scholarly journals Examination of Viscosity Effect on Cavitating Flow inside Poppet Valves Based on a Numerical Study

2021 ◽  
Vol 11 (23) ◽  
pp. 11205
Author(s):  
Cong Yuan ◽  
Lisha Zhu ◽  
Shiqi Liu ◽  
He Li
Keyword(s):  
Water Flow ◽  
Numerical Study ◽  
Underlying Mechanism ◽  
Cavitating Flow ◽  
Potential Core ◽  
Viscosity Effect ◽  
Lower Viscosity ◽  
Oil Flow ◽  
Flow Case ◽  
Poppet Valves

The higher susceptibility to cavitation in poppet valves due to the lower viscosity of water than the traditionally used mineral oil poses a challenge in fluid transmission technology. To reveal the underlying mechanism of cavitating flow physics associated with the variation in viscosity effect, the current paper examines both the water and oil cavitating flow dynamics inside poppet valves with varied structures through a numerical study. The simulation results are validated with a comparison to previous experimental data in terms of cavitation morphology and pressure distribution. According to the predicted cavitation distribution, three kinds of cavitation occurred at separated positions in both water- and oil-flow cases. The vortex cavitation, which in the oil-flow case displays a remarkable paired structure with favorable coherence, is featured with a scattered dispersion in the water-flow case, while the profound attached cavitation at the poppet trailing edge in the water-flow case almost disappears in the oil-flow case. Furthermore, the attached cavitation within the chamfered groove has higher stability in the oil-flow case, compared to the thorough detachment behavior featured with profound 3-dimensionality in the water-flow case. According to the potential core and vortex evolution, the strong 3-dimensionality due to the violent laminar-turbulent transition in the water-flow case together with the produced puff pattern of the potential core, to a large extent, interrupts the periodic behavior of cavitation, which is essentially preserved in the oil-flow case featured with favorable coherence.

Numerical Study of the Mean and Filtered Characteristics of Turbulent Jets Impinging on Convex and Flat Surfaces Using LES

2012 ◽  
Author(s):  
Adra Benhacine ◽  
Zoubir Nemouchi ◽  
Lyes Khezzar ◽  
Nabil Kharoua
Keyword(s):  
Convex Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Scale Model ◽  
Wall Jet ◽  
Potential Core ◽  
Flat Surfaces ◽  
Free Jet ◽  
Eddy Simulation

A numerical study of a turbulent plane jet impinging on a convex surface and on a flat surface is presented, using the large eddy simulation approach and the Smagorinski-Lilly sub-grid-scale model. The effects of the wall curvature on the unsteady filtered, and the steady mean, parameters characterizing the dynamics of the wall jet are addressed in particular. In the free jet upstream of the impingement region, significant and fairly ordered velocity fluctuations, that are not turbulent in nature, are observed inside the potential core. Kelvin-Helmholtz instabilities in the shear layer between the jet and the surrounding air are detected in the form of wavy sheets of vorticity. Rolled up vortices are detached from these sheets in a more or less periodic manner, evolving into distorted three dimensional structures. Along the wall jet the Coanda effect causes a marked suction along the convex surface compared with the flat one. As a result, relatively important tangential velocities and a stretching of sporadic streamwise vortices are observed, leading to friction coefficient values on the curved wall higher than those on the flat wall.

Study of Correctly Expanded Sonic Jet with Air Tabs

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Arun Prasad R ◽  
Thanigaiarasu S ◽  
Sembaruthi M ◽  
Rathakrishnan E
Keyword(s):  
Numerical Study ◽  
Cross Sectional ◽  
Potential Core ◽  
Convergent Nozzle ◽  
Jet Mixing ◽  
Pressure Profiles ◽  
Constant Diameter ◽  
Sonic Jet ◽  
Sectional Shape ◽  
Length Reduction

AbstractThe present numerical study is to understand the effect of air tabs located at the exit of a convergent nozzle on the spreading and mixing characteristics of correctly expanded sonic primary jet. Air tabs used in this study are two secondary jets issuing from constant diameter tubes located diametrically opposite at the periphery of the primary nozzle exit, normal to the primary jet. Two air tabs of Mach numbers 1.0 to 1.4, in steps of 0.1 are considered in this study. The mixing modification caused by air tabs are analysed by considering the mixing of uncontrolled (free) primary jet as a reference. Substantial enhancement in jet mixing is achieved with Mach 1.4 air tabs, which results in 80 % potential core length reduction. The total pressure profiles taken on the plane (YZ) normal to the primary jet axis, at various locations along the primary jet centreline revealed the modification of the jet cross sectional shape by air tabs. The stream-wise vortices and bifurcation of the primary jet caused by air tabs are found to be the mechanism behind the enhanced jet mixing.

