moreover, the position of the optimal partition was found to be equal to 0.8d i.e. one is placed on the top edge of the square cylinder and the second one is placed on the bottom edge. The maximum value of the lift coefficient is reached for a plate length Lp = 2d when the plates are placed at a distance g = 4. On the other hand, this coefficient has almost the same mean value for all spacings between the two plates. Similarly, the root means the square value of the lift coefficient (Clrms) admits zero values for low Reynolds numbers and then increases slightly until it reaches its maximum for Re = 300.

Aerodynamic Drag Reduction of Railroad Tank Wagons

Several geometrical modifications for passive flow control applied to a railroad tank wagon were investigated for the purpose of assessing the potential for the aerodynamic optimization of freight trains. The modifications were designed in accordance with applicable requirements and regulations. Four different modifications were investigated in the wind tunnel of the TU Berlin with 1:25 scaled wagon models: face radius, side skirts, fairing of the roof platform, and the newly introduced inter-wagon discs. In order to simulate the positions of the tested wagon at the end of a long train, the boundary layer on the train model setup was artificially thickened by spires. The Reynolds number was in the range of 0.4 × 106. The results of the experiments show that the proposed measures can reduce the aerodynamic drag of the individual wagon by up to 29%, depending on the location in the train consist. It was also shown that by combining different measures, the individual drag reductions add up. The device with the highest drag reduction was found to be the inter-wagon disc. Three different diameters of the inter-wagon disc were investigated. The largest diameter performed best and was less sensitive to the moving direction of the wagon in comparison to the smaller diameters.

Numerical analyses of a reference wing for combination of hybrid laminar flow control and variable camber

The objective of the LuFo VI-1 project CATeW (Coupled Aerodynamic Technologies for Aircraft Wings) consists in multifidelity analyses to assess the potential for aerodynamic efficiency increase by combined application of hybrid laminar flow control and variable camber technologies to the wing of a transonic transport aircraft. Individually, both technologies have proven to lead to major aerodynamic drag reductions. An evaluation of the coupled technologies is, therefore, expected to show an even higher potential due to synergy effects. To derive conclusions on system level, low-fidelity (LowFi) overall aircraft design methodologies will be applied for the analysis of a medium haul reference aircraft in the course of the project, while complex aerodynamic phenomena are modelled with high-fidelity (HiFi) computational fluid dynamics methods. The paper at hand presents results of aerodynamic analyses on both fidelity levels for the wing of the turbulent reference configuration CATeW-01, featuring the technology combination as a retrofit. Furthermore, this work encompasses adaptations and implementations performed within both the LowFi and HiFi toolchains. The LowFi toolchain already incorporates several modules for the proposed technology combination. A short presentation of the LowFi-toolchain is given, along with the modeling approach in the HiFi framework using mesh deformations and a mass flux boundary condition. Comparative studies of the turbulent flow field around the wing show good agreement of predicted load distributions in both numerical frameworks, studies based upon the HiFi approach attest the potential for efficiency increase due to the variable camber technology, incorporated by means of Adaptive Dropped Hinge Flap (ADHF) deflections. Considering the coupled application, four different constant suction mass flow rates are examined, where the maximum mass flow causes laminar flow extending over the entire suction panel, thus moving the transition location from the wing’s leading edge to the end of the suction panel. When being coupled with ADHF deflections, again the variable camber technology leads to a reduction of the wing’s pressure drag component with the simultaneous application of boundary layer suction further promoting drag reduction with increasing suction rate. While the combined application shows no mutual inhibition, major reciprocal effects are not directly observable when applying the combination as a retrofit to the reference configuration CATeW-01. This is mainly attributed to the limited extend of laminar flow, thus indicating the necessity for optimization in wing geometry and operating parameters, to achieve extensive areas of laminar flow and to promote the aspired synergy effects.

Hierarchical Model Predictive Control Approaches for Strategic Platoon Engagement of Heavy-Duty Trucks

For a group of vehicles, collaborative platooning can be valuable in certain situations due to aerodynamic drag reduction, while being detrimental or altogether impractical in others. This paper details a platoon engagement/disengagement controller, which alternates between velocity trajectory optimization (VTO) in isolation and a fused platooning and VTO approach, capable of disengaging a platoon during segments detrimental to fuel savings and rejoining the platoon afterwards without significant energy expenditure. The proposed approach leverages parallel model predictive control (MPC) computations that (i) can identify when a platoon should be engaged/disengaged and (ii) performs the engagement/disengagement in a fuel-optimal manner. Using a medium-fidelity Simulink model furnished by Volvo, two real-world trucking routes, and two different traffic scenarios, the effectiveness of the approach was compared against non-platooning VTO, as well as a baseline controller that uses a PI-based cruise controller that incorporates Gipps car-following model. Results for a two-vehicle platoon using a 1 vehicle following distance reveal a 9.6% to 11.9% decrease in aggregate fuel consumption for both vehicles within the platoon, as compared to the baseline, highlighting the ability to disengage and rejoin a platoon without expending unnecessary fuel consumption. Additionally, the approaches for disengaging a platoon result in a 4-7% decrease in aggregate fuel consumption, as compared to a VTO-only approach.

