On the Cooling of Gas Turbines

This article deals with measurements of convective heat transfer coefficients in three fluid flow patterns that concern both internal and external cooling of gas turbine components; in particular, the flow in a couple of smooth, or ribbed, ducts connected by a 180° sharp turn, a jet in cross-flow, and a jet impinging on a wall for short nozzle-to-wall distances. An infrared (IR) scanning radiometer, associated with the heated-thin-foil technique, is used to perform the experimental measurements. In the latter case, particle image velocimetry (PIV) is also used to characterize the velocity field. Channels with 60° ribs show spanwise asymmetry of heat tranfer maps because of secondary flows. For both tested rib pitches, the increase of turbulence due to the bend induces higher values of the Nusselt number in the outlet duct but the increase is lower than that relative to the smooth channel. For the jet in cross-flow, the normalized Nusselt number has values equal to unity outside the jet wake. Immediately downstream of the injection, a low heat transter zone is present; afterward, the Nusselt number increases and attains a maximum value, which first increases and then decreases for increasing injection ratio. For a jet impinging on a wall at short distances, the radial Nusselt number profile shows a minimum at the stagnation point, two maxima, and a minimum between them. As the impingement distance increases, minima and external maxima first become much milder and then disappear while internal maxima coalesce in the stagnation point. Results seems to agree with PIV measurements.