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Session: Control of separated/unsteady flows III
Session starts: Thursday 06 November, 11:00
Presentation starts: 11:40
Room: Commission roon 2

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Seungho Yoo (UNIST)
Jae Hwa Lee (UNIST)

Abstract:
Flow over an open cavity commonly occurs in various engineering applications, including landing gear wells, weapon bays, optical window openings in aircraft, and sunroofs in automobiles. The self-sustained oscillations in an open cavity flow induce intense pressure fluctuations, which may result in structural fatigue, excessive noise, and degradation of aerodynamic performance [1]. Many previous studies have been conducted to suppress the self-sustained oscillations, and the steady blowing upstream of the cavity has been shown to be effective in reducing the pressure fluctuations [2]. In compressible cavity flows, this control method has been adopted in both two-dimensional (2D) and three-dimensional (3D) steady blowing. Li et al. [3] conducted numerical simulations using a 2D steady blowing to investigate the effect on the shear layer when the steady blowing is applied. They found that the reduction of the pressure fluctuations is achieved due to the lifted shear layer, weakening the interaction with the cavity wall. In addition, Zhang et al. [4] employed a 3D steady blowing in compressible cavity flows and reported improved performance over the 2D steady blowing in terms of suppressing pressure fluctuations because of additional 3D disturbances. Although the steady blowing has been proved to be effective in reducing pressure fluctuations in compressible cavity flows, its effects on incompressible cavity flows have received less attention. Thus, Choi and Lee [5] performed large-eddy simulations (LESs) employing a 2D steady blowing in an incompressible turbulent cavity flow and achieved a reduction in pressure fluctuations. In this study, LESs are conducted to investigate the effect of a 3D steady blowing using multiple slot jets located upstream of the leading edge in an incompressible turbulent cavity flow (see Figure 1). Figure 2 shows the distribution of the root-mean-square of the pressure fluctuations (prms) along the internal cavity wall for various numbers of slots (Nslot). Here, a new coordinate s/D is defined along the internal cavity wall and the origin of the new coordinate is set to s/D = 0 at the leading edge (see the inset in figure 2b). As shown in figure 2(a), when Nslot = 4 and 8, the values of prms are enhanced compared to that of uncontrolled case (baseline) across most of the cavity wall, suggesting degraded control performance for small Nslot. However, a noticeable reduction in prms begins to appear when Nslot is greater than or equal to 16 compared to the baseline. In particular, when Nslot is 32, the suppression becomes more effective than that achieved by a 2D steady blowing, especially near the upstream wall. This result suggests that the 3D steady blowing improves the performance of the prms reduction. Figure 2(b) provides an enlarged view of a region near the trailing edge (3.6 ≤ s/D ≤ 4.0), where the vortical structures convecting along the shear layer impinge on the downstream wall. In this region, prms reaches its maximum due to a strong interaction between the vortical structures and the wall. Even in this region, prms is substantially reduced as Nslot increases, especially when Nslot exceeds 32. These results demonstrate that the 3D steady blowing provides an improved suppression of the pressure fluctuations compared to the 2D steady blowing in an incompressible cavity flow.