Development of a Pipeline Pulsating Pressure Excitation Device and System

The high turbulence of unstable combustion in the working process of liquid rocket engine will cause periodic pressure pulsation.Therefore,a pressure pulsation device that is easy to reuse,broadband,suited for poisonous media,and high pressure is designed and produced.Numerical and experimental studies show that the pulsator produces stable pressure waveforms at different flow rates,pressures,and frequencies,while the pressure waveform amplitude at the excitation frequency is larger.The pressure waveform amplitude increases exponentially with the flow rate and with smaller gaps and linear pressure increasing.The pressure waveform amplitude varies greatly at different frequencies along the pipeline.As the frequency increases,the pressure waveform amplitude of the excitation increases first and then decreases.The pressure waveform amplitude at low frequencies changes little along the pipeline.The pressure waveform amplitude at medium frequencies readily couples to the pipeline flow field and increases its value.The pressure waveform amplitude at high frequencies attenuates along the pipeline,where attenuation increases with frequency.The ability of the pulsator to provide stable excitation and high pressure is verified through normal and high pressure testsindifferentpipelinesystems.

Vibration analysis of large bulb tubular pump house under pressure pulsations

A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of the pumping station in both the time domain and the frequency domain. The pressure pulsation field of the whole flow passage was structured on the basis of pressure pulsations recorded at some locations of the physical model test. Dynamic time-history analysis of the pump house under pressure pulsations was carried out. At the same time, according to spectrum characteristics of the pressure pulsations at measuring points and results of free vibration characteristics analysis of the pump house, the spectrum analysis method of random vibration was used to calculate dynamic responses of the pump house. Results from both methods are consistent, which indicates that they are both reasonable. The results can be used for reference in anti-vibration safety evaluation of the Huaiyin third pumping station.

Research Status, Critical Technologies, and Development Trends of Hydraulic Pressure Pulsation Attenuator

Hydraulic pumps are a positive displacement pump whose working principle causes inherent output flow pulsation.Flow pulsation produces pressure pulsation when encountering liquid resistance.Pressure pulsation spreads in the pipeline and causes vibration,noise,damage,and even pipeline rupture and major safety accidents.With the development of airborne hydraulic systems with high pressure,power,and flow rate,the hazards of vibration and noise caused by pressure pulsation are also amplified,severely restricting the application and development of hydraulic systems.In this review paper,the mechanism,harm,and suppression method of pressure pulsation in hydraulic systems are analyzed.Then,the classification and characteristics of pulsation attenuators according to different working principles are described.Furthermore,the critical technology of simulation design,matching method with airborne piston pumps,and preliminary design method of pulsation attenuators are proposed.Finally,the development trend of pulsation attenuators is prospected.This paper provides a reference for the research and application of pressure pulsation attenuators.

Effect of bionic mantis shrimp groove volute on vortex pump pressure pulsation

In order to reduce pressure pulsation of vortex pumps,the mantis shrimp was chosen as biological prototype and a bionic engineering model was developed from its abdominal segment grooves.Bionic mantis shrimp groove volute vortex pump models with different numbers of grooves were developed,and numerical simulation methods were used to calculate the models to study the effects of the volute grooves on the pressure pulsation of a vortex pump.The results show that a bionic groove volute could effectively improve the pressure pulsation of a vortex pump outlet,and reduce the pressure pulsation around the pump’s tongue and other internal points.The pressure pulsation under different conditions is impacted by shaft frequency and blade frequency.The bionic groove structure has little effect on the external characteristics of the pump,but could improve the static pressure,velocity distribution,and vortex structure of the flow field.Additionally,pressure pulsation of the whole vortex pump is reduced.

