Wind Tunnel Experimental Study Research Articles

Acoustic wind tunnel experimental study of aerodynamic noise distribution in high-rise buildings

Wind-induced aerodynamic disturbance has become a major noise source affecting residents in super high-rise buildings. To investigate the distribution characteristics of aerodynamic noise on high-rise building surfaces in strong wind conditions and the impact of wind speed and direction, this paper pioneers the application of the acoustic wind tunnel method based on microphone array localization to the experimental study of the surface acoustic pressure field of a high-rise building model, the far-field noise spectrum of which is obtained using the microphone array sensor. The beamforming calculation method was used to obtain the spectrum and localization cloud. By comparing the spectra and cloud diagrams under different process conditions and based on existing building wind pressure reports, it is concluded that: the noise source is always located at the height of the connecting corridor where there is large wind pressure pulsation in the two building models; the aerodynamic noise is more pronounced around building gaps where the airflow is more disturbed and also in the oncoming wind trailing direction where the wind pressure pulsation is more pronounced. An increase in wind speed increased noise source amplitude from 30 dB to 60 dB, and the location of the noise source shifted backwards to the tail of the incoming wind. This paper shows that the acoustic wind tunnel method based on microphone array localization technology can obtain the aerodynamic noise intensity on the surfaces of super high-rise buildings and reasonably predict the location of the sound source. This article puts forward suggestions to reduce noise in high-rise buildings based on experimental results.

Suppression of wake-induced galloping of tandem cylinders by helical strakes

Helical strakes as a classic passive control method for vortex-induced vibration (VIV), have been extensively studied, but wake-induced galloping (WIG) control of three tandem cylinders has received no previous attention. The current wind tunnel experimental study tries to fill this gap in the context of mechanical science. WIG of three tandem cylinders considering different structures of helical strakes is modeled and investigated. Helical strakes with varying heights G, pitches P, and cross-sectional shapes (square “S”, involute “I”, and D-shaped “D”) are first designed. Wind tunnel tests are conducted to experimentally study the dynamics responses of tandem cylinders (m*ξ = 0.09) at different spacings, and three vibration modes are obtained. This study delves into the characterization and quantification of the impact of various parameters of helical strakes on WIG of three tandem cylinders. These aspects, scarcely addressed in existing research, are thoroughly explored through statistical analysis, focusing on vibration amplitude, vibration frequency, and wavelet analysis. It is found that helical strakes can effectively suppress the multi-frequency vibration instability of bare cylinders. For wind speeds below 6 m/s, the "S" helical strakes achieves a vibration suppression efficiency of up to 665 %; Three-dimensional computational fluid dynamics (3D-CFD) demonstrate the coupling effect in the flow field, revealing that the "S" helical strakes has a greater impact on boundary layer formation than the "D" helical strakes; Reducing the pitch of the helical strakes can enhance the disturbance ability of the spanwise position, thereby increasing its suppression effect. This work improves vibration reduction and sheds light on how the helical strakes' cross-section controls vibrations in the tandem cylinders.

Wind tunnel experimental study on the aerodynamic characteristics of straight-bladed vertical axis wind turbine

ABSTRACT To investigate the effect of structural parameters on the aerodynamic characteristics of a Straight-Bladed Vertical Axis Wind Turbine (SB-VAWT), a 4-bladed SB-VAWT without an intermediate support shaft was designed to allow flexibility in changing structural parameters. Wind tunnel tests were conducted to measure the rotational speed, total lift, drag and torque of the wind turbine with different structural parameters at varying wind speeds. Based on the experimental design and optimisation, the wind turbine achieved the highest rotational speed and optimal power generation when the blades were installed in the forward direction at an installation angle of 10°, an installation radius of 160 mm, and a length of 600 mm. Under these optimal conditions, the speed and power generation characteristics of the wind turbine were tested at different wind speeds These results provide valuable insights for the design and application of similar wind turbines.

