Separated Shear Layer Transition at Low Reynolds Numbers: Experiments and Stability Analysis

2007 ◽  
Author(s):  
Serhiy Yarusevych ◽  
John Kawall ◽  
Pierre Sullivan
Keyword(s):  
Stability Analysis ◽  
Shear Layer ◽  
Reynolds Numbers ◽  
Layer Transition ◽  
Low Reynolds Numbers ◽  
Separated Shear Layer ◽  
Low Reynolds

Separated-Shear-Layer Development on an Airfoil at Low Reynolds Numbers

AIAA Journal ◽  
2008 ◽  
Vol 46 (12) ◽  
pp. 3060-3069 ◽  
Author(s):  
Serhiy Yarusevych ◽  
John G. Kawall ◽  
Pierre E. Sullivan
Keyword(s):  
Shear Layer ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Separated Shear Layer ◽  
Low Reynolds ◽  
Layer Development

scholarly journals On vortex shedding from an airfoil in low-Reynolds-number flows

2009 ◽  
Vol 632 ◽  
pp. 245-271 ◽  
Author(s):  
SERHIY YARUSEVYCH ◽  
PIERRE E. SULLIVAN ◽  
JOHN G. KAWALL
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Vortex Shedding ◽  
Coherent Structures ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Frequency Scaling ◽  
Separated Shear Layer ◽  
Low Reynolds Number Flows ◽  
Low Reynolds

Development of coherent structures in the separated shear layer and wake of an airfoil in low-Reynolds-number flows was studied experimentally for a range of airfoil chord Reynolds numbers, 55 × 103 ≤ Rec ≤ 210 × 103, and three angles of attack, α = 0°, 5° and 10°. To illustrate the effect of separated shear layer development on the characteristics of coherent structures, experiments were conducted for two flow regimes common to airfoil operation at low Reynolds numbers: (i) boundary layer separation without reattachment and (ii) separation bubble formation. The results demonstrate that roll-up vortices form in the separated shear layer due to the amplification of natural disturbances, and these structures play a key role in flow transition to turbulence. The final stage of transition in the separated shear layer, associated with the growth of a sub-harmonic component of fundamental disturbances, is linked to the merging of the roll-up vortices. Turbulent wake vortex shedding is shown to occur for both flow regimes investigated. Each of the two flow regimes produces distinctly different characteristics of the roll-up and wake vortices. The study focuses on frequency scaling of the investigated coherent structures and the effect of flow regime on the frequency scaling. Analysis of the results and available data from previous experiments shows that the fundamental frequency of the shear layer vortices exhibits a power law dependency on the Reynolds number for both flow regimes. In contrast, the wake vortex shedding frequency is shown to vary linearly with the Reynolds number. An alternative frequency scaling is proposed, which results in a good collapse of experimental data across the investigated range of Reynolds numbers.

Low-Reynolds-Number Instability of the Laminar Flow Between Wavy Walls

2008 ◽  
Author(s):  
Tomasz A. Kowalewski ◽  
Jacek Szumbarski ◽  
Slawomir Blonski
Keyword(s):  
Stability Analysis ◽  
Flow Resistance ◽  
Unstable Mode ◽  
Reynolds Numbers ◽  
Remarkable Feature ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Preliminary Experimental Data ◽  
The Stability ◽  
Corrugated Wall

Instability of a viscous incompressible flow in a channel with wavy walls is investigated theoretically, numerically and experimentally. Linear stability analysis shows that appropriately chosen wall waviness leads to flow destabilization at surprisingly low Reynolds numbers. The unstable mode of disturbances forms a vortex array, which travels downstream. The remarkable feature is that the most destabilizing waviness does not introduce any additional flow resistance. The outcome of the stability analysis are consistent with the result of direct numerical simulation obtained using CFD finite volume package FLUENT (Ansys Inc.). Preliminary experimental data gained for a channel with appropriately corrugated wall seem to confirm these predictions.

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