Analysis of inner flow and outflow characteristics of different scramjet elliptical holes

ABSTRACT

The elliptical hole has the potential to promote jet breakup and improve atomization and mixing quality. The flow behavior in the nozzle and the outflow characteristics have an important influence on the atomization and mixing process of the downstream fuel. Therefore, the inner cavitation flow processes and outflow characteristics for elliptical holes for scramjet engine at injection pressures of 3 MPa and 5 MPa were investigated using the Volume of Fluid (VOF) method and Large Eddy Simulation (LES). The numerical findings demonstrated that the cavitation region and vortex structures of elliptical holes mainly appeared on the long axial plane. The cavitation intensity of elliptical holes was weaker than that of the circular hole. Compared with the circular hole, the gas phase volume fraction of elliptical hole with the aspect ratio of 4 was reduced by about 22.1 and 21.1% respectively under 3MPa and 5MPa injection pressure. The application of elliptical holes inhibited the generation of cavitation and had large mass flow rate and flow coefficient. The mass flow rate of the elliptical hole with the aspect ratio of 4 was the largest, and the mass flow rate increased by about 5.1% compared with that of the circular hole. Elliptical holes showed a smaller velocity coefficient and a larger area coefficient when cavitation existed. The elliptical hole with the aspect ratio of 4 held the smallest velocity coefficient and largest area coefficient, with the difference of 12.1% and 18.9% respectively from the circular hole. Another important point was that elliptical holes enhanced the turbulent disturbance at the hole outlet, which facilitated the breakup of downstream jet.

KEYWORDS:

• Elliptical hole
• scramjet engine
• VOF
• cavitation
• vortex structures

Disclosure statement

No potential conflict of interest was reported by the authors.

Nomenclature

VOF	=	Volume of Fluid
LES	=	Large Eddy Simulation
PISO	=	Pressure-Implicit with Splitting of Operators
$C_s$	=	Smagorinsky constant (dimensionless)
$K_N$	=	Cavitation number (dimensionless)
$P_{inj}$	=	Injection pressure (MPa)
$P_{back}$	=	Liquid phase evaporation pressure (MPa)
$P_v$	=	Ambient back pressure (MPa)
$d$	=	The closest distance to the wall (μm)
$A$	=	Hole exit cross-sectional area (μm2)
$A_{eff}$	=	Effective flow area at the hole outlet (μm2)
$C_d$	=	Flow coefficient (dimensionless)
$C_v$	=	Velocity coefficient (dimensionless)
$C_a$	=	Area coefficient (dimensionless)
$\text{dotm}$	=	Actual mass flow rate (g/s)
$\dot{M}$	=	Actual momentum flux (kg·m/s)
$u_{th}$	=	Theoretical flow velocity (m/s)
$u_{eff}$	=	Actual flow velocity (m/s)
$\alpha$	=	Gas phase volume fraction (dimensionless)
$\rho$	=	Fluid density (kg/m3)
${\rho }_l$	=	Liquid phase density (kg/m3)
${\rho }_g$	=	Gas phase density (kg/m3)

Additional information

Funding

This work was supported by National Natural Science Foundation of China [No.12002138]; Science and Technology on Scramjet Laboratory Project of China [WDZC614270302207]; Young Elite Scientists Sponsorship Program by Jiangsu Association for Science and Technology [TJ-2022-057]; China Postdoctoral Science Foundation [2022M721177]; Science and Technology on Scramjet Laboratory Project of China [STS/MY-KFKT-2017001]; The Priority Academic Program Development of Jiangsu Higher Education Institutions [PAPD].

Notes on contributors

Kang Zhang

Kang Zhang is currently studying as a postgraduate in the School of automotive and traffic engineering, Jiangsu University, Zhenjiang, China. He will receive his Master degree in Power Engineering and Engineering Thermal Physics in 2024 from Jiangsu University, China. His research interests are jet breakup process and characteristics of scramjet engine.

Bifeng Yin

Bifeng Yin is currently working as Professor in the School of automotive and traffic engineering, Jiangsu University, Zhenjiang, China. He received his PhD in Power Engineering and Engineering Thermal Physics in 2011 from Jiangsu University, China. His research interests are combustion process and emission pollutant control of internal combustion engine, Power train tribology, Power mechatronics and intelligent control technology and Development and application of new power system.

Shenghao Yu

Shenghao Yu is a lecturer and a researcher in the School of automotive and traffic engineering, Jiangsu University, Zhenjiang, China. He received his PhD in Power Engineering and Engineering Thermal Physics in 2020 from Jiangsu University, China. His research interests are liquid fuel spray and combustion characteristics.

Hekun Jia

Hekun Jia is currently working as Professor in the School of automotive and traffic engineering, Jiangsu University, Zhenjiang, China. He received his PhD in Power Engineering and Engineering Thermal Physics in 2013 from Jiangsu University, China. His research interests are combustion process and emission pollutant control of internal combustion engine.

Chen Chen

Chen Chen is currently working as Assistant Professor in the School of automotive and traffic engineering, Jiangsu University, Zhenjiang, China. He received his PhD in Mechanical Design and Theory in 2017 from Southwest Jiaotong University, China. His research interests are spray characteristics and engineering application of an open-end swirl injector.