Spanwise Distance Research Articles

Influence of large-scale free-stream turbulence on bypass transition in air and organic vapour flows

The free-stream turbulence (FST) induced transition in perfect and non-ideal gas zero-pressure-gradient flat-plate boundary layers is investigated by means of large-eddy simulations. The study focuses on the influence of large incoming disturbances over the laminar-to-turbulent transition, by comparing two different integral length scales $L_f$ , which differ by a factor of seven, at different FST intensities $T_u$ . High-subsonic dense-gas boundary layers of the organic vapour Novec649, representative of organic Rankine cycle applications, are compared with air flows at Mach numbers 0.1 and 0.9. Compressibility and non-ideal gas effects are shown to be of minor importance in comparison to the influence of the FST integral length scale $L_f$ . An increase of the inlet turbulent intensity always promotes transition, whereas an increase of $L_f$ has a double effect on the transition onset. At $T_u=2.5\,\%$ , increasing $L_f$ promotes the transition, while it tends to delay transition for an FST intensity of 4 %. Larger FST integral scales tend to increase the spanwise distance between laminar streaks generated in the boundary layer. Two competing transition scenarios are observed. When the incoming turbulence intensity and length scale are moderate, the classical bypass route consists in the linear non-modal growth of streaks, which then experience secondary instabilities (sinuous or varicose) and lead to the generation of turbulent spots. The second scenario is characterized by the appearance of $\Lambda$ -shaped structures near the inlet, which are further stretched to hairpin vortices before breaking down to turbulence. Spot inceptions can therefore occur at earlier locations than the streak growth. We are then faced with a competition between the classical bypass transition and nonlinear response mechanisms that ‘bypass’ this route. The present case at high $L_f$ and low $T_u$ is an example of a competing scenario, but even for the higher $T_u$ and $L_f$ conditions, only approximately one-third of turbulent spots are due to the $\Lambda$ -shaped events. The nonlinear alternative route has strong similarities with scenarios described previously in the literature in the presence of leading edge effects or due to passing wakes. Such a path is governed by the turbulence intensity, but also by the integral length scale, with both parameters playing a critical role in the generation of the $\Lambda$ -shaped structures near the inlet. This alternative mechanism is found to be robust under varying flow and thermodynamic conditions.

Aerodynamic force correlation of a foundational streamlined box girder under vortex-induced vibration in turbulent flow fields

Study on the vortex-induced vibration (VIV) performance of structures under vibration states in turbulent flow fields is closer to the essence of bridge VIV in real service environments, which has been lacking in existing research. The key parameter used in the VIV performance evaluation, vortex-induced force (VIF) correlation, was focused on in this paper. A foundational streamlined box girder was selected, and free vibration sectional model tests were conducted in turbulent flow fields using synchronous pressure-vibration measurement. The results indicate that turbulence have an impact on the VIV performance of streamlined box girder. The presence of turbulence is likely to decrease the VIV amplitude, but sometimes it may also increase it. The phase difference between the leading and trailing edges of the structural upper surface is approximately 100°, and the vortices on the upper surface do not drift continuously. The streamwise correlation of VIFs decreases to varying degrees with the increase in turbulence intensity. The aerodynamic force spanwise correlation when the structure is stationary is significantly weaker than when it is in a vibrational state. When the structure experiences sustained VIV, the spanwise correlation of VIFs decreases with increasing turbulence intensity, increases with increasing amplitude, and decreases with increasing spanwise distance and tends to be constant at a certain distance. Finally, an extended model based on Ricciardelli's correlation function was proposed, which can better describe the VIF spanwise correlation of streamlined box girders under different amplitudes.

