Effects of surface roughness on self-excited cavitating water jet intensity in the organ-pipe nozzle: Numerical simulations and experimental results

2019 ◽  
Vol 33 (27) ◽  
pp. 1950324
Author(s):  
Xiangdong Han ◽  
Yong Kang ◽  
Deng Li ◽  
Weiguo Zhao
Keyword(s):  
Numerical Simulation ◽  
Surface Roughness ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Intensity ◽  
Volume Fraction ◽  
Water Jet ◽  
The Self ◽  
Simulation Results ◽  
Organ Pipe

This study was conducted to investigate effects of surface roughness on self-excited cavitating water jet intensity in an organ-pipe nozzle. Roughness average (Ra) values are 0.8, 1.6, 3.2, 6.3, 12.5, and 25 [Formula: see text]m, respectively. Numerical simulation results indicate that at inlet pressure of 10 MPa, the maximum, minimum, and real-time pressures in the self-excited oscillation chamber reach their respective peak values. The turbulent kinetic energy intensity in the external flow region is also most intense at this point, the vapor volume fraction in orifice is the highest, the vortex distribution scope in the orifice is the largest under [Formula: see text], and the self-excited cavitating water jet intensity is the strongest. The opposite variations emerge at [Formula: see text] compared to those of [Formula: see text], where the intensity is weakest. Pressure varies only slightly as Ra varies from 0.8 [Formula: see text]m to 6.3 [Formula: see text]m. Turbulent kinetic energy intensity behaves similarly as Ra increases from 0.8 [Formula: see text]m to 3.2 [Formula: see text]m. At [Formula: see text], it was weaker than at Ra = 0.8–3.2 [Formula: see text]m. Similarly, there are only slight differences in vapor volume fraction and vortex distribution scope with Ra from 0.8 [Formula: see text]m to 6.3 [Formula: see text]m. The intensities at Ra = 0.8–3.2 [Formula: see text]m are similar, and weaker at Ra = 6.3 [Formula: see text]m. Pressure values are maximal at inlet pressure of 20 MPa, turbulent kinetic energy intensity is most intense, vapor volume fraction is highest, vortex distribution scope is largest under [Formula: see text] [Formula: see text]m, and intensity is strongest. Distinctions among pressure, turbulent kinetic energy intensity, vapor volume fraction, and vortex distribution scope values with Ra from 0.8 [Formula: see text]m to 3.2 [Formula: see text]m are slight. Differences in the corresponding intensities are also slight; all decrease with Ra from 12.5 [Formula: see text]m to 25 [Formula: see text]m as the intensity gradually weakens. Numerical simulation results were validated by comparison against corresponding experimental phenomena.

Investigating Multiphase Turbulence Statistics of Large-Scale Two-Way Coupled Gravity-Driven Flows

2014 ◽  
Author(s):  
Jesse Capecelatro ◽  
Olivier Desjardins ◽  
Rodney O. Fox
Keyword(s):  
Kinetic Energy ◽  
Kinetic Theory ◽  
Turbulent Kinetic Energy ◽  
Particle Velocity ◽  
Volume Fraction ◽  
Constitutive Relations ◽  
Granular Temperature ◽  
Particle Phase ◽  
Simulation Results ◽  
Filtering Approach

Starting from the kinetic theory (KT) model for monodisperse granular flow, the exact Reynolds-average (RA) equations were recently derived for the particle phase in a collisional gas-particle flow by Fox [1]. The turbulence model solves for the RA particle volume fraction, the phase-average (PA) particle velocity, the PA granular temperature, and the PA particle turbulent kinetic energy (TKE). A clear distinction is made between the PA granular temperature, which appears in the kinetic theory constitutive relations, and the particle-phase turbulent kinetic energy, which appears in the turbulent transport coefficients. Mesoscale direct numerical simulation (DNS) can be used to assess the validity of the closures proposed for the unclosed terms that arise due to nonlinearities in the hydrodynamic model. In order to extract meaningful statistics from simulation results, a separation of length scales must be established to distinguish between the PA particle TKE and the PA granular temperature. In this work, we introduce an adaptive spatial filter with an averaging volume that varies with the local particle-phase volume fraction. This filtering approach ensures sufficient particle sample sizes in order to obtain meaningful statistics while remaining small enough to avoid capturing variations in the mesoscopic particle field. Two-point spatial correlations are computed to assess the validity of the filter in extracting meaningful statistics. The filtering approach is applied to fully-developed cluster-induced turbulence (CIT), where the production of fluid-phase kinetic energy results entirely from momentum coupling with finite-size inertial particles. Simulation results show a strong correlation between the local volume fraction and granular temperature, with maximum values located just upstream of clusters (i.e., where maximum compressibility of the particle velocity field exists), and negligible particle agitation is observed within clusters.

