Fast Response Probes Measuring Unsteady Flows in High-Speed Research Compressors

It is well recognised that multi-sensor fast response probes are widely used on several applications concerning unsteady flow measurements. Often the size of these probes is larger than ideal. It is probably this reason that the single sensor probes are sometimes preferred in the survey of the unsteady flows in the turbomachinery applications. This in turn can be of benefit due to the limited space often found in compressors. The advent of these miniature probes has been made possible due to the availability of small sensors capable of withstanding relatively high temperatures. There is no doubt that as the technology improves, the size of the probes is likely to be reduced. This will make it possible to use these probes in lower cost, smaller scale facilities. The behavior of a fast response probe is examined in detail prior to the presentation of a set of unsteady measurements acquired near the impeller tip region. The data obtained from the calibration routine is then compared with the actual measurements. Errors that could possibly be arising due to temperature drift of the sensor are taken into account and reduced to a minimum. The fast response probe is largely sensitive to pressure fluctuations that, after correction with temperature, result in an actual pressure reading. The sensitivity of the probe has proved to be adequate for measurement of flow direction and total pressure over a broad angular range. The simple geometry and small size of the probe contributes to a reduction in the blockage effects, the enhancement of the near wall measurements, the reduction of the run-time costs, and raise the confidence in the experiment. This fast response probe was extensively used to traverse the blade passage width. Detailed measurements clearly showed that strong pulsations dominate the distorted impeller exit flow.