Experimental investigation on the improvement of film cooling efficiency with a V-shaped micro-vortex generator

An experimental investigation was performed to assess the impact of a V-shaped micro-vortex generator (VG) on film cooling (FC) efficiency. The study involves injecting coolant gas from a downstream inclined cylindrical hole, while measuring flow characteristics and film cooling efficiency using particle image velocimetry (PIV) and pressure-sensitive paint (PSP), respectively. The width and streamwise location of the VG are systemically studied to provide a comprehensive guideline for the selection of VG geometrical parameter. The data reveal that the width of VG can affect the strength of anti-counter-rotating vortex pair (anti-CVRP) and the spanwise distance between the two vortices in the anti-CVRP. There is an optimal VG width (i.e., W = 2.5D) for the enhancement of film cooling efficiency within the blowing ratio (BR) range of 0.2 ≤ M ≤ 0.8. In addition, it was found that the reduction of the streamwise distance between the VG and the cooling hole does not always improve film cooling performance. The attenuation of the cooling effect in the streamwise direction is significantly accelerated if the VG is placed nearby the cooling hole.

Stability analysis of a streaky boundary layer generated by miniature vortex generators

Delaying laminar-turbulent transition is an attractive method to reduce friction drag on streamlined bodies. In the case of natural transition, in which turbulence is triggered by the growth of two-dimensional Tollmien–Schlichting (TS) instabilities, this growth of TS instabilities can be attenuated by introducing steady streamwise streaks into the boundary layer. These streamwise streaks are generated by streamwise vortices, which rearrange the flow via the lift-up mechanism. Such streamwise vortices can be induced by so-called miniature vortex generators (MVGs). Although recently considerable attention has been devoted to the investigation of MVGs, and multiple studies investigated MVGs with different parameters, the previously investigated MVG configurations are likely suboptimal. This study aims at (partially) filling this knowledge gap by complementing previous studies by conducting a parametric study of rectangular MVGs and assessing them with local linear stability analysis. Three parameters are varied simultaneously: the height, the spanwise distance of the MVG pairs, and the distance between MVGs in each pair. First, the modelling approach is presented, which consist of an efficient base flow computation, and BiGlobal stability analysis. The base flow calculation is validated by comparing our results with the experiments of Shattarzadeh and Fransson (2015). Then, the streak amplitude, the growth factors of the TS-waves and the secondary shear-layer instabilities are analysed in a parametric study. It is shown that with the variation of the spanwise distances, the maximum amplitude and the streamwise extent of the streaks in the boundary layer can be controlled, reminiscent of the behaviour of the optimal vortices. The findings and the test of the methodology provide valuable insight, which may be useful for the optimisation of MVGs.

LES simulation study of wind turbine aerodynamic characteristics with fluid-structure interaction analysis considering blade and tower flexibility

As wind turbine blades become longer and more flexible, aerodynamic characteristics become increasingly complex and require complete investigations. In this study, a two-way fluid-structure interaction (FSI) model is proposed to analyze the effects of inflow conditions, including uniform and atmospheric boundary layer (ABL) winds, as well as blade and tower flexibility, on the aerodynamic characteristics of wind turbine blades. A 4.5 MW real wind turbine with the rotor diameter of 152 m and the hub height of 94 m is considered. Results show that the edgewise blade motion can be disregarded, while the motion of the tower and the flap-wise motion of blade significantly influence the aerodynamic characteristics of blades. The separation flow at the blade root suction side is more distinct and becomes less significant with an increase in spanwise distance, with stagnation points primarily distributed along the flow separation boundary at 0.45–0.95L (L is the blade length). The three-dimensional rotational effect of the blade induces notable fluctuations in the pulsating pressure coefficient, particularly within this region. Notably, a prominent peak is observed at the location of 0.65L. Consequently, it is recommended to allocate additional focus on this specific region to mitigate potential fatigue loads.

