Investigation of the structure of supersonic nitrogen microjets
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RESEARCH PAPER
Investigation of the structure of supersonic nitrogen microjets Vladimir Aniskin • Sergey Mironov Anatoliy Maslov
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Received: 24 July 2012 / Accepted: 11 October 2012 / Published online: 30 October 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract Results of research on microjets escaping into an ambient space from nozzles with diameters of 341–10.4 lm are described. A special Pitot microtube is used for studying the structure of supersonic microjets. The main feature of this microtube is a small diameter of the intake hole (12 lm). The main parameters of supersonic underexpanded microjets are identified, including the size of shock cells and the supersonic core length of the microjet. The results show a significant increase in the supersonic core length of microjets compared to macrojets. The Reynolds numbers of the laminar–turbulent transition in microjets are found to be in the range of 1,100–2,100. In addition, a classification of supersonic underexpanded axisymmetric microjets escaping into the ambient space is proposed. Keywords Microjets Pitot microtube Supersonic core length
1 Introduction In the last decade, there has been great interest in using gas microjets in various fields of engineering and technology (Tabeling 2005; Karnidakis et al. 2005). In particular, gas microjets have found applications in microjet engines (Bayt and Breuer 2001), in pneumonic microdevices, and in active control of gas-dynamic flows (Alvi et al. 2000;
V. Aniskin (&) S. Mironov A. Maslov Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Institutskaya str. 4/1, Novosibirsk 630090, Russian Federation e-mail: [email protected]
Lou et al. 2006; Kumar and Alvi 2006; Zhuang et al. 2006; Zhang and Zhong 2010). The main advantage of microjets is the local character of their impact and the ability to create high-density arrays of microjets without increasing flow rate. The effectiveness of supersonic microjets depends on the length of their supersonic core, which, in turn, is determined by the nozzle diameter and by the Mach number at the nozzle exit, the jet pressure ratio, and the ratio of specific heats of the gas. Unified dependences between the jet pressure ratio and its supersonic core length were presented in the literature (Shirie et al. 1967; Pogorelov 1977) on the basis of experimental data for macrojets, obtained in a wide range of nozzle sizes, Mach numbers, jet pressure ratios, and gas temperatures. The supersonic core length in these dependences, other factors being identical, is proportional to the nozzle diameter. There are very few experimental studies on the structure of supersonic microjets in the literature. The study of Scroggs and Settles (1996) was probably the first work on the subject. The working gas in the experiments was air. The nozzles were made of a glass capillary. The nozzles had contracting and expanding parts formed by heating and stretching of the glass capillary. The nozzle exit diameters were 1,200 and 600 lm, and the nozzle throat diameters were
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