Momentum transfer in the outflow cycle of a Synthetic jet: Comparison between a developed flow and an LE model

TL;DR

This study compares the momentum transfer predictions of a Lumped-element model with actual measurements of a synthetic jet's fully developed flow, revealing consistent trends but notable differences at higher sound pressures and flow regimes.

Contribution

It provides the first validation of LE model predictions against measurements of the detached, fully developed jet in synthetic jet flows, highlighting limitations and flow regime differences.

Findings

LE model predictions follow similar trends to measurements at high sound pressures

Significant differences observed between predictions and measurements at higher sound pressures

Flow decay rates vary notably between the neck region and downstream the cavity

Abstract

In the literature, flows produced by synthetic jets (SJ) have been studied extensively through experiments and numeric simulations. The essential physics of such a complex system has been simplified successfully to Lumped-element models in a wide range of conditions. LE models effectively predict the pressure in the cavity and the velocity in the neck of SJ. But, this does not comprise the complete dynamics of SJ. As soon as the flow starts separating from the neck of the SJ device, vortices and jets form at some distance downstream. These structures are the result of loosening the flow boundaries. Despite such a dramatic change, predictions of LE models remain unverified by measurements of the fully developed jet. We compared predictions of momentum transfer using an LE model with measurements of size and velocity of a fully developed jet/vortex detached from an SJ. Our SJ device operated with air as an active fluid. Comparing measurements and predictions, we found a constant difference for the higher sound pressures. However, the predictions and the measurements follow similar trends. Additionally, we found that the decay rate of the flow regime given by the relationship between the Reynolds and the Strouhal numbers differs significantly when the flow is studied within the neck and downstream the cavity.