Instantaneous flow field above the free end of finite-height cylinders and prisms

• Published in: International journal of heat and fluid flow 2013-10, Vol.43, p.120-128
• Main Authors: Rostamy, N., Sumner, D., Bergstrom, D.J., Bugg, J.D.
• Format: Article
• Language: English
• Subjects: Aspect ratio; Circular cylinders; Cylinders; Exact sciences and technology; Fluid dynamics; Fluid flow; Fundamental areas of phenomenology (including applications); Instantaneous flow; Instrumentation for fluid dynamics; Particle image velocimetry; Physics; Prisms; Rotational flow and vorticity; Separated flow; Separated flows; Surface-mounted bluff body; Turbulence; Turbulent flow; Vorticity
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2013.04.005

•PIV measurements of the flow above the free end of finite-height bodies.•Effect of cross-sectional shape of the models on the instantaneous flow.•Small-scale structures generated by the separated shear layer were revealed.•Effect of aspect ratio on the reattachment of the separated flow on the free end. The flow above the free ends of surface-mounted finite-height circular cylinders and square prisms was studied experimentally using particle image velocimetry (PIV). Cylinders and prisms with aspect ratios of AR=9, 7, 5, and 3 were tested at a Reynolds number of Re=4.2×104. The bodies were mounted normal to a ground plane and were partially immersed in a turbulent zero-pressure-gradient boundary layer, where the boundary layer thickness relative to the body width was δ/D=1.6. PIV measurements were made above the free ends of the bodies in a vertical plane aligned with the flow centreline. The present PIV results provide insight into the effects of aspect ratio and body shape on the instantaneous flow field. The recirculation zone under the separated shear layer is larger for the square prism of AR=3 compared to the more slender prism of AR=9. Also, for a square prism with low aspect ratio (AR=3), the influence of the reverse flow over the free end surface becomes more significant compared to that for a higher aspect ratio (AR=9). For the circular cylinder, a cross-stream vortex forms within the recirculation zone. As the aspect ratio of the cylinder decreases, the reattachment point of the separated flow on the free end surface moves closer to the trailing edge. For both the square prism and circular cylinder cases, the instantaneous velocity vector field and associated in-plane vorticity field revealed small-scale structures mostly generated by the separated shear layer.