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.

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 Simulation and Flow Field Analysis of Suspended Grid Stilling Pool Based on VOF Method

2012 ◽  
Vol 256-259 ◽  
pp. 2569-2572
Author(s):  
Zhan Ying Wu ◽  
Zhen Wei Mu
Keyword(s):  
Flow Field ◽  
Water Surface ◽  
Vof Method ◽  
Field Analysis ◽  
Water Stability ◽  
Mean Velocity ◽  
Diversion Tunnel ◽  
Cross Sectional ◽  
Flow Field Analysis ◽  
Grid Position

The unsteady flow RNG k ~ ε turbulence model and VOF Method are employed to numerically simulate 3-D flow field of diversion tunnel outlet stilling pool in Xinjiang dina river wuyi reservoir. The computational and experimental water surface elevation, pressure on the bottom and cross-sectional mean velocity of the suspended grid stilling pool are compared in well agreement. Suspended grid is used in stilling pool, the number of vortex and range are increased in the pool, and the size of the vortex is decreased along with the flow increase. The suspended grid position is determined at end of the vortex. In the suspended grid stilling pool water stability, flow regime is good.

scholarly journals Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

2020 ◽  
Vol 5 (10) ◽  
pp. 1199-1203
Author(s):  
Md. Mosharrof Hossain ◽  
Muhammed Hasnain Kabir Nayeem ◽  
Dr. Md Abu Taher Ali
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Flow Characteristics ◽  
Velocity Profiles ◽  
Mean Flow ◽  
Mean Velocity ◽  
Potential Core ◽  
Swirling Jets ◽  
The Mean ◽  
Sinusoidal Flow

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.

Numerical study on mean flow field of turbulent dual offset jet

2021 ◽  
pp. 095440622110007
Author(s):  
Tanmoy Mondal ◽  
Shantanu Pramanik
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Jet Flow ◽  
Separation Distance ◽  
Bottom Wall ◽  
Mean Flow ◽  
Reattachment Point ◽  
The Mean ◽  
Two Jets ◽  
Offset Jet

A numerical investigation on the mean flow and turbulence characteristics of dual offset jet for various separation distances between the two jets with a fixed offset height of the lower jet from the bottom wall is reported in this study. The numerical simulations have been performed by solving the Reynolds-averaged Navier-Stokes equations (RANS) with two-equation standard [Formula: see text] turbulence model. The Reynolds number based on the jet width and the inlet turbulence intensity are considered as 15,000 and 5%, respectively. The computational results for the mean flow reveal that after issuing from the nozzles, the adjacent shear layers of the offset jets meet together at the merging point and then the merged jets reattaches on the bottom wall at the reattachment point before they combine together at the combined point forming a single jet flow. In the far downstream, the flow field behaves like a classical single wall jet flow. The self-similarity of mean flow field is achieved at far down stream of combined point. An increase in separation distance between the two jets [Formula: see text] results in a decrease in magnitude of the streamwise maximum velocity of the combined jet but with same rate of decay. The converging region of the jets has depicted considerable growth of turbulence as the jet centrelines bend towards the merging point. According to the mean flow results, the distances of the reattachment point and the combined point from the nozzle exit gradually increase with the progressive increase in separation distance between the two jets within the range d/ w = 3–8.

Numerical Study of a Compact Wavy Heat Exchanger

2011 ◽  
Author(s):  
Riccardo Mereu ◽  
Emanuela Colombo ◽  
Fabio Inzoli
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Temperature Fields ◽  
Mean Velocity ◽  
Qualitative Comparison ◽  
Cross Sectional ◽  
Number Range

