We all know that drag plays a key role in our normal life when it acts opposite to the direction of movement of an object moving with respect to a surrounding fluid. It can be said that drag is the force prevents human reaching to new high levels, so finding ways to reduce drag are always the desires of many scientists, designers or athletes. Drag crisis is an interesting phenomenon in which an object experiences a sudden drop in drag coefficient at high Reynolds number while drag normally just increases with speed. Although this has been investigated well for some round bodies such as spheres and cylinders, airfoil objects which have better aerodynamic performances than cylinders or spheres are still not studied comprehensively about their drag crisis phenomenon.
Teardrop which is a combination of a cylinder and a symmetry airfoil has been applied in bicycle frame and considered as frame revolution became a popular choice. Teardrop-sharping forms became a basis of nearly every bike at 2015 Tour de France because of its drag coefficient reduction advantages – teardrop drag coefficient could be just 1/20 of circular cylinder drag coefficient. Therefore, a comprehensive study about the drag crisis phenomenon of this kind of shape can provide the necessary knowledge to develop teardrop advantages in the future.
Experiments were conducted on a teardrop model to investigate the phenomenon of drag crisis in wind tunnel in a range of Reynolds number 2 x 104 < Re < 8 x 104. Drag measurement experiment is carried out first in order to identify the Re range of the phenomenon with the angle of attack (AOA) = 0o. In addition, wake measurement and oil film results can provide further evidence about the critical regime when the drag crisis takes place. Then, results from the static pressure measurement experiment enable us to explore more about the characteristics of the laminar separation bubble (LSB) which is the main feature of the phenomenon. Drag crisis characteristics and its behaviors respecting to different AOA and roughness conditions are also investigated in this study.

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