Increasing Yaw Angle Research Articles

Numerical simulations of cross wind effects on cyclist aerodynamic resistance

Introduction : In outdoor cycling, cross wind can affect the race strategy and the final results. Ad-hoc strategies, like echelons and Belgian tourniquet formations, are indeed adopted by cyclists to reduce wind effects and aerodynamic drag. Forces and moments generated by cross winds have been often studied for isolated wheels [1,2] and for an entire isolated cyclist [3-5]. However, to the best of our knowledge, the impact of cross wind on a couple of cyclists has not yet been investigated. In this study, Computational Fluid Dynamics (CFD) simulations are used to evaluate the effect of cross wind on the aerodynamic resistance of a couple of cyclists in two different configurations: (1) when the trailing cyclist is placed in line with the leading cyclist (Fig. 1a) and (2) when both cyclists are staggered (Fig. 1b). To compare the results, additional simulations have been performed for a single cyclist. Moreover, the impact of the upstream turbulence intensity is investigated. CFD simulation: The cyclist geometry used in these simulations has been obtained by means of high resolution 3D laser scanning of elite cyclists. Further information is provided in Refs. (Defraeye, Blocken, Koninckx, Hespel, & Carmeliet, 2010) and (Blocken, Defraeye, Koninckx, Carmeliet, & Hespel, 2013). The computational grids consist of prismatic cells in the boundary layer region near the cyclist body while tetrahedral cells are adopted in the rest of the domain using proper growth factors. The total number of cells is about 8.3 M and 14.0 M, for the single and drafting cyclists, respectively. The simulations are performed using the commercial CFD code ANSYS/Fluent 15.0. The 3D steady Reynolds- Averaged Navier-Stokes (RANS) equations are solved in combination with the standard k- Iµ turbulence model with low Reynolds number modelling based on the one-equation Wolfshtein model. This choice was made since a good agreement with wind tunnel tests was achieved in a previous validation study for the case of zero yaw angle (Blocken, Defraeye, Koninckx, Carmeliet, & Hespel, 2013). The distance from the centre point of the wall adjacent cells to the cyclist body is about 30 I¼m corresponding to an average y* value of about 1. The simulations are performed for yaw angles between 0° and 45° in 5° intervals. Results: the results show that the drag of the leading cyclist is affected by the position of the trailing cyclist only at low yaw angles ( I¸ < 15 degrees). In this case, the drag area coefficient, C d A, is reduced by about 2.5% (not shown in the figures). The drag of the trailing cyclist however is highly influenced by his position with respect to that of the leading cyclist (Fig. 2). When the yaw angle is less than 15° the in line configuration is still advantageous while for larger angles the staggered configuration shows the best behavior both in terms of drag area coefficient and side force area coefficient, C s A. In the case of a single cyclist, a reduction of the drag area is obtained as the yaw angle increases. Conversely the side force area coefficient is increasing almost linearly with larger yaw angles. However the dimensional drag is almost constant until an angle of around 25°, while after it slightly increases. In future studies other configurations will be analyzed and bicycles will be included in the models.

Effects of yaw angle on the unsteady aerodynamic performance of the pantograph of a high-speed train under crosswind

In this study, the delayed detached eddy simulation approach based on the shear-stress transport κ-ω turbulent model was performed to simulate the unsteady aerodynamic performance of the pantograph of a high-speed train using yaw angles of 0°, 10°, 20°, and 30° with crosswind to determine how the yaw angle influenced the numerical simulation results. For validation, the simulation results were compared with wind tunnel test results, demonstrating good agreement. Additionally, the aerodynamic forces and instantaneous and time-averaged flow fields around the pantograph were analyzed. With increasing yaw angle, the flow field asymmetry and vortex intensity near the pantograph increased, the wake flow became more turbulent, and the unsteady aerodynamic characteristics became more obvious. Thus, the yaw angle affected the velocity field distribution near the pantograph considerably, especially in the wake flow area. The aerodynamic forces on the pantograph were also computed, and their time histories were used to reveal the characteristic frequencies of the flow motion around the pantograph. The time-averaged aerodynamic coefficients and their fluctuations increased with increasing yaw angle. In addition, the power spectral densities of the aerodynamic coefficients exhibited obvious peaks, while the aerodynamic coefficient frequency band was wider with crosswind than without crosswind.

