Physics 2065A/B Lecture Notes - Starting Vortex, Bernoulli'S Principle, Frisbee
13 Mar 2013
School
Department
Course
Professor
Document Summary
More streamlined shapes have less drag (see slide 3 for airfoil images) Recall for laminar flow (no turbulence) the streamlines around a sphere would be irrotational and symmetric. The front of a sphere would feel high pressure drag force due to the wind but . This drag force would be equal and opposite to the high pressure thrust (negative drag) behind the sphere (similar to the force of gravity vs. the normal force) Net result: a sphere feels no drag force. However, when the reynolds number is large enough, vortices begin to form. The vortices stay attached until re becomes large and then detaches from the sphere and break down to turbulence (view photos) Vortices have all types of different sizes and different flows and appear at different lengths behind the ball. Breakdown of the vortices= turbulence energy has to break down to smaller and smallers scales, acting as a drag force and slowing it down.
