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Fig. 2 Wind tunnel setup. (x, y, z) are streamwise, spanwise, and normal directions. Origin is at leading edge and mid-span

Figure 2 Wind tunnel setup. (x, y, z) are streamwise, spanwise, and normal directions. Origin is at leading edge and mid-span

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@, is displayed on a discrete colorbar whose step size matches the measurement uncertainty.
@, is displayed on a discrete colorbar whose step size matches the measurement uncertainty.
Fig. 3. Acoustic power spectra in an empty wind tunnel with flow at U = 6.7 m/s (Re = 40 k) and without flow. Note the change in axis scales The maximum absolute deflection amplitude, 7’, was measured at the free wing tip (/b = —1.0) from image sequences taken from the camera mounted on top of the wind tunnel. z/(a) was measured for Re = 40 and 60 k fo! the wing with all holes covered (the solid wing), and results are shown in Fig. 4. At Re = 40 k before and after the low- to high-lift transition, the wing tip deflection z//c ~ 0.11 %. At Re = 60 k, a difference in wing tip deflection is observed when SI-SII transition occurs. In the low-lift (ST state, z'/c ~ 0.2 %, and after transition to the high-lift (SID state, Z/c ~ 0.07 %. The difference is likely due to the increased influence of unsteady aerodynamic forces, which
Fig. 3. Acoustic power spectra in an empty wind tunnel with flow at U = 6.7 m/s (Re = 40 k) and without flow. Note the change in axis scales The maximum absolute deflection amplitude, 7’, was measured at the free wing tip (/b = —1.0) from image sequences taken from the camera mounted on top of the wind tunnel. z/(a) was measured for Re = 40 and 60 k fo! the wing with all holes covered (the solid wing), and results are shown in Fig. 4. At Re = 40 k before and after the low- to high-lift transition, the wing tip deflection z//c ~ 0.11 %. At Re = 60 k, a difference in wing tip deflection is observed when SI-SII transition occurs. In the low-lift (ST state, z'/c ~ 0.2 %, and after transition to the high-lift (SID state, Z/c ~ 0.07 %. The difference is likely due to the increased influence of unsteady aerodynamic forces, which
Fig. 4 Wing tip deflections normalized by the chord (z’//c) at Re = 40 and 60 k for the wing with all holes closed (i.e., solid wing)
Fig. 4 Wing tip deflections normalized by the chord (z’//c) at Re = 40 and 60 k for the wing with all holes closed (i.e., solid wing)
The SI-SII transition is accompanied by a forward chord- wise movement of the mean separation line. The early separation leaves sufficient time, in fractions of (c/U), so that transition to turbulence and reattachment can occur. Chordwise local disturbances could effectively promote this transition, and this concept was tested by leaving open
The SI-SII transition is accompanied by a forward chord- wise movement of the mean separation line. The early separation leaves sufficient time, in fractions of (c/U), so that transition to turbulence and reattachment can occur. Chordwise local disturbances could effectively promote this transition, and this concept was tested by leaving open
individual spanwise rows of holes at a given x/c location, while closing all others. For a row with open holes, 15 holes spaced 3.2 cm apart (Ay/b = 0.12) were left open across most of the span (—0.83 < y/b < 0.83). The C,(Cp) and L/D curves for the wing with selected rows of open holes located at x, = x/c = 0.1, 0.2, 0.3, 0.4 are shown in Fig. 7 (Re = 40 k) and Fig. 8 (Re = 60 k). abrupt jump in either L or D and the curves lie close to SII over all «. At Re = 40 k, the curves once again show sharp jumps between states when x, > 0.2, and for x, > 0.3, the performance curves are much closer to, though still mea- surably improved upon, the original solid baseline wing. At Re = 60 k, the curves show the sharp jumps when x, > 0.3. individual spanwise rows of holes at a given x/c location, and L/D curves for the wing with selected rows of open For both Re cases, single rows of open holes at specific chord locations allow the envelope of C;(Cp) and (L/D) (a) to be populated with results that are intermediate between the extremes where all holes are open or all closed. As the row location moves closer to the leading edge, the per- formance curves are pulled toward the SII state, as gen- erated with all holes open. When x, = 0.1, there is no The original design of the wing included two exit ports at the right wing tip, which were meant to be used for elec- trical connections. The results shown in Figs. 5, 6, 7, and 8 were for the wing with open exit ports. Figure 9 shows the L/D curves for the wing with different rows of open holes the right wing tip, which were meant to be used for elec-
