Design and Testing of an Internally-Cooled Radial Turbine With High Tip Speed

Radial impellers are not internally-cooled because of the manufacturing challenge. The conventional manufacturing method for internally-cooled components is an investment cast process using a ceramic core to create internal passages. This approach has been developed for axial gas turbines for the past few decades and is a low-risk manufacturing approach for single blade castings. However, conventional manufacturing methods are difficult to apply to a radial impeller in a cost-effective manner. For example, the entire impeller (blades and the hub) are typically manufactured from a single piece of material. Therefore, if one blade is poorly cast, the entire impeller must be thrown away. To overcome the complexity and reduce production risk, additive manufacturing can be used to build internally-cooled radial impellers. Additive manufacturing is a growing area and gaining operational experience is required to confidently build complex parts, such as a radial impeller with small, internal passages. In this paper, additive manufacturing is used to avoid the challenges of conventionally manufacturing. Multiple iterations of the internal cooling design are examined to illustrate lessons learned. Flow and heat transfer tests are used to verify the impeller cooling design. Material properties are discussed to verify that the impeller can withstand high rotational stresses.