Large Wind Tunnel Research Articles

Research on the Health Intelligent Management System of Large Wind Tunnel

In the national major projects, health management of key infrastructure has been paid more and more attention. Wind tunnel is a national strategic infrastructure. The health management system is of great significance to promote the safe, efficient and reliable operation of large-scale wind tunnel. In order to establish a wind tunnel health intelligent management system, it is necessary to realize the dynamic state monitoring, intelligent fault diagnosis, intelligent fault prediction, independent maintenance support and integrated equipment management. Facing the great demand of designing and constructing the world’s top wind tunnels, this paper makes an exploratory research on the health intelligent management system of large wind tunnel. By means of data mining, machine learning and virtual reality, the health management system can have the ability of self-study and self-improvement. So as to realize the development of the health management of wind tunnel to the depth intelligent.

Heat transfer of insulation structure for large cryogenic wind tunnel

In order to maintain the cryogenic environment of cryogenic wind tunnel in service, heat transfer of insulation structure is investigated in this work. Firstly, the design and material selection of insulation structure is conducted. Afterwards, theoretical calculation on heat transfer of insulation structure is carried out based on 1-D heat conduction model. Subsequently, the finite element model of insulation structure is established, on this basis, involving the actual work condition of cryogenic wind tunnel, heat transfer of the insulation structure is numerically calculated. Finally, the testing platform able to simulate the work environment of cryogenic wind tunnel is built and the temperature measurement experiments at the cryogenic condition and at the cryogenic pressure condition are carried out, respectively. The obtained results show that the designed insulation structure is in possession of great insulation characteristics to ensure the cryogenic environment of cryogenic wind tunnel. Additionally, the established testing platform can provide a testing method to investigate the heat transfer character of other materials or structures in cryogenic environment.

EXPERIMENTAL STUDY OF THE INFLUENCE OF ATMOSPHERIC TURBULENCE ON THE BOUNDARY LAYER FLOW ON THE GLIDER WING

Flight experiments aimed at studying the transition from the laminar to turbulent flow in the boundary layer on the glider wing at different levels of atmospheric turbulence performed in the 1980s are reviewed. The results are obtained by means of hot-wire measurements and visualization of the flow on the wing surface by the method of sublimating coatings. The transition is found to proceed in several stages: emergence, evolution, and failure of a discrete packet of instability waves in the region of the adverse pressure gradient. The data obtained in the study are compared with the results of similar investigations carried out in a large wind tunnel on the same real glider wing at realistic Reynolds numbers.

Opening Size Effects on Airflow Pattern and Airflow Rate of a Naturally Ventilated Dairy Building—A CFD Study

Airflow inside naturally ventilated dairy (NVD) buildings is highly variable and difficult to understand due to the lack of precious measuring techniques with the existing methods. Computational fluid dynamics (CFD) was applied to investigate the effect of different seasonal opening combinations of an NVD building on airflow patterns and airflow rate inside the NVD building as an alternative to full scale and scale model experiments. ANSYS 2019R2 was used for creating model geometry, meshing, and simulation. Eight ventilation opening combinations and 10 different reference air velocities were used for the series of simulation. The data measured in a large boundary layer wind tunnel using a 1:100 scale model of the NVD building was used for CFD model validation. The results show that CFD using standard k-ε turbulence model was capable of simulating airflow in and outside of the NVD building. Airflow patterns were different for different opening scenarios at the same external wind speed, which may affect cow comfort and gaseous emissions. Guiding inlet air by controlling openings may ensure animal comfort and minimize emissions. Non-isothermal and transient simulations of NVD buildings should be carried out for better understanding of airflow patterns.

Impact of Flow Blowing and Suction strategies on the establishment of an aerodynamic barrier for solar cavity receivers

This study compares two aerodynamic approaches to minimize convective losses from cavity receivers, namely blowing and suction. A laboratory-scale cavity receiver was operated in a large wind tunnel at varying wind speed and tilt angle. The inner surface of the cavity was heated to a constant temperature of 300 °C by finely controlled electrical heaters. The measured electric energy required to maintain the heaters at the same temperature was used to provide a direct measure of losses from the receiver. An air curtain was engineered to provide curtain of air blown either downward or upwards across the aperture. Suction was alternatively applied through a nozzle positioned below the aperture for a series of suction flowrates. A numerical study was also conducted using a commercial CFD package and validated with available data. It was found that the upward blowing air curtain performs better than the downward curtain for the buoyancy dominant conditions. Moreover, the measured effectiveness of the downward blowing air curtain at tilt angle of the cavity of 45° showed that the application of air curtain with higher velocities increases the convective heat losses over the case with no air curtain. When comparing the performance of air curtain with air suction, it was found that for the low range of relative momentum ratio of curtain to wind flow, suction performs better than blown air. Finally, this study highlights the need for adaptable strategies, based on operating condition, to minimize heat losses and improve the thermal efficiency of cavity receivers.

