Axisymmetric turbulent flow with a pressure gradient

 

 

An axisymmetric contraction on a turbulent pipe flow

 

-      To investigate the effects of an axisymmetric contraction fitted to a fully developed turbulent pipe flow

        Direct numerical simulation (DNS) and experiments using the hot-wire probes

        Fully-implicit fractional step method (Kim, Baek & Sung 2002)

        The generalized coordinates in the streamwise-radial plane (Choi, Moin & Kim 1993)

        The elliptic grid generation method (Spekreijse 1995)

        Averaged radial velocity at the centerline condition (Akselvoll & Moin 1995)

 

Schematic diagram of the experiment facility (top) and computational domain (bottom)

 

-      The effects of the contraction ratio — 2, 4 and 8

     For large contraction ratio,

        Diminished turbulent kinetic energy (TKE) in the core region

        Increased near-wall energy due to larger mean-shear rate

        Stretched turbulent vortical structures by the acceleration

 

Vortical structures with the Q2 event vector

 

(Jang, Sung & Krogstad, Journal of Fluid Mechanics, Vol. 687, pp.376-403, 2011)

 

 

DNS of turbulent flow in a conical diffuser

 

-      To investigate the structures of the turbulent flow in a conical diffuser

        Fully-implicit fractional step method (Kim, Baek & Sung 2002)

        The generalized coordinates in the streamwise-radial plane (Choi, Moin & Kim 1993)

        The elliptic grid generation method (Spekreijse 1995)

        Averaged radial velocity at the centerline condition (Akselvoll & Moin 1995)

 

 

Schematic diagram of the computational domain

 

-      The effects of total opening angle — 2, 4 and 8 degrees

        Augmented wake strength and shortened near-wall structure due to strong APG

        The streamwise merging of low-speed streaks by the retarded flow

        Stronger swirling motions of the individual hairpins in the outer region

 

Vortical structures identified by the swirling strength. Color indicates the radial position.

 

 (Lee, Jang & Sung, Journal of Turbulence, Vol. 13, No. 30, pp.1-29, 2012)


 

 

Two-phase turbulent flow

 

 

DNS of turbulent open-channel flow with an air-water interface

 

-      To investigate the influence of interface deformation on the turbulence structures near the mixed-boundary corner

        An open-channel flow with two sidewalls

        Coupled Level-set and Volume-of-fluid (CLSVOF) method for the interface tracking

        Semi-implicit fractional step method for the Navier-Stokes equation solver

 

Schematic diagram of the computational domain

 

 

-      Froude number (Fr) effects — 0.2, 0.5 and 0.8

      For higher Fr,

        Increased Reynolds stresses near the mixed-boundary corner

        Shortened coherent velocity structures near the corner

        Coherence between the secondary flows and the interface elevation

Iso-surfaces of the air-water interface (green), the swirling strength (yellow) and the low-speed structures (grey)

 

(Lee et al., Journal of Turbulence, Vol. 13, No. 18, pp.1-18, 2012)