Effect of Reynolds number on flow behavior and pressure drag of axisymmetric conical boattails at low speeds

• Published in: Experiments in fluids Vol. 60; no. 3; pp. 1 - 19
• Main Authors: Tran, The Hung, Ambo, Takumi, Lee, Taekjin, Ozawa, Yuta, Chen, Lin, Nonomura, Taku, Asai, Keisuke
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2019; Springer Nature B.V
• Subjects: Afterbodies; Axisymmetric flow; Boattails; Bubbles; Computational fluid dynamics; Drag coefficients; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Fluid flow; Fluid- and Aerodynamics; Friction; Friction measurement; Heat and Mass Transfer; Low speed; Pressure distribution; Pressure drag; Research Article; Reynolds number; Separation; Skin friction; Stress concentration; Viscosity
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-019-2680-y

The effect of Reynolds number on flow behaviors and pressure drag around axisymmetric conical boattails was experimentally investigated at low-speed conditions. Four conical boattails with slant angles of 12°, 16°, 20°, and 22° were studied. The Reynolds number ranged from 4.34 × 10 4 to 8.89 × 10 4 based on the model diameter. The global-luminescent-oil-film skin-friction measurement was employed to analyze the surface skin-friction topology. Quantitative skin-friction values at the centerline were obtained in this study. The results show that a separation bubble can be formed on boattail surfaces at angles from 12° to 20°. However, at a boattail angle of 22°, flow is fully separated near the boattail shoulder. The integrated afterbody pressure drag indicated that, at angles of 12°, 16°, and 22°, the Reynolds number has very small effect on the afterbody drag, while, at 20° the drag coefficient decrease was relatively large with increasing Reynolds number. We believe that this study provided the first results for a boattail angle of 20° and we observed that the size of the separation bubble decreased as the Reynolds number increased. The effect of the separation bubble on the pressure distribution was also examined in detail. Graphical abstract