The present work deals with the design of compact wavy heat exchangers, where high values of heat transfer area per unit volume are looked for in order to reduce size and increase efficiency. A numerical investigation of a rectangular cross-sectional shape geometry, with duct aspect ratio of 7.3, and a corrugation angle of 145° is here proposed. The Reynolds numbers (based on the duct hydraulic diameter) range from 300 to 5000. The numerical analysis is performed by means of a finite volume commercial CFD code. Laminar and Unsteady Reynolds Averaged Navier-Stokes (U-RANS) approaches are applied to a three-dimensional fluid domain over a single module with periodic conditions, respectively for, lower (<1000) and higher (≥1000) Reynolds numbers. Mean velocity and temperature fields are obtained. The average values of Fanning friction factor and Nusselt number are compared with experimental data from literature for the same geometry operating at the same Reynolds number range. For the evaluation of heat transfer quantities obtained in the numerical study the analogy between Sherwood and Nusselt number is used. The numerical results agree with experimental data, by showing the capability of laminar and U-RANS two-equation approach, via RNG model, to capture the mean fluid flow including the Taylor-Gortler instability that appear at low Reynolds numbers. The qualitative comparison of heat results shows an agreement between experimental and numerical data, whereas the extension to quantitative comparison is limited by some deficiencies in experimental correlation for mass/heat transfer analogy.

scholarly journals Numerical Study on Wave Induced Flow Field around a Vibrant Monopile Regarding Cross-Sectional Shape

2019 ◽  
Vol 3 (2) ◽  
pp. 1-9 ◽  
Author(s):  
Mohammad Mohammad Beigi Kasvaei ◽  
◽  
Mohammad Hossein Kazeminezhad ◽  
Abbas Yeganeh-Bakhtiary ◽  
◽  
...  
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Cross Sectional ◽  
Induced Flow ◽  
Sectional Shape ◽  
Wave Induced

Unstable waves on an axisymmetric jet column

1974 ◽  
Vol 65 (3) ◽  
pp. 541-560 ◽  
Author(s):  
G. E. Mattingly ◽  
C. C. Chang
Keyword(s):  
Flow Field ◽  
Shear Layer ◽  
Stability Theory ◽  
Jet Flow ◽  
Jet Flows ◽  
Water Tank ◽  
Mean Velocity ◽  
Core Diameter ◽  
Potential Core ◽  
Axisymmetric Jet

The growth of infinitesimal disturbances on an axisymmetric jet column is investigated theoretically and experimentally. The theoretical analysis is based upon inviscid stability theory, wherein axisymmetric, helical and double helical disturbances are considered from the spatial reference frame. In the jet flow field near the source, the mean velocity profile is observed to have a potential core and a thin, but finite, shear layer between the potential core and the quiescent ambient fluid. With downstream distance, the potential core diameter decreases and the shear-layer thickness increases. To incorporate these variations into the theory, a quasi-uniform assumption is adopted, whereby successive velocity profiles are analysed individually throughout the region in the jet flow where disturbances are observed to be small. The results of the theory indicate that initially, in the jet flow where the shear layer is thin and the potential core is larger, all disturbances considered are unstable. The dominant disturbance in the jet is an axisymmetric one. However, further downstream in the jet, where the half-breadth thickness of the shear layer is 55% of the potential core radius, a helical disturbance is found to dominate the axisymmetric and double helical modes. Nowhere in the jet flow field examined was the double helical disturbance found to be dominant. The cross-stream distributions of velocity and vorticity for the dominant disturbance modes are presented according to the spatial stability theory.The downstream development of the jet column and the characteristics of the disturbances amplifying on it were also studied in a water tank. No artificial stimulation of any particular disturbance was used. The experimental results show good agreement with the results of the theory in the region where the disturbances are small. However, conclusive confirmation of the switch in the hierarchy of dominant disturbances was not found. Half of the time the disturbance observed experimentally exhibits an axisymmetric character and the other half a helical one. This apparently is due to the similar spatial amplification rates experienced by both of these disturbance modes. It is concluded that this switching of dominant modes is, in large part, responsible for (i) the well-known natural drifting of disturbance characteristics in jet flows, and (ii) the wide variety of observations made in previous jet experiments.

