Monitoring the parameters of a reactor by low-frequency pressure pulsations

The pressure pulsations in the vaneless space of pump-turbines are extremely intense and always experience rapid time variations during transient scenarios, causing structural vibrations and even more serious accidents. In this study, the mechanism behind the rapid time variations of the vaneless space pressure pulsations in a model pump-turbine during runaway was analyzed through three-dimensional (3D) numerical simulations. These results show that the high-frequency pressure pulsation components originating from rotor–stator interactions (RSI) are dominant during the whole process. These components fluctuate significantly in frequency when the working point goes through the S-shaped region of the characteristic curve, with the amplitudes increasing. Meanwhile, some low-frequency pulsations are also enhanced and become obvious. These features can be attributed to the transitions of the inter blade vortex structures (IBVSs) to the forward flow vortex structures (FFVSs) and the back flow vortex structures (BFVSs) at the impeller entrance, when the pump-turbine operates in the region with S-shaped characteristics. The FFVSs mainly cause decreases in frequency and introduce low-frequency pulsations, while the BFVSs are responsible for the unstable fluctuations. These findings contribute to the understanding of how transient flow patterns evolve and may provide new ideas about avoiding severe pressure pulsations caused by rotating stalls in the pump-turbine during transient scenarios.

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The numerical simulation of low frequency pressure pulsations in the high-head Francis turbine

Computers & Fluids ◽

10.1016/j.compfluid.2015.01.007 ◽

2015 ◽

Vol 111 ◽

pp. 197-205 ◽

Cited By ~ 30

Author(s):

A.V. Minakov ◽

D.V. Platonov ◽

A.A. Dekterev ◽

A.V. Sentyabov ◽

A.V. Zakharov

Keyword(s):

Numerical Simulation ◽

Low Frequency ◽

Francis Turbine ◽

Pressure Pulsations ◽

High Head

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Statistical Considerations on Pressure Pulses from a Cavitating Venturi

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/pime_proc_1986_200_146_02 ◽

1986 ◽

Vol 200 (6) ◽

pp. 381-387

Author(s):

S Li ◽

Y Zhang ◽

F G Hammitt

Keyword(s):

Closed Loop ◽

Pressure Fluctuations ◽

Low Frequency ◽

Resonant Interaction ◽

Statistical Characteristics ◽

Pressure Pulsations ◽

Cavitation Inception ◽

Flow Noise ◽

Pressure Pulses ◽

Liquid Portion

Pressure pulses emitted from cavitating venturi flows are measured and investigated statistically. The results show that according to the degree of cavitation, the overall pressure pulsations consist of different combinations of three components, that is basic flow noise, cavitation pulses and low-frequency pressure fluctuations, due primarily to overall loop characteristics. The statistical characteristics are presented and compared. It is believed that the low-frequency fluctuations result from a resonant interaction between the cavitation ‘cloud’ and the liquid portion of the closed loop. They occur near cavitation inception, reach a maximum at a particular cavitation number, σres, then gradually disappear for increased σ. Their frequency is basically constant for all σ. An empirical-theoretical model of this behaviour is presented.

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Effects of the Radial Gap Between Impeller Tips and Volute Tongue Influencing the Performance and Pressure Pulsations of Pump as Turbine

Journal of Fluids Engineering ◽

10.1115/1.4026544 ◽

2014 ◽

Vol 136 (5) ◽

Cited By ~ 48

Author(s):

Sun-Sheng Yang ◽

Hou-Lin Liu ◽

Fan-Yu Kong ◽

Bin Xia ◽

Lin-Wei Tan

Keyword(s):

High Frequency ◽

Pressure Pulsation ◽

Low Frequency ◽

Pressure Pulsations ◽

Unsteady Pressure ◽

Pressure Fields ◽

Rotor Stator Interaction ◽

Rotating Impeller ◽

Overall Performance ◽

Radial Gap

The radial gap between the impeller tips and volute tongue is an important factor influencing the overall performance and unsteady pressure fields of the pump as turbine (PAT). In this paper, a numerical investigation of the PAT's steady performance with different radial gaps was first performed. The results show that there is an optimal radial gap for a PAT to achieve its highest efficiency. An analysis of the PAT's unsteady pressure fields indicates that the rotorstator interaction of a rotating impeller and stationery volute would cause high frequency unsteady pulsation within the volute and low frequency unsteady pressure pulsation within the impeller. The high frequency unsteady pressure pulsation would propagate through the PAT's flow channel. Thus, the unsteady pressure field within the impeller is the combined effect of these two kinds of pressure pulsations. The unsteady pressure pulsation within the outlet pipe is mainly caused by the propagation of unsteady pressure formed within the volute. With the increase of the radial gap, the amplitude of high frequency unsteady pressure pulsation within the volute caused by the rotor-stator interaction is decreased, while the amplitude of the low frequency unsteady pressure pulsation caused by the rotor-stator interaction within the impeller remains unchanged.

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On the Use of Helmholtz Resonators for Damping Acoustic Pulsations in Industrial Gas Turbines

Volume 2: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/2001-gt-0039 ◽

2001 ◽

Cited By ~ 4

Author(s):

Valter Bellucci ◽

Christian Oliver Paschereit ◽

Peter Flohr ◽

Fulvio Magni

Keyword(s):

Heat Release ◽

Gas Turbine ◽

Gas Turbines ◽

Structural Integrity ◽

Combustion Process ◽

Low Frequency ◽

Operating Regime ◽

Pressure Pulsations ◽

Helmholtz Resonators ◽

Resonance Frequencies

In modern gas turbines operating with premix combustion flames, the suppression of pressure pulsations is an important task related to the quality of the combustion process and to the structural integrity of engines. High pressure pulsations may occur when the resonance frequencies of the system are excited by heat release fluctuations independent of the acoustic field (“loudspeaker” behavior of the flame). Heat release fluctuations are also generated by acoustic fluctuations in the premixed stream. The feedback mechanism inherent in such processes (“amplifier” behavior of the flame) may lead to combustion instabilities, the amplitude of pulsations being limited only by nonlinearities. In this work, the application of Helmholtz resonators for damping low-frequency pulsations in gas turbine combustion chambers is discussed. We present a nonlinear model for predicting the acoustic response of resonators including the effect of purging air. Atmospheric experiments are used to validate the model, which is employed to design a resonator arrangement for damping low-frequency pulsations in an ALSTOM GT11N2 gas turbine. The predicted damper impedances are used as the boundary condition in the three-dimensional analysis of the combustion chamber. The suggested arrangement leads to a significant extension of the low-pulsation operating regime of the engine.

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