Wind tunnel experimental study of aerodynamic characteristics of co-flow jet wing with built-in air source

To further investigate the aerodynamic characteristics and control mechanisms of co-flow jet wings, this study presents the design of a co-flow jet wing (CFJ-CLARKY18) with an embedded micro centrifugal compressor. The CFJ-CLARKY18 wing, based on the CLARKY18 airfoil, incorporates a miniature centrifugal compressor positioned horizontally within the wing's cavity, with its rotor axis perpendicular to the wing chord line, thus alleviating geometric constraints and the compressor's exhaust swirl. The integration of the co-flow jet device with the wing is achieved through a split-flow channel design to ensure uniform co-flow jet injection, followed by verification of jet uniformity and calibration of six jet momentum coefficients. Subsequently, static and dynamic control experiments of the co-flow jet wing are conducted in an open-return wind tunnel, utilizing force measurement systems and high-speed particle image velocimetry tools to investigate its aerodynamic characteristics and control mechanisms. Static stall tests indicate that, compared to the original wing, the CFJ-CLARKY18 wing exhibits a significant increase in lift and a noticeable delay in stall angle. At low angles of attack, an increase in co-flow jet momentum leads to a reduction in drag coefficient, with the possibility of achieving negative drag (thrust) even at high co-flow jet momentum coefficients. The results of dynamic stall tests with force measurements indicate that, while keeping the reduced frequency constant, an increase in co-flow jet momentum coefficient results in higher maximum lift and average lift coefficients, accompanied by a significant reduction in average drag coefficient and the hysteresis loop area of the lift coefficient. Despite the increased reduced frequency exacerbating the wing's stall effect, the stall effect weakens significantly once the co-flow jet momentum coefficient is increased.

Wind-tunnel experimental study on aeroelastic response of flexible wind turbine blades under different wind conditions

The long and flexible blades of the offshore wind turbine are easily damaged during extreme wind conditions (e.g. typhoons or tornados). For this reason, a continuous aeroelastic model of a 5 MW wind turbine blade from National Renewable Energy Laboratory is designed and processed to depth analyze the aeroelastic response of flexible wind turbine blades. The effects of different pitch angles, wind speeds and spanwise positions on the aeroelastic response characteristics of wind turbine blades are studied by the model wind-tunnel experiments. The experimental results show that the aeroelastic model of flexible blades is reasonably designed for simulating the aeroelastic response under different wind speeds and directions. The pitch angles ranging from −120° to −105° and 45°–105° are unfavorable for this wind turbine blade. The root-mean-square (RMS) acceleration of the blade is significantly increased, which is considered to be a sensitive region for wind vibration. It has been observed that the blade is more susceptible to lock-in phenomenon when the blade profile is at incidences presenting shallower characteristic length (θ=90° and 105°). In addition, the large deformation is measured after the blade tip deflection exceeds the cut-out wind speed, which in turn aggravates the geometric nonlinearity and greatly reduces the aeroelastic stability. Besides, the aeroelastic response of blades is reduced by optimizing the twist angle distribution in spanwise position. This experimental study aims to further the understanding of the aeroelastic response of flexible blades for reduction of windstorm damage to wind turbines in the typhoon-prone regions.

Wind tunnel experimental study on static aerodynamic performance of SB-VAWT without intermediate support axes

Wind power generation is considered an effective way for ships to harness wind energy, and the aerodynamic characteristics of wind turbines determine wind energy utilization and efficiency. However, traditional vertical axis wind turbines have intermediate shafts and support rods, which result in large negative effects in the research of the wind turbine aerodynamic characteristics. To address this issue, a Straight-Bladed Vertical Axis Wind Turbine (SB-VAWT) without intermediate support axes is proposed. The turbine can flexibly change the number of blades, rotor diameter, and installation position of blades. The static aerodynamic performance of the wind turbine with different combinations was tested in a wind tunnel laboratory at 10 m/s. The results show that the radius of the wind turbine has a greater effect on the drag coefficient for the same number of blades, with an inverse relationship between the drag coefficient and radius, and a positive association between lift coefficient, static torque coefficient, and radius. The drag coefficient is proportional to the number of blades at the same radius, while the static torque coefficient is inversely proportional to the number of blades. According to the results, placing the initial location in the azimuth range between 30° and 50° can obtain the maximum initial starting torque. Moreover, a wind turbine with a radius of 16 cm can achieve a higher average torque. Changes in the number of blades can significantly impact turbine properties, resulting in wind turbines with distinct features.