scholarly journals Experimental Flow Field Investigation in a Centrifugal Compressor Vaned Diffuser

1995 ◽  
Author(s):  
Ali Pinarbasi ◽  
Mark W. Johnson
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Field Investigation ◽  
Vaneless Diffuser ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Impeller Blade ◽  
Vaned Diffuser ◽  
Flow Angle

The purpose of this study was to improve the understanding of the flow physics in a centrifugal compressor vaned diffuser. A low speed compressor with a 19 bladed backswept impeller and diffuser with 16 wedge vanes was used. The measurements were made at three inter-vane positions and are presented as mean velocity, turbulent kinetic energy and flow angle distributions on eight diffuser cross sectional planes. The impeller blade wakes mix out rapidly within the vaneless space and more rapidly than in an equivalent vaneless diffuser. Although the flow is highly non uniform in velocity at the impeller exit, there is no evidence in the results of any separation from the diffuser vanes. The results do however suggest that the use of twisted vanes within the diffuser would be beneficial in reducing losses.

Study of jets from rectangular nozzles with square grooves

2011 ◽  
Vol 115 (1165) ◽  
pp. 187-196 ◽  
Author(s):  
P. Arun Kumar ◽  
S. B. Verma ◽  
S. Elangovan
Keyword(s):  
Major Axis ◽  
Minor Axis ◽  
Equivalent Diameter ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Potential Core ◽  
Axis Direction ◽  
Square Configuration ◽  
Hotwire Anemometry ◽  
Axis Switching

AbstractAn experimental study has been carried out to understand jet flow development from plain and grooved rectangular nozzles of aspect ratio 2:1 using two-component hotwire anemometry. Grooves of square configuration (side 4mm) and length 5mm were introduced in the (i) minor-axis, (ii) major-axis and, (iii) in both minor- and major-axes directions. The equivalent diameter of the plain rectangular nozzle is 37·5mm. Studies were carried out for a nominal jet exit velocity of 20ms−1and for Reynolds number based on equivalent diameter of 54,000. The introduction of grooves in either plane does not show any influence on the potential-core length but results in faster jet-decay thereafter. It is observed that the grooves when introduced in minor-axis direction inhibit the jet growth in that plane while promoting the jet growth along major-axis plane and hence, delays the phenomena of axis-switching. However when introduced in major-axis direction, the grooves promote jet growth along major-axis plane while inhibiting jet-growth in minor-axis plane. Cross-sectional contours of mean-velocity suggest that the grooves modify the process of overall jet development significantly in the plane in which they are introduced relative to the plain jet and hence, significantly affect the axis-switching location in each case.

Numerical Study of the Combined Free-Forced Convection and Mass Transfer Flow Past a Vertical Porous Plate in a Porous Medium with Heat Generation and Thermal Diffusion

2006 ◽  
Vol 11 (4) ◽  
pp. 331-343 ◽  
Author(s):  
M. S. Alam ◽  
M. M. Rahman ◽  
M. A. Samad
Keyword(s):  
Mass Transfer ◽  
Flow Field ◽  
Differential Equations ◽  
Forced Convection ◽  
Heat Generation ◽  
Numerical Study ◽  
Porous Plate ◽  
Integration Scheme ◽  
Suction Parameter ◽  
Transfer Flow

The problem of combined free-forced convection and mass transfer flow over a vertical porous flat plate, in presence of heat generation and thermaldiffusion, is studied numerically. The non-linear partial differential equations and their boundary conditions, describing the problem under consideration, are transformed into a system of ordinary differential equations by using usual similarity transformations. This system is solved numerically by applying Nachtsheim-Swigert shooting iteration technique together with Runge-Kutta sixth order integration scheme. The effects of suction parameter, heat generation parameter and Soret number are examined on the flow field of a hydrogen-air mixture as a non-chemical reacting fluid pair. The analysis of the obtained results showed that the flow field is significantly influenced by these parameters.

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