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The drag reduction of commercial vehicles is the principal challenge to improving fuel saving and decreasing air pollution. Accordingly, several flow control devices, including gap fairing, cab roof fairing, boat tail, and side skirt were introduced to reduce the aerodynamic drag exerted on heavy vehicles. Although such devices have exhibited good drag reduction performance, their aerodynamic performance can be improved further. Moreover, a comprehensive and systematic research is required, including drag force measurement, flow field analysis and real-scale proving ground test, to evaluate the fuel consumption of heavy vehicles. In this study, the drag reduction effect of the aero full package (AFP) of a tractor–trailer, which integrated gap fairing, flap-type side skirt and lower inclined air deflector boat tail, was investigated through wind tunnel experiments and proving ground test. On the basis of the results of drag and PIV measurement, the integrated AFP was found to significantly modify the flow structure around the vehicle, thereby leading to a 26.5% reduction in drag coefficient compared with the reference tractor-trailer model (C D = 0.693). Furthermore, the proving ground test using real tractor–trailer verified that the integrated AFP provides 13.4% fuel saving. The present results will provide practical information for improving the aerodynamic performance and fuel efficiency of heavy vehicles. • The aero full package for tractor-trailer consist of gap fairing, flap-type side skirt and LIAD boat tail was newly proposed. • The aero full package reduces drag coefficient up to 26.5% compared with reference tractor-trailer. • The flow structures around tractor-trailer model is revealed through PIV experiments. • Real-scale proving ground test confirmed 13.4% fuel saving with the aero full package. [ABSTRACT FROM AUTHOR]

The recent popularity of electric vehicles and upcoming governmental regulations on emissions are forcing automotive manufacturers to build more efficient vehicles. An approach to improve the efficiency of a road vehicle is by reducing its aerodynamic resistance. One way of achieving this is through platooning, vehicles drive in close-proximity. Despite of the extensive literature available on platooning of multiple vehicle types, most studies have focused on the drag and flow effects around the truck only. This work aims to increase the understanding and recognize the usefulness of a truck-SUV platoon system as a whole using wind tunnel measurements on two scale models and CFD simulations. From the results of this study, it was found that the effects on the SUV are large and contribute to a significant portion of the drag reduction of the system, especially at short inter-vehicle distances where the drag of the car can become negative. The drag reduction for the truck is generally limited as the truck is a much larger vehicle. For the system, the results show that for very short distances it is beneficial for the truck to lead the platoon, while at longer separations there is no preferable order. • The combined drag of the platoon improves as the inter-vehicle distance decreases. • Very large drag reductions are possible for the SUV. • Significant difference in observed effects for the two vehicles due to their size. • Worse performance for truck when distances are very small. • The system is insensitive to yaw and vehicle order at longer separation distances. [ABSTRACT FROM AUTHOR]

The use of passive ducting from the vehicle nose out of the front wheel opening was studied as a method of modifying the wake profile of a NASCAR Xfinity Series race vehicle to influence its effect on the drag of a trailing vehicle. Utilizing a fixed inlet area due to geometric constraints, exit angle, height and exit/inlet area ratio were explored using multi-vehicle Computational Fluid Dynamics (CFD) simulations and wind tunnel validation. Results indicate that appropriately positioned ducts reduce trailing car drag throughout the range of vehicle spacing studied; most significantly, it reduces the drag peak for the trailing car at approximately 1/4 to 1/2 car length spacing. Increased exit area is shown to enhance drag reduction for the trailing car at all vehicle spacings. Increasing exit angle closer to perpendicular to the direction of travel was shown to be effective as well, even being capable of eliminating the drag peak for the trailing car. Aerodynamic efficiency was increased over the non-ducted baseline configuration with the duct exit angle nearer to the direction of travel, while it was negatively impacted with the duct exit angle perpendicular to the direction of travel. Wind tunnel testing confirmed that aerodynamic efficiency improvement was due to an increase in negative lift under the car, while Kiel probe measurements validated the shape and positioning of the wake changes caused by the ducts. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the yaw angle effect on the aerodynamic performance of a hatchback model fitted with a roof spoiler. Although the aerodynamic performance of road vehicles is highly dependent on its yaw angle, it has rarely been considered in studies pertaining to roof spoiler applications. Two common types of spoilers are studied, namely, strip and wing types. The hatchback model is based on the Ahmed body at 35 ° slant angle. The yaw angle affects the aerodynamic performance of the hatchback model negatively regardless of the presence of a spoiler. However, the impact is more pronounced with the absence of a spoiler, particularly at higher yaw angles. Most importantly, the use of a spoiler prevents the bi-stability behaviour of flow which occurred in the model without the spoiler. Furthermore, the strip spoiler reduces both the drag and lift coefficients (C d and C l), whereas the wing type results in a greater reduction in C l while penalising C d. The results of the surface pressures indicate that the changes in the flow around the rear slanted body are the main factors affecting the aerodynamic performance of the hatchback model using the spoiler. Highlights • The non-symmetric bi-stable flow are detected for the Ahmed body at critical yaw angle. • Use of spoilers prevented bi-stable flow. • Strip spoiler reduced both the drag and lift coefficients. • Rear wing produced greater reduction in lift coefficient while penalising drag coefficient. [ABSTRACT FROM AUTHOR]

