Jinhan Kim

Effect of Tip Clearance on the Cavitation Performance of a Turbopump Inducer

The characteristics of steady and unsteady cavitation in a two-bladed inducer for a turbopump are investigated. A helical inducer with inlet tip blade angle of 7.8 deg and a tip solidity of 2.7 is tested using water as a working fluid. To determine the effect of tip clearance on the inducer performance, a series of experiments is conducted at three different tip clearances. As the tip clearance increases, the inducer head decreases and the critical cavitation number increases. Unsteady pressure measurements at the inducer inlet indicate the existence of attached cavitation and cavitation surge, but no rotating cavitation in the test inducer. Attached cavitation and cavitation surge appear for all three cases of tip clearance. The cell number and propagation speed of the attached cavitation are determined through a cross-correlation analysis. In the case of attached cavitation, one cell rotates at the same speed as that of the inducer. In addition, the surge frequency decreases with a decrease in the cavitation number, and the ratio of surge frequency to inducer rotational frequency is found to range from 0.07 to 0.20.

Effects of Floating-Ring Seal Clearance on the Pump Performance for Turbopumps

Pumps for a turbopumpgenerally operate under high rotational speeds and large-head-rise conditions. Therefore, reliability is a prime design requirement. Floating-ring seals are frequently employed in a turbopump because of robustness despite relatively high leakage losses. A number of studies have been performed on the floating-ring seal itself, but the effects of the floating-ring seal on the performance of the whole pump are not widely studied, in spite of their importance. The effects of floating-ring seal clearance on the hydraulic and suction performances of a pumpare investigated byboth experimental and computationalmethods in the present study.The experimental results showed that the head rise and the efficiency increased as the floating-ring seal clearance decreased. The results also showed that the leakageflow injected into the inducer inlet enhanced the suction performance of the pumpbydiminishing the size of the backflows. The strength of the backflow becomes weak as the injected leakage flow at the inducer inlet prevents the flow from prerotation.

Rotordynamic Analysis of a Turbopump with the Casing Structural Flexibility

A critical speed analysis is performed for a 30-ton thrust demonstrator turbopump considering the casing structural flexibility. A full three-dimensional finite-element method including rotor and casing is used to predict rotordynamic behavior. The rotor-alone model and the rotor-casing-coupled model with fixed-fixed and free-free boundary conditions are calculated to investigate the effects of the casing structural flexibility. The stiffness of ball bearings is applied as unloaded and loaded values to consider rotor operating conditions in a vacuum and real engine, respectively. From the results of the numerical analyses, it is found that the effect of the casing structural flexibility reduces the critical speeds of the turbopump. Especially, the loaded rotor condition with higher bearing stiffness is affected dramatically more than the unloaded rotor condition with lower bearing stiffness.

Tip Clearance Effect on the Performance of a Shrouded Supersonic Impulse Turbine

An experimental investigation of the effect of tip clearance on the performance of a shrouded supersonic impulse turbine was performed in this study. A single-staged axial flow impulse turbine designed to have a rotor inlet relative Mach number of 1.7 was used for the experiment. Turbine efficiency was measured at various settings of tip clearances, rotational speeds, and turbine pressure ratios to observe the characteristics of the efficiency gradient. The overall efficiency of the supersonic impulse turbine was largely affected by rotational speed. For a fixed rotational speed, local maximum efficiency was found near a turbine pressure ratio at which the turbine nozzle was fully expanded. At a reference test point, the linearly estimated efficiency gradient was 0.09. However, efficiency variation with respect to tip clearance was nonlinear, and relatively larger efficiency gradients were found at small tip clearances and high rotational speeds. It has been found that the efficiency gradient varies linearly with the cube of rotational speed and shows its minimum value near the reference turbine pressure ratio.

Study on inducer and impeller of a centrifugal pump for a rocket engine turbopump

A hydraulic performance test is conducted for a fuel pump of a liquid rocket engine turbopump. The pump driven by an electric motor is tested in a water environment. Experimental results indicate that the inducer has a negligible effect on the head and efficiency of the pump but a significant effect on the cavitation performance. Additionally, an autonomous inducer test is carried out to investigate the effect of the inducer on the pump performance in more detail, and it is found out that the pump reaches a critical cavitation point when the inducer head is dropped by 55%. A reduction of required net positive suction head of the centrifugal pump by attachment of an inducer is also calculated considering the flow interference between the inducer and the centrifugal impeller, and it is found that the calculation shows a reasonable agreement with the test.

