EFFECTS OF MAINSTREAM TURBULENCE LEVEL AND INJECTION HOLE LOCATION ON FILM-COOLED STAGNATION MASS AND HEAT TRANSFER

摘要

The effects of a mainstream turbulence level and surface injection on the connective mass/heat transfer phenomena over a circular cylinder were investigated using the naphthalene sublimation technique. A test cylinder with one row of seven slanted injection holes was used to simulate the leading edge of a turbine blade. These injection holes were spaced at three hole's diameters and were angled at 30" and 90" from the surface in the spanwise and streamwise directions, respectively. Experiments were conducted at two different values of the mainstream turbulence level (Tu = 0.4%, 7.0%), three different angular locations of injection holes (Q_(inj) = 0°, 5°, 10°), and five different blowing ratio values (M = 0.0, 0.85, 1.12, 1.38, 1.63) at a constant mainstream Reynolds number of Re = 45,500. To clarify the complex nature of the flow field, the numerical simulations were also accomplished in the present work. Either an increase in the mainstream turbulence level or the presence of ejected flows produced an earlier onset of the critical flow regime on the cylinder surface. Generally, an increase of the blowing ratio resulted in an augmentation of the measured span-wise-averaged heat transfer coefficients in the front portions of the cylinder. The local heat transfer coefficients surrounding the injection holes are quite sensitive to small changes in angular location of the injection holes except for highly mainstream turbulence conditions. A higher mainstream turbulence level generally caused a quicker mixing of the ejected flows with the approaching mainstream downstream of the injection. Among the present tested conditions, there is no systematic relationship between the mainstream turbulence level and blowing ratio with the heat transfer rate on the film-cooled cylinder surface if a particular angular location of injection holes is chosen.