Quasi-non intrusive measurement of the transonic flow field in an axi-symmetric critical nozzle based on recovery temperature measurement using a thin thermocouple

摘要

Flow velocities from several m/s to supersonic of a gas having a Prandtl number different from unity were measured based on the recovery temperatures measurement using a very thin thermocouple, which produced almost no disturbance in the field. Very high space resolution in the 10 μm order as well as very small disturbance from the supports of the thermocouple wire were achieved because the sensing point of a themocouple wire was concentrated exactly at the contact point, which allows to use a long thermocouple wire to locate its supports far away from the measuring point. A thermocouple wire of 50 μmφ accompanied with a traversing system was settled through an axi-symmetrical critical nozzle with a throat diameter of 13.4 mmφ to measure the velocity field in the nozzle. The results agreed quite well with the one-dimensional isentropic theory even qualitatively as well as they showed the fine structure predicted by the two-dimensional isentropic theory. Furthermore, the results revealed complicated flow structures, which were unpredictable by these simple theories, such as oblique shocks and normal shock whose amplitude and location changed depending on the back pressure ratio applied on the nozzle in a complicated manner.