Drag Reduction System Research Articles

Study on aerodynamic development in Formula One racing

Formula One (F1) represents the pinnacle of automotive engineering. Aerodynamics is a critical factor that determines the performance of these high-speed racing machines. This paper aims to provide a comprehensive overview of the evolution and advancements in aerodynamic design and technology in Formula One over the years. Starting from the rudimentary designs of the 1950s, this paper traces the progression to the highly sophisticated Computational Fluid Dynamics (CFD) simulations and wind tunnel tests that dominate the sport today. Innovations like ground effects, diffusers, DRS (Drag Reduction System), and vortex generators are examined to elucidate how they contribute to increasing downforce, reducing drag, and thereby enhancing performance. This paper touches upon the future prospects of aerodynamic research in Formula One, including sustainability considerations and potential areas for innovation. Through a synthesis of historical trends, technical breakthroughs, and empirical data, this paper may provide a holistic understanding of aerodynamics in the context of Formula One racing.

Design of a Drag-reducing System for Smart Bar Conveying Chain Plate

This paper presents a solution to the issue of high frictional resistance between the chain plate and guide rail in cigarette conveying systems, which can result in chain plate failure. The proposed solution is an intelligent drag reduction system that incorporates lubrication and automatic dust removal. The system includes a conveyor chain plate, supporting roller assembly, air knife dust removal assembly, chain plate lubrication assembly, and controller. The controller manages the dust removal assembly's air source output and the lubrication of the chain plate assembly through the opening and closing of an electromagnetic valve, which controls the oil output to decrease resistance. Experimental testing of the system shows that it effectively reduces the chain plate's frictional resistance in the cigarette conveying line, resulting in improved system efficiency.

Wind tunnel testing of a Formula Student vehicle for checking CFD simulation trends

The aerodynamic performance analysis of Formula Student racecars has been mostly done by teams with CFD tools, for time and cost savings, that often lack proper validation. To address this, the FST Lisboa team performed a detailed wind tunnel (WT) test campaign, using a one-third scale model, under different configurations, including variable ride heights, bullhorn appendix, and rear wing flap settings, also replicated in CFD. The simulations used RANS with the SST k-omega turbulence model, with a 13.7 million polyhedral mesh for the test chamber region domain. Both experimental and numerical errors were estimated from the instrumentation and mesh convergence analysis, respectively. Comparisons were made between WT and CFD both in terms of local flow, using tufts for flow visualization, and global flow, using lift, drag, and pitching moment coefficients. Overall, the numerical streamlines agreed very well with the orientations of the tufts in experiments, but some discrepancies were found in regions of cross-flow and high-frequency unsteadiness, mainly caused by limitations of the visualization technique. The gamma transition model in CFD was abandoned as it could not replicate the WT observations. In terms of aerodynamic coefficients, a strong correlation was found between WT and CFD. The parametric studies revealed that the simulations captured the experimental sensitivity to each car setting parameter studied but the uncertainties did not enable a full quantitative evaluation of the aerodynamic performance. The drag reduction system significantly impacted the aerodynamic balance of the racecar, while the current bullhorn design proved to be ineffective. The ride height increase led to higher downforce, mostly due to the higher pitch angle of the vehicle, with negligible variation of the aerodynamic balance. This work validated the team CFD studies, building confidence in that trends estimated in numerical parametric studies are likely to be translated to the real prototype performance.

Aerodynamic Study of a Drag Reduction System and Its Actuation System for a Formula Student Competition Car

This work presents a computational fluid dynamic (CFD) analysis of a drag reduction system (DRS) used in a Formula Student competition vehicle, focusing on the interaction between the triple wing elements, as well as on the electrical actuators used to provide movement to the upper two flaps. The S1123 wing profile was chosen, and a 2D analysis of the wing profile was made. The trailing edge was rounded off to conform to Formula Student competition safety rules, resulting in around a 4% decrease in the lift coefficient and around a 12% increase in the drag coefficient for an angle of attack of 12°, compared to the original wing profile. The multi-element profile characteristics are: wing main plate with 4°, first flap 28°, and second flap 60°. To evaluate the wing operation, end plates and electrical linear actuators were added, generating a maximum lift coefficient of 1.160 and drag coefficient of 0.397, which provides around a 10% reduction in lift and a 9% increase in drag compared to the absence of the linear actuators. When activating the DRS, the flap rotation generates about a 78% decrease in the aerodynamic drag coefficient and 53% in the lift coefficient for the minimum aerodynamic drag setting.

Robust Superhydrophobic Surfaces via the Sand-In Method.