Performance and wake characteristics of a tidal turbine under yaw

In tidal streams and rivers, the flow of water can be at yaw to the turbine rotor plane causing performance degradation and a skewed downstream wake. The current study aims to quantify the performance variation and associated wake behavior caused by a tidal turbine operating in a yawed inflow environment. A three-dimensional computational fluid dynamics study was carried out using multiple reference frame approach using κ-ω SST turbulence model with curvature correction. The computations were validated by comparison with experimental results on a 1:20 scale prototype for a 0° yaw case performed in a laboratory flume. The simulations were performed using a three-bladed, constant chord, untwisted tidal turbine operating at uniform inflow. Yaw effects were observed for angles ranging from 5° to 15°. An increase in yaw over this range caused a power coefficient deficit of 26% and a thrust coefficient deficit of about 8% at a tip speed ratio of 5 that corresponds to the maximum power coefficient for the tested turbine. In addition, wake propagation was studied up to a downstream distance of ten rotor radius, and skewness in the wake, proportional to yaw angle was observed. At higher yaw angles, the flow around the turbine rotor was found to cushion the tip vortices, accelerating the interaction between the tip vortices and the skewed wake, thereby facilitating a faster wake recovery. The center of the wake was tracked using a center of mass technique. The center of wake analysis was used to better quantify the deviation of the wake with increasing yaw angle. It was observed that with an increase in yaw angle, the recovery distance moved closer to the rotor plane. The wake was noticed to meander around the turbine centerline with increasing downstream distance and slightly deviate towards the free surface above the turbine centerline, magnitude of which varied depending on yaw.

Passive VIV Reduction of An Inclined Flexible Cylinder by Means of Helical Strakes with Round-Section

A series of experimental tests of passive VIV suppression of an inclined flexible cylinder with round-sectioned helical strakes were carried out in a towing tank. During the tests, the cylinder models fitted with and without helical strakes were towed along the tank. The towing velocity ranged from 0.05 to 1.0 m/s with an interval of 0.05 m/s. Four different yaw angles (a=0°, 15°, 30° and 45°), defined as the angle between the axis of the cylinder and the plane orthogonal of the oncoming flow, were selected in the experiment. The main purpose of present experimental work is to further investigate the VIV suppression effectiveness of round-sectioned helical strakes on the inclined flexible cylinder. The VIV responses of the smooth cylinder and the cylinder with square-sectioned strakes under the same experimental condition were also presented for comparison. The experimental results indicated that the round-Sectioned strake basically had a similar effect on VIV suppression compared with the square-sectioned one, and both can significantly reduce the VIV of the vertical cylinder which corresponded to the case of a=0°. But with the increase of yaw angle, the VIV suppression effectiveness of both round- and square-section strakes deteriorated dramatically, the staked cylinder even had a much stronger vibration than the smooth one did in the in-line (IL) direction.

Interaction of twin synthetic jets in attached and separated boundary layers: effects of yaw angle and phase difference

This paper further extends our understanding of the interaction between twin synthetic jets (SJs) in attached and separated laminar boundary layers, following our previous works on twin SJs at zero yaw angle (Wen and Tang in J Fluids Eng Trans ASME 139:091203, 2017). In current investigation, the twin-SJ-induced streamwise vortices and their influence on attached and separated laminar boundary layers are examined at two nonzero yaw angles and four phase differences. Dye visualization and CFD simulations are conducted to compare the interaction of SJ-induced three-dimensional streamwise vortices and their impacts on the attached boundary layer. Two-dimensional PIV measurements are then conducted to evaluate the control effect of the twin SJs on the separated boundary layer. Our previous works have revealed that at zero yaw angle, the twin SJs interact in a constructive way regardless of their phase difference. Here, we further find that when the twin SJs operate with nonzero yaw angles, their interaction can be destructive due to the nonzero lateral distance, but the level of destruction can be mitigated by adjusting their phase difference. The strength of twin-SJ induced vortices and their impacts in the near-wall region are evaluated through streamwise vorticity flux and excess wall shear stress, respectively. In the separated boundary layer, although generally decreasing with the increase of yaw angle, significant influence of twin SJs can still be observed by varying the phase difference.

