Abstract: To reveal the fundamental characteristics of a drag-reducing micelle solution flowing turbulently in a suddenly expended pipe, the expansion loss coefficients, drag development and pressure distributions have been investigated experimentally in an expansion pipe with an area ratio of 1:4, using two weight concentrations of 1×10^-4 and 4×10^-4 of hexadecyl trimethyl ammonium bromide solutions. The drag-reducing micelle solutions in abruptly expanded pipes are different from drag-reducing polymer solutions in turbulent fundamental characteristics. At inlet Reynolds numbers of less than 1.2 times of the critical value, the pressure recovery maximum is greater than that for water, and the expansion loss coefficient is order of 90% of that for water, while at inlet Reynolds numbers greater than 1.2 times of the critical value, it is almost the same as for water, and the expansion loss coefficient is slightly above that for water. Furthermore, the pressure recovery length required to regain a fully developed flow in the expansion pipe is well above that for water. For the 1×10^-4 concentration of micelle solutions lost its drag-reducing ability in the upstream, 110 times of the downstream pipe diameter is necessary for recovering a fully developed drag-reducing flow. It can be concluded that these characteristics are associated with the reforming time characteristics of the micelle shear-induced structure.

Key words: abrupt expansion, micelle, turbulence fundamental characteristics