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To investigate the vortex-induced vibration (VIV) of a flexible cable in the uniform flow, experiments were conducted using a flexible cable with an external diameter of 80 mm and a length of 10.48 m in the wind tunnel. The characteristics of multi-modal VIV, time-frequency and traveling wave behavior of the flexible cable were analyzed. Moreover, the effects of twist direction, diameter and the single/double helical wire on the VIV characteristics of the flexible cable were investigated. It is found that the flexible cable experiences single and multi-modal VIVs in uniform flow at different incoming wind speeds, respectively. For the multi-modal VIV of the flexible cable, the vibration over the time history is dominated by two adjacent modal frequencies and shows a phenomenon of beat vibration. The multi-modal VIV responses of the flexible cable show a mix of standing and traveling wave behaviors, in which the effects of standing wave are more pronounced near both ends and the effects of traveling wave are more dominant in the middle region of the flexible cable. The twist direction of the helical wire has little effect on the VIV responses of the flexible cable. The VIV amplitudes of the flexible cable can be reduced by a single helical wire. With the diameter of the helical wire increases, the suppression effects of the single or double helical wire on the VIV of the flexible cable can be improved. Particularly, the double helical wire with diameter 0.10D can effectively suppress the VIV of the flexible cable. [ABSTRACT FROM AUTHOR]

Multiple rows of feathers, known as the covert feathers, contour the upper and lower surfaces of bird wings. These feathers have been observed to deploy passively during high angle of attack maneuvers and are suggested to play an aerodynamic role. However, there have been limited attempts to capture their underlying flow physics or assess the function of multiple covert rows. Here, we first identify two flow control mechanisms associated with a single covert-inspired flap and their location sensitivity: a pressure dam mechanism and a previously unidentified shear layer interaction mechanism. We then investigate the additivity of these mechanisms by deploying multiple rows of flaps. We find that aerodynamic benefits conferred by the shear layer interaction are additive, whereas benefits conferred by the pressure dam effect are not. Nevertheless, both mechanisms can be exploited simultaneously to maximize aerodynamic benefits and mitigate stall. In addition to wind tunnel experiments, we implement multiple rows of covert-inspired flaps on a bird-scale remote-controlled aircraft. Flight tests reveal passive deployment trends similar to those observed in bird flight and comparable aerodynamic benefits to wind tunnel experiments. These results indicate that we can enhance aircraft controllability using covert-inspired flaps and form insights into the aerodynamic role of covert feathers in avian flight. [ABSTRACT FROM AUTHOR]

Different technologies can be utilised to mitigate environmentally harmful ammonia (NH 3) emissions after field application of liquid animal manure (slurry). After a solid-liquid separation, air-plasma technology can acidify the liquid fraction and enrich its nutrient value by increasing the amount of inorganic nitrogen. The present work investigates the emissions of NH 3 and volatile organic compounds (VOC) after field application of the following fractions of pig slurry and slurry digestate: i) untreated slurry (UN), ii) liquid fraction of slurry (LF), iii) liquid fraction of slurry treated with air from the plasma treatment (LP). Emissions were measured with a system of wind tunnels and a cavity ring-down spectrometer for NH 3 concentration measurements and a proton-transfer-reaction mass-spectrometer for measurements of VOC. For both slurry types, the cumulative NH 3 emissions were in the following order UN > LF > LP. All the differences were significant (P < 0.05), except between pig slurry LF and LP. The reduction in cumulative NH 3 emission obtained by the treatments compared to UN were 55–74% and 70–89% for LF and LP, respectively. The slurry separation decreased dry matter by 46–54% and resulted in a rapid decrease in slurry exposed surface area after application, presumably due to high infiltration. Several VOCs were measured after application of the slurry, but continuous emission was undetectable for all VOCs. The very low VOC emission was presumably due to high infiltration of the low dry matter slurry treatments and low concentration of VOC in the digestate. Science4Impact Statement • Separation with decanter centrifuge reduced slurry DM by 46–54%. • Treatment with plasma treated air lowered slurry pH by 1.6–1.8 units. • Separation of slurry decreased cumulative NH 3 emissions by 55–74%. • Separation + treatment with plasma treated air reduced NH 3 emission by 70–89%. • All slurry types investigated had low VOC fluxes after application. [ABSTRACT FROM AUTHOR]

This study addresses the need to investigate footprint function features in urban areas and establish a validation database for numerical methods. Concentration and its flux footprints of a block-arrayed urban model were measured in a wind tunnel with a neutrally stratified boundary layer. The velocity and concentration were simultaneously measured by an X-probe hot wire anemometer and a fast-response flame ionization detector to evaluate the vertical flux. Experimental results highlighted the influence of the measurement heights on footprint distributions. Because the sensors were immersed in the roughness sublayer, their footprints showed strong heterogeneity across horizontal positions caused by building configurations. It was found that turbulent flux contributes up to 70% of total flux footprints, emphasizing the importance of accurate turbulent dispersion estimation in numerical methods. Furthermore, measured footprints were compared to those modeled by a widely used analytical method (Kormann and Meixner in Boundary-Layer Meteorol 99:207–224, 2001, https://doi.org/10.1023/ A:1018991015119). The measured footprints extended further along the streamwise direction and their spanwise dispersions were constrained by the rows of blocks, which failed to be reproduced in the analytical method. This indicates the significant effects of building configurations on footprint functions in urban areas. [ABSTRACT FROM AUTHOR]

The noise and flow characteristics of combined backwards-facing and forward-facing steps (BFS and FFS) are experimentally investigated in an acoustic wind tunnel using a far-field microphone array and Particle Image Velocimetry (PIV), respectively. The step models considered have a step height H of 10∼40 mm and a step gap L of 10∼100 mm, and the Reynolds number is (Re H =) 2.1 × 105∼1.1 × 106. The incoming flow boundary layer is laminar, and the step height is approximately 3∼28 of the boundary layer thickness. The results show that the noise is closely related to the step type, step height H and the gap L. In the step-only configuration, the BFS noise does not vary with the step height H 1 and is much lower than the FFS noise, of which the sound pressure level depends on U 0 5.8 ∼ U 0 6.2 within the height range H 2 . As for the combined step model (BFS&FFS), the noise spectrum changes significantly with the step heights and gaps. When H 1 > H 2 , the noise spectrum resembles the BFS-only due to the flow shield of the FFS from the upstream BFS. When H 1 < H 2 , the noise spectrum is dominated by the FFS, especially at higher H 2 or longer gap L due to more face area of the FFS exposed to the incoming flow. As H 1 = H 2 , the noise resembles the BFS in the low-frequency range and the FFS at high frequencies, respectively. Generally, the step-only and BFS&FFS have broadband noise characteristics, except when the ratio L/H is small, the noise spectrum has the characteristics of a typical cavity dominated by tonal peaks. [ABSTRACT FROM AUTHOR]

Experimental investigations are carried out to explore the aerodynamic performance and vortex shedding characteristics of S5010 and E214 airfoil-based wings to provide guidance for the design of MAVs and other low-speed vehicles. Force and wake shedding frequency measurements are carried out in a subsonic wind tunnel in the Reynolds number (Re) range of 4 × 104 - 1 × 105. The measurements with increasing Re show that the slope of the lift curve in the linear region increases by 14% for S5010, while this increment is 11% for E214. The peak lift coefficient of both airfoils reduces with reducing Re. For lower pitch angles, the influence of Re on drag coefficients is less significant, but at higher angles, the drag increases as the Re drops. Unlike pre-stall mountings, the pitch-down propensity of the airfoil enhances in the post-stall region for high Re flows. Moreover, the frequency of shed vortices reduces with rising angle of attack at a given Re. In contrast, the Strouhal number almost remains constant with varying Re at a fixed angle of attack. For S5010 and E214 airfoils, the Strouhal number is noticed to vary between 0.68 - 0.36 and 0.58 - 0.36, respectively, for pitch angle variation of 12°- 28°. The airfoils show a higher Strouhal number than the bluff body wakes, but this difference decreases for high angles of attack mountings. This finding reveals that the wake structure of the airfoil at a high post-stall angle behaves as bluff body wakes. [ABSTRACT FROM AUTHOR]

