EN
Collective flow is studied in a 3+1D fluid dynamical model with globally symmetric, peripheral initial conditions, taking into account the shear flow. At $\sqrt {s_{NN} } $ = 2.76 TeV in semi-peripheral Pb+Pb collisions this leads to rotation, while at more peripheral collisions with high resolution and low numerical viscosity, the initial development of a Kelvin-Helmholz instability is observed. This effect provides a precision tool for studying the viscosity of Quark-Gluon Plasma.