01. Experimental/Computational Fluid Dynamics

We have developed and produced a liquid nitrogen closed-loop test apparatus and a model turbopump with an axial inducer, of which there have been only a few examples before. The primary objective of this test apparatus is to advance three fundamental technologies for fluid machinery and systems, predicting pump performance and internal flow, understanding thermodynamic effects on cavitation performances, and cavitation instabilities in cryogenic flow. These technologies are especially crucial for developing liquid hydrogen turbopumps, which we consider one of the most essential components for a future energy supply system. One of the features of this test apparatus is the integrated structure from the pump motor to the pump's rotating shaft. This allows for direct measurement of rotating shaft torque by attaching a torque meter to the rotating shaft, instead of the conventional magnetically coupled pumps. A special seal and bearing system are developed to realize this complex test apparatus. As a result, this mechanism enables more accurate experimental measurements of pump performance in principle. In addition, this apparatus includes a visualization system for inducer blade surfaces utilizing a vacuum-insulated layer. It can perform synchronized visualization of cryogenic cavitation on inducer blades and pump performance measurement. Therefore, it is possible to evaluate the impact of cavitation and its thermodynamic effects on the unsteady performance of the tested pump. Experimental results of the centrifugal pump equipped with the inducer for liquid nitrogen generally agreed with the CFD simulation results conducted during the pump's design phase. This validation highlights the effectiveness of cryogenic pump measurement technology proposed by our developed testing apparatus. Moreover, preliminary test footage in the visualization system indicated that using this visualization mechanism enables capturing liquid nitrogen cavitation occurring on the inducer blade surfaces, while minimizing the influence of boil-off gas generation on its visibility as planned.