Wed March 2nd 2011 16:00 ZH286 | Seminar | Macroscopic effects of the spectral structure in turbulent flows Tuan Tran |

## Details:There is a missing link between the macroscopic properties of turbulent flows, such as the frictional drag of a wall-bounded flow, and the turbulent spectrum. The turbulent spectrum is a power law of exponent α (the ʽspectral exponentʼ) that gives the characteristic velocity of a turbulent fluctuation (or ʽeddyʼ) of size s as a function of s. Here we seek the missing link by comparing the frictional drag in soap-film flows, where α=3, and in pipe flows, where α=5/3. For moderate values of the Reynolds number Re, we find experimentally that in soap-film flows the frictional drag scales as Re-1/2, whereas in pipe flows the frictional drag scales as Re-1/4.Each of these scalings may be predicted from the attendant value of α by using a new theory, in which the frictional drag is explicitly linked to the turbulent spectrum. |