Effect of Microchannel on the Composite Cooling Performance of a Simulated Turbine Blade Leading Edge

Abstract As the turbine blade leading edge becomes one of the hottest regions in the engine, a microchannel structure was applied to further improve the cooling performance. Adiabatic and conjugate heat transfer analyses were conducted to compare the heat transfer and cooling performance of the leading edge with or without microchannels, while the influence of mass flowrate of coolant was also included. Based on the investigations on the effect of geometrical designs, the flow and composite cooling performance of the microchannels were further optimized. The results indicate that the internal heat transfer intensity was greatly enhanced with the arrangement of microchannels, while the adiabatic film coolant coverage was slightly deteriorated. On this basis, the composite cooling performance of the leading edge was effectively improved by at least 7.54%. However, the flow resistance of film cooling holes was obviously increased due to the obstruction of microchannels, and a larger thickness of microchannels would alleviate this feature. In addition, the composite cooling performance of the leading edge was further optimized by increasing the radius of microchannels, and the same effect was achieved by reducing the spanwise distance between the film cooling holes and the microjet holes. Compared with the leading edge model without microchannels, the former design increased the area-averaged overall cooling effectiveness of the leading edge by at least 11.17% under all the mass flow rates of coolant studied in this paper, while the latter design improved the composite cooling performance by at least 12.76%.

Experimental and numerical investigation of an aircraft wing with hinged wingtip for gust load alleviation

A recent consideration in aircraft design is using hinged wing tip devices to increase the aspect ratio, improving aircraft performance. Moreover, numerical studies have suggested using the wingtips during flight to provide additional gust load alleviation ability. This work aims to experimentally validate aeroelastic models of a wing with fixed and hinged wingtips. Validated numerical models of wings with hinged wingtips are essential to improve predictions and system knowledge and as a reference model for design optimisation. An elastic wing with hinged and fixed wingtips with different weights was tested. Static wind tunnel tests confirmed the ability of hinged wingtips to reduce gust loads. Aeroelastic models of the wing with the manufactured wingtips were developed, and time history gust responses validated the models. The validated models drove the design of a more efficient wingtip, which experimentally proved the improvement of load alleviation by reducing its mass and structural inertia. Based on this, a parametric study highlighted that increasing the wingtip mass alone, reducing the spanwise distance of the wingtip centre of mass from the hinge, or reducing the hinge stiffness reduces the maximum wing root bending moment.

Scaling of pressure fluctuations in compressible turbulent plane channel flow

The purpose of the paper is to identify Mach-number effects on pressure fluctuations$p'$in compressible turbulent plane channel flow. We use data from a specifically constructed$(Re_{\tau ^\star },\bar {M}_{{CL}_x})$-matrix direct numerical simulation (DNS) database, with systematic variation of the centreline streamwise Mach number$0.32\leqslant \bar {M}_{{CL}_x}\leqslant 2.49$and of the HCB (Huanget al.,J. Fluid Mech., vol. 305, 1995, pp. 185–218) friction Reynolds number$66\leqslant Re_{\tau ^\star }\lessapprox 1000$. Strong$\bar {M}_{{CL}_x}$effects (enhanced by the increasingly cold-wall condition) appear for$\bar {M}_{{CL}_x}\gtrapprox 2$, for all$Re_{\tau ^\star }$, very close to the wall ($y^\star \lessapprox 15$). Compared with incompressible flow at the same$Re_{\tau ^\star }$, the wall root-mean-square$[p'_{rms}]^+_w$(in wall-units, i.e. scaled by the average wall shear stress$\bar {\tau }_w$) strongly increases with$\bar {M}_{{CL}_x}$. In contrast, the peak level across the channel,$[p'_{rms}]^+_{PEAK}$, slightly decreases with increasing$\bar {M}_{{CL}_x}$. In order to study the near-wall coherent structures we introduce a new wall-distance-independent non-local system of units, based for all$y$on wall friction and the extreme values of density and dynamic viscosity, namely, for cold walls$\{\bar {\tau }_w,\min _y\bar {\rho },\max _y\bar {\mu }\}$. The average spanwise distance between streaks, scaled by this length-unit, is nearly independent of$\bar {M}_{{CL}_x}$at constant$Re_{\tau ^\star }$. Using the in-plane (parallel to the wall) Laplacian$\nabla ^2_{xz}p'$we find that the$(+/-)\text {-}p'$wave-packet-like structures appearing inside the low-speed streaks ($y^\star \lessapprox 15$) with increasing$\bar {M}_{{CL}_x}\gtrapprox 2$are part of a more complex wave system with spanwise extent over several streaks, whose spatial density decreases rapidly with decreasing$\bar {M}_{{CL}_x}$or increasing$y^\star$. These$p'$wave packets appear to be collocated with strong$(+/-)$-$v'$events and could be responsible for compensating towards 0 the negative incompressible-flow correlation coefficient$c_{p'v'}$, with increasing$\bar {M}_{{CL}_x}$very near the wall.

