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In a supersonic suction type of mixing layer wind tunnel, by employing nanoparticle-based planar laser scattering (NPLS) method, contrast experiments are carried out with the emphasis on the fine flow structures of planar mixing layer and the mixing layer induced by triangular lobed mixer. The normal-shock equation, isentropic equation and sound speed relationship are utilized to calculate the flow parameters. The calculated Mach numbers are 1.98 and 2.84 for upper and lower airstreams respectively with a convective Mach number of 0.2. The NPLS images clearly shows the Kelvin-Helmholtz vortices, streamwise vortices, shock waves and the pairing processes of large-scale vortex structures. The unsteady properties of development and evolution for large-scale vortices are obtained by contrasting the NPLS images at different times. Also, it has been demonstrated by the present experimental investigation that in supersonic mixing layer with low convective Mach number, the small shock waves are still existing. These small shock waves that occur have negative effects on the mixing process. It is because the convection flow process of upper and lower airstreams is non-isentropic, causing the total pressure to lose. Based on the NPLS results, flow structures and mixing characteristics are analyzed quantitatively by using fractal and intermittency theory. The results show that the mixing efficiency increases obviously with the introducing of large-scale streamwise vortices. The nibbling of vortex clusters induced by large-scale streamwise vortices obviously increases the interface area of mixing. Meanwhile, compared with planar mixing layer, larger spanwise structures roll up in triangular lobed mixing layer, leading to more entrainment of upper and lower airstreams. In the present investigation of supersonic planar mixing layer, the value of fractal dimension of fully turbulent region is stable at 1.55-1.6. Whereas the value of fractal dimension for triangular lobed mixing layer reaches 1.88 at the flow field far away downstream, which breaks through the value of fully developed turbulence for planar mixing layer. Besides, in triangular lobed mixing layer, the shear action between streamwise vortices and spanwise structures plays a leading role in promoting mixing. The mixing flow shows the property of apparent crushability and three-dimensional behavior, which plays a positive role in promoting mixing at a scalar level. The analysis of intermittency indicates that the interaction between streamwise and spanwise vortices dominates the mixing characteristics, and due to the entrainment of streamwise vortices, the mixing region induced by triangular lobed mixer becomes larger, and more fluids are engulfed into the mixing region to complete the mixing process.
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Keywords:
- supersonic mixing layer /
- lobed mixer /
- fractal /
- intermittency
[1] Curran E T 2001 J. Propul. Power 17 1138
[2] Drummond J P, Diskin G S, Cutler A D 2002 AIAA Paper 2002-3878
[3] Seiner J M, Dash S M, Kenzakowski D C 2001 J. Propul. Power 17 1273
[4] Fernando E M, Menon S 1993 AIAA J. 31 278
[5] Brown G L, Roshko A 1974 J. Fluid Mech. 64 775
[6] Azim M A, Islam A K M S 2003 Aeronaut. J. 107 241
[7] Zhang D D, Tan J G, L L 2015 Acta Astronaut. 117 440
[8] Gutmark E T, Schadow K C, Yu K H 1995 Annu. Rev. Fluid Mech. 27 375
[9] Freund J B, Lele S K, Moin P 2000 J. Fluid Mech. 421 229
