Spanwise characteristics of high-aspect-ratio synthetic jets

The spanwise characteristics, that is, the two dimensionality of two high-aspect-ratio, planar synthetic jets are investigated experimentally to evaluate their use as actuators for active flow control applications. The two jets, with different slit lengths, are generated through narrow axial slits on a cylinder by acoustical excitation at the cylinder terminations. Measurements of the mean and fluctuating velocities, as well as the phase of velocity fluctuations with respect to the excitation signal, are performed to study the effect of excitation frequency and amplitude on the steady and unsteady spanwise characteristics of the generated synthetic jet. The jet issuing from the long slit is found to exhibit large variations in the spanwise direction, in both its mean velocity and phase. These variations are also dependent on the level and frequency of acoustic excitation. For the short slit, the spanwise variations are substantially smaller. The test results indicate that the short slit is a favorable actuator for active control applications involving the generation of a planar synthetic jet with small spanwise variations. The long slit, however, may be useful for active control applications that require the inducement of large phase variations along the slit.