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To formulate the problems of increasing the resistance to cavitation erosion of the hydraulic parts of centrifugal pumps by selecting the most suitable steel grades and to review the experience of using cavitation-resistant steels for inducers of centrifugal pumps of JSC “VNIIAEN” specialization. Analytical and statistical analyses were carried out using research and experimental development data of cavitation-resistant steels for inducers of centrifugal pumps at JSC "VNIIAEN", as well as using data from open access publications. The article deals with the problem of centrifugal pump hydraulic part failure caused by cavitation. It has been actually demonstrated that the most effective way to improve the cavitation performance of centrifugal pumps is to use an inducer upstream of the first stage impeller. Therefore, the study of cavitation-resistant steels was carried out on inducers which are most exposed to cavitation when operating under condition of developed cavitation. The results of tests carried out on experimental model test rig and full – scale pumps are presented. The selection of steels resistant to cavitation has been optimized. The relationship between the chemical and mechanical properties of steels and resistance to cavitation is shown. In addition, the essential role of structural properties of steel is shown in terms of heat of steel 08Х15Н4ДМЛ. The article provides a rationale for the fact that the potential for improving the cavitation-erosion properties of the hydraulic parts of centrifugal pumps solely by improving their hydrodynamic characteristics is practically exhausted; therefore, more attention should be paid to the search for cavitation-resistant steels used for the manufacture of hydraulic parts. It is shown that in order to achieve the best cavitation-erosion properties, it is necessary to provide a certain interaction of the selected chemical and mechanical properties of materials. The possibility of achieving better resistance to cavitation erosion by modifying the melting process is shown in terms of steel 08Х15Н4ДМЛ.

This study investigates the influence of various inducer configurations upstream of a pump impeller on the single and two-phase flow performance. Three pitch values (P = 0.151, 0.251, and 0.351 m), as well as three different numbers of blades (N = 2, 3, and 4 blades), were studied, leading to a total of 9 different inducer geometries. The main objective of the present study is to analyze and compare the corresponding performances and the two-phase mixing behavior, which is necessary for improving the two-phase pumping ability. 3D steady-state simulations using the Moving Reference Frame (MRF) approach were applied for single-phase flow, while a transient setup using a moving-mesh approach was employed for two-phase simulations. Turbulence was modeled by the Reynolds Stress Model (RSM), whereas the Volume of Fluid (VOF) method was applied to model air-water interactions. The results show that the increase in the number of blades leads to a high performance drop at overload (high-flow) conditions, but only to a slight performance enhancement at part-load (low-flow) conditions. Additionally, the effective flow range of the inducer corresponding to high efficiency becomes narrower for a higher number of blades. Concerning the inducer pitch, at part-load conditions, a lower pitch is slightly beneficial to smoothly suck the flow and damp the low-flow vortices; employing a high pitch at these conditions results in intensified flow vortices, reducing slightly the performance. On the other hand, the blade pitch is very influential for the performance at optimal and overload conditions, where a lower pitch causes flow blockage, leading to significant performance deterioration and a very limited range of applications. Generally, it was found that a modification of the inducer configuration affects the performance much more at overload compared to part-load conditions. Concerning two-phase mixing performance, the highest pitch provides the best mixing since the inducer is able to effectively churn the two phases. Similarly, an increase in the number of blades amplifies the turbulence between the two phases, thus improving mixing. Overall, a higher inducer pitch and a low to moderate number of inducer blades best ensure high performance, wide working range, and efficient two-phase mixing.

