Experimental design and analysis for piezoelectric circular actuators in flow controlapplications

Abstract

Flow control can lead to saving millions of dollars in fuel costs each year by making anaircraft more efficient. Synthetic jets, a device for active flow control, operate byintroducing small amounts of energy locally to achieve non-local changes in theflow field with large performance gains. These devices consist of a cavity with anoscillating diaphragm that divides it into active and passive sides. The active side hasa small opening where a jet is formed, while the passive side does not directlyparticipate in the fluidic jet. Over the years, research has shown that synthetic jetbehavior is dependent on the active diaphragm and the cavity design; hence, thefocus of this work. The performance of the synthetic jet is studied under variousfactors related to the diaphragm and the cavity geometry. Three diaphragms,manufactured from piezoelectric composites, were selected for this study: Bimorph,Thunder® and Lipca. The overall factors considered are the driving signals, voltage, frequency, cavityheight, orifice size, and passive cavity pressure. Using the average maximum jet velocity asthe response variable, these factors are individually studied for each actuator, andstatistical analysis tools are used to select the relevant factors in the response variable. Thefactors are divided into two experimental fractional factorial design matrices, with fiveand four factors, respectively. Both experiments are chosen to be of resolutionV, where main factors are confounded with three-factor interactions. In the first experimentaldesign, the results show that frequency is not a significant factor, while waveformis significant for all the actuators. In addition, the magnitude of the regressioncoefficients suggests that a model that includes the diaphragm as a factor may bepossible. These results are valid within the ranges tested, that is low frequencies andsawtooth and sine waveform as driving signals. In the second experimental design,cavity dimensions are kept constant and four factors including back pressure areconsidered. In this case, each diaphragm produces different results with only onediaphragm, Thunder, showing a definite relationship between the studied factors.The other two diaphragms do not show conclusive results, indicating that theremay be other factors that need to be considered when pressure is a concern. Insummary, independently of the diaphragm utilized in a synthetic jet actuator,applied waveform is an important factor when maximizing peak jet velocity. Inaddition, frequency is found not to be significant in all cases within the limitsof the study. This indicates that the diaphragm and the driving signal shouldbe included in any optimization design of a piezoelectric synthetic jet actuator.