Large-scale Wind Tunnel Tests Research Articles

Scaling effects on peak wind load estimation for low-rise buildings: An experimental and analytical study

Though scaling effects on estimation of peak wind loads are extensively documented in the literature, there is a lack of systematic comparison of such scaling effects across different model scales tested in wind tunnels. Moreover, the limited studies on large-scale physical models accepted the inadequacy of simulating the large turbulent eddies rather than addressing the missing low-frequency turbulence simulation inherent in such large-scale testing. This study provides an in-depth comparison of estimates of peak wind loads obtained using a range of experimental scaled models (1:100 and 1:6 model scales) of the Wind Engineering Research Field Laboratory (WERFL) building while applying a Partial Turbulence Simulation (PTS) methodology to incorporate the effects of turbulence. Large-scale wind tunnel testing of structures provides the advantage of achieving an improved Reynolds number (Re) similarity, more accurate geometric similarity, and enhanced resolution of flow details such as corner vortices, than is possible with the use of smaller model scales. However, as the model scale increases, achieving turbulence similarity becomes challenging due to limitations in simulating the low-frequency turbulent eddies in the wind tunnel. The PTS method has been used in the recent past to account for the low-frequency turbulence effects in the peak wind load estimation. The method is referred to as 1DPTS when considering longitudinal turbulence components only and 2DPTS when considering both longitudinal and lateral turbulence components in the analysis. The computationally intensive 2DPTS can be further simplified by using a weighted average method as described in this paper as “weighted average PTS.” The current study explores the effect of scaling on peak wind load estimation by using the 1DPTS, 2DPTS, and weighted average PTS methods. Results from the multi-scale experimental tests demonstrate that using larger model scales and compensating for the low-frequency turbulence deficit in the post-test analysis significantly improve the agreement with the prototype data owing to the simulation of a higher Reynolds number. Furthermore, comparing the results of the proposed weighted average method with full-scale data reveals its potential as a substitute for the original 2DPTS method, offering enhanced accuracy, particularly at the roof corner for oblique wind directions. While the effects of Re are well known, the findings of this study explore its impact in conjunction with the application of the PTS methods on peak Cp estimation across five different model scales with Re ranging from 3.65 × 104 to 2.43 × 106, the latter being closest to the full-scale (field) Re. The findings provide new insights into how large-scale physical model testing in high Re flows, supported by analytical PTS-based compensation, can enhance the accuracy of peak wind load estimations for critical scenarios including cornering winds that generate conical vortices.

Codification of wind loads on hip roof overhangs of low-rise buildings

Recent funding opportunities for Wind Engineering research have generated a significant amount of knowledge that has the potential to both develop new or enhance existing wind standards and building codes of practice. Building codes tend to get more rigorous over time to better mitigate damage on buildings and structures. Roof overhangs which are an integral part of the roofing system in low-rise buildings, is particularly vulnerable to damage in wind events due to its exposure to wind-induced loads on both upper and lower surfaces. Large scale wind tunnel testing was carried out at the Wall of Wind (WOW) Research Experimental Facility to investigate the wind-induced loads on roof overhangs of low-rise residential buildings. The physical testing protocol included six 1:10 scaled models with varying geometrical parameters such as roof slope and roof overhang width. Peak wind pressures on both the upper and lower surfaces were measured to calculate the simultaneous net pressure coefficients along the overhangs. Area-averaged pressure analysis was carried out to investigate the pressure gradients on single or groups of taps on the overhangs, soffits, and walls. The experimentally derived area averaged GCp values were compared to previous and current versions of wind standards to evaluate their adequacy. The findings revealed that the provisions’ design guidelines are less conservative for some roofing and wall zones, which justified the need for a codification study that can provide enhanced design guidelines for overhangs and adjacent walls. A detailed discussion of the codified design guidelines, which are formed based on statistical determination rather than the enveloped procedures as commonly used, is presented in this paper.

The Application of maximum entropy technique to determine number concentration and size distribution in pneumatic transport

Based on laser-diffraction technique, the maximum entropy technique is applied to measure particle number concentration and size distribution in pneumatic transport. The information of particle number concentration and size distribution can be obtained simultaneously without distort the fluid and the particle trajectories. Detailed information about the distribution of the particle size and concentration in gas-solid two-phase flows near sand-bed surface are obtained in a large-scale wind tunnel test system. The experimental result shows that particle number concentration increases linearly with the increase of the wind speed. The mean particle size decreases exponentially with height (H > 3 cm), but almost unchanged for H < 3 cm. The weakly relationship of fluctuating velocity and particle-size dispersion is deduced from the underlying mechanism of equilibrium transport. This illustrates that transportation close to the mobile bed has selectivity for particle size.

