861 research outputs found

    NDM-511: PRESSURE FLUCTUATIONS ON THE ROOFS OF LOW-RISE BUILDINGS IN TURBULENT BOUNDARY LAYERS

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    Buildings are often exposed to the highly turbulent atmospheric boundary layer flows near the earth’s surface. Roofs of low-rise buildings in particular are vulnerable to the resulting aerodynamic loads, especially during the extreme wind storms. For flat-roofed, low-rise buildings with relatively large plan dimensions, the approach flow separates at the leading edge of the roof and then reattaches creating a separation bubble. This separation bubble is a turbulent recirculating flow region that is responsible for causing large-magnitude uplift on the roof surface. Such large, uplifting forces can cause damage to the roofs and roof-mounted structures. There are a limited number of studies present in literature focussing on the flow field and pressure fluctuations on the roof surface of the low-rise buildings and its dependency on the turbulence properties in the incident boundary layer flows compared to the studies performed on two-dimensional bluff bodies in uniform upstream flows. In this paper, the effects of the turbulence intensities and length scales in the boundary layer flows on surface pressure fluctuations for two low-rise building models are examined. The results indicate that roof surface pressure fluctuations strongly depend on roof height turbulence intensity and length scales in the approaching boundary layer flows. At lower levels of turbulence intensities, turbulence scales of significantly higher order of magnitudes compared to the building heights play important roles in characterizing the distribution of surface pressure fluctuations

    NDM-531: WIND TUNNEL TESTING OF RESIDENTIAL NEIGHBOURHOOD MODEL TO ANALYZE ROOF FAILURES IN HIGH WINDS

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    The EF-Scale estimates tornado wind speeds by the damage left in their wake, including the damage done to residential houses. The scale was developed based on an expert elicitation process, and so empirical testing is useful in determining its accuracy. Wind tunnel testing is often used to test low-rise buildings but building code configurations tend to be single, isolated houses, even though residential houses are much more common in suburban environments with many neighbouring buildings. The objective of this testing was to assess the roof-failure wind speeds for residential buildings in typical neighbourhood patterns and compare them to rural residence failure speeds and the EF-Scale. To this end, a 1:50 scale model of a suburban neighbourhood with 32 houses was built and tested in a wind tunnel. The effects of several variables such as wind direction and presence of dominant openings were also included in the study. After testing, it was concluded that neighbouring houses provided shielding and increased failure wind speeds in the range of 5 – 10%. Interestingly, when the shielding effects are considered, the range of failure wind speeds matches the range set out by the EF-Scale. Further work will analyze these points in greater detail

    NDM-509: FULL-SCALE TEST METHODS FOR MULTI-LAYER CLADDING SYSTEMS: WIND TUNNEL VS. MULTI-CHAMBER AIRBOX

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    Wind loads on multi-layer wall systems are complicated because the loads on each particular layer are poorly understood and difficult to quantify. This is because of pressure equalization, which is the mechanism whereby the pressures on the external building surface are transmitted through the air-permeable outer layer to interior layers. Recent testing at IBHS in a full-scale wind tunnel has shown that the extent of pressure equalization is more limited than is assumed in the test standard, ASTM D3679-13. Multi-chamber pressure testing performed by the authors at the Insurance Research Lab for Better Homes was able to capture these features in these results using more commonly utilized ASTM-style (airbox) testing. The objective of the current study is to examine the effects that the pressure time history inputs have when comparing the full-scale wind tunnel method data with that from the multi-chamber airbox method. This is accomplished by comparing the power spectral densities of the external and cavity pressures, as well as fitting the peak pressure equalization factor data to a Gumbel distribution. From a comparison of the power spectral densities of each airbox vs. the relevant full-scale, wind-tunnel external pressures, it was noted that larger airboxes created a larger source of error of the peak pressures in the system

    NDM-525: EFFECTS OF TORNADO WIND SPEEDS ON CONCRETE ROAD BARRIERS

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    Wind speeds can be difficult to measure during tornadoes due to their destructive nature. They pose a significant threat to lives and infrastructure in many parts of Canada and the U.S. The Enhanced-Fujita scale focuses on estimating these wind speeds by observing damage to different types of buildings, but significantly less research has been performed on the damage of other structures. Learning more about the effects of high wind speeds on these structures will help improve the ease and accuracy of future tornado classification. A wind tunnel study was performed at the Boundary Layer Wind Tunnel Laboratory of Western University. The study focusses on estimating the wind speeds that cause overturning in a standard 32” concrete “Jersey” barrier. On April 27, 2014, an EF4 Tornado struck Mayflower, Arkansas, and among the damage, several of these concrete barriers were blown over during the storm. The goal of this study was to find the overturning wind velocity and compare it to other damage in this event. This study was performed by placing a 1:8 scale-model of these barriers in a wind tunnel at a variety of orientations and wind speeds. Through analysis, it was determined that an instantaneous wind velocity of 4.55 to 4.85 m/s would cause overturning. These values correspond to an instantaneous wind speed of 340-360 km/h at full scale. It was estimated that the 3-second gust (used for EF rating) was 300-320 km/h, which sits at the top of the 267-322 km/h classification range for an EF4 tornado

