Semi-diurnal pressure fluctuation in the ERA40 Data

Tip clearance has a great effect on the flow and pressure fluctuation characteristics in a multiphase pump, especially at multiple operating points. The phase distribution and pressure fluctuation in tip clearance in a multiphase pump are revealed using the CFD (computational fluid dynamics) technology and high-speed photography methods. In this paper, the phase distribution, the gas-liquid two-phase velocity slip, and the pressure fluctuation intensity are comprehensively analyzed. Results show with the increase of the tip clearance, the multiphase pump pressurization performance is obviously deteriorated. In the meantime, the gas accumulation mainly occurs at the hub, the blade suction side (SS), and the tip clearance, and the maximum gas-liquid two-phase velocity difference is near the impeller streamwise of 0.4. In addition, the tip clearance improves the gas-liquid two-phase distribution in the pump, that is, the larger the tip clearance is, the more uniform the gas-liquid distribution becomes. Furthermore, the gas leads to the maximum pressure fluctuation intensity in the tip clearance which is closer to the tip leakage flow (TLF) outlet, and has a greater effect on the degree of flow separation in the tip clearance.

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Large Eddy Simulation of Periodic Transient Pressure Fluctuation in a Centrifugal Pump Impeller at Low Flow Rate

Symmetry ◽

10.3390/sym13020311 ◽

2021 ◽

Vol 13 (2) ◽

pp. 311

Author(s):

Renfei Kuang ◽

Xiaoping Chen ◽

Zhiming Zhang ◽

Zuchao Zhu ◽

Yu Li

Keyword(s):

Large Eddy Simulation ◽

Centrifugal Pump ◽

Flow Rate ◽

Pressure Fluctuation ◽

Low Frequency ◽

Pump Impeller ◽

Eddy Simulation ◽

Inlet Flow Rate ◽

Large Eddy ◽

Centrifugal Pump Impeller

This paper presents a large eddy simulation of a centrifugal pump impeller during a transient condition. The flow rate is sinusoidal and oscillates between 0.25Qd (Qd indicates design load) and 0.75Qd when the rotating speed is maintained. Research shows that in one period, the inlet flow rate will twice reach 0.5Qd, and among the impeller of one moment is a stall state, but the other is a non-stall state. In the process of flow development, the evolution of low-frequency pressure fluctuation shows an obviously sinusoidal form, whose frequency is insensitive to the monitoring position and equals to that of the flow rate. However, inside the impeller, the phase and amplitude in the stall passages lag behind more and are stronger than that in the non-stall passages. Meanwhile, the strongest region of the high-frequency pressure fluctuation appears in the stall passages at the transient rising stage. The second dominant frequency in stall passages is 2.5 times to that in non-stall passages. In addition, similar to the pressure fluctuation, the evolution of the low-frequency head shows a sinusoidal form, whose phase is lagging behind that by one-third of a period in the inlet flow rate.

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High-Speed Elevator Car Air Pressure Compensation Method Based on Coupling Analysis of Internal and External Flow Fields

Applied Sciences ◽

10.3390/app11041700 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1700

Author(s):

Lemiao Qiu ◽

Huifang Zhou ◽

Zili Wang ◽

Shuyou Zhang ◽

Lichun Zhang ◽

...

Keyword(s):

Pressure Fluctuation ◽

Iterative Learning Control ◽

High Speed ◽

Learning Control ◽

Flow Fields ◽

External Flow ◽

Iterative Learning ◽

Air Pressure ◽

Coupling Analysis ◽

Pressure Compensation

As the demand for high-speed elevators grows, the requirements of elevator performance have also developed. The high speed will produce strong airflow disturbances and drastic pressure changes, which is prone to cause passenger discomfort. In this paper, an elevator car air pressure compensation method based on coupling analysis of internal and external flow fields (IE-FF) is proposed. It helps to adaptively track the ideal air pressure curve (IAPC) inside the car and controls the air pressure fluctuation to improve the ride comfort of the elevator. To obtain the air pressure transient value in the elevator car, an IE-FF modeling method is proposed. Based on the IE-FF model, the air pressure compensation system is developed. To realize the air pressure compensation inside the car, an adaptive iterative learning control (A-ILC) algorithm is proposed, to eliminate the passengers’ ear pressing due to the severe air pressure fluctuation. To verify the proposed method, the KLK2 (Canny Elevator Co., Ltd., 2015, Suzhou, China) high-speed elevator is applied. The numerical experiment results show that the proposed method has higher tracking accuracy and convergence speed compared to the classical Proportion Integral Differential (PID) algorithm and the Proportion Integral-iterative learning control (PD-ILC) algorithm.

