Large Boundary Layer Wind Tunnel Research Articles

Full-scale experimental simulation of the stack effect pressure acting on an elevator door system in a high-rise building

The pressure-bearing performance of an elevator system under the stack effect in a super high-rise building is usually difficult to simulate directly in a laboratory environment due to the difficulty in fully meeting the similarity requirements. In this paper, a new full-scale experimental device for simulating stack pressure was designed in a large boundary layer wind tunnel laboratory, which was based on using wind pressure to simulate the action of thermal pressure on an elevator door system. By employing this approach, the pressure-bearing performances of an elevator door system under different levels of wind pressure of the static and dynamic conditions were systematically investigated, and the malfunction of the elevator door system due to the strong stack effect was successfully simulated. The critical pressure threshold of the elevator door system, which was difficult to evaluate accurately in previous studies, was then measured and it was approximately equal to 150 Pa. Meanwhile, the pressure-bearing state of the elevator door system was numerically simulated and compared with the wind tunnel experiment results. The study shows that the simulation employing the dynamic mesh model can accurately reflect the force characteristics of an elevator lobby door during its physical process of opening and closing. Finally, based on the experimental simulation results, the pressure-bearing thresholds of the elevator door systems of several typical high-rise buildings were estimated, and the reasonability of the full-scale simulation was finally verified by comparisons with field measurement data.

New Zealand Country Report 2021

This paper summarises the activities that have taken place in wind engineering in New Zealand since 2012 when the previous APEC-WW took place in Hanoi, Vietnam. Since that date there have been considerable activities in wind engineering in New Zealand, ranging from an increase in government funding for wind hazard research, an analysis of historical wind data throughout New Zealand which has been used to update the regional wind speeds and directional multipliers for the 2021 version of the wind loading standard, and the construction of a large boundary layer wind tunnel with a computer-controlled three dimensional traversing rig at the University of Auckland that has allowed extensive wind tunnel investigations to be carried out. In addition, this period has seen a strong link to Chinese universities develop through CSC-funded research students that have come to study in New Zealand. Finally, the very successful 9th Asia-Pacific Conference on Wind Engineering (APEC-WW) was held at the University of Auckland in December 2017.

Experiments in a Large Boundary Layer Wind Tunnel: Propagation of Noise through the Turbulent Boundary Layer

A series of acoustic propagation experiments was conducted in the University of Florida Boundary Layer Wind Tunnel (UFBLWT) to investigate tornadic infrasound propagation in the turbulent atmosphere. A synthetic acoustic wave was generated within a boundary layer wind field using a speaker, and distorted by the surrounding turbulent atmosphere as it propagated along the UFBLWT fetch where it was measured by an acoustic microphone 22 m downwind of the speaker. The wind tunnel operating speed and the configuration of the mechanical turbulence generating roughness elements were varied between experiments to alter the turbulence characteristics and thus the distortion of the acoustic wave. The wind field turbulence data were obtained by three Cobra probes mounted on an actuated and automated gantry. The turbulence-induced distortion of the acoustic wave was captured by analyzing the signal at its source and as-measured downwind. Data were characterized, organized, and curated into four stages.

The Influence of Slopes of Isolated Three-Dimensional Valleys on Near-Surface Turbulence

Motivated by a limited understanding of how valleys affect near-surface turbulence, characterizations of neutrally stable atmospheric-boundary-layer flows over isolated valleys are presented. In particular, the influence of the slopes of the three-dimensional ridges that form the idealized valleys are investigated. Flows over three distinct symmetric valley geometries were modelled in a large boundary-layer wind tunnel. For each valley geometry, the high-resolution measurements from the crests of each of the ridges and the midpoint between them are compared with an undisturbed moderately rough classed boundary-layer flow over flat terrain with homogeneous surface roughness. Flow separation originates above the crests of the first ridges of all geometries and generates recirculation zones. These are characterized by slope-dependent increases in three-dimensional near-surface turbulence when compared with the attached flows further upstream. The recirculation zones longitudinally extend to roughly half the valley width. Above the crests of the second ridges, the longitudinal velocity component decreases and turbulence intensity increases when compared with the flows above the crests of the first ridges. Results also exhibit significant increases of turbulence above the inner-valley regions of all geometries.

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.

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) ...

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.

