A numerical study of dynamic flow patterns in supercritical jet flows for various swirl numbers

IF 2.5 3区 工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS
Swapnil Tupkari, Hrishikesh Gadgil, Vineeth Nair
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Abstract

Three-dimensional large-eddy simulations (LES) of supercritical nitrogen injection are carried out over a range of swirl numbers (0S<2) to investigate the characteristics of the flow field. The swirl number is varied by varying the tangential velocity, keeping mass flow rate unchanged. Based on the observed flow dynamics, the swirl numbers are classified as (i) low, (ii) medium, or (iii) high. For low swirl numbers, recirculation zones are not observed and the flow pattern consists primarily of free shear layer instabilities arising out of forced convection that move helically around an intact jet potential core. For medium swirl numbers, a sudden drop in axial centerline velocity is observed due to large adverse pressure gradients. These gradients lead to recirculation regions in front of the injector forming a bubble-type aerodynamic bluff body outside the injector. As the swirl number is increased in this range, the bubble disappears forming a venturi-type flow with local acceleration of axial centerline velocity. For high swirl numbers, the recirculation region enters the injector, and a precessing vortex core (PVC) is observed in the flow field. Mean jet length and initial jet cone angle were found to have non-monotonic variations for medium and high swirl numbers. Finally, spectral analysis reveals the presence of a hydrodynamic frequency corresponding to shear layer instabilities and an acoustic mode corresponding to the injector for low and medium swirl numbers. For high swirl numbers, both these frequencies are suppressed noticeably and the dynamics is completely described by the PVC frequency.

Abstract Image

不同漩涡数下超临界射流动态流动模式的数值研究
在一定漩涡数(0≤S<2)范围内对超临界氮气喷射进行了三维大涡流模拟(LES),以研究流场特征。在保持质量流量不变的情况下,通过改变切向速度来改变漩涡数。根据观察到的流动动态,漩涡数被分为(i) 低、(ii) 中或(iii) 高。对于低漩涡数,未观察到再循环区,流动模式主要由强制对流产生的自由剪切层不稳定性组成,这些不稳定性围绕完整的射流势能核心螺旋运动。对于中等漩涡数,由于存在较大的不利压力梯度,轴向中心线速度会突然下降。这些梯度导致喷射器前方的再循环区域在喷射器外形成气泡型气动崖体。当漩涡数在此范围内增大时,气泡消失,形成通风型流动,轴向中心线速度局部加速。当漩涡数较高时,再循环区域进入喷射器,流场中会出现一个前冲涡核(PVC)。在中漩涡数和高漩涡数下,平均射流长度和初始射流锥角呈非单调变化。最后,频谱分析表明,在中低漩涡数情况下,存在与剪切层不稳定性相对应的流体力学频率和与喷射器相对应的声学模式。对于高漩涡数,这两个频率都被明显抑制,动力学完全由 PVC 频率描述。
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来源期刊
Computers & Fluids
Computers & Fluids 物理-计算机:跨学科应用
CiteScore
5.30
自引率
7.10%
发文量
242
审稿时长
10.8 months
期刊介绍: Computers & Fluids is multidisciplinary. The term ''fluid'' is interpreted in the broadest sense. Hydro- and aerodynamics, high-speed and physical gas dynamics, turbulence and flow stability, multiphase flow, rheology, tribology and fluid-structure interaction are all of interest, provided that computer technique plays a significant role in the associated studies or design methodology.
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