TY - JOUR
T1 - Dynamical separation of spherical bodies in supersonic flow
AU - Laurence, S. J.
AU - Parziale, N. J.
AU - Deiterding, R.
PY - 2012/12/25
Y1 - 2012/12/25
N2 - An experimental and computational investigation of the unsteady separation behaviour of two spheres in Mach-4 flow is carried out. The spherical bodies, initially contiguous, are released with negligible relative velocity and thereafter fly freely according to the aerodynamic forces experienced. In experiments performed in a supersonic Ludwieg tube, nylon spheres are initially suspended in the test section by weak threads which are detached by the arrival of the flow. The subsequent sphere motions and unsteady flow structures are recorded using high-speed (13Â kHz) focused shadowgraphy. The qualitative separation behaviour and the final lateral velocity of the smaller sphere are found to vary strongly with both the radius ratio and the initial alignment angle of the two spheres. More disparate radii and initial configurations in which the smaller sphere centre lies downstream of the larger sphere centre each increases the tendency for the smaller sphere to be entrained within the flow region bounded by the bow shock of the larger body, rather than expelled from this region. At a critical angle for a given radius ratio (or a critical radius ratio for a given angle), transition from entrainment to expulsion occurs; at this critical value, the final lateral velocity is close to maximum due to the same surfing' effect noted by Laurence & Deiterding (J. Fluid Mech., vol. 676, 2011, pp. 396-431) at hypersonic Mach numbers. A visualization-based tracking algorithm is used to provide quantitative comparisons between the experiments and high-resolution inviscid numerical simulations, with generally favourable agreement.
AB - An experimental and computational investigation of the unsteady separation behaviour of two spheres in Mach-4 flow is carried out. The spherical bodies, initially contiguous, are released with negligible relative velocity and thereafter fly freely according to the aerodynamic forces experienced. In experiments performed in a supersonic Ludwieg tube, nylon spheres are initially suspended in the test section by weak threads which are detached by the arrival of the flow. The subsequent sphere motions and unsteady flow structures are recorded using high-speed (13Â kHz) focused shadowgraphy. The qualitative separation behaviour and the final lateral velocity of the smaller sphere are found to vary strongly with both the radius ratio and the initial alignment angle of the two spheres. More disparate radii and initial configurations in which the smaller sphere centre lies downstream of the larger sphere centre each increases the tendency for the smaller sphere to be entrained within the flow region bounded by the bow shock of the larger body, rather than expelled from this region. At a critical angle for a given radius ratio (or a critical radius ratio for a given angle), transition from entrainment to expulsion occurs; at this critical value, the final lateral velocity is close to maximum due to the same surfing' effect noted by Laurence & Deiterding (J. Fluid Mech., vol. 676, 2011, pp. 396-431) at hypersonic Mach numbers. A visualization-based tracking algorithm is used to provide quantitative comparisons between the experiments and high-resolution inviscid numerical simulations, with generally favourable agreement.
KW - aerodynamics
KW - flow-structure interactions
KW - shock waves
UR - http://www.scopus.com/inward/record.url?scp=84870834546&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84870834546&partnerID=8YFLogxK
U2 - 10.1017/jfm.2012.453
DO - 10.1017/jfm.2012.453
M3 - Article
AN - SCOPUS:84870834546
SN - 0022-1120
VL - 713
SP - 159
EP - 182
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
ER -