Abstract
This paper describes the results of methodical investigations of the effect of the Pitot tube on measurements of gas-dynamic parameters of supersonic axisymmetric underexpanded real and model microjets. Particular attention is paid to distortions of Pitot pressure variations on the jet axis associated with the wave structure of the jet and to distortions of the supersonic core length. In experiments with model jets escaping from nozzles with diameters ranging from 0.52 to 1.06 mm into the low-pressure chamber, the measurements are performed by the Pitot tubes 0.05 to 2 mm in diameter. The results are analyzed together with the earlier obtained data for real microjets escaping from nozzles with diameters ranging from 10 to 340 µm where the parameters of real microjets were determined by the Pitot microtube 12 µm in diameter. Interaction of the Pitot tube with an unsteady jet in the laminar-turbulent transition region is investigated; the influence of this interaction on Pitot pressure measurements is determined, and a physical interpretation of this phenomenon is provided.
Highlights
The classification of channels in terms of their size, which was proposed in [1] and which is based on Knudsen numbers, implies that microchannels are those having the characteristic size from 10 to200 μm
The velocity of Pitot tube motion was determined experimentally—it was chosen in such a way that the pressure distributions measured by the Pitot tube with the external diameter of 0.4 mm moving along the jet axis away from the nozzle and back toward the nozzle were identical
Though exhaustion of model microjets as a whole occurs in the continuum regime, there are local regions of reduced density in the jet, which correspond to the transitional flow regime from the viewpoint of the Knudsen number
Summary
The classification of channels in terms of their size, which was proposed in [1] and which is based on Knudsen numbers, implies that microchannels are those having the characteristic size from 10 to. Having one macro-sized nozzle and choosing appropriate values of the ambient pressure and the pressure in the settling chamber, one can simulate a supersonic flow of microjets escaping from micronozzles of different diameters into the atmosphere Such macrojets can be called low-Reynolds-number jets or model microjets. A problem important for practice can be solved—determining the maximum possible diameter of the Pitot tube with respect to the nozzle diameter, which would ensure correct measurements of the wave structure and correct determination of the supersonic core length in microjets For solving this problem, we studied supersonic jets escaping from nozzles 0.52, 0.72, and 1.06 mm in diameter into a low-pressure chamber. It was of interest to study the influence of an unsteady axisymmetric underexpanded microjet flow in the laminar-turbulent transition region on results measured by the Pitot tube
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
