Stability characteristics of stationary crossflow vortices in three-dimensional boundary layer

Kawakami, Mitsuyoshi; Kohama, Yasuaki; Okutsu, Makoto

doi:10.2514/6.1999-811

Cited by 43 publications

(87 citation statements)

References 6 publications

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“…The axes of these structures form a considerable angle with the one of the primary waves and the spinning direction of the two modes is opposite. An interesting outcome of the simulations of Wassermann & Kloker (2002 is that, when the unsteady disturbance that triggers the secondary modes is switched off, the associated structures are advected downstream, thus confirming the findings of Kawakami et al (1999) and (Koch 2002) regarding the convective nature of these instability modes.…”

Section: Secondary Instabilitysupporting

confidence: 63%

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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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Section: Secondary Instabilitysupporting

confidence: 63%

“…Hotwire anemometry (HWA) boundary layer measurements were performed using precision sensor traversing systems (e.g. Reibert et al (1996); Deyhle & Bippes (1996); Kawakami et al (1999); White & Saric (2005)). Glauser et al (2014) reported the use of hot-film surface sensors.…”

Section: Background and Present Workmentioning

confidence: 99%

Three-dimensional organisation of primary and secondary crossflow instability

2016

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“…As shown in Figure 7, the presence of the control mode apparently affects the Z-mode of secondary instability much more than the Y-mode. This indicates that, if indeed transition is caused by the growth of the Z-mode as some experiments seem to suggest [17,18], the DRE is a very effective means to achieve transition delay in the present case.…”

Section: Linear Secondary Instability and Effect Of Controlmentioning

confidence: 83%

“…Of course, the receptivity characteristics of each of these modes will determine whether or not that mode gets excited with an adequately large initial amplitude in order to have a visible influence on the transition process. For example, previous experimental studies [17,18] indicate a preferential excitation of the z modes under certain conditions. Given this scenario, it seems prudent to track the N-factor envelopes for each mode family separately rather than a single envelope for all secondary instability modes.…”

Section: Linear Secondary Instability and Effect Of Controlmentioning

confidence: 99%

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Roughness Based Crossflow Transition Control: A Computational Assessment

Choudhari

Chang

et al. 2009

27th AIAA Applied Aerodynamics Conference

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A combination of parabolized stability equations and secondary instability theory has been applied to a low-speed swept airfoil model with a chord Reynolds number of 7.15 million, with the goals of (i) evaluating this methodology in the context of transition prediction for a known configuration for which roughness based crossflow transition control has been demonstrated under flight conditions and (ii) of analyzing the mechanism of transition delay via the introduction of discrete roughness elements (DRE). Roughness based transition control involves controlled seeding of suitable, subdominant crossflow modes, so as to weaken the growth of naturally occurring, linearly more unstable crossflow modes. Therefore, a synthesis of receptivity, linear and nonlinear growth of stationary crossflow disturbances, and the ensuing development of high frequency secondary instabilities is desirable to understand the experimentally observed transition behavior. With further validation, such higher fidelity prediction methodology could be utilized to assess the potential for crossflow transition control at even higher Reynolds numbers, where experimental data is currently unavailable.

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