Solute transport characteristics in the streambed due to rigid non-submerged plants: Experiment and simulations

The presence of aquatic plants in natural and artificial rivers can cause substantial changes in the flow pattern. In this study, laboratory experiments and numerical simulations are conducted to explore the influences of rigid non-submerged plant densities on the transport of solutes in the hyporheic zone. The laboratory experiments and numerical modelling results show that solute enters into the streambed around plant, and solute in the overlying water experienced a sharp decrease at the beginning, followed by a gradual decline phase. The concentration in the shallow pore water increases rapidly, and increases at a decreasing rate with the increase of depth. The presence of a plant causes pressure gradients at the sediment–water interface before and after the plant. Specifically, the presence of plants induces the convection exchange of surface water and pore water, enables the solute to transport in the streambed through three circulation flows. Solute tends to transport to the root of the plant, or bypass the plant and return to the overlying water over time. The rate and quantity of solute transport in the streambed are related to the streamwise and spanwise distances of the plant. When the plant densities reach the distance that affect the flow structures near each other, smaller streamwise distances lead to the transport of fewer solutes into the streambed and prevent them from penetrating to the deeper part of the streambed, while larger spanwise distances have the same effect on solute transport in the streambed. The solute effective exchange depth for streamwise distance of 20 cm is 4.3 times that of 3 cm, while which for spanwise distance of 3 cm is 5.05 times that of 15 cm at time of 28 h. This study shows that the presence of aquatic plants leads to the circulation of solutes in the hyporheic zone, which promotes the transport of pollutants from overlying water to streambed through hyporheic exchange after the occurrence of a water pollution event. Further, plants densely in the streamwise direction and sparsely in the spanwise direction will reduce the range of pollutants transport in the streambed. This study is of great significance for water ecological restoration through rational arrangement density of aquatic plants.

Numerical study of turbulent flow and heat transfer in a novel design of serpentine channel coupled with D-shaped jaggedness using hybrid nanofluid

This study aimed to examine numerically the effects of a dimpled surface over a mini-channel heat exchangeron the flow characteristics and heat transfer across a serpentine channel with a uniformrectangular cross-section. The dimples were arranged in parallel with a spanwise (y/d) distance of 3.125 and streamwise (x/d) distance of 11.25 along just one side of the serpentine channel's surface.Turbulent flow regime with Reynolds number ranging from 5 × 103 to 20 × 103 in the channel with the surface modificationwas studied using water and various volume concentrations(φ = 0.1%, 0.33%, 0.75%, 1%) ofAl2O3-Cu/waterhybrid nanofluid as the coolant to achieve a three-step passive heat transfer enhancement. Applying the Finite Volume Method (FVM), RNG k-e turbulence model, and a constant heat flux of 50 kW/m2, simulations were run assuming the mixture of Al2O3-Cunanoparticles homogenous using ANSYS 2020 R1. The second-order upwind approach is used forapproximation of solution and discretizationwith SIMPLE pressure–velocity coupling. Taking heat transfer increment and pressure drop penalty into consideration,the dimpled serpentine channel provides a 1.47-times improvement in thermal efficiency using water as the coolant, andthe dimpled channel with 1% vol.Al2O3-Cu/water nanofluid enhanced thermal efficiency by a remarkable maximumof 2.67-times at Re 5 × 103. The study also indicates that thermal efficiency increased with an increasing volume concentration of the nanofluid and increment in thermal efficiency gradually decreased as the Re increased.

