PROJECT)(LE FLOW

As is shown in [2], the greatest deviations between the experimental values for the friction stress on the wall and the computed values according to known dependences are observed for low referred fluid velocities. Hence, measurements in this paper are performed for values of the referred fluid velocity W~ between 0.12 and 1.2 m/sec~ Preliminary measurements showed that a significant drop in the friction stress on the wall occurs at the time of gas projectile passage. Moreover, as is shown in [2] for small W' 0 the projectile flow regime is characterized by high values of the relative intensity of the tangential stress fluctuations on thewall. This makes the assumption of the possible existence reverse flows near the wall natural in such modes at specific times. Consequently, a special methodology [5], permitting determination of the magnitude and direction of the instantaneous value of the friction stress on the wall, is applied in the paper. The measurement diagram is presented in Fig. 1. A double sensor 1 from two platinum plates of 0.02  0.3 mm section, framed flush with the wall of the tube, was used to determine the tangential stress. The spacing between the electrodes of the double sensor is around 0.03 ram. The currents in the sensor electrodes were magnified by dc amplifiers 3 and 4, then fed to the primary signal processing circuit 5. The system operating principle is the following. Upon delivery of a voltage to both electrodes of the double sensor, the electrode located lower in the stream is in the diffusion wake of the first electrode, whereupon the value of the current