Role of Duty Cycle in Burst-Modulated Synthetic Jet Flow Control

TL;DR

This study investigates how duty cycle ($DC$) and blowing ratio ($C_B$) in burst-modulated synthetic jet actuation influence flow reattachment, lift, and power efficiency over a stalled NACA 0025 airfoil at $\mathrm{Re}_c=10^5$ and $\alpha=10^{\circ}$. By using a $2\times12$ microblower array driven at $f_c=25.5$ kHz and $f_m=200$ Hz ($F^+=11.76$), the authors identify a threshold momentum coefficient $C_\mu$ that governs reattachment, achievable by increasing either $DC$ or $C_B$, after which lift gains saturate. They show that low-$DC$, high-$C_B$ actuation yields the best lift-for-power efficiency, while higher $DC$ improves flow stability at the cost of reduced efficiency. Vortical structures become more coherent and wall-adjacent with increasing $DC$, and a strong correlation between suction-peak pressure and lift enables rapid, single-point metrics for multivariate control testing and potential closed-loop applications. These findings provide a framework for selecting SJA control strategies that balance aerodynamic performance, stability, and power consumption in practical AFC deployments.

Abstract

The effect of duty cycle (DC) and blowing ratio on synthetic jet flow control over a stalled NACA 0025 airfoil at Re_c=10^5 was investigated experimentally. A finite-span microblower array operating with burst modulation was tested across a wide range of control parameters to assess aerodynamic performance, power consumption, and flow stability. Flow reattachment was achieved once a threshold momentum coefficient was met via increasing either the DC or blowing ratio. Control effectiveness increased sharply upon reattachment, with additional momentum providing incremental improvements in lift, spanwise control, and flow stability, though these effects eventually saturated. Substantial lift improvements are observed at DCs as low as 5%, indicating that brief, high-momentum bursts were the most power-efficient for achieving reattachment. However, flow stability was reduced at low DCs due to the inconsistent streamwise dissipation of spanwise vortices responsible for flow control. Higher DC control strategies resulted in more consistent boundary layer control. These results provide a framework for selecting control strategies that balance aerodynamic performance and stability with power efficiency.

Figures (20)

• Figure 1: Labelled schematic of the wind tunnel
• Figure 2: Labelled overhead view of the NACA 0025 airfoil in the test section
• Figure 3: Murata MZB1001T02 microblower
• Figure 4: Normalized lift coefficient versus reduced frequency for front and rear row actuation. Adapted from Xu2025
• Figure 5: Input signal configuration and power measurement setup for the SJA array