A turbine rotor blade (260, 760, 860, 960, 1060, 1160) for a turbine section of an engine, comprising: a platform; and an airfoil extending from the platform into a mainstream gas path of the turbine section, the airfoil comprising a pressure side wall (312, 712, 1012, 1162), a suction side wall (314, 714, 1014, 1164) joined to the pressure side wall (312, 712, 1012, 1162) at a leading edge (316,1166) and a trailing edge (318, 1168), and a tip cap (330, 740, 1042, 1130) extending between the suction side wall (314, 714, 1014, 1164) and the pressure side wall (312, 712, 1012, 1162); an internal cooling circuit (400, 1100) having a tip cap passage (420, 720, 820, 920, 1020, 1120) configured to deliver cooling air to the tip cap (330, 740, 1042, 1130); and a flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) positioned within the tip cap passage (420, 720, 820, 920, 1020, 1120) of the internal cooling circuit (400, 1100), wherein the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) is tear-drop or airfoil shaped and generally extends in a chordwise direction to prevent or mitigate turbulence through the tip cap passage resulting from the flow accelerator, and wherein the flow accelerator blocks a portion of the tip cap passage and the resulting reduction in flow area functions to increase the speed of the cooling air through the tip cap passage, wherein the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) is arranged to divide the tip cap passage (420, 720, 820, 920, 1020, 1120) into a first portion defined between the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) and the suction side wall (314, 714, 1014, 1164) and a second portion defined between the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) and the pressure side wall (312, 712, 1012, 1162). a platform; and an airfoil extending from the platform into a mainstream gas path of the turbine section, the airfoil comprising a pressure side wall (312, 712, 1012, 1162), a suction side wall (314, 714, 1014, 1164) joined to the pressure side wall (312, 712, 1012, 1162) at a leading edge (316,1166) and a trailing edge (318, 1168), and a tip cap (330, 740, 1042, 1130) extending between the suction side wall (314, 714, 1014, 1164) and the pressure side wall (312, 712, 1012, 1162); an internal cooling circuit (400, 1100) having a tip cap passage (420, 720, 820, 920, 1020, 1120) configured to deliver cooling air to the tip cap (330, 740, 1042, 1130); and a flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) positioned within the tip cap passage (420, 720, 820, 920, 1020, 1120) of the internal cooling circuit (400, 1100), wherein the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) is tear-drop or airfoil shaped and generally extends in a chordwise direction to prevent or mitigate turbulence through the tip cap passage resulting from the flow accelerator, and wherein the flow accelerator blocks a portion of the tip cap passage and the resulting reduction in flow area functions to increase the speed of the cooling air through the tip cap passage, wherein the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) is arranged to divide the tip cap passage (420, 720, 820, 920, 1020, 1120) into a first portion defined between the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) and the suction side wall (314, 714, 1014, 1164) and a second portion defined between the flow accelerator (430, 730, 830, 832, 834, 930, 1030, 1122) and the pressure side wall (312, 712, 1012, 1162).