DOI: 10.1615/TSFP9
EFFECT OF EXTERNAL TURBULENCE ON A TURBULENT WAKE
ABSTRACT
Direct numerical simulations are performed to study the evolution of a Re = 10,000 axisymmetric wake under the influence of unforced external (background) turbulence. The external turbulence has an integral length scale 4 times larger than that of the wake turbulence in contrast to Pal & Sarkar (2015) where this ratio was approximately unity. Entrainment of background turbulence leads to a reduction of the wake defect velocity relative to the undisturbed wake. The reduction is significant even when the initial r.m.s of background turbulence is only 1−3% of the body velocity, whereas a similarly strong reductions in the cases simulated by Pal & Sarkar (2015) required 5−7% initial turbulence levels. This difference is attributed to external turbulence having a slower decay relative to wake turbulence in the present cases owing to the larger eddy-turnover time.