An IDDES study of the near-wake flow topology of a simplified heavy vehicle

Abstract The complex wake flow of a GTS (ground transportation system) model contributes to large percentage of the aerodynamic drag force. Therefore, predicting accurate wake flow will help carry out the drag reduction strategies. In this paper, the near-wake flow topology of the GTS was studied at Re = 2.7×104 to assess the capability of a hybrid RANS/LES (Reynolds-averaged Navier–Stokes/large eddy simulation) approach, known as IDDES (improved delayed detached eddy simulation). The current study also aims to understand the effects of different computational parameters, e.g. the spatial resolution, time step, residual level, discretization scheme and turbulence model, on this asymmetrical wake flow configuration. A comparison of IDDES with previous water channel tests, well-resolved LES, partially averaged Navier–Stokes and URANS (unsteady RANS) was included to better understand the benefits of this hybrid RANS/LES approach. The results show that on the medium and fine grids, the IDDES produces an asymmetrical flow topology (known as flow state I) in the near-wake of the vertical midplane, as reported in previous studies. The recommended parameters for the time step (1×10–4 s) and residual level (1×10–4) provide sufficient accuracy of wake predictions to show good agreement with experiments. For the convective term of the momentum equation in IDDES, the bounded central difference discretization scheme is proposed to be adopted for discretization. Additionally, URANS cannot accurately capture this asymmetrical flow field. IDDES proves to be capable of predicting the wake flow field of this simplified heavy vehicle with high accuracy. All obtained conclusions can provide references for the aerodynamic drag reduction of the GTS.

The Flow Around a Lorry Platoon Subject to a Crosswind—a Detached Eddy Simulation

Technological developments in Connected and Autonomous Vehicles (AVs) have created opportunities to allow groups of vehicles to travel in close proximity, through methods known as platooning. There are potential benefits from platooning in terms of fuel consumption, through a reduction in aerodynamic drag for trailing vehicles in the platoon; however, it is still not understood whether these benefits remain when the platoon is subject to crosswind. For the first time, this study examines the flow structure and aerodynamic response of a platoon of eight closely spaced lorry type vehicles subjected to a crosswind with a 30o yaw angle. The numerical study is conducted using a Delayed Detached Eddy Simulation. It is observed that there is an increase in the overall drag when compared to a similar simulation with no crosswinds. Streamline illustrations indicate that a recirculation region is formed on the leeside of the lorries, which with the chosen vehicle spacing does not exhibit any interactions with the consecutive lorry, resulting in a diminished drag reduction. High pressure on the windward side of the lorries and a low pressure region on the top of the lorry boxes results in high lift, side force and rolling moment coefficients, but relatively minor pitching and yawing moments.

Drag reduction of high-speed trains via low-density gas injection

Aerodynamic drag reduction is crucial for the development of high-speed trains. This study considers the principle of supercavitation torpedo drag reduction and conducts wind tunnel tests and improved delayed detached eddy simulation numerical simulations to develop a drag reduction technique using low-density gas injection on the surface of a high-speed train. Models for jetting gases with different densities on the surface of the high-speed train were employed, and the aerodynamic drag, frictional resistance, pressure resistance, and flow field structure were compared and analyzed. The results demonstrated that jetting of low-density gas reduced the drag of the train, whereas air and high-density gas increased the drag. The jetting gas reduced the frictional resistance of the train to a certain extent and low-density gas injection significantly reduced the frictional resistance. However, the pressure resistance coefficient increased with an increase in the density of the jetting gas, resulting in increased drag. The density of the gas medium in the boundary layer significantly decreased when low-density gas was jetted and the effect of reducing the friction resistance was superior. The pressure resistance between the front and rear of the jet port increased with an increase in the gas density, thereby increasing the drag on the train.

Aerodynamic drag reduction based on static traveling wave structure

Aerodynamic drag reduction based on static traveling wave structure

Rational Analysis of Drag Reduction Variation Induced by Surface Microstructures Inspired by the Middle Section of Barchan Dunes at High Flow Velocity

Aerodynamic drag reduction is a key element for the design of aircrafts, and it is also considered to be affected by the flow velocity. Herein, the influence of high flow velocity on the drag reduction induced by the surface microstructure inspired by a cross-section of barchan dune was investigated by the computational fluid dynamics method in this work. Overall, the drag reduction ratio was decreased while the pressure drag and viscous resistance enhanced simultaneously with the augmentation of flow velocity. Otherwise, drag analysis revealed that the total drag was a power function of flow velocity, which meant that the effect of flow velocity on drag was extremely fierce. Additionally, the microstructure improved the thickness of the boundary layer with a growth rate of 14.2%, and then reduced the viscosity resistance with limits during the development process of flow velocity. Furthermore, the micro-vortex caused by the surface microstructure provided the reverse wall shear stress, with the maximum value ranging from −4.77 Pa to −51.27 Pa, and then reduced the velocity gradient above the microstructure, thereby improving the drag reduction. However, both Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) calculations showed that the excessive velocity could lead to the dissipation of micro-vortex, which augmented the contact area between the fluid and the surface, resulting in the enlargement of viscous resistance. Finally, it was confirmed that the variation of surface microstructure height had a significant influence on drag reduction at high flow velocity. The underlying mechanism of drag reduction could also provide theoretical guidance for the design and optimization of drag reduction coatings in aeronautical applications.