Measurement of Two-Dimensional Periodic Flow With a Cobra Probe

Abstract

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.

Strömungsuntersuchung in hydrodynamischen Wandlern: Zusammenspiel von Messung und Rechnung

“…Sie konnten Frequenzen bis max. 1 kHz auf-15sen [28,34] und kamen in hydraulischen Maschinen mit geringen Schaufeldurchgangsfrequenzen zum Einsatz. Ebenfalls fiir Messungen in Wasser entwickehe Castorph [10] eine Sonde (G = 8 ram), bei der die zylindrischen Halbleiter-Druckaufnehmer mit Metallmembran im Sondenkopf eingeldebt waren.…”

Enhanced performance of fast-response 3-hole wedge probes for transonic flows in axial turbomachinery

“…However the internal cavity underneath the measurement point and the capillary tube that transmits the pressure waves towards the sensor modifies the transfer function, introducing resonances that limit the bandwidth and may damp the high frequency fluctuations. A three-hole probe with sub-surface mounted sensors was investigated by Senoo et al (1973) and Matsunaga et al (1975) with frequency responses of about 1kHz. The fidelity to measure unsteady flows with those remote-sensor probes was later studied by Dibelius and Minten (1983) and by Bohn and Schnittfeld (1992).…”

Total and Static Quantity Measurements in Unsteady Flow — Effect of Unsteadiness

“…As an alternative approach to these techniques the last two decades have seen considerable progress towards the use of fast response aerodynamic probes based on conventional three and five hole probe geometry and silicon semi-conductor pressure transducers. Initially, these probes relied on sensors mounted in the interior of a probe (Senoo, Kita, Ookuma 1973;Matsunaga, Ishibashi, Nishi 1978). This first generation of probes, albeit with a faster response than conventional pneumatic probes, was still limited in bandwidth (typically 1kHz).…”