Effect of viscosity in speed measurements with double-throat Venturi tubes

In order to clarify the viscosity effect some experiments were made in the Gottigen low-pressure tunnel with the Bruhn double-throat Venturi tube. This type of tunnel makes it possible to vary the pressure and thereby the density within wide limits and consequently, to examine the viscosity effect. This, however, did not impair the results because pressure and temperature were determined at different periods.