The effect of torsion on the flow in a helical tube of circular cross-section is experimentally investigated over a range of Reynolds numbers from about 500 to 20000. Three cases of dimensionless curvature fi were studied, i.e. fi = 0.01, 0.05 and 0.1. The torsional parameter/30, which is defined as /30 = z/v/~ with dimensionless torsion r, was considered for seven cases between 0.45 and 1.72. The results reveal rather large effect of torsion on the flow: the friction factor of the flow at a fixed ~ deviates from that of the toroidally curved tube without torsion as/30 increases, and it decreases toward that of the straight tube as/30 further increases. It is also found that the torsion has a destabilizing effect on the flow. The critical Reynolds number at the onset of turbulence varies with/30 and has a minimum at/30 -~ 1.3. The minimum critical Reynolds number at 6 = 0.1 is about 800.

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Three semiconductor pressure transducers were inserted into a cobra probe to measure instantaneous condition of flow at the exit of a pump impeller. As it was difficult to calibrate a probe in a two-dimensional periodic flow which was similar to the periodic flow to be measured, the authors used the probe assuming that the steady flow characteristics were valid and examined the results in several ways. The results at different pump speeds satisfied the similarity law of flow from the impeller, and it was concluded that the time response of the probe and pressure transducer system was satisfactory. Almost identical results were obtained regardless of the orientation of the probe, and it was concluded that the calibration curve at steady state was applicable to the unsteady state. Finally, the static pressure calculated from the probe output agreed with the wall pressure which was directly measured with a semiconductor pressure transducer. The authors believe that the three steps are sufficient to prove that the results obtained with the probe are reliable and the probe system is suitable for measurement of periodic flow at the exit of impeller of a pump.

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