A cycling peloton is the main group of cyclists riding closely together to reduce aerodynamic drag and energy expenditure. Previous studies on small groups of in-line drafting cyclists showed reductions down to 70 to 50% the drag of an isolated rider at same speed and these values have also been used for pelotons. However, inside a tightly packed peloton with multiple rows of riders providing shelter, larger drag reductions can be expected. This paper systematically investigates the drag reductions in two pelotons of 121 cyclists. High-resolution CFD simulations are performed with the RANS equations and the Transition SST-k-ω model. The cyclist wall-adjacent cell size is 20 μm and the total cell count per peloton is nearly 3 billion. The simulations are validated by four wind-tunnel tests, including one with a peloton of 121 models. The results show that the drag of all cyclists in the peloton decreases compared to that of an isolated rider. In the mid rear of the peloton it reduces down to 5%–10% that of an isolated rider. This corresponds to an “equivalent cycling speed” that is 4.5 to 3.2 times less than the peloton speed. These results can be used to improve cycling strategies. [ABSTRACT FROM AUTHOR]

An athlete's riding posture is a key element for aerodynamic drag in cycling. Tandem cycling has the complication of having two athletes in close proximity to each other on a single tandem bicycle. The complex flow-field between the pilot and stoker in tandem cycling presents new challenges for aerodynamic optimisation. Aerodynamic drag acting on two tandem road race setups and two track time-trial setups were analysed with computational fluid dynamics (CFD) simulations. For validation purposes, wind tunnel measurements were designed providing drag measurements from both tandem athletes simultaneously using a quarter-scale model. A max drag force deviation of 4.9% was found between the wind tunnel experiments and CFD simulations of the quarter-scale geometry. Full-scale CFD simulations of upright, crouched, time-trial and frame-clench tandem setups were performed. The drag force experienced by individual athletes in all investigated tandem setups was compared to that of solo riders to enhance understanding of the aerodynamic interaction between both tandem athletes. The most aerodynamic tandem setup was found to be the frame-clench setup which is unique to tandem cycling and had a C D A of 0.286 m 2 , and could provide an advantage of 8.1 s over a standard time-trial setup for a 10 km time-trial event. [ABSTRACT FROM AUTHOR]

A consistent mesh refinement study, relating to the prediction of aerodynamic forces about an experimentally validated reference train geometry, is presented in this paper. The flow about a high-speed train has a multi-scale character which poses challenges for the design of computationally effective meshes. The purpose of this study is to assist in the development of guidelines for effective drag prediction of high-speed trains using numerical simulation. These guidelines should assist CFD practitioners by identifying the regions of the mesh that are critical for the correct estimation of drag as well as providing information on appropriate mesh characteristics, such as volume and surface element length scales. Numerical assessments are validated against an experimental drag measurement program and the extent to which RANS is sufficiently predictive for industrial design is discussed. The results obtained in the work suggest that the mesh about the train nose is essential for the proper assessment of the aerodynamic drag acting on the vehicle. [ABSTRACT FROM AUTHOR]

