Liquid Rocket Engine Turbopump Research Articles

Dynamic Response of a Rotor Supported on Hybrid Bearings in Air, Water, and Liquid Nitrogen: Measurements and Comparisons to Predictions

Abstract Modern liquid rocket engine turbopumps implement hybrid bearings, which combine hydrostatic and hydrodynamic fluid film principles, in compact and lightweight units known for their superior reusability, durability, and reliability. This study aims to provide extensive and reliable test data for the purpose of anchoring and benchmarking predictive tools for these bearings. This paper provides comprehensive dynamic response measurements of a rotor weighing 10.40 kg and approximately 60 mm in diameter at the bearing locations. The test rotor is supported on two hybrid journal bearings with a bearing length to bearing diameter ratio of approximately 0.42 and a bearing radial clearance to rotor radius ratio of around 0.0017. The bearings are tested with air, water, and liquid nitrogen, serving as surrogate test fluids for common propellants in liquid rocket engines. Rotor run-up and speed coast-down tests are conducted to measure shaft motion responses. The results clearly demonstrate that the rotordynamic characteristics of the test rotor supported on the hybrid journal bearings largely rely on properties of the test fluids and their feeding conditions. Notably, when air is pressurized into the test bearings, the shaft motion responses differ markedly from those observed with water and liquid nitrogen, primarily due to significantly lower stiffness and damping coefficients. Furthermore, rotor speed coast-down tests for each test fluid exhibit notable differences in coast-down speed over time characteristics, depending on the test fluid properties. The predicted rotor imbalance responses exhibit excellent correlation with the measurement data. The steady increase of demand and growth of the fluid film bearing technology for reusable rocket engines require accurate bearing design tools, the extensive component testing, and the implementation of the technology. The validated and developed bearing predictive models from previous research demonstrate well the characteristics of bearings under various operating fluids conditions. The findings and database presented in this work contribute not only to comprehending the performance of hybrid bearings but also to understanding and enhancing the dynamic characteristics of rotor systems supported on hybrid bearings.

Numerical prediction of passive speed and performance for multistage pump without power drive in natural flow process

With the development of engineering applications and the increase in system complexity, some particular fields, such as liquid rocket engine turbopumps, aircraft engine fuel systems, and marine natural flow cooling systems, are increasingly focusing on the performance characteristics of pumps under natural flow conditions. The pump is in the form of resistance components under natural flow conditions without a power drive. The impeller undergoes passive rotation by the impact of inlet flow. Due to the specificity of its operating conditions and performance indicators, the pump's natural flow performance cannot be evaluated by regular methods. Therefore, this paper proposed a numerical prediction method for pump natural flow performance based on a coupled computational fluid dynamics coupled with six-degrees-of freedom model. The performance of a multistage pump with guide vanes was evaluated under different natural flow conditions, and the accuracy was verified by experimental measurements. The transient variation mode of pump performance parameters with time at the initial stage of natural flow impact was analyzed. The flow field's transient evolution characteristics and the wall shear stress variation during natural flow were investigated. It was found that the impeller's passive rotational speed increases linearly with the natural flow rate, while the hydraulic loss shows an exponentially increasing trend. Meanwhile, the natural flow loss coefficient shows an exponentially decreasing trend and gradually tends to a stable value. The high turbulent kinetic energy inside the impeller is mainly distributed in the flow separation region and large velocity gradients. The distribution of shear stresses is closely related to the flow behavior inside the pump and the geometrical features of the hydraulic components.

Development of Ultra High DN Ceramic Ball Bearing for High Thrust Liquid Rocket Engine Turbopump

Development of Ultra High DN Ceramic Ball Bearing for High Thrust Liquid Rocket Engine Turbopump

Friction Characteristics of SUS440C/Si3N4 Lubricated by Polytetrafluoroethylene Under Cryogenic Environment

Abstract The friction characteristics of SUS440C-Si3N4 lubricated by polytetrafluoroethylene (PTFE) under cryogenic environment have not been researched well. The lubrication mechanisms in such friction condition need to be clarified to improve the fidelity of performance modeling for ball bearings used in liquid rocket engine turbopumps. This research experimentally investigated the friction coefficient of bearing materials via PTFE lubrication under cryogenic environment to clarify the friction characteristics of cryogenic turbopump ball bearings. These experiments revealed the dependence of the contact pressure on the friction coefficient. By several analyses, it was found that lower friction and better wear-resistance characteristics were caused by PTFE film that strongly adhered to metal fluoride formed on the surface of SUS440C due to moderate friction energy.