Scale model experiments of fire whirls over the non-fuel zone around an L-shaped fire source

The Hifukusho-ato fire whirl (HAFW) is a catastrophic fire accident in Tokyo in 1923 and a representative fire whirl phenomenon that occurs over the non-fuel zone around an L-shaped fire source. Previous studies have mainly focused on fire whirls above fire sources, while very limited work reported the HAFW-type fire whirls, which were found to be scale-dependent (more easily to occur in a large-scale wind tunnel test facility than small-scale ones due to the strong viscous effects in the latter) and thus not precisely discussed. In this study, a scale-independent method is proposed by fitting an additional fire source in the inside bend of an L-shaped fire source to mimic the flame-overhang region observed in the large-scale tests; the HAFW-type fire whirl is then successfully reconstructed in a small-scale test model (1/10,000th of the HAFW prototype). Meanwhile, the results show that the average fire whirl occurrence position in the flow direction in a large-scale test model (1/2,000th of the HAFW prototype) does not collapse with those in a small-scale test model (1/10,000th of the HAFW prototype without additional fire sources installed), but with those in the aforesaid scale-independent test model; such collapse can be summarized by a linear fitting correlation between a normalized fire whirl occurrence position and a modified Froude number under different fire source scales and lateral wind velocities. Based on the above experimental facts, updated scaling law to reproduce HAFW-type fire whirls and similar fire whirl occurrence positions is provided. This work advances a fundamental understanding of fire whirls generated by an L-shaped fire source; thus, helping guide fire-rescue operations, and benefiting future fire whirl model development.

Numerical and Experimental Analysis of Subsonic and Transonic Base Pressure

Base drag of space vehicles with large, truncated base usually forms a considerable component of overall drag. The base drag is usually difficult to be accurately predicted due to the intrinsic complexity of base flow. The subsonic and transonic base pressure characteristics were studied by large scale wind tunnel test and Reynolds-Averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) hybrid numerical simulation. The test results show that interferences of both tail sting and ventral blade varies evidently with Mach numbers. The RANS/LES hybrid method was proved to be effective as the calculated time-average base pressure and base drag agree well with wind tunnel test, and detailed flow structures were successfully captured. The base flow pattern is complicated in sub- and transonic regime that either single support scheme is not sufficient to obtain an accurate measurement of base drag. Various support schemes and high precision numerical method are recommended in similar studies.

Design of a synthetic jet actuator for flow separation control

This paper describes the development of a piezo-electric synthetic jet actuator (SJA) of the AFLoNext project. Active flow—loads and noise control on next generation wing (AFLoNext) is a project within European Union’s 7th Framework Program. One of the main project goals is the application of active flow control (AFC) techniques, such as SJAs and pulsed jet actuators (PJAs) in two different application scenarios to evaluate the potential benefit for retrofit of current aircraft and also for future aircraft designs. This paper is focusing on the SJAs. For large-scale wind tunnel testing, an actuator panel with 84 SJAs including the drive electronics system was designed and pre-tested in a laboratory environment. The performance exceeds 100 m/s with outlet nozzles of 2.5 mm diameter and a span wise clearance of 10 mm. A second actuator design was prepared for the application on the outer wing region and was investigated in a harsh environmental test campaign. Two span wise rows of five actuators were integrated in a panel with 10 × 0.5 mm2 slotted outlet nozzles. With this design also velocities exceeding 100 m/s were measured. The actuators withstand different harsh environmental conditions including extreme temperature, rain, mechanical vibration and shock. With the results of the project, a technology readiness level (TRL) evaluation will conclude the maturity of the technology. Depending on the final test and evaluation results, achievement of TRL4 is expected.

Local wind characteristics on bridge deck of twin-box girder considering wind barriers by large-scale wind tunnel tests

Traffic accidents on bridges occur occasionally and have attracted the wide attention of the whole society as well as world. Therefore, researching and exploring the wind environment on bridge deck is a significant and urgent incident, which is able to provide crucial reference for vehicle driving safety. In this paper, the wind environments on the bridge deck of twin-box girder with large scale of 1:20.4 are investigated through wide-ranging wind tunnel tests. During the tests, multiple wind barriers with different heights, porosities and opening forms are considered precisely. Also, the wind environments of truss girder are studied and compared in the process of experiment. Eventually, after handling with the data, analyzing the figures and comparing with other test results, the most significant disciplines are as follows: The wind environments of twin-box girder and truss girder are fairly various; the power spectrum and the wind velocity of twin-box girder are much larger, and there is a lag at the wind velocity stabilization point of truss structure. At the same time, while the parameters of wind barriers change, lower porosity creates lower wind velocity and lower power spectrum. And the height of the wind barriers affects the wind profiles a lot on the windward lanes and lower power spectrum. In addition, the effects of the opening form on windproof and power spectrum are relatively limited.