Wind loading on lattice structures is studied locally by considering the applied forces on individual angle members. This work represents a comprehensive Computational Fluid Dynamics (CFD) analysis of wind loading on angle members, which includes a quantitative evaluation of the aerodynamic drag and lift loading and also a qualitative investigation of the wake characteristics behind the angle member. The focus is on the flow around the angle member cross-section which has two equal length sides at a right angle to each other. CFD has been used to investigate the flow around a single angle member characterized by its length D , thickness T , and angle of incidence to the oncoming flow. Both Reynolds-Averaged Navier–Stokes (RANS) and Large-Eddy Simulation (LES) are evaluated for a Reynolds number of 37,700, where the k- ϵ RANS and Wall-Adapting Local Eddy-viscosity (WALE) LES models are respectively used. The results are compared with the wind tunnel experiments reported in the literature (Wardlaw, 1967; Slater, 1969; Prud'homme et al., 2014) and the National Building Code of Canada (Canadian Commission on Building and Fire Codes and National Building Code of Canada, 2005), where the drag and lift coefficients at a range of incidence angles were reported. Quantitatively, the RANS performs well when compared to experiments for the aerodynamic coefficients at a range of incidence angles and less well for angles where a cavity style flow is formed and the separation becomes influential. This is in contrast to other bluff body cases where RANS does not perform so well. The LES is thus run at selected incidence angles for comparison and to better understand the flow where the RANS performs well and less well. Details of the turbulence in the wake are difficult to interpret when using RANS modeling, but this behavior is well illustrated with the LES model and details are reported here. • Evaluation of the aerodynamic drag and lift loading on angle members. • Investigation of the wake characteristics behind the angle member. • Both RANS and LES are evaluated for a Reynolds number of 37,700. • RANS performs well againt litterature at a range of incidence angles. • LES better understand the flow where the RANS performs less well. • This study constitutes a basis for evaluating the mask effect over multiple members. [ABSTRACT FROM AUTHOR]

The paper investigates the response to crosswind of a high-speed freight train for intermodal transportation, through wind tunnel tests. A 1:20 model of a freight train composed by an engine and two flat-car vehicles was instrumented with force balances to measure the aerodynamic coefficients of the flat-car plus container assembly and of the container alone. Aerodynamic coefficients strongly affects the train stability and the anchorage limits of the container itself. During the wind tunnel tests, eight different loading configurations were considered and aerodynamic coefficients were determined for yaw angles (i.e. angle between train and wind) ranging from 0° to 90°. Experimental results show the benefits in terms of drag reduction due to the presence of a laden vehicle upstream. As far as the rollover risk is concerned, the less critical condition is found for a vehicle preceded by a fully laden wagon and followed by an empty one. More in particular, at low yaw angles, the worst condition for a vehicle occurs when the wagon ahead is empty while, for yaw angles between 45° and 55°, which are the most critical for ‘low speed’ trains, the differences with respect to the other configurations reduce significantly. [ABSTRACT FROM AUTHOR]

The effect of drafting on the aerodynamic drag of a long-track speed skater is investigated in-field, at the 400m ice-rink of Thialf, Heerenveen. The Ring of Fire system is used to measure the flow downstream of an elite, isolated skater at approximately 11 m/s, transiting repeatedly through a tunnel filled with Helium-filled soap bubble flow tracers. Large-scale stereoscopic particle image velocimetry is used at an acquisition frequency of 500 Hz to obtain the near to far wake up to 11 m distance behind the skater. Over these 11 m, the center of gravity of the wake can shift up to 10 cm laterally, depending on the phase of the skating motion, and it moves about 15 cm to the floor. The former suggests that a trailing skater should slightly adapt its trajectory to achieve the lowest aerodynamic drag by drafting. The drag reduction of a trailing skater is estimated from the measurements on the isolated rider, assuming that the trailing rider's drag reduction only stems from the loss in total pressure in the wake of the first rider. The drag reduction is obtained with varying lateral and longitudinal distance between the leading and hypothetical trailing rider. It is observed that the peak reduction (∼40%) steeply decays with increasing lateral offset: at an offset of 50 cm the reduction is negligible. Instead, with increasing longitudinal offset, the decay is more gradual: at a distance of 11 m the reduction of 17% remains significant. The in-field estimations of the drag reduction are supported by wind tunnel measurements conducted on scaled skater models. Finally, the results obtained on the ice-rink indicate that a trailing skater should follow a slightly wider trajectory of about 20 cm, in comparison to the leading skater, to achieve the peak drag reduction during the entire skating stroke. • The air flow in the wake of a transiting skater is measured on a 400-m ice rink using the Ring-of-Fire. • The wake's center of gravity can shift 10 cm laterally and 15 cm to the ice floor 11 m downstream of skater. • The aerodynamic drag reduction of a hypothetical trailing skater is estimated from the in-field wake velocity measurements. • The in-field estimated drag reductions are compared to wind tunnel experiments on scaled skater models. • For minimum aerodynamic drag, a trailing skater should follow a slightly wider trajectory, in comparison to the leading one. [ABSTRACT FROM AUTHOR]

