Momentum and energy injection by a wind-blown bubble into an inhomogeneous interstellar medium

We investigate the effect of mass-loading from embedded clouds on the evolution of wind-blown bubbles. We use 1D hydrodynamical calculations and assume that the clouds are numerous enough that they can be treated in the continuous limit, and that rapid mixing occurs so that the injected mass quickly merges with the global flow. The destruction of embedded clouds adds mass into the bubble, increasing its density. Mass-loading increases the temperature of the unshocked stellar wind due to the frictional drag, and reduces the temperature of the hot shocked gas as the available thermal energy is shared between more particles. Mass-loading may increase or decrease the volume-averaged bubble pressure. Mass-loaded bubbles are smaller, having less retained energy and lower radial momentum, but in all cases examined, they are still able to do significant PdV work on the swept-up gas. In this latter respect, the bubbles more closely resemble energy-conserving bubbles than the momentum-conserving-like behaviour of ‘quenched’ bubbles.