strategies to reduce the modal excitation however the ultimate result is the same a decrease in modal excitation caused by increased equality between the negative and positive contributions to the power integral this increased cancellation results in lower power flow into the vibration and reduced levels of resonant response an overall reduction in the magnitude of pressure f f 0 as a way of reducing power looks superficially similar to the invention but is not because its goal is not increased cancellation rather the invention reduces the requirements on the degree of flow actuation by improving the cancellation between dominant and non dominant regions rather than by suppressing flow inhomogeneity flow field modification is achieved by introducing flow modifiers typically wake generators upstream from a set of rotor blades the modifiers can be placed in the turbo machine in many ways selection of placement and configuration is determined by the pattern of air flow by the vibration pattern of the rotor blades and by practical considerations such as fitting into the machinery design flow modifiers can be placed on the case on the stator vanes and on radial struts as shown in fig2 6 deployment strategies include permanent flow modification continuously variable flow modification and on off flow modification because the inflow field is modified in a quasi static manner the bandwidth requirements on the actuator are very modest typically on the order of 1 hz in most cases open loop scheduling of the flow modifiers will be practical reducing the vibration to a level that will result in.