Purpose of the study. To formulate the problems of increasing the resistance to cavitation erosion of the hydraulic parts of centrifugal pumps by selecting the most suitable steel grades and to review the experience of using cavitation-resistant steels for inducers of centrifugal pumps of JSC “VNIIAEN” specialization. Research method. Analytical and statistical analyses were carried out using research and experimental development data of cavitation-resistant steels for inducers of centrifugal pumps at JSC "VNIIAEN", as well as using data from open access publications. Research results. The article deals with the problem of centrifugal pump hydraulic part failure caused by cavitation. It has been actually demonstrated that the most effective way to improve the cavitation performance of centrifugal pumps is to use an inducer upstream of the first stage impeller. Therefore, the study of cavitation-resistant steels was carried out on inducers which are most exposed to cavitation when operating under condition of developed cavitation. The results of tests carried out on experimental model test rig and full-scale pumps are presented. The selection of steels resistant to cavitation has been optimized. The relationship between the chemical and mechanical properties of steels and resistance to cavitation is shown. In addition, the essential role of structural properties of steel is shown in terms of heat of steel 08Х15Н4ДМЛ. Conclusions. The article provides a rationale for the fact that the potential for improving the cavitation-erosion properties of the hydraulic parts of centrifugal pumps solely by improving their hydrodynamic characteristics is practically exhausted; therefore, more attention should be paid to the search for cavitation-resistant steels used for the manufacture of hydraulic parts. It is shown that in order to achieve the best cavitation-erosion properties, it is necessary to provide a certain interaction of the selected chemical and mechanical properties of materials. The possibility of achieving better resistance to cavitation erosion by modifying the melting process is shown in terms of steel 08Х15Н4ДМЛ. Key words: cavitation, pump inducer, parameters of cavitation erosion, properties of steels, castings and forgings of steel 08Х15Н4ДМЛ., Цель исследования. Сформулировать проблематику повышения устойчивости к кавитационной эрозии рабочих органов центробежных насосов за счет поиска наиболее подходящих марок сталей и провести обзор по опыту использования кавитационно-стойких сталей для предвключённых колес центробежных насосов специализации АО«ВНИИАЭН». Метод исследования. Аналитический и статистический анализ проводился с использованием материалов по исследованию и экспериментальной отработки кавитационно-стойких сталей для предвключённых колес центробежных насосов в АО «ВНИИАЭН», а также с использованием материалов открытых публикаций. Результаты исследования. Данная статья посвящена проблеме разрушения рабочих органов центробежных насосов, возникающей вследствие воздействия кавитации. Продемонстрировано, что для центробежных насосов наиболее эффективным способом повышения кавитационных свойств является применение первой шнекоцентробежной ступени, поэтому исследование кавитационно-стойких сталей проводилось на предвключенных колесах, которые работая в режиме развитой кавитации наиболее подвергаются кавитационному воздействию. Приводятся результаты исследований на экспериментальных модельных стендах и натурных насосах. Проведена оптимизация выбора сталей, стойких против кавитационного воздействия. Показана взаимосвязь химических и механических свойств сталей с сопротивлением кавитационному воздействию. Помимо этого, на примере плавки стали 08Х15Н4ДМЛ показана важность структурных свойств стали. Выводы. В статье приведено обоснование того, что потенциал повышения кавитационно-эрозионных свойств рабочих органов центробежных насосов исключительно за счет улучшения гидродинамических характеристик проточной части практически исчерпан, поэтому большее внимание необходимо уделить поиску кавитационно-стойких сталей для изготовления рабочих органов. Показано, что для достижения лучших кавитационно-эрозионных качеств необходимо выдерживать определенное взаимодействие выбранных химических и механических свойств материалов. Продемонстрирована возможность за счет доработки технологического процесса плавки достижения лучшей стойкости к кавитационной эрозии на примере стали 08Х15Н4ДМЛ., Мета дослідження. Сформулювати проблематику підвищення стійкості до кавітаційної ерозії робочих органів відцентрових насосів за рахунок пошуку найбільш придатних марок сталей і провести огляд за досвідом використання кавітаційно-стійких сталей для передвключених коліс відцентрових насосів спеціалізації АТ «ВНДІАЕН». Метод дослідження. Аналітичний і статистичний аналіз проводився з використанням матеріалів за дослідженнями і експериментальними відпрацюваннями кавітаційно-стійких сталей для передвключених коліс відцентрових насосів в АТ «ВНДІАЕН», а також з використанням матеріалів відкритих публікацій. Результати дослідження. Ця стаття присвячена проблемі руйнування робочих органів відцентрових насосів, що виникає внаслідок впливу кавітації. Продемонстровано, що для відцентрових насосів найбільш ефективним способом підвищення кавітаційних властивостей є застосування першого шнековідцентрового ступеня, тому дослідження кавітаційно-стійких сталей проводилося на передвключених колесах, які працюючи в режимі розвиненої кавітації найбільш піддаються кавітаційному впливу. Наводяться результати досліджень на експериментальних модельних стендах та натурних насосах. Проведено оптимізацію вибору сталей, стійких до кавітаційного впливу. Показано взаємозв'язок хімічних і механічних властивостей сталей з опором до кавітаційного впливу. Крім цього, на прикладі плавки сталі 08Х15Н4ДМЛ показано важливість структурних властивостей сталі. Висновки. У статті наведено обґрунтування того, що потенціал підвищення кавітаційно-ерозійних властивостей робочих органів відцентрових насосів виключно за рахунок поліпшення гідродинамічних характеристик проточної частини практично вичерпаний, тому більшу увагу необхідно приділити пошуку кавітаційно-стійких сталей для виготовлення робочих органів. Показано, що для досягнення кращих кавітаційно-ерозійних якостей необхідно витримувати певну взаємодію обраних хімічних і механічних властивостей матеріалів. Продемонстровано можливість, за рахунок доопрацювання технологічного процесу плавки, досягнення кращої стійкості до кавітаційної ерозії на прикладі сталі 08Х15Н4ДМЛ.

The attachment of inducer in front of main impeller is a powerful method to improve cavitation performance; however, cavitation surge oscillation with low frequency occurs with blade cavity growing to each throat section of blade passage simultaneously. Then, one conceptual method of installing suction axi-asymmetrical plate has been proposed so as to keep every throat passage away from being unstable at once, and the effect on suppression of the oscillation were investigated. In the present study, cavitation behaviors in the inducer is observed with distributing multi-cameras circumferentially, recording simultaneously and reconstructing multi-photos on one plane field as moving a linear cascade. Observed results are utilized for discussion with other measuring results as casing wall pressure distribution. Then the suppression mechanism of oscillation by installing axi-asymmetrical inlet plate will be clarified in more details.