Investigation of self-excited oscillation chamber cavitation effect with special emphasis on wall shape

2020 ◽  
Vol 44 (2) ◽  
pp. 244-255 ◽  
Author(s):  
Zhaohui Wang ◽  
Yanan Hu ◽  
Si Chen ◽  
Lin Zhou ◽  
Wenxia Xu ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Volume Fraction ◽  
Growth Cycle ◽  
The Self ◽  
Energy Concentration ◽  
Wall Structure ◽  
Cavitation Effect ◽  
Excited Oscillation ◽  
Oscillating Jet

Analysis of the self-excited oscillating jet nozzle makes it possible to investigate the influence of structural and geometric shapes on the effect of self-excited oscillation cavitation and energy efficiency. In this paper, a new self-excited oscillation chamber structure was obtained using a Bézier curve to reconstruct the wall transition surface, and the cavitation airbag energy concentration was maximized to efficiently utilize the pulse energy. Numerical analysis and simulation were used to study the turbulent kinetic energy, steam volume fraction, and vortex growth cycle of the outlet. The results showed that the novel chamber wall structure weakens the interior secondary vortex in the self-excited oscillation chamber and forms a large cavitation airbag area and reduces energy dissipation. In addition, using the new chamber with redesigned wall structure, the peak turbulent kinetic energy, the velocity at the jet exit, and the vapor volume fraction inside the chamber increased approximately 10.3%, 14.6%, and 9.1%, respectively.

scholarly journals A New Method to Determine the Impact of Individual Field Quantities on Cycle-to-Cycle Variations in a Spark-Ignited Gas Engine

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4136
Author(s):  
Clemens Gößnitzer ◽  
Shawn Givler
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Negative Impact ◽  
Operating Conditions ◽  
Engine Operation ◽  
Gas Engine ◽  
Cycle Simulation ◽  
Simulation Results ◽  
The Impact

Cycle-to-cycle variations (CCV) in spark-ignited (SI) engines impose performance limitations and in the extreme limit can lead to very strong, potentially damaging cycles. Thus, CCV force sub-optimal engine operating conditions. A deeper understanding of CCV is key to enabling control strategies, improving engine design and reducing the negative impact of CCV on engine operation. This paper presents a new simulation strategy which allows investigation of the impact of individual physical quantities (e.g., flow field or turbulence quantities) on CCV separately. As a first step, multi-cycle unsteady Reynolds-averaged Navier–Stokes (uRANS) computational fluid dynamics (CFD) simulations of a spark-ignited natural gas engine are performed. For each cycle, simulation results just prior to each spark timing are taken. Next, simulation results from different cycles are combined: one quantity, e.g., the flow field, is extracted from a snapshot of one given cycle, and all other quantities are taken from a snapshot from a different cycle. Such a combination yields a new snapshot. With the combined snapshot, the simulation is continued until the end of combustion. The results obtained with combined snapshots show that the velocity field seems to have the highest impact on CCV. Turbulence intensity, quantified by the turbulent kinetic energy and turbulent kinetic energy dissipation rate, has a similar value for all snapshots. Thus, their impact on CCV is small compared to the flow field. This novel methodology is very flexible and allows investigation of the sources of CCV which have been difficult to investigate in the past.

Modeling Recrystallization for 3D Multi-Pass Forming Processes

2007 ◽  
Vol 558-559 ◽  
pp. 1201-1206 ◽  
Author(s):  
Mihaela Teodorescu ◽  
Patrice Lasne ◽  
Roland E. Logé
Keyword(s):  
Numerical Simulation ◽  
Grain Size ◽  
Present Model ◽  
Static Recrystallization ◽  
Volume Fraction ◽  
The Other ◽  
Finite Element Code ◽  
3D Numerical Simulation ◽  
Fraction Distribution ◽  
Simulation Results

The present work concerns the simulation of metallurgical evolutions in 3D multi-pass forming processes. In this context, the analyzed problem is twofold. One point refers to the management of the microstructure evolution during each pass or each inter-pass period and the other point concerns the management of the multi-pass aspects (different grain categories, data structure). In this framework, a model is developed and deals with both aspects. The model considers the microstructure as a composite made of a given (discretized) number of phases which have their own specific properties. The grain size distribution and the recrystallized volume fraction distribution of the different phases evolve continuously during a pass or inter-pass period. With this approach it is possible to deal with the heterogeneity of the microstructure and its evolution in multi-pass conditions. Both dynamic and static recrystallization phenomena are taken into account, with typical Avrami-type equations. The present model is implemented in the Finite Element code FORGE2005®. 3D numerical simulation results for a multi-pass process are presented.

