Masaharu Uchiumi

Improvement of Inlet Flow Characteristics of LE-7A Liquid Hydrogen Pump

LE-7A engine inducers require high head rise and high suction performance in spite of cavitating conditions because a low-speed, low-pressure pump is not used in front of the main pump in the LE-7A engine. During the development phase, use of the LE-7A fuel turbopump with an original inducer resulted in a noticeable deterioration of suction performance near the required net positive suction head. When the pump inlet pressure was gradually reduced, the inducer caused sudden remarkable head degradation, and the rotor vibration was greatly amplified because the frequency of the vibration almost coincided with that of the second critical speed of the turbopump. This vibration was caused by a rotating-stall-type phenomenon, which is considered to be closely related to backflow cavitation at the inducer inlet. Improvement of the inducer was indispensable for enhancement of the reliability of the hydrogen turbopump. Thus, an inlet flow coefficient larger than that of the original inducer was selected to reduce the inlet backflow. A redesign of the original inducer and test results of the hydrogen turbopump with the newly developed inducer are reported.

Suppression of Cavitation Instabilities in an Inducer by J Groove

The suppression of cavitation instabilities was attempted through the control of tip leakage vortex cavitation. The control was made by using shallow grooves, called J groove, on the casing wall. With J grooves, the onset regions of the rotating cavitation and the asymmetric cavitation could be diminished. However, a cavitation surge appeared at higher cavitation numbers. From the observation of cavitation, it was found that the cavitation surge occurred when the tip leakage vortex cavitation started to interact with the leading edge of the next blade. This type of cavitation surge could be avoided by extending the leading edge of the J groove upstream. However, in this case, another tyr of cavitation surge occurred at much lower cavitation numbers, which was caused by the cavitation between the blade surface and the tip leakage vortex cavitation. These results highlight the importance of the tip leakage vortex cavitation for cavitation iritabilities.

Rotordynamic Forces Acting on Three-Bladed Inducer Under Supersynchronous/Synchronous Rotating Cavitation

Asymmetric cavitation, in which cavity lengths are unequal on each blade, is known as a source of cavitation induced shaft vibration in turbomachinery. To investigate the relationship of the uneven cavity length and rotordynamic force in a cavitating inducer with three blades, we conducted two experiments. In one, the growth of cavity unevenness at the inception of synchronous rotating cavitation in cryogenic flow was observed, and in the other, the rotordynamic fluid forces in water were examined by using a rotordynamic test stand with active magnetic bearings. Rotordynamic performances were obtained within a wide range of cavitation numbers, and whirl/shaft speed ratios included supersynchronous/synchronous rotating cavitation. These experimental results indicate that the shaft vibration due to the rotating cavitation is one type of self-excited vibrations arising from the coupling of cavitation instability and rotordynamics.

Internal Flow and Axial Thrust Balancing of a Rocket Pump

Large axial thrust is produced on the rotor assembly of high-pressure rocket pumps. Thus, to ensure the reliability of bearings supporting the high rotational speed rotor, precise axial thrust balancing is essential. To realize complete axial thrust balancing, the back shroud of the main impeller is employed as the balance piston of a self-balancing type axial thrust balancing system in which the rotor assembly moves axially to compensate unbalance axial force. In this balancing system, which is often applied, complicated internal flow characteristics and pressure distributions are very important for predicting the precise characteristics of the axial thrust produced by the system. In the present study, a calculation method for analyzing the internal flow system taking into account effects of boundary layer conditions and angular momentum change in the impeller side-chambers is applied to the system combining the balance piston and grooves on the casing wall of the balance piston chamber. The analysis program is able to detect phenomena which could not be captured in past calculations and is effective for calculating internal flow characteristics much faster than possible with CFD analysis. A combination of balance piston and grooves on the casing wall of the balance piston chamber was confirmed to be suitable for extending the dynamic range of axial thrust balancing although installation of the grooves increased the leakage flow rate and friction torque at the same time.

Improvements of Inducer Inlet Backflow Characteristics Using 3-D Inverse Design Method

The three-dimensional inverse design method was applied to improve the inlet backflow characteristics of highly loaded turbopump inducers for a liquid hydrogen rocket engine. Flow mechanisms, both for conventional and inverse design inducers, were investigated experimentally by flow field measurements and flow visualization, as well as numerically by the application CFD. The conventional inducer, which had been designed for the H-IIA rocket LE-7A engine turbopump, had a strong inlet backflow at the design point. Optimizing the blade loading distribution using the 3-D inverse design method and a CFD analysis eliminated this inlet backflow. Water model tests confirmed the elimination of inlet backflow in the inverse design inducers. However, it was confirmed that the suppressed inlet backflow tended to make cavitation occur in the blade passages and reduced suction performance. Cavitation visualization and FFT analysis of unstable phenomena were also performed in this study.