Static Load Characteristics of Hydrostatic Journal Bearings: Measurements and Predictions.

Hydrostatic bearings for liquid rocket engine turbopumps provide distinctive advantages, including high load capacity even with low viscosity cryogenic fluid and extending life span by minimizing friction and wear between rotor and bearing surfaces. Application of hydrostatic bearings into turbopumps demands a reliable test database with well-quantified operating parameters and experimentally validated accurate performance predictive tools. The present paper shows the comprehensive experimental data and validation of predicted static load characteristics of hydrostatic journal bearings lubricated with air, water, and liquid nitrogen. Extensive experiments for static load characteristics of hydrostatic bearings are conducted using a turbopump-rotor-bearing system simulator while increasing supply pressure (Ps) into the test bearings. The test results demonstrate notable effects of the test fluids and their temperatures, as well as Ps, on the bearing performance. In general, the measured bearing flow rate, rotor displacement, and stiffness of the test bearings steadily increase with Ps. The static load bearing characteristics predictions considering flow turbulence and compressibility matched well with the experimental results. The work with independent test data and engineering computational programs will further the implementation of hydrostatic bearings in high-performance turbopump shaft systems with improved efficiency and enhanced reusability of liquid rocket engine sub-systems.

Natural Flow Characteristics of Liquid Rocket Engine Turbopump during Startup

When the liquid rocket engine turbopump starts, the tank valve opens first before the pump is driven. Due to the tank and hydrostatic pressure, there is a passive flow phenomenon inside the pump called natural flow. The impeller is passively rotated by hydraulic impact, which impacts the stability of the turbopump during the initial startup period. In order to study the unsteady natural flow characteristics of the turbopump, the coupled CFD/6DOF solver is used for simulation and obtaining the variation of rotational speed, flow loss, and torque with time. The characteristics of the turbopump impeller

Effect of Radial Height of Helical Static Blade on the Cavitation Performance of Inducer

Cavitation is a major concern in liquid rocket engine turbopumps, and as an effective measure to improve cavitation quality, an inducer with helical static blades has attracted attention in recent years. In order to study the effect of the radial height of helical static blades on the cavitation performance of the inducer, CFD methods based on the Reynolds-averaged N-S equation, the standard k-ε turbulent model, and the Schnerr and Sauer cavitation model are employed to analyze the cavitation flow characteristics of a certain inducer with different helical static blades. The results show that with the increase in radial height, the backflow in the flow field is enhanced. Affected by this situation, the head is improved, the efficiency is reduced, and the low-pressure zone on the suction surface at entrance is enlarged. The helical static blade can delay the channel blocking of cavitation by providing an extra channel for the extension of bubbles. However, the effectiveness is restricted because the cavitation area enlarges with the radial height of the helical static blade. Although the effect of radial height on the head and the cavitation performance is opposite, there is an optimal radial height from 0.05 to 0.125 that improves both at the same time.

Development and Implementation of the Technology for Obtaining Channels in the Turbopump Units Bodies

The article describes the design and purpose of a turbopump unit, in particular, the pump body of the liquid rocket engine turbopump unit. The technology and technological equipment for obtaining complex profile holes in the turbopump units body are presented. The design features of technological process and equipment for electrochemical processing are considered. The proposed technology and devices allows to process parts of the liquid rocket engine turbopump unit with special holes.

Choice of gas temperature at the turbopump turbine inlet

The article considers some issues of choosing the gas temperature at the inlet of a liquid rocket engine turbopump turbine. The turbine is one of the key elements of the engine and its operability depends on the gas temperature. In addition, the turbine inlet gas temperature determines its power and main parameters of the engine chamber pressure and thrust. The higher turbine inlet gas temperature, the higher the chamber pressure and the better engine performance. The permissible temperature of the turbine structure is determined by the required safety margins and durability of the turbine rotor blades. For expendable engines, the safety margin is determined by the material short-term strength at maximum gas temperature. For reusable engines with a long service life, the safety factor is determined by the material long-term strength. The article presents the main factors affecting the choice of the generator gas temperature. It shows that one of the main factors is the non-uniformity of the temperature field at the turbine inlet. The choice of maximum admissible temperature is determined not so much by the engine schematic with the afterburning of oxidizing or reducing generator gas, but by the strength and durability of the structure with account of the influence of temperature factors.

