Numerical Investigation to Forcing Frequency and Amplitude of Synthetic Jet Actuators

摘要

A three-dimensional large eddy simulation was performed to investigate the influence of the forcing frequency and amplitude to the effectiveness of a synthetic jet actuator. The effectiveness of the synthetic jet actuator was defined by elimination of the laminar separation bubble in a boundary layer with an adverse pressure gradient The numerical results of the synthetic jet actuator's effectiveness were compared to identify the significance in changes made by varied forcing frequency at fixed forcing amplitude and by varied forcing amplitude at a fixed forcing frequency. Consistent with the wind-tunnel experiments, large eddy simulation results showed that the effectiveness of the synthetic jet actuator depends more on the forcing frequency than on the forcing amplitude. They support the inference from the experiments that instability due to adverse pressure gradient to seed the nonfunctional Kelvin-Helmholtz instability in a short laminar separation bubble be a source for enhancing the frictional Tollmien-Schlichting instability triggered by a synthetic jet actuator to resist the laminar separation. To make a micro synthetic jet actuator effective, all the instabilities in the base flow and generated by the actuators should be used. Understanding of the optimal uses of these instabilities is challenging.