Constructed with used plastic bottles, the eco-cooler has been widely adopted in resource-poor communities in Bangladesh and other countries. We tested the eco-cooler under controlled conditions using a scientific wind tunnel in a climatic chamber. In our tests, we used seven eco-cooler designs in 27 climate conditions typical of Bangladesh (temperatures of 40 °C, 35 °C, and 30 °C; humidity levels of 70%, 60%, and 40%; and wind speeds of 4.0 m s−1, 2.0 m s−1, and 0.2 m s−1) in 92 experiments (N = 7686 measurements in 87 short experiments and N = 23,428 measurements in five long experiments). We found no significant temperature reductions with eco-cooler use, except at low wind speeds, where temperature reduced by up to 0.2 °C. In theoretical calculations extending our empirical findings, the greatest temperature drop was 0.85 °C at 4.0 m s−1 with a 40 °C static air inflow temperature. However, this temperature drop did not extend beyond the nozzles of the bottles in the eco-cooler. The eco-cooler did not work effectively as an indoor air cooler. [ABSTRACT FROM AUTHOR]

The flow characteristics around the frontal face of a square cylinder with a frontal jet injection were experimentally studied in a closed-loop wind tunnel using the PIV technique. Four characteristic flow modes were identified based on the injection ratio: swinging jet, deflected oscillating jet, deflection jet, and penetrating jet. At low injection ratio, the flow mode denoted as the swinging jet is characterised by two recirculation regions and a four-way saddle point. At moderate injection ratio, the flow mode termed deflected oscillating jet is characterised by a recirculation region and a counterclockwise rotating vortex within the recirculation region. At moderately high injection ratio, the flow mode is denoted as deflection jet, where a clockwise rotating vortex appears in the flow field. At high injection ratio, the flow mode is termed as penetrating jet, with no vortex formation in the flow field. The strength of the turbulence intensities increases considerably with high injection ratios. The time histories of instantaneous velocity for non-injection case, swinging jet, and deflected oscillating jet modes show periodic oscillations, whereas those of deflection jet and penetrating jet modes do not show periodic oscillations. The study presents and discusses the time-averaged velocity vectors, and streamlines, vorticity contours, velocity properties, velocity time histories, and power spectral density function under different flow modes. [ABSTRACT FROM AUTHOR]

C/C–HfC–SiC composites were prepared by reactive melt infiltration using Hf–Si alloy (Hf, more than 95 wt%) with a density of 3.86 g/cm3 and an open porosity of 8.34%. The microstructure, mechanical properties, and ablation behavior at high temperatures were studied in detail. SiC played a crucial role in alleviating the thermal mismatch between HfC and PyC, which formed at the interface between the carbon matrix and the HfC matrix. The flexural strength and modulus of C/C–HfC–SiC composites were 237 MPa and 37.6 GPa, respectively. The C/C–HfC–SiC composites exhibited excellent ablation resistance with a linear ablation rate of 8.9 × 10−3 mm/s and maintained a surface temperature above 2925°C during ablation. During this process, HfO₂ remained in a molten state with high viscosity and served as a thermal barrier, while the volatilization of SiO₂ effectively removed heat, protecting the composites from further ablation. [ABSTRACT FROM AUTHOR]

In air-assisted spraying, pesticide droplet retention on crop leaves is key to evaluating spray effectiveness. However, airflow can deform leaves, reducing droplet retention and affecting spray performance. This study used wind tunnels and high-speed cameras to capture leaf deformation at different airflow speeds and the motion of droplets on curved leaf surfaces. The results showed that leaf curvature during bending deformation is generally less than 0.05 mm-1. Critical wind speed for droplet movement is negatively correlated with droplet size and leaf curvature, with a 24.8% difference between different leaf curvatures and a 17.5% difference between droplet sizes. The droplet's dimensionless shape variable is positively correlated with both droplet size and leaf curvature. The maximum shape variable on curved leaves reaches 0.24, with acceleration differences of about 30%, while droplets of different sizes show a maximum shape variable of 0.18 and an acceleration difference of up to 68%. These findings enhance understanding of droplet-leaf interactions and provide insights for improving pesticide efficiency. [ABSTRACT FROM AUTHOR]

Self‐supporting concrete shell structures are highly efficient in distributing loads, which can result in very reduced thicknesses (ultra‐thin), giving them remarkable slenderness. Due to their geometric complexity, it is difficult to predict how they interact with wind action. The main aim of the present study is to assess the mean surface pressure coefficient distribution in a shell with a triangular plan shape and three supports for different angles of wind incidence. To determine the distribution of surface pressure coefficients and lift and drag force coefficients, an experimental study was carried out in a wind tunnel, and a numerical simulation study was performed through computational fluid dynamics. The experimental and numerical results were analyzed and compared, and making it possible to identify the most critical surface zones and wind incidences when the shell is under the wind action. [ABSTRACT FROM AUTHOR]

With the increased usage of air filtration and deodorization devices in livestock houses, the demand of agricultural axial flow fans with higher pressure has been raised. To improve the aerodynamic performance of an agricultural axial fan and expand its operating range, a new axial fan was developed using the theory of variable circulation method design via wind tunnel experiments and numerical simulations. The purpose is to change the structural form at the hub of the existing blade to improve the internal flow pattern of the agricultural axial fan, so as to achieve the purpose of improving the aerodynamic performance of the agricultural axial fan and expanding the range of stable operation. In this paper, a new agricultural axial flow fan is designed using the variable circulation method with 0.91m agricultural axial flow fan size and target airflow as design parameters. Secondly, the structural parameters at the hub of the axial fan are optimized by combining the simulation results of the flow field of the designed fan. Factors such as hub diameter d, the placement angle α and the number of moving blades n are analyzed individually, revealing the basic law of the influence of the changes of these factors on the performance of the fan, and the influence of the changes of each factor on the internal flow field of the fan is observed in combination with post-processing. using the better intervals for each factor derived from the one-factor optimisation results, the ventilation volume Q and the energy efficiency ratio N were selected as response values, and a response surface simulation study was carried out for the hub diameter d, the placement angle α, and the number of moving blades n. The response surface simulation study was carried out for the hub diameter d, the placement angle α, and the number of moving blades n. The response surface functional equations were obtained and the better parameter combinations were determined. The correctness of the functional model is further verified by observing the flow field characteristics and external characteristics through post-processing. Finally, the optimised impeller was fabricated by 3D printing technology and wind tunnel tests were conducted, and the results of the actual tests further confirmed the accuracy of the optimisation results. The numerical simulation results of the study show that the optimum combination of these parameters is d=260 mm, α=-0.369°, and n=4 pieces. Experimental test results show that the optimized axial fan performance is better than initial axial fans. On the high-pressure level (120 Pa), the ventilation volume Q of agricultural axial fan increased by 163%, and the energy efficiency ratio N increased by 18.9%. This study proves the feasibility of the variable circulation method in the design of high-pressure agricultural axial flow fan, and the optimization of structural parameters can further reduce the internal vorticity of the fan. The optimized axial fan reduced the secondary flow in the internal flow field, increased the work capacity of the blades, and improved the aerodynamic performance of the fan, ensuring that the axial fan can achieve air circulation and regulation more efficiently in agricultural applications. [ABSTRACT FROM AUTHOR]