The attachment of inducer in front of main impeller is a powerful method to improve cavitation performance. In operating condition at partial flow rate and extremely low suction pressure, cavitation surge oscillation occurs and the stable operating range becomes narrower. It has been found from previous experimental study of authors that the cavitation surge oscillation with low frequency occurs with close relation between the inlet back-flow cavitation and the growth of blade cavity to the throat section of blade passage. One method, which is to install an axi-asymmetrical plate upstream of inducer, has been proposed to suppress the cavitation surge oscillation. It is considered conceptually to be the suppression mechanism of oscillation that the inlet flow distortion by suction axi-asymmetric plate avoids the flow at all throat sections getting unstable simultaneously. In the present study, in order to clarify the suppression mechanism experimentally observation of rotating behavior of cavitation in the inducer is performed with distributing multi cameras circumferentially, recording simultaneously and arranging the pictures to show the entire view of the flow around the linear cascade. The observed cavitation behavior is utilized for discussion on the suppression mechanism of oscillation with other measuring results such as casing wall pressure distribution and velocity distributions with LDV. Then the suppression mechanism of oscillation by installing the axi-asymmetrical plate will be clarified in more details.

High fidelity computations were carried out to analyze the orbiter LH2 feedline flowliner. Computations were performed on the Columbia platform which is a 10,240-processor supercluster consisting of 20 Altix nodes with 512 processors each. Various computational models were used to characterize the unsteady flow features in the turbopump, including the orbiter Low-Pressure-Fuel-Turbopump (LPFTP) inducer, the orbiter manifold and an experimental test article used to represent the manifold. Unsteady flow originating from the orbiter LPFTP inducer is one of the major contributors to the high frequency cyclic loading that results in high cycle fatigue damage to the gimbal flowliners just upstream of the LPFTP. The flow fields for the orbiter manifold and representative test article are computed and analyzed for similarities and differences. An incompressible Navier-Stokes flow solver INS3D, based on the artificial compressibility method, was used to compute the flow of liquid hydrogen in each test article.

Synchronous rotating cavitation is known as one type of cavitation instability, which causes synchronous shaft vibration or head loss. On the other hand, cavitation in cryogenic fluids has a thermodynamic effect on cavitating inducers because of thermal imbalance around the cavity. It improves cavitation performances due to delay of cavity growth. However, relationships between the thermodynamic effect and cavitation instabilities are still unknown. To investigate the influence of the thermodynamic effect on synchronous rotating cavitation, we conducted experiments in which liquid nitrogen was set at different temperatures (74K, 78K, and 83K). We clarified the thermodynamic effect on synchronous rotating cavitation in terms of cavity length, fluid force, and liquid temperature. Synchronous rotating cavitation occurs at the critical cavity length of Lc∕h≅0.8, and the onset cavitation number shifts to a lower level due to the lag of cavity growth by the thermodynamic effect, which appears significantly with rising liquid temperature. Furthermore, we confirmed that the fluid force acting on the inducer notably increases under conditions of synchronous rotating cavitation.

For experimental investigations of the thermodynamic effect on a cavitating inducer, it is nesessary to observe the cavitation. However, visualizations of the cavitation are not so easy in cryogenic flow. For this reason, we estimated the cavity region in liquid nitrogen based on measurements of the pressure fluctuation near the blade tip. In the present study, we focused on the length of the tip cavitation as a cavitation indicator. Comparison of the tip cavity length in liquid nitrogen (80K) with that in cold water (296K) allowed us to estimate the strength of the thermodynamic effect. The degree of thermodynamic effect was found to increase with an increase of the cavity length. The temperature depression was estimated from the difference of the cavitation number of corresponding cavity condition (i.e., cavity length) between in liquid nitrogen and in cold water. The estimated temperature depression caused by vaporization increased rapidly when the cavity length extended over the throat. In addition, the estimated temperature inside the bubble nearly reached the temperature of the triple point when the pump performance deteriorated.

Recent testing of high-speed cavitating turbopump inducers has revealed the existence of more complex instabilities than the previously recognized cavitating surge and rotating cavitation. This paper explores one such instability that is uncovered by considering the effect of a downstream asymmetry, such as a volute on a rotating disturbance similar to (but not identical to) that which occurs in rotating cavitation. The analysis uncovers a new instability that may be of particular concern because it occurs at cavitation numbers well above those at which conventional surge and rotating cavitation occur. This means that it will not necessarily be avoided by the conventional strategy of maintaining a cavitation number well above the performance degradation level. The analysis considers a general surge component at an arbitrary frequency ω present in a pump rotating at frequency Ω and shows that the existence of a discharge asymmetry gives rise not only to beat components at frequencies, Ω−ω and Ω+ω (as well as higher harmonics), but also to rotating as well as surge components at all these frequencies. In addition, these interactions between the frequencies and the surge and rotating modes lead to “coupling impedances” that effect the dynamics of each of the basic frequencies. We evaluate these coupling impedances and show not only that they can be negative (and thus promote instability) but also are most negative for surge frequencies just a little below Ω. This implies potential for an instability involving the coupling of a surge mode with a frequency around 0.9 Ω and a low-frequency rotating mode about 0.1 Ω. We also examine how such an instability would be manifest in unsteady pressure measurements at the inlet to and discharge from a cavitating pump and establish a “footprint” for the recognition of such an instability.

