Wind Tunnel Experimental Study Research Articles

Computational fluid dynamics modelling to design and optimise power kites for renewable power generation

Power kites provide the potential rewards of obtaining the disused energy supply from high altitude wind. This paper aims to provide a design of power kite and optimise the potential for renewable power generation. The power kite was modelled using computational fluid dynamics to study its characteristics. The numerical modelling results were compared against the wind tunnel experimental study and two 3D printed power kites. The design was optimised using several variables, of which include aerofoil choice, surface roughness, wind speed and operating parameters. The results suggest that operating the kites at minimum 15 m horizontal separation is favourable, with the trailing kite operating below the leading, removing the potential for this kite to operate in the wake turbulence of the first. This paper presents relevant, applicable data which can be used for predicting the performance, and potentially optimising further power kite design.

Comfort cooling by wind towers in the Australian residential context – Experimental wind tunnel study of comfort

Comfort performance of a wind tower in a residential setting was evaluated in a series of wind tunnel experiments using a sealed, four storey apartment building model at 1:100 scale. This study was structured into three phases; first, the pressure distribution over the wind tower openings and the building fenestrations were measured in a boundary layer wind tunnel. From these data, internal bulk flow air change rates and mean indoor room air speeds were derived. Second, the pressure coefficient results of the first phase were applied to the Sydney Typical Meteorological Year (TMY) to assess the ventilation performance of the wind tower in terms of hourly indoor air speed. Wind tower results were benchmarked against through-window cross ventilation. In the third phase, increased indoor air speeds under wind tower ventilation were processed through the Standard Effective Temperature (SET*) comfort model to compute the additional comfort degree hours resulting from inclusion of a wind tower. Results indicate that the wind tower reduced indoor SET* values by an average 3.2 ​°C relative to conventional through-window cross-ventilation during Sydney’s summer when outdoor temperatures were warmer than neutral.

Detection and isolation of Tollmien-Schlichting waves in shear flows using blind source separation

Abstract A blind source separation (BSS) method for the detection and isolation of Tollmien-Schlichting (TS) waves in sub-critical transitional shear flows is presented. The method is based on an adaptation of the celebrated independent component analysis (ICA) technique to the problem at hand, using appropriate modeling of the flow field and the disturbances acting on it. This modeling is founded on the representation of the acquired flow measurements as mixtures (generated by an a priori unknown mixing process) of disturbance sources. Only the disturbance mixtures, as measured by the sensors embedded in the flow field, are input to the new method. Linear stability theory (LST) is used to model the measured mixtures of sources acquired by sensors placed in the shear flow field. A physics-based design criterion, assuming prior knowledge of the TS wavelengths, is derived for proper sensor placement in order to successfully separate TS wave disturbances. The criterion is verified both numerically, for wall-bounded shear flows, and experimentally, via a wind-tunnel experimental study of flow over a flat plate. The new disturbance detection and isolation approach is expected to prove useful in various applications, including closed-loop flow control problems.

Fiber-Optics-Based Aeroelastic Shape Sensing

This paper presents a numerical and experimental wind tunnel study of aeroelastic shape sensing using fiber-optic sensors. Strain measurements via both discrete and distributed dynamic fiber-optic sensing technologies were used to estimate a wing’s deformed shape and modal displacements using a strain-to-displacement transformation algorithm. The performance of the fiber-optic sensors and the algorithm were tested in a set of validation tests, in which the displacement response to static loads and to initial conditions was recovered and compared with that from a reference motion tracking cameras system. Excellent match of the responses validated the capabilities of the sensing configuration. The wing was tested in the wind tunnel in static conditions as well as in dynamic conditions close to and at flutter. Fiber-optics strains data were used to recover the deformed shape at static conditions, which was compared with that from aeroelastic analysis. At flutter, strain data were used to compute the wing’s dynamic response and extract the flutter speed, frequency, and complex flutter mode. These were compared with aeroelastic flutter analysis and were found to be in good agreement. Overall, the study has experimentally demonstrated that strain-based aeroelastic shape sensing, both static and dynamic, is feasible and provides accurate deformations and modal responses even when based on sparse strain measurements, and when the modes used for the strain-to-displacement transformation are not the exact eigenmodes of the aeroelastic system.

