Turbine rotor airfoil and corresponding method for reducing pressure loss in a cavity within a blade

A turbine rotor airfoil comprising:

• a leading edge and a trailing edge joined by a pressure side and a suction side, a tip end, and a radially opposite root end, wherein the tip end designates a radially outward position and the root end designates a radially inward position;
• and
• at least two multiple pass serpentine flow cooling circuits with radial coolant cavities formed within the airfoil to provide cooling for the airfoil comprising;
• a leading edge circuit comprising forward direction cavities comprising at least a first forward direction cavity located within the airfoil and a second forward direction cavity forward along a chordal axis from the first forward direction cavity, wherein the leading edge circuit flows forward with at least two substantially 180-degree turns at the tip end and the root end of the airfoil providing at least a penultimate forward direction cavity and a last forward direction cavity, wherein the last forward direction cavity is located along the leading edge of the airfoil;
• and
• a trailing edge circuit comprising aft direction cavities comprising at least a first aft direction cavity located aft of the first forward direction cavity, wherein the trailing edge circuit flows aft with at least two substantially 180-degree turns at the tip end and the root end of the airfoil providing at least a penultimate aft direction cavity (46d) and a last aft direction cavity, wherein the last aft direction cavity is located along the trailing edge of the airfoil;
• wherein the 180-degree turn into an entrance of a second radial coolant cavity from an exit of a first radial coolant cavity narrows from a consistent cavity width and then expands out back to the consistent cavity width downstream,
• wherein a diameter of a space between the first radial coolant cavities and the second radial coolant cavity expands at the entrance of the second radial coolant cavity and then reduces to a consistent diameter of space that is maintained between the first radial coolant cavity and the second radial coolant cavity the rest of the first radial coolant cavity and the second radial coolant cavity path.