The response of backflow at the inlet of an inducer to the flow rate fluctuation is studied by using three-dimensional numerical calculations based on the k-ϵ turbulence model for the discussion of its effect on cavitation instabilities. It is first shown that the size of the backflow region can be correlated with the angular momentum in the upstream and the phase of the backflow significantly delays behind the quasi-steady response even at a very low frequency. It is then shown that the conservation relation of angular momentum is satisfied with minor effects of the shear stress on the boundary. The supply of the angular momentum by the negative flow is shown to be quasi-steady due to the fact that the pressure difference across the blade causing the backflow is quasi-steady at those frequencies examined. A response function of the angular momentum in the upstream to flow rate fluctuation is derived from the balance of the angular momentum and the results of the numerical calculations. This clearly shows that the backflow responds to the flow rate fluctuation as a first-order lag element. The effects of the backflow cavitation on cavitation instabilities are discussed assuming that the delay of cavity development is much smaller than the delay of the backflow. It was found that the backflow cavitation would destabilize low frequency disturbances due to the effects of the positive mass flow gain factor but stabilize high frequency disturbances due to the effect of the cavitation compliance.

Cavitation is a serious problem in the development of high-speed turbopumps, and an inducer is often used to avoid cavitation in the main impeller. Thus, the inducer often operates under the worst conditions of cavitation. If it could be possible to control and suppress cavitation in the inducer by some new device, it would also be possible to suppress cavitation occurring in all types of pumps. The purpose of our present study is to develop a new, effective method of controlling and suppressing cavitation in an inducer using shallow grooves, called “J-Grooves.” J-Grooves are installed on the casing wall near the blade tip to use the high axial pressure gradient that exists between the region just downstream of the inducer leading edge and the region immediately upstream of the inducer. The results show that the proper combination of backward-swept inducer with J-Grooves improves the suction performance of the turbopump remarkably, at both partial flow rates and the design flow rate. The rotating backflow cavitation occurring at low flow rates and the cavitation surge which occurs near the best efficiency point can be almost fully suppressed by installing J-Grooves.

The cavitation behavior of a four-blade rocket engine turbopump inducer is simulated. A two-dimensional numerical model of unsteady cavitation was applied to a blade cascade drawn from an inducer geometry. The physical model is based on a homogeneous approach of cavitation, coupled with a barotropic state law for the liquid/vapor mixture. The numerical resolution uses a pressure-correction method derived from the SIMPLE algorithm and a finite volume discretization. Unsteady behavior of sheet cavities attached to the blade suction side depends on the flow rate and cavitation number. Two different unstable configurations of cavitation are identified. The mechanisms that are responsible for these unstable behaviors are discussed, and the stress fluctuations induced on the blade by cavitation instabilities are estimated.

The paper presents full 3D numerical simulations and experimental investigations of the cavitating flow through three axial inducers. These inducers are identified by the tip blade angle at the leading edge β1T=8, 10, and 13deg. The numerical and experimental investigations were carried out at the LEMFI laboratory (Laboratoire d’Energétique et de Mécanique de Fluides Interne) of the ENSAM-Paris center (Ecole Nationale Supérieure d’Arts et Métiers). A review of the cavitating regime modeling and the cavitation homogeneous model used for this paper’s calculations is first presented. The numerical model is based on a combination of the multiphase flow equations with a truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse processes of bubbles. The mass transfers due to cavitation are source/sink terms in continuity equations of the liquid and vapor phases. The cavitation model also features a solution methodology which implicitly couples the continuity and momentum equations together. The main results are presented for the inducers at a range of flow rates and cavitation numbers: (1) Experimental results concerning: (i) the overall performances: Pressure head coefficient and efficiency versus flow rates; (ii) critical cavitation number (5% and 15% of drop) versus the flow rate; (2) Numerical results concerning: (i) the overall performances; (ii) the numerically investigated water vapor volume fraction distributions and other CFD results, which enable us to explain the cavitating behavior for these inducers; (iii) the location and sizes of the blade cavity and backflow vortex. Finally, the comparisons between experimental and simulated results on the overall performances, cavity sizes and cavity location are discussed. A qualitative agreement between experimental and predicted results was found for two inducers for a range of flow rates. The head breakdown in the simulations started at a different cavitation coefficient than that in the experiment.

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.

The attachment of an inducer upstream of the main impeller is a powerful method to improve the cavitation performance. It is known, however, that the cavitation surge oscillation, which is focused in the present paper, occurs under operation condition of partial flow rate and low suction pressure. The attempts to suppress the cavitation surge were made by installing a ring-shaped obstacle plate just upstream of inducer. The ring-shaped inlet plates with various blockage rates of 14%, 27% and 39% were tested to examine the effect of blockage rates on the suppression of cavitation surge for two kinds of inducers having two blades with the solidity of 2.0 and the different blade angle of 14° and 8°at the blade tip. In the present paper, the changes of the onset region of cavitation surge are clarified and the mechanism of cavitation surge suppression is discussed with casing wall pressure distribution and inlet velocity distribution.

