TEMPORAL AND SPATIAL CORRELATED PROPERTIES OF SURFACE PRESSURE AND GUST FORCES ON A RECTANGULAR SECTION IN VERTICAL FLUCTUATING WINDS

Abstract

Chordwise and spanwise correlated properties of surface pressures and gust forces (lift force, pitching moment) on a rectangular cross section due to vertical gusts were investigated through wind tunnel experiments. Relationships between these characteristics and the intrinsic flow pattern with separating shear layer around the cross section were focused through the discussion. A 2-D model with rectangular cross section (B/D=5, B: chord length, D: depth) was used for the measurements and discussion. In the 2-D sinusoidal gusts, the formation of separation vortex near the leading edge and its convection to the trailing edge were deduced based on the unsteady pressure on the side surface. It was confirmed that this flow pattern was realized only in the characteristic reduced frequency domain where the shear layer instability is enhanced by the approaching vertical wind fluctuations. The spatially expanding characteristics of the surface pressure along chordwise as well as spanwise directions were captured in the 3-D gusts. The amplitude of vertical wind velocity is not uniform along spanwise. It was concluded that the separation vortex is hardly expanding towards spanwise direction, but that the entire formation of the separation bubble in lower reduced frequency than the characteristic frequency domain encourage the pressure transport. This observation agrees with the higher spanwise coherence of gust force in lower reduced frequency.