Heat Transfer on a Stationary Test Cylinder with Wake Generators

Introduction I N modern gas turbines, one of the most critical heat transfer regions on a turbine blade is near the blunt leading edge, where there is a stagnation point with a thin boundary layer, which leads to high heat transfer. By obtaining a semi-analytical solution, Frossling1 provided the Frossling factor, Nu/ √ Re, as a function of the angular position from the stagnation point. The correlation was valid on the front surface of a cylinder with θ ≤ 60 deg in a laminar flow region. Churchill and Bernstein2 studied the heat transfer of forced convection in a crossflow over a circular cylinder. They proposed correlation of experimental heat transfer data on a cylinder under both constant heat flux and constant wall temperature boundary conditions. Simoneau et al.3 investigated the effect of an upstream rotor on the heat transfer on a circular cylinder. They found that doubling the rotor–stator distance had only a small effect on both turbulence and Nusselt number. O’Brien4 explored both time-averaged (steady-state) and time-resolved (instantaneous) effects of wake passing on the heat transfer in the stagnation region of a cylinder. He reported that the time-averaged heat transfer were asymmetric with respect to the stagnation line. Han et al.5 investigated the influence of unsteady wake on the heat transfer coefficient of a gas turbine blade. Funazaki6 measured the time-averaged heat transfer distributions around the leading edge of a blunt body that was under the influence of incoming periodic wakes. He found that the wakes passing over the leading edge cause a significant increase in heat transfer before flow separation. Park et al.7 used a digital particle image velocimetry/thermometry (DPIV/T) technique to measure the velocity and temperature distribution of the wake on a heated circular cylinder. They demonstrated that DPIV/T could be a viable method to measure velocity and temperature accurately in turbulent flows. In the present experimental study, a test cylinder is submerged in the wake of an upstream array of cylinders (rods) of smaller diameter than that of the test cylinder. The influence of the wakes on the heat transfer over the test cylinder is investigated by varying the freestream Reynolds number, the number of upstream rods n, and the adjustable shift angle between the rods and the test cylinder,