The effects of the inlet casing configurations on unsteady cavitation were examined with a 3-bladed inducer. The inlet flow and cavitation pattern in two different casings were visualized using PIV (particle image velocimetry) and high-speed video. It was found that the rotating cavitation would be suppressed when the tip clearance at the inducer inlet was increased. The vortex cavitation in tip leakage flow and cavitation in back flow is considered to affect the appearance of the rotating cavitation by the inlet casing configuration.

Turbopump inducers often have swirling backflow under a wide range of flow rates because they are designed with a certain angle of attack even at the design point in order to attain high cavitation performance. When the flow rate is decreased, the backflow region extends upstream and may cause various problems by interacting with upstream elements. It is also known that the backflow vortex structure occurs in the shear layer between the main flow and the swirling backflow. Experimental studies on the backflow from an inducer have given us insight into the characteristics of backflow vortex structure, but the limited information has not lead to the complete understanding of the phenomena. Numerical studies based on Reynolds-averaged Navier-Stokes (RANS) computations usually deteriorate when the flow field of interest involves large-scale separations, as shown by a previous study by Tsujimoto et al. (2005). On the other hand, the numerical approach using the Large Eddy Simulation (LES) technique has the potential to predict unsteady flows and/or flow fields that include regions of large-scale separation much more accurately than RANS computations does in general. The present paper describes the application of the LES code developed by one of the authors (Kato) to further understand the backflow vortex structure at the inlet of an inducer. First, the internal flow of the inducer was simulated, as a way to evaluate the validity of the proposed method, under a wide range of inlet flow coefficients. The static pressure peformance and the length of the backflow region was compared with measured values, and good agreement was obtained. Second, using the validated LES code, the fundamental characteristics of the backflow vortex was investigated in detail. It was found that the backflow vortices are formed in a circumferentially twisted manner at the boundary between the swirling backflow and the straight inlet flow. Also, the backflow vortices rotate in the same direction as the inducer, but with half of the circumferential flow velocity in the backflow region. Another finding was that the backflow region expands toward the center of the flow field and the number of vortices decrease, as the flow coefficient decreases. To the best of our knowledge, this is the first computation of the backflow at the inducer inlet to achieve quantitative agreement with measured results, and give new findings to the complicated three-dimensional structure of the backflow, which was very limited under experimental studies.

The effects of the inlet casing configurations on unsteady cavitation were examined with a 3-bladed inducer. The inlet flow and cavitation pattern with two casings were visualized using by PIV and high-speed video. It was found that the rotating cavitation would be suppressed when the tip clearance at the inducer inlet was increased. The vortex cavitation in tip leakage flow and cavitation in back flow effected the suppression of the rotating cavitation through the inlet casing configuration.

Variations of performance and NPSH of a turbo pump inducer were measured. The flows at the inlet and the outlet of the inducer were also experimentally investigated by measuring flow velocity and angle using a 3-hole Pilot tube. Performance and velocity profiles show a similarity for tested speeds, however not for efficiencies. Strong recirculating flows appears at the inlet of inducer even at the design condition. Cavitating flows were also visualized at several NPSH`s.

The onset of cavitation causes head and efficiency of a main pump to be reduced significantly and generates vibration and noise. In order to avoid these phenomena, the inlet of the pump is fitted with a special rotor called an inducer, which can operate satisfactorily with extensive cavitation. The motivation of this study is to find out cavitation modes from the inducer inlet pressure signals and event characteristics from outlet ones at various operating conditions. The cavitation modes are analyzed by using a cross-spectral density of fluctuating pressures at the inducer inlet. The time-frequency characteristics of wall pressures downstream of the inducer are presented in terms of event frequency, its duration time, and number of events by using the Choi-Williams distribution.

As a part of the developmental effort towards the realization of a staged combustion cycle based liquid rocket engine, a program on simulation of the LOX booster pump for performance characterization has been taken up. Earlier reported work shows that the pump inducer works satisfactorily under cavitating conditions for the throttling range varying from 90% to 113%. However stall occurs below 90% of the designed flow rate which is to be strongly associated with the inlet backflow vortices due to flow separation [1]. It is envisaged that leading edge sweep may help in to controls the incipience and growth of the backflow vortices at the inlet leading edge tip of axial flow inducer leading to a wider operating range. In this paper, steady state 3D CFD analysis of rotating inducer is performed to examine the effect of leading edge sweep on the performance of axial flow LOX pump inducer using ANSYS® CFX and has been compared with the performance of the inducer reported by Mishra and Ghosh [1].

