scholarly journals Investigation on Unsteady Cavitation Flow and Excited Pressure Fluctuations in Regulating Valve

Machines ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 32
Author(s):  
Xiumei Liu ◽  
Jie He ◽  
Yongwei Xie ◽  
Beibei Li ◽  
Yujia Zhang ◽  
...  
Keyword(s):  
Flow Field ◽  
Measurement System ◽  
High Speed ◽  
Pressure Pulsation ◽  
Pressure Fluctuations ◽  
Inlet Pressure ◽  
Maximum Pressure ◽  
Cavitation Flow ◽  
Measuring Point ◽  
The Mean

A multi-field synchronous measurement system for the cavitation flow in a regulating valve was established. The system combines a high-speed full-flow field display system with a pressure measurement system to realize the simultaneous acquisition of cavitation shapes and pressure pulsations. Cavitation flow occurs near the throttle orifice, which is obviously a quasi-periodic behavior. The unsteady cavitation flow mainly includes three stages: the growth of the attached cavity, the fracture and shedding of the attached cavity and the growth and collapse of the free cavity. The time evolution of the cavitation behaviors is highly related with excited pressure fluctuations. With the increasing attached cavity area, the corresponding pressure in the flow field decreases slowly. When the attached cavity falls off and develops downstream, the cavity area decreases gradually, and the pressure increases gradually. When the free cavity shrinks and collapses, the pressure in the flow field reaches the peak value. The pressure pulsation and the change of cavity area have the same dominant frequency, around 2000 Hz, at the monitoring point in the upstream, throat and expansion monitoring points. Furthermore, with increasing inlet pressure, the mean and variance values of cavitation area become larger, and the excited pressure fluctuation at each measuring point becomes more intense. The mean value of pulsating pressure at the throat gradually increases, while the pressure in the expansion section presents a downward trend. The variance of pressure pulsation and the maximum pressure also increase gradually with the increase in inlet pressure. The change of cavitation area and the pressure pulsation in the regulating valve complement each other. The results in this paper could provide experimental guidance on optimizing the structure of the valve, inhibiting cavitation occurrence and prolonging the service life of the valve.

scholarly journals Numerical Analysis and Characterization of Surface Pressure Fluctuations of High-Speed Trains Using Wavenumber–Frequency Analysis

2019 ◽  
Vol 9 (22) ◽  
pp. 4924
Author(s):  
Lee ◽  
Cheong ◽  
Kim ◽  
Kim
Keyword(s):  
Flow Field ◽  
Open Field ◽  
Frequency Analysis ◽  
Surface Pressure ◽  
High Speed ◽  
Pressure Fluctuations ◽  
Interior Noise ◽  
High Speed Train ◽  
Pressure Fields ◽  
Time Space

The high-speed train interior noise induced by the exterior flow field is one of the critical issues for product developers to consider during design. The reliable numerical prediction of noise in a passenger cabin due to exterior flow requires the decomposition of surface pressure fluctuations into the hydrodynamic (incompressible) and the acoustic (compressible) components, as well as the accurate computation of the near aeroacoustic field, since the transmission characteristics of incompressible and compressible pressure waves through the wall panel of the cabin are quite different from each other. In this paper, a systematic numerical methodology is presented to obtain separate incompressible and compressible surface pressure fields in the wavenumber–frequency and space–time domains. First, large eddy simulation techniques were employed to predict the exterior flow field, including a highly-resolved acoustic near-field, around a high-speed train running at the speed of 300 km/h in an open field. Pressure fluctuations on the train surface were then decomposed into incompressible and compressible fluctuations using the wavenumber–frequency analysis. Finally, the separated incompressible and compressible surface pressure fields were obtained from the inverse Fourier transform of the wavenumber–frequency spectrum. The current method was illustratively applied to the high-speed train HEMU-430X running at a speed of 300 km/h in an open field. The results showed that the separate incompressible and compressible surface pressure fields in the time–space domain could be obtained together with the associated aerodynamic source mechanism. The power levels due to each pressure field were also estimated, and these can be directly used for interior noise prediction.

Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder

2011 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Unsteady Flow ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Mean Flow ◽  
The Mean ◽  
Velocity Spectra

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α = 60° to α = 90°. Multi-point fluctuating surface pressure and hotwire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, span-wise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused and was still present and correlated from front to back, at least for the larger yaw angles investigated. When the cylinder was yawed to α = 60°, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.

scholarly journals Comparative Analysis of Surface Pressure Fluctuations of High-Speed Train Running in Open-Field and Tunnel Using LES and Wavenumber-Frequency Analysis

2021 ◽  
Vol 11 (24) ◽  
pp. 11702
Author(s):  
Songjune Lee ◽  
Cheolung Cheong ◽  
Byunghee Kim ◽  
Jaehwan Kim
Keyword(s):  
Open Field ◽  
Surface Pressure ◽  
High Speed ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
External Flow ◽  
High Speed Train ◽  
Wall Panel ◽  
Mean Flow ◽  
The Mean

