Vibration of Hydraulic Machinery

Wu, Yihui; Sheng-cai, LI; Qian, Zhongdong; Liu, Shuhong; Dou, Hua-Shu

doi:10.1007/978-94-007-6422-4

Cited by 59 publications

(29 citation statements)

References 65 publications

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“…The frequency of RC decreases with cavitation number to 1.2 times rotor frequency. This is consistent with typical values observed in literature [1,4,18]. At cavitation numbers below 0.025 the dynamic behavior is dominated by in-plane oscillations that become more prominent below σ=0.018 where cavitation surge (CS) is observed.…”

Section: Dynamic Behaviorsupporting

confidence: 92%

“…The turbopumps are one of the most critical components in the engine and often up to 50% of the development costs are ascribed to their design and testing [1]. To provide the required propellant mass flow rate and pressure rise while maintaining low system mass the turbopumps must operate at high rotational speeds, which in turn lead to the formation of vapor cavities at the inlet.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Rotating Cavitation in a Four Bladed Inducer

Lettieri¹,

Spakovszky²,

Jackson³

et al. 2016

52nd AIAA/SAE/ASEE Joint Propulsion Conference

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This work aims to characterize the dynamic behavior of a four bladed inducer and clarify the physical mechanism that leads to the onset of rotating cavitation. The inducer under consideration is representative of a low-pressure liquid oxygen pump (LPOP) inducer of modern design and incorporates several standard design features used in rocket turbopumps to suppress rotating cavitation. The mechanism is characterized based on a combination of two-phase numerical simulations and inducer experiments. Experimental measurements demonstrate a supersynchronous rotating cavity in the periphery of the inducer inlet at frequencies between 1.2 and 1.6 times rotor frequency and a synchronous 2 nd spatial harmonic pattern associated with alternate blade cavitation. The analysis indicates a causal link between alternate blade cavitation and rotating cavitation, with a distinct cut-on cut-off behavior. Numerical calculations and high-speed videos elucidate the mechanism of breakdown of alternate blade cavitation and the formation of rotating cavitation. The present work suggests that rotating cavitation is caused by the coupling of the cavities on adjacent blades during alternate blade cavitation. Due to the nearly tangential flow, the vortex lines from one of the non-cavitating blades wrap around the blade leading edge of the adjacent blade, which yields a drop in static pressure and cavity formation. The tip vortex cavity interaction with the leading edge of the blade leads to sheet cavity breakdown with periodic growth and collapse of cavities, creating the apparent super-synchronous rotation of the cavitating region.

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Section: Dynamic Behaviorsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Characterization of Rotating Cavitation in a Four Bladed Inducer

Lettieri¹,

Spakovszky²,

Jackson³

et al. 2016

52nd AIAA/SAE/ASEE Joint Propulsion Conference

View full text Add to dashboard Cite

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“…These facts fully justify the application of condition monitoring techniques to LHG. The basics of these techniques are well known: a significant change in the monitored parameter indicates the development of damage, and the adequate analysis of the symptoms allows the damage diagnosis [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Experimental Estimation of Journal Bearing Stiffness for Damage Detection in Large Hydrogenerators

Brito

Machado

Neto

2017

Shock and Vibration

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Based on experimental pieces of evidence collected in a set of twenty healthy large hydrogenerators, this article shows that the operating conditions of the tilting pad journal bearings of these machines may have unpredictable and significant changes. This behavior prevents the theoretical determination of bearing stiffness and damping coefficients with an adequate accuracy and makes damage detection difficult. Considering that dynamic coefficients have similar sensitivity to damage and considering that it is easier to monitor bearing stiffness than bearing damping, this article discusses a method to estimate experimentally the effective stiffness coefficients of hydrogenerators journal bearings, using only the usually monitored vibrations, with damage detection purposes. Validated using vibration signals synthesized by a simplified mathematical model that simulates the dynamic behavior of large hydrogenerators, the method was applied to a journal bearing of a 700 MW hydrogenerator, using two different excitations, the generator rotor unbalance and the vortices formed in the turbine rotor when this machine operates at partial loads. The experimental bearing stiffnesses obtained using both excitations were similar, but they were also much lower than the theoretical predictions. The article briefly discusses the causes of these discrepancies, the method's uncertainties, and the possible improvements in its application.