Numerical Simulation of the Kinetic Energy Projectile Oblique Penetration into the Concrete

2014 ◽  
Vol 989-994 ◽  
pp. 982-985
Author(s):  
Jun Chen ◽  
Xiao Jun Ye
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Kinetic Energy ◽  
Three Dimensional ◽  
Test Results ◽  
Destruction Process ◽  
3D Finite Element ◽  
Finite Element Software ◽  
Simulation Results ◽  
Target Characteristics

ANSYS-LS/DYNA 3D finite element software projectile penetrating concrete target three-dimensional numerical simulation , has been the target characteristics and destroy ballistic missile trajectory , velocity and acceleration and analyze penetration and the time between relationship , compared with the test results , the phenomenon is consistent with the simulation results. The results show that : the destruction process finite element software can better demonstrate concrete tests revealed the phenomenon can not be observed , estimated penetration depth and direction of the oblique penetration missile deflection .

ACTIVE TRACKING CONTROL OF THE HYPERCHAOTIC LORENZ SYSTEM

2008 ◽  
Vol 22 (19) ◽  
pp. 1859-1865 ◽  
Author(s):  
XINGYUAN WANG ◽  
DAHAI NIU ◽  
MINGJUN WANG
Keyword(s):  
Numerical Simulation ◽  
Tracking Control ◽  
Chaotic Systems ◽  
Lorenz System ◽  
The Self ◽  
Hyperchaotic System ◽  
Reference Signals ◽  
Tracking Controller ◽  
Hyperchaotic Lorenz System ◽  
Simulation Results

A nonlinear active tracking controller for the four-dimensional hyperchaotic Lorenz system is designed in the paper. The controller enables this hyperchaotic system to track all kinds of reference signals, such as the sinusoidal signal. The self-synchronization of the hyperchaotic Lorenz system and the different-structure synchronization with other chaotic systems can also be realized. Numerical simulation results show the effectiveness of the controller.

Uncertainty analysis of CFD and performance prediction for an pumpjet propulsor

2020 ◽  
pp. 2150083
Author(s):  
Chao Liu ◽  
Hongxun Chen ◽  
Zhengchuan Zhang ◽  
Zheng Ma
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Uncertainty Analysis ◽  
Turbulent Kinetic Energy ◽  
Guide Vane ◽  
Outer Region ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Operating Characteristics ◽  
Standard Formula

In order to reveal the operating characteristics of the pumpjet propulsor, standard [Formula: see text]–[Formula: see text], standard [Formula: see text]–[Formula: see text], RNG [Formula: see text]–[Formula: see text] and SST [Formula: see text]–[Formula: see text] turbulence models were used to conduct steady calculation for the whole flow channels. By comparing the calculation results with experimental data, it was found that the calculation errors were very large in some operating conditions. Therefore, the uncertainty analysis was carried out at all operating conditions of the pumpjet propulsor and the error source was finally determined that it is mainly derived from the model error. Then, the applicability of different turbulence models was analyzed to numerical simulation for the pumpjet propulsor by comparing the internal and external characteristics. It can be seen that the strong turbulent kinetic energy in the guide vane will inevitably cause energy loss, but not necessarily in the impeller. In this area, the increase of turbulent kinetic energy will enhance the mixing and transport of fluids, and the impeller makes the fluids get more energy. In addition, a modified hybrid Reynolds Average Numerical Simulation/Large Eddy Simulation (RANS/LES) model was proposed for unsteady calculation, and the performances, internal flow states and the interaction between the pump and the outer region were further revealed under various conditions of the pumpjet propulsor, which provides some references for predicting accurately and selecting conditions optimally in the future.