Numerical Study of Heavy Oil Flow on Horizontal Pipe Lubricated by Water

2012 ◽  
pp. 99-118 ◽  
Author(s):  
Tony Herbert Freire de Andrade ◽  
Kelen Cristina Oliveira Crivelaro ◽  
Severino Rodrigues de Farias Neto ◽  
Antonio Gilson Barbosa de Lima
Keyword(s):  
Heavy Oil ◽  
Numerical Study ◽  
Horizontal Pipe ◽  
Oil Flow

Numerical study of cavitating flow over hydrofoil in the presence of air

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Włodzimierz Wróblewski ◽  
Krzysztof Bochon ◽  
Mirosław Majkut ◽  
Krzysztof Rusin ◽  
Emad Hasani Malekshah
Keyword(s):  
Numerical Study ◽  
Cavitating Flow ◽  
Cavitation Model ◽  
Two Phase ◽  
Content Type ◽  
Flow Simulations ◽  
Cavity Structure ◽  
Dynamic Forces ◽  
High Dynamic ◽  
The Impact

Purpose The presence of air in the water flow over the hydrofoil is investigated. The examined hydrofoil is ClarkY 11.7% with an angle of attack of 8 deg. The flow simulations are performed with the assumption of different models. The Singhal cavitation model and the models which resolve the non-condensable gas including 2phases and 3phases are implemented in the numerical model. The calculations are performed with the uRANS model with assumption of the constant temperature of the mixture. The two-phase flow is simulated with a mixture model. The dynamics and structures of cavities are compared with literature data and experimental results. Design/methodology/approach The cavitation regime can be observed in some working conditions of turbomachines. The phase transition, which appears on the blades, is the source of high dynamic forces, noise and also can lead to the intensive erosion of the blade surfaces. The need to control this process and to prevent or reduce the undesirable effects can be fulfilled by the application of non-condensable gases to the liquid. Findings The results show that the Singhal cavitation model predicts the cavity structure and related characteristics differently with 2phases and 3phases models at low cavitation number where the cavitating flow is highly dynamic. On the other hand, the impact of dissolved air on the cloud structure and dynamic characteristic of cavitating flow is gently observable. Originality/value The originality of this paper is the evaluation of different numerical cavitation models for the prediction of dynamic characteristics of cavitating flow in the presence of air.

Experimental/Numerical Study on Cavitating Flow around Clark Y 11.7% Hydrofoil

2012 ◽  
Author(s):  
Hiroki Matsunari ◽  
Satoshi Watanabe ◽  
Yusuke Konishi ◽  
Naoto Suefuji ◽  
Akinori Furukawa
Keyword(s):  
Numerical Study ◽  
Cavitating Flow

scholarly journals Numerical Study of the Velocity Decay of Offset Jet in a Narrow and Deep Pool

Water ◽  
2018 ◽  
Vol 11 (1) ◽  
pp. 59 ◽  
Author(s):  
Xin Li ◽  
Maolin Zhou ◽  
Jianmin Zhang ◽  
Weilin Xu
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Potential Core ◽  
Early Region ◽  
Flow Development ◽  
Offset Jet

The present study examines the configuration of an offset jet issuing into a narrow and deep pool. The standard k-ε model with volume-of-fluid (VOF) method was used to simulate the offset jet for three exit offset ratios (OR = 1, 2 and 3), three expansion ratios (ER = 3, 4 and 4.8), and different jet exits (circular and rectangular). The results clearly show significant effects of the circumference of jet exits (Lexit) in the early region of flow development, and a fitted formula is presented to estimate the length of the potential core zone (LPC). Analysis of the flow field for OR = 1 showed that the decay of cross-sectional streamwise maximum mean velocity (Um) in the transition zone could be fitted by power law with the decay rate n decreased from 1.768 to 1.197 as the ER increased, while the decay of Um for OR = 2 or 3 was observed accurately estimated by linear fit. Analysis of the flow field of circular offset jet showed that Um for OR = 2 decayed fastest due to the fact that the main flow could be spread evenly in floor-normal direction. For circular jets, the offset ratio and expansion ratio do not affect the spread of streamwise velocity in the early region of flow development. It was also observed that the absence of sudden expansion of offset jet is analogous to that of a plane offset jet, and the flow pattern is different.

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