The effects of deflectors on the aerodynamic drag and near wake of an Ahmed model with a 25° slant angle were experimentally investigated. Experiments were conducted in a closed circuit low speed wind tunnel at a Reynolds number of 8.7×10 5 , based on the free stream oncoming velocity ( U ∞ ) and model length ( l ). The deflectors were placed at the side edges and leading edge of the slant. The height or width of the deflectors was 1%, 2% and 3% of l . Pressure distribution on the rear slanted surface and the vertical base was measured using pressure scanners. The flow velocities and static pressure were measured by Cobra probe at 0.5 l and l downstream in the near wake. Oil film flow visualization technique was deployed to capture the flow structure on the slant. In the absence of control, shear layer separation from the side edges and leading edge of the slant results in remarkable local low pressure regions on the slant, which contribute significantly to the aerodynamic drag. There is a D-shape separation bubble on the slant and the near wake is dominated by one pair of counter rotating trailing vortices. When the height of the deflector placed at the side edges of the slant is 1% of l , its effects on the near wake are negligibly small and the corresponding drag is increased slightly, compared to the uncontrolled case. With the deflector height increased to 2% and 3% of l , the D-shape separation bubble and the trailing vortices were noticeably suppressed, with the drag reduction reaching 3.5% and 7.2%, respectively. The deflector at the leading edge of slant changes the near wake of the model similar to that behind an Ahmed model of larger slant angle (e.g. 30° or 35°), eliminating the D-shape separation bubble on the slant. The corresponding drag reduction reaches 9.3%, 10.7% and 10.9% for the deflector width of 1%, 2% and 3% of l , respectively. For the 25° slant Ahmed model, the deflector placed at the leading edge of the slant is more efficient in reducing drag and suppressing the trailing vortices than those at the side edges of slant. [ABSTRACT FROM AUTHOR]

The flow field around a rigid finite square cylinder inclined away from the vertical direction was numerically investigated via large eddy simulations. The cylinder under investigation had a height-to-width ratio of 18 and the inclination angle, defined as the angle between the cylinder orientation and the vertical direction, varied from forward inclination to backward inclination. Pressure measurements and flow visualizations were taken in a wind tunnel to validate the numerical simulations. The forward inclination is found to enhance the downwash, which is initially observed behind the free end of the vertical cylinder, and amplify it to a downward axial flow. Conversely, the backward inclination promotes upwash, which originates behind the base of the vertical cylinder, to be an upward axial flow. On the other hand, the vertical cylinder produces two pairs of counter-rotating streamwise vortices (quadrupole wake) in its wake, but only one pair of vortices (dipole wake) is observed to form behind both the forward and backward inclined cylinders. Moreover, only a free-end vortex pair is exhibited behind the forward inclined cylinder whereas a base vortex pair exists behind the backward inclined cylinder. They are considered to generate the downward and upward axial flow respectively. It is anticipated that the presence of the axial flow significantly influence both the pedestrian-level wind conditions and the aerodynamic characteristics of the cylinder. [ABSTRACT FROM AUTHOR]

For a passenger vehicle, approximately 25% of the total aerodynamic drag originates from the wheels, making the aerodynamics of wheels a significant factor for the overall performance of a vehicle. To understand the complex flow field created by the rotational condition and geometry of these bluff-bodies, numerical simulations are often used. However, computations are frequently performed in domains that replicate open road conditions, differing from the conditions of wind tunnels. Therefore, to properly validate a CFD procedure and to correlate physical tests to numerical results, interference effects of the wind tunnel need to be investigated and their impact on the aerodynamics of wheels analysed and compared to that of open road calculations. In this study, numerical simulations on the DrivAer model were performed using different tyres and rims in both open road conditions and with the inclusion of a detailed model of a slotted walls wind tunnel. The results of the simulations are compared to experimental data, consisting of forces and flow field measurements. It was found that the inclusion of the wind tunnel in the computations improves the prediction of the flow fields, resulting in better prediction of both the absolute drag values and the drag deltas between configurations. • The drag prediction improves with the wind tunnel geometry in the simulations. • The largest discrepancies between domains occur for tyres with lateral grooves. • Open road simulations overpredict the drag difference between open and closed rims. • The wind tunnel blockage alters separations at the tyre and rim. • The ground simulation changes the interaction between the front and the rear wheels. [ABSTRACT FROM AUTHOR]