Comparison of simulations and wind tunnel measurements for the improvement of design tools for Vertical Axis Wind Turbines

As wind turbines are getting larger and cost reductions through up-scaling are reaching a limit, there is increasing pressure to reduce their installation and operating costs, making the business case for Vertical Axis Wind Turbines (VAWTs) more interesting again. However, in order to properly assess the economic potential of large-scale VAWTs, improved design tools are required. As the research budget for VAWT projects is generally too small to carry out expensive large-scale wind tunnel tests and field measurements, alternative methods are required. In this work, the application of small-scale, lower budget methods for improving VAWT design tools is assessed. It is shown that (a) currently available tools for VAWT design have not been sufficiently validated, (b) lower budget, small-scale wind tunnel tests can be effective for examining VAWT performance in terms of average power coefficient vs. tip speed ratio as well as the dynamics of the torque, and (c) Detached Eddy Simulations on small-scale VAWTs can be effective for examining their performance in terms of average power coefficient vs. tip speed ratio as well as the forces on the blades. Based on these results, a process for the transfer of the results of lower budget, small-scale measurements and simulations into recommendations for improved design tools is being developed.

Design of a pulsed jet actuator for separation control

A pulsed jet actuator for separation control has been developed for application in a real-scale wind tunnel experiment with focus on separation behind the pylon-wing junction. This paper covers the last steps of hardware design and testing on the way to a successful demonstration of flow control at the pylon-wing junction. The concept of the actuator is based on fluidic technology and applies pulsed blowing without the help of moving parts. Design parameters are given by numerical simulations of the experimental application case and are validated in ground test. Results of these ground tests are presented and parameters for wind tunnel test settings are derived. The further evaluation of ground test results yields a relation of momentum coefficient, supply mass flow and wind tunnel velocities. It is shown that for the given wind tunnel experiment levels of constant momentum coefficient approximately coincide with levels of constant velocity ratio. All requirements with respect to flow control parameters and model geometry can be satisfied with the presented design, paving the way for a successful demonstration of flow control in a large-scale wind tunnel test.

Fluidic actuators for separation control at the engine/wing junction

PurposeThe area behind the engine/wing junction of conventional civil aircraft configurations with underwing-mounted turbofans is susceptible to local flow separation at high angles of attack, which potentially impacts maximum lift performance of the aircraft. This paper aims to present the design, testing and optimization of two distinct systems of fluidic actuation dedicated to reduce separation at the engine/wing junction.Design/methodology/approachActive flow control applied at the unprotected leading edge inboard of the engine pylon has shown considerable potential to alleviate or even eliminate local flow separation, and consequently regain maximum lift performance. Two actuator systems, pulsed jet actuators with and without net mass flux, are tested and optimized with respect to an upcoming large-scale wind tunnel test to assess the effect of active flow control on the flow behavior. The requirements and parameters of the flow control hardware are set by numerical simulations of project partners.FindingsThe results of ground test show that full modulation of the jets of the non-zero mass flux actuator is achieved. In addition, it could be shown that the required parameters can be satisfied at design mass flow, and that pressure levels are within bounds. Furthermore, a new generation of zero-net mass flux actuators with improved performance is presented and described. This flow control system includes the actuator devices, their integration, as well as the drive and control electronics system that is used to drive groups of actuators.Originality/valueThe originality is given by the application of the two flow control systems in a scheduled large-scale wind tunnel test.

Large-Scale Wind Tunnel Tests of Canopies Attached to Low-Rise Buildings

AbstractCanopies attached to residential and other buildings are predominantly lightweight structures with both surfaces exposed to the wind; therefore, their design is mostly governed by wind-induced loads. Currently, only limited information exists for the design of attached canopies against wind action in building codes and wind standards, which justifies the need to further investigate the wind effects on these structures to establish reliable design recommendations. The pressure distribution on the canopy surfaces, as well as the net component, is highly affected by the wind field around the canopy; therefore, its dimensions, location, and wind direction need to be considered. To investigate the effects of these parameters, in this study, a set of six 1:6 scaled model configurations of a low-rise building with different attached canopy dimensions and locations were tested at boundary-layer flow in the Wall of Wind Research Facility at Florida International University. The results are presented as loc...

