Further experiments on Irwin's surface wind sensor

Wu, Hanqing; Stathopoulos, T.

doi:10.1016/0167-6105(94)90095-7

Cited by 45 publications

(24 citation statements)

References 2 publications

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“…The differential pressure measured with the Irwin sensor can be calibrated against surface shear stress when mounted flush with the surface. Its use within laboratory investigations is extensive (Irwin, 1981;Wu and Stathopoulos, 1994; Monteiro and Viegas, 1996;Crawley and Nickling, 2003) and derived shear stress measurements show very good agreement with direct surface shear stress drag meters (Crawley and Nickling, 2003) and hot-wire anemometry (Irwin, 1981). These sensors were systematically positioned at the surface based on vegetation clusters to resolve the average surface flow field and also provide information on the position of the maximum and minimum shear stress areas within the area of the vegetation community being monitored ( Fig.…”

Section: Surface Shear Stressmentioning

confidence: 96%

Aeolian shear stress ratio measurements within mesquite-dominated landscapes of the Chihuahuan Desert, New Mexico, USA

2006

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A field study was conducted to ascertain the amount of protection that mesquite-dominated communities provide to the surface from wind erosion. The dynamics of the locally accelerated evolution of a mesquite/coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated. Sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements. Although shear stress partition models exist that can describe this, their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements. This study combines the use of meteorological towers and surface shear stress measurements with Irwin sensors to measure the partition of shear stress in situ. The surface shear stress within preferentially aligned vegetation (within coppice dune development) exhibited highly skewed distributions, while a more homogenous surface stress was recorded at a site with less developed coppice dunes. Above the vegetation, the logarithmic velocity profile deduced roughness length (based on 10-min averages) exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned, while the site with more homogenously distributed vegetation showed very little variation in the roughness length. This distribution in roughness length within an area, defines a distribution of a resolved shear stress partitioning model based on these measurements, ultimately providing potential closure to a previously uncorrelated model parameter.

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Section: Surface Shear Stressmentioning

confidence: 96%

Aeolian shear stress ratio measurements within mesquite-dominated landscapes of the Chihuahuan Desert, New Mexico, USA

2006

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“…1a) to determine the spatial and temporal variation of the shear stress τ s (t, x, y) (Irwin 1981;Wu and Stathopoulos 1993). The pressure difference p measured at the Irwin sensor was calibrated against the friction velocity u * in the constant-stress layer measured with the two-component hot-film anemometer.…”

Section: Surface Shear-stress Sensorsmentioning

confidence: 99%

“…To predict the average surface shear-stress partition (τ s /τ ) 1/2 , we set m = 1. Some wind-tunnel and field investigations have used Irwin sensors (Irwin 1981;Wu and Stathopoulos 1993) to obtain point measurements of surface shear stress at positions where the largest shear-stress values were expected (Crawley and Nickling 2003;King et al 2006;Brown et al 2008). These measurements support the Raupach et al (1993) model (Eq.…”

Section: Introductionmentioning

confidence: 97%

Spatio-Temporal Surface Shear-Stress Variability in Live Plant Canopies and Cube Arrays

Benjamín

Gromke²,

Leonard

et al. 2012

Boundary-Layer Meteorol

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This study presents spatiotemporally-resolved measurements of surface shearstress τ s in live plant canopies and rigid wooden cube arrays to identify the sheltering capability against sediment erosion of these different roughness elements. Live plants have highly irregular structures that can be extremely flexible and porous resulting in considerable changes to the drag and flow regimes relative to rigid imitations mainly used in other wind-tunnel studies. Mean velocity and kinematic Reynolds stress profiles show that well-developed natural boundary layers were generated above the 8 m long wind-tunnel test section covered with the roughness elements at four different roughness densities (λ = 0, 0.017, 0.08, 0.18). Speed-up around the cubes caused higher peak surface shear stress than in experiments with plants at all roughness densities, demonstrating the more effective sheltering ability of the plants. The sheltered areas in the lee of the plants are significantly narrower with higher surface shear stress than those found in the lee of the cubes, and are dependent on the wind speed due to the plants ability to streamline with the flow. This streamlining behaviour results in a decreasing sheltering effect at increasing wind speeds and in lower net turbulence production than in experiments with cubes. Turbulence intensity distributions suggest a suppression of horseshoe vortices in the plant case. Comparison of the surface shear-stress measurements with 123 338 B. Walter et al. sediment erosion patterns shows that the fraction of time a threshold skin friction velocity is exceeded can be used to assess erosion of, and deposition on, that surface.