An inducer performance has been explored with and without the implementation of a stability control device. Multiphase, time-accurate computational fluid dynamic simulations have been conducted at the design flow coefficient and at two low off-design flow coefficients. At the design flow coefficient, the inducer performance was similar with and without the stability control device. At low flow coefficients, the inducer without the stability control device exhibited significant cavitation instabilities, which led to high rotordynamic forces on the inducer blades. When the stability control device was incorporated into the inducer design, nearly all of the cavitation instabilities were suppressed at low flow coefficients and the rotordynamic forces were reduced by more than an order of magnitude. Stable operation at flow coefficients far below the design value leads to a significant increase in the suction performance of the inducer, allowing pumps to operate at lower inlet pressures.Copyright © 2014 by ASME

An attachment of inducer is a powerful method to improve the cavitation performance of a turbo-pump. Cavitation surge phenomena, occurring under the severe suction pressure at a partial flow rate, is focused in the present paper. Flow measurements were carried out at the inlet and outlet sections of a flat-plate helical inducer with the solidity of 2.0 and tip blade angle of 11° by using a total-head yaw-meter with a phase locked sampling method in one period of the shaft rotation or the cavitation oscillation. Time variation of the flow distributions during the oscillation is clarified with observed cavitation behaviors. After these results are compared with those in conditions just before and after the oscillations, the fluctuating blade forces are estimated from the blade to blade distributions of casing wall pressures measured in these conditions.

Cavitation tests have been carried out for helical inducer with various blade lengths. Effects of inducer blade lengths on head characteristics and cavitation induced oscillation phenomena are described in the present paper. The oscillation occurring in the case of inducers with lower solidity less than 1.0 differs from that with the solidity of 2.0. Change of the flow distributions during the oscillation is measured from by using a single hole yawmeter with the phase locked sampling method to the oscillation. By compared with the results for higher solidity inducer, the behaviors of cavitation induced oscillation are clarified.

A cavitation surge oscillation in the range of partial flow rate and low NPSH hinders the wide operation of an inducer for industrial turbo-pumps, though it is very effective to improve the cavitation performance. The harmful oscillation of cavitation surge occurs in the case of inducers with high solidity more than 1.0. This oscillation might be suppressed if a tandem bladed inducer, having a front inducer with low solidity less than 1.0, would be employed. Experiment tests to examine its effect are described in the present paper. Results show that the amplitude of the oscillation takes almost zero when a relative peripheral or axial position between the front and rear blades is properly chosen. The reasons are discussed with measured casing wall pressure distributions and observed cavitation behaviors.

Development of a high suction performance pump inducer is required for a high-performance rocket system to reduce total weight of a launch vehicle and to increase its reliability. It is very important for a high suction performance inducer design that the relation between flow patterns and cavitation structures makes clear. In this study, flow patterns observed with PIV system and cavitation structures observed with a high-speed camera are reported and discussed about their relationship.

Development of a high suction performance pump inducer is required for a reusable rocket engine to reduce total weight of a launch vehicle and to increase its reliability. But, flow patterns or pressure distributions in an inducer are not well known. Therefore, observations of flow patterns around an inducer by PIV (Particle Imaging Velocimetry) method were planned for the foundation data for a high suction performance inducer design. In this study, structures of the backflow and the reversed flow are minutely described and discussed.

Oscillating cavitation of an inducer was observed through unsteady inlet pressure measurements and by use of high speed video picture, covering a wide range of flow coefficient and cavitation number. One of the purposes of the study is to identify a mode of rotating cavitation predicted by a linear analysis, and the other is to obtain a general view of oscillating cavitation. The number of rotating cavitation cells and their propagation velocity were carefully determined from the phase difference of pressure fluctuations at various circumferential locations. Various kinds of oscillating cavitation were observed: rotating cavitation rotating faster/slower than impeller rotation, cavitation in backflow vortices, and surge mode oscillations. Effects of inlet and outlet (effective) pipelength were also studied.

Hydrodynamics of Pumps is a reference for pump experts and a textbook for advanced students. It examines the fluid dynamics of liquid turbomachines, particularly pumps, focusing on special problems and design issues associated with the flow of liquid through a rotating machine. There are two characteristics of a liquid that lead to problems and cause a significantly different set of concerns than those in gas turbines. These are the potential for cavitation and the high density of liquids, which enhances the possibility of damaging, unsteady flows and forces. The book begins with an introduction to the subject, including cavitation, unsteady flows and turbomachinery, basic pump design and performance principles. Chapter topics include flow features, cavitation parameters and inception, bubble dynamics, cavitation effects on pump performance, and unsteady flows and vibration in pumps - discussed in the three final chapters. The book is richly illustrated and includes many practical examples.