Partial turbulence simulation method for predicting peak wind loads on small structures and building appurtenances

Large-scale wind tunnel testing is preferred for small structures and building appurtenances for maintaining modeling accuracy and minimizing Reynolds number effects. In these circumstances the ability to obtain a large enough turbulence integral scale is usually compromised by the limited dimensions of the wind tunnel. So, it is not normally possible to fully simulate the low frequency end of the turbulence spectrum. In this paper the approach is taken of dividing the turbulence into two distinct statistical processes, one at high frequencies which can be simulated in the wind tunnel, and one at low frequencies which can be treated in post-test analysis using the assumptions of quasi-steady theory. In this Partial Turbulence Simulation (PTS) method the contribution of both the high and low frequency turbulence on the wind loads on structures is included by using the probability of load from each of the two processes, with one part coming from the wind tunnel data representing the high frequency component and the remainder from the assumed probability distribution (taken in this paper as Gaussian for generic boundary layer flow) of the missing low frequency component. The two processes are approximated as independent of each other. The efficacy and validity of the method and its various assumptions are assessed by comparing predicted local peak pressure coefficients from tests on large scale models of the Silsoe cube and Texas Tech University (TTU) building in the Wall of Wind facility at Florida International University (FIU) with the corresponding full-scale data. Generally good agreement was found between the model results and full scale, particularly when comparing the highest overall peak pressure coefficients. These results, although limited to peak local pressures on the two test buildings for which good full scale data are available, are encouraging and invite further experiments to explore the range of applicability of the PTS method. This method, although developed in the Wall of Wind facility at FIU, can be equally used in conventional boundary layer wind tunnels and has the potential to enhance the ability of existing boundary layer wind tunnel facilities to predict full scale wind loads.

Improvement in spatial resolution of background-oriented schlieren technique by introducing a telecentric optical system and its application to supersonic flow

A telecentric optical system is applied to the background-oriented schlieren (BOS) technique to improve accuracy, overcoming the drawbacks of conventional diverging light observation. This paper describes the optical arrangement and formula for telecentric BOS measurement and presents measurement results obtained by the colored-grid background-oriented schlieren technique to confirm the theoretical prediction. The application of the new approach for a large-scale supersonic wind tunnel test is reported.

Future needs and laminar flow technology

Abstract After highlighting the need for laminar flow technology, we give an overview of the large-scale laminar flow wind tunnel and flight tests performed within European programmes and consider the prospects of the latest developments.

RTRI's Large-scale Low-noise Wind Tunnel and Wind Tunnel Tests

This article describes the specifications of the Large-scale Low-noise Wind Tunnel completed at Maibara, Japan in 1996. It is used to study aerodynamic noise and other aerodynamic phenomena related to the operation of high-speed trains and to test systems to reduce deleterious effects. Two features stand out: extremely low background noise and a device that enables simulation of the movement of airflow between a testing subject and the ground. Future tasks include making wind tunnel measurements more accurate and conducting field tests to establish comparisons to actual operations.

Long-range Schmidt-Cassegrain laser velocimeter for large wind-tunnel applications

A two-component dual-beam laser velocimeter was designed and fabricated for use in the NASA Ames 40 X 80 ft wind tunnel. The instrument design was predicated on the use of inexpensive, high-quality, large-aperture Schmidt-Cassegrain telescope optics to perform both the laser beam focusing and scattered light collection functions. The instrument was configured to measure the streamwise and cross-stream components of velocity and enclosed in a streamlined optical assembly mounted on a two-dimensional traverse on the floor of the test section. The laser velocimeter probe volume was translated in the vertical direction by means of zoom optics. Coaxial backscattered light was collected through the same optical system and analyzed for Doppler shift. Single-mode polarization-maintaining fiber optics transmitted light from the remotely located laser into the optical assembly. A multimode fiber conveyed the scattered light to remotely located photodetectors. Standard frequency domain processing permitted analysis of Doppler signals with very poor signal-to-noise ratio. The system was evaluated in an optics laboratory in preparation for wind-tunnel test program applications. Sample data from this evaluation were presented as representative of the capability of the instrument. Statement of the Problem I N recent decades the laser Doppler velocimeter1 (LV) has seen increasing application to the study of aerodynamic phenomena. The LV provides a noninvasive measurement capability that is critical for the study of many phenomena. The dual-beam or differentialDoppler configuration of the instrument2 has been shown to have many practical advantages and is used extensively in small-scale wind-tunnel testing. Although several new techniques offer increased potential for global measurement capability,3'4 the LV remains a very important instrument for any aeronautical research facility. Although significant progress has been made,5 LV has not been widely used in large-scale wind-tunnel testing. To maintain the noninvasive quality of the measurement, it is necessary to place the instrument outside the wind-tunnel test section, or at least far enough away to limit its effect on the flowfield of interest. In largescale wind tunnels, this means large separation between the probe volume (laser beam intersection volume) where Doppler shifted light is scattered and the receiving optics where that light is collected and focused on a photodetector. This large separation or longrange operation requirement demands high laser power density in the probe volume to achieve high scattered intensity of the Doppler shifted light and a large collection solid angle to concentrate it on the photodetector. For a closed jet wind tunnel, it is further necessary to use windows of sufficient quality that the laser beams launched into the test section as well as the scattered light collected from the probe volume are not significantly degraded. In particular, the laser beams must not be refracted by striae in the windows so as to significantly reduce beam overlap in the probe volume. The window aperture must be sufficient to access the entire flow region of interest. The National Full-Scale Aerodynamics Complex at NASA Ames Research Center is composed of two large wind tunnels and a static (hover) test facility. The 40 x 80 ft wind tunnel is the smaller of the two wind tunnels, with a speed capability up to 300 kn (154 m/s).

