Interior cooling configurations for turbine rotor blades

A rotor blade for use in a turbine of a gas turbine that includes:

• an airfoil defined between a concave pressure face and a laterally opposed convex suction face, wherein the pressure face and the suction face extend axially between opposite leading and trailing edges and radially between an outboard tip and an inboard end that attaches to a root configured to couple the rotor blade to a rotor disc;
• an interior cooling configuration that includes one or more cooling channels for receiving and directing a coolant through an interior of the rotor blade, wherein the one or more cooling channel includes a section configuration that comprises:
• a main channel divided into three non-overlapping segments in which an upstream segment connects to a downstream segment via a transition segment positioned therebetween, wherein the transition segment comprising a variable cross-sectional flow area that accommodates a main channel flow area reduction occurring between the upstream segment and the downstream segment;
• and
• one or more branching channels extending from the main channel via connections each of the one or more branching channels makes to the transition segment, wherein the one or more branching channels comprise a total branching channel flow area;
• wherein the section configuration comprises a section channel ratio indicating the main channel flow area reduction divided by the total branching channel flow area;
• wherein the section channel ratio comprises a predetermined value that relates to a desired flow characteristic for the coolant moving through the section configuration during operation.