Direct Numerical Simulation of Air Heated Cylinder Wake in Transitional State. Part I: Cylinder Heating Effect on Strong Turbulence Anisotropy (STA), and Determination of STA Suppression

Abstract

A variation of strong turbulence anisotropy (STA) with cylinder heating, and, as a result, STA suppression, are here first elucidated in the air heated wake in the transitional state at Reynolds number Re = 300 and Richardson number Ri = 0.3. Simultaneously, new facts for variations of velocities u, v, and w, i.e., the upward, horizontal, and spanwise directions, and wake motion by cylinder heating are first elucidated. Here STA is defined such that, in velocities u, v, and w, laminar velocities arise in at least one directions but turbulence arises in the remainder of directions.

1.	STA is determined to arise in isothermal and heated wakes by employing the new method. With cylinder heating, STA is found to be suppressed because the turbulent region in w is decreased, the three-dimensionality is suppressed, but the two-dimensionality and laminarization are enhanced in the heated wake.
2.	With cylinder heating, the spanwise velocity |w| is found to be suppressed strongly in the probability density function (PDF), whose peak value is decreased strongly near w ≈ 0, and becomes 20% of that in the isothermal wake.
3.	The above decrease in |w| is found to be equivalent to the increase of laminar state in time records. With cylinder heating, the laminar region is increased, but the region with turbulence is decreased.
4.	The wake stability is extremely different in thermal flows with or without turbulence in w. When w has turbulence, here u and v are laminar, STA arises, and the thermal flow field becomes the transitional state, has instability, and is destabilized.
5.	When w does not have turbulence, and is laminar, velocities u, v , and w are all laminar, form only 3-D flow, and do not have turbulence anisotropy. The wake does not have instability, and is stabilized.

Notes

Tu, turbulent; Tr, transitional; S, strong; M, moderate.

Tu, turbulent; Tr, transitional; L, laminar; S, strong; M, moderate; N, none.