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Investigation into the Relationship between Super-Knock and Misfires in an SI GDI Engine

Energies ◽

10.3390/en14082099 ◽

2021 ◽

Vol 14 (8) ◽

pp. 2099

Author(s):

Jian Gao ◽

Anren Yao ◽

Yeyi Zhang ◽

Guofan Qu ◽

Chunde Yao ◽

...

Keyword(s):

Pressure Fluctuation ◽

Direct Injection ◽

Exhaust Valve ◽

Gasoline Direct Injection ◽

Exhaust Pipe ◽

Pressure Transducers ◽

Spark Plug ◽

Si Engines ◽

Gdi Engine ◽

The Relationship

The super-knock poses new challenges for further increasing the power density of spark ignition (SI) engines. The critical factors and mechanism connecting regarding the occurrence of super-knock are still unclear. Misfire is a common phenomenon in SI engines that the mixture in cylinder is not ignited normally, which is often caused by spark plug failure. However, the effect of misfire on engine combustion has not been paid enough attention to, particularly regarding connection to super-knock. The paper presents the results of experimental investigation into the relationship between super-knock and misfires at low speed and full load conditions. In this work, a boosted gasoline direct injection (GDI) engine with an exhaust manifold integrated in the cylinder head was employed. Four piezoelectric pressure transducers were used to acquire the data of a pressure trace in cylinder. The spark plugs of four cylinders were controlled manually, of which the ignition system could be cut off as demanded. In particular, a piezoelectric pressure transducer was installed at the exhaust pipe before the turbocharger to capture the pressure traces in the exhaust pipe. The results illustrated that misfires in one cylinder would cause super-knock in the other cylinders as well as the cylinder of itself. After one cylinder misfired, the unburned mixture would burn in the exhaust pipe to produce oscillating waves. The abnormal pressure fluctuation in the exhaust pipe was strongly correlated with the occurrence of super-knock. The sharper the pressure fluctuation, the greater the intensity of knock in the power cylinder. The cylinder whose exhaust valve overlapped with the exhaust valve of the misfired cylinder was prone to super-knock.

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Numerical and Experimental Analysis of Flow and Pulsation in Hump Section of Siphon Outlet Conduit of Axial Flow Pump Device

Applied Sciences ◽

10.3390/app11114941 ◽

2021 ◽

Vol 11 (11) ◽

pp. 4941

Author(s):

Fan Yang ◽

Yiqi Zhang ◽

Yao Yuan ◽

Chao Liu ◽

Zhongbin Li ◽

...

Keyword(s):

Flow Field ◽

Flow Rate ◽

Vortex Structure ◽

Pressure Fluctuation ◽

Axial Flow ◽

Mean Value ◽

Hydraulic Loss ◽

Pressure Amplitude ◽

Measuring Point ◽

Outlet Conduit

In order to study the variation law of the flow field and pressure fluctuation in the hump section of the siphon outlet conduit, the flow field characteristics and frequency spectrum characteristics of the flow field were analyzed by combining a physical model test and numerical simulation under the conditions of the interaction between the axial flow pump and siphon outlet conduit, and the influence of the residual circulation at the outlet of the guide vane on the siphon outlet flow was investigated. Based on the influence of the flow field and hydraulic loss in the conduit, the equivalent surface method based on the Q criterion was used to analyze the vortex structure in the siphon outlet conduit and to analyze the internal vortex state. The results showed that with the increase of the flow rate, the intensity of the vortices in the cross-section of the hump section of the siphon outlet conduit decreased gradually, the average velocity circulation decreased gradually and the axial velocity distribution uniformity increased and tended to be stable; water flow stratification existed under three characteristic conditions with no circulation, and the hydraulic loss was greater with the circulation flow while it had a circulation under the small flow condition. Under the low flow rate conditions, the hydraulic loss was 6.6 times higher under the condition of circulation than without. Under a high flow condition, it was 1.3 times. Under the condition of a small flow rate, the vortex structure was distributed centrally at the inlet of the flow conduit, and under the other two characteristic conditions, the vortex structure mostly appeared as a strip; the pressure fluctuation in the hump section had obvious periodicity, and with the increase of the flow rate, the maximum pressure fluctuation amplitude in the hump section decreased gradually; with the decrease of the rotational speed, the pressure amplitude at the same measuring point in the hump section decreased gradually and at the optimum condition. Under the following conditions, the mean value of the pressure amplitude at the top of the hump section was reduced by 69.63%, and the mean value of the pressure amplitude at the bottom of the hump section was reduced by 63.5%. Under all the calculation conditions, the main frequency of pulsation at each measuring point of the hump section was twice the frequency of the rotation.

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