Investigation of discharge coefficient for wind-driven naturally ventilated dairy barns

It is important to estimate the ventilation rate of animal houses accurately for the purpose of reducing emissions and providing comfortable indoor climate. The orifice equation is widely applied for estimating the airflow rate of naturally ventilated dairy barns. However, to regard openings’ discharge coefficient (Cd) as a constant maybe not true for large openings. To gain basic knowledge of the opening size effects on Cd values, experiments with a scaled model were carried out in a large boundary layer wind tunnel. Seven cases with different sidewall opening ratios, varying from 18.6% to 81.4%, were investigated under 8 m/s wind speed conditions. The airflow rates, Cd values of windward openings and airflow patterns were analysed. It was found that the Cd value was considerably dependent on the opening size and varied from 0.67 to 0.94 when the opening ratio increased from 18.6% to 62.7%. This is due to the assumptions of pure pressure-driven flow and uniform velocity distributions in the opening were not satisfied for large opening cases. Our study suggests that Cd should be regarded as a variable under different opening size conditions when using the orifice equation to determine the airflow rate of large openings.

Lidars for Wind Tunnels - an IRPWind Joint Experiment Project

Measurement campaigns with continuous-wave Doppler Lidars (Light detection and ranging) developed at DTU Wind Energy in Denmark were performed in two very different wind tunnels. Firstly, a measurement campaign in a small icing wind tunnel chamber at VTT in Finland was performed with high frequency measurements for increasing the understanding of the effect of in-cloud icing conditions on Lidar signal dynamics. Secondly, a measurement campaign in the relatively large boundary-layer wind tunnel at NTNU in Norway was performed in the wake of a scaled test turbine in the same configuration as previously used in blind test comparisons for wind turbine wake modelers. These Lidar measurement activities constitute the Joint Experiment Project” L4WT - Lidars for Wind Tunnels, with applications to wakes and atmospheric icing in a prospective Nordic Network” with the aim of gaining and sharing knowledge about possibilities and limitations with lidar instrumentation in wind tunnels, which was funded by the IRPWind project within the community of the European Energy Research Alliance (EERA) Joint Programme on Wind Energy.

Wind tunnel testing of a closed-loop wake deflection controller for wind farm power maximization

This paper presents results from wind tunnel tests aimed at evaluating a closed- loop wind farm controller for wind farm power maximization by wake deflection. Experiments are conducted in a large boundary layer wind tunnel, using three servo-actuated and sensorized wind turbine scaled models. First, we characterize the impact on steady-state power output of wake deflection, achieved by yawing the upstream wind turbines. Next, we illustrate the capability of the proposed wind farm controller to dynamically driving the upstream wind turbines to the optimal yaw misalignment setting.

Roughness Effects on Wind-Turbine Wake Dynamics in a Boundary-Layer Wind Tunnel

Increasing demand in wind energy has resulted in increasingly clustered wind farms, and raised the interest in wake research dramatically in the last couple of years. To this end, the present work employs an experimental approach with scaled three-bladed wind-turbine models in a large boundary-layer wind-tunnel. Time-resolved measurements are carried out with a three-component hot-wire anemometer in the mid-vertical plane of the wake up to a downstream distance of eleven turbine diameters. The major issue addressed is the wake dynamics i.e. the flow and turbulence characteristics as well as spectral content under two different neutral boundary-layer inflow conditions. The wind tunnel is arranged with and without roughened surfaces in order to mimic moderately rough and smooth conditions. The inflow characterization is carried out by using all three velocity components, while the rest of the study is focused on the streamwise component’s evolution. The results show an earlier wake recovery, i.e. the velocity deficit due to the turbine is less persistent for the rough case due to higher incoming turbulence levels. This paves the way for enhanced mixing from higher momentum regions of the boundary layer towards the centre of the wake. The investigation on the turbulent shear stresses is in line with this observation as well. Moreover, common as well as distinguishing features of the turbulent-scales evolution are detected for rough and smooth inflow boundary-layer conditions. Wake meandering disappears for rough inflow conditions but persists for smooth case with a Strouhal number similar to that of a solid disk wake.

