Thermodynamic effects of cryogenic medium have not been researched adequately for the accurate solution of the turbopump axial thrust, which is a key technique for the reusable rocket engine. In this paper, a liquid oxygen turbopump was chosen to reveal the influence of thermodynamic effects. Experimental tests using liquid nitrogen were carried out to verify the numerical model, and the numerical results under liquid oxygen were discussed to reveal the thermodynamic effects. The results show that the head coefficients and the efficiencies decrease under all operating conditions, due to the alterations of the physical properties caused by the thermodynamic effects of cryogenic medium. The total axial thrusts decrease in the range of 1.63% to 3.22%, the maximum variations of the axial thrust acting on the impeller shroud and hub are 2.96% and 2.69%, separately, owing to the divergences of the cavity structure. The entropy generation rate was chosen to analyze the power loss, and the minimum deviation caused by the thermodynamic effects is 5.01% at the normal condition; the distributions of the entropy generation rate in the rotor-stator cavities are obviously changed due to the addition of the thermodynamic effects. The new omega method was selected to compare the vortex distribution. The vortex strength changes slightly, owing to the reduction of the medium viscosity caused by the temperature rise. It is critical to consider the thermodynamic effects of cryogenic media for accurately calculating the axial thrust of a high power-density turbopump.

Hydrostatic guideways have varied applications in precision or ultra-precision machine tools due to their high motion accuracy and low friction coefficient. Slider motion straightness is an important accuracy index for evaluating precision of hydrostatic guideways. It can be defined as the linear deviation of the slider center within the entire or any assigned stroke. This paper mainly focuses on the relationship between the keeper rail (upper guiderail) preload and slider motion straightness in the closed hydrostatic guideways, where the slider is enveloped by the guiderails. A finite element method was used to calculate keeper rail deformation under different screw preloads, slider motion straightness was measured by laser interferometer. Mapping relationship between screw preload and slider motion straightness was obtained. Experimental results shown that the end of the keeper rail had larger deformation for same preload conditions on all screws. This had an obvious effect on slider motion straightness. When oil supply pressure was 0.85 Mpa, slider motion straightness was 2.08 μm and 1.85 μm (within the entire stroke 330 mm) with torque on all screws as 15Nm and 20Nm, respectively. After uneven preload was employed, slider motion straightness was 0.87 μm and 0.84 μm for the above mentioned two cases. Accuracy increased by more than 50 percent. Screw preload approach proposed in this study can be used to guide the assembly processes of closed hydrostatic guideways with other forms for improving the motion straightness.

As a key factor of a reusable turbopump, axial thrust directly determines the reliability of the bears and seals, especially considering the influence of rotational speeds and thermodynamic effects. In this study, numerical simulations and experimental tests were conducted to explore the impact of rotational speeds and the divergences of the turbopump performance with/without the thermodynamic effects. The experimental data obtained at 15000 r/min are in good agreement with the numerical results, illustrating the validity of the numerical model. The results show that the head deviations based on the affinity laws are relatively smaller, only 0.1% difference at normal condition, yet the efficiency increases from 72.5% to 73.8%, which need to be modified through the formula correction. Notably, the axial thrusts acting on impeller are significantly affected by the rotational speeds, and the values at rated flowrate decrease 17.6% after increasing the operating condition to rated speed. The affinity laws are not applicable for obtaining the turbopump axial thrusts under different speeds. Furthermore, due to the changes of the local physical properties, the values of head coefficient and efficiency decrease 2.8% and 1.3% at rated flowrate, respectively, when the thermodynamic effects of liquid oxygen are considered. Meanwhile, the relative variations of axial thrust are between 1.46% and 3.74% within the whole flow range. Finally, an in-depth analysis of the internal flow was conducted through the velocity field and vorticity method. In conclusion, both the rotational speeds and thermodynamic effects significantly affect the performance of a cryogenic turbopump, especially the axial thrust, and the unsteady results of the rotor-stator cavity leakage flow need to be analyzed in the future.