Effects of Air Entrainment on the Ability of Air Vessels in the Pressure Surge Suppressions

2000 ◽  
Vol 122 (3) ◽  
pp. 499-504 ◽  
Author(s):  
T. S. Lee
Keyword(s):  
Unsteady Flow ◽  
Air Entrainment ◽  
Pipeline System ◽  
Transient Pressure ◽  
Fluid System ◽  
Pressure Peak ◽  
Free Case ◽  
Pressure Surge ◽  
Static Head ◽  
Peak Increase

This paper describes a new and efficient model for the study of air entrainment effects on the responses of a typical horizontal air vessel. The effects of air entrainment on the pressure surges for unsteady flow in a pipeline system were investigated. Studies showed that entrained, entrapped, or released gases in the transient fluid system tend to amplify the first pressure peak, increase surge damping, and produce asymmetric pressure surges with respect to the static head. The pressure surges showed longer periods of down-surge and shorter periods of upsurge. The upsurge was considerably amplified and down-surge was marginally reduced when compared with the gas-free case. With the horizontal air vessel installed, studies showed that the effects of air entrainment on the maximum transient pressure can be considerably reduced with an appropriately configured air vessel. [S0098-2202(00)00203-0]

scholarly journals The impact of the simple orifice schemes of the buffer device in boom refuelling system in the transient pressure of the pipeline

2021 ◽  
Vol 233 ◽  
pp. 04015
Author(s):  
Zhangzhi Dong ◽  
Xiaogang Li ◽  
Yanyan Hou ◽  
Bin Li ◽  
Yujuan He
Keyword(s):  
System Reliability ◽  
Pressure Pulsation ◽  
Simulation Analysis ◽  
Pipeline System ◽  
Transient Pressure ◽  
Pressure Shock ◽  
Flow Area ◽  
Suppression Effect ◽  
Pressure Peak ◽  
The Impact

The boom refuelling system has a large refueling flow, and the refueling joint when the refueling is interrupted in an emergency will cause pressure shock and pressure pulsation. In severe cases, it will cause vibration of the pipeline system, reduce system reliability, and seriously endanger flight safety. Adding a device similar to an accumulator at the end of the pipeline where pressure shock occurs can well absorb the shock pressure. This paper uses a certain type of aircraft as a background to simulate the construction of a rigid air refueling pipeline system with a buffer device. The emphasis is on the pressure shock suppression characteristics of the buffer device. The simulation analysis of the opening parameters of the expansion cavity entrance includes the number and size of the buffer device. The impact of pressure shock performance. The results show that: the more openings and the larger the pore size, the larger the first pressure peak and the smaller the second pressure peak; while increasing the total flow area can effectively reduce the pressure shock suppression effect of the buffer device.

Fluid Transient Responses With Check Valves in Pipe Flow System With Air Entrainment

1997 ◽  
Author(s):  
T. S. Lee ◽  
L. C. Leow
Keyword(s):  
Transient Flow ◽  
Flow System ◽  
Check Valve ◽  
Air Entrainment ◽  
Pipeline System ◽  
Piping System ◽  
Transient Responses ◽  
Fluid System ◽  
Free System ◽  
Fluid Transient

A common flow system arrangement in piping system consists of a lower reservoir, a group of pumps with a check valve in each branch, and a pipeline discharging into a upper reservoir. In earlier studies of check valves performances in transient flow, none considered the effects of air entrainment into a pipeline system and the subsequent effects on the check valve performances in transient flow. Studies on pressure surges during pump tripped in pumping systems showed that by including an air entrainment variable wave speed model, reasonable predictions of fluid transient responses with proper phasing and attenuation of pressure peaks can be obtained. The most severe case where all the pumps in the station fail simultaneously due to power failure was analysed for their maximum and minimum pressure variation along the pipeline. A numerical model is now set up in the present work to investigate the check valve performances in transient flow for a pumping system with air entrainment. The analyses examine a fluid system with a variable air entrainment content (ε) and studied numerically it effects on the flow reversal time and hence determine the appropriate valve selection for a given fluid system to minimize problems of check valve slamming. Present numerical computations show that the air content in a fluid system can adversely affect the check valve transient responses. With the fluid system operating within a critical range of air entrainment values, analysis showed that there is a possibility of “check valve slamming” when the check valves were selected based on the analysis of an air free system. The above phenomena is confirmed through physical field measurements.

