“…The upper limit 'r max ' can be any radial distance at which the effect of MVGs cannot be felt. 80 A smaller 'H' value is desirable as it denotes that the boundary layer is less 'momentum deficit' and can better resist an adverse pressure gradient. Azimuthal modulations in the incompressible shape factor (H) at 20 mm upstream of the compression corner are plotted in Figure 24.…”
Section: Streamwise Vortices and Boundary Layer Entrainmentmentioning
confidence: 99%
“…The trapezoidal (TZ) shape was derived from the tapered micro-vane actuators that were evaluated by Anderson et al, 60 with the difference being that the leading and trailing edges of the vanes were joined together to convert it into a wedge shaped device as shown in Figure 4(b). 80 The split ramp (SR) design depicted in Figure 4(c) was taken from the investigations performed by Nolan and Babinsky, 70 who showed that its vortices had a lesser decay rate than the ones originating from the BR. Thick vanes and RV were adopted from the computational works carried out by Lee et al 77,78,82 and are shown in Figure 4(d) and (e), respectively.Figure 4.MVG configurations under study: (a) baseline ramp (BR); (b) trapezoidal ramp (TZ); (c) split ramp (SR); (d) thick vanes (TV) and (e) ramped vanes (RV).…”
Section: Wind Tunnel Testingmentioning
confidence: 99%
“…74 Control performance of vane type devices is superior to that of wedge-shaped devices, 75 but the latter are structurally more robust. 76 Various innovative designs [77][78][79][80] have also been proposed in recent years to control shockinduced separations, but to the best of our knowledge, these different shapes have not been studied in compression corner flows. There also seems to be very few published studies 63,67,71,81 that report the effect of MVGs on axisymmetric flare-induced separations.…”
This study evaluates the ability of five micro vortex generator (MVG) geometries in attenuating the flow separation induced by an axisymmetric compression corner. Experimental and computational investigations were carried out at Mach 2 on a cone–cylinder–flare model, with a flow deflection angle of 24° at the cylinder/flare juncture. The MVG shapes considered were baseline ramp, trapezoidal ramp, split ramp, thick vanes and ramped vanes. A circumferential array of these MVGs having a device height (h) of 1.4 mm and an inter-device spacing of 10.5 mm (7.5 h) was introduced 50 mm upstream of the compression corner. Streamwise counter-rotating vortex pairs that originated from these devices created alternate bands of upwash and downwash regions in the incoming boundary layer, which resulted in suitable three-dimensional alterations of the separation region’s size. Furthermore, surface streamline visualizations showed that the vortices induced profound topological transformations in the separated flow structure. In the absence of MVGs, spectral analysis of the pressure signal obtained from the separation shock’s intermittent region revealed a relatively broadband dominant frequency range of 0.55 kHz–0.9 kHz. The MVGs did not cause any significant change in the dominant frequency, but made the bandwidth slightly narrower. Among the different MVG designs that were studied, the ramped vanes (RV) induced the most momentum augmentation in the near wall region and thereby caused the maximum downstream shift in the separation shock’s position.
