Instabilities of Decaying Flow in a Rectangular Channel

Ramalingam, N.; Das, S. P.

doi:10.1007/s40032-020-00590-7

Cited by 1 publication

(3 citation statements)

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“…The effects of spatial and temporal pressure gradient conditions on vortex formation and associated instabilities have been extensively examined experimentally under trapezoidal mean flow conditions coupled with various geometrical configurations (Das & Arakeri 1998;Das et al 2013Das et al , 2016Ramalingam & Das 2020). Trapezoidal flows, in contrast to pulsating ones, are appropriate for investigating the effects of constant acceleration and deceleration on flow dynamics.…”

Section: Introductionmentioning

confidence: 99%

“…Das et al (2013) analysed flow structures originating from bluff bodies and critical time scales for similar mean flow conditions. Recently, Ramalingam & Das (2020) performed a detailed visualization study on the flow structures in a water channel flow using direct visualization and particle image velocimetry. Das et al (2016) conducted a fascinating experimental investigation in a diverging water channel to investigate the transition mechanism in APG conditions.…”

Section: Introductionmentioning

confidence: 99%

“…(2013) analysed flow structures originating from bluff bodies and critical time scales for similar mean flow conditions. Recently, Ramalingam & Das (2020) performed a detailed visualization study on the flow structures in a water channel flow using direct visualization and particle image velocimetry. Das et al.…”

Section: Introductionmentioning

confidence: 99%

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The onset of turbulence in decelerating diverging channel flows

Sarath

Manu

2023

J. Fluid Mech.

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This work investigates the stability and transition to turbulence in a diverging channel subjected to a time-varying trapezoidal-shaped inflow boundary condition. Numerical simulations are performed for different deceleration rates and Reynolds numbers while maintaining a constant acceleration rate. The flow transition begins with two-dimensional primary instability with the formation of inflectional velocity profiles, followed by local separation and the emergence of an array of shear layer vortices. We divide simulation cases systematically into three categories based on the onset of secondary instability and the generation of streamwise vorticity. At low and medium Reynolds numbers (type I), the spanwise vortex rolls formed by inflectional instability remain two-dimensional and diffuse at the channel centre without exhibiting further instabilities. At high Reynolds numbers and deceleration rates (type II), the rolled shear layer exhibits secondary instability during the zero mean inflow phase, followed by local incipient turbulent structure formation. The streamwise vorticity that develops over the shear layer structures causes oscillations with a spanwise wavelength similar to those associated with the elliptic instability in a counter-rotating vortex pair. Using the Lamb–Oseen approximation of vortices in conjunction with the dynamic mode decomposition algorithm of the three-dimensional flow field, we captured successfully the characteristics of the secondary instability. The third category (type III) is characterized by periodic unsteady separation, secondary instability, and merging of shear layer vortices, which occurs when Reynolds numbers are high and deceleration rates are low.

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Section: Introductionmentioning

confidence: 99%