Numerical study of the effect of potato cuboids separation in a convective drying

A numerical study (conjugate modeling) of potato cuboid separation in convective drying is performed with the Large Eddy Simulation approach. Any in-line potato array is represented by a single interacted zone through periodic boundary conditions. Numerical code is validated with four experimental studies focused on hydrodynamics (two cases), heat transfer (one case), and mass transfer (one case). Twelve case studies have been proposed to study the effect of streamwise and spanwise distances on heat and mass transfer. Results show that low streamwise separations (0.25) strongly affect the potato drying by the presence of a quasi-stationary wake that causes a blocking effect. The potato cuboid’s best thermal uniformity and mass transfer are presented at a spanwise distance (0.75) and streamwise separations (1.0). Results can be applied to get uniform heat and mass transfer in drying chambers.

Spanwise correlation and coherent structures of separated flow around rectangular 5:1 cylinder

Spanwise correlation and coherent structure of separated flow around a rectangular cylinder with a side ratio of B/D = 5 (B: breadth; D: depth of cylinder) are numerically investigated by Large Eddy Simulation (LES) at Reynolds number Re = 22,000. The investigation utilizes one series of three-dimensional simulations with various spanwise lengths up to 10D at a grid resolution of D/16 and another series of simulations with various spanwise grid resolutions as small as D/40 at a spanwise length of 5D, in addition to a two-dimensional simulation. The results show that a spanwise coherent flow structure with a wavelength of roughly 1.4D, associated with longitudinal vortices, exists in the separated flow. A spanwise length of 3D seems long enough to eliminate the influence of spanwise coherent flow structure on the global aerodynamic parameters and leads to convergent simulation results. The spanwise correlations of sectional forces and surface pressures decay with the spanwise distance. A finer spanwise resolution results in decreased spanwise correlations in the investigated spanwise resolution region. The results also imply that it is necessary to consider the combined effects of multiple interacting factors such as numerical method, three-dimensional grid discretization and turbulence model when selecting the spanwise resolution.

Experimental and Numerical Investigations on the Mixing Process of Supercritical Jet Injected into a Supersonic Crossflow

The mixing process and distribution characteristics of a supercritical endothermic hydrocarbon fuel (EHF) jet injected into a supersonic crossflow were investigated by experimental and numerical methods, respectively. The schlieren system and acetone planar laser-induced fluorescence (PLIF) optical system were used to capture the flow-field structural characteristics and instantaneous plume. The mixture and real gas models were employed to calculate the interaction of a transverse jet and supersonic crossflow and reveal a good accuracy with the experimental results. The mixing efficiency and total pressure loss were analyzed based on the numerical results. The results indicate that the supercritical-state EHF directly changes to a gaseous state as it enters the supersonic crossflow from the injector. The EHF jet plume boundary increases with the increasing momentum flux ratio (q). As the streamwise and spanwise distance increases, the traverse heights and expand width increase, and the EHF jet plume presents a semicircle shape in the cross-sectional plane. With the increase in the traverse direction, the concentration distribution shows a fast and then slow power exponential decreasing law; the highest concentration point starts from the near-wall region and rises in the transverse direction with the flow distance increasing. For the same injection condition, the higher the inflow Mach number, the higher the mixing efficiency. For the same Ma, the mixing efficiency is better for the case with low injection pressure and high injection temperature. The total pressure loss is greater in the higher Ma, and high injection pressure conditions cause greater total pressure loss.

Investigation on overall performance of double-jet film cooling holes with various spanwise distance

The overall film cooling performances of double-jet film cooling (DJFC) holes on a flat plate were evaluated experimentally and numerically including the film cooling effectiveness (η), heat transfer coefficient (HTC) ratio, as well as the net heat flux reduction (NHFR) parameter. The spanwise distance (p/d) varied as 0.5, 1.0, 1.5, and the streamwise distance (s/d) was kept as 3.0. Results show that p/d = 0.5 has the highest cooling effectiveness and the highest net heat flux reduction parameter among all configurations. When the blowing ratio is low, all the DJFC configurations have high film cooling effectiveness and positive NHFR values. However, the NHFR becomes negative for the cases of p/d = 1.0, 1.5 at high blowing ratios, which means the increased heat flux is larger than the case without film cooling. From the flow field, film effectiveness distribution is largely affected by the anti-kidney vortex which is relevant to p/d and blowing ratios (M). The heat transfer coefficient ratio profile is mainly connected to the turbulent kinetic energy (TKE) enhanced by the jet interaction.