Adverse weather conditions in the northern regions during winter might lead to accumulation of ice or snow on bridge cables and consequently trigger ice shedding. The falling ice poses a risk for the traffic and pedestrians below, which often results in bridge closures and/or insurance claims. A passive surface-modifying device in the form of a steel wire mesh tautened on the surface of a cable sheath was previously found to substantially reduce the risk associated with falling ice through improved ice retention. In this paper, the cross-flow aerodynamic behaviour of bridge cables fitted with steel wire meshes is investigated in detail. The wire mesh generally resulted in higher levels of aerodynamic drag when compared with a plain cable sheath, although the Reynolds number dependence was highly reduced. Several angles of attack were investigated and no instability issues with respect to the across-wind vibrations were observed for any of the tested wire mesh configurations based on the quasi-steady theory. Even though vortex shedding was still present in all cases, the intensity of the fluctuating lift forces was much lower than that of the plain cable. To investigate basic aspects of the flow structure produced by the wire mesh, two flow visualisation techniques, combined with streamwise wind speed measurements in the near wake, were further used and are discussed. • Innovative surface modifications of bridge cables are investigated in a wind tunnel. • Three wire mesh configurations with a different number of wire ropes are compared. • The wire mesh was designed to reduce the risk of ice shedding from bridge cables. • The test methods include static tests, wake measurements and flow visualisation. • Aerodynamic damping is evaluated using quasi-steady theory. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of the aerodynamic performance of a Hyperloop pod equipped with an axial compressor using CFD simulation. The compressor is expected to reduce the drag if the operational speed of the pod exceeds the Kantrowitz Limit (KL). To evaluate the effectiveness of the compressor, two types of pod have been designed: those with and those without a compressor. A validation study was undertaken for supersonic flow around a cylindrical body in a wind tunnel. Several combinations of pod Mach number and blockage ratios were examined. The axial compressor was modeled with the fan interface model and our original method, which we call the source terms model. Results are similar, but our model has the advantage that it can be applied to higher pressure ratios without inducing numerical instabilities. The power consumption was reduced owing to the compressor by decreasing the pressure accumulated in front of the pod. The effectiveness of the compressor was shown to be greater for conditions well above the KL, with a maximum power reduction of 47.5%. Simulations performed half-scale, and at a different system pressure, showed that the effectiveness of the compressor was not greatly influenced by these parameters. [Display omitted] • Pods with and without an axial compressor are compared by CFD. • The compressor is modeled by the source term in NS equations. • The pressure upstream of the pod is reduced by the axial compressor. • Maximum power reduction is estimated to be 48%. [ABSTRACT FROM AUTHOR]

Abstract: An effective technique for measuring the drag force on a solar concentrator in a subsonic wind tunnel with a simply-fabricated, low-cost force sensing mechanism is described. The measurement uncertainty was reduced by ensuring operation near full scale of the load sensor employed, and by averaging a large number of samples to reduce chance variations due to turbulent fluctuations in the system. The resulting drag coefficients from our apparatus successfully duplicated previously published experimental data from a geometrically-similar, parabolic trough style solar collector. [Copyright &y& Elsevier]

Abstract: This work reports the drag coefficients (C d) for three wind directions measured in low turbulence flow and in turbulent flow with characteristics of the atmospheric boundary layer wind, and the Strouhal numbers (St) of an approximately trapezoidal flanged section, used in the boom girder of a 100m high port crane. These experimental results were obtained at the Boundary Layer Wind Tunnel of the Dept. Aeronautica at the Universidad Nacional de La Plata, in the range of Reynolds numbers between 30,000 and 180,000. The drag coefficients in the three studied directions showed a reduction for turbulent flow. Further measurements were carried out for the model with an inclination of 80° relative to the flow direction, the position of the crane boom when out of service, giving practically the same drag coefficients. [Copyright &y& Elsevier]

