Effects of high turbulence and wakes on mass transfer from gas turbine blades

The effect of wakes in the presence of varying levels of background freestream turbulence on the mass transfer from simulated gas turbine blades is investigated. The mass transfer tests (using the naphthalene sublimation technique as an analogy to heat transfer) are conducted in a four-blade linear cascade arranged in a central passage configuration. The flow in the cascade channels is balanced by adjusting outer-wall bleeds and two tailboards trailing the outer two blades. A section of one blade is cast in naphthalene and exposed to varying flow conditions. Local mass transfer measurements are made on both the suction and pressure sides of the turbine blade in the two-dimensional and three-dimensional regions of the flow. For each test, the local naphthalene sublimation is measured using a four axis measurement table. The base case tests are for an array of wake-generating blades with a pitch spacing equal to that of the turbine blade row. Comparisons are made between the base case conditions and tests with different wake-generating pitch, different blade-row separations, different Reynolds number and different levels of background turbulence. The results indicate that the wake and turbulence disturbances have only a small effect on the mass transfer near the endwall where secondary flows develop. However, the disturbed flows produce a strong effect on other parts of the blade surface, particularly along the suction side, where an earlier start for transition to a turbulent boundary layer on the surface occurs for increased background turbulence, higher Reynolds number and for wakes shed from wake-generating blades near the leading edge of the turbine blade.