An erosion technique for the measurement of the shear stress field on a flat plate

Abstract

A simple technique for the measurement of the shear stress field on a flat surface is presented. The technique is based on a correlation established between the erosion patterns of fine grains spread on a horizontal smooth plate and the known shear stress values obtained by conventional, well established, means for the flow produced by a round jet perpendicular to a flat plate. The critical shear stress values are found to be practically independent of the overall flow configuration and properties, and depend on the particle distribution and characteristics. Various granular materials of different sizes, shapes and densities were used at varying surface concentration and flow conditions. The experimental scatter of the results is small enough to make the erosion technique useful for quantitative assessment of wall shear stresses with an accuracy compatible with most practical applications. Furthermore it combines simplicity with promptness, given that in each run a curve of constant shear stress is obtained instead of a single local value.

Determination of critical shear stress of non‐cohesive soils using submerged jet test and turbulent kinetic energy

“…The positive slopes observed in this study were attributed to change in density of distribution (relative thickness) of sand particles as r c increases. As reported by Viegas and Borges () there is dependence of τ c values on density of distribution of sand particle layer with increasing r c , but the effect is small and should not alter values of τ c significantly. This is supported in this study by the slopes of Figure .…”

“…Regression comparisons of τ c from (a) TKE and (b) Viegas and Borges () methods to theoretical values of τ c .…”

“…In Zone 4 and as shown in Figure b, the mean applied hydraulic shear stress ( τ ) grows rapidly until it reaches a maximum at r / H ≈ 0.25, after which it decays rapidly due to an unrestrained spanwise spread of momentum (Poreh and Hefez, ; Beltaos and Rajaratnam, ; Hanson et al ., ; Phares et al ., ; Rajaratnam and Mazurek, ; Sequeiros et al ., ). In this zone, the shear stress at any point along the radius for r / H > 0.22 can be predicted using Equations and after the work of Viegas and Borges (): …”

Structural design of a natural windbreak using computational and experimental modeling

“…The first wind-tunnel experiments were conducted using the sand-erosion technique [15], in which a thin layer of sieved and calibrated sand is exposed to gradually higher wind speeds. The contours were recorded continuously using a digital video camera, for posterior image processing.…”

Sand erosion technique applied to wind resource assessment

“…It is based on the erosion of sand placed on a model. Different authors developed methodologies to use the technique for wind comfort assessment: Viegas and Borges (1986), Williams (1986), Livesey et al (1992), Blocken and Carmeliet (2004);. In practice, the model is placed in a wind tunnel and covered with a thin layer of 1 mm-1.5 mm of sieved sand.…”