A CFD study on the Irwin probe flows. Issue 219 (December 2021) - Brito, Pedro M.
Abstract: Irwin probes are surface sensors commonly used to determine the shear stress in near-wall regions, by calibration of related pressure signals. These devices have been widely used in wind tunnel studies dealing with pedestrian-level wind conditions. In this work, three-dimensional Computational Fluid Dynamics (CFD) simulations are performed to characterize the complex flow field and pressure distribution developed around and within the Irwin probe, at three distinct low-Reynolds number regimes. The emergence of coherent flow structures past the sensor is categorised and preventive spacing intervals, necessary to mitigate mutual interference, is numerically evaluated. The computations corroborate the original spacing recommendations by Irwin. For typical operation conditions, long streamwise tip vortices are observed in the wake of a single sensor. In addition, the predictions suggest the existence of a low-Reynolds number threshold, below which such structures are supressed, resulting in diminished interference effects. Numerical results also suggest a nearly uniform axial pressure distribution and place in evidence very interesting flow field characteristics. Highlights: Irwin probes are used to measure wind speed and shear stress close to surfaces. CFD methods are used to examine flow features inside and in the wake of the sensor. Mutual interference effects are quantified and tolerable spacing intervals reviewed. Inner-sensor pressure distribution is characterized in detail.