Ground effects on the stability of separated flow around a NACA 4415 airfoil at low Reynolds numbers

He, Wei1,2; Yu, Peng2; Li, Larry K. B.1

2018-01

10.1016/j.ast.2017.10.039

AEROSPACE SCIENCE AND TECHNOLOGY   影响因子和分区

1270-9638

1626-3219

We perform a linear BiGlobal modal stability analysis on the separated flow around a NACA 4415 airfoil at low Reynolds numbers (Re = 300-1000) and a high angle of attack (a = 20), with a focus on the effect of the airfoil's proximity to two different types of ground: a stationary ground and a moving ground. The results show that the most dominant perturbation is a Kelvin-Helmholtz mode, which gives rise to a supercritical Hopf bifurcation to a global mode, leading to large-scale vortex shedding at a periodic limit cycle. As the airfoil approaches the ground, this mode can become more unstable or less unstable, depending on the specific type of ground: introducing a stationary ground to an otherwise groundless system is destabilizing but introducing a moving ground is stabilizing, although both effects weaken with increasing Re. By performing a Floquet analysis, we find that short-wavelength secondary instabilities are damped by a moving ground but are amplified by a stationary ground. By contrast, long wavelength secondary instabilities are relatively insensitive to ground type. This numerical-theoretical study shows that the ground can have an elaborate influence on the primary and secondary instabilities of the separated flow around an airfoil at low Re. These findings could be useful for the design of micro aerial vehicles and for improving our understanding of natural flyers such as insects and birds. (C) 2017 Elsevier Masson SAS. All rights reserved.

Ground effect Separation Flow instability Modal analysis

SCI ; EI

英语

通讯

Special Program for Applied Research on Super Computation of the NSFC - Guangdong Joint Fund[U1501501]

Engineering

Engineering, Aerospace

WOS:000423893800006

ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER

20174604392103

Air cushion vehicles ; Angle of attack ; Antennas ; Ground effect ; Hopf bifurcation ; Micro air vehicle (MAV) ; Modal analysis ; Reynolds equation ; Reynolds number ; Sailing vessels ; Separation

Fluid Flow, General:631.1 ; Aerodynamics, General:651.1 ; Aircraft, General:652.1 ; Small Marine Craft:674.1 ; Chemical Operations:802.3 ; Mathematics:921

ENGINEERING

Web of Science

1.Hong Kong Univ Sci & Technol, Hong Kong, Hong Kong, Peoples R China
2.Southern Univ Sci & Technol, Shenzhen, Peoples R China

He, Wei,Yu, Peng,Li, Larry K. B.. Ground effects on the stability of separated flow around a NACA 4415 airfoil at low Reynolds numbers[J]. AEROSPACE SCIENCE AND TECHNOLOGY,2018,72:63-76.

He, Wei,Yu, Peng,&Li, Larry K. B..(2018).Ground effects on the stability of separated flow around a NACA 4415 airfoil at low Reynolds numbers.AEROSPACE SCIENCE AND TECHNOLOGY,72,63-76.

He, Wei,et al."Ground effects on the stability of separated flow around a NACA 4415 airfoil at low Reynolds numbers".AEROSPACE SCIENCE AND TECHNOLOGY 72(2018):63-76.