Preliminary Design and Analysis for the LE-X Engine Components

JAXA is planning to develop the next booster engine called LE-X with higher reliability and at significantly reduced cost. The LE-X is under study for the future expendable launcher (post H-2A) with enhanced reliability and at reduced cost. We aimed to achieve significant cost reduction by drastic simplification of the components and innovation of the manufacturing process. In 2007, we had optimized the engine baseline configuration. We examined components designs which have potentially achieved cost-cutting targets. This paper reports the progress of the component design. The key design of each component described. At the present, it appears that preliminary design of the LE-X components is successfully conducted. Feasibility of the components designs and the manufacturing process was confirmed.

Ground-Test and Flight Results of LE-7A FTP with an Alternate Inducer

An alternate inducer for the LE-7A fuel turbopump (FTP) was newly developed to eliminate the deterioration of suction performance of the original inducer at low net positive suction head (NPSH). Detailed data of the pump inducer were obtained in tests of both the turbopump alone and the engine system. In these tests, a hydrogen inlet feed line of the same configuration as that employed in actual flight was used. The tests were conducted in wide ranges of inlet pressures and flow rates. The second test flight of the H-IIA launch vehicle, in which the LE-7A FTP with the alternate inducer was installed, was successfully carried out in February 2002. Many flight data concerning the LE-7A FTP were obtained and analyzed. The results of both ground tests and test flights of the FTP with the alternate inducer are presented in this paper.

Rotordynamic Characteristics of Floating Ring Seals in Rocket Turbopumps

Floating ring seals offer an opportunity to reduce leakage flows significantly in rotating machinery. Accordingly, they have been applied successfully to rotating machinery within the last several decades. For rocket turbopump applications, fundamental behavior and design philosophy have been revealed. However, further work is needed to explore the rotordynamic characteristics associated with rotor vibrations. In this study, rotordynamic forces for floating ring seals under rotor’s whirling motions are calculated to elucidate rotordynamic characteristics. Comparisons between numerical simulation results and experiments demonstrated in our previous report are carried out. The three-dimensional Reynolds equation is solved by the finite-difference method to calculate hydrodynamic pressure distributions and the leakage flow rate. The entrance loss at the upstream inlet of the seal ring is calculated to estimate the Lomakin effect. The friction force at the secondary seal surface is also considered. Numerical simulation results showed that the rotordynamic forces of this type of floating ring seal are determined mainly by the friction force at the secondary seal surface. The seal ring is positioned almost concentrically relative to the rotor by the Lomakin effect. Numerical simulations agree quite well with the experimental results.

Computational Analysis of Unsteady Flow in a Partial Admission Supersonic Turbine Stage

Turbines used in upper stage engine for a rocket are sometimes designed as a supersonic turbine with partial admission. This study deals with numerical investigation of supersonic partial admission turbine in order to understand influences on the unsteady flow pattern, turbine losses and aerodynamic forces on rotor blades due to partial admission configuration. Two-dimensional CFD analysis is conducted using “Numerical Turbine” code. Its governing equation is URANS (Unsteady Reynolds Averaged Navier-Stokes Simulation) and fourth-order MUSCL TVD scheme is used for advection scheme.The unsteady simulation indicates that strongly non-uniform circumferential flow field is created due to the partial admission configuration and it especially becomes complex at 1st stage because of shock waves. Some very high or low flow velocity regions are created around the blockage sector. Nozzle exit flow is rapidly accelerated at the inlet of blockage sector and strong rotor LE shock waves are created. In contrast, at rotor blade passages and Stator2 blade passages existing behind the blockage sector, working gas almost stagnates. Large flow separations and flow mixings occur because of the partial admission configuration. As a result, additional strong dissipations are caused and the magnitude of entropy at the turbine exit is approximately 1.5 times higher than that of the full admission.Rotor1 blades experience strong unsteady aerodynamic force variations. The aerodynamic forces greatly vary when the Rotor1 blade passes through the blockage inlet region. The unsteady force in frequency domain indicates that many unsteady force components exist in wide frequency region and the blockage passing frequency component becomes pronounced in the circumferential direction force. Unsteady forces on Rotor2 blades are characterized by a low frequency fluctuation due to the blockage passing.Copyright

Effects of Swirl Brakes on the Leakage Flow Between the Casing and the Shroud of a Centrifugal Impeller

CFD simulations were performed for the leakage flow in the gap between the casing and the shroud of a centrifugal impeller. The effects of swirl brakes created in the casing on the leakage flow were numerically investigated. The leakage flow swirling due to impeller rotation was trapped inside a swirl brake and interacted with the walls of the swirl brake, generating a very complex flow and a vortex structure inside. By the interaction with swirl brakes, the leakage flow rapidly lost its angular momentum mainly in the outer region of the swirl brake. The loss of swirl resulted in a decrease of the pressure difference in the radial direction due to the centrifugal force effect. The radial distribution of pressure in the gap between the casing and the shroud was largely modified, and thus the axial thrust force on the impeller was changed as well. The thrust balance of the impeller can be adjusted by an appropriate design of swirl brakes and the instability of rotating shaft can be reduced by decreasing the swirl of the leakage flow.Copyright