Phase-resolved characterization of vortex shedding in the near wake of a square-section cylinder at incidence

Oudheusden, B.W. van; Scarano, Fulvio; Hinsberg, Nils Paul van; Watt, David W.

doi:10.1007/s00348-005-0985-5

Cited by 332 publications

(174 citation statements)

References 20 publications

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“…This approach has proven successful in characterizing the vortex shedding process in low-speed near wakes. 54 No significant correlation could be found, however, between any of the temporal coefficients considered in the present study. This is thought to be the result of variations in the cyclic vortex shedding process induced by the small-scale velocity fluctuations, or turbulence within the flow, as well as the presence of random noise and occasional poor data quality associated with the experimental data.…”

Section: ͑13͒contrasting

confidence: 64%

“…More specifically, the eigenmodes at Mach 1.46 display distinct regions of relatively large velocity fluctuations of alternating sign, indicative of the train of quasistreamwise vortices associated with a convected vortex street. 54 Here, pairing occurs between several of these eigenmodes ͑e.g., eigenmodes 5 and 6͒. This pairing can be explained by the fact that the mechanism of the sinuous mode can be represented by a traveling wave composed of eigenmodes in phase quadrature.…”

Section: -11mentioning

confidence: 99%

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Unsteady flow organization of compressible planar base flows

2007

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The unsteady flow features of a series of two-dimensional, planar base flows are examined, within a range of low-supersonic Mach numbers in order to gain a better understanding of the effects of compressibility on the organized global dynamics. Particle image velocimetry is used as the primary diagnostic tool in order to characterize the instantaneous near wake behavior, in combination with data processing using proper orthogonal decomposition. The results show that the mean flowfields are simplified representations of the instantaneous flow organizations. Generally, each test case can be characterized by a predominant global mode, which undergoes an evolution with compressibility, within the Mach number range considered. ͑The term "global mode" is defined herein as an organized global dynamical behavior of the near wake region, recognizing that the near wake dynamics may be describable in terms of several global modes.͒ At Mach 1.46, the predominant global mode can be characterized by a sinuous or flapping motion. With increasing compressibility, this flapping mode decreases, and the predominant global mode evolves into a pulsating motion aligned with the wake axis at Mach 2.27. These global modes play an important role in the distributed nature of the turbulence properties. The turbulent mixing processes become increasingly confined to a narrower redeveloping wake with increasing compressibility. Global maximum levels of the streamwise turbulence intensity and the kinematic Reynolds shear stress occur within the vicinity of the mean reattachment location, and show no systematic trend with compressibility. In contrast, the global maximum level of the vertical turbulence intensity moves upstream from the redeveloping wake toward the mean reattachment location. The vertical turbulence intensity decays thereafter more slowly than the other turbulence quantities. Overall, the local maximum levels of the turbulence properties decrease appreciably with increasing compressibility.

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Section: ͑13͒contrasting

confidence: 64%

Section: -11mentioning

confidence: 99%

Unsteady flow organization of compressible planar base flows

2007

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“…In particular, this symmetric layout is observed for (quasi)-two-dimensional (2D) cylinders placed perpendicular to the freestream direction (see, e. g., [1]), since this geometry is ambiguous towards the incidence angle of attack. In contrast, van Oudheusden et al [2] investigate a 2D body with square cross section, revealing distinct changes in the structure of the wake for di¨erent angles of attack in the range of 0 • to 15 • . The wake of three-dimensional (3D), cylindrical geometries placed in freestream direction can be interpreted as a rotationally symmetric, toroidal extension of 2D test cases.…”

Section: Introductionmentioning

confidence: 93%

“…The results discussed in the current work only represent planar slices of a toroidal vortex system. The structure of this system is of great interest in case of the nonsymmetric wake layout (e. g., β = 0 • ) and is believed to add further insight to the observed phenomena, particularly as the wake of 2D blub odies in contrast seems more indi¨erent towards incidence angles [2].…”

