Hello Anju,

Generally, in COMSOL you'll used the physic's model called Piezoelectric device (if we talk about piezoelectric energy harvesting system). In fact, we are connect this model through the physical COMSOL interface to the Circuit model (COMSOL). As results, we find the eigenfrequency, voltage generated during mechanical vibration, mechanical and electrical power depends on external frequencies (in structural mechanic as load). If you need to simulate piezoelectric or other system into the flow, you can integrated all models with additional fluid-structure interaction COMSOL's physic. It's depends on your wishes.

Regards