Effect of boattail angles on the flow pattern on an axisymmetric afterbody surface at low speed

• Published in: Experimental thermal and fluid science Vol. 99; pp. 324 - 335
• Main Authors: Tran, The Hung, Ambo, Takumi, Lee, Taekjin, Chen, Lin, Nonomura, Taku, Asai, Keisuke
• Format: Journal Article
• Language: English
• Published: Philadelphia Elsevier Inc 01.12.2018; Elsevier Science Ltd
• Subjects: Afterbodies; Axisymmetric bodies; Axisymmetric body; Axisymmetric flow; Boattail flow; Boattails; Boundary layer; Computational fluid dynamics; Conical flow; Film thickness; Flow pattern; Flow separation; Flow topology; Fluid flow; Friction; Friction measurement; GLOF; Low speed; Luminescence; Position measurement; Reynolds number; Separation; Skin; Skin friction; Surface flow; Topology; Turbulence; Boattail flow; Axisymmetric body; Flow topology; Skin friction; GLOF
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2018.07.034

•Flow topology was built on the boattail surfaces.•Three distinctive flow regimes were observed.•The separation bubble develops in size with growth of the angles.•The length of separation bubble increases linearly with the angles. The surface flow pattern over a conical boattail on an axisymmetric body was investigated experimentally under low-speed and turbulent-boundary-layer conditions. Seven conical boattails with the same length but different angles from 10° to 22° were tested at a Reynolds number around 4.3 × 104, based on the model diameter. The study used the global luminescent oil-film (GLOF) skin friction measurement technique. The skin friction fields were measured and the corresponding flow topologies were extracted from the GLOF measurements. The effect of oil-film thickness on the separation position was also evaluated. Experimental results showed three different flow types on the boattail surface: (1) flow without separation, (2) flow with a separation bubble, and (3) fully separated flow. The critical angles for the transitions are discussed and compared with classic results for similar boattail models. The separation bubble generated at moderate boattail angles was observed for what we believe to be the first time under low-speed conditions, and the flow topology was clearly shown by the GLOF results. The azimuthally-averaged skin friction projected on the centerline showed different trends inside and behind the reattachment position when the boattail angle increased.