Seyed Sobhan Aleyasin 1 Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB R3T 5V6, Canada e-mail: aleyasss@myumanitoba.ca Nima Fathi Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM 87131 e-mail: nfathi@unm.edu Mark Francis Tachie Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB R3T 5V6, Canada e-mail: mark.tachie@umanitoba.ca Peter Vorobieff Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM 87131 e-mail: kalmoth@unm.edu Mikhail Koupriyanov Price Industries Limited, Winnipeg, MB R2K 3Z9, Canada e-mail: mikek@priceindustries.com On the Development of Incompressible Round and Equilateral Triangular Jets Due to Reynolds Number Variation The aim of this study is to examine the effects of Reynolds number (Re ¼ 6000–20,000) on mean and turbulent quantities as well as turbulent structures in the near and interme- diate regions of equilateral triangular and round sharp contraction jets. The results show shorter potential core length, faster growth of turbulence intensity, and faster diffusion of turbulent structures to the centerline of the triangular jets, implying enhanced mixing in the near field of these jets. On the other hand, the velocity decay and jet spread rates are higher in the round jets. The obtained data in the round jets show that the jet at Re ¼ 6000 has the most effective mixing, while an increase in Reynolds number reduces the mixing performance. In the triangular jets, however, no Reynolds number effects were observed on the measured quantities including the length of the potential core, the decay and spread rates, the axis-switching locations, and the value of the Reynolds num- ber. In addition, the asymptotic values of the relative turbulence intensities on the jet cen- terline are almost independent of the Reynolds number and geometry. The ratios of transverse and spanwise Reynolds stresses are unity except close to the jet exit where the flow pattern in the major plane of the triangular jet deflects toward the flat side. Proper orthogonal decomposition (POD) analysis revealed that turbulent structures in minor and major planes have identical fractional kinetic energy. The integral length scales increased linearly with the streamwise distance with identical slope for all the test cases. [DOI: 10.1115/1.4040031] Keywords: equilateral triangular jet, Reynolds number, sharp contraction nozzle, swirling strength, two-point correlation, integral length scales, POD 1 Introduction Turbulent jets have diverse applications in mechanical and aerospace engineering including combustor injection systems, jet pumps and heating, ventilation, and air conditioning systems. In all of these applications, enhanced mixing is of great importance. It is well documented that the mixing performance and flow prop- erties of a turbulent jet are acute function of the flow at the jet ori- gin, usually termed initial conditions. The initial conditions ranged from Reynolds number (Re) [1–6], the level of exit turbu- lence intensity [7], initial momentum thickness [8] to nozzle type [9–12], nozzle geometry and aspect ratio [13–18]. Quinn’s study [9] on orifice and smooth contraction (SC) round jets at Re ¼ 184,000 revealed higher mixing capabilities of the former jet. This conclusion was made based on the shorter poten- tial core length, faster mean static pressure recovery, higher veloc- ity decay and jet spread rates, and faster growth of turbulence intensity on the centerline of the orifice jet. Xu and Antonia [11] compared the flow properties of SC and fully developed pipe round jets issuing at Re ¼ 78,000. It was observed that the center- line velocity decay and jet spread rates are, respectively, 14% and 10% higher in the SC jet. In addition, the peak values of the Reyn- olds stresses in the contraction jet were larger, implying a stronger shear in the mixing layer of the SC jet. However, the differences between the jets decreased as x/d increased. The different behaviors of the jets were attributed to the existence of aperiodic structures in pipe jets and quasi-periodic passage of coherent structures in orifice and SC jets, although the structures were more energetic in the orifice jets [9,10]. The studies on the effects of Reynolds number on the flow properties of turbulent jets have mainly focused on plane and round SC jets. The investigation conducted by Deo et al. [1] on plane SC jets at Re ¼ 1500–16,500 revealed considerable Reyn- olds number effects on both the mean and turbulent fields includ- ing the length of potential core, velocity decay and jet spread rates, the onset of self-similarity region, and the asymptotic value of relative turbulence intensity on jet centerline (u rms =U cl ). The velocity decay and spread rates, for instance, varied from 0.22 to 0.16, and 0.14 to 0.09, respectively, as Reynolds number increased from 1500 to 16,500, while the asymptotic values of u rms =U cl increased from 0.16 to 0.23. The study performed by Namer and € Ot€ ugen [2] on plane jets at Re ¼ 1000–7000, on the other hand, showed that although the velocity decay and jet spread rates decreased with increasing of Re, the asymptotic values of u rms =U cl decreased from 0.3 to 0.2. The effects of Reynolds num- bers (Re ¼ 4000–20,000) on SC round jets were investigated by Mi et al. [3]. It was observed that velocity decay and jet spread rates decreased with increasing of Re and they attained their asymptotic values at Re  10,000; however, no Re effect was observed on the length of potential core. The small-scale turbu- lence properties including the Kolmogorov length scale (g) and Taylor microscale (k T ) also varied with Re, and their dependence was a strong function of Re range. For example, the Kolmogorov length scale was inversely proportional to Re (g  Re 1 ) for Re < 10,000 but the dependence reduced to g  Re 3=4 for Re  1 Corresponding author. Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received January 3, 2018; final manuscript received April 12, 2018; published online May 18, 2018. Assoc. Editor: Devesh Ranjan. Journal of Fluids Engineering NOVEMBER 2018, Vol. 140 / 111202-1 Copyright V C 2018 by ASME Downloaded From: http://fluidsengineering.asmedigitalcollection.asme.org/ on 09/28/2018 Terms of Use: http://www.asme.org/about-asme/terms-of-use