The significance of coherent flow structures for the turbulent mixing ...

7 Investigation of the yz-plane
wall structures presented in the previous chapter, and the ªSÔÔŸչ¥»‹Ö=¹¥»n¼r×r¹¥»‹ÖØ×pû ½ correlation,
shown in the upper left image of figure 7.6, indicates the spatial extent of the dominant flow
structures which are moving towards and away from the wall. With increasing wall distance
from the fixed point, the correlations increase in size but it should be noted that the total
size is always below the size of the ªS·· correlation. When the ªSÙ¥ÙÚ¸º¹&»nÖ=¹&»‰¼[×p¹&»ÇÖØ×pû ½
correlation in figure 7.7 is considered, it can be concluded that the various primary correlations
are always stretched in the direction of the velocity fluctuation. However, the dimension of the
stretching which is related to the region where a correlated motion can be observed is quite
different. Another interesting feature is the butterfly shape of the ªSÙ¥Ù correlation, especially
¹ »ÜÛ °
for . The fact that the correlation is further away from the wall with ÝÞÃ » Ý
increasing
indicates that the influence of a span-wise motion being present ¹ » ¬5Âc at , for example, is
quite limited. This might be related to the fact that the span-wise motion is restricted by the
R (y
+
=30)
vv
R (y
+
=200)
vv
+
y + ∆
+
y
+
y + ∆
+
y
+
y + ∆
+
y
R (y
+
=50)
vv
R (y
+
=300)
vv
R (y
+
=100)
vv
R (y
+
=400)
vv
142
∆ z +
∆ z
+
FIGURE 7.6: ˜ ÔÔÄ © »nÆ © »pÈ8É © »¾ÆËÉÌw»¾Í correlation measured at © » šßΧž ÆËÏ ž ÆÐ žž ÆËÑ žž Æ Î§ž±ž ÆÒ žZž .