Numerical and Experimental Investigations of the Supersonic Microramp Wake

Sun, Zhengzhong; Scarano, Fulvio; Oudheusden, B.W. van; Schrijer, F.F.J.; Yan, Ya; Liu, Chaoqun

doi:10.2514/1.j052649

Cited by 22 publications

(12 citation statements)

References 23 publications

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“…At x/h = 15, the K-H vortices appear to grow in size and to increase their azimuthal range due to self-induction of the legs. Eventually, the leg pairs connect at the bottom to produce full ring vortices, as shown in figure 9(b) (Movie 1) and observed in previous studies (Sun et al 2014a;Yan et al 2014). The random traces of small-scale vortices near the wall (y/h < 0.5), are solely ascribed to the effect of measurement noise.…”

Section: Evolution Of K-h Vorticessupporting

confidence: 65%

“…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: 99%

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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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Section: Evolution Of K-h Vorticessupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Boundary layer transition mechanisms behind a micro-ramp

Schrijer

Scarano

2016

J. Fluid Mech.

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“…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%

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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“…Although numerical calculation with RANS method is unable to accurately predict the parameters in the boundary layer, the results can display a qualitative trend agreement well with experimental data [37,38]. Thus, comparisons and analyses of flow field characteristics based on RANS method are feasible to reveal the flow physics of ramp structure.…”

Section: Peak Efficiency Pointmentioning

confidence: 89%

Investigation on shock-induced separation loss mitigation method considering radial equilibrium in a transonic compressor rotor

Liu

Zhao

et al. 2022

Aeronaut. j.

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A shock-induced separation loss reduction method, using local blade suction surface shape modification (smooth ramp structure) with constant adverse pressure gradient with the consideration of radial equilibrium effect to split a single shock foot into multiple weaker shock wave configuration, is investigated on the NASA Rotor 37 for promoting aerodynamic performance of a transonic compressor rotor. Numerical investigation on baseline blade and improved one with blade modification on suction side has been conducted employing the Reynolds-averaged Navier–Stokes method to reveal flow physics of ramp structure. The results indicate that the passage shock foot of baseline is replaced with a family of compression waves and a weaker shock foot generating moderate adverse pressure gradient on ramp profile, which is beneficial for mitigating the shock foot and shrinking flow separation region as well. In addition, the radial secondary flow of low-momentum fluids within boundary layer is decreased significantly in the region of passage shock-wave/boundary-layer interaction on blade suction side, which mitigates the mass flow and mixing intensity of tip leakage flow. With the reduction of flow separation loss induced by passage shock, the adiabatic efficiency and total pressure ratio of improved rotor are superior to baseline model. This study herein implies a potential application of ramp profile in design method of transonic and supersonic compressors.

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Numerical and Experimental Investigations of the Supersonic Microramp Wake

Abstract: This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link

Cited by 22 publications

References 23 publications

Boundary layer transition mechanisms behind a micro-ramp

Boundary layer transition mechanisms behind a micro-ramp

Micro Vortex Generators for Boundary Layer Control: Principles and Applications

Investigation on shock-induced separation loss mitigation method considering radial equilibrium in a transonic compressor rotor

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