Superhydrophobic surfaces have gained sustained attention because of their extensive applications in the fields of self-cleaning, anti-icing, and drag reduction systems. Water droplets must have large apparent contact angle (CA) (>150°) and small CA hysteresis (<10°) on these surfaces. However, previous research usually involves complex fabrication strategies to modify the surface wettability. It is also challenging to maintain the temporal and mechanical stability of the delicate surface textures. Here, we develop a one-step solvent-free sand-in method to fabricate robust superhydrophobic surfaces directly atop various substrates with an apparent CA up to ∼163.8° and hysteresis less than 5°. The water repellency can withstand 100 Scotch tape peeling tests and remain stable after being stored under ambient humid conditions in Houston, Texas, for 18 months or being heated at 130 °C in air for 24 h. The superhydrophobic surfaces have excellent anti-icing ability, including a ∼2.6× longer water freezing time and ∼40% smaller ice adhesion strength with the temperature as low as -35 °C. Since the surface layers are fabricated by sanding the substrates with the powder additives, the surface damage can be repaired by a direct re-sanding treatment with the same powder additives. Further sand-in condition screenings broaden surface wettability from hydrophilic to superhydrophobic. The sand-in method induces the surface modification and the formation of the tribofilm. Surface and materials characterizations reveal that both microstructures and nanoscale asperities of the tribofilms contribute to the robust superhydrophobic features of sanded surfaces.

Drag reduction of a commercial bus with add-on aerodynamic devices

In the automotive industry, the implementation of drag reduction systems has provided considerable decreases in fuel consumption. These outcomes are in line with the increasing demands of the environmental regulations and consumers’ requirements. Although some studies explain how aerodynamic devices reduce the aerodynamic drag on light and heavy vehicles such as Ahmed bodies and trucks, buses have received almost no attention. For this reason, the flow over the Marcopolo Paradiso 1200 G7 commercial bus and the influence of several aerodynamic devices on the drag force and fuel consumption of the bus are discussed in this article. Three distinct devices (vortex generators, lateral devices, and rails) were proposed after flow visualization tests on the baseline bus. Thus, the entire evaluation consisted of 11 arrangements by combining the three aerodynamic devices. The changes in drag due to all arrangements are estimated using wind tunnel tests, which are validated using Computational Fluid Dynamics simulations. The fuel consumption is evaluated in a simplified long-haul driving cycle between two cities. The devices were able to alter the flow behavior on the bus, resulting in a maximum decrease of 8.63% in the drag coefficient and 3.92% in fuel consumption. Given that the devices used are just first prototypes, we estimate that greater reductions can be achieved with optimized systems. Likewise, this paper probably leads to real applications in other commercial buses due to the evident drag reductions.

Research on Turbulent Drag Reduction of Surfactant-Polymer Mixed Solution Using Flow Visualization Technique

Objective: To explore the drag reduction effect of surfactant-polymer composite system in a turbulent flow. Methods: The turbulent drag reduction experiment of the one-component solution and the composite solution was carried out in a rectangular pipeline platform, respectively. Moreover, Particle Image Velocimetry (PIV) was utilized to measure the turbulent flow field of the drag-reducing flow. Results: Experimental results show that the composite drag reduction system has a drag reduction gain effect in comparison with the one-component surfactant or polymer solution. Especially in the destroyed drag reduction zone, the composite drag reduction system has a strong shear resistance. When Polyacrylamide (PAM) is added, the Reynolds drag reduction range of Cetyltrimethylammonium Chloride (CTAC) solution is broadened and the drag reduction gain efficiency reaches 46%, which will provide favorable conditions for oil transportation and other industries. Conclusion: Compared with a one-component CTAC solution, the mean velocity distribution of the composite solution moves up in the logarithmic-law layer, the velocity fluctuation peaks of the streamwise direction shift away from the inner wall of pipe, and the inhibition degree of the normal velocity fluctuation increases with the augment of PAM concentration. In contrast with water, the Reynolds shear stress of one-component CTAC solution and composite solution is reduced significantly, and the vortex structures in the region near the wall are suppressed dramatically with the decrease of vorticity intensity.

