Is there a Simulator that I can use with QGroundControl for flights and parameters testing?

Is there Simulator/Emulator available that I can use with QGroundControl instead of connecting the physical drone device?
I have a custom AirFrame created in QGroundControl with my own specifications.

I am creating a drone with custom AirFrame and I want to make that as VTOL. Actual need of simulator/emulator is to do the testing of the flights with the parameters to make them work in the VTOL.

I heard about Gazebo & jMAVSim, are they worth trying and can fulfill my purpose?

I can’t speak about your purpose, but the PX4 developer team primarily uses simulators for testing, it’s easy, you can read more on the dev guide.