In the ABL wind tunnel, three inverted umbrella-shaped membrane structure groups were subjected to simultaneous pressure measurement model test. Time series of the fluctuating wind pressure were collected from 24 different wind angles. Upon examining the correlation coefficient of the fluctuating wind pressure between the upper and lower surfaces at the same pressure tap, it was discovered that the fluctuating wind pressure of the upwind roof exhibited asynchronous changes, which is a characteristic of a negative correlation area and has detrimental effects on the structure's wind resistance. The local areas with non-Gaussian properties were evaluated by analyzing the probability density function of representative pressure taps. The mechanism behind non-Gaussian wind pressure was elucidated through considerations of the central limit theorem and spatial correlation of fluctuating wind pressure. This study introduces a quantitative classification criterion for identifying the non-Gaussian distribution area of fluctuating wind pressure, setting the threshold at an 80% cumulative probability for both skewness and kurtosis. The analysis showed that the steady airflow of the structure corresponds to the Gaussian distribution area, while the non-Gaussian distribution area is primarily concentrated at the front edge of the upwind roof and the rear edge of the downwind roof. To ascertain the peak factor for the non-Gaussian distribution, the improved peak factor method was utilized, providing insights into the range of peak factor in the non-Gaussian distribution area of this particular roof configuration. This information serves as a foundation for the wind resistance design of this structure. [ABSTRACT FROM AUTHOR]

Grids such as perforated plates are of fundamental importance in flow turbulence study and are commonly utilised to promote mixing. An orificed perforated plate (OPP) and its reversed counterpart, the converging-nozzle perforated plate (CNPP), were applied to produce quasi-isotropic turbulence inside a wind tunnel. The three orthogonal velocity components were measured using a triple hotwire at 10D downstream of the perforated plate for Reynolds numbers, ReD, 18,700 and 28,400, where D is the diameter of the perforated holes. The statistics of the grid-generated turbulence was analysed using the time-averaged local velocity profile and turbulence intensity, which revealed a more homogeneous distribution of the flow field with a higher level of turbulence for the OPP. Fourier and wavelet analyses were employed to investigate the energy of the eddies as a function of frequency and multiscale characteristics of the fluctuating velocity, respectively. At ReD = 18,700, the turbulent energy remains prominently with large-scale vortical structures which are non-intermittently present in the flow for both perforated plates. The thickness of the converging channels of the CNPP appears to provide the venue for spawning intermittent fluctuations. At higher ReD 28,400, the effect of this intermittent behaviour becomes evident for the CNPP, leading to a multiscale distribution of turbulent energy. [ABSTRACT FROM AUTHOR]

To ensure only one train operates in each ventilation section within an extra-long tunnel, a ventilation shaft was typically installed to divide the entire tunnel into multiple sections. Given the crucial role of piston wind in the metro tunnel environment and ventilation, a deeper understanding of train-induced unsteady airflow in a metro tunnel with a ventilation shaft is desirable. This study uses the unsteady flow theory of the Bernoulli equation to mathematically model piston wind in metro tunnels both with and without ventilation shafts. The influence of various shaft parameters on piston wind development is systematically analyzed. The results indicate that the shaft significantly impacts the piston wind. The maximum piston wind speed and ventilation rate in tunnels with ventilation shafts surpass those in tunnels without them. Moreover, shaft location and the cross-sectional area notably affect the maximum piston wind speed, ventilation rate, and airflow in the shaft, whereas shaft height has no significant effect. It is found that a ventilation shaft with a larger cross-sectional area positioned in the middle of the tunnel enhances the performance of piston ventilation. [ABSTRACT FROM AUTHOR]

A procedure is proposed to correct temperature drift for hot wire anemometry measurements in turbulent fields where the facility is not equipped with temperature control. The procedure consists of evaluating the wire sensitivity to the temperature by building a voltage-temperature curve. The voltages of both the calibration points and the measurement points are corrected, shifting the voltage values to an arbitrary reference temperature. The correction can be applied to the instantaneous voltages by performing synced temperature measurements with constant current anemometry or constant voltage anemometry cold wire. The efficacy of the method is tested on a turbulent shear layer that develops on the side of an open jet wind tunnel not equipped with temperature control. The velocity statistics show a good match with respect to reference particle image velocimetry measurements, evidencing the self-similarity of the shear layer in contrast with the non-corrected data and the data corrected using the semi-empirical and analytical relation based on King's law modification. A correction based only on the temperature statistics shows indistinguishable results with respect to the instantaneous correction. [ABSTRACT FROM AUTHOR]

A flow-control method is applied to enhance the efficiency and flow homogeneity of three-dimensional diffusers used in open-jet wind tunnels. Suitably shaped grooves are introduced in the diffuser diverging walls. The grooves promote the relaxation of the non-slip condition along the streamlines bounding the small recirculation regions forming passively inside the grooves. That reduces momentum losses and results in a downstream boundary layer with higher momentum, which is more separation-resistant. The proposed flow-control device has been successfully validated for plane diffusers [Mariotti et al., "Separation control and efficiency improvement in a 2D diffuser by means of contoured cavities," Eur. J. Mech.-B 41, 138–149 (2013); and Mariotti et al., "Control of the turbulent flow in a plane diffuser through optimized contoured cavities," Eur. J. Mech.-B 48, 254–265 (2014)]. In this study, we examined circular and square-section diffusers with different degrees of flow separation. Given that the investigated diffusers are part of open-jet wind tunnels, the entire wind tunnel geometry was included in the numerical simulation. The grooves significantly enhanced performance in circular diffusers by reducing the extent of separation and promoting an axisymmetric and spatially uniform flow. However, negligible benefits were observed for square-section diffusers. In these cases, since flow separation originates from one of the four inclined edges of the diffuser, placing grooves along the diverging walls does not effectively reduce the separation extent. Nonetheless, the grooves become effective again in diffusers with rectangular cross sections of high aspect ratio. [ABSTRACT FROM AUTHOR]

The uncertain factors in wind tunnel experiments, especially the interference effects, will cause the flow around the test model to differ from that under the free flow condition. The wind tunnel wall interference effects are challenging to be eliminated, especially in transonic flow regions where classical linear correction methods are ineffective. To address this issue, an efficient wind tunnel wall interference correction framework based on data assimilation is proposed for steady and shock buffet flows around the airfoils in the transonic region in this work. The ensemble Kalman filter (EnKF) is used to find the combination of inflow conditions, which minimizes the differences between the pressure coefficients measured in the wind tunnel experiment and those estimated by computational fluid dynamics (CFD). The polynomial chaos expansion method is used to propagate uncertainty in the forecast step of the EnKF in order to improve efficiency. Typical wind tunnel wall interference correction problems are studied, including two steady cases: the transonic flow around the Royal Aircraft Establishment 2822 (RAE2822) and the National Aerospace Laboratory 7301 (NLR7301) airfoils, and one unsteady case: the transonic shock buffet on the National Aeronautics and Space Administration supercritical (phase 2)-0714 (NASA SC(2)-0714) airfoil. It is demonstrated that with the corrected Mach number and angle of attack, the estimated CFD results are in better agreement with the measured experimental data than traditional linear methods and the computational efficiency is improved compared to the original EnKF. [ABSTRACT FROM AUTHOR]

It is curious that whether the typical herringbone pattern of bird flight feathers plays a role in attenuating aeroacoustic noise. Being motivated by this, experiments are conducted to investigate noise reduction of the NACA0012 (National Advisory Committee for Aeronautics) airfoil-based model with one side surface covered by bio-inspired herringbone patterns of riblets. The herringbone-ribbed surface is defined by the divergent angle β (= 60°) of the riblets pattern, the spanwise wavelength λ (= 0.2c and 0.4c) of the pattern, and the riblet height h (= 0.6%c and 1.2%c), where c is the chord length of the airfoil. While far-field sound pressure fluctuations are measured via microphones in an anechoic wind tunnel, flow fields around the model are captured using particle image velocimetry (PIV) in a water tunnel. The effective angle of attack of the test models ranges from αeff = −11.1° to 11.1° and Reynolds number considered is from Re = 2.3 × 105 to 7.8 × 105. Compared with the baseline smooth models, the models with the riblet pattern on the pressure side are able to substantially suppress the tonal noise, associated with considerable reduction in the overall noise. The reduction in the overall sound pressure levels of the tonal noise and the overall noise are up to 21.3 dB and 20.5 dB, respectively, at αeff = −2.2° and Re = 3.6 × 105. The noise reduction is attributed to the transition of laminar to turbulent boundary layers over the herringbone-ribbed surface, particularly in the saddle location where the spanwise-repeated herringbone pattern converges. Behavior of shear layers separating from the trailing edge of the model is examined, corroborating the proposition that the acoustic feedback loop is impaired by the herringbone-ribbed surface. [ABSTRACT FROM AUTHOR]

