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Laboratory measurements of the drag coefficient over a fixed shoaling hurricane wave train
Brian C. Zachry,Chris W. Letchford,Delong Zuo,Andrew B. Kennedy 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.16 No.2
This paper presents results from a wind tunnel study that examined the drag coefficient and wind flow over an asymmetric wave train immersed in turbulent boundary layer flow. The modeled wavy surface consisted of eight replicas of a statistically-valid hurricane-generated wave, located near the coast in the shoaling wave region. For an aerodynamically rough model surface, the air flow remained attached and a pronounced speed-up region was evident over the wave crest. A wavelength-averaged drag coefficient was determined using the wind profile method, common to both field and laboratory settings. It was found that the drag coefficient was approximately 50% higher than values obtained in deep water hurricane conditions. This study suggests that nearshore wave drag is markedly higher than over deep water waves of similar size, and provides the groundwork for assessing the impact of nearshore wave conditions on storm surge modeling and coastal wind engineering.
Wind tunnel study of wind loading on rectangular louvered panels
D. Zuo,C.W. Letchford,S. Wayne 한국풍공학회 2011 Wind and Structures, An International Journal (WAS Vol.14 No.5
Drag forces on a rectangular louvered panel, both as a free-standing structure and as a component in a generic low-rise building model, were obtained in a wind tunnel study. When tested in a building model, the porosity ratio of the wall opposite the louvered panel was varied to investigate its effect on the loading of the louvered panel. Both mean and pseudo-steady drag coefficients were obtained. Comparisons with the provisions for porous walls in contemporary loading standards indicate that for some opposite wall porosity ratios, the standards specify significantly different wind loads (larger and smaller) than obtained from this wind tunnel study.
Wind tunnel study of wind loading on rectangular louvered panels
Zuo, D.,Letchford, C.W.,Wayne, S. Techno-Press 2011 Wind and Structures, An International Journal (WAS Vol.14 No.5
Drag forces on a rectangular louvered panel, both as a free-standing structure and as a component in a generic low-rise building model, were obtained in a wind tunnel study. When tested in a building model, the porosity ratio of the wall opposite the louvered panel was varied to investigate its effect on the loading of the louvered panel. Both mean and pseudo-steady drag coefficients were obtained. Comparisons with the provisions for porous walls in contemporary loading standards indicate that for some opposite wall porosity ratios, the standards specify significantly different wind loads (larger and smaller) than obtained from this wind tunnel study.
Laboratory measurements of the drag coefficient over a fixed shoaling hurricane wave train
Zachry, Brian C.,Letchford, Chris W.,Zuo, Delong,Kennedy, Andrew B. Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.16 No.2
This paper presents results from a wind tunnel study that examined the drag coefficient and wind flow over an asymmetric wave train immersed in turbulent boundary layer flow. The modeled wavy surface consisted of eight replicas of a statistically-valid hurricane-generated wave, located near the coast in the shoaling wave region. For an aerodynamically rough model surface, the air flow remained attached and a pronounced speed-up region was evident over the wave crest. A wavelength-averaged drag coefficient was determined using the wind profile method, common to both field and laboratory settings. It was found that the drag coefficient was approximately 50% higher than values obtained in deep water hurricane conditions. This study suggests that nearshore wave drag is markedly higher than over deep water waves of similar size, and provides the groundwork for assessing the impact of nearshore wave conditions on storm surge modeling and coastal wind engineering.
Meroney, R.N.,Letchford, C.W.,Sarkar, P.P. Techno-Press 2002 Wind and Structures, An International Journal (WAS Vol.5 No.2
Mean surface pressures and overall wind loads on hemispherical domes immersed in a boundary layer were obtained by numerical simulation. The effects of alternative turbulence models, Reynolds Number and surface roughness were examined and compared with earlier studies. Surface pressures on dual hemispherical domes were also calculated for three wind orientations ($0^{\circ}$, $45^{\circ}$, and $90^{\circ}$) to evaluate flow field interactions. Calculated values were compared to wind-tunnel measurements made in equivalent flow conditions.
Wind pressure measurements on a cube subjected to pulsed impinging jet flow
Mason, M.S.,James, D.L.,Letchford, C.W. Techno-Press 2009 Wind and Structures, An International Journal (WAS Vol.12 No.1
A pulsed impinging jet is used to simulate the gust front of a thunderstorm downburst. This work concentrates on investigating the peak transient loading conditions on a 30 mm cubic model submerged in the simulated downburst flow. The outflow induced pressures are recorded and compared to those from boundary layer and steady wall jet flow. Given that peak winds associated with downburst events are often located in the transient frontal region, the importance of using a non-stationary modelling technique for assessing peak downburst wind loads is highlighted with comparisons.
Wind pressure measurements on a cube subjected to pulsed impinging jet flow
M.S. Mason,D.L. James,C.W. Letchford 한국풍공학회 2009 Wind and Structures, An International Journal (WAS Vol.12 No.1
A pulsed impinging jet is used to simulate the gust front of a thunderstorm downburst. This work concentrates on investigating the peak transient loading conditions on a 30 mm cubic model submerged in the simulated downburst flow. The outflow induced pressures are recorded and compared to those from boundary layer and steady wall jet flow. Given that peak winds associated with downburst events are often located in the transient frontal region, the importance of using a non-stationary modelling technique for assessing peak downburst wind loads is highlighted with comparisons.
A forensic study of the Lubbock-Reese downdraft of 2002
Holmes, J.D.,Hangan, H.M.,Schroeder, J.L.,Letchford, C.W.,Orwig, K.D. Techno-Press 2008 Wind and Structures, An International Journal (WAS Vol.11 No.2
This paper discusses engineering aspects of the rear-flank downdraft that was recorded near Lubbock, Texas on 4 June 2002, and produced a gust wind speed nearly equal to the design value (50-year return period) for the region. The general characteristics of the storm, and the decomposition of the time histories into deterministic 'running mean' and random turbulence components are discussed. The fluctuating wind speeds generated by the event can be represented as a dominant low-frequency 'running mean' with superimposed random turbulence of higher frequencies. Spectral and correlation characteristics of the residual turbulence are found to be similar to those of high-frequency turbulence in boundary-layer winds. However, the low-frequency components in the running-mean wind speeds are spatially homogeneous, in contrast to the low-frequency turbulence found in synoptic boundary-layer winds. With respect to transmission line design, this results in significantly higher 'span reduction factors'.
A forensic study of the Lubbock-Reese downdraft of 2002
J. D. Holmes,H. M. Hangan,J. L. Schroeder,C. W. Letchford,K. D. Orwig 한국풍공학회 2008 Wind and Structures, An International Journal (WAS Vol.11 No.2
This paper discusses engineering aspects of the rear-flank downdraft that was recorded near Lubbock, Texas on 4 June 2002, and produced a gust wind speed nearly equal to the design value (50-year return period) for the region. The general characteristics of the storm, and the decomposition of the time histories into deterministic ‘running mean’ and random turbulence components are discussed. The fluctuating wind speeds generated by the event can be represented as a dominant low-frequency ‘running-mean’, with superimposed random turbulence of higher frequencies. Spectral and correlation characteristics of the residual turbulence are found to be similar to those of high-frequency turbulence in boundary-layer winds. However, the low-frequency components in the running-mean wind speeds are spatially homogeneous, in contrast to the low-frequency turbulence found in synoptic boundary-layer winds. With respect to transmission line design, this results in significantly higher ‘span reduction factors’.