General-Purpose Object-Oriented Framework for Vorticity-Dominated Flow Simulation

This paper describes the development of a computational framework for aerodynamic simulations based on the unsteady vortex lattice method under the object-oriented programming paradigm. The effort aims to fulfill the fluid-dynamics portion of the fluid–structure interaction problem in the multiphysics field. The construction and implementation of an object-oriented model is introduced along with its analysis and design stages, focusing on the generality and versatility. The overall class organization is presented, and the main classes’ characteristics are discussed. The software validation indicates that the transient and the steady-state aerodynamics for the impulsively started motion of a body are accurately captured by the simulations. In addition, comparisons against experimental results show that rotors in hover flight are acceptably represented for small angles of attack of the blades, within the limitations of the flat-plate representation and the inviscid hypothesis of the model. Regarding applications, six different models are analyzed: 1) a single propeller rotor, 2) a small-scale quadcopter drone, 3) a flying-wing drone, 4) a joined-wing aircraft, 5) a drag-reduction system for cars, and, 6) a flapping-wing insect. In all cases, the results indicate that a well-tuned simulation based on vorticity-dominated flows is widely suitable for the aerodynamic study of several cases. All simulations expose the main advantages of a modular object-oriented program: the ability to change the case of analysis with minimal reprogramming, and the flexibility to link with different models in a co-simulation strategy.

Drag bookkeeping on an aircraft with riblets and NLF control

In the frame of aerodynamic drag reduction for low-emission target, Natural Laminar Flow (NLF) control and riblets are the most interesting passive techniques. The drag breakdown in the case of riblets installed is a topical matter for understanding on which form of drag riblets act. Indeed, linear theories and flat-plate experiments show that riblets act on friction drag whereas other experiments in pressure-gradient flow revealed an increased performance of riblets that was not interpreted. A contribution to clarify this effect has been recently provided analyzing the effect of riblets on form drag in two-dimensional pressure-gradient flows. In the present paper the effect of riblets on pressure drag is discussed also in three-dimensional flows analyzing CFD solutions of the flow around an innovative regional turbo-prop aircraft (wing-body configuration) with NLF and riblets installed. For the first time, the contribution of each of two drag reduction systems is identified and a deep analysis on which form of drag riblets act in three-dimensional flow is proposed thanks to a far-field aerodynamic drag breakdown.

An improved active drag reduction system for formula race cars

Drag reduction systems are largely employed in racing car competitions to help drivers in overtaking manoeuvres, ensuring a good show to the public. This paper presents a full-design approach to drag reduction systems that includes the computational fluid dynamics estimation of the forces acting on the rear wing, the dynamic analysis of the drag reduction system mechanism and the whole vehicle behaviour through the simulation of an overtaking manoeuvre. For the purposes of this work, a novel drag reduction system mechanism is proposed that features lower aerodynamic disturbance and comparable manufacturing costs than those of drag reduction systems of the main Formula categories.

Passive, active, and interactive drag-reduction technique to reduce friction and enhance the mixing intensity in rotating disk apparatus

Rotating disks are applied in many industrial heat and mass transfer systems because of their high mixing performance. The presence of non-Newtonian viscous liquids in these systems limits the mixing performance, thereby affecting the required heat and mass transfer. In this study, passive, active, and interactive drag-reduction techniques are proposed to enhance the mixing and drag-reduction performance of rotating disks and are experimentally tested. An SV-grooved surface (triangular shaped) is engraved on a disk attached to a rotating disk apparatus to test the liquid resistance based on torque readings and the velocity profile using a miniature laser Doppler velocimeter (Mini-LDV, MicroPro). The polymer polyisobutylene and the surfactant sodium lauryl ether sulfate are chosen as the passive–active integrated drag-reduction components in an experiment using different additive concentrations and polymer–surfactant complexes in the same tests. The experimental results show that the selected passive design of the riblets can enhance flow by 8% and that this percentage increases when polymeric additives and polymer-surfactant complexes are introduced. The velocity profile results show that high-velocity zones are created above the rotating surface and that these zones contribute significantly to enhancing the mixing intensity in the drag-reduction system.

Aerodynamic optimisation of Formula student vehicle using computational fluid dynamics

This work aims to improve the external aerodynamic characteristics of the 2017 University of Huddersfield Formula SAE vehicle. To improve dynamic performance in the SAE events, a multiple-element rear wing was developed, which incorporated adjustable elements to constitute a drag reduction system (DRS). A numerical modelling approach was adopted to produce a suitable design. A simplified model of the vehicle was created to obtain baseline coefficients of lift (CL) and drag (CD). The rear wing was optimised to find the peak configuration generating maximum downforce. The results show that the incorporated rear wing improved the vehicle’s CL from 0.21 acting in the positive Y axis (lift) to 1.15 acting in the negative Y axis (downforce), whereas the CD increased from 0.71 to 1.21. However, the DRS configuration reduced the CD to 0.79. Using the obtained lift and drag coefficients, vehicle performance was estimated, such as maximum cornering speed, straight-line top speed and straight-line acceleration capabilities. The rear wing improved the theoretical maximum cornering speed by 3.1% for a corner radius of 13 m. The DRS increased the theoretical top speed by 18.2% compared to a fixed wing configuration. Acceleration potential increased by 15.7% at 25 m/s with the DRS open. The final section of the study used an online simulator (FSAESim) to make predictions of the acceleration event time, which were compared to the track results from the 2017 Hungary SAE event. The results showed a 97% similarity.