Exploring the impact of vertically separated flows on wind loads of multi-level structures

The complex dynamics of vertically separated flows pose a significant challenge when it comes to assessing the wind loads on multi-level structures, demanding a nuanced understanding of the intricate interplay between atmospheric conditions and architectural designs. Previous studies and wind loading standards provide insufficient guidance for designing wind pressures on multi-level buildings. The behavior of wind around perpendicularly attached surfaces is not quite similar to that of individual flat roofs or walls. When a body is composed of several surfaces with right or oblique angles, the separated flow from surfaces and their interactions will cause complex flow patterns around each surface. A wind tunnel experimental study was carried out on bluff bodies with attached flat plates and other adjacent bluff bodies with different heights to examine the wind-induced pressures on such complex shapes. Mean and peak pressure coefficients were measured to determine the flow interaction patterns and location of localized peak pressures. The results were compared to the Tokyo Polytechnic University Aerodynamic Database of isolated low-rise buildings without eaves. The research findings indicated that there was a noteworthy disparity between the minimum and maximum values and locations of peak pressures on both the wall and roof surfaces of the models used in this study, as compared to the results obtained by the Tokyo Polytechnic University. Moreover, the study conceivably pointed to the difference between the peak negative and positive pressure coefficient locations with the ASCE 7-22 wind loading zones. The peak suction zones were affected by the combined flows at perpendicular faces, and as a result, different wind load zones were obtained dissimilar to those introduced by ASCE 7-22. Wind loading standards may need to be modified to account for the wind pressures on complex building structures with an emphasis on the location of the peak negative pressure zones.

Experimental wind-tunnel study of the dynamics of inverted foils for energy harvesting

Abstract This paper describes the methodology used to analyse oscillations of foils of a wide range of aspect ratios, 0.5 ≤ AR ≤ 4, and Reynolds numbers, 104 ≤ Re ≤ 105, for energy harvesting purposes. The foils were fixed at their trailing edge, and their dynamical behaviour was captured as the wind speed was varied. The foil response was then analysed as a function of velocity, Reynolds number, oscillation amplitude and frequency. Additionally, the forces and moments acting on the foils were measured, utilising an aerodynamic scale, designed and built in-house. An empirical power generation equation was derived to determine the foil characteristics for maximum energy harvesting production. The results show that a flexible foil with AR = 3 with oscillations in the large-amplitude regime is the most effective for energy harvesting.

Full-scale investigation of heliostat aerodynamics through wind and pressure measurements at a pentagonal heliostat

Wind loads on heliostats are often investigated through experimental wind tunnel studies or numerical simulations. However, these approaches cannot consider the full-scale conditions but require a reproduction and simulation of both the heliostat structure and the wind conditions. Complementary full-scale investigations are therefore crucial but are at the same time relatively costly, as it is cumbersome to set up large heliostats with measurement devices. This paper introduces a new pressure measurement system which is easy-to-apply to a real-scale heliostat and enables full-scale investigations with minimized effort. The results of a first field study are presented during which wind and pressure measurements were taken simultaneously over periods of 10 min at a 48.5 m2 pentagonal Stellio heliostat. The non-dimensional pressure distributions are investigated and it is shown that the mean cp-values are very consistent amongst the measurement periods and reach values between 2.2 and 2.6. These values, in turn, are found to agree well with results of a wind tunnel study. Moreover, the behavior of the load coefficients with varying angles of attack is studied and the aerodynamic admittance functions are evaluated which give in-depth insight into the generation of aerodynamic loads. The admittance functions are found to start decreasing at a non-dimensional frequency of approximately 0.2. This finding indicates that eddies which are about the size of the heliostat or larger are fully effective in generating aerodynamic loads while the effectiveness of smaller eddies is reduced.