Experimental Research on Noise Reduction for Continuous Transonic Wind Tunnel Loop

The noise level of wind tunnel test section is respected as one of the most important performance specifications to represent the flow field quality, especially for large scale wind tunnel. According to the acoustic experimental research conducted in the 0.6 m continuous transonic wind tunnel of CARDC, main noise sources in the tunnel loop included the compressor, the high-speed diffuser and the test section. To reduce the noise in the test section, it is necessary to prevent the test section from the compressor noise propagated both forward and backward. In 0.6 m wind tunnel loop, acoustic treatments were installed on both the compressor rear cone and the fourth corner to prevent the noise emitted from the compressor from propagating forward. The vanes in the forth corner were filled with glass fibers and covered with perforated panels. And the compressor rear cone was covered with three layers of micro-perforated panels. With acoustic treatment in the tunnel loop and the second throat throttling, the fluctuation pressure coefficient (ΔCp) is lower than 0.8%, which is close to the international advanced level.

Airflow Characteristics Downwind a Naturally Ventilated Pig Building with a Roofed Outdoor Exercise Yard and Implications on Pollutant Distribution

The application of naturally ventilated pig buildings (NVPBs) with outdoor exercise yards is on the rise mainly due to animal welfare considerations, while the issue of emissions from the buildings to the surrounding environment is important. Since air pollutants are mainly transported by airflow, the knowledge on the airflow characteristics downwind the building is required. The objective of this research was to investigate airflow properties downwind of a NVPB with a roofed outdoor exercise yard for roof slopes of 5°, 15°, and 25°. Air velocities downwind a 1:50 scaled NVPB model were measured using a Laser Doppler Anemometer in a large boundary layer wind tunnel. A region with reduced mean air velocities was found along the downwind side of the building with a distance up to 0.5 m (i.e., 3.8 times building height), in which the emission concentration might be high. Additional air pollutant treatment technologies applied in this region might contribute to emission mitigation effectively. Furthermore, a wake zone with air recirculation was observed in this area. A smaller roof slope (i.e., 5° slope) resulted in a higher and shorter wake zone and thus a shorter air pollutant dispersion distance.

Experiments in a Large Boundary Layer Wind Tunnel: Upstream Terrain Effects on Surface Pressures Acting on a Low-Rise Structure

AbstractAn extensive series of experiments in a large boundary layer wind tunnel (BLWT) was carried out at the University of Florida (UF) Natural Hazard Engineering Research Infrastructure (NHERI) ...

3D Generalized Inverse Beamforming in wind tunnel aeroacoustic testing: application to a Counter Rotating Open Rotor aircraft model

Inverse methods are gaining relevance in the aeroacoustic community for their capability to accurately localize and quantify noise sources. Indeed, since modern aircraft are more targeted to the reduction of fuel consumption, and very often some design choices, like Open Rotor (OR) propulsion systems, cause excessive acoustic emissions, accurate knowledge of noise source locations is of fundamental importance. This paper describes the use of an inverse method, namely Generalized Inverse Beamforming (GIBF), to characterize a Counter Rotating Open Rotor (CROR) installed on a 1/7th scale aircraft model. The model was tested in a large Low-Speed Wind Tunnel (WT) at The Pininfarina Aerodynamic and Aeroacoustic Research Center in Turin, Italy, within the framework of the FP7 EU Clean-Sky WENEMOR (Wind tunnel tests for the Evaluation of the installation effects of Noise EMissions of an Open Rotor advanced regional aircraft) project. With respect to previous works already published, the pros and cons of 3D GIBF formulation will be discussed on data collected from an industrial test case. A comparison of L2 and L1 norm formulations, as well as multiplicative approach and single array processing in 3D GIBF, will be performed, discussing their differences in terms of source localization accuracy. Since a quantitative analysis on real data cannot be provided because of confidentiality issues, the capability of the present approach to correctly quantify the source strength will be evaluated by considering a synthetic monopole source emitting white noise at different signal-to-noise-ratios (SNRs). Finally, it will be shown that 3D GIBF can provide engineers with more reliable data regarding the acoustic behavior of CROR-based aircrafts, this proving the advantages in exploiting this inverse method in WT aeroacoustic applications.

