Energy transfer and non-linear interactions in an urban boundary layer using Stochastic Estimation

Abstract

ABSTRACTThe non-linear energy transfer between the most energetic structures in the logarithmic layer (referred to here as large-scales) and those in the roughness sublayer induced by the presence of the roughness (referred to here as small-scales) is studied in a boundary layer developing over a rough-wall consisting of staggered cubes with a plan area packing density, = 25%, in the wind tunnel using combined Particle Image Velocimetry (PIV) and Hot-Wire Anemometry (HWA). The energy transfer between the mean flow, large-scales and small-scales is quantified using scale decomposition of the Turbulent Kinetic Energy (TKE) budget. Multi-time delay Linear Stochastic Estimation (LSE) is used to decompose the flow into large- and small-scales. Using scale decomposition of the TKE budget it is shown that although the greatest mean energy transfer occurs between the mean flow and the small-scales a significant instantaneous energy transfer between the large- and small-scales exists. Finally, it is confirmed through spatio-temporal cross correlation that the non-linear relationship that exists between large-scale coherent structures and small-scales created through interaction with the roughness elements is linked to instantaneous energy transfer between these structures.