This paper presents the result of design optimization for three-bladed pump inducer using a three-dimensional (3-D) inverse design approach, Computational Fluid Dynamics (CFD) and DoE (Design of Experiments) taking suction performance and cavitation instability into consideration. The parameters to control streamwise blade loading distribution and spanwise work (free vortex or non-free vortex) for inducer were chosen as design optimization variables for the inverse design approach. Cavitating and non-cavitating performances for inducers designed using the design variables arranged in the DoE table were analyzed by steady CFD. Objective functions for non-cavitating operating conditions were the head and efficiency of inducers at a design flow (Qd ), 80% Qd and 120% Qd . The volume of the inducer cavity region with a void ratio above 50% was selected as the objective function for inducer suction performance. In order to evaluate cavitation instability by steady CFD, the dispersion of the blade surface pressure distribution on each blade was selected as the evaluation parameter. This dispersion of the blade surface pressure distribution was caused by non-uniformity in the cavitation length that was developed on each inducer blade and increased when the cavitation number was reduced. The effective design parameters on suction performance and cavitation instability were confirmed by sensitivity analysis during the design optimization process. Inducers with specific characteristics (stable, unstable) designed using the effective parameters were evaluated through experiments.Copyright © 2011 by ASME

A liquid oxygen turbopump has been developed for the main engine (LE-7) of the H-II rocket. The LE-7 LOX pump requires an inducer with quite high suction performance and high head, because a low-speed and low-pressure pump is not used ahead of the main pump in the LE-7 engine. The inducer was designed using the customary method, and its hydraulic and mechanical performances were investigated in tests of LE-7 LOX turbopumps. The original combination of an inducer and an inducer housing satisfied the required hydraulic performance criteria. However, this combination was found to result in supersynchronous shaft vibrations due to rotating cavitation which occurred in the inducer. This problem was almost completely solved by a simple modification of the inducer upstream housing. Furthermore, the rotating cavitation of the present inducer was investigated using a new theory of such cavitation. I. Introduction A LIQUID oxygen turbopump has been developed for the main engine (LE-7) of the H-II rocket, the next generation of Japanese launch vehicle. This turbopump requires a high-flow, high-pressure liquid oxygen pump. Because a low-speed, low-pressure pump is not used ahead of the main pump in the LE-7 engine, it is very important to operate the main pump at higher speed to obtain a smaller-size, lighterweight turbopump. The operational speed of the present turbopump was restricted by the suction performance of the main pump inducer. In this article, we report both the design and test results of the inducer. The main pump of the LE-7 LOX turbopump has a singlestage centrifugal impeller with an inducer. 1 The inducer is characterized by a low flow coefficient, a small inlet angle, a sharp leading edge, etc., to achieve higher suction performance. The inducer was designed using the customary method.2-3

International audience; This study was led in collaboration with the French Space Agency (CNES) and the Rocket Engine Division of Snecma. The main aims were the simulations and the analyses of cavitating flows in the rocket engine turbopump inducers, where the operating fluids are LH2 and LOx under cryogenic conditions. A rho(P,T) state law modeling the cavitation phenomenon was integrated by the laboratory LEGI in the commercial computational fluid dynamics (CFD) code FINE/TURBOTM, developed by Numeca International. Various 3D numerical results are given for an inducer geometry and comparisons are made with experimental data (head drop curves) obtained by NASA.

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 super-synchronous/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.Copyright © 2008 by ASME

International audience; Temperature depression within the leading edge cavities on a space inducer is measured in Refrigerant 114 using miniature thermocouples mounted on the rotating blades. Time-averaged values of cavity temperature depression are determined all along the descent in cavitation number and correlated with the extent of cavities. In addition to mean values, temperature fluctuations are analyzed with respect to the onset of cavitation instabilities, namely, alternate blade cavitation and supersynchronous rotating cavitation. Temperature spectra relative to a rotating frame of reference are compared with pressure spectra obtained in a fixed frame of reference. Temperature oscillations issued from different blades are compared, and phase shifts between consecutive and opposite blades are evaluated in the case of the supersynchronous instability regime.

International audience; The thermodynamic effect on a cavitating inducer is investigated from joint experiments in cold water and Refrigerant 114. The analysis is focused on leading edge cavitation and cavitation instabilities, especially on alternate blade cavitation and supersynchronous rotating cavitation. The cavity length along cylindrical cuts at different radii between the hub and casing is analyzed with respect to the local cavitation number and angle of attack. The similarity in shape of the cavity closure line between water and R114 is examined and deviation caused by thermodynamic effect is clarified. The influence of rotation speed on cavity length is investigated in both fluids and analyzed on the basis of a comparison of characteristic times, namely, the transit time and a thermal time. Thermodynamic delay in the development of leading edge cavities is determined and temperature depressions within the cavities are estimated. Thresholds for the onset of cavitation instabilities are determined for both fluids. The occurrence of cavitation instabilities is discussed with respect to the extent of leading edge cavitation. The thermodynamic delay affecting the occurrence of cavitation instabilities is estimated and compared with the delay on cavity development.

