scholarly journals Experimental Research and Numerical Analysis of Pressure Fluctuation Characteristics of Rim Driven Propulsion Pump Outlet

Machines ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 293
Author(s):  
Zhipeng Zhu ◽  
Houlin Liu
Keyword(s):  
Numerical Simulation ◽  
Frequency Band ◽  
Pressure Fluctuation ◽  
Large Scale ◽  
Low Frequency ◽  
Monitoring Point ◽  
Transient Velocity ◽  
Velocity Pressure ◽  
Good Agreement ◽  
Dominant Frequencies

The pressure fluctuation characteristics of a rim driven propulsion pump are studied by an experimental method firstly, and then its unsteady inner flow is studied by numerical simulation to reveal the generating mechanism of the pressure fluctuation. In the experiment, a monitoring point was set in a downstream region with a distance of 1D (D, Diameter of impeller) to the impeller. The monitoring point’s dominant frequencies within a low frequency band are 1APF (APF, Axial Passing Frequency) and 2APF. In the numerical simulation, the main fluctuation near the impeller region appears at 1BPF (BPF, Blade Passing Frequency) and as the monitoring point moves downstream, the amplitude becomes smaller. The 1BPF fluctuation nearly disappears when the distance exceeds 1D, and the main frequency moves to 1APF and 2APF, which is in good agreement with the experimental results in the low frequency band. The transient velocity, pressure and vorticity distribution were studied to reveal the causes of 1BPF, 1APF and 2APF fluctuation. The main cause of 1BPF is the jet from the tail of the blade and the main cause of 2APF is the movement of a large-scale double vortex structure on both sides of the low-pressure zone. The movement of the vortex group near the wall may be the main cause that induces the 1APF fluctuation.

scholarly journals Ferrite-Loaded Spidron Fractal Loop VHF Antenna for UAV Applications

2020 ◽  
Vol 10 (15) ◽  
pp. 5392 ◽  
Author(s):  
Won Bin Park ◽  
Young-Mi Park ◽  
Keum Cheol Hwang
Keyword(s):  
Frequency Band ◽  
High Frequency ◽  
Magnetic Loss ◽  
Low Frequency ◽  
Loop Antenna ◽  
High Frequency Band ◽  
Ferrite Material ◽  
Aerial Vehicle ◽  
Flat Ground ◽  
Good Agreement

In this letter, an electrically small Spidron fractal loop antenna operating in the VHF band is proposed. The ferrite material, which consists of a nickel-zinc combination, is loaded into inside of the loop antenna to increase the gain of the antenna in the low frequency band. To minimize the magnetic loss of the ferrite in the high frequency band, the amount and configuration of the ferrite are optimized using a genetic algorithm. Through this optimization step, the amount of the ferrite is decreased to 37.5% and the gain of the antenna in the high frequency band is improved. The size of the proposed antenna is 0.0242 × 0.0242 × 0.0051 λL3 at the lowest operating frequency. The proposed antenna was fabricated to verify the performance, and the simulated and measured results are in good agreement. The measured peak gains varied from −31.6 to −1.9 dBi within the measured frequency band. To examine the performance of the proposed antenna mounted on an unmanned aerial vehicle model (UAV), the antenna on a UAV was also simulated and the results were discussed. The simulated realized peak gains of the antenna on the UAV and on flat ground are similar.

Coherent structures and dominant frequencies in a turbulent three-dimensional diffuser

2012 ◽  
Vol 699 ◽  
pp. 320-351 ◽  
Author(s):  
Johan Malm ◽  
Philipp Schlatter ◽  
Dan S. Henningson
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Bulk Velocity ◽  
Time Signal ◽  
Mean Flow ◽  
The Mean ◽  
Dominant Frequencies