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Section: Introductionmentioning

confidence: 99%

“…They are a central component in LREs as they control both injection pressure and propellant mass flow rate to the combustor. The design and analysis of turbopumps is highly complex due to high rotational speeds, and potential for the onset of vibrations and flow instabilities while simultaneously needing to meet the stringent performance and weight requirements of the system [1,2].The mass and size constraints imposed to the turbopump means that a high rotational speed (often over 20,000 rpm) is needed in order to deliver the required mass flow rate of propellants to the combustor. Because of the high rotational speeds, cavitation is likely to arise on the suction side of the blade passages as the static pressure of the liquid drops down to its vapour pressure [1].…”

mentioning

confidence: 99%

Turbulence Modeling of Cavitating Flows in Liquid Rocket Turbopumps

Mani

Cervone

Hickey

2016

Journal of Fluids Engineering

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An accurate prediction of the performance characteristics of cavitating cryogenic turbopump inducers is essential for an increased reliance on numerical simulations in the early turbopump design stages of liquid rocket engines. This work focuses on the sensitivities related to the choice of turbulence models on the cavitation prediction in flow setups relevant to cryogenic turbopump inducers. To isolate the influence of the turbulence closure models for Reynolds-averaged Navier-Stokes equations, four canonical problems are abstracted and studied individually to separately consider cavitation occurring in flows with a bluff body pressure drop, adverse pressure gradient, blade passage contraction and rotation. The choice of turbulence model plays a significant role in the prediction of the phase-distribution in the flow. It was found that the sensitivity to the closure model depends on the choice of cavitation model itself; the barotropic-based cavitation models are far more sensitive to the turbulence closure than the transportbased models. The sensitivity of the turbulence model is also strongly dependent on the type of flow. For bounded cavitation flows (blade passage), stark variations in the cavitation topology are observed based on the selection of the turbulence model. For unbounded problems, the spread in the results due to the choice of turbulence models is similar to non-cavitating, single-phase flow cases. A set of considerations for turbopump designers are provided for an informed decision on the selection of turbulence models. * Corresponding author IntroductionTurbopumps in liquid rocket engines (LRE) deliver propellants, such as liquid hydrogen (LH2) and liquid oxygen (LO2), from low pressure storage tanks to a high pressure combustion chamber [1]. They are a central component in LREs as they control both injection pressure and propellant mass flow rate to the combustor. The design and analysis of turbopumps is highly complex due to high rotational speeds, and potential for the onset of vibrations and flow instabilities while simultaneously needing to meet the stringent performance and weight requirements of the system [1,2].The mass and size constraints imposed to the turbopump means that a high rotational speed (often over 20,000 rpm) is needed in order to deliver the required mass flow rate of propellants to the combustor. Because of the high rotational speeds, cavitation is likely to arise on the suction side of the blade passages as the static pressure of the liquid drops down to its vapour pressure [1]. Cavitation is to be avoided as it leads to a reduction of the pump efficiency, mixing losses, erratic mass flow rate, insufficient power to the fluid, and can result in dangerous vibrations and instabilities. In a turbopump assembly, an axial impeller called inducer is placed in front of the main impeller on the same shaft with the same rotational speed [1]. The inducer marginally increases the liquid pressure such that cavitation is avoided or severely reduced at the main impeller inl...

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Vibration of Hydraulic Machinery

Cited by 59 publications

References 65 publications

Characterization of Rotating Cavitation in a Four Bladed Inducer

Characterization of Rotating Cavitation in a Four Bladed Inducer

Experimental Estimation of Journal Bearing Stiffness for Damage Detection in Large Hydrogenerators

Turbulence Modeling of Cavitating Flows in Liquid Rocket Turbopumps

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