Turbulent Viscosity in Line-driven Stellar Winds

Abstract Radiation-driven winds from massive stars generate powerful outflows known to be intrinsically turbulent. Despite this, standard hydrodynamic models have historically restricted the application of macroscopic turbulent viscosity to rotationally supported disks, neglecting its dynamic role in the supersonic expansion regime of the wind. We evaluated the dynamical relevance of macroscopic turbulent momentum transport in accelerating line-driven stellar outflows of rotating B supergiants. We introduced a generalized strain-limited viscous prescription within a stable, time-dependent one-dimensional m-CAK hydrodynamic framework using the FARGO3D code. We compared inviscid, constant-viscosity, and strain-limited models to analyze their effects on the radial velocity, density stratification, mass-loss rate, and angular momentum transport. The strain-limited prescription produces a radially structured viscosity that primarily acts as a broad radial braking term. With the viscosity bounded through a prescribed maximum mixing length, the viscous acceleration remains subdominant to the total radiative acceleration but is dynamically relevant to the advective acceleration. In the strongest-viscosity model, the terminal velocity decreased by ∼39% and the mass-loss rate by ∼58% relative to the inviscid model in the stationary state. The flow remains radiatively driven, and angular-momentum transport remains dominated by advection, maintaining a quasi-conserving v ϕ ∝ r −1 scaling. Turbulent viscosity exerts a measurable dynamic effect on supersonic line-driven winds. When bounded by the local macroscopic strain, it modifies the radial momentum balance and the resulting mass-loss rate without forcing the wind into a disk-like regime of strong viscous angular-momentum redistribution.