Abstract
In-plane velocity measurements from PIV are used to estimate the pressure field above and within the canopy of two staggered arrays of cuboids, with distinct height distributions, via 2D-RANS and 2D-TH. The viability of this approach is examined by first comparing the mean drag profiles against reported wind-tunnel measurements that were carried out under similar test conditions and numerical simulations (LES and DNS). The surface drag is extrapolated from the nearest data point surrounding the roughness elements. Second, estimates of the friction velocity U_{tau }^p and the zero-plane displacement height d^p are obtained by integrating the axial pressure difference across each individual obstacle, assuming it is spanwise uniform. These are compared against direct measurements of the wall-shear stress from a floating-element balance and a pressure-tapped cube, as well as against estimates from indirect methods. In addition to mean pressure maps, snapshots of the pressure field are obtained via 2D-TH, based on Taylor’s Hypothesis, which are used to compute the RMS of the pressure fluctuations on the surface of a cube. The results indicate that 2D-RANS and 2D-TH perform adequately, providing reasonable estimates of the mean pressure distribution and of the boundary-layer flow parameters, outperforming indirect methods which rely on equilibrium assumptions that are often not verified.Graphic abstract
Highlights
Experimental studies of boundary-layer flows over urban environments are generally limited to velocity data
We investigated the potential of using two-dimensional, PIVbased pressure reconstruction methods to achieve a more complete description of the flow field over two staggered arrays of cuboids (C10U and C10R)
Empirical analyses suggest that the error induced by the missing out-of-plane components of velocity and acceleration could be problematic within the canopy layer, where the flow meanders around the roughness obstacles, it cannot be quantified without a priori knowledge of the flow conditions
Summary
Experimental studies of boundary-layer flows over urban environments are generally limited to velocity data. Few provide a detailed description of the surface pressure over the roughness obstacles and it is not yet clear how direct measurements of the surrounding pressure field could possibly be achieved. Only Cheng et al (2007) and Claus et al (2012b) have examined the change in pressure
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