The Effects of a Tripped Turbulent Boundary Layer on Vortex Shedding from a Blunt Trailing Edge Hydrofoil

Abstract

Experiments on vortex shedding from a blunt trailing edge symmetric hydrofoil operating at zero angle of attack in a uniform high speed flow, Reh=16.1·103-96.6·103, where the reference length h is the trailing edge thickness, are reported. The effects of a tripped turbulent boundary layer on the wake characteristics are analyzed and compared with the condition of a natural turbulent transition. The foil surface is hydraulically smooth and a fully effective boundary layer tripping at the leading edge is achieved with the help of a distributed roughness. The vortex shedding process is found to be strongly influenced by the boundary layer development: the tripped turbulent transition promotes the re-establishment of organized vortex shedding. In the context of the tripped transition and in comparison with the natural one, significant increases in the vortex span-wise organization, the vortex-induced hydrofoil vibration, the wake velocity fluctuations, and the vortex strength are revealed. Although the vortex shedding frequency is decreased, a modified Strouhal number based on the wake width at the end of the vortex formation region is constant and evidences the similarity of the wakes in terms of spatial distribution for the two considered boundary layer transition processes.

Numerical Investigation on Vortex Shedding from a Hydrofoil with a Beveled Trailing Edge

“…Ausoni [10] (also refer to Zobeiri et al [11]) had a similar finding and experimentally gave St = 0.25, which may be approximately read from their figure. They used a hydrofoil with a 100 mm chord length and 150 mm span length.…”

“…This hydrofoil has the same cross-section as the experimental model used by Ausoni et al [9], Ausoni [10], and Zobeiri et al [11]. Ten percent of the original chord was removed from the trailing-edge region of the NACA 0009 hydrofoil.…”

“…The hydrofoil geometry is further detailed in Ausoni [10]. The maximum thickness, as normalized by the chord length , is max / = 0.1 and the thickness at the trailing edge TE / is 0.0322.…”

“…Ausoni et al [9] performed laboratory-scale experiments to investigate the von Kármán vortex street generated in the wake of a 2D hydrofoil with a truncated trailing edge. Their experiments were performed at a zero angle of attack for a Reynolds number ranging from 5.0 × 10 5 to 2.0 × 10 6 , based on the hydrofoil chord length [9,10]. Their experimental results showed that a lock-in phenomenon occurs, where the vortex shedding frequency is locked onto the natural frequency of a hydrofoil.…”

“…With these numerical schemes, we numerically investigate vortex shedding from various beveled trailing edges of a NACA 0009 hydrofoil at a Reynolds number of 10 6 . We then compare our numerical results with experimental data [10,11] to assess the capability of our numerical methodology. In addition, we investigate the influence of periodically varying free-stream flows on vortex shedding to better understand the vortex shedding mechanism.…”