Rotating cavitation in inducers is known as one type of cavitation instability, in which an uneven cavity pattern propagates in the same direction as the rotor with a propagating speed ratio of 1.0-1.2. On the other hand, cavitation in cryogenic fluids has a thermodynamic effect because of the thermal imbalance around the cavity. To investigate the influence of the thermodynamic effect on rotating cavitation, we conducted experiments in which liquid nitrogen was set at different temperatures (74 K, 78 K and 83 K) with a focus on the cavity length. At higher cavitation numbers, super-synchronous rotating cavitation occurred at the critical cavity length of Lc/h approximately equal to 0.5 with a weak thermodynamic effect in terms of the fluctuation of cavity length. In contrast, synchronous rotating cavitation occurred at the critical cavity length of Lc/h approximately equal to 0.9-1.0 with a strong thermodynamic effect in terms of the unevenness of cavity length. Furthermore, we confirmed that the amplitude of the shaft vibration depended on the degree of the unevenness of the cavity length through the thermodynamic effect., 資料番号: AA0064094000, レポート番号: JAXA-RM-08-004

A reduced order model for preliminary design and noncavitating performance prediction of tapered axial inducers is illustrated. In the incompressible, inviscid, irrotational flow approximation, the model expresses the 3D flow field in the blade channels by superposing a 2D cross-sectional vorticity correction to a fully guided axisymmetric flow with radially uniform axial velocity. Suitable redefinition of the diffusion factor for bladings with non-negligible radial flow allows for the control of the blade loading and the estimate of the boundary layer blockage at the specified design flow coefficient, providing a simple criterion for matching the hub profile to the axial variation of the blade pitch angle. Carter’s rule is employed to account for flow deviation at the inducer trailing edge. Mass continuity, angular momentum conservation, and Euler’s equation are used to derive a simple second order boundary value problem, whose numerical solution describes the far-field axisymmetric flow at the inducer discharge. A closed form approximate solution is also provided, which proved to yield equivalently accurate results in the prediction of the inducer performance. Finally, the noncavitating pumping characteristic is obtained by introducing suitably adapted correlations of pressure losses and flow deviation effects. The model has been verified to closely approximate the geometry and noncavitating performance of two space inducers tested in Alta’s Cavitating Pump Rotordynamic Test Facility, as well as the measured pumping characteristics of a number of tapered-hub inducers documented in the literature.

Based on the length of the tip cavitation as an indication of cavitation, we focused on the effect of thermodynamics on cavitation performances and cavitation instabilities in an inducer. Comparison of the tip cavity length in liquid nitrogen (76K and 80K) as working fluid with that in cold water (296K) allowed us to estimate the strength of the thermodynamic effect on the cavitations. The degree of thermodynamic effect was found to increase with an increase of the cavity length, particularly when the cavity length extended over the throat of the blade passage. In addition, cavitation instabilities occurred both in liquid nitrogen and in cold water when the cavity length increased. Subsynchronous rotating cavitation appeared both in liquid nitrogen and in cold water. In the experiment using liquid nitrogen, the temperature difference between 76K and 80K affected the range in which the subsynchronous rotating cavitation occurred. In contrast, deep cavitation surge appeared only in cold water at lower cavitation numbers. From these experimental results, it was concluded that when the cavity length extends over the throat, the thermodynamic effect also affects the cavitation instabilities as a “thermal damping” through the unsteady cavitation characteristics.

Unsteady cavitation phenomena such as rotating cavitation and cavitation surge are often observed in a turbopump inducer of a rocket engine, sometimes causing undesirable oscillation of the system. Investigation of their mechanism and prediction of such unsteady phenomena are, therefore, crucial in the design of inducers. As many experiments have shown, the appearance of cavitation instability is highly related to the flow rate as well as to the inlet casing geometry. Experimental observations have shown that a very complex flow structure, including such phenomena as backflow and vortices, appears upstream of the inducer. In this work, therefore, we conducted 3D unsteady computational fluid dynamics simulations of noncavitating flow in a turbopump inducer, mainly focusing on the vortex structure, for three types of inlet casing geometry with various flow rates. Simulation results showed that the vortex structure for the geometry of the inlet casing and that for the flow rate differed. Especially, it was found that development of the tip leakage vortex was dependent on the inlet casing geometry and the flow rate. This tendency is analogous to that observed between the appearance of rotating cavitation and the casing geometry and flow rate in cavitation tunnel tests. This result strongly implies that the tip leakage vortex is responsible for the appearance of rotating cavitation. By adding a gutter to the inlet casing, it was found that backflow was completely confined to the gutter regardless of flow rates. This numerical result implies that the volume of cavity generated in the backflow region should be stable despite a change of the flow rate, resulting in the suppression of increase of the mass flow gain factor. This result also supports the experimental result that cavitation surge was effectively suppressed using such a casing with a gutter.

International audience; The numerical simulation of cavitating flows in turbomachinery is studied at the Turbomachinery and Cavitation team of LEGI (Grenoble - France) in collaboration with the French space agency (CNES) and the rocket engine division of SNECMA Moteurs. A barotropic state law is proposed to model the cavitation phenomenon and this model has been integrated in the commercial CFD code Fine/TurboTM, developed and commercialized by Numeca International. The numerical aspects of the work are mainly focused on numerical stability and reliability of the algorithm, when introducing large density variations through the strongly non linear barotropic state law. This research conducted first to changes in the way preconditioning parameters are calculated. Internal flows in turbomachinery have been deeply investigated. A methodology allowing the numerical simulation of the head drop induced by the development of cavitation has been proposed on the basis of computations in inducers and centrifugal pumps. These simulations have allowed the characterization of the mechanisms leading to the head drop and the visualization of the effects of the development of cavitation on internal flows.