A Wind Tunnel Experimental Study on the Flexible Flapping Wing With an Attached Airfoil to the Root

With the purpose to improve the performance of the flexible membrane flapping wing, a kind of flapping wing with an attached airfoil to the root is designed and tested in a wind tunnel. In order to study, the actual performance improvement of the flapping wing, the flight performance is calculated and compared instead of the aerodynamic performance. A method to establish a semi-empirical cycle-averaged mathematical model for the flapping wing with high precision based on the wind tunnel experiment is proposed to calculate the flight performance. The established continuous mathematical model can solve the problem of how to obtain the trimmed state by using discrete experimental data. By attaching the airfoil EPPLER 378 with a thickness of 4.07% chord length to the root, the cruise velocity envelope is expanded, especially with a small cruise velocity. Although the attached airfoil to the root can cause a slight decrease in endurance and range of the flapping wing, it will greatly enhance the climbing performance and effectively reduce the demand for the takeoff sites. Besides, the flapping wing with an attached airfoil to the root will result in a significant reduction in the radius of steady turning and will improve the maneuverability. In addition, the airfoil EJ 85, which is similar to the airfoil EPPLER 378 in shape and camber but has a larger thickness of 6.5% chord length, is attached to the root of the original flapping wing. The same experiment and modeling procedure are performed on the airfoil EJ 85 to analyze the difference in performance of the flapping wing with different airfoil thickness.

Wind tunnel experimental study on noise of flexible thin plate wing with fluid-solid interaction effects

The flexible structure may generate fluid-structure coupled vibration in the wind field. At this time its noise characteristics are more complicated than the aeroacoustics of the rigid structure in the flow field. Through the acoustic wind tunnel test, the noise characteristics of different flexible thin plate-wing models under fluid were studied. Experiments show that with the increase of structural flexibility, the OASPL of the thin wing is more sensitive to changes of wind speed and angle of attack. The spectral characteristics and sound source position of the flexible plat-wing noise are obviously different from that of the rigid wing. The study found that the aeroacoustic intensity suddenly and remarkably increases at a specific angle of attack and wind speed. The preliminary law of the aeroacoustics variation of the plate-wing under the fluid-solid coupling is given, which provides the experimental support for the theoretical analysis and numerical simulation of the relevant fluid-structure coupled vibration noise.

Comparison of turbulence modelling approaches in simulation of a feather shuttle: a porous conical bluff body

The aerodynamics of a feather shuttlecock, a porous conical bluff body, are unique in comparison to other sports projectiles. Experimental wind tunnel studies have been published that present values of drag coefficient (Cd) for traditional feather shuttles that vary widely (0.48 < Cd < 0.74). It is difficult to compare published experimental data, due to a lack of clarity concerning experimental apparatus. All studies have used traditional sting mounts inserted aft of the shuttle base, and it is believed this has a strong influence on Cd, as significant air movement is known to occur in this region. Flow passes through gaps formed by individual feather shafts, or rachis, inserted into the shuttle base. The use of computational fluid dynamic (CFD) simulation in the analysis of shuttles has great potential as analysis can be performed without the need of an experimental sting. This study presents the first CFD simulations of a geometrically realistic feather shuttle. Careful consideration must be given to applied grids, numeric, and turbulence models (unsteady RANS vs scale resolving) if results obtained are to be reliable. CFD results present detailed insights of shuttle aerodynamics, and the significance of flow passage between the feather rachis and internal to the shuttle. The study raises significant concerns regarding the appropriateness of rear sting mounts in shuttle wind tunnel experiments.

Performance enhancement of downwind sails due to leading edge flapping: A wind tunnel investigation

This work presents a wind tunnel experimental study on the effect of the leading edge flapping on the aerodynamic performance of a spinnaker. Four J80-class spinnaker models, combining two different assembling structures (panel layout) and two different sail materials are tested at various wind speeds and wind angles in a wind tunnel. Results show that, for the wind angle range the spinnaker is designed for, the sustained periodic flapping of the sail leading edge has a significant benefit on performance, with 10% increase in drive force. In these model-scale tests, the sail structural properties did not show significant differences in performance, but affect the point where flapping sets in: a model with a stiffer material and a cross-cut panel layout starts flapping for a longer sheet length, compared to a lighter cloth and a tri-radial layout. Finally, it is shown that the non-dimensional flapping frequency is rather constant ≃0.4 in the design range of wind angle, but it varies with the wind speed and sail structural properties on a smaller wind angle where the spinnaker is more stretched.