AbstractDominant frequencies and coherent structures are investigated in a turbulent, three-dimensional and separated diffuser flow at $\mathit{Re}= 10\hspace{0.167em} 000$ (based on bulk velocity and inflow-duct height), where mean flow characteristics were first studied experimentally by Cherry, Elkins and Eaton (Intl J. Heat Fluid Flow, vol. 29, 2008, pp. 803–811) and later numerically by Ohlsson et al. (J. Fluid Mech., vol. 650, 2010, pp. 307–318). Coherent structures are educed by proper orthogonal decomposition (POD) of the flow, which together with time probes located in the flow domain are used to extract frequency information. The present study shows that the flow contains multiple phenomena, well separated in frequency space. Dominant large-scale frequencies in a narrow band $\mathit{St}\equiv fh/ {u}_{b} \in [0. 0092, 0. 014] $ (where $h$ is the inflow-duct height and ${u}_{b} $ is the bulk velocity), yielding time periods ${T}^{\ensuremath{\ast} } = T{u}_{b} / h\in [70, 110] $, are deduced from the time signal probes in the upper separated part of the diffuser. The associated structures identified by the POD are large streaks arising from a sinusoidal oscillating motion in the diffuser. Their individual contributions to the total kinetic energy, dominated by the mean flow, are, however, small. The reason for the oscillating movement in this low-frequency range is concluded to be the confinement of the flow in this particular geometric set-up in combination with the high Reynolds number and the large separated zone on the top diffuser wall. Based on this analysis, it is shown that the bulk of the streamwise root mean square (r.m.s.) value arises due to large-scale motion, which in turn can explain the appearance of two or more peaks in the streamwise r.m.s. value. The weak secondary flow present in the inflow duct is shown to survive into the diffuser, where it experiences an imbalance with respect to the upper expanding corners, thereby giving rise to the asymmetry of the mean separated region in the diffuser.

PARALLEL SIMULATION OF EXPLOSION IN AN UNLIMITED ATMOSPHERE

2010 ◽  
Vol 24 (13) ◽  
pp. 1349-1352 ◽  
Author(s):  
TIANBAO MA ◽  
CHENG WANG ◽  
GUANGLEI FEI ◽  
JIANGUO NING
Keyword(s):  
Numerical Simulation ◽  
Parallel Algorithm ◽  
Large Scale ◽  
Three Dimensional ◽  
Parallel Simulation ◽  
Data Dependency ◽  
Empirical Results ◽  
Parallel Speedup ◽  
Good Agreement ◽  
Impact Problem

In this paper, a parallel Eulerian hydrocode for the simulation of large scale complicated explosion and impact problem is developed. The data dependency in the parallel algorithm is studied in particular. As a test, the three dimensional numerical simulation of the explosion field in an unlimited atmosphere is performed. The numerical results are in good agreement with the empirical results, indicating that the proposed parallel algorithm in this paper is valid. Finally, the parallel speedup and parallel efficiency under different dividing domain areas are analyzed.

A CONDUCTION MODEL OF THE ELECTRORHEOLOGICAL EFFECT

1994 ◽  
Vol 08 (20n21) ◽  
pp. 2731-2745 ◽  
Author(s):  
P. ATTEN ◽  
J.-N. FOULC ◽  
N. FELICI
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Approximate Analysis ◽  
Conduction Model ◽  
Electrorheological Effect ◽  
Nonlinear Conduction ◽  
Surface Conduction ◽  
Solid Spheres ◽  
Good Agreement ◽  
Conduction Properties

A conduction model is proposed to explain the electrorheological effect under D.C. or low frequency A.C. fields. An approximate analysis taking into account the bulk conduction of the solid and the nonlinear conduction properties of the liquid is confirmed by experiments on large scale spheres. A good agreement between measurements and predictions is also obtained when air replaces the liquid. Finally the predictions are extended to the case of surface conduction of the solid spheres.

scholarly journals Numerical simulation of leakage flow field and acoustic characteristics for safety valve

2021 ◽  
Vol 336 ◽  
pp. 01007
Author(s):  
Fan Qian ◽  
Minghui Hu
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Pressure Fluctuation ◽  
Large Scale ◽  
Safety Valve ◽  
Sound Field ◽  
Wall Pressure ◽  
Small Scale ◽  
Acoustic Analogy ◽  
Wall Pressure Fluctuation

Aiming at the internal leakage problem of spring type nuclear safety valve at the sealing surface, the flow field and sound field characteristics at the leakage height of 0.5mm between the valve disc and the valve seat sealing surface were studied, and the numerical simulation was carried out based on large eddy simulation(LES) and mohring acoustic analogy method, and compare the effects of acoustic wall pressure fluctuation(AWPF) and turbulent wall pressure fluctuation(TWPF) as the excitation source on the external sound field of the valve. The simulation results show that: the change gradient of velocity field and pressure field at the leakage port of safety valve is significant and form vortices of different sizes. The small-scale vortices are mainly in the leakage port, while the large-scale vortices mainly exist in the flow channel; When the valve is leaking, the noise is mainly dominated by high-pressure injection noise, its spectrum curve shows wide-band characteristics, and the external noise of the valve is mainly caused by AW P F. The above research results can provide a theoretical basis for the safety valve online detection method.