The aerodynamic loadings of a 5:1 rectangular cylinder in one-dimensional sinusoidal flows are experimentally tested in a multiple-fan active control wind tunnel. A series of single-frequency streamwise sinusoidal flows, which are fully coherent in the spanwise direction, are generated by changing the frequency and amplitude. Spectral analysis indicates that the total drag, lift forces, and pitching moment contain the inflow-induced components as well as those induced by vortex shedding. To identify the two-dimensional aerodynamic admittances (2D AAF), the vortex-induced components are separated from the inflow-induced components by using the POD method. Subsequently, the 2D AAFs of the drag, lift forces and pitching moment are identified and compared with the empirical or theoretical models. Results show that the inflow amplitude has a limited influence on the 2D AAFs, while the angle of attack (AoA) can cause significant changes in them. At a zero AoA, the 2D drag AAF is in alignment with the Davenport function and the 2D lift AAF is close to Horlock's AAF at low frequencies. Meanwhile, the 2D drag AAF is less influenced by the AoA than the lift and moment AAFs. The relationships between the inflow-induced and vortex shedding-induced components of the total forces are also discussed. The two-dimensional drag, lift, and moment aerodynamic admittances of a 5:1 rectangular cylinder are experimentally identified in one-dimensional streamwise sinusoidal flows. The vortex-induced components of total forces are separated from the inflow-induced ones and the latter is utilized to identify the two-dimensional aerodynamic admittances. Results show that the inflow amplitude has limited influences on the 2D AAF, while the angle of attack (AoA) causes significant changes in them. At zero AoA, the 2D drag AAF is in agreement with Davenport's AAF, and the 2D lift AAF is close to the Horlock's AAF at low frequencies (ω ​≤ ​5). On the other hand, the 2D lift and moment AAF at zero AoA are much higher than those at non-zero AoAs, indicating more unsteady features. The present method can be applied in the buffeting analyses of large-span line-like structures. Image 1 • Aerodynamic forces on a 5:1 rectangular cylinder are measured in sinusoidal flows. • Inflow-induced and vortex-induced components of the total forces are separated. • Two-dimensional drag, lift, and moment aerodynamic admittance (AAF) are identified. • Effects of inflow amplitude and attack angle on the AAFs are analyzed. [ABSTRACT FROM AUTHOR]

Wind tunnel experiments on flow interference of adjacent (spacing ratio P / B ​= ​1.75) twin square cylinders in various attack angles α were conducted at a Reynolds number of 8.0 ​× ​104 considering both horizontal and diagonal arrangements of models. Investigations on the mean and fluctuating aerodynamic force coefficients, mean and fluctuating wind pressure coefficients, spanwise correlations, power spectrum densities (PSD) of lift, and Strouhal numbers of two cylinders, as well as the inter-cylinder correlations between them, are presented. The results show that the aerodynamic characteristics of two diagonal cylinders differ significantly from those of horizontal ones. Compared with the single-cylinder, the pressure distributions on adjacent cylinders are dramatically changed, leading to the negative drag, attractive lift, or repulsive lift on the downstream cylinder. At small α , diagonal cylinders present stronger mean drag and higher fluctuating forces than horizontal cylinders do. Besides, a stronger spanwise correlation is found for the diagonal ones. The vortex shedding pattern can be divided into four stages for the horizontal arrangement and six for the diagonal case. PSD curves and Strouhal numbers are similar between two cylinders for both arrangements, suggesting that the two closely spaced cylinders act like one bluff body in the vortex shedding. • Horizontal and diagonal cylinders have quite different aerodynamic properties. • Two closely spaced square cylinders act like one bluff body in vortex shedding. • Negative drag and attractive lift on the downstream cylinder exist at α ​≤ ​30°. [ABSTRACT FROM AUTHOR]