Aerodynamic and aeroacoustic investigation of an innovative regional turboprop scaled model: numerical simulations and experiments

An extensive aeroacoustic and aerodynamic investigation of an innovative regional turboprop aircraft has been carried out experimentally and numerically under the framework of two research projects funded by the European Union through the CleanSky Research Programme. Experimental tests have been performed in the RUAG Large Subsonic Wind Tunnel in Switzerland and CFD results have been validated against the experimental data. The A/C high-lift performance, stability and control derivatives, aerodynamic noise sources, and low-noise solutions for high-lift devices, have been investigated under representative conditions in cruise, take-off, and landing configurations. The aerodynamic and aeroacoustic investigation has been carried out parametrically, in terms of several reference quantities, including the propellers’ thrust and rpm, the speed of the air-flow, the incidence angle of the aircraft and the position of the microphone array used for the acoustic investigation. The present paper gives an overview of relevant results obtained for selected aircraft configurations which have been tested in the wind tunnel and analyzed through CFD simulations. The focus lies on the overall aerodynamic characterization and on the noise sources identification carried out using standard beamforming techniques.

Turbine Wake Deflection Measurement in a Wind Tunnel with a Lidar WindScanner

Wind turbines are typically closely spaced in wind farms, and thus operate in the wake of upstream turbines and experience power losses. Currently, one of the techniques to reduce the wake interaction between turbines within a wind farm is to yaw the upstream turbine with regards to the incident wind direction. The objective is to deflect the wake, which can potentially increase the overall power output and the annual energy production of the wind farm. Experimental data can aid the process to thoroughly analyse the wake deflection under different inflow conditions, which is necessary to apply a yaw-based wind farm control model. The aim of the present research is to investigate the possibility and accuracy of the experimental setup to measure the wake characteristics with a high spatial and temporal resolution through the use of a short-range Lidar WindScanner, within the wind tunnel of ForWind-Oldenburg. This technique provides the opportunity to analyse the flow structures at different operational and inflow conditions in a relative fast manner without disturbing the flow. Experiments were conducted using a model wind turbine in a large cross-section wind tunnel. The short-range Lidar WindScanner is used as the primary instrument to map the wind turbine wake at different downstream locations. The flow structures of the wake were measured from 1 D up to 10 D downstream of the turbine rotor. A stable flow within the wind tunnel segment is measured, which is crucial for the analyses of the evolution of the wake. In addition, a high detailed spatial resolution of the wake profile is observed, showing the symmetric and asymmetric behaviour of the wake, for unyawed and yawed conditions, respectively. Furthermore, the calculation of the thrust coefficient from the velocity data show expected behaviour, giving further credibility to the measurement technique.

Wake meandering in a model wind turbine array in a high Reynolds number turbulent boundary layer

Wake meandering is the dynamic shift observed in the spatial location of a wind turbine wake as it evolves downstream, considered to be caused primarily by the interaction of large flow structures in the atmospheric boundary layer with the turbulent wake. Experiments were conducted in a large boundary layer wind tunnel to investigate meandering in the wakes of both individual model wind turbines and in a wind turbine array with a large number of model turbines (19 rows x 5 columns = 95 model turbines). Unlike bluff body vortex shedding, the meandering phenomenon for a turbine wake is not characterized by a well-pronounced peak in the frequency domain, but rather by a broad spread over a low-frequencies range. For individual turbine models, both rotating three-bladed models and non-rotating porous disks, frequencies and peak energies observed in the velocity spectrum in the wake return to those of the incoming high Reynolds number turbulent boundary layer. Wake meandering also presents itself in the large wind turbine array. Here, frequencies and peak energies observed in the velocity spectrum in the wake do not return to those of the incoming turbulent boundary layer. Instead, a lower dominant frequency corresponding to the wind velocity at hub height and array spacing is observed within the array, indicating forcing of the meandering by the array itself (a type of resonance). Higher peak energies are observed in the array due to large flow structures representative of the turbine spacing.