Section: Concluding Remarks and Outlookmentioning

confidence: 99%

Base-flow sensitivity of a generic rocket forebody towards small freestream angles

Wolf

You

Hörnschemeyer

et al. 2013

Progress in Flight Physics

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Experimental and numerical investigations have been conducted regarding the wake §ow of a generic rocket model in subsonic freestream conditions. The blu¨base geometry evokes a recirculation area represented by counterrotating vortices. Experiments using Particle Image Velocimetry (PIV) demonstrate that the spatial organization of this area is heavily dependent on small freestream angles (α, β < 1 • ), associated with a signi¦cant shift in the base pressure distribution. Numerical studies using Reynolds-Averaged Navier Stokes (RANS) methods with one-and twoequation turbulence models are able to predict the mean velocity ¦eld as well as tendencies regarding α and β, but lack the sensitivity of the experiments. The mean pressure level on the base is calculated within 10% of the experimental value using the two-equation turbulence model, although the pressure distributions on the base show distinct di¨erences. NOMENCLATURE c p,baseBase pressure coef¦cient D Diameter DEHS Di-Ethyl-Hexyl-Sebacat k, TKE Turbulent kinetic energy L Model length Ma ∞

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“…A second feature stems from the fact that the sought instability modes are inherently convective (Kawakami et al 1999;Wassermann & Kloker 2002;Bonfigli & Kloker 2007). As such, the POD procedure will generate a harmonically coupled pair of POD modes, shifted by π/2, for each physical convecting coherent structure (Van Oudheusden et al 2005). Both these features have been used as selection criteria in this study in order to identify the POD modes corresponding to the relevant instability modes in the transitional boundary layer.…”

Section: Spatial Organisationmentioning

confidence: 99%

Three-dimensional organisation of primary and secondary crossflow instability

2016

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An experimental investigation of primary and secondary crossflow instability developing in the boundary layer of a 45 • swept wing, at a chord Reynolds number of 2.17·10 6 is presented. Linear stability theory is applied for preliminary estimation of the flow stability while surface flow visualisation using fluorescent oil is employed to inspect the topological features of the transition region. Hot-wire anemometry is extensively used for the investigation of the developing boundary layer and identification of the statistical and spectral characteristics of the instability modes. Primary stationary as well as unsteady type-I (z-mode), type-II (y-mode) and type-III modes are detected and quantified. Finally, three-component, three-dimensional measurements of the transitional boundary layer are performed using tomographic particle image velocimetry. This research presents the first application of an optical experimental technique for this type of flow. Among the optical techniques tomographic velocimetry represents, to date, the most advanced approach allowing the investigation of spatially correlated flow structures in threedimensional fields. Proper orthogonal decomposition (POD) analysis of the captured flow fields is applied to this goal. The first POD mode features a newly reported structure related to low-frequency oscillatory motion of the stationary vortices along the spanwise direction. The cause of this phenomenon is only conjectured. Its effect on transition is considered negligible but, given the related high energy level, it needs to be accounted for in experimental investigations. Secondary instability mechanisms are captured as well. The type-III mode corresponds to low frequency primary travelling crossflow waves interacting with the stationary ones. It appears in the inner upwelling region of the stationary crossflow vortices and is characterised by elongated structures approximately aligned with the axis of the stationary waves. The type-I secondary instability consists instead of significantly inclined structures located at the outer upwelling region of the stationary vortices. The much narrower wavelength and higher advection velocity of these structures correlate with the higher-frequency content of this mode. The results of the investigation of both primary and secondary instability from the exploited techniques agree with and complement each other and are in line with existing literature. Finally, they present the first experimental observation of the secondary instability structures under natural flow conditions.

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Phase-resolved characterization of vortex shedding in the near wake of a square-section cylinder at incidence

Cited by 332 publications

References 20 publications

Unsteady flow organization of compressible planar base flows

Unsteady flow organization of compressible planar base flows

Base-flow sensitivity of a generic rocket forebody towards small freestream angles

Three-dimensional organisation of primary and secondary crossflow instability

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