An official website of the United States government
Thunderstorm downburst winds are a major cause of severe damage to buildings and other infrastructure. The initiative of the NSF-NHERI Wall of Wind (WOW) Experimental Facility to design and develop a downburst simulator was established to open new horizons for multi-hazard engineering research by extending the current capabilities of the facility to enable the simulation of non-synoptic winds. Five different downburst simulator designs have been tested in the 1:15 small-scale replica of the WOW to identify the optimal design. The design concepts tested herein considered both the 2-D impinging jet and the 2-D wall jet simulation methods. The basic design methodology consists of transforming the available atmospheric boundary layer (ABL) wind simulator into downburst winds by adding an external modification device to the exit of the flow management box. A flow characterization comparison among the five contending downburst simulators, along with comparisons to real downbursts and previous literature findings, has been conducted. The study on the effect of surface roughness length on the height of the peak wind velocity showed that the implementation of a 2-D plane wall jet enables large-scale outflows (higher peak velocity height) with high Reynold numbers, which is advantageous in terms of reducing scaling effects. In general, the current research work showed that four downburst simulation methods were suitable for adoption; however, only one downburst simulator was recommended based on the feasibility of construction in the facility. The chosen downburst simulator consisted of a two louver slat system near the bottom, with a blockage at the top. This configuration enables producing a large rolling vortex passing through the testing section, which would serve adequately in the further study of turbulent flow characterization and testing of larger scale test models.
more »
« less
Open-jet boundary-layer processes for aerodynamic testing of low-rise buildings
Investigations on simulated near-surface atmospheric boundary layer (ABL) in an open-jet facility are carried out by conducting experimental tests on small-scale models of low-rise buildings. The objectives of the current study are: (1) to determine the optimal location of test buildings from the exit of the open-jet facility, and (2) to investigate the scale effect on the aerodynamic pressure characteristics. Based on the results, the newly built open-jet facility is well capable of producing mean wind speed and turbulence profiles representing open-terrain conditions. The results show that the proximity of the test model to the open-jet governs the length of the separation bubble as well as the peak roof pressures. However, test models placed at a horizontal distance of 2.5H (H is height of the wind field) from the exit of the open-jet, with a width that is half the width of the wind field and a length of 1H, have consistent mean and peak pressure coefficients when compared with available results from wind tunnel testing. In addition, testing models with as large as 16% blockage ratio is feasible within the open-jet facility. This reveals the importance of open-jet facilities as a robust tool to alleviate the scale restrictions involved in physical investigations of flow pattern around civil engineering structures. The results and findings of this study are useful for putting forward recommendations and guidelines for testing protocols at open-jet facilities, eventually helping the progress of enhanced standard provisions on the design of low-rise buildings for wind.
more »
« less
- Award ID(s):
- 1361908
- PAR ID:
- 10041267
- Date Published:
- Journal Name:
- Wind and Structures
- Volume:
- 25
- Issue:
- 3
- ISSN:
- 1226-6116
- Page Range / eLocation ID:
- 233-259
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This project has investigated the wind-induced pressure loads on a realistic low-rise building within an urban area (Y2E2 building in Stanford Engineering Quad). Experiments were conducted at two wind tunnels; the NHERI Wall of Wind (WOW) wind tunnel at the Florida International University facility, and the NHERI terraformer Boundary Layer Wind Tunnel at the University of Florida (UF). First, the building is considered as isolated with suburban terrain in both WT facilities. Consequently, the surrounding buildings were included onto the turntable, and pressure measurements were conducted on the target building. In all experiments, the measurements were performed across a total of 28 wind directions, encompassing the complete wind rose.more » « less
-
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.more » « less
-
This dataset includes files from an extensive wind tunnel study of stepped-roof buildings conducted at the Wall of Wind facility at Florida International University. The aim of the study was to clarify the key factors that affect aerodynamic forces on complex architectural shapes. While ASCE7-22 offers a guideline for wind loads on building components and roofs, it falls short of providing the detailed data needed by engineers to calculate wind loads on the surfaces of stepped-roof buildings. This study fills that gap. The main subject under investigation was the impact of wind loads on different building geometries such as stepped roofs, U-shaped buildings, podium structures, and low-rise buildings with carport extensions. This involved a detailed examination of how various structural features influenced wind pressure distribution, with a specific emphasis on understanding the behavior of wind forces on these models. The outcomes include a series of detailed findings on wind pressure coefficients for each building model. These results offer insights into the wind load characteristics for different architectural forms, contributing to a better understanding of structural behavior under wind forces. The study findings will furnish additional data to enable engineers and scholars to more accurately assess and comprehend wind loads on buildings with multi-level roofs. The dataset includes diagrams of each model’s geometry and wind pressure data. The data highlighted key areas where wind pressures were most significant and how different building features either mitigated or exacerbated these pressures. The data gathered from this study can be reused in multiple ways. It can serve as a reference for designing wind-resilient buildings, particularly in regions susceptible to strong winds or hurricanes. The empirical data can also aid in validating and refining computational models for predicting wind loads on buildings. Additionally, it can be used in academic research for further exploration into wind engineering, urban planning, and architectural design, potentially leading to innovations in building safety standards and construction practices.more » « less
-
A hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) system was developed for quantitative measurements of temperature in a laboratory-scale supersonic jet facility. Measurements were recorded at low pressures and densities relevant for supersonic and hypersonic environments, with special interest in exploring the feasibility of deploying this technique in the 20-inch Mach 6 and 31-inch Mach 10 wind tunnels located at NASA Langley Research Center. Modifications to the existing supersonic jet facility were made to simulate a test section with a width of 31 inches, so that the size of the test section is relevant for either wind tunnel. The CARS system was designed such that a similar beam geometry can be used in the laboratory to acquire point-based fs/ps CARS measurements along two axes of translation. Rotational Raman transitions of O2 and N2 were targeted.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.12989/was.2017.25.3.233