Although there has been much research on the gas–solid separation equipment of cyclone plate, there is still a lot of research space for miniaturization, low resistance, and easy maintenance. In this paper, parallel gas–solid separation equipment is designed based on computational fluid dynamics and experimental verification methods to address the practical problems faced by the fresh air system of the enterprise plant. The internal flow field of the separator is studied by numerical simulation, and the structural parameters of the separator are optimized according to the performance indicators provided by the enterprise. The optimal structure that meets the performance requirements and has the best effect is determined. Subsequently, the actual performance of the optimal structure was verified by wind tunnel experiments, and the deviation between the experimental results and the numerical simulation results was compared. The results show that increasing the number of blades, adjusting the blade angle, and increasing the height of the outer cylinder are beneficial in improving the internal flow field of the separator. Among them, the blade angle significantly affects the tangential velocity and axial velocity of the separator. When these three parameters are increased, the filtration efficiency increases first and then decreases. Finally, when the number of blades is 8, the blade angle is 50°, and the height of the outer cylinder is 0.63 m, the separation efficiency is the highest, and the pressure drop is the lowest. This structure satisfies all performance indicators. The experimental results show that the minimum filtration efficiency is 92.4%, and the maximum pressure drop does not exceed 500 Pa. Compared with the numerical simulation results, the experimental value is 0.29% lower, which shows that the structure has good separation performance and has a significant reference value for the fresh air system of the industrial workshop. [ABSTRACT FROM AUTHOR]

A cooling film (Mach 2.3) is injected into a supersonic wind tunnel's (Mach 3.8) flow field. As the curvature radius decreases, mixing layer destabilization is delayed on the CV (convex wall) and advanced on the CC (concave wall). When x = 20–60 mm, wall pressure is influenced by the cooling film, and when x = 100–220 mm, curvature dominates. As the curvature radius decreases, pressure on the concave wall increases more rapidly, while that on the convex wall decreases more swiftly. IP (impulse for bulk dilation) values on the CC-1500 and CV-1500 walls are approximately twice those on the CC-3000 and CV-3000 walls, respectively. [ABSTRACT FROM AUTHOR]

The characterization of passive area sources, emitting odours due to wind-driven convection, poses significant challenges. The present experimental study aims to evaluate the performance, in terms of fluid dynamics and mass transfer, of a recently developed wind tunnel, with a more compact design and reduced weight, compared to the one proposed by the Italian regulations. The results show that the new design outperforms the Italian standard in several aspects. From a fluid dynamic point of view, the new wind tunnel exhibits a slightly more homogenous and uniform velocity distribution, and it does not reveal airflow preferential channels inside the central body. The pressure tests highlight that the presence of fillers in the new wind tunnel does not significantly alter the pressure inside the hood and therefore the gas–liquid equilibrium conditions; actually, the slight overpressure may help to prevent the infiltration of external air. Finally, mass transfer tests on the standard device show a vertical concentration gradient along the outlet duct, highlighting concentration values that differ up to a factor of two depending on the measurement point. The new design has almost completely solved this issue, thanks to the use of fillers that promote mixing of the outlet flow. [ABSTRACT FROM AUTHOR]

Methods and technologies to control the noise coming from turbulent flows impinging on outlet guide vanes in turbofan engines are tremendously needed nowadays to comply with new legislation on acoustic environment pollution. The following paper relies on preliminary research proposing a new experimental design of active noise control system to be further integrated into a jet engine outer guide vane prototype, consisting of multiple flush-mounted piezoelectric cells. Here, three active cells are placed on the bottom wall of a wind tunnel with upstream acoustic excitation generating grazing incident waves for different airflow velocities. Using a downstream microphone as an error sensor, the active system succeeds in improving the transmission loss of the sample by 2.5 dB at the target frequency (670 Hz) corresponding to the main piezo acoustic mode with airflow velocities up to 20 m.s−1. These early experimental results confirm the ability of the concept to interact with the ambient acoustics without disturbing the airflow as in passive solutions using porous materials, for instance, leading the path to future experiments with realistic turbulence generating acoustic sources on the leading edge of the vane profile. [ABSTRACT FROM AUTHOR]

Flying animals such as insects and birds use wing flapping for flight, occasionally pausing wing motion and transitioning into gliding to conserve energy for propulsion and achieve high flying efficiency. In this study, we have investigated the gliding performance of a gliding model based on a flapping-wing robot developed in a previous study, with the aim of developing a highly efficient flying robot that utilizes bio-inspired intermittent flight. Wind tunnel experiments with a gliding model have shown that the attitude of the wings has a strong influence on gliding performance and that a tail is effective in improving gliding performance. The results of this study provide important insights into the development of flying robots that can travel long distances with high efficiency. [ABSTRACT FROM AUTHOR]

As a laminar flow control device for delaying the crossflow-induced transition of a three-dimensional boundary layer, sinusoidal roughness elements (SREs) are placed in a Falkner-Skan-Cooke boundary layer, and the resultant laminarizing effect is numerically investigated in comparison with discrete roughness elements (DREs). Because SREs are elongated in the streamwise direction and designed to avoid flow tripping, the critical height of SREs is much higher than that of DREs. Moreover, the wake flow behind SREs efficiently generates and sustains crossflow vortices that are not dangerously unstable against secondary instabilities but able to strongly distort the mean crossflow profile into a less unstable one. By measuring this mean flow distortion by SREs and DREs, the laminarizing effect is compared among them. It is shown that the effect of SREs is higher than that of DREs and can be enhanced by choosing the appropriate height, angle, and wavelength depending on the local boundary-layer profile. [ABSTRACT FROM AUTHOR]

Tunnel fires are generally detected using various sensors, including measuring temperature, CO concentration, and smoke concentration. To address the ambiguity and inconsistency in multi-sensor data, this paper proposes a tunnel fire detection method based on an improved Dempster-Shafer (DS) evidence theory for multi-sensor data fusion. To solve the problem of evidence conflict in the DS theory, a two-level multi-sensor data fusion framework is adopted. The first level of fusion involves feature fusion of the same type of sensor data, removing ambiguous data to obtain characteristic data, and calculating the basic probability assignment (BPA) function through the feature interval. The second-level fusion derives basic probability numbers from the BPA, calculates the degree of evidence conflict, normalizes the BPA to obtain the relative conflict degree, and optimizes the BPA using the trust coefficient. The classical DS evidence theory is then used to integrate and obtain the probability of tunnel fire occurrence. Different heat release rates, tunnel wind speeds, and fire locations are set, forming six fire scenarios. Sensor monitoring data under each simulation condition are extracted and fused using the improved DS evidence theory. The results show that there is a 67.5%, 83.5%, 76.8%, 83%, 79.6%, and 84.1% probability of detecting fire when it occurs, respectively, and identifies fire occurrence in approximately 2.4 s, an improvement from 64.7% to 70% over traditional methods. This demonstrates the feasibility and superiority of the proposed method, highlighting its significant importance in ensuring personnel safety. [ABSTRACT FROM AUTHOR]