Analysis of pressure pulsation mechanism and dynamic characteristics of axial piston pump

The pressure pulsation of axial piston pump is not only an important cause of rotation speed fluctuation,vibration noise and output stability of the hydraulic system,but also the main information source for obtaining fault information.Hydraulic system is characterized by strong noise interference,which leads to low signal-to-noise ratio(SNR)of detection signals.Therefore,it is necessary to dig deep into the system operating state information carried by pressure signals.Firstly,based on flow loss mechanism of the plunger pump,the mapping relationship between flow pulsation and pressure pulsation is analyzed.After that,the pressure signal is filtered and reconstructed based on standard Gabor transform.Finally,according to the time-domain waveform morphology of pressure signal,four characteristic indicators are proposed to analyze the characteristics of pressure fluctuations under different working conditions.The experimental results show that the standard Gabor transform can accurately extract high-order harmonics and phase frequencies of the signal.The reconstructed time-domain waveform of pressure pulsation of the axial piston pump contains a wealth of operating status information,and the characteristics of pulsation changes under various working conditions can provide a new theoretical basis and a method support for fault diagnosis and health assessment of hydraulic pumps,motors and key components.

Pressure pulsation in stages of electric submersible pump at shut-off under various speeds

Electric submersible pumps were widely used in agricultural fields,petroleum and various other industries. The pressure pulsation caused fatigue failure due to vibration in electric submersible pump and affects the life and performance of its system. The objective of this study was to experimentally investigate the characteristics of pressure pulsation which were generated at various stages of a multistage electric submersible pump during closed valve operation at different speeds. An electric submersible pump with five stages was selected for conducting experiments. A variable frequency drive( VFD)was used to operate the electric submersible pump at five different speed settings from 40 to 60 Hz. Piezoresistive pressure transducers were mounted at each stage of the electric submersible pump to capture the unsteady pressure signals. At each speed setting,the electric submersible pump was operated at the shut-off condition and the signals of unsteady pressure from all the five stages were captured. A fast fourier transformation( FFT) was carried out on the pressure signals to convert into frequency domain.From the spectra of pressure pulsation signals,the characteristics of pressure pulsation are obtained for each stage and for various speed settings which were then used to understand its variation with speed and stages.

A METHOD OF CALCULATING PRESSURE DISTRIBUTION OF PERIODIC PULSATION FLUID TRANSPORTED IN PIPING NETWORK

The pressure pulsation induced by the pumped periodic pulsation fluid is the main factor of causing fluid resonance and stimulating pipelines vibrations and noise. In order to reduce the faults caused by the vibrations of pipelines, two aspects have been researched: one is to develop high quality filters, weaken and restrain the crest of pulsation pressure; the other is to design structural parameters of the piping network and eliminate the fluid resonance. Both need calculating the pressure pulsations of different structural parameters and frequencies, and knowing the amplitude frequency. In this paper the stiffness matrix technique is used for treating the coupling of subsystems of pipelines and calculating the pressure distribution of the piping network and it is tested by simulation and experiments.

Numerical Study on the Low-Frequency Pressure Fluctuation Characteristics of Liquid Oxygen Delivery System Based on Acoustic Theory

Aiming at the low-frequency pressure fluctuation phenomena in certain liquid oxygen delivery systems during dual engine operation,a numerical study on the intrinsic frequency of the liquid oxygen delivery system was conducted by adopting an acoustic unit in Abaqus.Factors such as condensation characteristics of the oxygen-enriched gas gas in the liquid oxygen’s pipeline between pumps,flexibility of the accumulator,and cavitation flexibility of the engine were considered in the simulation models.The simulation results show that the second order frequency of the liquid oxygen delivery system is 8.77 Hz,and the phase difference of the corresponding acoustic modal is 180°,which is the liquid circuit frequency of the small loop between the two branches of the tee.This is consistent with the low-frequency fluctuation phenomenon during flight.Moreover,the simulation results were consistent with the liquid circuit frequency solved via the transfer matrix,which also verified the effectiveness of the frequency analysis method based on acoustic theory.