The interior noise of a high-speed train due to the external flow disturbance is more than ever a major problem for product developers to consider during a design state. Since the external surface pressure field induces wall panel vibration of a high-speed train, which in turn generates the interior sound, the first step for low interior noise design is to characterize the surface pressure fluctuations due to external disturbance. In this study, the external flow field of a high-speed train cruising at a speed of 300 km/h in open-field and tunnel are numerically investigated using high-resolution compressible LES (large eddy simulation) techniques, with a focus on characterizing fluctuating surface pressure field according to surrounding conditions of the cruising train, i.e., open-field and tunnel. First, compressible LES schemes with high-resolution grids were employed to accurately predict the exterior flow and acoustic fields around a high-speed train simultaneously. Then, the predicted fluctuating pressure field on the wall panel surface of a train was decomposed into incompressible and compressible ones using the wavenumber-frequency transform, given that the incompressible pressure wave induced by the turbulent eddies within the boundary layer is transported approximately at the mean flow and the compressible pressure wave propagated at the vector sum of the sound speed and the mean flow velocity. Lastly, the power levels due to each pressure field were computed and compared between open-field and tunnel. It was found that there is no significant difference in the power levels of incompressible surface pressure fluctuations between the two cases. However, the decomposed compressible one in the tunnel case is higher by about 2~10 dB than in the open-field case. This result reveals that the increased interior sound of the high-speed train running in a tunnel is due to the compressible surface pressure field.

Shear/Pressure Driven Internal Condensing Flows and Their Sensitivity to Inlet Pressure Fluctuations

2011 ◽  
Author(s):  
M. Kivisalu ◽  
N. Gorgitrattanagul ◽  
S. Mitra ◽  
R. Naik ◽  
A. Narain
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rectangular Cross Section ◽  
Pressure Fluctuations ◽  
Inlet Pressure ◽  
Bottom Surface ◽  
Exit Pressure ◽  
Condensing Flows ◽  
The Mean

The reported experimental results are for annular zones of fully condensing flows of pure FC-72 vapor. The flow condenses on the bottom surface (316 Stainless Steel) of a horizontal, rectangular cross-section duct. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) values of mass flow rate, inlet (or exit) pressure, and wall cooling conditions. It has been reported elsewhere that, with the condenser mean (time averaged) inlet mass flow rate, mean inlet (or exit) pressure, and wall cooling condition held at quasi-steady values, there is a very strong sensitivity to certain impositions of pressure fluctuations and accompanying flow rate pulsations at the condenser inlet. For these impositions, it was found that the mean exit (or inlet) pressure changes to significantly affect mean test-section pressure difference, local heat-flux variations over the annular portion of the flow, and the nature of the annular flow regime. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of pressure fluctuations imposed on the inlet of the condenser from the vapor line. It has been found that, for various frequencies of interest, there are typically two classes of responses to inlet pressure fluctuations. These are termed supercritical (for the larger amplitudes for which a strong sensitivity exists) and subcritical (for the smaller amplitudes for which a weak sensitivity exists).

scholarly journals Unsteady Numerical Calculation of Oblique Submerged Jet

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4728
Author(s):  
Weixuan Jiao ◽  
Di Zhang ◽  
Chuan Wang ◽  
Li Cheng ◽  
Tao Wang
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Pressure Coefficient ◽  
High Energy ◽  
Impact Pressure ◽  
Maximum Pressure ◽  
Flow Angle ◽  
Free Jet ◽  
Velocity Flow ◽  
The Impact

A water jet is a kind of high-speed dynamic fluid with high energy, which is widely used in the engineering field. In order to analyze the characteristics of the flow field and the change of law of the bottom impact pressure of the oblique submerged impinging jet at different times, its unsteady characteristics at different Reynolds numbers were studied by using the Wray–Agarwal (W-A) turbulence model. It can be seen from the results that in the process of jet movement, the pressure at the peak of velocity on the axis was the smallest, and the velocity, flow angle, and pressure distribution remain unchanged after a certain time. In the free jet region, the velocity, flow angle, and pressure remained unchanged. In the impingement region, the velocity and flow angle decreased rapidly, while the pressure increased rapidly. The maximum pressure coefficient of the impingement plate changed with time and was affected by the Reynolds number, but the distribution trend remained the same. In this paper, the characteristics of the flow field and the law of the impact pressure changing with time are described.

