Large- and Very Large-scale Structures - Transport and Coherent Structures in Wall Turbulence - page 399

() ()

whether , indicating that there is an

amplitude modulation effect of large-scale structures on
()

L u ++

> 0 or

L u ++

< 0

S u ++ . 6

Figure 6.20. Isocontours of premultiplied spectral density at .

Re

τ =

7, 300

y + The sign +, respectively, indicates the inner peak at and outer peak

= 15

at . This figure is adapted from [MAT 09]

y Λ= 0.06

0

6 A second observation arising from Figure 6.21 is the apparent
modification of the interval between the zero-crossings of

()

S u ++ , which

()

L u ++ <

tends to increase (or, respectively, decrease) significantly when

0

()

L u ++ >

(or, respectively, when

0

). The frequency of the zero-crossings of

()

S u ++ decreases during negative excursions of the footprints of the large-
scale structures emanating from the logarithmic sublayer. It would be
interesting to analyze the plausible effect of these excursions on local
dissipation by means of an analysis similar to that performed by
Kailasnath and Sreenivasan [KAI 93].