Air Entrainment Effects on the Pressure Transients of Pumping Systems With Weir Discharge Chamber

2002 ◽  
Vol 124 (4) ◽  
pp. 1034-1043 ◽  
Author(s):  
T. S. Lee ◽  
K. L. Ngoh
Keyword(s):  
Discharge Chamber ◽  
Field Measurements ◽  
Air Entrainment ◽  
Pipeline System ◽  
Extreme Pressure ◽  
Fluid System ◽  
Pressure Transients ◽  
Proposed Model ◽  
Design Characteristics ◽  
Surface Vortex

This paper presents a new model for the study of air entrainment on the extreme pressure surges in pumping systems. For the present fluid system considered with a weir discharge chamber, numerical investigations showed that, with the proposed model of the air entrainment, reasonable predictions of transient pressures with proper phasing and attenuation of pressure peaks can be obtained. The results obtained are consistent with observations from field measurements made when the pumps were operating at low pump cutout levels where air entrainment due to attached surface vortex and falling jets from the inflow near the pump intake were present. Further studies were also made on the design characteristics of the weir discharge chamber on the extreme pressure transients for the unsteady flow in the pipeline system with various degrees of air entrainment.

Experimental Investigation of Surge Phenomena in a Transonic Centrifugal Compressor

2019 ◽  
Author(s):  
Sasuga Ito ◽  
Masato Furukawa ◽  
Satoshi Gunjishima ◽  
Hiroki Usuki ◽  
Takafumi Ota ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Static Pressure ◽  
High Response ◽  
Low Flow ◽  
Pipeline System ◽  
Flow Phenomenon ◽  
Pressure Transducers ◽  
Transonic Centrifugal Compressor ◽  
Response Pressure

Abstract Surge is an unsteady flow phenomenon occurring at low flow rates in the pipeline system including compressors. The surge is a phenomenon that must be avoided because of the danger in the operation: the pipeline equipment can be damaged or the operation cannot be continued. Experimental work is required not only to understand the unsteady behavior but to also validate the CFD used for more localized analysis and development of the understanding of the flow phenomena when operating near surge. Nevertheless, there are still many unclear points not only about the flow phenomenon at the inception of the surge which is important for the prediction of the surge but also about the surge behavior itself. Especially, as for the surge occurring in transonic centrifugal compressors, there are currently few experimental research cases due to the difficulty of the unsteady measurement. In this research, we measured the time variations in pressure and flow rate in a transonic centrifugal compressor for a vehicle turbocharger which consists of an impeller, vaneless diffuser and scroll. In the experiments, the measurement pipes were set upstream and downstream of the compressor and the velocity and the wall static pressure were measured with an I-type hot wire probe and high response pressure transducers, respectively. In addition, to investigate the process and the occurrence point of the back flow in surge, the wall static pressure was measured by means of high response pressure transducers which were mounted on the shroud upstream of the impeller and the diffuser hub at the two-circumferential positions, respectively. As the result of the experiments, the unsteady flow process during the mild and deep surges was measured and the inception of deep surge was clarified.

scholarly journals Effects of non-Newtonian lubricants and elastic coating on transient elastohydrodynamic lubrication at impact squeeze loading

2019 ◽  
Vol 11 (7) ◽  
pp. 168781401986607
Author(s):  
Li-Ming Chu ◽  
Yuh-Ping Chang ◽  
Hsiang-Chen Hsu
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Flow Index ◽  
Transient Pressure ◽  
Academic Innovation ◽  
Pressure Profiles ◽  
The Impact ◽  
Peak Increase ◽  
Ball Motion ◽  
Lubricant Viscosity ◽  
Peak Value

This study explores the effects of non-Newtonian lubricants on elastohydrodynamic lubrication with coating at impact and rebound loading using power law lubricants. The coupled transient modified Reynolds, rheology, elasticity deformation, and ball motion equations are solved simultaneously, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities and accelerations. The effect of the flow index ( n) is equivalent to enhancing the lubricant viscosity, also enlarging the damper effect. The simulation results reveal that the film thickness, the primary peak, and the secondary peak increase with increasing the flow index. The greater the flow index is, the earlier the dimple form, and the smaller the maximum value of the impact force is. The rebounding velocity and the peak value of acceleration increase with decreasing the flow index. Moreover, this research possesses academic innovation and industrial application.