scholarly journals The Numerical Prediction and Analysis of Propeller Cavitation Benchmark Tests of YUPENG Ship Model

2019 ◽  
Vol 7 (11) ◽  
pp. 387 ◽  
Author(s):  
Zheng ◽  
Liu ◽  
Huang
Keyword(s):  
Numerical Simulation ◽  
Pressure Fluctuation ◽  
Measured Data ◽  
Simulation Methods ◽  
Ship Model ◽  
Benchmark Tests ◽  
Monotonic Convergence ◽  
Numerical Simulation Methods ◽  
Fluctuation Measurement ◽  
Good Agreement

The numerical simulation of propeller cavitation benchmark tests of YUPENG ship model is studied based on OpenFOAM, an open-source CFD (Computational Fluid Dynamics) platform, and the benchmark tests are introduced as well. The propeller cavitation shape and the hull pressure fluctuation are measured and predicted, respectively. The uncertainty in hull pressure fluctuation measurement is also analyzed, and the analysis showed the uncertainty is below 10%. The cavitation shape and the hull pressure fluctuation predicted show quite good agreement with the observations and measured data, and the influences of the grid resolutions on the unsteady propeller cavitation and the hull pressure fluctuation are investigated as well. The monotonic convergence achieved and the quite small grid uncertainty illustrate the reliability of the numerical simulation methods.

Numerical simulation of the flow field in a bioreactor

2000 ◽  
Vol 41 (4-5) ◽  
pp. 207-210 ◽  
Author(s):  
S. Ester ◽  
X. Guo ◽  
A. Delgado
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Numerical Method ◽  
Mechanical Behaviour ◽  
Numerical Code ◽  
Measurement Instruments ◽  
Local Flow ◽  
Velocity Pressure ◽  
Detailed Picture ◽  
Good Agreement

In order to give detailed information about the local flow field in a bioreactor a numerical method has been developed. This method gives information about the velocity, pressure and temperature in each point of the reactor, avoiding the problems caused by placing measurement instruments inside. Comparisons of experiments and numerical results show good agreement. The functionality and physical fundamentals of this tool are described. This is followed by explaining a reasonable application of the numerical code in the field of biological reactors. The reactors considered are filled with polydisperse, spherical support particles. From the results of the simulation a detailed picture of a reactor's fluid mechanical behaviour is drawn. This includes the quantification of mechanical stresses on the biofilm surface as well as information about the inflow, outflow and channelling behaviour of a reactor. Furthermore the effect of polydisperse support carries in discussed.

scholarly journals On the time-scales of the downward propagation and of the tropospheric planetary wave response to the stratospheric circulation

2010 ◽  
Vol 28 (2) ◽  
pp. 339-351 ◽  
Author(s):  
G. Nikulin ◽  
F. Lott
Keyword(s):  
Time Scales ◽  
Frequency Band ◽  
Large Scale ◽  
Planetary Wave ◽  
Vertical Component ◽  
Low Frequency ◽  
Planetary Waves ◽  
Polar Regions ◽  
Wave Response ◽  
Downward Propagation

Abstract. Three datasets (the NCEP-NCAR reanalysis, the ERA-40 reanalysis and the LMDz-GCM), are used to analyze the relationships between large-scale dynamics of the stratosphere and the tropospheric planetary waves during the Northern Hemisphere (NH) winter. First, a cross-spectral analysis clarifies the time scales at which downward propagation of stratospheric anomalies occurs in the low-frequency band (that is at periods longer than 50 days). At these periods the strength of the polar vortex, measured by the 20-hPa Northern Annular Mode (NAM) index and the wave activity flux, measured by the vertical component of the Eliassen-Palm flux (EPz) from both the troposphere and the stratosphere, are significantly related with each other and in lead-lag quadrature. While, in the low-frequency band of the downward propagation, the EPz anomalies of the opposite sign around NAM extremes drive the onset and decay of NAM events, we found that the EPz anomalies in the troposphere, are significantly larger after stratospheric vortex anomalies than at any time before. This marked difference in the troposphere is related to planetary waves with zonal wavenumbers 1–3, showing that there is a tropospheric planetary wave response to the earlier state of the stratosphere at low frequencies. We also find that this effect is due to anomalies in the EPz issued from the northern midlatitudes and polar regions.

