Ali Shirinzad | Searcharxiv

arXiv2024

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

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.

physics.flu-dyn↗

arXiv2024

On the Role of the Wall Curvature in the Development of Flows Reattached over an Airfoil through Unsteady Blowing

An array of twelve circular-orifice synthetic jet actuators (SJAs) was used to provide the unsteady forcing required for flow separation control over a National Advisory Committee for Aeronautics (NACA) 0025 airfoil at a chord-based Reynolds number of 100000 and an angle of attack of 10°. Two distinct high- and low-forcing frequencies corresponding to the shear layer and wake instabilities were used at an identical blowing strength for flow control. Particle image velocimetry (PIV) was used to measure the velocity fields at the centerline of the airfoil. The results showed the presence of a turbulent shear layer stretching from the edge of the reattached boundary layer to the irrotational flow with an invariant mean spanwise vorticity in the wall-normal direction. It was revealed that the coherent structures for the high-frequency controlled case are advected along the boundary of the rigid-body rotation shear layer and the irrotational flow, whereas for the low-frequency actuation, some structures directly pass through the rigid-body rotation region, disrupting the wall-normal balance of vorticity. Analytical expressions were derived for the variation of the mean spanwise vorticity in the rigid-body rotation region and the curvature-multiplied mean angular momentum in the irrotational flow region based on order-of-magnitude analysis and semi-empirical grounds. The resulting patterns showed an excellent agreement with the measured experimental data.

physics.flu-dyn↗