Aerodynamic Load Distribution and Wake Measurements on a Sub-scale Wind Turbine

Wind tunnel testing of wind turbines is critical for better understanding the blade aerodynamics and wakes as well as for producing data necessary to validate computational models. In this work, a 2 m diameter wind turbine that was designed to produce a wake with characteristics similar to that of an industrial scale turbine was tested in a large wind tunnel environment. Unsteady inflow, unsteady blade load distribution, and instantaneous wake measurements were obtained to characterize wake development and near-wake behavior. The results showed that the measurement of both blade loading and wake properties facilitate understanding of the wake’s behavior, and the blade load distribution can be used to explain the near-wake structure. Tests covering a wider range of conditions would be valuable for validating simulations of wind turbine flows.

EXPERIMENTAL INVESTIGATION OF WIND ENERGY PLANT WITH HELICOIDAL ROTOR

The article is devoted to design and investigation of a helicoidal wind rotor in the wind tunnel, which is a modification of the Darrieus rotor – the most promising rotor type for vertical axis wind turbines. The graphs of power and rotation of the investigated wind generator depending on the incoming air flow speed are obtained. Investigation of the helicoidal rotor in a large wind tunnel has shown that the helicoidal rotor type has a high potential for use in vertical axis wind turbines. The high cut in speed of the incoming air flow is caused by the phenomenon of "sticking" of the axial generator with steel cores, as well as by the absence of an additional starting Savonius rotor, which could create the initial torque moment at rhe low speed of the incoming air flow.Iit is necessary to enlarge diameter of the generator and to reduce the air gap between the magnets and the stator to increase electric power.

Effectiveness of ridge vent to wind-driven natural ventilation in monoslope multi-span greenhouses

A large eddy simulation (LES) model and wind tunnel experiments were used to investigate the wind-driven ventilation of monoslope greenhouses with ridge vents. The accuracy of the numerical simulation was verified by the results of wind tunnel experiments. The numerical model was then employed to systematically examine the influences of wind direction, opening configuration and greenhouse length on the cross ventilation. In addition, an analytic model, based on inviscid flow assumption and mass conservation, was used to compute the ventilation rate. The results showed that the total ventilation rates of the multi-span greenhouses with open ridge vents were much larger than that of with closed ridge vents. The windward ridge vent (directly facing the wind direction when θ = 180°) can substantially increase the ventilation rate of multi-span monoslope greenhouses, as compared to the leeward ridge vent when wind direction θ = 0°. In other words, to take full advantage of the wind-driven ventilation the ridge vents of the greenhouses should directly face the prevailing wind direction. The ventilation rates can be reduced by adjusting the degree of opening and the number of the operable ridge vents.

High-solidity straight-bladed vertical axis wind turbine: Numerical simulation and validation

This study uses 2.5D large eddy simulations (LES) and wind tunnel experiments to investigate aerodynamics of high-solidity straight-bladed vertical axis wind turbines (SBVAWTs). The experimental setup and numerical simulation strategy of a high-solidity SBVAWT are first introduced. The self-start performance of the high-solidity SBVAWT is then assessed. The aerodynamic forces acting on the rotating high-solidity SBVAWT are computed by 2.5D LES method, and the numerical results are compared to those from the wind tunnel experiments. The numerical and experimental results indicate that the high-solidity SBVAWT has a good self-start capability. The results also indicate that 2.5D LES method can provide satisfactory prediction to the aerodynamic forces, especially for the straight blade in the upwind zone. Flow characteristics of the high-solidity SBVAWT with different tip speed ratios (TSRs) are finally analyzed, and the mechanism of variation of aerodynamic forces in one rotational circle is revealed. By comparing the flow characteristics of the high-solidity SBVAWT with the moderate-solidity SBVAWT, it is observed that high solidity introduces complex flow field and the aerodynamic force curves of the high-solidity SBVAWT are different from those of the moderate-solidity SBVAWT.

Comparative Study of Free Vortex and Random Vortex in the Design of Wind Tunnel Axial Fan

The design methods of axial flow fan mainly include free vortex design method and random vortex design method. The random vortex design method and free vortex design method were used to design aerodynamic parameters of two fan systems, and then the performance of these two fan systems was compared by numerical simulation. In the numerical simulation, the random vortex method and free vortex method are applied, respectively, based on the fan design parameters given by the acoustically guided wind tunnel fan section, and the physical model was established, the numerical simulation comparison study was conducted for the two sets of fan systems. The comparative analysis of the numerical simulation results shows that compared with the free vortex method, the fan designed by the random vortex method can reduce the local separation of tip and root of the blade, and the axial velocity distribution of fan blade and fan section outlet can be more uniform, and there is a certain increase in fan blade efficiency. These results verify that the design method of random vortex fan is feasible in large wind tunnels, especially in wind tunnels with aerodynamic noise reduction requirements, and can provide powerful conditions for optimizing aerodynamic and acoustic performance of the fan.

