Separated-Flow Transition: Part 2 — Experimental Results

Abstract

The present paper focuses on presenting the results of the experimental investigation of the transition process in separated boundary layers on a flat plate at zero incidence, with imposed adverse pressure gradients. The combined effects of Reynolds number and adverse pressure gradient strength on the transition mechanism, bubble geometry, and bubble bursting process are studied. The flow structures and the unsteady aspects associated with separated-flow transition are analyzed for three representative experimental cases. Surface pressure results and detailed boundary layer measurements using hot-wire anemometry are presented as mean and rms velocity profiles, and Reynolds shear stress distribution. Turbulent intermittency and spectral analysis results are briefly introduced.

Wall-resolved large eddy simulation for aeroengine aeroacoustic investigation

“…According to Hatman and Wang (20) , this is a typical laminar separationshort bubble transition mode, dominated by the Kelvin-Helmholtz (K-H) instability. Hatman and Wang (16) found the maximum value of the rms velocity for this transition mode was approximately 0.18, which is similar to the present compressible NLES results of approximately 0.17, found in the region around the reattachment point x/C = 0.98.…”

“…A typical value of H at separation in a laminar boundary layer is approximately 3.5 (20) . As Hatman and Wang (16) reported, H reaches a maximum value in the region around the maximum displacement of the separated shear layer x MD . From Fig.…”

“…7 at location x/C = 0.86.

Figure 9. Separated boundary-layer profile distortion by hot-wire measurements, Hatman and Wang (16) .

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“…The maximum displacement (MD) area is located at x/C 0.86-0.88, and the transition region is located at . Separated boundary-layer profile distortion by hot-wire measurements, Hatman and Wang (16) .…”

Numerical investigations of separation-induced transition on high-lift low-pressure turbine using RANS and LES methods

“…He also tried to identify critical parameters for the bursting onset and showed that for the longer bubbles and low freestream turbulence, much of the flow within the bubble is laminar and Tollmien-Schlichting instabilities have been observed. The phenomenon of transition triggered by separation bubble was also described by Hatman and Wang [5] [6][7] [8]. For constant freestream conditions (turbulence intensity and adverse pressure gradient) when lowering the Reynolds number the bubble size increases.…”