The actively controlled jet in crossflow

This study quantifies the dynamics of actuation for the temporally forced, round gas jet injected transversely into a crossflow, and incorporates these dynamics in developing a methodology for open loop jet control. A linear model for the dynamics of the forced jet actuation is used to develop a dynamic compensator for the actuator. When the compensator is applied, it allows the jet to be forced in a manner which results in a more precisely prescribed, temporally varying exit velocity, the RMS amplitude of perturbation of which can be made independent of the forcing frequency. Use of the compensator allows straightforward comparisons among different conditions for jet excitation. Clear identification can be made of specific excitation frequencies and characteristic temporal pulse widths which optimize transverse jet penetration and spread through the formation of distinct, deeply penetrating vortex structures

Properties of modulated and demodulated systems with implications to feedback limitations

It is well known that the poles, zeros and delay of a system play an important role in determining the associated feedback performance limitations. In this paper, we first derive an approximate transfer function for a modulated and demodulated system of a particular form. We next analyse the behaviour of the poles, zeros and delay of this transfer function when the modulation frequency is varied. Some implications of these results are also briefly discussed

Actively controlled transverse gas injection

In general the problem of feedback control for an unsteady fluid flow is nonlinear. Especially challenging is the control of mixing processes in a hot, potentially reactive environment. Because of the high temperatures present, realistic sensors can only operate mainly in cool regions, e.g., away from flames and hot exhaust regions. Consequently, there is often a large time lag between the time at which an actuator would modify, for example, a fuel or dilution air jet's characteristics in a combustion chamber, and the time at which a sensor would measure the effect of this action on the jet's mixing and/or reaction processes. During this time lag, flow dynamics, mixing, and combustion chemistry, if present, are dominated by nonlinear effects. A goal of the present study is to develop control strategies to optimize the mixing characteristics associated with the actively driven jet in crossflow. As a consequence of the differences between signal generator input function and jet exit velocity temporal variation (which is the actuation for the flowfield), it becomes necessary to design for the jet actuator a feedback controller which is distinct from the plant controller used for the overall experiment. Moreover, in developing a controller for the transverse jet problem there is an interesting trade-off between the complexity of actuating and sensing