Pneumatically actuated micromachined synthetic jet modulators

Abstract

Results presented in the synthetic jet literature have focused on the demonstration of and application of one or more single-orifice synthetic jet actuators in jet vectoring and other aerodynamic applications. For these applications, amplitude and phase modulation techniques are often used in conjunction with the oscillatory nature of the synthetic jet flow to achieve the desired results. In this work the authors present a multi-orifice synthetic jet actuator and investigate the feasibility of using integrated microvalves for dynamic orifice output modulation. A multi-orifice synthetic jet consists of a micromachined orifice array with integrated microvalves for flow modulation and a shared membrane actuator for synthetic jet generation. Individual orifice output modulation using microvalves could be used to compensate for manufacturing-induced or spatial variations in orifice output in a multi-orifice synthetic jet. Moreover, dynamic orifice output modulation could also be used to alter locally the zero net-mass-flux nature of the synthetic jet flow, producing localized flow regions over the multi-orifice synthetic jet in which the net-mass-flux is positive or negative instead of zero as in the case of traditional single-orifice synthetic jets. For instance, if a single oscillatory actuator is used to generate in parallel synthetic jet flow from an array of orifices, the microjet modulator associated with a particular orifice could be sequenced to open only during the intake (or exhaust) stroke of the actuator, creating a localized low (or high) pressure region at the given orifice. The use of dynamic modulation to create these localized regions with non-zero net mass flux could be harnessed to improve the efficiency synthetic jets in jet vectoring, flow control, or other applications. This paper discusses the fabrication and characterization of pneumatically actuated, micromachined synthetic jet modulator arrays and demonstrates the use of these synthetic jet modulators for dynamic modulation of multi-orifice synthetic jet flows. The multi-orifice synthetic jet presented here utilizes a traditionally machined synthetic jet actuator for generation of synthetic jet flows (5–20 m/s) and an array of individually addressable micromachined synthetic jet modulators for manipulation of the resulting synthetic jet flows. Included are qualitative and quantitative experimental results that demonstrate static on-off modulation and dynamic flow modulation at the jet generation frequency. Continuous variation of the output of individual jets from suction-only operation to exhaust-only operation was achieved by changing the phase of the modulation signal relative to the jet generation signal. Also presented is phase formulation of the modulated synthetic jet flow, which compares favorably with measurements of the exit pressure of the modulated synthetic jet flow. A sample application of the pneumatic microjet modulator array, a lateral air pump, is also presented to demonstrate the use of dynamic synthetic jet modulation to create localized regions with non-zero net mass flux.