To alleviate the shock boundary layer interaction adverse effects, various active or passive flow control strategies have been investigated in the literature. This research sheds light on the behavior of perforated plates as passive flow control techniques applied to NACA0012 airfoils in cascade configurations. Two identical perforated plates with shallow cavities underneath are accommodated on the upper and lower surfaces of each airfoil in the cascade arrangement. Six different cascade arrangements, including a baseline configuration with no control applied, are additively manufactured, with different perforated plate orifice sizes in the range of 0.5–1.2 mm. A high-speed wind tunnel with Schlieren optical diagnosis and wall static pressure taps is used to investigate the changes in the shock waves pattern triggered by the perforated plates. Steady 3D density-based numerical simulations in Ansys FLUENT are conducted for further analysis and validation. In the cascade configuration, the perforated plates alter the shock structure, and the strong normal shock wave is replaced by a weaker X-type shock structure. Eventually, a 1% penalty in overall total pressure loss is induced by the perforated plates because of the negative loss balance between the reduced shock losses and the enhanced viscous losses. Further studies on perforated plate geometrical features are needed to improve this outcome in a cascade arrangement. [ABSTRACT FROM AUTHOR]

This article reports about a wind‐tunnel experiment carried out in the ONERA F2 low‐speed wind tunnel on a model of the DU 97‐W‐300Mod airfoil designed for wind turbine application. The wind tunnel, the airfoil model, and experimental techniques used are presented, with special emphasis on the data processing and corrections required to derive airfoil forces and pressure distribution. To better document the flow physics at play, the results are illustrated by infrared thermography and surface oil flow visualization. The test allowed investigating Reynolds number effects between 1 and 3.8 millions. To ameliorate the understanding of the benefits and limitations of such airfoil testing, one section is devoted to the comparison of present results with previous experiments in other wind tunnels. Some of the difficulties arising in airfoil testing are evidenced and discussed to contribute to the improvement of test methods. [ABSTRACT FROM AUTHOR]

Based on the performance and acoustic data files of reduced-size open-rotor engines in low-speed wind tunnels, the static sound pressure level was derived by converting the 1-foot lossless spectral density into sound-pressure-level data, the background noise was removed, and the results were corrected according to the environmental parameters of the low-speed wind tunnels. In accordance with the requirements of Annex 16 of the Convention on International Civil Aviation Organization and Part 36 of the Civil Aviation Regulations of China on noise measurement procedures, the takeoff trajectory was physically modeled; the static noise source was mapped onto the takeoff trajectory to simulate the propagation process of the noise during takeoff; and the 24 one-third-octave center frequencies that corresponded to the SPL data were corrected for geometrical dispersion, atmospheric absorption, and Doppler effects, so that the takeoff noise could be corrected to represent a real environment. In addition, the audible processing of noise data with a 110° source pointing angle was achieved, which can be useful for enabling practical observers to analyze the noise characteristics. [ABSTRACT FROM AUTHOR]

To understand the asymmetric flow of a slender body with low-aspect ratio fins, a wind tunnel experiment was carried out, and the asymmetric flow was observed when the pair of fins had a symmetric deflection angle of 30° at a small angle of attack and zero sideslip angle at transonic speeds. The unsteady characteristics of flow around the moving fins, especially for the evolution of the asymmetric flow, was carefully numerically investigated via the RANS method. To verify the numerical method, the experimental steady wind tunnel data of the NACA 0012 airfoil with sinusoidal pitching motion were adopted. A hysteresis loop exists as a function of the deflection angle during the upstroke and downstroke motions. The side force is periodic due to the asymmetric flow peaks at the downstroke and their peak value appeared at around δz = 25°, which was independent of the deflection frequency. As the deflection frequency increased, the asymmetric flow formed at a higher deflection angle during the upstroke motion, but decayed at a lower deflection angle during the downstroke motion, resulting in a more significant unsteady hysteresis effect. [ABSTRACT FROM AUTHOR]

To investigate the nonlinear flutter characteristics of long-span suspension bridges under different deck ancillary structures and configurations, including those with and without a central wind-permeable zone, as well as to analyze the hysteresis phenomenon of a subcritical flutter and elucidate the mechanisms leading to the occurrence of nonlinear flutter, this paper studies first the post-flutter characteristics of the torsion single-degree-of-freedom (SDOF) test systems and vertical bending–torsion two-degree-of-freedom (2DOF) test systems under different aerodynamic shape conditions are further analyzed, and the role of the vertical vibration in coupled nonlinear flutter is discussed. The results indicate that better flutter performance is achieved in the absence of bridge deck auxiliary structures with a central wind-permeable zone. The participation of vertical vibrations in the post-flutter vibration increases with the increase in wind speed, reducing the flutter performance of the main girder. Furthermore, the hysteresis phenomenon in the subcritical flutter state is observed in the wind tunnel experiment, and its evolution law and mechanism are discussed from the perspective of amplitude-dependent damping. Finally, the vibration-generating mechanism of the limit oscillation ring is elaborated in terms of the evolution law of the post-flutter vibration damping. [ABSTRACT FROM AUTHOR]

Splash functions delineate the intricate interaction between wind‐driven particles and the bed. However, due to limitations in measurement methods, achieving a comprehensive understanding of splash functions remains challenging. In this study, we utilized a high‐speed system and particle trajectory tracking algorithm to reconstruct 857 collision events involving natural sand particles obtained from field samples and artificial glass microspheres interacting with a bed composed of analogous particles in a wind tunnel. During the experiments, the ratio of the wind shear velocity (u*) to the impact threshold (u*ti) consistently ranged between approximately 1.22 and 1.79. Our findings indicate that the impact angle remains independent of both impact velocity and particle size, maintaining an approximate value of 10.5 ± 6.5°. The evaluation of splash functions depends on the criterion used to define ejection, that is, the ratio of the centroid's height of the liftoff particles to their particle size (H/d). Additionally, at the same critical height (H/d = 1.5), our splash functions show differences of varying degrees from previous experiments and theoretical studies performed under no wind conditions. We believe that the main reason for these differences may be that the energy exchange between the bed surface and the airflow increases the looseness of the large‐particle (>0.1 mm) bed surface. These findings hold significant implications for accurately modeling sand‐bed collisions in natural environments. Plain Language Summary: The interaction mechanism between natural sand and the bed within the aeolian flow yields crucial insights into explaining the initiation of sand or dust emission. Due to the extremely low airflow velocity near the loose bed surface, previous studies have elucidated the interaction relationship between sand and the bed through experiments and theoretical studies conducted under no wind conditions. In our study, we observed a large number of particle‐bed collision processes within the saturated aeolian flow through high‐speed cameras and particle trajectory tracking algorithms and contributed previously unexplored insights into the interaction mechanism between natural sand and the bed. We derived coupling relation functions between key movement parameters (velocity, angle and number) of liftoff particles and their relative height above the bed, as well as the velocity at which incident particles reach the bed surface. Consequently, our findings will be pertinent for future modeling efforts aimed at understanding the interactions between transported particles and the bed in models of wind‐blown sand transport. Key Points: Eight hundred and fifty seven collision events in airflow were investigated through wind tunnel experiments utilizing high‐speed photography on a loose surfaceThe effect of the criterion used for defining ejection on splash functions was investigatedThe splash functions in airflow deviate to different extents from theoretical simulation and experimental results under windless conditions [ABSTRACT FROM AUTHOR]

The Golmud-Korla Railway in the Gobi area faces operational challenges due to sand hazards, caused by strong and variable winds. This study addresses these challenges by conducting wind tunnel tests to evaluate the protective benefits of High Density Polyethylene (HDPE) board sand fences, focusing on their orientation relative to various wind directions (referred to as 'wind angle'). This study found that the size of the low-velocity zone on the leeward side of the sand fences (LSF) expanded with an increase in the wind angle (WA). At 1H (the height of the sand fence) and 2H positions on the LSF, the wind speed profiles (WSP) exhibited a segmented logarithmic growth, constrained by Z = H at varying WAs. The efficacy of the sand fence in obstructing airflow escalated as WA increased. The size of the WA has a significant impact on the protective efficiency of HDPE board sand fences. Furthermore, compared to typical sandy surfaces, the rate of sand transport across the Gobi surface diminishes more slowly with height, attributed to the gravel's rebound effect. This phenomenon allows some sand particles to bypass the fences, rendering them less effective at blocking wind and trapping sand than in sandy environments. This paper offers scientific evidence supporting the practical use and enhancement of HDPE board sand fences in varied wind conditions. [ABSTRACT FROM AUTHOR]

