Influence of polymer admixtures on the turbulence structure of flow behind a grating

Experimental investigations of the action of small (20–80 ppm) polymer admixtures on the turbulence structure in the wake behind a grating are performed in a water channel of closed type. The velocity fluctuations are measured by using a single-component Doppler laser velocimeter (DLV). A signal from the DLV was recorded on magnetic disc from three channel sections and the onedimensional energy and dissipation spectra were computed therefrom. It is shown that polymer insertion resulted in reduction of the turbulence level at short ranges from the grating and its increase far from the grating. Influence of the polymer in the spectral distribution appeared in an energy increase in the low-frequency domain and its fast degeneration in the high-frequency band, accompanied by contraction of the spectrum width.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 4, pp. 550–556, April, 1990.