Experimental investigation of thermal effect on cavitation characteristics in a liquid rocket engine turbopump inducer

The objective of this paper is to investigate the effect of water temperature on cavitation characteristics in a turbopump inducer, a series of experiments at different temperatures have been conducted in a newly developed visualization test facility. It is found that higher temperature shows little influence on the non-cavitation performance and breakdown characteristic in the investigated range. The relationship between cavitation development and pressure fluctuation has been discussed in detail. Higher temperature displays a remarkable stabilization effect on the cavitation excited pressure. In particular, the inception cavitation numbers of both the super-synchronous rotating cavitation and synchronous rotating cavitation are decreased at higher temperatures, and the corresponding frequencies are not affected, while the amplitudes are distinctly reduced, and the occurrence range of synchronous rotating cavitation is significantly narrowed. A generalized Rayleigh-Plesset equation has been employed to account for the thermal effect on the bubble development, which may provide a deep insight in understanding the experimental results. Thermal effect is found to act as a remarkable dissipation mechanism to suppress the bubble growth, smooth the collapse. In particular, the excited pressure during collapse is smaller at higher temperatures, which may lead to the stabilization effect of high temperature in this study.

State diagnosing of automatic relief valve circuit and parkiing seal of liquid rocket engine turbopump unit

State diagnosing of automatic relief valve circuit and parkiing seal of liquid rocket engine turbopump unit

К расчету потерь в проточных частях агрегатов подачи жидкостных ракетных двигателей

Designing more sophisticated contemporary liquid rocket engines requires a precise understanding of the hydrodynamics in the blading sections of the pressurisation station, which is most often a turbopump. Friction loss in blade passages and outlets forms a significant proportion of all losses. The paper shows that it is necessary to account for the initial region of hydrodynamically unbalanced flow in the boundary layer, which is most characteristic of relatively short passages in blading sections of liquid rocket engine turbopumps. We performed the analysis required to select friction drag laws for components of pressurisation station blading sections. We considered and proposed a method for numerically integrating a system of equations to determine the variation in characteristic thickness of a spatial boundary layer and friction loss, accounting for the inertial component of the flow core velocity, depending on which flow modes occur in the components of pressurisation station blading sections in a liquid rocket engine. We show that it is necessary to correctly select the friction laws and to take the initial region into account so as to precisely determine the power parameters

Wear Mechanism of Liquid Rocket Engine Turbopump Mechanical Seal Graphite Surface in the N2O4 Environment

Wear Mechanism of Liquid Rocket Engine Turbopump Mechanical Seal Graphite Surface in the N2O4 Environment

Preliminary Design and Optimization of New Methods of Mass Clamped-free Liquid Rocket Engine Turbopump Feed System Open Cycle using the Gradient Algorithm

n this paper, a new method and modern for Preliminary design and optimization mass turbopump in a liquid propellant rocket engine (LPRE) using the gradient algorithm has been developed. The cycle type of LPRE is open cycle and configuration of turbopump feed system consists of a impulse Turbine at the end of the shaft, an oxidizing centrifugal pumps and a fuel pump centrifugal that have been each other back-to-back on a common shaft. The proposed approach is based on four characteristics, optimal power system performs turbopump. These four characteristics are to achieve the desired characteristic of cavitation in pumps, in particular pump-balanced oxidizer turbine production capacity and total power consumption of the rotor pump-structures and also to estimate the mass of the turbopump feeding system as a result of this process. The design of the input parameters for the preliminary design of each component is determined and then use algorithms that are designed for the pump and turbine box design, preliminary design done. This is the optimal point, the gradient algorithm is obtained and the results with data from a real engine with a similar orbit, have been compared. Compare the results with similar inputs real engine design, the proposed method proves correct and improve the performance characteristics of the power system shows turbopump.