Wind Tunnel Test Study for the Influence of Reynolds Number on the Aerodynamic Performance of High-speed Trains

The low temperature variable Reynolds number wind tunnel test for a high-speed train model (EMU) with a leading car and half of middle car is done to study the aerodynamic performance of high-speed trains in the Reynolds number range between 106 and 107, and the conformity test is performed with a scaled ICE3 model. The test results show that the drag of the leading car decreases almost monotonically with increasing yaw angle, while the side and lift force increases with increasing yaw angle. The Cmxlee, which is the most important parameter with respect to cross-wind stability, also increases with increasing yaw angle. The drag force coefficient (Cfx) of the leading car decreases with higher Reynolds number for yaw angles of 0°. The Cfx drops about 0.03 when the Reynolds number is raised from 1 million to 10 million. The lift force coefficient decreases with higher Reynolds numbers.

Analysis of wind turbine blades aeroelastic performance under yaw conditions

The aeroelastic modeling of Tjæreborg wind turbine blades was performed based on the unsteady Reynolds Averaged Navier-Stokes equations (URANS) combined with Finite Element Method (FEM) in a loosely coupled manner. This method was verified by comparing numerical and experiment results at four axial inflow wind speeds. Furthermore, the aeroelastic performance of Tjæreborg wind turbine under yaw angle of 10°, 30° and 60°were computed and analyzed. The results showed that the average power and thrust of the wind turbine decreased with increasing yaw angle, along with the increasing oscillation amplitude under large yaw angle. The aerodynamic load showed periodic change within one revolution of rotor, resulting in the blade deflection and the strain present considerably asymmetric distributions. The maximum deflection and strain occurred at azimuth angle of about90° and their minimum values occurred at azimuth angle of about 270°. Besides, both the maximum deflection and strain under yaw conditions became larger than those in axial inflow condition do. For Tjæreborg wind turbine, the coupled solver gave a higher average power and thrust than the CFD solver alone. The aerodynamic performances showed more asymmetrical characters under the combined effect of yaw and fluid structure interaction (FSI).

Transient aerodynamic characteristics of vans overtaking in crosswinds

Crosswinds affect the aerodynamic characteristics of vehicles involved in overtaking. To investigate such effects, we performed simulations on two identical vans during the overtaking process under different crosswind conditions. The yaw angle between the resultant velocity and the centerline of the overtaken model was varied from 0° to 30°. The results show that the crosswind affects the aerodynamic forces on the two vans significantly, especially on the overtaken van. As the yaw angle increases, the aerodynamic coefficients of the overtaking van increase, but the coefficients of the overtaken van present special patterns at different stages. The pressure fields and flow streamlines for yaw angles β = 0° and 20° were presented to illustrate the potential influence of crosswinds on the two vans. It is obvious that the flow field becomes more complicated under crosswinds, and the varying band of pressure field is expanded. When the front end of the overtaking van exceeds the rear of the overtaken van by a quarter of its body length, the aerodynamic force coefficients of the two vans are considerably large, and the handling stabilities of them decrease greatly. The drivers should pay more attention to safety when driving in crosswinds during the overtaking process.

The effect of yaw angle on VIV suppression for an inclined flexible cylinder fitted with helical strakes

Experimental studies were carried out to investigate the response features of an inclined flexible bare cylinder as well as a straked cylinder in a towing tank, with the main purpose of further improving the understanding of the effect of yaw angle on vortex-induced vibration (VIV) suppression. Four yaw angles (a=0°, 15°, 30°, 45°), which is defined as the angle between the cylinder axis and the plane orthogonal to the oncoming fluid flow, were tested. The cylinder model was towed along the tank to generate a uniform fluid flow. The towing velocity was in the range of 0.05–1.0m/s with an interval of 0.05m/s. The corresponding Reynolds number ranged from 800 to 16000. The strakes selected for the experiments had a pitch of 17.5D and a height of 0.25D, which is generally considered as the most effective configuration for VIV suppression of a flexible cylinder in water. The experimental results indicate that VIV suppression effectiveness of the inclined flexible straked cylinder is closely related to the yaw angle. The displacement amplitudes are significantly suppressed in both cross-flow (CF) and in-line (IL) directions at a=0°. However, with increasing yaw angle, the suppression efficiencies of the CF and IL displacement amplitudes gradually decrease. In addition, the CF dominant frequencies of the straked cylinder obviously deviate from those of the bare cylinder at a=0° and 15°. This deviation is substantially alleviated with increasing yaw angle. The IL dominant frequencies show less dependency on the yaw angle. Similar trends are also observed on the dominant modes of vibration and the mean drag coefficients.

