A vortex element representation of two-dimensional unsteady separated flow fields

1994 ◽  
Author(s):  
Stephen Huyer ◽  
John Grant ◽  
James Uhlman
Keyword(s):  
Separated Flow ◽  
Flow Fields ◽  
Two Dimensional ◽  
Vortex Element ◽  
Unsteady Separated Flow

Influence of Airflow Separation on the Turbulent Flow Structure Over Wind-Generated Water Waves

2009 ◽  
Author(s):  
Nasiruddin Shaikh ◽  
Kamran Siddiqui
Keyword(s):  
Reynolds Stress ◽  
Flow Separation ◽  
Water Waves ◽  
Separated Flow ◽  
Flow Fields ◽  
Velocity Fields ◽  
Transport Processes ◽  
Wave Crest ◽  
Two Dimensional ◽  
Momentum Exchange

An experimental study is conducted to investigate the airside flow behavior within the crest-trough region over wind generated water waves. Two-dimensional velocity fields in a plane perpendicular to the surface were measured using particle image velocimetry (PIV). The experiments were conducted in a wind wave flume 0.45 m wide, 0.9 m high and 3 m long. The measurements were made at a fetch of 2.1 m and at the wind speeds of 3.7 and 4.4 m s−1. An algorithm was developed to segregate separated and non-separated velocity fields within the measured dataset. The results show lower magnitudes of the streamwise velocity and higher magnitudes of Reynolds stress and turbulent kinetic energy for the separated flow fields than that for the non-separated flow fields, indicating that the flow separation significantly enhances turbulence in the near surface region. The enhanced Reynolds stress is positive which indicates that the flow separation increases downward momentum transfer from wind to the wave. The two dimensional plot of instantaneous velocity showed that the separation vortices are restricted to the region bounded by the wave crest and trough. The presented results demonstrate that the flow separation plays a significant role in the interfacial transport processes and therefore, it can be concluded that the understanding of the airflow field within the crest-trough region is vital to improve our knowledge about the air-water heat, mass and momentum exchange.

DNS of Two-Dimensional Unsteady Separated Flow and Heat Transfer Around an Inclined Downward Step

2004 ◽  
Vol 2004 (0) ◽  
pp. 79-80
Author(s):  
Aya KITOH ◽  
Eiji NAKAO ◽  
Kazuaki SUGAWARA ◽  
Hiroyuki YOSHIKAWA ◽  
Terukazu OTA
Keyword(s):  
Heat Transfer ◽  
Separated Flow ◽  
Two Dimensional ◽  
Flow And Heat Transfer ◽  
Unsteady Separated Flow

Computation of Unsteady Separated Flow Fields Using Anisotropic Vorticity Elements

1996 ◽  
Vol 118 (4) ◽  
pp. 839-849 ◽  
Author(s):  
S. A. Huyer ◽  
J. R. Grant
Keyword(s):  
Experimental Data ◽  
Velocity Field ◽  
Separated Flow ◽  
Flow Fields ◽  
Single Element ◽  
Force Coefficient ◽  
Pitching Airfoil ◽  
Advection Term ◽  
Vorticity Production ◽  
Unsteady Separated Flow

A novel computational methodology to compute two-dimensional unsteady separated flow fields using a vorticity based formulation is presented. Unlike traditional vortex methods, the elements used in this method are designed to take advantage of the natural anisotropy of most external flows. These vortex elements are disjoint and of compact support. The vorticity is uniform over rectangular elements whose initial thickness is set by a diffusion length scale. The elements are a mathematical construction which enables the vorticity of the flow to be created and followed numerically, and the Biot-Savart integral to be performed. This integral specifies the associated velocity field. Since the vorticity of a single element is of finite extent, the velocity associated with an element is given by a nonsingular expression. Viscous diffusion effects are modeled using random walk and the advection term is computed by transporting the vorticity elements with the local velocity field. Consequently, this Lagrangian mesh continually evolves through time. Since pressure does not explicitly appear in the formulation, surface pressures are computed using a stagnation enthalpy formulation. These elements are used to compute vorticity production, accumulation, transport and viscous diffusion mechanisms for unsteady separated flow fields past a pitching airfoil. Dynamic stall vortex initiation and development were examined and compared with existing experimental data. Surface pressure data and integrated force coefficient data were found to be in excellent agreement with experimental data. Effects of geometry were provided with baseline calculations of the unsteady flow past an impulsively started cylinder. Both qualitative and quantitative comparisons with experimental data for equivalent test conditions establish the applicability of this approach to depict unsteady separated flow fields.

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