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

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 allo-wing 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 con-tour of spanwise vorticity and that of the streamwise vorticity at x/d= 1 0 ,due to the strong rolling up effect of the spanwise vortex.As x/d increases,the similarity betweenωx andωy 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 as-sociated 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 w~*~θ* contour inside the negatively signed vortex is close to the vortex center,while the w~*~θ* inside the positive one is stretched to the saddle point aligning with the diverging separatrix.As x/d increases,the negative w~*~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 con-tributes similarly to the longitudinal and spanwise heat flux components.