PLANETARY BOUNDARY LAYER MODELING AND TALL BUILDING DESIGN
Emil Simiu, Liang Shi, DongHun Yeo
Recent research into Planetary Boundary Layer (PBL) flows accounts for the difference between �neutral� and �conventionally neutral� flows. Of interest in structural engineering are �conventionally neutral� PBL flows, that is, flows affected by transport into the PBL of momentum from the stably stratified free flow as characterized by the Brunt-V�� frequency. The note reviews research results allowing the estimation of the PBL�s integral measures � the geostrophic drag coefficient Cg, the cross-isobaric angle α0, and the depth H. It is shown that PBL heights estimated on the basis of such results can be approximately half as large as those obtained by using the classical asymptotic similarity approach, and one order of magnitude greater than those specified in North American building codes. Included in the note is a simple method for estimating the friction velocity and PBL height as functions of specified surface roughness and geostrophic speed. Based on published results of PBL studies it was found that the contribution to the resultant mean flow velocity of the component V normal to the surface stress is negligible, and that the veering angle is only of the order of 5 degrees even at 800 m above the surface. In the authors� view additional research by boundary-layer meteorologists working in cooperation with structural engineers is needed for the development of comprehensive tall building design criteria for wind loads.