“…The upper limit 'r max ' can be any radial distance at which the effect of MVGs cannot be felt. 80 A smaller 'H' value is desirable as it denotes that the boundary layer is less 'momentum deficit' and can better resist an adverse pressure gradient. Azimuthal modulations in the incompressible shape factor (H) at 20 mm upstream of the compression corner are plotted in Figure 24.…”
Section: Streamwise Vortices and Boundary Layer Entrainmentmentioning
confidence: 99%
“…The trapezoidal (TZ) shape was derived from the tapered micro-vane actuators that were evaluated by Anderson et al, 60 with the difference being that the leading and trailing edges of the vanes were joined together to convert it into a wedge shaped device as shown in Figure 4(b). 80 The split ramp (SR) design depicted in Figure 4(c) was taken from the investigations performed by Nolan and Babinsky, 70 who showed that its vortices had a lesser decay rate than the ones originating from the BR. Thick vanes and RV were adopted from the computational works carried out by Lee et al 77,78,82 and are shown in Figure 4(d) and (e), respectively.Figure 4.MVG configurations under study: (a) baseline ramp (BR); (b) trapezoidal ramp (TZ); (c) split ramp (SR); (d) thick vanes (TV) and (e) ramped vanes (RV).…”
Section: Wind Tunnel Testingmentioning
confidence: 99%
“…74 Control performance of vane type devices is superior to that of wedge-shaped devices, 75 but the latter are structurally more robust. 76 Various innovative designs [77][78][79][80] have also been proposed in recent years to control shockinduced separations, but to the best of our knowledge, these different shapes have not been studied in compression corner flows. There also seems to be very few published studies 63,67,71,81 that report the effect of MVGs on axisymmetric flare-induced separations.…”
This study evaluates the ability of five micro vortex generator (MVG) geometries in attenuating the flow separation induced by an axisymmetric compression corner. Experimental and computational investigations were carried out at Mach 2 on a cone–cylinder–flare model, with a flow deflection angle of 24° at the cylinder/flare juncture. The MVG shapes considered were baseline ramp, trapezoidal ramp, split ramp, thick vanes and ramped vanes. A circumferential array of these MVGs having a device height (h) of 1.4 mm and an inter-device spacing of 10.5 mm (7.5 h) was introduced 50 mm upstream of the compression corner. Streamwise counter-rotating vortex pairs that originated from these devices created alternate bands of upwash and downwash regions in the incoming boundary layer, which resulted in suitable three-dimensional alterations of the separation region’s size. Furthermore, surface streamline visualizations showed that the vortices induced profound topological transformations in the separated flow structure. In the absence of MVGs, spectral analysis of the pressure signal obtained from the separation shock’s intermittent region revealed a relatively broadband dominant frequency range of 0.55 kHz–0.9 kHz. The MVGs did not cause any significant change in the dominant frequency, but made the bandwidth slightly narrower. Among the different MVG designs that were studied, the ramped vanes (RV) induced the most momentum augmentation in the near wall region and thereby caused the maximum downstream shift in the separation shock’s position.
“…Energetic air is transferred from the primary vortex pair, and the velocity close to the surface depends on the liftoff of the vortices [19]. The gap between ramp-type VGs creates secondary counter-rotating vortices and reduces the interaction between counterrotating vortex pairs [20]. For an oblique shock reflection with microramp VGs, the momentum flux that is added to the separation bubble increases linearly with h * .…”
A flap can be used to control wing camber and as a high-lift device. A convex corner is a simplified model of the upper surface of a flap. At transonic speeds, shock-induced boundary layer separation (SIBLS) occurs at greater freestream Mach numbers and deflection angles. This results in energy losses and a reduction in aerodynamic performance. This study installs ramp-type vortex generators (VGs) upstream of a convex corner, and the effect of the height of the VG on SIBLS is determined. As the height of the VG increases, the magnitude of the mean surface pressure upstream of the corner increases and downstream expansion decreases, which results in a reduction in lift. A reduction in peak surface pressure fluctuations, the separation length, and the frequency of shock oscillation is also determined. For flow control and lift enhancement, micro-VGs are more effective.
“…Depending on their design, the MVGs generate co-rotating (29,30) or counter-rotating (31)(32)(33) stream-wise vortices that entrain high momentum fluid from the upper part of the boundary layer into the low momentum region close to the wall, thereby enabling the boundary layer to more effectively resist the adverse pressure gradient generated by the shock. Various shapes (34)(35)(36)(37)(38)(39) including standard designs such as microramps (31,32) and micro-vanes (30,33) were introduced in different shock-boundary layer interaction flowfields to examine their ability to reduce the flow separation and alleviate its ill effects. The control performance was found to improve with increase in the size of the MVG (31,40) but so did the wave drag associated with it.…”
The ability of microramps to control shock - boundary layer interaction at the vicinity of an axisymmetric compression corner was investigated computationally in a Mach 4 flow. A cylinder/flare model with a flare angle of 25° was chosen for this study. Height (h) of the microramp device was 22% of the undisturbed boundary layer thickness (δ) obtained at the compression corner location. A single array of these microramps with an inter-device spacing of 7.5h was placed at three different streamwise locations viz. 5δ, 10δ and 15δ (22.7h, 45.41h and 68.12h in terms of the device height) upstream of the corner and the variations in the flowfield characteristics were observed. These devices modified the separation bubble structure noticeably by producing alternate upwash and downwash regions in the boundary layer. Variations in the separation bubble’s length and height were observed along the spanwise (circumferential) direction due to these devices.
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