Investigation of Drag Reduction Technologies for Light-Duty Vehicles Using Surface, Wake and Underbody Pressure Measurements to Complement Aerodynamic Drag Measurements.

Amulti-year, multi-vehicle study was conducted to quantify the aerodynamic drag changes associated with drag reduction technologies for light-duty vehicles. Various technologies were evaluated through fullscale testing in a large low-blockage closed-circuit wind tunnel equipped with a rolling road, wheel rollers, boundary-layer suction and a system to generate road-representative turbulent winds. The technologies investigated include active grille shutters, production and custom underbody treatments, air dams, wheel curtains, ride height control, side mirror removal and combinations of these.This paper focuses on mean surface-, wake-, and underbody-pressure measurements and their relation to aerodynamic drag. Surface pressures were measured at strategic locations on four sedans and two crossover SUVs. Wake total pressures were mapped using a rake of Pitot probes in two cross-flow planes at up to 0.4 vehicle lengths downstream of the same six vehicles in addition to a minivan and a pick-up truck. A smaller rake was used to map underbody total pressures in one cross-flow plane downstream of the rear axle for three of these vehicles.The results link drag reduction due to various technologies with specific changes in vehicle surface, rear underbody and wake pressures, and provide a database for numerical studies. In particular, the results suggest that existing or idealized prototype technologies such as active grille shutters, sealing the external grille and ride height control reduce drag by redirecting incoming flow from the engine bay or underbody region to smoother surfaces above and around the vehicle. This mechanism can enhance the reduction in wheel drag due to reduced wheel exposure at lowered ride height. Sealing the external grille was found to redirect the flow more efficiently than closing the grille shutters, and resulted in greater drag reduction. Underbody treatments were also found in some cases to redistribute the flow around the vehicle to reduce pressure drag in addition to underbody friction drag. The magnitude and spatial extent of the measured pressure changes due to the various technologies were often consistent with the amount of drag reduction.

Airframe noise measurements in a large hard-walled closed-section wind tunnel

The airframe noise of a 1:2 scaled aircraft model is investigated through a series of experiments in the hard walled closed test section of a large non-anechoic wind tunnel. A surface mounted phased microphone array is used to acquire the wall pressure fluctuations generated by the interaction of the wind tunnel flow and the propagating noise. Data from two measurement campaigns are analysed. The wind tunnel acoustic behaviour and the array performance are first assessed evaluating the results obtained from a reference sound source installed in the centre of the test section. The combination of different airflow speeds, array positions and sound sources are tested. The airframe noise is evaluated acquiring pressure fluctuations in different configurations. The main parameters varied during the tests are the flight configuration, the speed of the airflow, the incidence angle of the model and the position of the microphone array. Data are processed and then analysed in the frequency domain and using a conventional beamforming algorithm to retrieve the sound source maps over the regions of interest. Source maps are deconvolved with a CLEAN-SC routine and single source contributions determined through integration of auto-powers. The resulting spectra are finally scaled determining the exponents of the pertinent scaling laws.

A Proposed Calibration Procedure for the Simulation of Wind-Driven Rain in Small-Scale Wind Tunnel

The simulation of wind-driven rain in the wind tunnel should ensure a realistic representation of rainfall events in a laboratory environment. It necessitates therefore an understanding of how the governing input parameters of the tunnel relate to its outputs. In this perspective, a preliminary calibration should be carried out in order to grant the reproduction of a homogeneous volume of rainwater and a natural raindrop size distribution. A precise and straightforward procedure to be followed is missing. Based on experimental investigations, this study outlines a series of calibration steps that should be performed in the wind tunnel before the rain simulation takes place. It applies in particular to small scale facilities as opposed to the large wind tunnels designed for full-scale testing of building components and vehicles. Such procedure concentrates on the following aspects: wind speed calibration by vane anemometer; calibration of the sprinkler system and rain intensity measurements for assessing its spatial distribution. The main findings include the introduction of a governing function for the sprinkler system, a method for rain mapping as well as the individuation of an optimal set-up in the wind tunnel for rain simulation.