Decay of the supersonic turbulent wakes from micro-ramps

Sun, Zhengzhong; Schrijer, F.F.J.; Scarano, Fulvio; Oudheusden, B.W. van

doi:10.1063/1.4866012

Cited by 39 publications

(19 citation statements)

References 27 publications

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“…The co-existence of the streamwise vortices and K-H vortices triggers the vortex interaction. Cross-correlation of their intensities revealed that the generation of K-H vortex decreases the strength of streamwise vortices [23]. It is well known that the streamwise vortices execute the flow control function, the reduced streamwise vortex intensity due to vortex interaction, in the transient sense, may affect the control result.…”

Section: Instantaneous Flow Organizationmentioning

confidence: 94%

“…The decay of wake velocity profile was also studied by Herges et al [22] using Stereo-PIV. Sun et al [23] paid special attention on the decay behavior till downstream position of x/h=30 in the center plane using planar PIV and formulated an exponential decay law for both the maximum deficit velocity (Umin) and peak upwash velocity (Vmax). The recovery of deficit velocity as well as the elevation of the deficit region are visualized in figure 11, whereas the decay of upwash velocity in center plane can be seen in figure 12.…”

Section: The Velocity Fieldmentioning

confidence: 99%

“…A first effort on the analysis of the generation of K-H vortex chain was given by Li & Liu [32]. According to the analysis of Sun et al [33], the K-H vortex is subject to growth from the arc-shape to a full ring, based on the spatial auto-correlation in different regions in the wake center plane [23]. The co-existence of the streamwise vortices and K-H vortices triggers the vortex interaction.…”

Section: Instantaneous Flow Organizationmentioning

confidence: 99%

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Micro Vortex Generators for Boundary Layer Control: Principles and Applications

Sun¹

2015

International Journal of Flow Control

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This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractA review is given to the major developments in the boundary layer control by means of micro vortex generator (MVG). The appearance of MVG dates back to about three decades from the present review and this class of device rapidly spreads as an efficient and robust boundary layer control strategy for flows with separation in particular. Substantial successful applications of MVG have been achieved in subsonic flows and its application into supersonic flow is under progressive development, which requires the current status and capability of MVG to be reviewed. The fundamental aspects of MVG are first summarized, including its working principle and various geometries. Understanding of the fluid mechanics involved in the wake of a MVG device is of uppermost importance: the timeaveraged and instantaneous wakes are discussed respectively. In the former, effects from the MVG geometry parameters are presented; while in the latter, focus is placed on the phenomenon associated with flow instability inside the wake. MVG's applications in the subsonic regime are discussed, which covers the fundamental flow separation investigations and studies to tackle several practical problems. The ongoing studies in supersonic regime dealing with shock wave boundary layer interaction (SWBLI) induced separation are reviewed later, where the presentation is organized according to different types of SWBLI with emphasis on the interaction region.

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Section: Instantaneous Flow Organizationmentioning

confidence: 94%

Section: The Velocity Fieldmentioning

confidence: 99%

Section: Instantaneous Flow Organizationmentioning

confidence: 99%

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Micro Vortex Generators for Boundary Layer Control: Principles and Applications

Sun¹

2015

International Journal of Flow Control

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“…Previous studies of the micro-ramp wake have dealt with the streamwise evolution of the momentum deficit and characterized its turbulent recovery (Ghosh, Choi & Edwards 2010;Sun et al 2014b). In the present case, the momentum deficit and the properties of the shear layer induced by the micro-ramp pertain to the laminar regime and the velocity profile in the symmetry plane (z/h = 0) is compared with that of the undisturbed boundary layer.…”

Section: Momentum Deficit and Log-layermentioning

confidence: 99%

“…The instantaneous flow organization shows the presence of a train of arc-shaped vortices at the edge of the wake due to the K-H instability. In the downstream wake region of the micro-ramp, the K-H instability at the upper shear layer further develops with the onset of vortex pairing (Sun et al 2014b). In a more recent numerical study, Sun et al (2014a) also investigated the temporal evolution of the latter vortices, concluding that the onset of arc-like vortices pairing and connection at the bottom in the downstream region contributes to the distortion of the streamwise counter-rotating vortex pair.…”

Section: Introductionmentioning

confidence: 98%

Boundary layer transition mechanisms behind a micro-ramp

Schrijer

Scarano

2016

J. Fluid Mech.

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The early stage of three-dimensional laminar-to-turbulent transition behind a micro-ramp is studied in the incompressible regime using tomographic particle image velocimetry. Experiments are conducted at supercritical micro-ramp height h based Reynolds number Re h = 1170. The measurement domain encompasses 6 ramp widths spanwise and 73 ramp heights streamwise. The mean flow topology reveals the underlying vortex structure of the wake flow with multiple pairs of streamwise counter-rotating vortices visualized by streamwise vorticity. The primary pair generates a vigorous upwash motion in the symmetry plane with a pronounced momentum deficit. A secondary vortex pair is induced closer to the wall. The tertiary and even further vortices maintain a streamwise orientation, but are produced progressively outwards of the secondary pair and follow a wedge-type pattern. The instantaneous flow pattern reveals that the earliest unstable mode of the wake features arc-like Kelvin-Helmholtz (K-H) vortices in the separated shear layer. Under the influence of the K-H vortices, the wake exhibits a high level of fluctuations with a pulsatile mode for the streamwise momentum deficit. The K-H vortices are lifted up due to the upwash induced by the quasi-streamwise vortex pair, while they appear to undergo pairing, distortion and finally breakdown. Immediately downstream, a streamwise interval of relatively low vortical activity separates the end of the K-H region from the formation of new hairpin vortices close to the wall. The latter vortex structures originate from the region of maximum wall shear, induced by the secondary vortex pair causing strong ejection events which transport low-speed flow upwards. The whole pattern features a cascade of hairpin vortices along a turbulent/non-turbulent interface. The wedge-shaped cascade signifies the formation of a turbulent wedge. The turbulent properties of the wake are inspected with the spatial distribution of the velocity fluctuations and turbulence production in the developing boundary layer. Inside the wedge region, the velocity fluctuations approach quasi-spanwise homogeneity, indicating the development towards a turbulent boundary layer. The wedge interface is characterized by a localized higher level of velocity fluctuations and turbulence production, associated to the deflection of the shear layer close to the wall and the onset of coherent hairpin vortices inducing localized large-scale ejections.

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