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2 Machine Dynamics Research

2 2011

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Thermal Boundary Condition Influence on Bi-Periodic Channel Flow with High Thermal Gradient

Aulery F., Baux Y., Toutant A., Bataille F.

Machine Dynamics Research

2011

Vol. 35, No. 1

19-28

This study focuses on TLES (Thermal Large Eddy Simulation). We study the influence of thermal boundary conditions on mean and fluctuating profiles for a turbulent bi-periodic channel with a thermal gradient. TLES simulations show that mean profiles of longitudinal velocity, transversal velocities and their fluctuations are not affected by the therm 1 boundary conditions (flux or temperature imposed at wall). Profiles of mean temperature and mean vertical velocity are slightly changed by the thermal boundary conditions. The thermal gradient at wall is stronger and temperature slope in the middle of channel is lower with imposed temperature boundary conditions. Although there are the same in the middle of the channel, temperature fluctuations profiles are very different near to the wall according to thermal boundary conditions. In fact, with flux boundary conditions, the temperature fluctuation profile is similar close to the wall than in the middle of channel; with imposed temperature boundary conditions, theses profiles tend to zero close to the wall. This result is very important for industrial process because thermal fatigue due to thermal fluctuations at wall can damage it.

Bluff Body Wake Stability Enhancement by Mean of Non-Isothermal Blowing

Mathelin L., Bataille F.

Machine Dynamics Research

2011

Vol. 35, No. 1

108-122

The influence of blowing or suction from the surface of a porous circular cylinder in crossflow onto the dynamics of its near wake is numerically studied for flows close to the onset of the wake vortex shedding regime at a Reynolds number of 49. Two cases are considered: the blowing may be at the same temperature as the mainstream fluid or at a lower temperature. The latter case is mainly motivated by arguments of thermal protection of the cylinder from a hot incident flow. Local and global instability growth rates are investigated under the effect of different blowing locations and temperatures. It is shown that both blowing and suction have a dramatic impact on the absolutely unstable region, thus affecting the wakr behavior, eventually leading to the suppression of vortex shedding.