### Session LK: Multiphase Flows V

3:35 PM–5:45 PM, Monday, November 23, 2009
Room: 101J

Chair: Marios Soteriou, United Technologies Research Center

Abstract ID: BAPS.2009.DFD.LK.10

### Abstract: LK.00010 : An identification of coherent structures in an inhomogeneous turbulence

5:32 PM–5:45 PM

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#### Author:

Ryuichi Nagaosa
(RISS, AIST)

This study proposes a proper scaling of a vortex indicator for practical identification of coherent structures (CS) from an inhomogeneous wall turbulence at the Reynolds numbers of $Re_{\tau}=180$ and $400$. The Laplacian of the pressure, $\Theta$, is scaled by its time-space average $\Theta_{ave}$ and root-mean-square value $\Theta_{rms}$ to obtain a proper scaling for effective identification of CS, $\hat\Theta=\left(\Theta-\Theta_{ave}\right)/\Theta_{rms}$. Numerical turbulent flow realizations with a wall and a gas-liquid interface obtained by a direct numerical simulation technique are employed to confirm suitability of the proposed scaling. The results of this study exhibit that the probability density function (PDF) of $\hat\Theta$ is very similar without respect to the distance from the wall, unlike PDF of unscaled $\Theta$. Because of this statistical similarity, identification of CS based on $\hat\Theta$ is shown advantageous to separate all the essential CS from disorganized turbulent background using a unique threshold level, especially in the region adjacent to the wall and the gas-liquid interface. Several turbulent flow signatures at the gas-liquid interface suggest that a threshold of $1\le\Theta\le 2$ is preferable to identify all the essential CS in the whole of the turbulent flow domain, without contamination'' caused by misidentification of meaningless structures.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.DFD.LK.10