The present study thoroughly investigates the spanwise topology and streamwise evolution of a divergent trailing edge airfoil (DTE) configuration that combines boundary layer growth and wake dynamics. The near wake topology was examined versus different levels of free stream turbulence and angles of attack, while the downstream development was investigated versus different levels of free stream turbulence (FST). The present results for the DTE airfoil indicate that the FST effects significantly change the second order turbulence statistics profiles and play a key role in the reduction of von Karman vortices strength and the acceleration of the wake transition towards the far wake state and thus selfpreservation. However, the primary vortex shedding Strouhal number remains insensitive to their variations. Quasi-periodical spanwise variations in the mean velocity and turbulence intensities were observed for the smooth inlet flow condition, these variations were attributed to the passage of organized streamwise vortical structures (ribs). The results suggest that the statistical spanwise distribution of ribs is independent of inlet and geometrical conditions (i.e., angle of attack) effects as long as the vortex shedding Strouhal number remains approximately similar. This strengthens the argument that the secondary shear layer instability is amplified by disturbances of comparable wavelength to the Kelvin Hemholtz instability. Phase averaged velocity vectors obtained from simultaneous multi-hot-wire measurements indicated the existence of these streamwise vorticies and also that their arrangement is topologically similar to Williamson's mode B for circular cylinder laminar wake. Moreover, the present results indicate that while the spanwise wavelength lambda increases when the Strouhal number (St) decreases, the two parameters are not just simply inversely proportional, with nonlinear effects influencing their behavior and thus lambada is proportional to f(1/St).
Three-dimensional wake dynamics of a blunt and divergent trailing edge airfoil
Dreidimensionale Nachlaufströmungsdynamik eines stumpfen und divergenten Hinterkantenströmungsprofils
Experiments in Fluids ; 44 , 5 ; 705-718
2008
14 Seiten, 12 Bilder, 37 Quellen
Article (Journal)
English
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