[10] Martens S, Kinzie K W, Mclaughlin D K 1994 AIAA Paper 1994-0822
[11] Doty M J, Mclaughlin D K 2000 AIAA J. 38 1871
[12] Sunami T, Wendt M, Nishioka M 1998 AIAA Paper 1998-3271
[13] Heeb N, Gutmark E, Kailasanath K 2015 Phys. Fluids 26 086102
[14] Brinkerhoff J R, Oria H, Yaras M I 2013 J. Propul. Power 29 1017
[15] Tew D E, Hermanson J C, Waitz I A 2004 AIAA J. 42 2393
[16] Paterson R W 1982 NASA Paper CR-3492
[17] Gang D D, Yi S H, Zhao Y F 2015 Acta Phys. Sin. 64 054705 (in Chinese) [冈敦殿, 易仕和, 赵云飞 2015 64 054705]
[18] Zhao Y X, Yi S H, Tian L F 2009 Sci. China: Ser. E 52 3640
[19] Wu Y, Yi S H, Chen Z, Zhang Q H, Gang D D 2013 Acta Phys. Sin. 62 084219 (in Chinese) [武宇, 易仕和, 陈植, 张庆虎, 冈敦殿 2013 62 084219]
[20] Tew D E 1997 Ph. D. Dissertation (Cambridge: Massachusetts Institute of Technology)
[21] Nastase I, Meslem A 2010 Exp. Fluids 48 693
[22] Dimotakis P E 1991 AIAA Paper 1991-2012
[23] Rossmann T, Mungal M G, Hanson R K 2002 J. Turbul. 3 9
[24] Olsen M G, Dutton J C 2003 J. Fluid Mech. 486 51
[25] Jahanbakhshi R, Vaghefi N S, Madnia C K 2015 Phys. Fluids 27 105105
[26] Sreenivasan K R 1991 Annu. Rev. Fluid Mech. 23 539
[27] Humble R A, Peltier S J, Bowersox R D W 2012 Phys. Fluids 24 106103
[28] Zhao Y X, Yi S H, Tian L F, He L, Cheng Z Y 2009 Sci. China: Ser. G 51 1134
[29] Humble R A, Peltier S J, Bowersox R D W 2012 Phys. Fluids 24 106103
[30] Christensen E M 1973 Annu. Rev. Fluid Mech. 5 101
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[1] Curran E T 2001 J. Propul. Power 17 1138
[2] Drummond J P, Diskin G S, Cutler A D 2002 AIAA Paper 2002-3878
[3] Seiner J M, Dash S M, Kenzakowski D C 2001 J. Propul. Power 17 1273
[4] Fernando E M, Menon S 1993 AIAA J. 31 278
[5] Brown G L, Roshko A 1974 J. Fluid Mech. 64 775
[6] Azim M A, Islam A K M S 2003 Aeronaut. J. 107 241
[7] Zhang D D, Tan J G, L L 2015 Acta Astronaut. 117 440
[8] Gutmark E T, Schadow K C, Yu K H 1995 Annu. Rev. Fluid Mech. 27 375
[9] Freund J B, Lele S K, Moin P 2000 J. Fluid Mech. 421 229
[10] Martens S, Kinzie K W, Mclaughlin D K 1994 AIAA Paper 1994-0822
[11] Doty M J, Mclaughlin D K 2000 AIAA J. 38 1871
[12] Sunami T, Wendt M, Nishioka M 1998 AIAA Paper 1998-3271
[13] Heeb N, Gutmark E, Kailasanath K 2015 Phys. Fluids 26 086102
[14] Brinkerhoff J R, Oria H, Yaras M I 2013 J. Propul. Power 29 1017
[15] Tew D E, Hermanson J C, Waitz I A 2004 AIAA J. 42 2393
[16] Paterson R W 1982 NASA Paper CR-3492
[17] Gang D D, Yi S H, Zhao Y F 2015 Acta Phys. Sin. 64 054705 (in Chinese) [冈敦殿, 易仕和, 赵云飞 2015 64 054705]
[18] Zhao Y X, Yi S H, Tian L F 2009 Sci. China: Ser. E 52 3640
[19] Wu Y, Yi S H, Chen Z, Zhang Q H, Gang D D 2013 Acta Phys. Sin. 62 084219 (in Chinese) [武宇, 易仕和, 陈植, 张庆虎, 冈敦殿 2013 62 084219]
[20] Tew D E 1997 Ph. D. Dissertation (Cambridge: Massachusetts Institute of Technology)
[21] Nastase I, Meslem A 2010 Exp. Fluids 48 693
[22] Dimotakis P E 1991 AIAA Paper 1991-2012
[23] Rossmann T, Mungal M G, Hanson R K 2002 J. Turbul. 3 9
[24] Olsen M G, Dutton J C 2003 J. Fluid Mech. 486 51
[25] Jahanbakhshi R, Vaghefi N S, Madnia C K 2015 Phys. Fluids 27 105105
[26] Sreenivasan K R 1991 Annu. Rev. Fluid Mech. 23 539
[27] Humble R A, Peltier S J, Bowersox R D W 2012 Phys. Fluids 24 106103
[28] Zhao Y X, Yi S H, Tian L F, He L, Cheng Z Y 2009 Sci. China: Ser. G 51 1134
[29] Humble R A, Peltier S J, Bowersox R D W 2012 Phys. Fluids 24 106103
[30] Christensen E M 1973 Annu. Rev. Fluid Mech. 5 101
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