Flow characteristic of highly underexpanded jets from various nozzle geometries

• Published in: Applied thermal engineering Vol. 125; pp. 240 - 253
• Main Authors: Li, Xiaopeng, Zhou, Rui, Yao, Wei, Fan, Xuejun
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.10.2017; Elsevier BV
• Subjects: Aircraft; Flapping; Flow characteristics; Fluid dynamics; Fluid mechanics; Jet aircraft; Large eddy simulation; Mach reflection; Noncircular jets; Nozzle geometry; Nozzles; Penetration; Planes; Pressure ratio; Rectangular jets; Stability; Turbulence; Two dimensional jets; Underexpanded jets; Vortices; Underexpanded jets; Nozzle geometry; Noncircular jets; Large eddy simulation
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2017.07.002

•The effect of nozzle geometry on underexpanded jet flows is investigated using LES.•Circular and square jets both correspond to a 3D helical instability mode.•Elliptic and rectangular jets have a flapping instability in their minor axis plane.•The formation and development of the intercepting shocks are highly different.•The elliptic jet penetrates slowest, and has the largest overall mixing area. Flow characteristics of highly underexpanded jets at the same nozzle pressure ratio of 5.60 but issuing from four different nozzles, i.e., the circular, elliptic, square, and rectangular nozzles, are studied using large eddy simulations. The results show that the square jet penetrates fastest, although the turbulence transition is similar for different jets. The penetration rates of different jets show the similar linear dependency on the square root of time, but the penetration constant Γ for the noncircular jets deviates more than 5% from the theoretical value of 3.0. The circular and square jets both correspond to a three-dimensional helical instability mode, while the elliptic and rectangular jets have a two-dimensional flapping instability in their minor axis planes. All the jets undergo a Mach reflection forming the Mach disk, but the Mach disk in the elliptic and rectangular jets is not easily visible. The intercepting shocks in the square jet originate at the four corners of the nozzle exit at first, while the formation of the intercepting shocks is only observed in the major axis planes for the elliptic and rectangular jets. In addition, great differences are observed on the mixing characteristics between different jets. In particular, the elliptic jet penetrates slowest, has the shortest length of jet potential core, and takes the largest mixing area.