Intelligent Identification of Rotating Stall for Centrifugal Compressor Based on Pressure Pulsation Signals and SDKAE Network

Most accidents of centrifugal compressors are caused by fluid pulsation or unsteady fluid excitation.Rotating stall,as an unstable flow phenomenon in the compressor,is a difficult point in the field of fluid machinery research.In this paper,a stack denoising kernel autoencoder neural network method is proposed to study the early warning of rotating stall in a centrifugal compressor.By collecting the pressure pulsation signals of the centrifugal compressor under different flow rates in engineering practice,a double hidden layer sparse denoising autoencoder neural network is constructed.According to the output labels of the network,it can be judged whether the rotation stall occurs.At the same time,the Gaussian kernel is used to optimize the loss function of the whole neural network to improve the signal feature learning ability of the network.From the experimental results,it can be seen that the flow state of the centrifugal compressor is accurately judged,and the rotation stall early warning of the centrifugal compressor at different speeds is realized,which lays a foundation for the research of intelligent operation and maintenance of the centrifugal compressor.

FREQUENCY DOMAIN ANALYSIS AND COMPUTER SIMULATION OF PRESSUREPULSATION RESONANCE IN HIGHPRESSURE PIPI

The characteristics of the pressure pulsation resonance in HP fluid piping networks have been researched by means of computer simulation. It can be used as an auxiliary means to acquaint the effects of the structural parameters of complex fluid pipelines. It has provided the basis for reasonably configurating pipelines and avoiding the pressure pulsation resonance in fluid pipelines. It is of great applied value to engineering.

Pressure characteristics of landslide-generated impulse waves

The destructiveness of impulse waves generated by landslides(IWL) originates from the wave’s movement and load, wherein the impulse wave’s load is the major cause of sub-aerial building damage and casualties. In this study, an experiment involving 16 groups of physical tests for the wave pressure generated by a landslide was designed, consisting of 4 sets of IWL and 4 opposite bank slope angles. A high-frequency strain system was used to measure the total pressure of the impulse wave in a water tank. The tests showed that the dynamic pressure caused by the IWL can be divided into two types: impact pressure generated by the jetflow and the pulsating pressure caused by the wave. Under the same impulse wave conditions, the maximum run-up becomes smaller as the opposite bank’s slope angle increases, and the jetflow maximum impact pressure experienced by the opposite bank increases, while the maximum pulsating pressure caused by the impulse wave is slightly decreased. Different from previous studies, the spatial maximum pressure distributions of the wave generated by landslide were concluded that the position of the maximum pulsating pressure appears adjacent to the still water surface, and the overall spatial distribution pattern of maximum wave pressure is presented as an inclined 'M' shape.Meanwhile, this study is the first to quantitatively analyzed that impact pressure has a very short action time, is even 7 times of the pulse pressure value, and there is a simple mathematical linear relationship between the two. Currently, some wave-load formulas for wind waves and tides are not applicable to calculating the loads of IWL. Research on the load of IWL will explain the hazard of impulse wave very clearly, and will greatly contribute to hazard prevention, mitigation and risk assessment work associated with IWL.

Influence of impulse waves generated by rocky landslides on the pressure exerted on bank slopes

Rocky landslides on river banks can result in the generation of ultra-high waves,which may destroy structures on the opposite bank.Existing methods to calculate the pressure on bank slopes under the effect of impulse waves generated by landslides are,however,few and of low precision.Therefore,in this study,a three-dimensional physical model test was conducted by taking into account factors such as landslide geometry parameters and the bank slope angle.The model test section was generalized on the basis of a certain section of the Three Gorges reservoir area as a prototype,after which the wave parameters and wave pressure acting on the bank slope were measured.Subsequently,the magnitude,acting point,and distribution of the pressure of the impulse waves generated by the rocky landslide upon the bank slope were determined.The distribution curve of the impact pressure was similar to that calculated using theСНиПⅡ57-75 formula,and the experimental pulsating pressure value was close to the value calculated using the Subgrade formula.Based on the test results,a power function of the relative pulsating pressure steepness with respect to the reciprocal of the wave steepness,relative water depth,and slope ratio was proposed.The acting point of the maximum pulsating pressure was found to be located near the still water level.Finally,an empirical formula for calculating the envelope of the maximum pulsating pressure distribution curve was proposed.These formulas can serve as a theoretical basis for the prediction of impulse wave pressure generated owing to landslides on bank slopes.

