Self-excited wire method for the control of turbulent mixing layers

A new method for the control of the evolution of a turbulent, two-stream (planar) mixing layer is reported. A (music) wire strung across the flow and placed in the zone near the trailing edge of the splitter plate is used to excite the flow. The wire is self-excited by the shear flow. The vibrating wire, whose frequency can be adjusted, transfers energy to the flow in a very efficient way due to a local high degree of coupling. Results are reported for a velocity ratio of 0.674 and Re θ = 1380, with excitation frequencies between 85 and 400 Hz. Depending on the frequency of wire vibration, different modes of large structures are excited, determining the spreading rate of the mixing layer. It is also possible to control the directional evolution of the mixing layer and, thus, potentially the entrainment ratio between the two streams. This is achievable by adjusting the wire position in the lateral direction, inside the mixing layer. These characteristics are the result of the highly localized energy input of the wire into the shear layer, compared to other methods.