On the scaling of three-dimensional shock-induced separated flow due to protuberances

Supersonic flow over three-dimensional bodies protruding out of the turbulent boundary layer was investigated by means of experiments and numerical computations. A parametric study was performed by varying the shape and dimensions of the protuberance, as well as the freestream Mach numbers (1.5, 2, 2.5, 2.89, and 3.5). Surface streak line visualization, surface pressure measurements, and time-resolved Schlieren visualization were employed along with Reynolds-averaged Navier–Stokes computations to elicit the complex flow features such as the separation line, shock pattern, and the horseshoe vortex, which greatly influence the flow dynamics in the separated region. The rise in surface pressure at mid-span due to separation (plateau pressure) was dependent only on the incoming flow parameters and independent of protuberance geometry. The two-dimensional free interaction theory, applied for normal shock-induced separation, closely predicts the mid-span plateau pressure. Although protuberances are of varying shapes and dimensions, the inviscid bow shock (obtained from Euler computations) provided generalized scales, whose effects on shock boundary layer interactions are analyzed. The radius of curvature of the inviscid shock on the wall plane at the nose, which is theoretically related to the local second derivative (along the shock) of pressure jump, was found to be a determining parameter of mid-span separation length (Lsep). Since the spanwise distance of the sonic point on the inviscid shock was found to be strongly correlated with its nose radius of curvature, it follows that the “strong” portion of the inviscid bow shock fixes the mid-span separation location. These observations concerning mid-span plateau pressure, and the role of strong shock portion in fixing mid-span separation, suggest that the Lsep shall be predicted from a modification of the scaling laws for the length of plateau pressure region in two-dimensional shock boundary layer interaction, with the inclusion of a spanwise relieving effect. A correlation is obtained relating the Lsep with various incoming flow parameters and inviscid shock nose radius. The mid-span vortex core position was found to be linearly related to the Lsep. The radius of curvature of the separation shock is, however, found to be influenced by the entire inviscid shock, including the “weak” portion.

Flutter of a finite rectangular Wing’D mill in pitch and heave

Exact solutions of flutter are explored for a mode suitable for an oscillating 2D hydrofoil version of the summarised FlutterWing windpump which radically surpasses the old rotary fanpump. The imaginary part G of the 1D Theodorsen wake lift factor T rises singularly from the steady to allow 1D pure pitch flutter around the leading edge at low frequency. But its logarithmic infinite negative pitch damping by the shed vorticity is capped by the log of the 2D span. The downwash of an oscillating trailing (tip) vortex is reduced by a function of the reduced frequency based on spanwise distance. Its lag damps pitch and further raises the pitch unstable aspect ratio A to above 36. All binary pitch & heave neutral flutter frequency contours in (inertia, imbalance) space still pass through a nexus of the same total pitch inertia and imbalance as the corrected virtual mass concentrated at ¾ chord, a very high total in water. The internal bound windwise vortex from ¼ chord to trailing edge reduces as A−2 the 1D lift slope at all frequencies. It expands the 1D T = ½ double root of high frequency elliptical contours kissing the low frequency limit line at the nexus to make them dip below the line to the right of the nexus as hyperbolae with the nexal ray as left asymptote. Thus low A discovers a new wedge of high frequency binary flutter with real mass moments less than the virtual, as in water.

