Energy Separation in the Wake of a Cylinder

Energy separation is a spontaneous redistribution of total energy (enthalpy) in a fluid without external work or heat flow, resulting in some portion of fluid having higher total energy (enthalpy) and another portion having lower energy (enthalpy) than the surrounding fluid. The present study investigates the mechanism of energy separation in the vortex field behind an adiabatic circular cylinder. Time-averaged velocity and temperature measurements are carried out in the wake of a cylinder in a cross flow of air. The measurements are performed at downstream locations of three, five, seven, and ten diameters, for a Reynolds number, based on upstream velocity and cylinder diameter, of 9.2×104 and freestream Mach number of 0.22. The measured velocity and recovery temperature data are expressed in nondimensional form as an energy separation factor. The distribution of energy separation factor indicates that the main cause of energy separation is the periodic vortex flow in the wake. The vortex strength and the separation effect decrease as the flow moves downstream. However, energy separation is observed even ten diameters downstream.