<a href="https://en.wikipedia.org/wiki/drag_coefficient" class="extiw" title="en:drag coefficient">Drag coefficient</a> <i>C</i><sub>d</sub> for a sphere as a function of <a href="https://en.wikipedia.org/wiki/Reynolds_number" class="extiw" title="en:Reynolds number">Reynolds number</a> <i>Re</i>, as obtained from laboratory <a href="https://en.wikipedia.org/wiki/experiment" class="extiw" title="en:experiment">experiments</a>. The solid line is for a sphere with a smooth surface, while the dashed line is for the case of a rough surface. The numbers along the line indicate several flow regimes and associated changes in the drag coefficient:
<ul><li>2: attached flow (<a href="https://en.wikipedia.org/wiki/Stokes_flow" class="extiw" title="en:Stokes flow">Stokes flow</a>) and steady <a href="https://en.wikipedia.org/wiki/flow_separation" class="extiw" title="en:flow separation">separated</a> flow,</li>
<li>3: separated unsteady flow, having a <a href="https://en.wikipedia.org/wiki/laminar_flow" class="extiw" title="en:laminar flow">laminar</a> <a href="https://en.wikipedia.org/wiki/boundary_layer" class="extiw" title="en:boundary layer">boundary layer</a> upstream of the separation, and producing a <a href="https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_vortex_street" class="extiw" title="en:Kármán vortex street">vortex street</a>,</li>
<li>4: separated unsteady flow with a laminar boundary layer at upstream side, before flow separation, with downstream of the sphere a chaotic <a href="https://en.wikipedia.org/wiki/turbulence" class="extiw" title="en:turbulence">turbulent</a> <a href="https://en.wikipedia.org/wiki/wake" class="extiw" title="en:wake">wake</a>,</li>
<li>5: post-critical separated flow, with a turbulent boundary layer.</li></ul>
NASA
2010-08-24
<a rel="nofollow" class="external free" href="http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html">http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html</a>