סמינר של בית הספר להנדסה מכאנית

יום ב' 14 במאי 2012 שעה 15:00,

חדר 206, בניין וולפסון להנדסה מכאנית

Vortex shedding of elongated bluff bodies

Dr. Zachary Taylor

Turbulence Structure Laboratory, School of Mechanical Engineering, Tel Aviv University

Long-span suspension bridges are known to suffer from aerodynamic instabilities.  A recent example of flow induced motion of a bridge is the case of the Storebælt Bridge (Denmark) in 1998.  Although these massive structures are tested in wind tunnels prior to construction, aerodynamics are rarely the primary focus in the design process.  The typical shape of a bridge cross-section causes the flow to separate at the leading edge.  The along-wind direction of the bridges is also sufficiently long to allow the flow to reattach to the body before separating at the trailing edge once more which starts the vortex shedding process of the wake.  We term bodies with these characteristics elongated bluff bodies.

Elongated bluff bodies are then a combination of two classical aerodynamic phenomena: separating-reattaching flow and trailing edge vortex shedding.  Many engineers assume trends are maintained from bodies exhibiting only trailing edge vortex shedding (e.g., a circular cylinder).  However, our results have shown that the leading edge geometry of these bodies plays a significant role in the eventual formation of the wake. This issue will be addressed in the presentation along with our recent experimental investigation including extensive surface pressure measurements synchronized with Particle Image Velocimetry.

By analyzing the dynamics of the formation region, we have shown that the way in which a wake evolves varies considerably due to the leading edge geometry.  There are many consequences which result from changes to the wake formation.  Fundamental trends from shorter bluff bodies of vortex street parameters (e.g., shedding frequency, vortex spacing and vortex convection speed) do not hold for elongated bluff bodies.  We suggest how these parameters are all influenced by the leading edge geometry and show that even subtle changes to the leading edge geometry can act as a type of passive flow control.

Short Bio:

Zachary Taylor received both his Bachelor’s of Engineering Science in Mechanical Engineering and his Ph.D. in Civil and Environmental Engineering from the University of Western Ontario in London, Canada.  After completing his doctoral studies in September 2011, Dr. Taylor accepted a position as a post-doctoral fellow at Tel Aviv University in the School of Mechanical Engineering.  Under the supervision of Dr. Alex Liberzon and in collaboration with Dr. Roi Gurka (BGU), he is studying the evolution of turbulent patches in a stably-stratified environment.