Flutter performance of long-span suspension bridges under non-uniform inflow

This study takes an ideal thin flat plate as a bridge deck section and derives its flutter derivatives at different angles of attack as well as different wind directions using computational fluid dynamics simulations. The effects of wind velocity distribution, angle of attack, and wind direction on flutter performance of a long-span suspension bridge under non-uniform inflow are then analyzed by the finite element program ANSYS. The results show that the adverse effects of higher wind velocities or larger angles of attack on the flutter performance of bridge are more remarkable than the beneficial effects of lower components when the inflow is non-uniform, leading to the reduction of flutter stability, and the decreasing range increases with the increase in non-uniformity of inflow. Moreover, the flutter critical state of bridge could be even controlled by the antisymmetric torsional modal branch if the inflow with a larger angle of attack at which the streamlined plate presents the characteristics of a bluff body acts on the two ends of bridge simultaneously. For skew wind, increasing yaw angle is favorable to the improvement of the flutter critical wind speed of bridge, but the flutter performance is mainly governed by lower yaw angles when the inflow is non-uniform.

Flow structures in end-view plane of slender delta wing

Present investigation focuses on unsteady flow structures in end-view planes at the trailing edge of delta wing, X/C=1.0, where consequences of vortex bursting and stall phenomena vary according to angles of attack over the range of 25° ≤ α ≤ 35° and yaw angles, β over the range of 0° ≤ β ≤ 20°. Basic features of counter rotating vortices in end-view planes of delta win with 70° sweep angle, Λ are examined both qualitatively and quantitatively using Rhodamine dye and the PIV system. In the light of present experiments it is seen that with increasing yaw angle, β symmetrical flow structure is disrupted continuously. Dispersed wind-ward side leading edge vortices cover a large part of flow domain, on the other hand, lee-ward side leading edge vortices cover only a small portion of flow domain.

The Effect of Yaw Angle on a Compressible Rectangular Cavity Flow

Experiments are performed to determine the characteristics of a compressible flow over yawed rectangular cavities for Mach numbers of 0.64, 0.70, and 0.83. The cavity’s length-to-depth ratio varies from 4.43 to 21.50 and the length-to-width ratio is unity. The yaw angle is 0°–45°. The upstream compression and downstream expansion near the front and rear corners of a cavity decrease when the value of the yaw angle increases. The amplitude of the fluctuating pressure is a maximum for an open cavity with a yaw angle of 15°. An increase in the yaw angle results in a reduction in the pressure fluctuations for both open and transitional cavities. In the span-wise direction, variations in the mean and fluctuating pressure are less significant than those in the chord-wise direction. The oscillating frequency of resonance varies slightly with the yaw angle, but the amplitudes for the power spectral density are significantly reduced when the yaw angle is larger than 30°. For lower Mach numbers, the lower mode plays an important role in self-sustained oscillations for an open cavity when there is an increase in the yaw angle.

Hydrodynamic coefficients of a yawed square cylinder in oscillatory flows

The effect of yaw angle (α) on hydrodynamic forces and vortex shedding regime classification of a square cylinder oscillating in still water is examined. The Independent Principle (IP), which states that the Strouhal number and the drag coefficient are independent of α if the normal velocity component is used, was examined in oscillatory flows. Hydrodynamic forces were measured over a Keulegan-Carpenter number (KC) range of 3–30 and a Stokes parameter (β) range of 500–1600. For KC=8-20, the drag coefficient at α=45° is about 46% higher than that at α=0°, indicating the invalidity of the IP in oscillatory flow over this KC range. The inertia coefficient decreases with the increase of the yaw angle, except for KC=8–20, where the sudden drop in the distribution is absent at α=45°. Apart from this KC range, the inertia coefficient follows the IP better than the drag coefficient does. In addition, the lift coefficient increases with the increase of cylinder yaw angle. The results of the lift force spectra and the lift coefficients imply that the existence of the cylinder yaw angle has an intensified effect on the vortex shedding process around a square cylinder in oscillatory flows.

