ABSTRACT
Among all heat-transfer enhancement techniques, jet impingement has the most signicant potential to increase the local heat-transfer coefcient. However, the construction of this ow arrangement weakens the structural integrity, and therefore impingement cooling is used in locations where thermal loads are excessively high. Jet impingement heat transfer is most suitable for the leading edge of a rotor airfoil (bucket), where the thermal load is highest and a thicker cross section of this portion of the airfoil can suitably accommodate impingement cooling. The structural strength required in a stator airfoil (vane) is less than that required in a rotor airfoil; therefore, jet impingement in the midchord region is used for stator airfoils. There are several arrangements possible with cooling jets, and different aspects need to be considered before optimizing an efcient heat-transfer design. Figure 4.1 shows a schematic conguration of cooling jets in an inlet guide vane (Taylor, 1980). The shape of the jet nozzle, the layout of jet holes, the shape of connement chambers, and the shape of target surfaces have a signicant effect on the heat-transfer coefcient distribution. The following sections discuss these features in details.
