Absolute/Convective Instability Investigation of Primary and Secondary Crossflow Vortices

Bertolotti, F. P.; Hein, Stefan; Koch, Werner; Stolte, A.

doi:10.1007/978-3-540-45060-3_5

Cited by 2 publications

(1 citation statement)

References 23 publications

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“…It has been viewed that theoretical investigation of spatio-temporal evolution of instabilities in spatially periodic base flows is a challenging issue. Although the criterion for absolute instability could be derived using Floquet theory (Brevdo & Bridges 1996), its technical complexity has limited its application to only few cases for the linearized Navier-Stokes system (Bertolotti et al 2004;Pier 2007). For this reason, most of previous studies examined the spatio-temporal evolution of instabilities using numerical simulation (Brancher & Chomaz 1997;Brandt et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Stabilization of absolute instability in spanwise wavy two-dimensional wakes

2013

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Controlling vortex shedding using spanwise varying passive or active actuation (namely three-dimensional control) has recently been reported as a very efficient method for regulating two-dimensional bluff-body wakes. However, the mechanism why and how the designed controller regulates vortex shedding has not been clearly understood. To understand this mechanism, we perform a linear stability analysis of two-dimensional wakes, of which the base flow is modified with the given spanwise waviness. Absolute and convective instabilities of the spanwise wavy base flows are investigated using Floquet theory. Two types of the base-flow modification are considered: varicose and sinuous modifications. Both of the base-flow modifications attenuate absolute instability of twodimensional wakes. In particular, the varicose modification is found much more effective in the attenuation than the sinuous one, and its spanwise lengths resulting in the maximum attenuation show good agreement with those in three-dimensional controls. The physical mechanism of the stabilization is found to be associated with formation of streamwise vortices from tilting of two-dimensional Kármán vortices and the subsequent tilting of these streamwise vortices by the spanwise shear in the base flow. Finally, the sensitivity of absolute instability to spanwise wavy base-flow modification is investigated. It is shown that absolute instability of two-dimensional wakes is much less sensitive to spanwise wavy base-flow modification than to two-dimensional modification. This suggests that the high efficiency observed in several three-dimensional controls is not due to sensitive response of wake instability to the spanwise waviness in base flow.

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Section: Introductionmentioning

confidence: 99%

Stabilization of absolute instability in spanwise wavy two-dimensional wakes

2013

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Direct numerical simulation and stability analysis of the transitional boundary layer on a marine propeller blade

Jing

Ducoin

2020

Physics of Fluids

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It is generally assumed that the cross-flow instability exists on propeller blade boundary layers due to their similarity with the rotating disk flow. However, to the best of our knowledge, there is no experimental or numerical evidence that directly shows the existence of the cross-flow instability on propellers. In this paper, we present a direct numerical simulation of the boundary layer flow around a marine propeller blade. For the investigated case, the cross-flow velocity inside the attached laminar boundary layer is smaller than the rotating disk case, but it is large enough to lead to the cross-flow instability. The wave-numbers and wave-direction of the cross-flow vortices observed agree well with the prediction of linear stability theory. Linearized Navier–Stokes simulations show that the boundary layer is absolutely unstable in the radial direction but convectively unstable in the streamwise direction. A significant flow direction deviation between laminar and turbulent regions is also observed on the blade surface. In the separation bubble, there is an unusually large radial velocity (around 50% of the inviscid streamwise velocity). Both the flow direction deviation and the large radial velocity in the separation bubble can be explained by the relationship between Coriolis forces and circumferential velocities.

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Absolute/Convective Instability Investigation of Primary and Secondary Crossflow Vortices

Cited by 2 publications

References 23 publications

Stabilization of absolute instability in spanwise wavy two-dimensional wakes

Stabilization of absolute instability in spanwise wavy two-dimensional wakes

Direct numerical simulation and stability analysis of the transitional boundary layer on a marine propeller blade

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