3-D Time-Accurate CFD Simulations of a Multi-Megawatt Slender Bladed HAWT under Yawed Inflow Conditions

In the present study numerical investigations of a generic Multi-Megawatt slender bladed Horizontal-Axis Wind Turbine (HAWT) under yawed inflow conditions were conducted. A three-dimensional URANS flow solver based on structured overlapping meshes was used. The simulations were conducted at wind speeds of 7m/sec, 11 m/sec and 15 m/sec for different yaw angles ranging from +60° to -60°. It was concluded that, for below rated wind speeds, under small yaw angles (below ±15°) the magnitudes of the blade forces are slightly increased, while under high yaw angles (above ±15°) there is a significant decrease. Moreover, the load fluctuations, for the different yaw angles, have the same frequency but different amplitude and oscillation shape. It was concluded that at the above rated wind speed of 15 m/sec, the blade aerodynamic loads are significantly affected by the yaw inflow conditions and the magnitude values of the loads are decreased with increasing yaw angle. It can be concluded that the angle of attack and the tower interference are the utmost variables affecting the yawed turbines.

CFD study on the impact of yawed inflow on loads, power and near wake of a generic wind turbine

AbstractThis article deals with the influence of yawed inflow conditions on the performance of a single generic 2.4MW wind turbine. It presents the results of studies performed at the Institute of Aerodynamics and Gas Dynamics by means of computational fluid dynamics, using a fully meshed wind turbine with all boundary layers being resolved. The block‐structured flow solver FLOWer is used; a dual‐time stepping method for temporal discretization and a second‐order Jameson–Schmidt–Turkel method for the calculation of the convective fluxes are applied. All simulations are carried out using a detached eddy simulation approach. In detail, two different wind speeds and a yaw angle range between −50° and +50° are evaluated in the paper. Based on these data, it is shown that the reduction of power output follows a cosine to the power of X function of the yaw angle. Furthermore, the growing azimuthal non‐uniformity of the load distributions with increasing yaw angle magnitude is analysed by spanwise load distributions. As a central influence on the load distributions, the advancing and retreating blade effect is identified. Moreover, the deflection of the wake as a result of the inflow is investigated, and the deflection angles are compared with a modelling approach. A connection line between wake deflection and load asymmetry is drawn. The results are of particular importance for wind park situations with downstream turbines facing the distorted inflow created from upstream ones. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Influences of yaw angle and turbulence intensity on the performance of a 20 kW in-stream hydrokinetic turbine

Three-dimensional transient CFD (Computational Fluid Dynamics) simulations are performed to study the hydrodynamic performance of an ocean current turbine with a 3.0 m diameter 3-bladed rotor. Simulations are based on the RANS (Reynolds Averaged Navier–Stokes) equations and the shear stress transport k-ω turbulent model is utilized. The influence of yaw angle and upstream TI (turbulence intensity) on the turbine performance is studied. The CFD method is first validated using existing experimental data and good agreement is obtained. The performance of the turbine, including power, thrust and wake characteristics are then studied at different TSR (tip speed ratios). The turbine obtains a maximum coefficient of power (Cp) of 0.4642 at TSR = 6 and the coefficient of thrust (Ct) increases over the entire evaluated TSR range to a value of 0.8788 at a TSR = 10. Simulations are also performed at four different yaw angles, 0°, 5°, 10° and 15° which show that both Cp and Ct decrease as yaw angle increases. Finally simulations of three different TIs, 3%, 6% and 9%, are performed and analyzed. Results show that TI minimally affects Cp and Ct for the considered TI range, but greatly influences the downstream wake structure.

Influence of yawing force frequency on angular motion and ballistic characteristics of a dual-spin projectile

Abstract A roll-decoupled course correction fuze with canards can improve the hit accuracy of conventional unguided ammunitions. The fuze increases accuracy by reducing the effect of angular and translational motion produced by the cyclical yawing forces applied on the projectile. In order to investigate the influence of yawing forces on angular motion, a theoretical solution of the total yaw angle function with the cyclical yawing forces is deduced utilizing the 7 degrees of freedom (7-DOF) model designed for this calculation. Furthermore, a detailed simulation is carried out to determine the influence rules of yawing force on angular motion. The calculated results illustrate that, when the rotational speed of the forward part is close to the initial turning rate, the total yaw angle increases and the flight range decreases sharply. Moreover, a yawing force at an appropriate frequency is able to correct the gun azimuth and elevation perturbation to some extent.