Alleviation of Spin-Entry Tendencies through Localization of Wing-Flow Separation

Studies have been made on several wing leading-edge modifications applicable at present to single-engine light aircraft, which produce stabilizing vortices at stall and beyond. These vortices have the effect of fixing the stall pattern of the wing such that the various portions of the wing upper surface stall nearly symmetrically. The lift coefficient produced is maintained at a high level to angles of attack significantly above the stall angle of the unmodified wing, and the divergence in roll usually is reduced to a controllable level. It is hypothesized that these characteristics will help prevent inadvertent spin entry after a stall. Results are presented from recent large-scale wind-tunnel tests of a typical light aircraft, both with and without the modifications. The data indicate (hot the static stall and poststall characteristics of this aircraft, in a typical landing-approach condition, are noticeably improved when it suitable leading-edge modification is employed; and also that no appreciable aerodynamic penalties are evident in the normal flight envelope.

On the Calculation of Laminar and Turbulent Boundary Layers on Longitudinally Curved Surfaces

Chakrabartty, S. K., Aerodynamic Characteristics of Wings of Arbitrary Planform, To appear in Journal of Aeronautical Society of India. Corsiglia, V. R. and Koenig, D. G., Large Scale Wind Tunnel Tests on a Low Aspect Ratio Delta-Winged Model Equipped with Sharp Edged Strakes, NASA TN D-3621. Wentz, W. H. and McMahon, M. C., Experimental Investigations of the Flowfield about Delta and Double Delta Wings at Low Speeds, NASACR-521. Sacks, A. H. and Burnell, J. A., On the Use of Impact Theory for Slender Configurations Exhibiting Flow Separation, Vidya 92, Itek Corp., March 1963. with

Hybrid Upper Surface Blown Flap Propulsive-Lift Concept for the QSRLP

The hybrid upper surface blowing concept consists of wing-mounted turbofan engines with a major portion of the fan exhaust directed over the wing upper surface to provide high levels of propulsive lift, but with a portion of the fan airflow directed over selected portions of the airframe to provide boundary-layer control. NASAsponsored preliminary design studies identified the hybrid upper surface blowing concept as the best propulsive lift concept to be applied to the Quiet Short-Haul Research Aircraft (QSRA) that is planned as a flight facility to conduct flight research at low noise levels, high approach lift coefficients, and steep approaches. Data from NASA in-house and NASA-sponsored small-and large-scale wind-tunnel tests of various configurations using this concept are presented. Nomenclature b = wing span BLC = boundary-layer control CL = lift coefficient, L/qS Cia = 0 = h'ft coefficient at zero angle of attack CL^ ~ 2. ' = lift coefficient at an angle of attack of -2 ° CL^ax = maximum lift coefficient C/ = rolling-moment coefficient, rolling moment/qSb Cn = yawing-moment coefficient, yawing momQnt/qSb CT = thrust coefficient, gross thrust/qS C/z = blowing momentum coefficient, gross thrust from BLC nozzle/qS L -lift Pl£IP^ = pressure ratio, total pressure at engine nacelle exit/tunnel static pressure q = freestream dynamic pressure S = wing area V = velocity W/S = wing loading a = angle of attack 6/r = deflection angle of thejrailing-edge flap