# Stresslet coefficient in fluid dynamics

I encountered a parameter called stresslet coefficient in several literatures, which seems related with viscosity and stream function (also influencing the far field displacement). But there's no Wikipedia page for this concept. Can anyone explain what it is? Thanks!

## 1 Answer

Stresslet coefficient is an important part of Faxen's laws - laws "relating a sphere's velocity $U$ and angular velocity $\Omega$ to the forces, torque, stresslet and flow it experiences under low Reynolds number (creeping flow) conditions."

Forces, torque and flow seems familiar, but stresslet? So, stresslet is "a function that represents the symmetric first moment of the surface stress of a body in a flowing fluid." It is a part of a theory of traction moments on a stationary particle.

Now we come to the stresslet coefficient (or coefficient of the stresslet). After Constantine Pozrikidis: "The symmetric part of the first-order moment is the coefficient of the stresslet expressing the symmetric part of the point force dipole in the multipole expansion".

I especially recommend reading the last reference.