Adjuvants are included in many pesticide spray mixtures to enhance the performance of the applied chemical. Many adjuvants which modify the emulsion or extensional viscosity of the tank‐mixture have been found to offer benefits in drift management, primarily by eliminating or reducing the 'Fine' droplets included in the spray with diameters <100–200 μm that can move off‐target in unfavorable conditions during ground, airblast and aerial pesticide applications. Among wind tunnel and field studies conducted around the world, there is consensus that while some adjuvants are effective for drift management, the performance varies on a case‐by‐case basis, requiring verification for each adjuvant which could be achieved through a programme such as certification based on showing a reduction in Fine droplets and/or a reduction in airborne drift. These can be measured in wind tunnel studies according to international standards. This article provides a review of the current science in this subject area, from the approaches to data collection to a review of existing data and regulatory application for encouraging and rewarding the use of appropriate adjuvants that have been demonstrated to reduce airborne spray drift potential and therefore the size of no‐spray buffer zones appropriate to protect nontarget sensitive areas from drift exposure. Some adjuvants can offer the same reduction in drift as offered by hooded sprayer retrofits. A drift reduction programme based on adjuvant use could include testing candidate adjuvants for their effect on droplet size and reduction in Fine droplets when sprayed through reference nozzles and compared against sprays without the adjuvant. Testing could also be based alternatively on measurements of drift potential on collectors such as monofilament line in wind tunnel or field studies. Once shown to be effective in reducing 'Fines' or spray drift, adjuvants could be certified and then referenced on pesticide labels and/or regulatory or best management practice schemes to encourage their use and offer reductions in use restrictions or no‐spray buffer zone sizes based on drift management. Studies have shown that some adjuvants can reduce pesticide leaching into soils and contamination of groundwater, as well as runoff of active ingredients from plants into the environment. Performance depends on the adjuvant type, the pesticide with which it is used, the soil or plant type, the timing and mass of water input from rainfall and climatic factors. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

This study presents the design of a small open-circuit wind tunnel for laboratory use and a method for preparing columnar ice. The ice formation process was analyzed in terms of temperature and ice thickness variations under varying environmental temperatures and wind speeds. Observations revealed that as wind speed increased, the grain size of the columnar ice decreased. Key findings include the following: (1) the selection and validation of two cubic arcs for the wind tunnel contraction section, achieving an acceleration ratio of 6.7–6.8 and stable wind speeds of 1–10 m/s; (2) real-time temperature monitoring indicated rapid cooling before freezing and slower cooling post-freezing, with lower ambient temperatures and higher wind speeds accelerating the icing process; (3) the −1/2 power of grain size was found to be positively correlated with wind speed; and (4) the method's feasibility for studying mechanical properties of polar columnar ice was confirmed. This technique offers a controlled approach for producing columnar ice in the laboratory, facilitating comprehensive research on ice properties and providing a foundation for future studies on the mechanical behavior of ice under windy polar conditions. [ABSTRACT FROM AUTHOR]

This paper describes analysis and measurements of the yaw response of tail fins for small wind turbines. It is based on an extension of unsteady slender body theory (USBT) to cover non-slender fins and high angles of incidence, both of which make the theory nonlinear. We provide three main additions to the substantial literature on linearized USBT for tail fins. First, USBT is extended to high angles by modeling the nonlinear vortex dynamics. Second, the restriction to slender bodies is removed by modeling the chordwise load variation. Third, we consider the effect of time-varying wind speed. The extended theory is compared to wind tunnel measurements of the yaw behavior of delta, elliptical, and rectangular tail fins without a rotor and nacelle. The fins were released from initial yaw angles of −40° and −80°; the latter is of sufficient magnitude to show the importance of the nonlinear yaw dynamics. Generally good agreement was found between the theory and measurements, and the theory was shown to be more accurate than a "polar" or quasi-steady model which uses only the lift and drag of a delta planform. Of the three planforms, the rectangular one showed the lowest accuracy in terms of frequency but the damping was accurately predicted. Overall, the results demonstrate the importance of nonlinearity in the response of a yawing tail fin, particularly for the higher aspect ratio fins at large yaw angles. [ABSTRACT FROM AUTHOR]

This study proposes a modified flow-induced vibration-based energy harvester. To accomplish this objective, a bluff body inspired by nature is complemented by a second fixed body, and its impact is examined. This research is focused on theoretical and experimental studies of approaches to increase fluid induced vibration. To do so, a comprehensive examination of the near-wake flow using particle image velocimetry is conducted. Subsequently, the electromechanical equation of motion for the vibration-based energy harvester utilizing piezoelectricity is derived. Then, a series of wind tunnel experiments are conducted to prove the positive effect of the downstream rectangular plate and its impact on the energy harvester efficiency. Results show that the proposed changes in the energy harvesting system can effectively increase the amount of produced energy. In order to improve the merging of vortices over the bluff body, the so-called nondimensional distance is defined and investigated. It has been demonstrated that utilizing the system with optimal parameters can improve the output voltage by more than 80% and consequently increase the efficiency of the system. [ABSTRACT FROM AUTHOR]

Wind tunnel experiments were performed to quantify the coupling mechanisms between incoming wind flows, power output fluctuations, and unsteady tower aerodynamic loads of a model wind turbine under periodically oscillating wind environments across various yaw misalignment angles. A high-resolution load cell and a data logger at high temporal resolution were applied to quantify the aerodynamic loads and power output, and time-resolved particle image velocimetry system was used to characterize incoming and wake flow statistics. Results showed that due to the inertia of the turbine rotor, the time series of power output exhibits a distinctive phase lag compared to the incoming periodically oscillating wind flow, whereas the phase lag between unsteady aerodynamic loads and incoming winds was negligible. Reduced-order models based on the coupling between turbine properties and incoming periodic flow characteristics were derived to predict the fluctuation intensity of turbine power output and the associated phase lag, which exhibited reasonable agreement with experiments. Flow statistics demonstrated that under periodically oscillating wind environments, the growth of yaw misalignment could effectively mitigate the overall flow fluctuation in the wake region and significantly enhance the stream-wise wake velocity cross correlation intensities downstream of the turbine hub location. [ABSTRACT FROM AUTHOR]

Stall flutter is a serious threat to the operational integrity in turbomachinery, particularly in the final stage rotors of steam turbines and in compressors. Although computer science has developed rapidly and much of the research can be carried out using numerical tools, the simulation of some phenomena, such as stall flutter, is still very challenging and needs to be supported by experimental data. This paper presents an innovative experimental linear blade cascade design with five prismatic blades with pitch degrees of freedom, designed to be operated in a low subsonic wind tunnel. The geometry of the blade cascade was chosen on the basis of the experimental and numerical tests to allow stall flutter initiation. New suspension, measurement and electromagnetic excitation systems were developed and experimentally tested to allow accurate measurement of aerodynamic damping during controlled flutter tests. The novelty of the experimental blade cascade is the possibility of single pulse excitation of the blades. The cascade can be brought to the edge of stability by adjusting the angle of attack and flow velocity, and then the pulse can be used to induce stall flutter. Measurement of both mechanical and flow characteristics, also demonstrated in this paper, will provide data for in-depth analysis of stall flutter initiation and propagation. [ABSTRACT FROM AUTHOR]

