the compression driver and the converging nozzle of
the synthetic-jet actuator.
Performance and compensation of a synthetic jet actuator
The actuator used to control the cavity flow resonance is a two-dimensional synthetic-jet type issuing from a high aspect-ratio converging nozzle embedded in the cavity leading edge as shown in Fig. 1. Actuation is provided by the movement of the titanium diaphragm of a Selenium D3300Ti compression driver attached to the contoured nozzle that exhausts at an angle of 30 degrees with respect to the main flow through a 1-mm high slot spanning the whole width of the cavity. |
|
| Figure 1: Cutout of the cavity-flow facility showing the compression driver and the converging nozzle of the synthetic-jet actuator. |
When used as designed, i.e. for producing sound connecting it to an acoustic diffuser, the compression driver has a relatively flat frequency response. In the rather unconventional arrangement above, the compression driver exhibits a highly frequency-dependent behavior where some frequencies are reinforced while others are reduced. Measurements of the synthetic-jet velocity at its exit slot obtained with a miniature hot wire, Fig. 2, evidence this behavior. For instance Fig. 3 presents the variation of the positive-velocity peak at the actuator exit slot with the frequency of sinusoidal excitation for various voltages in absence of main flow. Conversely, at all frequencies the amplitude response is approximately a linear function of the input voltage level, as can be judged from the same figure. |
 |
 | |
| Figure 2: Miniature hot-wire for velocity measurements at the actuator exit slot. |
Figure 3: Positive-velocity peak at the actuator exit slot with the frequency of sinusoidal excitation for various rms voltages. |
The highly frequency-dependent behavior of the actuator is also revealed in Fig. 4 presenting the acoustic transfer function of the actuator (blue) in response to white noise excitation (black). |
 |
| Figure 4: Noise (blue) measured at the actuator exit slot with white noise excitation (black). |
The results above compare well with those observed by other researchers using high aspect ratio rectangular synthetic jets. |
A highly frequency-dependent behavior is not a desirable characteristic for an actuator. With the colleagues of CCCS I developed a feedback-based compensator that alleviates this behavios by flattening the actuator response. |
Additional information on this research can be found in:
|
| MD previous research | MD research | MD home |