In this study, the performance characteristics of a centrifugal pump according to fluid viscosity which is applied to a liquid rocket engine with turbopump propellant feed system were investigated. Various factors affecting the power loss of the centrifugal pump were analyzed and the cause of the change in pump efficiency was identified. In particular, we tried to derive quantitative results of pump efficiency variation caused by disc friction loss due to viscosity of pump fluids, which is the main cause of power loss change. For the three types of centrifugal pumps with different shapes, various comparative analyzes were carried out based on the results of the room temperature fluid and the cryogenic fluid and the test results of the actual medium. Based on the test results of the centrifugal pumps using the room temperature water as the test medium, the efficiency reduction effect for the high viscous fluid in the case of the fuel pump and the efficiency increase due to the low viscosity of the cryogenic fluid in the case of the oxidizer pump were confirmed.
In the component test of the oxidizer pump, the change of the pump characteristics on the hydraulic performance and the suction performance due to the low temperature environment could be reviewed by the test of the pseudo-medium using normal temperature water and liquid nitrogen. In the turbopump real-propellant test, the power balance between the pumps and the turbine was analyzed through the performance derived from each single component test for oxidant pump, fuel pump and turbine. The power balance analysis showed that the efficiency of the oxidizer pump as measured by the pseudo-medium could be reconsidered in the overall flow rate range including the design point and off-design point in a real medium environment.
The change of the pump efficiency due to the working fluid was greatly influenced by the increase and decrease of the disk frictional loss coefficient to the fluid viscosity. The tendency of this change could be confirmed by the ratio of the frictional loss power of the disk to the hydraulic power of the pump. In the case of an oxidizer pump using liquid oxygen as a real fluid, it was possible to present a empirical correlation of correction factor for the pump efficiency change due to the low viscosity effect in the cryogenic environment by analyzing the performance results of various test fluids such as room temperature water, liquid nitrogen and liquid oxygen.
From the results of this study, it was confirmed that the efficiency of the centrifugal pump with various operating fluids and test conditions were changed and its correlation was shown. These results enable to predict the performance of the centrifugal pump applied to the liquid rocket engine turbopump from the single component performance of the low rotational speed condition through the pseudo-medium such as room temperature water to the actual medium and the design rotational speed. Furthermore, it is expected that the exact operating point of the turbopump assembly can be set and used to more accurately predict the operating point of the liquid rocket.