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“…3). Once calibrated, the Irwin sensor can be used to measure surface shear stresses at frequencies greater than 10 Hz (Irwin 1980;Wu and Stathopoulos 1994) and has been used successfully in a variety of flow conditions and surface roughness configurations (Irwin 1980;Wu andStathopoulos 1994, Monteiro andViegas 1996;Crawley and Nickling 2003).…”

Section: Introductionmentioning

confidence: 99%

Shear stress partitioning in large patches of roughness in the atmospheric inertial sublayer

Gillies

Nickling

King

2006

Boundary-Layer Meteorol

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Drag partition measurements were made in the atmospheric inertial sublayer for six roughness configurations made up of solid elements in staggered arrays of different roughness densities. The roughness was in the form of a patch within a large open area and in the shape of an equilateral triangle with 60 m long sides. Measurements were obtained of the total shear stress (τ ) acting on the surfaces, the surface shear stress on the ground between the elements (τ S ) and the drag force on the elements for each roughness array. The measurements indicated that τ S quickly reduced near the leading edge of the roughness compared with τ , and a τ S minimum occurs at a normalized distance (x/h, where h is element height) of ≈ −42 (downwind of the roughness leading edge is negative), then recovers to a relatively stable value. The location of the minimum appears to scale with element height and not roughness density. The force on the elements decreases exponentially with normalized downwind distance and this rate of change scales with the roughness density, with the rate of change increasing as roughness density increases. Average τ S : τ values for the six roughness surfaces scale predictably as a function of roughness density and in accordance with a shear stress partitioning model. The shear stress partitioning model performed very well in predicting the amount of surface shear stress, given knowledge of the stated input parameters for these patches of roughness. As the shear stress partitioning relationship within the roughness appears to come into equilibrium faster for smaller roughness element sizes it would also appear the Boundary-Layer Meteorol (2007) 122:367-396 shear stress partitioning model can be applied with confidence for smaller patches of smaller roughness elements than those used in this experiment. List of SymbolsA f frontal area of roughness elements (m 2 ) A u unit area over which surface shear stress associated with a roughness element is distributed (m 2 ) b element breadth (m) Cd surface drag coefficient Cd e roughness element drag coefficient Cd r rough surface drag coefficient Cd s smooth surface drag coefficient cv coefficient of variation d displacement height (m) F force on a roughness element (N) g acceleration due to gravity (m s −2 ) h element height (m) IBL internal boundary layer ISL inertial sublayer m empirical constant between 0 and 1 n number of roughness elements occupying the ground area of the roughness array NDD normalized downwind distance (x/h) NED normalized element drag R average friction velocity ratio R l local friction velocity ratio at different positions in a roughness array Re Reynolds number R t threshold wind friction velocity ratio SD standard deviation of a mean value u wind speed (m s −1 ) u * wind friction velocity (m s −1 ) u * tR threshold wind friction velocity with roughness elements (m s −1 ) u * tS threshold wind friction velocity of bare surface (m s −1 ) x downwind distance (m) z reference height above surface (m) z w roughness sublayer height (m) z o a...

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Further experiments on Irwin's surface wind sensor

Cited by 45 publications

References 2 publications

Aeolian shear stress ratio measurements within mesquite-dominated landscapes of the Chihuahuan Desert, New Mexico, USA

Aeolian shear stress ratio measurements within mesquite-dominated landscapes of the Chihuahuan Desert, New Mexico, USA

Spatio-Temporal Surface Shear-Stress Variability in Live Plant Canopies and Cube Arrays

Shear stress partitioning in large patches of roughness in the atmospheric inertial sublayer

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