Theoretical research on aggregative dynamic pressure damper

To broaden the frequency width and increase the damping coefficient of a dynamic pressure damper, we designed an aggregative dynamic pressure damper (ADPD). Combined with the advantages of traditional dynamic pressure dampers (TDPD), ADPD can not only increase the damping coefficient in wide frequency range for valve control system, but also absorb partial pressure pulsations and impacts in the low and high frequency fields. Based on the theoretical research and the analysis compared with TDPD, we concluded that the ADPD was superior to the TDPD in the middle high frequency field, and the main parameters influencing the performance of the damper were the damping stiffness, orifice flow coefficient, pre-charge pressure, and the volume of the damper accumulator.

Influence of specific speed on hydraulic performances and pressure fluctuations in mixed-flow pumps

A series of steady and unsteady numerical calculations of the internal flow in mixed-flow pumps with three different specific speeds were carried out based on the N-S equation coupled with the standard k-εturbulence model under different operating conditions to investigate the relationship between the impeller specific speed and the pump performance as well as pressure pulsations.Meanwhile,the pump performance and pressure pulsations inside the mixed-flow pump with three different specific speeds were also analyzed and compared with the corresponding test data.From the results,the averaged deviations between the predicted and tested head among different impellers are below 5%,and with respect to the equivalent impeller specific speeds of 280 and 260,the values are 4.30%and 3.69%,respectively.For all the impeller schemes,the best efficiency point of the mixed-flow pump is found at the flow rate of 1.2 Q_(d) and the higher head deviation occurs at lower flow rates.Especially,it can be found that the specific speed has a slight effect on the pressure fluctuation in the impellers.Eventually,it is determined that the pump performance curves calculated by numerical simu-lations have good agreement with the relevant experimental results,which verifies that the numerical methods used in the present study are accurate to a certain extent.Furthermore,the results also provide some references to the pressure pulsation analysis and the performance improvement of the mixed-flow pump design.

Mid-Latitude Pc1, 2 Pulsations Induced by Magnetospheric Compression in the Maximum and Early Recovery Phase of Geomagnetic Storms

We investigate the properties of interplanetary inhomogeneities generating long-lasting mid-latitude Pc1, 2 geomagnetic pulsations. The data from the Wind and IMP 8 spacecrafts, and from the Mondy and Borok midlatitude magnetic observatories are used in this study. The pulsations under investigation develop in the maximum and early recovery phase of magnetic storms. The pulsations have amplitudes from a few tens to several hundred pT and last more than seven hours. A close association of the increase (decrease) in solar wind dynamic pressure (Psw) with the onset or enhancement (attenuation or decay) of these pulsations has been established. Contrary to high-latitude phenomena, there is a distinctive feature of the interplanetary inhomogeneities that are responsible for generation of long-lasting mid-latitude Pc1,2. It is essential that the effect of the quasi-stationary negative Bz-component of the interplanetary magnetic field on the magnetosphere extends over 4 hours. Only then are the Psw pulses able to excite the above-mentioned type of mid-latitude geomagnetic pulsations. Model calculations show that in the cases under study the plasmapause can form in the vicinity of the magnetic observatory. This implies that the existence of an intense ring current resulting from the enhanced magnetospheric convection is necessary for the Pc1, 2 excitation. Further, the existence of the plasmapause above the observation point (as a waveguide) is necessary for long-lasting Pc1 waves to arrive at the ground.