Wind tunnel study on power output and yaw moments for two yaw-controlled model wind turbines

Abstract. In this experimental wind tunnel study the effects of intentional yaw misalignment on the power production and loads of a downstream turbine are investigated for full and partial wake overlap. Power, thrust force and yaw moment are measured on both the upstream and downstream turbine. The influence of inflow turbulence level and streamwise turbine separation distance are analyzed for full wake overlap. For partial wake overlap the concept of downstream turbine yawing for yaw moment mitigation is examined for different lateral offset positions. Results indicate that upstream turbine yaw misalignment is able to increase the combined power production of the two turbines for both partial and full wake overlap. For aligned turbine setups the combined power is increased between 3.5 % and 11 % depending on the inflow turbulence level and turbine separation distance. The increase in combined power is at the expense of increased yaw moments on both the upstream and downstream turbine. For partial wake overlap, yaw moments on the downstream turbine can be mitigated through upstream turbine yawing. Simultaneously, the combined power output of the turbine array is increased. A final test case demonstrates benefits for power and loads through downstream turbine yawing in partial wake overlap. Yaw moments can be decreased and the power increased by intentionally yawing the downstream turbine in the opposite direction.

Wind Pressures on 4∶12-Sloped Hip Roofs of L- and T-Shaped Low-Rise Buildings

AbstractA comprehensive wind tunnel experimental study for 4∶12-sloped hip roofs of L- and T-shaped low buildings was carried out in a simulated open terrain exposure to examine wind load character...

Wind Tunnel Experimental Study for Anti-icing Performance of Wind Blades with Hydrophobic Coatings

Wind Tunnel Experimental Study for Anti-icing Performance of Wind Blades with Hydrophobic Coatings

Wind Tunnel Investigation of a Circulation Control Wing with Dual-Radius Flaps

The objective of this research is to investigate the efficacy of circulation control (CC) at low Reynolds numbers () with relatively low and high blowing rates on a circulation control wing (CCW). Four dual-radius flap geometries are developed and tested by varying specific flap parameters from a previously studied baseline configuration. A two-dimensional low-speed wind-tunnel experimental study is undertaken to evaluate the effect of trailing edge upper slot blowing at cruise flight and takeoff (0° and 30° flap deflection). The wind tunnel tests are conducted at Mach numbers of 0.03, with momentum coefficients of blowing () ranging from 0.0 to 0.3. The research presented in this paper is the natural outgrowth of results reported in previous work related to the wind tunnel testing of a CCW with dual-radius flaps. This investigation explores the design of CC dual-radius flaps to improve the performance of existing CC flap configurations. This research also provides insight into how the characteristics of the CC flap geometry affect CC performance.

Experimental result analysis for scaled model of UiTM tailless blended wing-body (BWB) Baseline 7 unmanned aerial vehicle (UAV)

Blended wing-body (BWB) aircraft having planform configuration similar to those previously researched and published by other researchers does not guarantee that an efficient aerodynamics in term of lift-to-drag ratio can be achieved. In this wind tunnel experimental study, BWB half model is used. The model is also being scaled down to 71.5% from the actual size. Based on the results, the maximum lift coefficient is found to be 0.763 when the angle is at 27.5° after which the model starts to stall. The minimum drag coefficient is 0.014, measured at zero angle of attack. The corrected lift-to-drag ratio (L/D) is 15.9 at angle 7.8°. The scaled model has a big flat surface that surely gives an inaccurate data but the data obtained shall give some insights for future perspective towards the BWB model being tested.

