Blade with stress-reducing bulbous projection at turn opening of coolant passages

A turbine rotor blade comprising an airfoil defined by a concave pressure side outer wall and a convex suction side outer wall that connect along leading and trailing edges and, therebetween, form a radially extending chamber for receiving the flow of a coolant, the turbine rotor blade further comprising:

• a rib configuration including:
• a rib partitioning the radially extending chamber into a first passage on a first side of the rib and an adjacent second passage on an opposing second side of the rib, each passage enclosed at an end of the radially extending chamber by an end member of the radially extending chamber;
• and
• a turn opening defined in an end of the rib through which the coolant passes between the first passage and the second passage within the end member of the radially extending chamber;
• and
• a bulbous projection extending along the end of the rib and on opposing radially extending sides of the turn opening.