  Tidal disruption event (TDE) can launch an ultrafast outflow. If the black
hole is surrounded by large amounts of clouds, outflow-cloud interaction will
generate bow shocks, accelerate electrons and produce radio emission. Here we
investigate the interaction between a non-relativistic outflow and clouds in
active galaxies, which is manifested as outflow-BLR (broad line region)
interaction, and can be extended to outflow-torus interaction. This process can
generate considerable radio emission, which may account for the radio flares
appearing a few months later after TDE outbursts. Benefitting from efficient
energy conversion from outflow to shocks and the strong magnetic field,
outflow-cloud interaction may play a non-negligible, or even dominating role in
generating radio flares in a cloudy circumnuclear environment if the CNM
density is no more than 100 times the Sgr A*-like one. In this case, the
evolution of radio spectra can be used to directly constrain the properties of
outflows.
