Daniel R. Raichel
Ken Takabayashi
Dept. of Mech. Eng., Cooper Union, 51 Astor Pl., New York, NY 10003
According to the Raichel--Kapfer theory [J. Appl. Mech. 40 (Series E), 1--6 (1973)], propagation of even the purest sinusoidal sound wave through a fluid will cause higher harmonics to appear, due to the nonlinear nature of fluid motion. Moreover, any deviation of the fluid's constitutivity from Newtonian behavior will cause these harmonics to change in their amplitudes with respect to the fundamental. In the effort to verify these effects, a sonic viscometer was constructed and operated. The device consisted of a 15-cm-diam, 182-cm-long tube that is filled with specimen fluid. A series of pure sine waves, varied octave-wise from 500 Hz to 8 kHz, was introduced through an electromagnetic driver at one end of the tube into distilled water first and then into a 1% solution of polyethylene oxide which effectively rendered the water non-Newtonian. Fast Fourier transform analyses of the signals intercepted by a hydrophone at the other end of the tube indicate that pronounced changes occur in the second and third harmonics, as predicted by the Raichel-Kapfer theory. [Work supported by the NY State Science Foundation and the Howard Hughes Medical Foundation.]