Experimental study on the water lubrication of non-contacting face seals for turbopumps

Purpose – A new type of hydrostatic and hydrodynamic non-contacting face seals has been designed to meet the requirements of lower leakage, longer life and more repeatedly start and stop on shaft seals raised by liquid rocket engine turbopumps. And an experimental study on the performance of the face seal in the actual liquid oxygen turbopump was completed where low-viscosity water was selected as the seal fluid for the sake of safety. The paper aims to discuss these issues. Design/methodology/approach – Different performances of face seals under preset conditions were obtained by repeatedly running tests, and the main performance parameters encompass leakage, fluid film pressure between the faces, operating power, face temperature, and so on. Findings – The results indicate that the designed face seal has a smaller amount of leakage, with a minimum value of 3 ml/s. Furthermore, the designed face seal has been proved to demand lower operating power. Since its operating power changes slightly with different sealed fluid pressures, the new seal can be deployed in the harsh working condition with high pressure or with high speed (greater than 20,000 rpm). However, one proviso is that when liquid is employed as the seal fluid, the groove depth should be relatively deeper (greater than 10 μm). Research limitations/implications – In response to future engineering requirements, study on the controllable spiral-groove face seals to improve the current design is being conducted. Originality/value – The advancement of such non-contacting face seals proffers important insights to the design of turbo-pump shaft seal in a new generation of liquid rocket engine with regard to the requirement of frequent start and stop as well as long life on it.

Improvement of the quality of the surfaces of monowheel blades of liquid rocket engine turbopump assemblies

Considered the problem of poor quality of blade surfaces monowheels after the electroerosion. The recommendations on selection of electrolyte composition and parameters of the treatment regime. Proposed the use of special equipment to implement the process of electrochemical surface treatment of blades monowheels.

System performance tests and start transient analysis of a liquid rocket engine turbopump

This article describes a series of development tests of a turbopump, which can be applied to a gas generator cycle rocket engine with liquid oxygen and kerosene propellants. A turbine drives both an oxidizer pump and a fuel pump in the turbopump assembly. In the tests, liquid oxygen and kerosene are supplied to the oxidizer pump and the fuel pump, respectively, while either cold hydrogen gas or hot gas from the gas generator is supplied to the turbine. The turbopump is operated reliably at both on-design and off-design conditions, meeting all the performance requirements. The test results are compared with those of the turbopump component tests, where model fluids are used, that is, water for the oxidizer pump and the fuel pump, and cold air for the turbine. The turbopump tests results agree well with the turbopump component test results. The speed buildup of the turbopump at start period is calculated when pressurized gas is used to initially spin the turbine. A differential equation which represents the torque balance between the turbine and the pumps is solved. The calculation shows a good agreement with the test result. When the mechanical loss of the turbopump is considered, a better estimation is obtained.

Experimental study on friction and wear behaviour of amorphous carbon coatings for mechanical seals in cryogenic environment

The service life and the reliability of contact mechanical seal are directly affected by the wear of seal pairs (rotor vs. stator), especially under the cryogenic environment in liquid rocket engine turbopumps. Because of the lower friction and wear rate, amorphous carbon (a-C) coatings are the promising protective coatings of the seal pairs for contact mechanical seal. In this paper, a-C coatings were deposited on 9Cr18 by pulsed DC magnetron sputtering. The tribological performances of the specimen were tested under three sealed fluid conditions (air, water and liquid nitrogen). The results show that the coatings could endure the cryogenic temperature while the friction coefficients decrease with the increased contact load. Under the same contact condition, the friction coefficient of the a-C coatings in liquid nitrogen is higher than that in water and that they are in air. The friction coefficients of the a-C coatings in liquid nitrogen range from 0.10 to 0.15. In the cryogenic environment, the coatings remain their low specific wear rates (0.9×10−6 to 1.8×10−6mm3N−1m−1). The results provide an important reference for designing a water lubricated bearing or a contact mechanical seal under the cryogenic environment that is both reliable and has longevity.

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.

Rotordynamic analysis of a high thrust liquid rocket engine fuel (Kerosene) turbopump

A rotordynamic analysis is performed for a high thrust class liquid rocket engine turbopump considering the dynamic force characteristics of ball bearings and pump impeller seals. Complex eigenvalue problems are solved to predict the rotating natural frequencies and damping ratios as a function of rotor speed. Synchronous rotor mass unbalance response and time transient response analyses are also performed to predict the rotor critical speed and the onset speed of instability. From the numerical analysis, it is found that the rear bearing stiffness is the most important parameter for the critical speed and instability because the first vibration mode is turbine side shaft bending mode. The pump seal effect on the critical speed increases as the rear bearing stiffness decreases and the front bearing stiffness increases.