Structural analysis on a hemisphere-cylinder at moderate Reynolds number and high angle of attack

2013 ◽  
Author(s):  
Soledad Le Clainche Martinez ◽  
Francisco Gomez Carrasco ◽  
Ivy Li ◽  
Julio Soria ◽  
Vassilios Theofilis
Keyword(s):  
Reynolds Number ◽  
Structural Analysis ◽  
Angle Of Attack ◽  
High Angle ◽  
High Angle Of Attack ◽  
Moderate Reynolds Number

Anisotropy-Invariant Mapping of Turbulence in a Flow Past an Unswept Airfoil at High Angle of Attack

2005 ◽  
Vol 128 (3) ◽  
pp. 559-567 ◽  
Author(s):  
N. Jovičić ◽  
M. Breuer ◽  
J. Jovanović
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Separation Bubble ◽  
Flow Behavior ◽  
Angle Of Attack ◽  
High Angle ◽  
High Angle Of Attack ◽  
Fine Grid ◽  
Flow Past ◽  
Moderate Reynolds Number

Turbulence investigations of the flow past an unswept wing at a high angle of attack are reported. Detailed predictions were carried out using large-eddy simulations (LES) with very fine grids in the vicinity of the wall in order to resolve the near-wall structures. Since only a well-resolved LES ensures reliable results and hence allows a detailed analysis of turbulence, the Reynolds number investigated was restricted to Rec=105 based on the chord length c. Admittedly, under real flight conditions Rec is considerably higher (about (35-40)∙106). However, in combination with the inclination angle of attack α=18 deg this Rec value guarantees a practically relevant flow behavior, i.e., the flow exhibits a trailing-edge separation including some interesting flow phenomena such as a thin separation bubble, transition, separation of the turbulent boundary layer, and large-scale vortical structures in the wake. Due to the fine grid resolution applied, the aforementioned flow features are predicted in detail. Thus, reliable results are obtained which form the basis for advanced turbulence analysis. In order to provide a deeper insight into the nature of turbulence, the flow was analyzed using the invariant theory of turbulence by Lumley and Newman (J. Fluid Mech., 82, 161–178, 1977). Therefore, the anisotropy of various portions of the flow was extracted and displayed in the invariant map. This allowed us to examine the state of turbulence in distinct regions and provided an improved illustration of what happens in the turbulent flow. Thus, turbulence itself and the way in which it develops were extensively investigated, leading to an improved understanding of the physical mechanisms involved, not restricted to a standard test case such as channel flow but for a realistic, practically relevant flow problem at a moderate Reynolds number.

Plasma Flow Control Simulation of an Airfoil of Wind Turbine at an Intermediate Reynolds Number

2013 ◽  
Author(s):  
Hikaru Aono ◽  
Taku Nonomura ◽  
Aiko Yakeno ◽  
Kozo Fujii ◽  
Koichi Okada
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Wind Turbine ◽  
Shear Layer ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Plasma Actuator ◽  
Dominant Factor ◽  
High Angle ◽  
High Angle Of Attack

The flow over a National Renewable Energy Laboratory S825 airfoil was simulated for a chord Reynolds number of 7.5×105 and an angle of attack of 22.1 deg. These conditions approximately matched a blade element condition of 75% radius of 42-m-diameter wind turbine operating 2.5 rpm under a free-stream of 10 m/s. Computed flow of the uncontrolled case characterized massive separation from near the leading edge due to high angle of attack. With the active flow control by a dielectric barrier discharge plasma actuator, separation was reduced and the lift-to-drag ratio increased from 2.25 to 6.52. Impacts of the plasma actuator on the shear layer near the leading edge were discussed. Direct momentum addition provided by the case setup of plasma actuator considered in current study seemed to be a dominant factor to prevent the separation of shear layer near the leading edge rather than influence of small disturbances induced by the plasma actuator operated in a burst modulation. However, due to the high angle of attack and the thick airfoil, the control authority of the plasma actuator with the setup (i.e. the operating condition and number of plasma actuators installed on the wing surface) considered was insufficient to completely suppress the separation over the NREL S825 airfoil.

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