Viewed as sinews and muscles of fluid motion, coherent vortical structures with their interactions are key to understanding the flow dynamics. Based upon this observation, we explore the possibility of efficient flow control by directly manipulating vortices numerically inside the flow field based on the vortex definition and identification system of Liutex. The objective is twofold: (1) to study the vortex dynamics, for example, by observing the response of the flow to strengthening or weakening of certain vortices, and (2) to obtain efficient vortex-based control strategies which might lead us to practical applications. In the present numerical study, the manipulating of vortices is achieved by introducing additional source (force) terms to the Navier-Stokes equations, which hereafter will be collectively called Liutex force field model. Methodologies including controlling the rotation strength and centripetal force of particular vortices are detailed in a flow past a cylinder with different control purposes at Reynolds number of 200. Further examples are provided with a cavitating flow around two-dimensional Clark-Y hydrofoil, with particular interests on cavitation suppression. It is illustrated particular vortex with cavitation encircled could be effectively suppressed.