    On the estimation of time dependent lift of a European Starling during flapping

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    We study the role of unsteady lift in the context of flapping wings in birds' flight. Both aerodynamicists and biologists attempt to address this subject, yet it seems that the contribution of the unsteady lift still holds many open questions. The current study deals with the estimation of unsteady aerodynamic forces on a freely flying bird through analysis of wingbeat kinematics and near wake flow measurements using time resolved particle image velocimetry. The aerodynamic forces are obtained through unsteady thin airfoil theory and lift calculation using the momentum equation for viscous flows. The unsteady lift is comprised of circulatory and non-circulatory components. Both are presented over wingbeat cycles. Using long sampling data, several wingbeat cycles have been analyzed in order to cover the downstroke and upstroke phases. It appears that the lift varies over the wingbeat cycle emphasizing its contribution to the total lift and its role in power estimations. It is suggested that the circulatory lift component cannot assumed to be negligible and should be considered when estimating lift or power of birds in flapping motion

    Northern Tornadoes Project. Northern Tornadoes Flyover Project: Summary Technical Report of the Year 1 Pilot Study

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    Summary Northern Tornadoes Flyover Project: Summary Technical Report of the Year 1 Pilot Study Gregory A. Kopp, Emilio Hong and Joanne Kennell Faculty of Engineering, University of Western Ontario David Sills Environment and Climate Change Canada 12 January 2018 The objectives of the Year 1 Pilot Study were to (i) develop a methodology for determining tornado occurrence in Northern Ontario, and (ii) obtain research quality data for at least one event. Because of the isolation of many regions, the approach assumed the use of radar data analysis combined with aerial surveys. These objectives were achieved. Aerial surveys were conducted for a total of seven events in Ontario and southern Quebec and 15 confirmed or probable tornadoes identified. Archival geo-tagged imagery was obtained for six of these events. Ten confirmed or probable tornadoes were identified in Ontario, five of which were not in the OSPC database. In addition, 5 tornadoes were confirmed in Quebec. For the 2017 season, the OSPC had a list of 10 verified tornadoes, as of December 21, 2017. The pilot project raises this number to 15. In total, 4 EF2 tornadoes and 1 EF3 tornado were identified via aerial photography. The remainder were EF1 or EF0. UPDATE – 1 March 2021 Based on the analysis of newly available Planet.com high-resolution satellite imagery and the use of related tools, events were reassessed and six additional tornadoes were discovered. However, four tornadoes were reassessed as downbursts. Overall, an additional two tornadoes were added to the 2017 count. The updated events are listed in a revised 2017 summary table appended at the end of this document

    FEDSM2002-31431 THE MEASUREMENT OF MEAN FLOW ANGLES BETWEEN AN AUTOMOTIVE FAN AND STATOR

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    ABSTRACT Measurements of the mean velocity vector were conducted to determine the exit angle from an automotive engine cooling fan module. The measurements were made at 15 locations along a radius between the hub and the band. The radius investigated was located in a plane roughly half-way between the blade trailing edge and stator leading edge. A two-component laser Doppler velocimeter and a four-wire hot-wire probe were used to measure the flow fields. It was found that the results obtained from hot-wire anemometry will have significant bias errors when used to measure the velocity vectors between the fan and the stator unless phase-averaged data are obtained with the probe re-oriented by phase. The differences between the techniques occur because the distribution of instantaneous swirl angles is bi-modal. Further, the mean flow angle is close to a local minimum in the probability density function of the swirl angle. This will act to increase errors in measurement devices whose accuracy depends on flow direction (the quantity being measured) such as five-hole probes which are used in industry. INTRODUCTION Knowing the exit velocity directions from automotive fans are key to designing the downstream stators. Since the flow field is elliptic, the stators will influence the flow coming through the fan. In industry, the velocity fields pertaining to the radiator-fan-stator assemblies are typically measured with fivehole probes due to their ease of use and robustness. However, due to the high turbulence levels and large velocity gradients, the reliability of these five-hole measurements is uncertain. Measurements to determine the mean swirl velocity projection and mean swirl angle from the fan blades upstream of the stator stage were conducted. Estimates of the average swirl angle, defined as that subtended by the swirl velocity projection relative to the fan axis, were obtained based on full three component resolution of the mean velocity vector. To thi
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