A Fast-response Entropy Probe For Unsteady Flow In Turbomachinery

The internal flow of turbomachinery is so complex, because of abverse pressure gradient, shock wave, complex vortex mixing, flow instability, unsteady flow, three dimensional flow. And they are related to each other. With the research of flow losses and flow instability mechanism in the turbomachinery, especially for three-dimensional unsteady turbulence nature, more advanced high-frequency responsing measurement technology is demanded. Researchers want to know more about loss of the internal flow, include efficiency in turbomachinery. And efficiency is related to loss. Entropy production is the best for loss, but entropy can not be measured directly. Fast response entropy probe can measure total temperature and pressure at the same time, which helps people know internal flow better. Also it can verify CFD result.Entropy is very difficult to measure for five reasons.1) Unsteady flow produced by the rotor need high frequency. Although micro-pressure sensors have high frequency, but total temperature is very difficult to measure.2) High frequency sensors usually are fragile in turbomachinery, so they can not work for a long time.3) The internal flow of turbomachinery is so complex, so the direction of flow is large and changeable, it is hard to measure accurately.4) The tip and root of blade is the area where loss mainly produces. The probe needs to manufacture small enough to measure this area, and it seems difficult.5) Entropy can not measure directly, it should measure total pressure and total temperature at same time.This paper mainly designs a dynamic entropy probe, the principle of this probe, manufacture, calibration, material, accuracy of measurement, angle of measurement, frequency response constitute main part of this paper. There are mainly three parts in this paper:The first part is the principle and structure of the entropy probe. Total and static pressure are used to calculate entropy, combined with voltage from hot wire. The hot wire system has been widely used, so it can adapt to turbomachinery. Kiel entrance measure flow which angle is large and changeable, it also protests hot wire. Semi-infinite pipe can make probe small. The probe has two pressure transducer and one hot wire, entropy can be calculated from total pressure and total temperature. The second part is to calibrate the probe. In order to calibrate probe, a wind tunnel is set up. The exit of wind tunnel is tested, and the flow is uniformity and stable. Pulse signal from compressor is used to calibrate pressure tube, the transfer function of total pressure can ensure the probe frequency response. Hot wire works in different temperature is calibrated, and the hot wire is sensitive to both temperature and velocity.The last part discusses the probe using on jet flow and axial compressor. This probe can distinguish jet flow and axial compressor wake clearly. The semi-infinite pressure tube fast response entropy measurement method is capable of measuring the complex unsteady three-dimensional flows in turbomachinery.