Numerical Analysis of Unsteady Flow Field in the RWT for the Prediction of the Potential for Air Ingression Into the ECC Supply Lines During the SBLOCA at the KSNPs

2007 ◽  
Author(s):  
Jong Chull Jo ◽  
Seon Oh Yu
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Water Level ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Vortex Flow ◽  
Air Entrainment ◽  
Water Tank ◽  
Outlet Valve

This paper addresses the three-dimensional analysis of unsteady flow in the RWT (Refueling Water Tank) for the prediction of the potential for air ingression into the ECC (Emergency Core Cooling) pump during the SBLOCA (Small Break Loss Of Coolant Accident) at KSNPs (Korean Standard Nuclear Power plants). Upon the receipt of RAS (Recirculation Actuation Signal) by the occurrence of SBLOCA, the RWT outlet valve is designed to be isolated manually. At the nuclear power plants without the provision of automatic isolation operation of the valve on the downstream of the RWT line, the refueling water begins to discharge from the RWT, which may result in forming and developing the vortex flow in the RWT, under the condition of the minimum pressure of containment and minimum water level of containment recirculation sump during the phase of RAS. Due to the vortex flow, when the water level is below the critical height, a dip starts to develop, causing air ingression before the refueling water drains fully. Hence it can be surmised that there is a possibility of ECC pump failure due to air ingression into the ECC supply line even before the RWT is fully drained. Therefore, in this work, when the RAS is actuated followed by the SBLOCA occurrence, a quantitative evaluation for the maximum limiting allowable time for the manual closing of RWT outlet valve is carried out to eliminate the possibility of air ingression into the ECC pump from the RWT. To do this, the unsteady flow field in the RWT including the drain pit with the connected discharge piping in the process of SBLOCA is analyzed using a CFD (Computational Fluid Dynamics) code. In addition, the transient flow behavior accompanying air entrainment resulting from the dip formation due to vortex flow at the upper part of RWT is examined and the applicable limiting time of the isolation valve closing for preventing air ingression is assessed.

Kalman Filter and Model-Free Adaptive Control Theory Applied to the Unsteady Flow State Estimation of Product Pipelines

2020 ◽  
Author(s):  
Lei He ◽  
Kai Wen ◽  
Jing Gong
Keyword(s):  
Unsteady Flow ◽  
Linear Model ◽  
Flow Model ◽  
Transient Flow ◽  
Linear Method ◽  
Model Parameters ◽  
Flow State ◽  
Transient Pressure ◽  
Linear Flow ◽  
Model Based

Abstract The accurate online estimation of unsteady flow state provides important operation information for product pipelines real-time scheduling. In practice, affected by the parameter drift and observation noises, traditional estimation methods based on the first principle can hardly provide accurate results within acceptable time. The nonlinear and fast transient characteristics of pipeline flow make it difficult to realize on-line adaptive modification of model parameters. In order to meet the requirements of computational efficiency and accuracy simultaneously, this paper proposes a methodology with two-level adaptive adjustment to realize the digital twin of pipeline nonlinear transient flow process by using simplified linear flow model. In terms of improving computing efficiency, the linear flow model based on frequency response and difference transforming is established to process the on-line state estimation of transient flow. To reduce the deviation between the actual observed value and the linear model estimation, we first introduce mode-free adaptive control method as linear compensation of the reduced order unsteady flow model. The compact form dynamic linearization method has been adopted to design the virtual input of the linear flow model. To further improve the adaptability of the linear model, the model parameters are online adjusted by using the recursive least squares with forgetting factor method. The uncertainty of the model and the interference of observation noise is eliminated by adopting Kalman filter to the state space model based on modified linear model. The effectiveness of the proposed methodology is evaluated by applying to the digital twin process of a product pipeline transient pressure in a multistation pipeline. The results show that the proposed method can make transient pressure estimation of second-order linear model agree well with the value of nonlinear flow model even under unforeseen conditions and noise interference. The performance of the proposed method is better than model-based linear method, data-driven linear method and nonlinear method.