Experimental investigation of micro-ramp control for shock train under various incoming flow conditions

For supersonic/hypersonic propulsion systems, the shock train in the inlet/isolator play a dominant role in compressing the incoming flow and providing suitable airflow to the engine. In this study, a detailed wind tunnel experimental study is performed in a supersonic isolator to investigate the potential of a micro-ramp as a form of shock train control. The results show that the micro-ramp modifies the structure of the shock train, inhibits the oscillation and upstream propagation of the shock train, and thus improves the total pressure recovery coefficient and safe working range of the hypersonic inlet/isolator.

Wind-tunnel experimental studies of the spatial snow distribution over grass and bush surfaces

Wind-tunnel experimental studies of the spatial snow distribution over grass and bush surfaces

Wind Conditions at Pedestrian Level in Different Types of Residential Urban Development for a High Degree of Land Use Efficiency

This paper addresses wind conditions in urban building development at the pedestrian level. The article aimed to identify aerodynamic phenomena around three types of multi-family housing developments with different forms and the same urban parameters of building development density (high density was taken into account). The aim of the research was mainly to achieve qualitative results that would lead to understanding fundamental processes and phenomena. Wind tunnel experimental studies were conducted on physical models at a scale of 1: 400 using visualization and erosion methods. These experiments yielded data regarding the arrangement of airflow directions and changes in airflow velocity, expressed as the amplification coefficient (α), the occurrence of which was caused by the presence of buildings. An analysis was conducted concerning wind conditions that constitute pedestrian comfort and influence the possibility for ventilation of spaces between buildings for the three selected models. The research results were compared, and an attempt was made to assess the most beneficial and the least favorable building development types in this respect.

Determining the Aerodynamic Characteristics of a Propeller-Driven Anti-UAV Fighter While Designing Air Propellers

Abstract Given the rising importance of unmanned aerial vehicles (UAVs), this article addresses the urgent scientific problem of determining the aerodynamic characteristics of a UAV while laying out the propellers for the wings. We discuss the methodology for experimental wind-tunnel studies of aircraft configurations with propellers. It is shown that a characteristic feature of the configuration small-elongation wing with propellers is the absence of elements that are not affected by propellers. This feature makes it difficult to implement and automate a wind tunnel experiment, since there are problems with providing similar criteria for a working propeller; it is difficult to achieve perfect balancing for solid drive propellers, which causes vibration, the level of which depends on uncontrolled factors; the inability to neglect the presence of the body elements influence to the blades of propellers; the difficulty of direct measuring propeller thrust and torque. The presented methodology involves the integrated usage of experimental and numerical methods to eliminate the difficulties in conducting physical experiments in a wind tunnel. This approach makes it possible to combine the high credibility of experimental data in the study of the physical essence of phenomena with high efficiency and accuracy in determining aerodynamic characteristics by numerical methods. Using this approach, we established dependences of the aerodynamic characteristics of the small-elongation wing configuration with counter-rotating propellers on the geometric and kinematic parameters of the configuration for other extensions and constrictions of the wings. These data can serve as the basis for the development of recommendations for the selection of sensible geometric parameters of the aerodynamic configuration of a small-elongation wing with counter-rotating propellers.

A Wind Tunnel Experimental Study on the Icing Characteristics of a Cylinder Rotating around a Vertical Axis

Rotating machinery in cold and humid regions is prone to icing. For exploring the characteristics of icing on objects rotating around a vertical axis, such as vertical axis wind turbines (VAWT), a cylinder rotating around the vertical axis was selected as the research object in this study. Three cylinders with different diameters were selected, and icing tests carried out under different tip speed ratios (TSR) in a self-built icing wind tunnel. The icing characteristics were quantitatively analyzed using characteristic parameters, including the icing area, the dimensionless icing area, the stagnation point thickness and the dimensionless stagnation point thickness. The dimensionless stagnation point thickness decreased with increases in the diameter of the cylinder. The icing limit decreased with an increase in the rotational speed of the cylinder, and reached 50% under the high TSR condition. Various icing characteristics were also analyzed for two rotation modes: rotation around the vertical axis and around the horizontal axis. The research findings in the present study lay the theoretical and experimental foundations for exploring VAWT icing in depth.