This study deals with the effects of wind turbulence on the mean aerodynamic drag, lift and moment coefficients of a stationary ice-accreted section model of a bridge cable for different wind angles of attack. The experiments were conducted in the Reynolds number range between 2.5·104 and 1.36·105. While the yawed/inclined cable model was experimentally iced in a climatic wind tunnel, the development of the ice shape was registered using photogrammetry. Later on, the ice-accreted model was reproduced on a smaller scale via three-dimensional printing. For the model in cross-flow, a series of wind tunnel tests were performed in low and moderately turbulent flow conditions with turbulence intensities of 3% and 12%, respectively. The obtained results were compared with those obtained experimentally for a circular smooth cylinder. The principal finding is that the flow turbulence significantly reduces the drag coefficient. • The experimental process was conducted to create an ice accretion on a cable model. • The ice-accreted model was reproduced in smaller scale by 3D printing method. • The aerodynamic coefficients were tested in low and moderately turbulent wind. • The effect of wind turbulence on aerodynamic coefficients was examined. [ABSTRACT FROM AUTHOR]

The impact of flow-normal ribs and small-scale surface roughness on the drag and vortex shedding of a circular cylinder was investigated. Three rib heights, four relative rib spacings and three different forms of micro-roughness were combined to produce 28 unique surface coatings for the cylinder. The drag was measured in a wind tunnel for Reynolds numbers in the range 20,000 < R e < 160,000 , representing nearly a decade change centred about the drag crisis. The drag measurements were complemented by hot-wire measurements in the wake to investigate the vortex shedding frequency. The results show significant average drag reduction, up to 23%, for most of the ribbed geometries compared to a smooth cylinder for R e < 160,000. Increasing the rib height was found to reduce the critical Reynolds number and increase the minimum drag coefficient. Varying the rib spacing resulted in an "optimal" spacing, approximately five times the rib height, that caused the lowest critical Reynolds number. Increasing the micro-roughness resulted in a reduction in the critical Reynolds number and an increase in the minimum drag coefficient. • Extensive parametric study of micro roughness superimposed on ribs on a cylinder. • Identification of a passive reduction of 23% in average drag over the test Re range. • Optimal rib spacing is 5 ​h. [ABSTRACT FROM AUTHOR]

In this article, we illustrate the potential of aerodynamic modifications of road signs to reduce wind-induced vibrations. Using a real-world sign structure operated by the Minnesota Department of Transportation, we focus on two modification variants, one based on the simple removal of secondary panels and one based on the addition of drag reducing rear extensions to the main panel. Our main analysis tool is a computational fluid dynamics framework based on the finite element method, which is validated against experiments with a scaled sign model that were conducted in the towing tank and the wind tunnel of the St. Anthony Falls Laboratory. We demonstrate computationally that aerodynamic modifications constitute an effective way of reducing the vibration amplitude in the example structure for head wind at the average operating wind speed. The present study can be seen as a first step towards establishing the use of aerodynamic devices for road sign structures. • Potential of aerodynamic modifications of road signs to reduce wind-induced vibrations is explored computationally. • The CFD analysis tool based on the finite element method is validated with experiments. • Effective modifications minimize drag and control aerodynamic admittance. • The need for detailed studies that take into account aeroelastic effects is highlighted. [ABSTRACT FROM AUTHOR]

This paper presents a wind tunnel investigation of the autorotation of plates. The effects of geometry, the Reynolds number, and rotation direction on the aerodynamics of the plate, including the rotation rate, lift and drag coefficient, are analyzed. The autorotation rate of plate with smaller aspect ratio is more sensitive to the thickness ratio, whereas when the aspect ratio is larger than 1.5, its effect on the sensitivity of the autorotation rate to the thickness ratio can be ignored. The lift coefficient of plate with larger aspect ratio and smaller thickness ratio is larger when aspect ratio is smaller than 2. Otherwise, the lift coefficient increases first and then decreases with an increase in the thickness ratio. Meanwhile, the lift coefficient of plate decreases as Reynolds number increases, and the relationship between the lift coefficient and the Reynolds number is close to a straight line in logarithmic coordinate. Moreover, the clockwise rotation direction leading to upward lift was found to have a higher absolute value of the lift coefficient than the counterclockwise direction leading to downward lift, especially at low rotation rates. However, the drag coefficient, which fluctuates around a constant of 1.3, is independent of such factors. • The geometry effect on the aerodynamics of rotating plate was investigated. • Previous interpretation of Reynolds number effect on lift and drag coefficient is inaccurate. • The lift coefficient is found to be a function of geometry, Reynolds numbers and rotation direction. • The drag coefficient, which fluctuates around a constant of 1.3, is independent of such factors. [ABSTRACT FROM AUTHOR]