Three-dimensional vorticity and heat transport in a circular cylinder wake using phase-averaging method

©, 2015, Shiyan Liuti Lixue/Journal of Experiments in Fluid Mechanics. All right reserved. This work aims to provide insight into the three-dimensional aspects of momentum and heat transport in a turbulent cylinder wake. All three components of the velocity and vorticity vectors, along with the fluctuating temperatures, were simultaneously measured with an 8 hot-wire vorticity probe and four cold-wire probes. Measurement was made at x/d=10~40 at a Reynolds number of 2540. A phase-averaging technique has been developed to detect reliably the coherent events, thus allowing the coherent contributions from various quantities associated with the vectors as well as passive scalar fields to be quantified accurately. The results show that there is a close similarity between the contour of spanwise vorticity and that of the streamwise vorticity at x/d=10, due to the strong rolling up effect of the spanwise vortex. As x/d increases, the similarity between ωx and ωy contours can still be observed, resulting from the contributions of the rib-like structures. It exhibits significant three-dimensional qualities of the vortex structure in the near wake. While the coherent heat flux is largely associated with the spanwise vortex rolls, the incoherent (or "remainder") heat flux occurs between two successive opposite-signed vortices, rather than in the saddle region. Due to the combined effect of the spanwise vortex and the rib-like structure, the spanwise heat flux behaves quite differently at different locations. The ω* θ* contour inside the negatively signed vortex is close to the vortex center, while the ω* θ* inside the positive one is stretched to the saddle point aligning with the diverging separatrix. As x/d increases, the negative ω* θ* contour becomes dominant and moves towards the vortex border, which contributes to the net heat transport out of the spanwise vortex. In addition, coherent motion contributes similarly to the longitudinal and spanwise heat flux components.