1 Copyright © Firenze University Press Proceedings of PHYSMOD2003: International Workshop on Physical Modelling of Flow and Dispersion Phenomena 3-5 September 2003, Prato, Italy INVESTIGATION OF FLOW AND PRESSURE PHENOMENA AROUND PYRAMIDAL STRUCTURES M. Ikhwan & B. Ruck Laboratory of Building- and Environmental Aerodynamics Institute for Hydromechanics, University of Karlsruhe, Kaiserstr. 12, 76128 Karlsruhe, Germany ABSTRACT An experimental investigation of the flow and pressure characteristics around pyramidal buildings is presented. The experiments were conducted in an atmospheric boundary layer wind tunnel at the University of Karlsruhe. The velocities of the flow around the pyramids were measured using 2D Laser Doppler Anemometry (LDA), and the pressure distribution on the pyramid surfaces were measured using standard pressure tapping technique. This study discusses the flow and pressure phenomena around pyramidal structure with varying pyramid base angles and wind directions. The results show for four different pyramids (base angle 20°, 30°, 45° and 70°) that base angle and angle of wind direction characteristically influence the flow and pressure field yielding differences in integral flow describing quantities and wind loads on the structure. NOMENCLATURE B Dimension reference C f Force Coefficient C m Moment coefficient Cp Pressure coefficient h Pyramid height h 70 Height of pyramid P70 l Pyramid length M z Moment at z-axes p Pressure P20 Pyramid with 20° base angle P30 Pyramid with 30° base angle P45 Pyramid with 45° base angle P70 Pyramid with 70° base angle q Dynamic pressure Re Reynolds number U ∞ Velocity at the boundary U ref Velocity at the reference height x Horizontal axes in x-direction y Horizontal axes in y-direction z Vertical axes Z ref Refference height ζ Base angle of the pyramid α Exponential law coefficient γ Wind direction ρ Air density 1. INTRODUCTION Pyramids are often associated with historical buildings or tombs. In particular the Cheops pyramid in Egypt that was built thousands of years ago and is famous as one of the Seven Wonders of the World. The word pyramid originally comes from the Greek words Pyramis and Pyramidos, derived from the word “Pyre” which means fire. The meaning of the word Pyramis is obscure and it may relate to the shape of a pyramid. The word Pyramidos has been translated as "Fire In The Middle". From aerodynamic engineering point of view, a pyramidal building has its own interesting characteristics. However, despite its particular characteristics, very limited literature can be found in this specific area (i.e. pyramidal buildings). Most of the studies are related to rectangular and tall buildings, and emphasize to provide information such as the reliability of performance and the improvement of the economy of design [4]. Furthermore, the technical layout of the pyramidal buildings with respect to wind load assumptions is usually not listed in standard tables. Therefore, it is important to study the flow and pressure on pyramidal buildings. Ruck and Roth [6, 7] in 1997 carried out experimental investigations that involved 2 types of pyramids. They were able to show interesting phenomena of the flow and pressure characteristic. The flow pattern on the leeward face indicates that the mean structures of the recirculation wakes are different than those of other building shapes. Furthermore, the aerodynamic loadings of pyramids are distinct from rectangular building, since the wall taper results in different surface pressure distributions. Abuomar & Martinuzzi [1] in 2000 investigated steep pyramids with three different base angles (ζ=45°, 60° and 67.5°). This study showed that the flow (i.e. separation and reattachment zone) and pressure characteristics do not significantly depend on the base angle. On the other