Fluctuations of density, pressure and temperature in a turbulent mixing region

1984 ◽  
Vol 395 (1809) ◽  
pp. 203-228 ◽  
Keyword(s):  
Mach Number ◽  
Temperature Gradient ◽  
Shear Layer ◽  
Turbulent Mixing ◽  
Pressure Fluctuations ◽  
Density Fluctuations ◽  
Maximum Pressure ◽  
Local Pressure ◽  
Mean Temperature ◽  
The Mean

Observations of density fluctuations have been made in a turbulent mixing jet with variable Mach number and enthalpy. On the basis of mean velocity and enthalpy distributions the density fluctuations have been related to local pressure and temperature fluctuation intensities. It is found that the pressure fluctuations determined in this way are in agreement with previous microphone-based observations, although there is some uncertainty about the use of microphones in turbulent flows. The present observations show the maximum pressure fluctuations in the shear layer close to the nozzle to be in excess of the values estimated from turbulence intensity data by 26%, while closer agreement is found in the self-preserving region further away from the nozzle. The temperature fluctuations were found to be consistent with observations made with fine wire probes, and the pressure-temperature covariance showed a reversal of sign across the shear layer consistent with mixing in the presence of the mean property gradients. Increases of flow Mach number substantially reduced the relative intensity of both pressure and temperature fluctu­ations. For mixing conditions dominated by a large mean temperature gradient, turbulent scales and spectra were similar to those of velocity fluctuations. Under conditions where the mean temperature gradient was eliminated and pressure fluctuations dominated the density variations, the scales were significantly increased and the spectra showed a more rapid decrease with frequency.

Vortex-Shedding From Various Yawed Tandem Circular Cylinder Arrangements

2012 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Circular Cylinder ◽  
Flow Field ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Cylinder Wall ◽  
Pressure Measurements ◽  
Mean Flow ◽  
The Mean

The struts of a landing gear can be modeled as a tandem cylinder system where one cylinder is yawed to the mean flow direction. The current experimental investigation will examine the effect that yawing either the front or rear cylinder will have on the pressure fluctuations and associated unsteady flow field. This will be accomplished using 24 simultaneous unsteady wall pressure measurements on the cylinder wall. Two yaw angles will be examined here, α = 80° and α = 60°, for both the yawed upstream and yawed downstream cases.

scholarly journals Experimental Study of Pressure and Velocity Fluctuations Induced by Cavitation in a Small Venturi Channel

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6478
Author(s):  
Linrong Zhang ◽  
Guangjian Zhang ◽  
Mingming Ge ◽  
Olivier Coutier-Delgosha
Keyword(s):  
High Speed ◽  
Pressure Fluctuations ◽  
Vapour Phase ◽  
Stream Velocity ◽  
High Speed Photography ◽  
Transient Pressure ◽  
Velocity Fluctuations ◽  
Turbulent Fluctuations ◽  
The Mean ◽  
The Impact

The purpose of this paper is to investigate experimentally the influence of the cavitation extent on the pressure and velocity fluctuations in a small convergent–divergent channel. The mean cavity length is determined from high-speed photography images. The mean pressure and the intensity of the pressure fluctuations are obtained from the transient pressure signals recorded by two pressure transducers at the inlet and outlet of the test section. The statistical turbulence quantities are derived from the instantaneous velocity fields measured by the laser-induced fluorescent particle image velocimetry (PIV-LIF) technique. The experimental results show that the decrease of the cavitation number (the increase in the extent of cavitation) leads to a rise in the turbulent fluctuations in the wake region due to the impact of vapour clouds collapsing, while the presence of a vapour phase is found to reduce the streamwise and cross-stream velocity fluctuations in the attached cavity. It might be attributed to two mechanisms: the presence of a vapour phase modifies the vortex-stretching process, and the cavitation compressibility damps out the turbulent fluctuations. Similar effects of cavitation are also observed in the pressure fluctuations.

scholarly journals Simulation of Particle Motion Behavior in Fluidized Bed Opposed Jet Mill

2021 ◽  
Vol 2125 (1) ◽  
pp. 012040
Author(s):  
Kangwei Yang ◽  
Xuewen He
Keyword(s):  
Flow Field ◽  
Fluidized Bed ◽  
High Speed ◽  
Collision Energy ◽  
Inlet Pressure ◽  
Acceleration Process ◽  
Total Collision ◽  
Motion Behavior ◽  
Opposed Jet ◽  
Nozzle Spacing

Abstract In order to study the influence of the internal flow field of the fluidized bed opposed jet mill on the motion behavior of particles, Computational Fluid Dynamics (CFD) and Discrete Dlement Method (DEM) are used for coupling calculations. By adjusting the nozzle spacing and inlet pressure, Numerical simulation is carried out on the process of particles collisions with each other after accelerating under the high-speed jet produced by the nozzle. The trajectory of the particles in the flow field of the collision area and the change of the collision state of the particles are analyzed. Finally, the best parameters are selected based on the total collision energy. The results show that the particles will gradually shift and spread during the acceleration process. The reduction of the nozzle spacing is beneficial to increase the probability of particle collisions. However, if the spacing is too small, the particles cannot be fully accelerated; the increase in inlet pressure will increase the kinetic energy of the particles, and number of collisions is almost unaffected. By comparing the total collision energy, the best-simulated preparation conditions are selected as 110mm and 1.1MPa.

Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Hot Wire ◽  
Mean Flow ◽  
The Mean ◽  
Velocity Spectra

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α=60 deg to α=90 deg. Multipoint fluctuating surface pressure and hot-wire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, spanwise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused. When the cylinder was yawed to α=60 deg, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.

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