Air Influence on Similarity of Hydraulic Transients and Vibrations

1996 ◽  
Vol 118 (4) ◽  
pp. 706-709 ◽  
Author(s):  
T. S. Lee ◽  
S. Pejovic
Keyword(s):  
Wave Speed ◽  
Phase Flow ◽  
Water Mixture ◽  
Transient Pressure ◽  
Fluid System ◽  
Hydraulic Transients ◽  
Two Phase ◽  
Speed Variation ◽  
Air Content ◽  
Local Wave

The effects of wave speed variation due to air content on the validity of similarity laws for model studies of hydraulic transients and hydraulic vibrations were investigated. Studies show that hydraulic similarities between geometrically similar model and prototype are reduced substantially for cases involving two- or three-phase flow. For flow with intensive cavitation, analysis shows that there is no hydraulic similarity between model and prototype. For pump discharge pipeline and turbine draft tube where two phase flow of air-water mixture occurs, analysis shows that the natural frequency and the response characteristics of the fluid system are a strong function of the local wave speed variation within the fluid system. This local wave speed variation is a function of the local transient air content and transient pressure.

New Method Based on Model-Free Adaptive Control Theory and Kalman Filter for Multi-Product Unsteady Flow State Estimation

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Lei He ◽  
Jing Gong ◽  
Kai Wen ◽  
Changchun Wu ◽  
Yuan Min
Keyword(s):  
Adaptive Control ◽  
Unsteady Flow ◽  
State Estimation ◽  
Flow Model ◽  
Transient Flow ◽  
Pipeline System ◽  
Flow State ◽  
Flow Estimation ◽  
Model Based ◽  
Model Free

Abstract In this paper, a new methodology is proposed to realize real-time unsteady flow estimation for a multi-product pipeline system. Integrating transient flow model, adaptive control theory, and adaptive filter, this method is developed to solve the contradiction between the efficiency and accuracy in traditional model-based methods. In terms of improving computational efficiency, the linear flow model based on frequency response and difference transforming is established to replace the traditional nonlinear flow model for transient flow state estimation. To reduce the deviation between actual observations and linear model estimates, we first introduce a model-free adaptive control method as linear compensation of the reduced order unsteady flow state model. To overcome the interference of observation noise, the Kalman filter method is applied to the modified state space model to obtain the one-step-ahead transient flow estimation. The proposed method is applied to the transient flow state estimation of a multi-product pipeline system and compared with the model-based method and two data-driven methods. The proposed method can reduce the deviation of transient flow estimation between the reduced order linear model and the traditional nonlinear model to less than 0.5% under unforeseen conditions and shows strong robustness to noise interference and parameter drift.

Pressure Pulsation Analysis of Aircraft Hydraulic Power Pipelines System

2010 ◽  
Vol 97-101 ◽  
pp. 2861-2864 ◽  
Author(s):  
Wei Liu ◽  
Tao Wei ◽  
Zhu Feng Yue
Keyword(s):  
Hydraulic System ◽  
Pressure Pulsation ◽  
Excitation Frequency ◽  
Pipeline System ◽  
Transient Pressure ◽  
Hydraulic Power ◽  
Network Chain ◽  
Output Pressure ◽  
Fluid Network ◽  
Pulsation Model

The output pressure pulsation model for the aircraft hydraulic power pipelines was established by the methods of transfer function and fluid network chain-rules; the dissipation caused by frequency-dependent friction was taken into account. Dynamic characteristics of hydraulic system were discussed in frequency-domain and time-domain respectively, the pumping excitation frequency influenced the frequency-response of hydraulic pipeline system, and several resonance frequency bands were obtained. The inverse fast Fourier transform was applied to simulate the transient pressure pulsation waves under pump starting and steady-running state.

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