Investigation of transition and separation in the presence of free-stream turbulence using direct numerical simulations

Shirzad Hosseinverdi, Hermann F. Fasel

Research output: Contribution to conferencePaperpeer-review

3 Scopus citations

Abstract

Flow separation for a flat plate boundary layer in the presence of free-stream turbulence (FST) is investigated using Direct Numerical Simulations (DNS) based on the incompressible Navier-Stokes equations. To induce separation on the flat plate, a suction/blowing velocity distribution is applied along the upper boundary of the computational domain. The suction/blowing velocity distribution is chosen such that the resulting downstream pressure gradient closely matches that of accompanying water-tunnel experiments where the bubble was generated by an airfoil-shape displacement body in the free stream4, 23. First, two-and three-dimensional DNS were performed without free-stream turbulence. Flow transition cannot occur, of course, for 2-D DNS. However, transition to turbulence was also not observed in the 3-D simulation and the bubble was much longer than in the experiments. In the water-tunnel experiments free-steam turbulence, albeit small, is present of course, which will accelerate transition, and as consequence, reduce the size of the separation bubble. Therefore it can be concluded that the background disturbances in our numerical simulation, which originate from round-off and truncation errors, were not sufficient to reproduce "realistic" separation bubbles. To investigate the effect of free-stream turbulence, a numerical model for generating isotropic grid turbulence is employed for our 3-D simulations. For a simulated low level of free-stream turbulence (0.08%), the separation length is significantly reduced in comparison to the undisturbed (no FST) case and good agreement with the experimental data is obtained. Based on detailed analysis of the timedependent flow field and linear stability theory (LST) calculations, indications are that the dominant mechanism causing transition in the bubble is due to an inviscid Kelvin-Helmholtz instability of the inflectional velocity profile in the separated flow region.

Original languageEnglish (US)
StatePublished - Dec 1 2012
Event50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition - Nashville, TN, United States
Duration: Jan 9 2012Jan 12 2012

Other

Other50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition
CountryUnited States
CityNashville, TN
Period1/9/121/12/12

ASJC Scopus subject areas

  • Aerospace Engineering

Fingerprint Dive into the research topics of 'Investigation of transition and separation in the presence of free-stream turbulence using direct numerical simulations'. Together they form a unique fingerprint.

Cite this