Wind-blown snow is a frequent phenomenon in high-elevation and polar regions which impacts the surface energy and mass balance of these areas. Loose surface snow gets eroded and transported by wind, which influences the snow particles' physical properties (size, shape, optical properties) that determine the characteristics of the emerging wind-impacted snowpack layer. During airborne snow transport, the governing processes happen on the micro-scale while the particles are transported over long distances. The unfolding processes and the evolution of the particles' physical properties are thus difficult to observe in situ. Here, we used cold-laboratory ring wind tunnel experiments as an interim solution to study the governing processes during airborne snow transport with stable water isotopes as tracers for these micro-scale processes. Repeated analysis of airborne-sampled snow by micro-computed tomography (µ CT) documented a growing and rounding of snow particles with transport time, with a concurrent decrease in specific surface area. Stable water isotope analysis of airborne snow and water vapour allowed us to attribute this evolution to the process of airborne snow metamorphism. The changes observed in the snow isotopic composition showed a clear isotopic signature of metamorphic deposition, which requires particle–air temperature gradients. These results question the validity of the thermal-equilibrium assumption between particles and air inside the saltation layer of wind-blown snow events, where the conditions are similar to the ones found in the wind tunnel. Our results thus refine the understanding of the governing processes in the saltation layer and suggest that the snow's isotopic composition can inform on local wind-blown snow events as the original snow isotope signal gets overprinted by airborne snow metamorphism. Within transport times of 3 h, we observed changes in the isotope signal of airborne snow of up to +1.47 ‰ in δ18 O, ±5.7 ‰ in δ D, and -6.1 ‰ in d-excess. Thus, airborne snow metamorphism has the potential to influence the climate signal stored in snow and ice core stable water isotope records. [ABSTRACT FROM AUTHOR]

In this work, micro air vehicles (MAVs) equipped with bio-inspired wings are investigated experimentally in wind tunnel. The starting point is that insects such as dragonflies, butterflies and locusts have wings with rigid tubular elements (corrugation) connected by flexible parts (profiling). So far, it is important to understand the specific aerodynamic effects of corrugation and profiling as applied to conventional wings for the optimization of low-Reynolds-number aerodynamics. The present study, in comparison to previous investigations on the topic, considers whole MAVs rather than isolated wings. A planform with a low aperture-to-chord ratio is employed in order to investigate the interaction between large tip vortices and the flow over the wing surface at large angles of incidence. Comparisons are made by measuring global aerodynamic loads using force balance, specifically drag and lift, and detailed local velocity fields over wing surfaces, by means of particle image velocimetry (PIV). This type of combined global–local investigation allows describing and relating overall MAV performance to detailed high-resolution flow fields. The results indicate that the combination of wing corrugation and profiling gives effective enhancements in performance, around 50%, in comparison to the classical flat-plate configuration. These results are particularly relevant in the framework of low-aspect-ratio MAVs, undergoing beneficial interactions between tip vortices and large-scale separation. [ABSTRACT FROM AUTHOR]

Piezoelectric wind-induced vibration energy harvesters (PWVEHs) offer a promising solution for powering wireless sensor networks by converting wind energy into electrical energy. While conventional PWVEHs rely on vortex-induced vibration (VIV) and galloping to work, little has been done to investigate the coupling mechanisms between VIV and galloping and their influences upon energy harvesting performances of flow-induced vibration (FIV). To address this, we propose 36 bluff bodies (BBs) with various frontbody and afterbody shape combinations and conduct FIV experiments in a wind tunnel. The voltage output of each BB is recorded and analyzed based on whether pure VIV, pure galloping vibration, or concurrent VIV-galloping vibrations are involved. Hysteresis analyses are performed for BBs exhibiting concurrent VIV-galloping vibrations. The energy harvesting performances of all BBs are compared to circular and square cross-section BBs, revealing a BB shape that achieved 23.18 % and 16. 57 % higher maximum output than circular and square BBs, respectively. Computational analysis is conducted to investigate the flow field behind the given BBs. These findings provide valuable insights for developing efficient energy harvesters utilizing VIV and galloping by optimizing the involved BBs. [ABSTRACT FROM AUTHOR]

The shock/boundary-layer interaction induced by a 20° compression ramp in a Mach 2 flow was investigated using fast pressure-sensitive paint with a bandwidth of about 10 kHz. The mean separated flow length-scale is about two upstream boundary layer thicknesses, which indicates the interaction is weak. The primary analysis consists of cross-correlations, coherence, and time-domain filtering. Two different frequency bands were investigated: low-frequency (f < 2000 Hz; StL < 0.1) and mid-frequency (0.1 < StL < 0.26). The low-frequency band time sequences and coherence reveal the shock-foot motion is mainly correlated with the reattachment region, which is indicative of the well-established breathing motion of the separation bubble. The breathing motion is observed to occur locally and globally (spanwise-averaged). Furthermore, in the low-frequency band, fluctuations in the upstream boundary layer are moderately correlated with the reattachment region fluctuations, but show no correlation with the intermittent region fluctuations. In the mid-frequency band, the intermittent region, separation bubble and reattachment region all exhibit significant correlation with the upstream boundary layer fluctuations, with the upstream fluctuations leading. The time-sequences in this frequency band reveal broad regions of pressure fluctuations that sweep through the interaction and affect the entire interaction. There is no known turbulent source for such large-scale fluctuations and they are believed to be due to a wind tunnel phenomenon. It is concluded that the dominant low-frequency breathing motion follows an oscillator model, but there remain significant correlations to upstream fluctuations that are not tied to the dominant breathing motion and seem to follow an amplifier model. [ABSTRACT FROM AUTHOR]

To enhance the aerodynamic performance of compressors in advanced aeroengines, a compound flow control method combining positively bowed blades and bionic-wavy leading edges is proposed for improving the aerodynamic performance of compressor cascades with controlled diffusion airfoils. This study verified the effectiveness of the compound control method through low-speed wind tunnel experiments using five-hole probe measurements and surface oil-flow visualization techniques. Additionally, the flow field structure was analyzed, and vortex models were established to thoroughly discuss the mechanism of the compound flow control method. The results show that within the incidence angle range of 0°–4° studied in this paper, the composite control method achieved significantly effective control, with a maximum reduction in overall total pressure loss of 25.8% compared to straight blade cascades. Three vortex models were established. The positive bowed blade cascade induced a complex vortex structure in the concentrated shedding vortex region, increasing losses in the concentrated shedding vortex (CSV) region but reducing profile losses. The coupled method further reduced profile losses and optimized the flow field in the CSV region. This study not only validates the feasibility of the compound method but also provides guidance for applying flow control methods to bowed blade cascades. [ABSTRACT FROM AUTHOR]

In this paper, the flow field around a tandem arrangement of two identical oscillating NACA (National Advisory Committee for Aeronautics) 0012 airfoils was investigated using the continuous wavelet transform. Wind tunnel experiments were conducted on a test stand that provided a wide range of sinusoidal pitching motion with frequencies up to 10 Hz. This study aims to explore the flow physics of the tandem airfoils that oscillate with independent reduced frequencies. For this sake, experiments were performed at a reduced frequency of 0.15 for the front airfoil and five different reduced frequencies for the rear airfoil, ranging from 0.05 to 0.3. The chord-based Reynolds number was 6 × 104, and the horizontal distance between airfoils was equal to one chord length. The unsteady surface pressure was measured, and the wavelet transform was employed to analyze the pressure fluctuations. Findings indicate that the presence of the rear airfoil in the wake of the front airfoil prevents the formation of the laminar separation bubble. Also, the ratio of upstream/downstream airfoil reduced frequencies appears as one of the dominant frequencies of pressure fluctuations on the rear airfoil. Furthermore, when the reduced frequency ratio of the airfoils is lower than one, the normal force on the rear airfoil is often less than that experienced by an isolated single airfoil. Specifically, at equal reduced frequencies of 0.15 for both upstream/downstream airfoils, the maximum value of the normal force coefficient on the rear airfoil decreases by 30% compared to the single airfoil. [ABSTRACT FROM AUTHOR]

