Dr. Hideyo Negishi (JAXA) recently presented at the 2019 AIAA Propulsion and Energy Forum titled: “Numerical Study of Tip Clearance Effects in a Centrifugal Pump with Unshrouded Impeller for Liquid Rocket Engines.” JAXA used CRUNCH CFD to model a full-stage LE-X liquid hydrogen pump.
Using an unshrouded impeller in liquid rocket pumps is a relatively new technology. The conventional shrouded impeller has been widely used in conventional liquid rocket engines. One of disadvantages of an unshrouded impeller is the drop in performance due to the tip leakage induced between the casing and the impeller blades. Therefore, understanding the tip clearance effects on the flow field and pump performance is indispensable to realizing high-performance unshrouded impellers. This study ran steady-state compressible Reynolds-averaged Navier-Stokes simulations to investigate the tip clearance effects in a liquid hydrogen centrifugal pump with an unshrouded impeller taking into account the fluid properties of parahydrogen. First, the computed results were validated against the results obtained in the pump test. Second, the parametric study on the tip clearance effects was done considering five different tip clearance ratios relative to the mean blade height at the impeller inlet and outlet. The computed and experimental results agreed well and revealed several key characteristics related to the tip clearance in theunshrouded impeller.