Effect of Solidity on the Performance of Turbopump Inducer

The hydraulic and suction performance of an inducer varies sensitively with the inducer geometry and this paper deals with solidity as the inducer geometry parameter. The typical performance characteristics of a basic inducer was investigated and tests with another three inducers of which the solidity is different from each other were performed, so the effect of solidity on the inducer performance was experimentally investigated. For a fixed flow coefficient, required NPSH of the inducer did not follow the conventional similarity rule, so this paper suggested another empirical formula. The hydraulic and suction performance was measured at four cases of the tip solidity ranged from 1.32 to 2.76. As long as the tip solidity had the value above 1.84, the hydraulic and suction performance of the inducer increased with decrease in the tip solidity. With further decrease in the tip solidity up to 1.32, however, inducer head decreased and the suction performance dropped sharply.

Numerical Study on the Hydrodynamic Performance Prediction of a Turbopump Inducer

In the present paper, computational studies on the hydrodynamic behavior of the inducer for the rocket-engine turbopump are presented including the effect of the mass flow rate. As the mass flow rate is increased, the inducer showed better performance with weak back flows which may have deleterious effects upon the anti-cavitation ability. But the adopted inducer showed low head rise with high volume flow rates, which may be caused by the small passage area near the trailing edge. The static pressure distributions at the shroud surface are compared with experimental results showing very good agreements except near the leading edge where strong back flows are present. The overall performance of the inducer such as, efficiency, head rise is also compared with experiments. The computational results are generally in good agreements with experimental ones near the design point, but two results show discrepancy at the high flow rate.冗⨀

Effect of Inducer on Hydraulic Performance of a Turbopump

A hydraulic performance test is conducted for a fuel pump of a liquid rocket engine turbopump. The pump driven by an electric motor is tested in a water environment. Experimental results indicate that the inducer has a negligible effect on the head and efficiency of the pump but a significant effect on the cavitation performance. Additionally, an autonomous inducer test is carried out to investigate the effect of the inducer on the pump performance in more detail, and it is found out that the pump reaches a critical cavitation point when the inducer head is dropped by 55%. I. Introduction hereas the KSR-III rocket launched in 2002 employed a pressure-fed liquid rocket engine, current research and development efforts at the Korea Aerospace Research Institute (KARI) are direct to developing a turbopump demonstrator for application to a gas generator cycle liquid (LOX and kerosene) rocket engine with 30-ton thrust level. 1 An oxidizer pump, a fuel pump and a turbine are assembled in series on an axis constituting a turbopump. Each pump has a single stage centrifugal impeller with an inducer and the turbine is of a single stage impulse type. The LOX pump has an axial inlet while fuel pump has a radial inlet. This paper presents the test results for the fuel pump of which design requirements are shown in Table 1. Normally for each pump of a turbopump, an inducer is installed upstream of a main centrifugal impeller to improve the cavitation performance of the pump. Inducer design is focused on obtaining sufficient cavitation margin rather than high efficiency. As a consequence, an inducer has a low flow coefficient, a small inlet angle, a sharp leading edge, and so on. In this study, conventional hydraulic and cavitation performance tests are performed for a pump, and then a pump test without the inducer is performed to investigate the inducer effect. Moreover, an autonomous inducer test is carried out to validate the performance of the inducer itself.

Water Tests of Fuel Pump for 75-ton Class Liquid Rocket Engine

A series of water tests of a fuel pump for liquid rocket engines are performed at a room temperature. According to the test results, the head coefficient of the pump follows the conventional similarity rule - unlike this, the pump shows better efficiency with higher rotational speed. Also, it is found that the pressure at the rear bearing outlet is higher than expected because the inlet of bypass pipe line is narrow. Furthermore, the cavitation performance of the fuel pump is found to be sufficient for the engine operation and is better at the lower flow ratio and higher rotational speed.

Numerical Simulation of Cavitating Flow Around Turbopump Inducer

The computational studies on the cavitating flow around a turbopump inducer were performed to see the effect of the cavitation on the performance of the inducer. The development of cavities around the inducer blades and the head drop of the inducer are observed as the inlet pressure reduces. The change of the backflow at the inducer inlet is also observed with the development of the cavities. The size of the backflow reduces as the inlet pressure is reduced due to the development of the cavities around the blades. The predicted suction performances of the inducer were compared with the experimental results. The results show that the computations overestimate the suction performances of the inducer than the experiments.