Time-resolved PIV investigations on the laminar-turbulent transition over laminar separation bubbles

2009 ◽  
pp. 177-182
Author(s):  
Rainer Hain ◽  
Christian J. Kähler ◽  
Rolf Radespiel
Keyword(s):  
Time Resolved ◽  
Laminar Separation ◽  
Turbulent Transition ◽  
Separation Bubbles ◽  
Laminar Turbulent Transition ◽  
Laminar Separation Bubbles

scholarly journals On the Calculation of Laminar Separation Bubbles Using Different Transition Models

1997 ◽  
Author(s):  
Wolfgang Sanz ◽  
Max F. Platzer
Keyword(s):  
Transition Process ◽  
Navier Stokes ◽  
Laminar Separation ◽  
Controlled Diffusion ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Separation Bubbles ◽  
Turbomachinery Blades ◽  
Transition Models ◽  
Laminar Separation Bubbles

Laminar separation bubbles are commonly observed on turbomachinery blades and therefore require effective methods for their prediction. The location and size of the bubbles is critically dependent on the laminar-to-turbulent transition process. Therefore, in this paper the transition models of Solomon et al., Abu-Ghannam & Shaw, Mayle, Calvert, and Choi & Kang are incorporated into an upwind-biased Navier-Stokes solver and the computed results are compared with the measurements of Elazar & Shreeve in a cascade with controlled-diffusion blades. It is found that none of the models predicts the measured bubbles very well, although most of them give reasonable results as long as transition is predicted to occur within the bubble.

scholarly journals On the Navier-Stokes Calculation of Separation Bubbles With a New Transition Model

1996 ◽  
Author(s):  
Wolfgang Sanz ◽  
Max F. Platzer
Keyword(s):  
Navier Stokes ◽  
Transition Model ◽  
Compressor Cascade ◽  
Laminar Separation ◽  
Turbulent Transition ◽  
Separation Bubbles ◽  
Turbomachinery Blades ◽  
Naca 0012 ◽  
Onset Location ◽  
Laminar Separation Bubbles

Laminar separation bubbles are commonly observed on turbomachinery blades and therefore require effective methods for their prediction. Therefore, a newly developed transition model by Gostelow et al. (1995) is incorporated into an upwind-biased Navier-Stokes code to simulate laminar-turbulent transition in the boundary layer. A study of the influence of the two adjustable parameters of the model, the transition onset location and the spot generation rate, is conducted and it is found that it can predict laminar separation bubbles, measured on a NACA 0012 airfoil. Additional results are presented for separation bubbles in an annular compressor cascade.

On the Navier–Stokes Calculation of Separation Bubbles With a New Transition Model

1998 ◽  
Vol 120 (1) ◽  
pp. 36-42 ◽  
Author(s):  
W. Sanz ◽  
M. F. Platzer
Keyword(s):  
Navier Stokes ◽  
Transition Model ◽  
Compressor Cascade ◽  
Laminar Separation ◽  
Turbulent Transition ◽  
Separation Bubbles ◽  
Turbomachinery Blades ◽  
Naca 0012 ◽  
Onset Location ◽  
Laminar Separation Bubbles

Laminar separation bubbles are commonly observed on turbomachinery blades and therefore require effective methods for their prediction. Therefore, a newly developed transition model by Gostelow et al. (1996) is incorporated into an upwind-biased Navier–Stokes code to simulate laminar—turbulent transition in the boundary layer. A study of the influence of the two adjustable parameters of the model, the transition onset location and the spot generation rate, is conducted and it is found that it can predict laminar separation bubbles, measured on a NACA 0012 airfoil. Additional results are presented for separation bubbles in an annular compressor cascade.

Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jet effects

2012 ◽  
Vol 53 (1) ◽  
pp. 173-186 ◽  
Author(s):  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini
Keyword(s):  
Synthetic Jet ◽  
Laminar Separation ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

Dynamic Stall Flow Structure and Forces on Symmetrical Airfoils at High Angles of Attack and Rotation Rates

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
R. R. Leknys ◽  
M. Arjomandi ◽  
R. M. Kelso ◽  
C. H. Birzer
Keyword(s):  
Flow Structure ◽  
Boundary Layer Separation ◽  
Vortex Structures ◽  
Dynamic Stall ◽  
Aerodynamic Load ◽  
Laminar Separation ◽  
Rotation Rates ◽  
Constant Pitch ◽  
Separation Bubbles ◽  
Laminar Separation Bubbles

This article describes a direct comparison between two symmetrical airfoils undergoing dynamic stall at high, unsteady reduced frequencies under otherwise identical conditions. Particle image velocimetry (PIV) was performed to distinguish the differences in flow structure between a NACA 0021 and a NACA 0012 airfoil undergoing dynamic stall. In addition, surface pressure measurements were performed to evaluate aerodynamic load and investigate the effect of laminar separation bubbles and vortex structures on the pressure fields surrounding the airfoils. Airfoil geometry is shown to have a significant effect on flow structure development and boundary layer separation, with separation occurring earlier for thinner airfoil sections undergoing constant pitch-rate motion. Inertial forces were identified to have a considerable impact on the overall force generation with increasing rotation rate. Force oscillation was observed to correlate with multiple vortex structures shedding at the trailing-edge during high rotation rates. The presence of laminar separation bubbles on the upper and lower surfaces was shown to dramatically influence the steady-state lift of both airfoils. Poststall characteristics are shown to be independent of airfoil geometry such that periodic vortex shedding was observed for all cases. However, the onset of deep stall is delayed with increased nondimensional pitch rate due to the delay in initial dynamic-stall vortex.

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