Airfoil flow separation control with plasma synthetic jets at moderate Reynolds number

Abstract

An array of 26 plasma synthetic jet actuators (PSJA) is flush-mounted on a NACA-0015 airfoil model to control the leadingedge flow separation at moderate Reynolds number (Re c = 1.7 × 10 5). The stall angle of this airfoil is postponed from 15.5 • to approximately 22 • , and the peak lift coefficient is increased by 21%. PSJAs exhibit distinctive separation control mechanisms depending on the relative location between actuation and separation and reduced frequency of actuation (F *). At an angle of attack of = 15.5 • , the non-actuated flow separates approximately 4% chord length downstream of the jet orifices. Plasma synthetic jets (PSJs) applied at F * ≥ 0.5 can displace the separation point downstream to mid-chord position, as a result of the energizing of the incoming boundary layer through mixing enhancement. As a comparison, with actuation frequency of F * ≤ 0.25 , the separation point at = 15.5 • remains near the leading edge and the zero-velocity line is periodically swept towards the suction surface by the convecting spanwise vortices generated from PSJ actuation, leading to a reduction of timeaveraged backflow area. For the case of separation control at = 22 • , the separation point resides always upstream of the actuation position, regardless of actuation frequency. The peak lift coefficient is attained at F * = 1 , and the decreasing lift at high actuation frequency (F * = 2) is ascribed to the severe interaction between adjacent spanwise vortices at short spacing.

Experimental study on airfoil flow separation control via an air-supplement plasma synthetic jet

“…In practical flow control applications, focus should be placed on enhancing the vortex mixing effect to further improve the PSJ flow control effect. The mechanism summarized above is similar to that obtained by Zong et al [13]. A PSJ with an appropriate actuation position and frequency can make the zero-velocity line periodically close to the airfoil upper surface through the mixing enhancement effect on the boundary layer flow, which plays a role in inhibiting flow separation.…”

“…The installation position of the jet outlet was determined based on the flow separation point position. Amitay et al [25] and Zong et al [13] demonstrated that the jet near the separation point has the best control effect. At low speeds, the flow separation point of the NACA0021 airfoil was concentrated near x/c = 0.2, where x is the distance from the airfoil surface position projection on the chord length to the leading edge.…”

“…Su et al [12] designed a new type of multi-channel discharge PSJ and found that a 12-channel PSJ could effectively inhibit the flow separation of the airfoil suction surface, increase lift, and delay stall. At a moderate Reynolds number (Re c = 1.7 × 10 5 ), Zong et al [13] used 26 PSJ actuators arranged at 0.25c from the leading edge of a NACA0015 wing model for flow separation control. The maximum stall angle was delayed from 15.5° to approximately 22°, and the maximum lift coefficient was increased by 21%.…”

“…(a) Non-actuation, α = 10° (b) Non-actuation, α = 11° (c) Non-actuation, α = 12°( d) d = 0.8 mm, α = 10° (e) d = 0.8 mm, α= 11° (f) d = 0.8 mm, α = 12°( g) d = 1.2 mm, α = 10° (h) d = 1.2 mm, α = 11° (i) d = 1.2 mm, α = 12°( j) d = 1.6 mm, α = 10° (k) d = 1.6 mm, α = 11° (l) d =1.6 mm, α = 12°( m) d = 2.0 mm, α = 10° (n) d = 2.0 mm, α = 11° (o) d =2.0 mm, α = 12°Fig 13. Flow field velocity contours for different jet orifice diameters…”

Use of synthetic jet to a fully-active flapping foil for power extraction enhancement

“…6,7 Many promising applications of SJA have been completed for various purposes, including jet vectoring, 8 boundary layer separation control, 9 heat transfer enhancement, 10 and flow mixing improvement. 11 In particular, because of quasi-two-dimensional flow profile, slot-type synthetic jet (SJ) is commonly employed in airfoil flow control, 12–19 which has become a topic of intense investigations in recent years. In these studies, it is noted that the airfoil is usually fixed, and the SJ is used to control the flow separation to achieve better aerodynamic performance.…”