A case study on thermo-hydraulic performance of jet plate solar air heater using response surface methodology

In this present work, the multi-hole jet impingement approach is used to augment the performance of the jet plate solar air heater by improving the rate of heat transfer coefficient between absorber plate and impinging air. The system's usefulness is analytically analyzed, and the influence of airflow rate, length of the collector, jet diameter, pitch distances at a stream, and span-wise directions on thermo-hydraulic efficiency is investigated by adopting Response Surface Methodology (RSM). A quadratic equation is generated by using the RSM technique, which is used to predict the thermohydraulic efficiency. The results show that the optimized results of the design parameters are at the airflow rate of 0.01386 kg/s, 1.5108 m of length, 0.0046 m of jet diameter with a stream-wise pitch distance of 0.05108 span-wise pitch distance of 0 0.03414 m. The comparison results show that the RSM model evaluated values have a deviation within a range of ±1.78% compared with the analytical values developed by the model.

Thermo-fluid performance enhancement of a fin-and-tube heat exchanger by rectangular winglets

In this study, numerical simulations have been performed to investigate the influence of rectangular winglets as Vortex generators for enhancement of thermo-fluid performance in a fin-and-tube type heat exchanger having five staggered rows of tubes. The influence of placement of winglets over different pair of tubes, attack angles of the winglet pair, and their location has been examined under laminar flow conditions for Re ranging 400–1500. For the present analysis rectangular winglet pairs having “common-flow-up” orientation were employed for vortex generation. The effect of placement of different number of rectangular winglet pairs (1–5) has been investigated and the maximum enhancement in thermo-fluid performance was obtained as 27.4% compared to the baseline model (without winglet model). The winglets attack angle (5°, 10°, 15°, 20°, and 25°) were also investigated for best thermo-fluid performance and the optimum attack angle resulted in enhancement up to 33% over the baseline model. The optimum stream-wise and span-wise locations were identified which resulted in enhancement up to 29% and 25%, respectively, over the baseline model. Correlations for the prediction of Nusselt number, friction factor, and enhancement factor have been developed for stream-wise distance, span-wise distance, and attack angle of the winglets.

Vortex-induced vibration control of a streamline box girder using the wake perturbation of horizontal axis micro-wind turbines

The horizontal axis micro-wind turbine (HAMWT), a wind energy harvesting device, always engenders the streamwise component vorticity, which can potentially be applied to perform 3-D spanwise-varying control. As vortex shedding behind a bluff body is always efficiently suppressed via a 3-D spanwise-varying method, the HAMWT can be used to efficiently suppress the vortex-induced vibration (VIV). The control effect on mitigating the VIV of a streamline box girder is investigated through wind tunnel tests with HAMWTs installed in the spanwise direction. The results show that spanwise-distributed HAMWTs have significant control effects in suppressing the vortex-induced response with a symmetrical arrangement. As the spanwise distance and the height of the HAMWT decrease, the control effects improve. When the spanwise distance L < 3H and the height h < 0.3H (where H is the bridge deck height), the vortex-induced vibration is almost completely suppressed. Moreover, HAMWTs with a staggered arrangement are more effective than those with a symmetrical arrangement, and ultimately suppress the VIV response at different spanwise distances (at least at L = 1H–6H). Furthermore, wake analysis results indicate that wind turbines suppress vortex shedding, and the vortex-induced resonance is significantly weakened.

Control of Vortex-Induced Vibration of a Long-Span Bridge by Inclined Railings

The addition of railings inevitably changes the aerodynamic shape of a main girder, which in turn has a great effect on the vortex-induced vibration (VIV) of a long-span bridge. To ensure the railing has a positive effect, this study presents an inclined railing with improved columns arranged with a spanwise distance of 1–5H (H is the height of the bridge). The design of the improved column is inspired by a passive vortex generator (PVG). The streamwise vortices developed downstream of PVG columns can trigger the three-dimensional instability of a wake, making the shear layer less susceptible to rolling up into mature vortex streets, which are the source of VIV. An experimental study is conducted to compare the influence of traditional and inclined railings on the VIV performance of a closed-box section bridge. It is shown that the addition of a traditional railing deteriorates the VIV performance of the bare girder. However, both vertical and torsional VIVs can be completely suppressed by installing an inclined railing. The results of wake analysis indicate that an inclined railing can greatly decrease the streamwise fluctuation velocity and reduce the spanwise correlation of the streamwise velocity in the wake.