scholarly journals Numerical Study on Pressure Pulsation in a Slanted Axial-Flow Pump Device under Partial Loads

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1404
Author(s):  
Fan Yang ◽  
Pengcheng Chang ◽  
Wenzhu Hu ◽  
Beibei Mao ◽  
Chao Liu ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
Pressure Pulsation ◽  
Low Frequency ◽  
Axial Flow ◽  
Flow Channel ◽  
Monitoring Point ◽  
Inlet Flow ◽  
Main Frequency ◽  
Axial Flow Pump ◽  
Flow Pump

The 30° slanted axial-flow pump device is widely used in agricultural irrigation and urban drainage in plains areas of China. However, during the actual operation process, the 30° slanted axial-flow pump device is prone to vibration, noise, cracks in the blades, and other phenomena that affect the safe and stable operation of the pump device. In order to analyze the flow pressure pulsation characteristics of the 30° slanted axial-flow pump device under different flow conditions, the time–frequency domain analysis method was used to analyze the pressure pulsation of each flow structure of the 30° slanted axial-flow pump device. The results showed that the internal pulsation law of the elbow oblique inlet flow channel is similar. At the 1.2 Qbep condition, the amplitude fluctuation of the pressure pulsation was small, and the main frequency is 4 times the rotating frequency. The monitoring points at the outlet of the elbow oblique inlet flow channel were affected by the impeller rotation, and the pressure pulsation amplitude was larger than that inside the elbow oblique inlet flow channel. The pressure fluctuation of each monitoring point at the inlet surface of the impeller was affected by the number of blades. There were four peaks and four valleys, and the main frequency was 4 times the rotating frequency. The amplitude of pressure fluctuation increased gradually from the hub to the rim. The main frequency of pressure fluctuation at each monitoring point of the impeller outlet surface was 4 times of the rotating frequency, and the low frequency was rich. The amplitude of pressure fluctuation was significantly lower than that of the impeller inlet. With the increase of flow rate, the peak fluctuation of pressure coefficient decreased gradually, and the amplitude of pressure fluctuation tended to be stable. Under 0.8 Qbep and 1.0 Qbep conditions, the large fluctuation of the pressure fluctuation amplitude on the outlet surface of the guide vane was mainly affected by the low-frequency fluctuation. Under the 1.2 Qbep condition, the pressure fluctuation amplitude changed periodically.

Okak Bay AMT data‐set case study: Lessons in dimensionality and scale

Geophysics ◽  
2003 ◽  
Vol 68 (1) ◽  
pp. 70-91 ◽  
Author(s):  
Alan G. Jones ◽  
Xavier Garcia
Keyword(s):  
Frequency Band ◽  
Large Scale ◽  
Three Dimensional ◽  
Low Frequency ◽  
3D Numerical Modeling ◽  
Data Set ◽  
Corrected Data ◽  
Mineralized Zone ◽  
Lateral Extent

Electromagnetic (EM) exploration for base metals using the natural‐source audio‐magnetotelluric (AMT) technique has increased significantly during the last five years due to enhancements in all aspects of AMT and to the demand for imaging deeper than conventional controlled‐source EM methods. However, regional currents induced by natural sources can be problematic in certain situations, and the appropriate interpretational dimensionality must be known. Herein we demonstrate that a two‐dimensional (2D) interpretation is valid for a defined frequency band, but that the effects of large‐scale three‐dimensional (3D) structures must be considered at lower frequencies. Using an AMT dataset from an area located north of Voisey's Bay, Labrador, Canada, we analyse the responses to determine the appropriate dimensionality and to test them for internal consistency. Maps of the distortion‐corrected data identify the lateral extent of connected conducting mineralization intersected by a drilling program. One‐dimensional (1D) inversions of the corrected data from those sites on top of the mineralized zone show the resolution properties of the data. We constructed a pseudo‐3D model from 2D inversions of the data in the frequency band 1000–10~Hz from all profiles, and this model images the mineralized body sufficiently for exploration purposes. We suggest that the anomalous low‐frequency responses observed at sites close to the mineralized zone are possibly due to charges impinged on the mineralized body's boundaries by currents induced in the Atlantic Ocean some 50 km away. Although 3D numerical modeling studies exhibit some of the effects observed, we are unable to reproduce numerically the observed behavior.

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