Aircraft icing seriously threatens flight safety. This paper describes a modified shallow-water icing thermodynamic model that is applicable to unstructured grids and considers the effects of changes in water physical parameters and sublimation on icing. An icing calculation method enables the automatic determination of whether freezing occurs and the type of icing. An autonomous icing calculation program is developed to extract the geometric coordinates and mesh information of the icing surface and combine this information with the multiphase flow field of air-supercooled water droplets. The icing equations in the Godnov format are discretized to produce a large-scale sparse matrix that is solved iteratively using the biconjugate gradient stabilized method. The output includes parameter distributions for the ice thickness, water film thickness, and equilibrium temperature. Taking the National Advisory Committee for Aeronautic 0012 airfoil as the study object, the results of icing simulations are compared with experimental data from an ice wind tunnel and the ice shapes calculated by the FENSAP-ICE software. The results are found to be in good agreement with the experimental data, and the ice height errors at stagnation points are less than 15%. In the case of rime ice, single-horned ice shapes are simulated for both conventional and large supercooled droplets. For mixed ice and glaze ice, double-horned ice shapes are simulated for both droplet conditions. FENSAP-ICE fails to simulate the ice horns and produces large errors in ice thickness and ice range. [ABSTRACT FROM AUTHOR]

Due to the complex nature of the built environment, urban wind flow is unpredictable and characterised by high levels of turbulence and low mean wind speed. Yet, there is a potential for harnessing urban wind power by carefully integrating wind turbines within the built environment at the optimum locations. This requires a thorough investigation of wind resources to use the suitable wind turbine technology at the correct location—thus, the need for an accurate assessment of wind resources at the proposed site. This paper reviews the commonly used wind assessment tools for the urban wind flow to identify the optimum tool to be used prior to integrating wind turbines in urban areas. In situ measurements, wind tunnel tests, and CFD simulations are analysed and reviewed through their advantages and disadvantages in assessing urban wind flows. The literature shows that CFD simulations are favoured over other most commonly used tools because the tool is relatively easier to use, more efficient in comparing alternative design solutions, and can effectively communicate data visually. The paper concludes with recommendations on best practice guidelines for using CFD simulation in assessing the wind flow within the built environment and emphasises the importance of validating CFD simulation results by other available tools to avoid any associated uncertainties. [ABSTRACT FROM AUTHOR]

Purpose: An experimental investigation of hemispherical forebody interaction effects on the drag coefficient of a D-shaped model is carried out for three-dimensional flow in the subcritical range of Reynolds number 1 × 105 ≤ Re ≤ 1.8 × 105. To study the interaction effect, hemispherical shapes of various sizes are attached to the upriver of the D-shaped bluff body model. The diameter of the hemisphere (b1) varied from 0.25 to 0.75 times the diameter of the D-shaped model (b2) and its gap from the D-shaped model (g/b2) ranged from 0.25 to 1.75 b2. Design/methodology/approach: The experiments were carried out in a low-speed open-circuit closed jet wind tunnel with test section dimensions of 1.2 × 0.9 × 1.8 m (W × H × L) capable of generating maximum velocity up to 45 m/s. The wind tunnel is equipped with a driving unit which has a 175-hp motor with three propellers controlled by a 160-kW inverter drive. Drag force is measured with an internal six-component balance with the help of the Spider 3013 E-pro data acquisition system. Findings: The wind tunnel results show that the hemispherical forebody has a diameter ratio of 0.75 with a gap ratio of 0.25, resulting in a maximum drag reduction of 67%. Research limitations/implications: The turbulence intensity of the wind tunnel is about 5.6% at a velocity of 18 m/s. The uncertainty in the velocity and the drag coefficient measurement are about ±1.5 and ±2.83 %, respectively. The maximum error in the geometric model is about ±1.33 %. ractical implications: The results from the research work are helpful in choosing the optimum spacing of road vehicles, especially truck–trailer and launch vehicle applications. Social implications: Drag reduction of road vehicle resulting less fuel consumption as well as less pollution to the environment. For instance, tractor trailer experiencing approximately 45% of aerodynamics drag is due to front part of the vehicle. The other contributors are 30% due to trailer base and 25% is due to under body flow. Nearly 65% of energy was spent to overcome the aerodynamic drag, when the vehicle is traveling at the average of 70 kmph (Seifert 2008 and Doyle 2008). Originality/value: The benefits of placing the forebody in front of the main body will have a strong influence on reducing fuel consumption. [ABSTRACT FROM AUTHOR]

Highlights Air velocity characteristics within soybean rows were monitored to inquire about potential spray droplet movement inside dense foliage. Magnitude of air velocity at high and middle canopy heights decreased with decreasing row spacing and increasing plant canopy leaf area index. The objective of this study was to characterize air velocities within a group of soybean plants under controlled conditions in a University of Tennessee biosystems engineering low-speed wind tunnel. The wind tunnel had 13 module sections that were each sized 1.22 m long, 2 m high, by 2 m wide, and was powered with a 93.25-kW motor and variable frequency drive at a mean air velocity of 1.4 m s-1. Extreme high air velocities were avoided to reduce the impact and added complexities of plant structural deflections. Wind tunnel tests were conducted with soybeans grown in pots placed in the wind tunnel with pot row spacings selected as 0.25, 0.38, and 0.51 m to vary the openness of the plant canopy. These row spacings represented narrow production practices that were perceived as difficult for spray droplets to penetrate. Soybeans were grown in pots outdoors to achieve plants that resembled the hardy structural characteristics of those in field production. Plants reached the R3 growth stage when the air velocity experiments started, and mean plant height and width were 0.51 and 0.46 m, respectively. Outdoor plant canopy leaf area index (LAI) measured at heights of 0.28 and 0.43 m for pot row spacings of 0.25, 0.38, and 0.51 m were 8.27, 6.66, and 5.59 m2 m-2 and 7.04, 6.49, and 5.01 m2 m-2, respectively. Thus, increased measurement height and increased row spacing reduced LAI values as expected. Soybean pots were placed in rows oriented along the length of the wind tunnel. Air velocity component values in the foliar canopy were the greatest for longitudinal components, followed by vertical and lateral components. A complex system of three-dimensional air velocities was observed along soybean rows of various row spacings. The soybean canopy was perceived as the root cause of wind velocity blockage resulting in mean longitudinal wind velocities ranging from -0.01 to 0.61 m s-1 depending on row spacing, location between- or in-row and measurement height. Using ambient wind to reliably and consistently aid spray penetration and droplet movement into soybeans grown under conditions with dense foliage appeared to further compound the issue of spray penetration. [ABSTRACT FROM AUTHOR]

In this paper, the unsteady aerodynamic characteristics of a three-car grouped high-speed train (HST) with different bogie fairing configurations under the crosswind are studied using improved delayed detached eddy simulation (IDDES) at Re = 1.85 × 106. The numerical method results are validated against the previous wind tunnel experiments. There are three cases with original half-fairing configuration (HFC), non-fairing configuration (NFC) and full-fairing configuration (FFC), respectively. The numerical results show that the bogie fairing configuration has significant effects. Compared to the HFC case, the drag force coefficients of the head, middle and tail cars with NFC increase by 53.13%, 14.87% and 27.04%, and corresponding parts of the FFC case decrease by 49.98%, 24.40% and 12.41%, respectively. The FFC case can also optimize the pressure distribution on the windward and leeward sides of the HST, and the flow structure and vertex distribution around the car body are also optimized. In addition, the increasing encirclement of the fairing configurations reduces the maximum lateral flow velocity inside the bogie cavities by 70% for HFC and 50% for FFC compared to the NFC. Overall, the FFC presents better aerodynamic performance than the NFC and HFC cases under crosswind, which is recommended for the design of the HST. [ABSTRACT FROM AUTHOR]