A turbine airfoil (10) includes a flow displacement element (26A-B, 26A′-B′) positioned in an interior portion (11) of an airfoil body (12) between a pair of adjacent partition walls (24) and comprising a radially extending elongated main body (28). The main body (28) is spaced from the pressure and suction side walls (16, 18) and further spaced from one or both of the adjacent partition walls (24), whereby a first near wall passage (72) is defined between the main body (28) and the pressure side wall (16), a second near wall passage (74) is defined between the main body (28) and the pressure side wall (18) and a central channel (76) is defined between the main body (28) and a respective one of the adjacent partition walls (24). The central channel (76) is connected to the near wall passages (72, 74) along a radial extent. One or more radial ribs (64) are positioned in the central channel (76) that extend partially across the central channel (76) between the main body (28) and the respective adjacent partition wall (24).