Wind loads of moving vehicle on bridge with solid wind barrier

A wind tunnel experimental study is conducted to study the wind loads acting on a moving vehicle model on a bridge installed with a solid wind barrier. The repeatability of the tests is verified by the cases with different wind and vehicle speeds. For comparison purposes, the difference of the results between the static and moving vehicle models are discussed. The effects of different heights of wind barriers and wind directions on the wind loads acting on the vehicles are analyzed. Finally, the wind loads acting on the vehicles are further evaluated to assess the potential impact of wind barriers on traffic safety. The results show that the relative movement between the vehicle, bridge and solid wind barriers affects the aerodynamic characteristics of the vehicle. The variation patterns of aerodynamic characteristics with different yaw angles are altered by the solid wind barriers with different heights, and there is a most unfavorable yaw angle for the protective effect of solid wind barriers in terms of side force. The wind direction has some impact on the five-component coefficients of vehicles after installing a solid wind barrier. However, the solid wind barrier has similar protective efficiency in terms of the side force acting on the vehicle under different wind directions.

Experimental wind tunnel study of a smart sensing skin for condition evaluation of a wind turbine blade

Condition evaluation of wind turbine blades is difficult due to their large size, complex geometry and lack of economic and scalable sensing technologies capable of detecting, localizing, and quantifying faults over a blade’s global area. A solution is to deploy inexpensive large area electronics over strategic areas of the monitored component, analogous to sensing skin. The authors have previously proposed a large area electronic consisting of a soft elastomeric capacitor (SEC). The SEC is highly scalable due to its low cost and ease of fabrication, and can, therefore, be used for monitoring large-scale components. A single SEC is a strain sensor that measures the additive strain over a surface. Recently, its application in a hybrid dense sensor network (HDSN) configuration has been studied, where a network of SECs is augmented with a few off-the-shelf strain gauges to measure boundary conditions and decompose the additive strain to obtain unidirectional surface strain maps. These maps can be analyzed to detect, localize, and quantify faults. In this work, we study the performance of the proposed sensing skin at conducting condition evaluation of a wind turbine blade model in an operational environment. Damage in the form of changing boundary conditions and cuts in the monitored substrate are induced into the blade. An HDSN is deployed onto the interior surface of the substrate, and the blade excited in a wind tunnel. Results demonstrate the capability of the HDSN and associated algorithms to detect, localize, and quantify damage. These results show promise for the future deployment of fully integrated sensing skins deployed inside wind turbine blades for condition evaluation.

Wind tunnel experimental study on droplet drift reduction by a conical electrostatic nozzle for pesticide spraying

Abstract: Droplet drift wastes pesticide, pollutes the environment, and has become one of the focus issues of agricultural crop protection. Electrostatic spray technology reduces drift to a certain degree. In order to investigate the droplet drift pattern of a conical electrostatic nozzle, the droplet drift mass center distance was defined as an experimental index and used to conduct experimental wind tunnel studies on droplet drift. A mathematical model of the droplet drift mass center distance versus electrostatic voltage and wind speed was created via the regression method. The test results showed that the electrostatic voltage had an insignificant effect on droplet drift, the wind speed and its interaction with the electrostatic voltage had significant effects on droplet drift. When the wind speed was less than 3 m/s and stable, the crop adsorbability of a droplet had a dominant effect on the droplet drift; the droplet drift decreased with the increase of electrostatic voltage. When the wind speed exceeded 3 m/s and was stable, the reduced droplet particle size had a dominant effect on droplet drift, where droplet drift increased as the electrostatic voltage increased. When the wind speed was 0 m/s and the electrostatic voltage was 12 kV, the minimum droplet drift mass center distance was 35.5 mm, which was 56 mm less than that of conventional nozzle droplet drift. Therefore, a conical electrostatic nozzle is inapplicable for operation in an environment where wind speeds exceed 3 m/s. This study provides a reference for optimizing operational parameters of conical electrostatic nozzles and improving the anti-drift capability of droplets. Keywords: pesticide spraying, conical electrostatic nozzle, droplet drift, wind tunnel, experimental study, electrostatic sprayer DOI: 10.3965/j.ijabe.20171003.3074 Citation: Zhang W, Hou Y R, Liu X, Lian Q, Fu X M, Zhang B, et al. Wind tunnel experimental study on droplet drift reduction by a conical electrostatic nozzle for pesticide spraying. Int J Agric & Biol Eng, 2017; 10(3): 87–94.