individual spanwise rows of holes at a given x/c location, while closing all others. For a row with open holes, 15 holes spaced 3.2 cm apart (Ay/b = 0.12) were left open across most of the span (—0.83 < y/b < 0.83). The C,(Cp) and L/D curves for the wing with selected rows of open holes located at x, = x/c = 0.1, 0.2, 0.3, 0.4 are shown in Fig. 7 (Re = 40 k) and Fig. 8 (Re = 60 k). abrupt jump in either L or D and the curves lie close to SII over all «. At Re = 40 k, the curves once again show sharp jumps between states when x, > 0.2, and for x, > 0.3, the performance curves are much closer to, though still mea- surably improved upon, the original solid baseline wing. At Re = 60 k, the curves show the sharp jumps when x, > 0.3. individual spanwise rows of holes at a given x/c location, and L/D curves for the wing with selected rows of open For both Re cases, single rows of open holes at specific chord locations allow the envelope of C;(Cp) and (L/D) (a) to be populated with results that are intermediate between the extremes where all holes are open or all closed. As the row location moves closer to the leading edge, the per- formance curves are pulled toward the SII state, as gen- erated with all holes open. When x, = 0.1, there is no The original design of the wing included two exit ports at the right wing tip, which were meant to be used for elec- trical connections. The results shown in Figs. 5, 6, 7, and 8 were for the wing with open exit ports. Figure 9 shows the L/D curves for the wing with different rows of open holes the right wing tip, which were meant to be used for elec-
Fig. 10 Power spectra at Re = 40 k and « = 10° for the wing with open holes at x/c = 0.1 and open exit port measured at various distances, z/c, from the top surface
Fig. 10 Power spectra at Re = 40 k and « = 10° for the wing with open holes at x/c = 0.1 and open exit port measured at various distances, z/c, from the top surface
Fig. 11 Power spectra at Re = 40 k. a No wing; b wing with closed holes; ¢ wing with open holes (x/c = 0.1) and open exit port; d wing with open holes (x/c = 0.1) and closed exit port. For b-d, « = 10°
Fig. 11 Power spectra at Re = 40 k. a No wing; b wing with closed holes; ¢ wing with open holes (x/c = 0.1) and open exit port; d wing with open holes (x/c = 0.1) and closed exit port. For b-d, « = 10°
Fig. 12 Schematic of cavities interconnected by a channel. Each cavity was designed to house speakers with an adjacent channel for wiring
Fig. 12 Schematic of cavities interconnected by a channel. Each cavity was designed to house speakers with an adjacent channel for wiring
affect the global behavior. When holes are present, the flow state switches from SI to high-lift SII, with no other control input necessary. The mechanism is entirely passive, and a control strategy might simply involve sliding lids open and shut to modify local flow characteristics. 4 Discussion On a wing that 1s characterized by abrupt jumps 1n lift and drag coef ficient between what we have termed SI, where the flow separates at some point between mid-chord and the trailing edge, and SII, where separation close to the leading ed ge is followed by reattachment, the dynamics are very sensitive to a number of different perturbations. In a study originally aimed at acoustic forcing of the flow, it was found , quite by accident, that the presence of the holes themselves in the wing suction surface was sufficient to The effect on the wing is approximately local, so that chordwise strips can affect local sectional c; and cg. Since each local flow state is either in SI or SIL, one may think of the wing as a device whose lift and drag coefficients can be manipulated under digital control. Local states can be on or off, and asymmetries across the span will lead to rolling
affect the global behavior. When holes are present, the flow state switches from SI to high-lift SII, with no other control input necessary. The mechanism is entirely passive, and a control strategy might simply involve sliding lids open and shut to modify local flow characteristics. 4 Discussion On a wing that 1s characterized by abrupt jumps 1n lift and drag coef ficient between what we have termed SI, where the flow separates at some point between mid-chord and the trailing edge, and SII, where separation close to the leading ed ge is followed by reattachment, the dynamics are very sensitive to a number of different perturbations. In a study originally aimed at acoustic forcing of the flow, it was found , quite by accident, that the presence of the holes themselves in the wing suction surface was sufficient to The effect on the wing is approximately local, so that chordwise strips can affect local sectional c; and cg. Since each local flow state is either in SI or SIL, one may think of the wing as a device whose lift and drag coefficients can be manipulated under digital control. Local states can be on or off, and asymmetries across the span will lead to rolling
