= Rotlet dipole
{title2=$\mathbf u_{RD}=-3D(\mathbf e\cdot\mathbf r)(\mathbf e\times\mathbf r)/(8\pi\mu r^5)$}
A <rotlet> dipole is the derivative of a <rotlet> along the separation of two opposed torques. A <torque>-free bacterium can have this far field because its rotating flagella and counterrotating body exert spatially separated internal <torque> reactions. The displayed axial formula uses the observation-coordinate derivative convention and signed <torque> moment $D$.
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