Velocity field measurements in critical nozzles using Recovery Temperature Anemometry (RTA)

摘要

Recovery Temperature Anemometry (RTA) was used to investigate flow fields in critical flow nozzles without perturbing the flows. In RTA, the recovery temperature in the flow field is measured by using a very thin thermocouple wire, and the measured temperature is then converted into a flow velocity on the basis of the recovery factor. Because the sensitivity of the thermocouple wire is concentrated precisely at its contact point, the spatial resolution of RTA is extremely high, for example, 10-50 μm in the present measurements. Results measured by RTA, using the square root of the Prandtl number as the recovery factor, agreed well with 1D and 2D theoretical predictions. RTA was also shown to be capable of detecting the boundary layer generated on the throat wall of the nozzle. The results also revealed the presence of an interaction between a moving shock wave, the location of which depended on the pressure ratio, and an oblique shock system, the position of which was fixed by the geometry of the nozzle; this interaction is considered to be related to the premature unchoking phenomenon in which a critical nozzle fails to choke at high pressure ratios.