the predominant frequency varied with impingement length and inflow velocity. Without the perforated plate, the shear ayer was separated with an inflection point, while with a perforated plate, the shear layer was bounded with no inflection point. It was also suggested in [4] that unified, arge-scale motion occurs through the plate perforations and induces jet flow at the downstream end of the perfo- rated plate. The long-wavelength instabilities along a per- forated plate of length L can be expressed as a Strouhal number, fZ/U, where f is a shedding or oscillation fre- quency. The reported values of fL/U are on the order of 0.5—0.6 [8]. If the chord of the wing is used as an effective plate length, the calculated fL/U ~ 8 is an order of mag- nitude larger. moments, while symmetrically (about mid-span) actuated hole opening can yield pre-determined total lift and drag from the envelope of possibilities. The performance characteristics of the perforated wing could be due to some form of cavity flow. In general, cavity flow can be categorized into three main types, as detailed in [20]: (a) fluid-dynamic, where oscillations come from the instability of the cavity shear layer and are enhanced through a feedback mechanism, (b) fluid-resonant, where oscillations are strongly coupled with resonant (standing) wave effects, and (c) fluid-elastic, where oscillations are linked to solid boundary motion. It is also possible to have combinations of different types of cavity flow.
the predominant frequency varied with impingement length and inflow velocity. Without the perforated plate, the shear ayer was separated with an inflection point, while with a perforated plate, the shear layer was bounded with no inflection point. It was also suggested in [4] that unified, arge-scale motion occurs through the plate perforations and induces jet flow at the downstream end of the perfo- rated plate. The long-wavelength instabilities along a per- forated plate of length L can be expressed as a Strouhal number, fZ/U, where f is a shedding or oscillation fre- quency. The reported values of fL/U are on the order of 0.5—0.6 [8]. If the chord of the wing is used as an effective plate length, the calculated fL/U ~ 8 is an order of mag- nitude larger. moments, while symmetrically (about mid-span) actuated hole opening can yield pre-determined total lift and drag from the envelope of possibilities. The performance characteristics of the perforated wing could be due to some form of cavity flow. In general, cavity flow can be categorized into three main types, as detailed in [20]: (a) fluid-dynamic, where oscillations come from the instability of the cavity shear layer and are enhanced through a feedback mechanism, (b) fluid-resonant, where oscillations are strongly coupled with resonant (standing) wave effects, and (c) fluid-elastic, where oscillations are linked to solid boundary motion. It is also possible to have combinations of different types of cavity flow.
Fig. 17 Instantaneous spanwise vorticity fields over the aft portion of the wing (beginning at x/c = 0.5) at Re = 40 k and « = 10° with 15 open holes at x/c = 0.1. The time between successive vorticity fields is 0.1 s
Fig. 17 Instantaneous spanwise vorticity fields over the aft portion of the wing (beginning at x/c = 0.5) at Re = 40 k and « = 10° with 15 open holes at x/c = 0.1. The time between successive vorticity fields is 0.1 s
Fig. 19 Relationship between Helmholtz frequency, fy, and tube length (neck height), h, for constant orifice/tube radius and variable cavity volume (a), and for constant cavity volume and variable orifice/tube radius (b)
Fig. 19 Relationship between Helmholtz frequency, fy, and tube length (neck height), h, for constant orifice/tube radius and variable cavity volume (a), and for constant cavity volume and variable orifice/tube radius (b)
Fig. 20 ACgii for the E387 airfoil at Re = 60k among different facilities [22], and ACp. usc between open and closed holes for the E387 wing at Re = 60 k
Fig. 20 ACgii for the E387 airfoil at Re = 60k among different facilities [22], and ACp. usc between open and closed holes for the E387 wing at Re = 60 k
Related topics:
Aerospace EngineeringSeparation ControlHelmholtz ResonanceFlow Separation ControlLow Reynolds Number
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