Three-Dimensional Vortex Structure in a Leading-Edge Separation Bubble at Moderate Reynolds Numbers

Abstract

This paper describes the results of a flow visualization study which concerns three-dimensional vortex structures in a leading-edge separation bubble formed along the sides of a blunt flat plate. Dye and hydrogen bubbles were used as tracers. Reynolds number (Re), based on the plate thickness, was varied from 80 to 800. For 80 < Re < 320, the separated shear layer remains laminar up to the reattachment line without significant spanwise distortion of vortex filaments. For 320 < Re < 380, a Λ-shaped deformation of vortex filaments appears shortly downstream of the reattachment and is arranged in-phase in the downstream direction. For Re > 380, hairpin-like structures are formed and arranged in a staggered manner. The longitudinal and spanwise distances of the vortex arrangement are presented as functions of the Reynolds number.

Self-Sustained Oscillations in Flows Around Long Blunt Plates

“…No boundary layer spanwise instability was observed in the simulations with c/t"6. Flow structures similar to those classi"ed as Pattern B by Sasaki & Kiya (1991) were observed when c/t"10 and 13 at both Re"350 (see Figure 10) and 400. These were hairpin-like structures arranged in a staggered manner on both sides of the plate.…”

“…The streamwise wavelengths were approximately 3t when c/t"10 and 4t when c/t"13. Both the streamwise and spanwise wavelengths are within the range of experimental uncertainty of those observed experimentally (Sasaki & Kiya 1991). Pattern A shedding (vortices aligned) has been more di$cult to capture, possibly due to the shorter plate lengths employed in the simulations.…”

“…In addition, the formation of three-dimensional patterns in the boundary layer along the plate, and in the trailing-edge wake, are investigated. The boundary layer hairpin vortical structures are compared with those from the experiments of Sasaki & Kiya (1991) and the predicted streamwise modes in the wake are compared with those found in the case of circular cylinders (Williamson 1988;Thompson et al 1996;Barkley & Henderson 1996). …”

Effect of secondary flows due to buoyancy and contraction on heat transfer in a two-section plate-fin heat sink

“…5c. In the present configuration, the recirculation bubble attached to the flow-contracting fin sidewall, a distinctive feature of flow separation around elongated obstacles [28,29], appears distorted towards its ends due to the influence of the endwalls and forms a hairpin-shaped vortical structure (Fig. 5c).…”

Automatic Hybrid RANS/LES Strategy for Industrial CFD

“…First, a Kelvin-Helmholtz vortex shedding appear at the separation point followed by a pairing process highlighted by the hotwire techniques experiment of Troutt et al [6]. Hairpin vortices have been observed in the recirculation bubble by Kiya and Sasaki [7]. On the other side, several researcher agree in indicating the presence of another unsteady phenomenon, called flapping motion, which is a low frequency instability.…”