Experiments in the wind turbine far wake for the evaluation of an analytical wake model

Nowadays, not only the size of single wind turbines but also the size of wind farms is increasing. Understanding the interaction between the turbines and especially the wakes formed behind them are getting more important to further improve such wind turbine arrays. Consequently, new issues in wind energy research arise. An experimental wind tunnel study was conducted, in order to analyze and understand the far wake of a wind turbine. The experimental results were used to test if an analytical wake model derived by H. Schilichting for blunt bodies can be used to describe the velocity and width development in the far wake of wind turbines. The results of the evaluation show that the wake of a wind turbine agrees fairly well with the model according to Schlichting. The velocity deficit as well as the width in the wake behind the turbine, are found to deviate with around only 2% from the results obtained applying the analytical model. Thus, it can be concluded that the analytical wake model by Schlichting is well suited to estimate the velocity deficit and the width in the far wake of a wind turbine.

Potential Use of BEST® Sediment Trap in Splash - Saltation Transport Process by Simultaneous Wind and Rain Tests.

The research on wind-driven rain (WDR) transport process of the splash-saltation has increased over the last twenty years as wind tunnel experimental studies provide new insights into the mechanisms of simultaneous wind and rain (WDR) transport. The present study was conducted to investigate the efficiency of the BEST® sediment traps in catching the sand particles transported through the splash-saltation process under WDR conditions. Experiments were conducted in a wind tunnel rainfall simulator facility with water sprayed through sprinkler nozzles and free-flowing wind at different velocities to simulate the WDR conditions. Not only for vertical sediment distribution, but a series of experimental tests for horizontal distribution of sediments was also performed using BEST® collectors to obtain the actual total sediment mass flow by the splash-saltation in the center of the wind tunnel test section. Total mass transport (kg m-2) were estimated by analytically integrating the exponential functional relationship using the measured sediment amounts at the set trap heights for every run. Results revealed the integrated efficiency of the BEST® traps at 6, 9, 12 and 15 m s-1 wind velocities under 55.8, 50.5, 55.0 and 50.5 mm h-1 rain intensities were, respectively, 83, 106, 105, and 102%. Results as well showed that the efficiencies of BEST® did not change much as compared with those under rainless wind condition.

Experimental testing of axial induction based control strategies for wake control and wind farm optimization

In state-of-the-art wind farms each turbine is controlled individually aiming for optimum turbine power not considering wake effects on downstream turbines. Wind farm control concepts aim for optimizing the overall power output of the farm taking wake interactions between the individual turbines into account. This experimental wind tunnel study investigates axial induction based control concepts. It is examined how the total array efficiency of two in-line model turbines is affected when the upstream turbine's tip speed ratio (λcontrol) or blade pitch angle (β-control) is modified. The focus is particularly directed on how the wake flow behind the upstream rotor is affected when its axial induction is reduced in order to leave more kinetic energy in the wake to be recovered by a downstream turbine. It is shown that the radial distribution of kinetic energy in the wake area can be controlled by modifying the upstream turbine's tip speed ratio. By pitching out the upstream turbine's blades, however, the available kinetic energy in the wake is increased at an equal rate over the entire blade span. Furthermore, the total array efficiency of the two turbine setup is mapped depending on the upstream turbines tip speed ratio and pitch angle. For a small turbine separation distance of x/D=3 the downstream turbine is able to recover the major part of the power lost on the upstream turbine. However, no significant increase in the two-turbine array efficiency is achieved by altering the upstream turbine's operation point away from its optimum.

Computational Flow Optimization of Heliostat Aspect Ratio for Wind Direction and Elevation Angle

Abstract The choice of heliostat aspect ratio has previously been shown to have an effect on the wind loading coefficients experienced by the structure due to an attacking atmospheric wind. Knowing the wind loads on heliostats is important in order to allow for adequate sizing of all components. The preferred method for determining such loadings is experimental wind tunnel studies, with Computational Fluid Dynamics (CFD) being less popular. A CFD model capable of predicting the mean wind loadings on a heliostat structure subjected to an attacking atmospheric wind and turbulence intensity profile was developed and validated using experimental results available in the open literature. The commercial software package ANSYS Fluent V15.0 was used together with the ANSYS Workbench Design Explorer toolset to study the influence of aspect ratio on the wind loading coefficients.