岛礁护岸结构裂缝缺陷内脉动压强特征试验研究

波浪作用下珊瑚礁礁坪上会产生高速波生流,在高速水流的冲击下岛礁护岸结构易发生破坏、失稳.因此,开展了珊瑚礁礁坪上波生流与有裂缝缺陷护岸结构相互作用的物理模型试验,对裂缝内脉动压强的频谱密度、特征值分布、强度分布等特征进行了研究和分析,揭示了护岸结构裂缝缺陷内脉动压强的变化规律.研究表明,礁坪上护岸结构裂缝缺陷特征位置处脉动压强的主频值与入射波频率对应.护岸结构上、下部沉箱间的裂缝入口处脉动压强分布较为平稳,沿裂缝缺陷逐渐延伸分布的各测点脉动压强脉动剧烈程度提升,且复杂湍流在裂缝缺陷内发生扩散且于垂直方向摆动幅度提升.同时,湍流的脉动作用在裂缝缺陷内形成的负压持续增大,导致中间位置脉动压强均方根值突增,突变数值约为入口附近7倍.当礁坪长度分别取1 m、2 m和3 m时,裂缝缺陷内中间位置处脉动压强系数分别约为入口处的1.59倍、1.49倍和1.46倍.裂缝缺陷内沿程各测点位置处的脉动压强系数对于大坡度礁前斜坡更为敏感,且礁前斜坡率越大,脉动压强系数越大.存在1个临界坡度,当礁前斜坡率大于临界坡度且礁上相对淹没度位于0.61~1.04时,脉动压强系数值下降约34%;当礁前斜坡率小于临界坡度时,脉动压强系数沿程分布与礁前斜坡率之间相关性较弱.

叶根倒圆角对离心泵性能及压力脉动影响研究

针对低比转速离心泵压力脉动引起泵体振动损伤问题,对某引水工程离心泵进行物理模型试验,并采用基于κ-ε湍流模型的数值模拟方法对原模型和设置了不同半径的叶根倒圆角模型进行全流道三维定常与非定常数值模拟,计算模型性能、分析内部流场、研究其压力脉动特性和湍动能分布规律,发现叶根倒圆角对离心泵外特性和内流场分布均有影响,设置叶根倒圆角能够提升离心泵扬程、改善流动状态、抑制后盖板附近的压力脉动和流动紊乱。

分流叶片非谐对离心压气机叶轮气动噪声特性的影响研究

为探讨非谐设计在分流叶片离心叶轮上的可行性及气动降噪程度,以离心压气机叶轮为研究对象,采用全流道非定常数值模拟和FW-H气动噪声模型,对比分析了4种分流叶片非谐叶轮和原始均匀叶轮的气动噪声特性,通过叶片表面压力脉动频谱特性和湍动能分布揭示了非谐设计对气动噪声的影响机理。结果表明:分流叶片周向角非谐设计在保证气动性能的同时,可以降低离散单音噪声;在采用的对比方案中,叶轮A1降噪效果最为明显,在第1、2和3阶处叶片通过频率的声谱密度分别下降43百分点、44百分点和50百分点,对应的压力脉动幅值分别下降25百分点、25百分点和30百分点,同时宽频噪声水平相比原始均匀叶轮明显增加。

混流式水轮机压力脉动及叶片裂纹生长分析

目前,水轮机转轮叶片出现裂纹甚至脱落的情况时有发生,严重影响了电站的安全运行.本文以某水电站机组为研究对象,基于流固耦合理论和扩展有限元方法对该水轮机全流道及转轮结构进行仿真分析,提取不同运行工况下转轮叶片的压力脉动信息,进行其转轮结构强度及叶片疲劳裂纹扩展情况分析.研究表明转轮内部的压力脉动主要由转轮旋转、导叶出口不均匀流场以及低频尾水涡带所引起.在不同运行工况下,叶片所受应力分布大致相同,且均在叶片出水边与上冠以及下环交接处附近存在应力集中的现象.当转轮出水边靠近下环连接处出现裂纹时,裂纹会从出水边逐渐向转轮下环附近扩展,并最终发展为贯穿性裂纹.且叶片出现贯穿性裂纹所经历的载荷循环次数与应力大小以及裂纹的扩展形状有关.

压力脉动对安全阀开启压力的影响分析

安全阀作为航空液压系统的关键组件,其性能优劣会直接影响航空飞行的安全与稳定。针对某航空液压系统用安全阀出厂试验与外厂检验开启压力不同的现象展开,以试验台压力脉动对安全阀开启压力的影响作为切入点,经过理论推导得到关于压力脉动幅值的安全阀开启压力数学表达式,并进行试验验证。试验结果证明:压力脉动频率对于安全阀开启压力没有影响,但是压力脉动幅值与开启压力呈现负相关。基于此结论,安全阀外场检验开启压力高的问题得以解决。本研究对航空液压元件测试、元件理论性能与实际性能一致性测试具有指导和借鉴意义。