EXPERIMENTAL AND NUMERICAL ANALYSIS OF ADDITIVELY MANUFACTURED INCONEL 718 COUPONS WITH LATTICE STRUCTURE

In the present paper, lattice geometries have been developed and tested for application in internal cooling of gas turbine blades. These geometries are suitable for embedding within a near surface or double wall cooling configuration. Two types of unit cells with variation in number of ligaments and porosity, were used to generate two lattice configurations. The first type of unit cell consisted of six ligaments of 0.5 mm parameter joined at a common vertex situated at the middle. As such, three ligaments were located on each side of the common fiddle vertex. In addition, the top half of the unit cell was stated 60 degrees compared to the bottom half of the unit cell. the second type of unit cell was derived from the first type but with four mutually perpendicular ligaments added in the middle lane. Two lattices, referred to as L1 and L2, were obtained by repeating the type 1 and type 2 unit cells, respectively, in both streamwise and spanwise directions. The test coupons consisted these lattice structures embedded inside a channel of 2.54 height, 38.07 mm width and 38.1 mm in length. The coupons were fabricated using Inconel 718 powder through elective laser sintering (SLS) process. The heat transfer and pressure drop performance was evaluated using steady state tests with constant wall temperature boundary condition and for channel Reynolds number ranging from 2,800 to 15,000. In addition, steady state numerical conjugate heat transfer simulations were conducted to obtain a detailed insight into the prevalent flow field and temperature distribution. Experimental results showed a heat transfer enhancement of upto 3 times at the highest Reynolds number compared to a smooth channel. Both the heat transfer and pressure drop increased with a decrease in the porosity from L1 to L2. The numerical results revealed formation of prominent vortical structures in the interunit cell spaces. These vortical structures were located in the upper half of the channel causing an increased heat transfer on the top end wall. As a result, these lattice structures provided an augmented heat transfer with a potential for favorable redistribution of the coolant.