Experimental investigation on wake characteristics behind a yawed square cylinder

The wake vortical structures of a square cylinder at different yaw angles to the incoming flow (α=0°, 15°, 30° and 45°) are studied using a one-dimensional (1D) hot-wire vorticity probe at a Reynolds number (Re) of about 3600. The results are compared with those obtained in a yawed circular cylinder wake. The Strouhal number (StN) as well as the mean drag coefficient (CDN), normalized by the velocity component normal to the cylinder axis, follow the independent principle (IP) satisfactorily up to α=40°. Using the phase-averaging analysis, both the coherent and the remaining contributions of velocity and vorticity are quantified. The flow patterns of the coherent spanwise vorticity (ωz) display obvious Kármán vortex streets and their maximum concentrations decrease as α increases. Similar phenomena are also shown in the coherent contours of the streamwise (u) and transverse (v) velocities as well as the Reynolds shear stress (uv). The contours of the spanwise velocity (w) and Reynolds shear stress (uw), however, experience an increasing trend for the maximum concentrations with increasing yaw angle. These results indicate an enhancement of the three-dimensionality of the wake and the reduction of vortex shedding strength as α increases. While general similarities to the wake behind a yawed circular cylinder are found in terms of flow features, some differences between the two wakes at different yaw angles are highlighted.

CFD simulations of the flow around a cyclist subjected to crosswinds

For the first time, an extensive numerical study of the effect of crosswinds on the flow around a cyclist on a bicycle with stationary wheels has been undertaken for crosswind (yaw) angles ranging from 0° to 90°. The flow field and the aerodynamic forces have been obtained using three numerical techniques: Reynolds Averaged Navier Stokes (RANS), Detached Eddy Simulation (DES) and Large Eddy Simulation (LES). RANS simulations have been undertaken for all the range of yaw angles to provide a general insight of the flow around a cyclist, whilst DES and LES have been undertaken at 15° yaw angle in order to investigate the time-varying flow physics in detail. The aerodynamic forces have been compared with a series of wind tunnel experiments. The RANS results showed the development of large flow separation around the bicycle with increasing yaw angles. The instantaneous flow structures and the auto-spectral densities of the time histories of the force coefficients are identified and revealed that the DES and LES turbulence models are able to predict the dominant frequencies found in the physical experiments. This work provides an improved understanding of the flow characteristics around a cyclist in crosswinds that will hopefully help to improve the safety of cyclists.

Aerodynamic Analysis of a Passenger Car at Yaw Angle and Two-Vehicle Platoon

Abstract Experimental and computational studies were performed to study the drag forces and the pressure distributions of a one-fifth scale model FIAT Linea at increasing yaw angle and two-vehicle platoon. Experiments were performed in the Uludag University Wind Tunnel (UURT) only for the yaw angles of 0 deg, 5 deg, and 10 deg due to the test section dimensional restriction. Supplementary tests were performed in the Ankara Wind Tunnel (ART) to evaluate the aerodynamic coefficients up to yaw angle of 40 deg. The test section blockage ratios were 20% and 1%, respectively, in the UURT and ART tunnels. The blockage effects for the yaw angles up to 10 deg were studied by the comparison of two wind tunnel results. The aerodynamic tests of two-vehicle platoon were performed in the ART tunnel at spacings of “x/L” 0, 0.5, and 1. Static pressure distributions were obtained from the model centerline and three vertical sections. In the numerical study, three-dimensional, incompressible, and steady governing equations were solved by star-ccm+ code with realizable k-ɛ two-layer turbulence model. Experimental and numerical Cp distributions and Cd values were found in good agreement for considered yaw angles and two-vehicle platoon. Maximum drag coefficient was obtained at yaw angle of 35 deg for both experimental and numerical calculations. The two-vehicle platoon analysis resulted with the significant drag coefficient improvement for the leading car at spacings of x/L = 0 and 0.5, while for the tail car drag coefficient remained slightly above the vehicle in isolation.