Temperature correlations with vorticity and velocity in a turbulent cylinder wake

• Published in: The International journal of heat and fluid flow 2020-08, Vol.84, p.108606, Article 108606
• Main Authors: Chen, J.G., Zhou, Y., Antonia, R.A., Zhou, T.M.
• Format: Article
• Language: English
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2020.108606

•All the components of fluctuating velocity and vorticity vectors are experimentally measured.•The correlation between velocity and temperature exhibits different features from that between vorticity and temperature.•A large-scale streamwise structure occurs in the wake at x* = 40. This work aims to understand the difference in the correlations between the fluctuating temperature and the vorticity from that between the fluctuating temperature and the velocity in a turbulent cylinder near wake. Measurements are made at x/d = 10, 20 and 40, where x is the streamwise distance from the cylinder axis and d is the cylinder diameter, with a Reynolds number of 2.5×103 based on d and the free-stream velocity. The three components of the fluctuating velocity vector ui(i = 1, 2 and 3), vorticity vector ωi (i = 1, 2 and 3), and temperature θ in the plane of the mean shear are measured simultaneously with a multi-wire probe consisting of four X-hotwires and four cold wires. It is found that at x/d = 10, both correlations between uiand θ and between ωi and θ predominantly take place at St = 0.21, due to the concentric distribution of the Kármán vortices and the heat. With increasing x/d, the correlation between ωi (i = 1, 2 and 3) and θ drops rapidly, as a result of the weakened Kármán vortices; in contrast, the correlation between u1 and θ increases appreciably, largely due to an enhanced correlation between u1 and θ at low frequencies or scales of motions larger than the Kármán vortex. The slowly decreasing (along x) two-point autocorrelations of u1 and θ suggest that the very-large-scale motions (VLSMs) found in wall flows occur also in the turbulent wake and are responsible for the high correlation between u1 and θ at low frequencies.