Pseudo-turbulent gas-phase velocity fluctuations in homogeneous gas–solid flow: fixed particle assemblies and freely evolving suspensions

2015 ◽  
Vol 770 ◽  
pp. 210-246 ◽  
Author(s):  
M. Mehrabadi ◽  
S. Tenneti ◽  
R. Garg ◽  
S. Subramaniam
Keyword(s):  
Kinetic Energy ◽  
Phase Velocity ◽  
Turbulent Kinetic Energy ◽  
Gas Phase ◽  
Reynolds Stress ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Particle Assemblies

Gas-phase velocity fluctuations due to mean slip velocity between the gas and solid phases are quantified using particle-resolved direct numerical simulation. These fluctuations are termed pseudo-turbulent because they arise from the interaction of particles with the mean slip even in ‘laminar’ gas–solid flows. The contribution of turbulent and pseudo-turbulent fluctuations to the level of gas-phase velocity fluctuations is quantified in initially ‘laminar’ and turbulent flow past fixed random particle assemblies of monodisperse spheres. The pseudo-turbulent kinetic energy $k^{(f)}$ in steady flow is then characterized as a function of solid volume fraction ${\it\phi}$ and the Reynolds number based on the mean slip velocity $\mathit{Re}_{m}$. Anisotropy in the Reynolds stress is quantified by decomposing it into isotropic and deviatoric parts, and its dependence on ${\it\phi}$ and $Re_{m}$ is explained. An algebraic stress model is proposed that captures the dependence of the Reynolds stress on ${\it\phi}$ and $Re_{m}$. Gas-phase velocity fluctuations in freely evolving suspensions undergoing elastic and inelastic particle collisions are also quantified. The flow corresponds to homogeneous gas–solid systems, with high solid-to-gas density ratio and particle diameter greater than dissipative length scales. It is found that for the parameter values considered here, the level of pseudo-turbulence differs by only 15 % from the values for equivalent fixed beds. The principle of conservation of interphase turbulent kinetic energy transfer is validated by quantifying the interphase transfer terms in the evolution equations of kinetic energy for the gas-phase and solid-phase fluctuating velocity. It is found that the collisional dissipation is negligible compared with the viscous dissipation for the cases considered in this study where the freely evolving suspensions attain a steady state starting from an initial condition where the particles are at rest.

Development of Venturi-Tube With Spiral-Shaped Fin for Water Treatment

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Dong Ho Shin ◽  
Yeonghyeon Gim ◽  
Dong Kee Sohn ◽  
Han Seo Ko
Keyword(s):  
Water Treatment ◽  
Numerical Analysis ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Volume Fraction ◽  
Volume Flow Rate ◽  
Numerical Data ◽  
The Body ◽  
Venturi Tube ◽  
Type Water

Detailed numerical data were presented for the development of a venturi-type water purifier which had a cavitation nozzle to enhance turbulent kinetic energy and vapor volume fraction. Numerical analysis for cavitation was conducted in multiphase flow using the software, cfx. The numerical method used in this study was verified by the experimental data of pressure distribution in tube and the observation of cavitation from previous studies. From the result of the numerical analysis, a logarithmic relation between the vapor volume fraction and volume flow rate of water according to the area ratio between the throat and the entrance of a venturi-tube was derived. In addition, spiral-shaped fins were developed to enhance the turbulent kinetic energy in the body of a venturi-tube. Thus, it was confirmed that the volume fraction and turbulent kinetic energy of the developed water purifier were enhanced compared with the normal venturi-tube without the spiral-shaped fin. Finally, the improved water treatment performance of the advanced design of the venturi-tube was confirmed by the removal test of the representative solutions.

Study on the Rheology of Foam Fracturing Fluid with Mixture Model

2012 ◽  
Vol 512-515 ◽  
pp. 1747-1752 ◽  
Author(s):  
Xiao Sun ◽  
Shu Zhong Wang ◽  
You Lian Lu
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Gas Phase ◽  
Mixture Model ◽  
Turbulent Viscosity ◽  
Bubble Diameter ◽  
Fracturing Fluid ◽  
Viscosity Increase ◽  
Change Trend ◽  
Simulation Results

Numerical simulation study on the rheology or foam fluid was carried through by treating inner phase as granular fluid with mixture model. The simulation results show that the gas phase is well distributed on cross-section. Besides, the higher the foam quality, the higher the velocity gradient near the wall. For turbulent properties, the turbulent kinetic energy and viscosity increase as the foam quality increases. With the same foam quality, the bigger the bubble diameter, the higher the turbulent viscosity and turbulent kinetic energy. What’s more, the foam quality 63% is a catastrophe point at which the rheology of foam fracturing fluid changes sharply. The change trend of turbulent viscosity along radial direction is different between the regions where the foam quality is below and over catastrophe point, and in the latter the change trend is flatter. From the simulation results it can be seen that the mixture model is more applicable and effective to the region where foam quality is over 63%.

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