A Wind Tunnel Experimental Study of Icing on NACA0012 Aircraft Airfoil with Silicon Compounds Modified Polyurethane Coatings.

Ice formation on the aerodynamic surfaces of an aircraft is regarded as a major problem in the aerospace industry. Ice accumulation may damage parts, sensors and controllers and alter the aerodynamics of the airplane, leading to a range of undesired consequences, including flight delays, emergency landings, damaged parts and increased energy consumption. There are various approaches to reducing ice accretion, one of them being the application of icephobic coatings. In this work, commercially available polyurethane-based coatings were modified and deposited on NACA 0012 aircraft airfoils. A hybrid modification of polyurethane (PUR) topcoats was adopted by the addition of nanosilica and three-functional spherosilicates (a variety of silsesqioxane compound), which owe their unique properties to the presence of three different groups. The ice accretion on the manufactured nanocomposites was determined in an icing wind tunnel. The tests were performed under three different icing conditions: glaze ice, rime ice and mixed ice. Furthermore, the surface topography and wetting behavior (static contact angle and contact angle hysteresis) were investigated. It was found that the anti-icing properties of polyurethane nanocomposite coatings strongly depend on the icing conditions under which they are tested. Moreover, the addition of nanosilica and spherosilicates enabled the reduction of accreted ice by 65% in comparison to the neat topcoat.

Comparison of the turbulence in the wakes of an actuator disc and a model wind turbine by higher order statistics: A wind tunnel study

Knowledge of the turbulence in the wakes of wind turbines is important to improve the operation and lifetime of downstream turbines exposed to these wakes. As the investigation of a rotating turbine can be challenging, both experimentally and numerically, static actuator discs can substitute rotating turbines. To investigate the similarity of the turbulence in the wakes and how turbulent inflow alters the result, an experimental wind tunnel study is presented that compares hot-wire measurements in the central wakes of an actuator disc and a model wind turbine (diameter-based Reynolds number Re ≈ 300000). Two turbulent inflows are investigated, an intermittent, i.e. gusty, atmospheric-like inflow generated by an active grid, and a non-intermittent inflow generated by a regular grid. The data is investigated using one-point and higher-order two-point statistics. We find that the wakes of both models have similar properties for all investigated quantities within the far wake. The turbulence in the central wake is independent of the inflow conditions, and both models filter larger scale intermittency in the far wake with regard to the inflow. Also, we find that the turbine generates its own kind of turbulence that dominates the ambient turbulence and has strong features of homogeneous, isotropic turbulence.

Design and implementation of an innovative airborne electric propulsion measure system of fixed-wing UAV

The electric propulsion system combination of unmanned aerial vehicles (UAVs) plays a vital role in improving the endurance time for newly designed aircraft. To realize the measurement of the parameters of the electric propulsion system in an actual flight, a novel airborne powered test scheme is proposed and developed in this work. Both the flight test and wind tunnel experimental study are performed to estimate the accuracy of the test approach by discussing the effect of the airspeed on the electric aircraft powered system. Additionally, the thrust, torque, and efficiency curves are also studied as the increase of revolutions per minute (RPM) in flight tests. The results suggest that the innovatively designed electric-powered test system is capable of measuring the aircraft propulsion efficiency parameters within 4% when compared to a wind tunnel experiment. Compared with the wind tunnel experiment, the uncertainty of the airborne test is 0.32% (motor speed), 0.83% (voltage), 1.17% (current), 0.93% (thrust), and 2.0% (torque). This kind of airborne test method can replace the high cost of wind tunnel test, which is more suitable for fixed-wing aircraft, has high application potential for the propulsion system optimization, and real-time state monitoring of power equipment.

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.