Friction of Droplets Sliding on Microstructured Superhydrophobic Surfaces.

Liquid transport is a fundamental process relevant to a wide range of applications, for example, heat transfer, anti-icing, self-cleaning, drag reduction, and microfluidic systems. For these applications, a deeper understanding of the sliding behavior of water droplets on solid surfaces is of particular importance. In this study, the frictional behavior of water droplets sliding on superhydrophobic surfaces decorated with micropillar arrays was studied using a nanotribometer. Our experiments show that surfaces with a higher solid area fraction generally exhibited larger friction, although friction might drop when the solid area fraction was close to unity. More interestingly, we found that the sliding friction of droplets was enhanced when the dimension of the microstructures increased, showing a distinct size effect. The nonmonotonic dependence of friction force on solid area fraction and the apparent size effect can be qualitatively explained by the evolution of two governing factors, that is, the true length of the contact line and the coordination degree of the depinning events. The mechanisms are expected to be generally applicable for other liquid transport processes involving the dynamic motion of a three-phase contact line, which may provide a new means of tuning liquid-transfer behavior through surface microstructures.

Novel Approach for Endurance Testing of Riblet-Structured Thin Sheets Under Realistic Loading Conditions in Active Drag-Reduction Systems

Abstract A novel fatigue testing device for bending loading was developed that resembles loading conditions in aerodynamic drag-reduction systems, creating transversal surface waves to modify the surfaces' turbulent boundary layer. The setup uses Lorentz force actuators and is employed in fully reversed loading (R = −1) at a testing frequency of around 100 Hz. Tests were run on riblet-structured Alclad 2024 T351 material. The damage mechanisms for this material are found to be similar for axial and flexural loading. In the high cycle fatigue regime up to a few 106 load cycles, the S/N-curves are also comparable for both loading modes. One distinct difference between the loading modes is a less pronounced threshold behavior in the S/N-curve for bending. Furthermore, a higher stress level has to be applied for fatigue failure in this case.

A study of performance parameters on drag and heat flux reduction efficiency of combinational novel cavity and opposing jet concept in hypersonic flows

The drag reduction and thermal protection system applied to hypersonic re-entry vehicles have attracted an increasing attention, and several novel concepts have been proposed by researchers. In the current study, the influences of performance parameters on drag and heat reduction efficiency of combinational novel cavity and opposing jet concept has been investigated numerically. The Reynolds-average Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flowfields, and the first-order spatially accurate upwind scheme appears to be more suitable for three-dimensional flowfields after grid independent analysis. Different cases of performance parameters, namely jet operating conditions, freestream angle of attack and physical dimensions, are simulated based on the verification of numerical method, and the effects on shock stand-off distance, drag force coefficient, surface pressure and heat flux distributions have been analyzed. This is the basic study for drag reduction and thermal protection by multi-objective optimization of the combinational novel cavity and opposing jet concept in hypersonic flows in the future.

Bio-Inspired Extreme Wetting Surfaces for Biomedical Applications.

Biological creatures with unique surface wettability have long served as a source of inspiration for scientists and engineers. More specifically, materials exhibiting extreme wetting properties, such as superhydrophilic and superhydrophobic surfaces, have attracted considerable attention because of their potential use in various applications, such as self-cleaning fabrics, anti-fog windows, anti-corrosive coatings, drag-reduction systems, and efficient water transportation. In particular, the engineering of surface wettability by manipulating chemical properties and structure opens emerging biomedical applications ranging from high-throughput cell culture platforms to biomedical devices. This review describes design and fabrication methods for artificial extreme wetting surfaces. Next, we introduce some of the newer and emerging biomedical applications using extreme wetting surfaces. Current challenges and future prospects of the surfaces for potential biomedical applications are also addressed.

