Turbulent flow characterization near the edge of a steep escarpment

Abstract

Characteristics of turbulent flow over a steep escarpment were studied using a 1:25 scale model of the Bolund hill in a wind tunnel under neutral atmospheric stability conditions. The influence of Reynolds number, inflow shear profile, and escarpment geometry were investigated in relation to flow behavior including separation and reattachment, Reynolds stresses, vorticity, Turbulent Kinetic Energy (TKE) production, and Gaussianity. Multi-camera Particle Image Velocimetry (PIV) was used to examine the flow in the vicinity of the escarpment leading edge. Four test cases were studied across a Reynolds number range of 1 × 10 5 < R e h < 5 × 10 5 . Two different inflow profiles were evaluated, as well as two different leading edge geometries – a round edge with non-dimensional radius of curvature a η ≈ 0.2 and a sharp edge with η ≈ 0 . A sharp leading edge was found to produce a well-defined separation bubble, yielding distributions and magnitudes of Reynolds stress, vorticity and TKE production closely resembling those of flow over an idealized forward facing step, as well as full-scale measurements of TKE. Gaussianity of the flow was significantly modified by the escarpment, with high skewness and kurtosis occurring in the sharp edge case along the boundary of the separation bubble. • Small changes in escarpment leading edge sharpness greatly influence turbulent flow behavior. • Sharp edge caused relocation of area of peak turbulent kinetic energy. • Turbulent flow of sharp edge case better approximated full-scale measurements. • Turbulent flow of sharp edge case similar to canonical forward-facing step. • Gaussianity modified along separation bubble boundary.