PIV technique implementation for wind mapping in complex topographies

An experimental study was conducted to demonstrate PIV's capability to provide a detailed characterization of the flow field over complex topographic terrain in a large boundary layer wind tunnel setup. Two-dimensional velocity fields were measured in horizontal and vertical planes over a 1:3000 scaled topographic model. The non-uniform seed distribution was found to be a major issue which could affect the PIV velocity vectors. A novel scheme was developed to automatically detect the regions with low seed density and exclude them from further analysis. The mean and turbulent velocities obtained from PIV and previous hotwire measurements are compared and show good agreement. The study shows that PIV can be successfully used to measure flow over complex geometries in large wind tunnel setups, enabling the flow structure to be mapped with a very high spatial resolution.

Large-scale quasi-steady modelling of a downburst outflow using a slot jet

This article synthesizes the literature on the meteorology, experimental simulation, and wind engineering ramifications of intense downburst outflows. A novel design of a large-scale test facility and experimental evidence of its validity are presented. A two-dimensional slot jet is used to simulate only the outflow region of a downburst. Profiles of mean velocity and turbulence quantities are acquired using hot-wire anemometry. Comparison with the literature provides empirical evidence that supports the current approach. A geometric analysis considers the validity of applying a two-dimensional approximation for downburst wind loading of structures. This analysis is applicable to power transmission lines in particular. The slot jet concept can be implemented in a large boundary layer wind tunnel to enable large-scale laboratory experiments of thunderstorm wind loads on structures.

Physical modelling of a complex forest area in a wind tunnel—comparison with field data

The impact of biogenic trace gases on tropospheric chemistry, air quality, and the formation of secondary products affecting our climate on a regional and global scale are far from being understood. A considerable lack of knowledge exists concerning a typical forest stand as a net source of reactive trace compounds into the troposphere. The concept of this study was to combine field experiments, laboratory experiments investigating emission and uptake of trace compounds by the plants, and modelling experiments simulating the chemistry of biogenic trace gases and the dynamics of a forest stand under well-defined conditions. The chosen site was the forest area surrounding the Forschungszentrum Juelich (Juelich Research Centre, Germany). In order to simulate the dynamical properties, the forest area was modelled to a scale of 1:300 and studied in the large boundary layer wind tunnel at the Meteorological Institute of Hamburg University. An area 3150 m long and 1200 m wide was replicated, including the upwind edges of the forest. The model of the forest must reproduce the resistance to the wind generated by this porous environment. Rings of metallic mesh were used to represent the trees following preliminary tests to find an arrangement of these rings that provided the appropriate aerodynamic characteristics for a forest. The turbulence properties of the flow were measured in the wind tunnel within and above the canopy. Subsequently, they were compared with field data obtained at the Juelich Research Centre, in order to test the quality of the modelling concept. The comparison showed a good agreement and results were consistent with previous studies. Tracer-gas experiments were carried out in the field within the canopy, which were then replicated in the wind tunnel. The order of magnitude of the dimensionless concentration downwind of the point source was in agreement.

Construction of boundary layer wind tunnel for long-span bridges

In order to carry out final verification of the aeroelastic safety of the Akashi Kaikyo(strai) Bridge, which has a main span of 1,990 m and two side spans of 960 m and a truss stiffening girder, its full aeroelastic model wind tunnel tests were planned and are now in progress. A geometrical 1 100 scale model was selected and primary dimensions required for the test section of wind tunnel were determined as follows: width 41 m, height 4 m and length 30 m. This paper presents some discussions related to this large boundary layer wind tunnel facility and some new ideas of modeling for the bridge.

Galloping response of towers

In the present paper the extended application of the quasi-steady theory of galloping to towers of square section in simulated natural winds is examined. In the experiments, the wind was produced in a large boundary layer wind tunnel, and represented a full scale wind typical of a “suburban” exposure. The static measurements were made on towers instrumented with pressure taps so that the variation with height of the sectional pressure distribution and force could be determined. The dynamic measurements were made on rigid towers pivotted elastically at the base, and mounted with very low, but variable, viscous-type damping. In the quasi-steady theory, the variation with height of the wind speed and sectional transverse force were incorporated, an improvement over the averaged-force method used previously. The results showed that there was an important variation of sectional lateral force over the height of the towers tested, and that good agreement between predicted and observed variations of galloping amplitude with wind speed was obtained when this sectional force variation was incorporated in the theory. The paper also examines effects on galloping behaviour of the proximity of resonance of a tower with its wake vortex system, and the implications of this for the galloping of full-scale towers.