Leading-edge roughness as a transition control mechanism

Saric, William S.; Carrillo, Ruben; Reibert, Mark S.

doi:10.2514/6.1998-781

Cited by 167 publications

(150 citation statements)

References 11 publications

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“…It is interesting to observe that, regardless of the disturbance wavelength, crossflow disturbances with sufficiently large initial amplitude exhibit a peak in the fundamental amplitude, followed by a significant decrease in fundamental amplitude in the immediately downstream region. In other words, no extended regions of quasi-saturation observed for the lower Reynolds number, NLF-0415(b) configuration [3,7] are noted in the present case. Figure 2 illustrates a typical sequence of velocity contours during the nonlinear evolution of an unstable crossflow mode.…”

Section: Stationary Crossflow Vortices and Effect Of Controlcontrasting

confidence: 53%

“…All of the results presented in this paper correspond to the inboard measurement location at Test Point 27 [3]. For this case, the Reynolds number Re c based on the free-stream velocity and the streamwise chord length is equal to 7.15x10 6 and the angle of attack over the test article is -4.69 degrees.…”

Section: Flow Configuration and Analysis Codesmentioning

confidence: 99%

“…One of those concepts involves the delay of crossflow-induced transition over a swept aerodynamic surface using control input in the form of appropriately positioned Discrete Roughness Elements (DREs) near the leading edge [3]. A bulk of the existing experimental and computational studies of the DRE concept have been carried out for either incompressible or supersonic configurations with modest wing-chord Reynolds numbers of up to approximately 8 million [4,5], and with pressure distributions that may or may not be optimal for wing designs for subsonic transport aircraft flying at Mach numbers between 0.75 to 0.90.…”

Section: Introductionmentioning

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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Section: Stationary Crossflow Vortices and Effect Of Controlcontrasting

confidence: 53%

Section: Flow Configuration and Analysis Codesmentioning

confidence: 99%

Section: Introductionmentioning

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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“…These campaigns made use of very quiet wind tunnels, exhibiting a free stream turbulence level typically lower than 0.1% of the free stream velocity. Surface flow visualisation was performed by means of infrared thermography (Saric et al 2011), hydrogen bubbles tracing (Bippes Three-dimensional organisation of primary and secondary crossflow instability 3 1999), naphthalene sublimation techniques (Dagenhart et al 1989;Saric et al 1998;White & Saric 2000) and fluorescent mineral oil (Serpieri & Kotsonis 2015a,b). Hotwire anemometry (HWA) boundary layer measurements were performed using precision sensor traversing systems (e.g.…”

Section: Background and Present Workmentioning

confidence: 99%

“…These observations were at the base of the study done by Saric et al (1998) and White & Saric (2000), centred on the idea of forcing a subcritical mode, which is a mode with a wavelength smaller than that of the most amplified mode. The experiment of Saric et al (1998), done at the same flow conditions as the one of Reibert et al (1996), led to the remarkable conclusion that subcritical forcing can delay transition to turbulence for stationary crossflow instability boundary layers.…”

Section: Primary Instabilitymentioning

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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