Aerodynamic Brake for Formula Cars

In the last years, in formula racing cars championships, the aerodynamic had reached an ever more important stance as a performance parameter. In the last four seasons, Red Bull Racing Technical Officer had designed their Formula 1 car with the specific aim to generate the optimal downforce, in relation to the car instantaneous setup. However, this extreme research of higher downforce brings some negative effects when a car is within the wake of another car; indeed, it is well known that under these condition the aerodynamic is disturbed, and it makes difficult to overtake the leading car. To partially remedy this problem, Formula 1 regulations introduced the Drag Reduction System (DRS) in 2011, which was an adjustable flap located on the rear wing; if it is flattened, allowing to reduce the downforce, increasing significantly the velocity and, therefore, the chances to overtake the leading car. Vice versa, when the flap is closed, it ensures a higher grip, which is very useful especially in medium-slow speed turns. Keeping the focus on the rear wing, but by shifting attention from the increased top speed to increase the grip in the middle and slow speed curves, we decided to study a similar device to the DRS, but with the opposite effect. The aim is to design an aerodynamic brake integrated with the rear wing. In particular, the project idea was to sculpt, on the upper surface of the wing (pressure side), a series of C shaped cavity, normally covered by adequate sliding panels. These cavities, when they are discovered, at the beginning of the braking phase, produce a turbulence and additional increase downforce, lightening the load on the braking system and allowing the pilot to substantially reduce slippage and to delay the braking. Since it seems that the regulations adopted by the FIA Formula 1 Championship do not allow such a device, it has been decided to apply the concept on a Formula 4 vehicle. This paper describes the design and analyzes the effects of these details on a standard wing cavity, using a commercial CFD software.

Numerical study on modulation of microbubbles on turbulence frictional drag in a horizontal channel

Although many investigations on the drag reduction by microbubbles have been conducted, a general mechanism guiding the design of the drag reduction system has not been achieved yet. The drag reduction by microbubbles was investigated in detail with the Euler–Lagrange two-way coupling method in order to understand the drag reduction mechanism by microbubbles in this paper. The liquid velocity field was solved with direct numerical simulations (DNS), and the bubble trajectory was calculated by Newtonian motion equation. The mutual momentum transfer between gas and liquid phases was bridged by interphase forces. The computational results show that a low drag-reduction rate is obtained, the liquid-phase velocity is slightly increased in the region away from the channel wall (i.e., the channel side containing microbubbles), and the turbulence intensity and Reynolds shear stress of the liquid phase are changed along the whole channel height. The present analysis shows that the drag reduction depends on mutual interactions between microbubbles and the liquid turbulence with the help of interphase forces.

On the scaling of air entrainment from a ventilated partial cavity

AbstractThe behaviour of a nominally two-dimensional ventilated partial cavity was examined over a wide range of size scales and flow speeds to determine the influence of Froude, Reynolds, and Weber number on the cavity shape, dynamics, and gas entrainment rate. Two geometrically similar experiments were conducted with a 14:1 length scale ratio. The results were compared to a two-dimensional semi-analytical model of the cavity flow, and Froude scaling was found to be sufficient to match basic cavity shapes. However, the air flux required to maintain a stable cavity did not scale with Froude number alone, as the dynamics of the cavity closure changed with increasing Reynolds number. The required air flux differed over one order of magnitude between the lowest and highest Reynolds number flows. But, for sufficiently high Reynolds numbers, the rate of scaled entrainment appeared to approach Reynolds number independence. Modest changes in surface tension of the small-scale experiment suggested that the Weber number was important only at the lowest speeds and smaller length scale. Otherwise, the Weber numbers of the flows were sufficiently high to make the effects of interfacial tension negligible. We also observed that modest unsteadiness in the inflow to the large-scale cavity led to a significant increase in the required air flux needed to maintain a stable cavity, with the required excess gas flux nominally proportional to the flow’s perturbation amplitude. Finally, discussion is provided on how these results relate to model testing of partial cavity drag reduction (PCDR) systems for surface ships.

Application of Rheology for Energy Saving Air Conditioning System

Surfactant drag reduction is well known as the energy saving technology which is able to cause drastic reduction of pumping power during the fluid transportation. The combination of certain type of cationic surfactant with suitable counter ion is often chosen as the drag reduction agents. Power saving up to 70∼80% is available in straight pipe line system by using surfactant additives. Design problem, in particular, the scale up law in surfactant drag reduction system was solved by using the modified viscoelastic damping factor model along with the measurements of nonlinear viscoelastic properties of surfactant solution. Based on the prediction of the proposed model, it was demonstrated that the surfactant drag reduction technology is promising to construct the large scale energy saving system for air conditioning. Up to now, over 150 sites of building air conditioning had adopted the surfactant drag reduction in Japan, and the practical pumping energy reduction had been reported as 20∼50% compared with the case of no drag-reducing agent.