The effects of actuation frequency on the separation control over an airfoil using a synthetic jet

Abstract

The simulation of separation control using a synthetic jet (SJ) is conducted around an NACA (National Advisory Committee for Aeronautics) 0015 airfoil by large-eddy simulation (LES) with a compact difference scheme. The synthetic jet is installed at the leading edge of the airfoil and the e¨ects of an actuation frequency F + (normalized by chord length and velocity of freestream) are observed. The lift-drag coe©cient is recovered the most for F + = 6. The relationship between momentum addition by turbulent mixing and large vortex structures is investigated using a phase-averaging procedure based on F + . The Reynolds shear stress is decomposed into periodic and turbulent components where the turbulent components are found to be dominant on the airfoil. The strong turbulent components appear near the large vortex structures that are observed in phase-and span-averaged §ow ¦elds.

Multifactorial Effects of Operating Conditions of Dielectric-Barrier-Discharge Plasma Actuator on Laminar-Separated-Flow Control

“…The difference in the lift/drag ratio between D c 0.0025 and D c 0.16 is approximately 20% in the case of "2.5% F 6," in which the difference in the momentum coefficient is 64 times between these cases. Compared with the result for the synthetic jet with the same flow condition and Reynolds number [65], almost the same lift/drag ratio can be obtained using one-10th the momentum coefficient for the synthetic jet. These results indicate that laminar-separation control can be efficiently conducted when the location and operating conditions of the plasma actuator are optimal.…”

“…These momentum coefficients do not change with the burst frequency or base frequency in the present study. Compared with other microdevices for active separation control, such as the synthetic jet [64,65], the momentum coefficients from the plasma actuator used in the present study are much smaller.…”

Spatial Growth of the Spanwise Disturbance Induced by a Synthetic Jet on Separation Control over an Airfoil

“…In this study, the momentum coefficient C µ is set to 0.2% which is smaller than that used in the previous study 7 ; the actuation frequency is set to F + = 6.0; the synthetic jet is installed to the leading edge. The actuation frequency F + = 6.0 shows the better aerodynamic performances compared to the other frequencies 9,8 . The spanwise wave number k yin /2π is varied for 0 ≤ k yin /2π ≤ 95. boundary condition † Cµ is set to 0.002; synthetic jet is installed at the leading edge; actuation frequency is set to F + = 6.0.…”

“…Therefore, the jet is slightly entrained to the blowing direction by the external flow near the edge of the orifice exit (z 0.0025) although the phases 1, 13 and 17 correspond to the suction phases. The turbulent components of u Cavity ( [ u Cavity φ ]) are most amplified in the blowing phase 9 because of strong turbulent structures generated in the cavity 6,8 . Note that the phase-averaged spanwise component of u Cavity ( [ v Cavity φ ]) is assumed to be zero despite the actual averaged procedure yields nonzero values.…”

“…They also reported that the key mechanisms of separation control include not only the modification of twodimensional boundary layer profile by adding or removing momentum in the freestream direction, but also three-dimensional turbulent mixing. More quantitatively, our recent study has shown that the turbulent structure is significant in terms of the momentum exchange based on Reynolds shear stress, and the large vortex structure appearing in phase-and spanwise-averaged flow fields specifically entrains the turbulent component of Reynolds shear stress 8 . Considering these results, we have investigated the significance of three-dimensional turbulent structures induced from the synthetic jet, 9 where the synthetic jet was modeled by the deforming cavity (Cavity model) and two-dimensional jet profile of the boundary condition (Bc model), and the controlled flows were compared.…”