Dynamic characteristics of supersonic turbulent free jets from four types of circular nozzles

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Mingli He ◽  
Guang Zhang ◽  
Shaohua Hu ◽  
Cheng Wang
Keyword(s):  
Dynamic Characteristics ◽  
Axial Velocity ◽  
Working Pressure ◽  
Perfect Agreement ◽  
Potential Core ◽  
Free Jets ◽  
Eddy Simulation ◽  
Work Pressure ◽  
Velocity Decay ◽  
Spreading Rates

Abstract The effects of nozzle structures and working pressure on the dynamic characteristics of supersonic turbulent free jets have been investigated numerically. Four types of nozzles (namely Laval, pipe, contraction I, and contraction II, respectively) and four pressure conditions (namely K = 0.8, 1, 1.5, and 2, respectively) were considered. A Standard k-ε model was utilized for the calculation of the supersonic turbulent free jets. Validation of the model was performed on the Laval jet by comparing it with the experiment and large-eddy simulation (LES). A perfect agreement was achieved in terms of the centerline and radial axial velocity profiles. The jets issuing from the Laval and the pipe had a longer potential core and a larger centerline axial velocity with the same outlet momentum. The length of the potential core was proportional to the working pressure, but variations of the centerline axial velocity decay rate were inverse for all nozzles. The effects of nozzle structures and work pressure on the spreading rates of the jets were insignificant. No obvious change trend could be observed on the kinematic and geometric virtual origins. The study can provide references for the nozzle and working pressure selection in practical application.

Momentum Flux Development From Three-Dimensional Free Jets

1976 ◽  
Vol 98 (2) ◽  
pp. 256-260 ◽  
Author(s):  
J. P. Narain
Keyword(s):  
Axial Velocity ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Core Region ◽  
Potential Region ◽  
Potential Core ◽  
Free Jets ◽  
Flow Development ◽  
Velocity Decay

The momentum-flux development from three-dimensional free jets has been investigated. The analysis is presented for free jets from circular, triangular, rectangular and elliptical orifices. The bluff jets, with eccentricity near unity, show the usual potential region and the axisymmetric decay region for the maximum axial velocity decay. The slender jets, with smaller than one eccentricity values, show three zones of flow development. The potential core region is followed by a characteristic decay region where velocity decay is dependent on the shape and eccentricity of the orifice. The maximum axial velocity of all slender jets finally decay axisymmetrically with increasing downstream distances.

Enhanced Mixing of 2D Lobed Nozzles

1995 ◽  
Author(s):  
Huo-Xing Liu ◽  
Shou-Sheng Wu
Keyword(s):  
Axial Velocity ◽  
Small Scale ◽  
Test Results ◽  
Low Velocity ◽  
Rapid Decay ◽  
Potential Core ◽  
Aspect Ratios ◽  
Viscous Shear ◽  
Velocity Decay ◽  
Scale Turbulence

The jet axial velocity decay and velocity distributions of two 2D Lobed Nozzles (2DLN), and three baseline nozzles, one circular and two rectangular with different aspect ratios (AR), were measured and compared at low velocity (M0 <0.35) and ambient temperature conditions. The five nozzles have the same exit area. Test results show: 1) The jet axial velocity decay of the 2DLN may be characterized by three distinct regions; i.e., “potential core region”, where the jet axial velocity almost remains constant; “rapid decay region”, where streamwise and normal vortices play major roles for enhanced mixing; and, “smooth-down decay region”, where the mixing process is dominated by viscous shear layer spreading and small-scale turbulence. 2) The jet potential core length of the two 2DLN tested is only half to one-third that of the baseline rectangular nozzle (AR=4.37), and about one-fourth to one-sixth compared with the baseline circular nozzle. The length, in which the jet mixed with surrounding air is nearly uniform, is one to two times that of the 2DLN equivalent exit diameter, and depends on lobe design.

Three-Dimensional Free Jets

1967 ◽  
Vol 71 (684) ◽  
pp. 858-859
Author(s):  
N. Rajaratnam ◽  
K. Subramanya
Keyword(s):  
Three Dimensional ◽  
Flow Characteristics ◽  
Maximum Velocity ◽  
Potential Core ◽  
Free Jets ◽  
Axisymmetric Jet ◽  
Plane Jets ◽  
Velocity Decay ◽  
Different Shapes ◽  
Semi Empirical

Fairly elegant semi-empirical theories are available for predicting the turbulent diffusion of axisymmetric and plane jets. However, there are relatively few investigations on the non-axisymmetric jets, herein denoted as three-dimensional jets. The extensive investigations conducted at the Polytechnic Institute of Brooklyn on three-dimensional jets have shown that the flow field is characterised by three distinct regions; the potential core, the characteristic decay (CD) region and the axisymmetric decay (AD) region. In the CD region the velocity profiles in the direction of the minor axis are similar but the maximum velocity decay curves are different for different shapes. In the AD region the flow characteristics are similar to that of an axisymmetric jet. Yevdjevich has recently conducted another investigation on rectangular jets.

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.

Effect of Secondary Force on Rigidity of Oil Film of the Slipper Pair Based on Hydrostatic Support

2012 ◽  
Vol 468-471 ◽  
pp. 1380-1383
Author(s):  
Hui Wang ◽  
Yu Xin Wang
Keyword(s):  
Computer Simulation ◽  
Friction Coefficient ◽  
Simulation Model ◽  
Dynamic Characteristics ◽  
Mathematics Model ◽  
Support Structure ◽  
Oil Film ◽  
Work Pressure ◽  
The Impact

Rigidity of oil film is an important hydrostatic support performance of the slipper pair. This paper establishes the mathematics model of hydrostatic support structure on the basis of considering secondary force. And establish the simulation model of rigidity of oil film by using the toolbox of Simulink. Study the dynamic characteristics of rigidity of oil film under the influence of secondary force through computer simulation. And reach a conclusion that the impact of secondary force on rigidity of oil film has a relationship with friction coefficient and work pressure.

Investigation of Extinction and Reignition Events Using the Flamelet Generated Manifold Model

2018 ◽  
Author(s):  
Hossam Elasrag ◽  
Shaoping Li
Keyword(s):  
Boundary Layer ◽  
Axial Velocity ◽  
Bluff Body ◽  
Grid Turbulence ◽  
Eddy Simulation ◽  
Flamelet Generated Manifold ◽  
Spray Droplets ◽  
The Mean ◽  
Lift Off ◽  
Flame Brush

Simulations for the Cambridge swirl bluff-body spray burner are performed near blow-out conditions. A hybrid stress blended eddy simulation (SBES) model is utilized for sub-grid turbulence closure. SBES blends the RANS-SST model at the boundary layer with large eddy simulation dynamic Smagorinsky model outside the boundary layer. The injected N-heptane spray droplets are tracked using a typical Eulerian-Lagrangian approach. Heat transfer coupling between the bluff-body walls and the near-walls fluid is accounted for by coupling the solid and fluid energy equations at the bluff-body surface. Mixing and chemistry are modeled using the Flamelet Generated Manifold (FGM) model. The study investigates how successful the FGM model is in predicting finite rate effects like local extinction and flame lift-off height. To this end, two near blow-out spray flames, the H1S1 (75% to blow-out) and H1S2 (88% to blow-out) are simulated. Good results are shown matching the spray Sauter mean diameter (SMD) and axial velocity mean and rms experimental data. The results also show that the FGM model captured reasonably well the flame structure and lift-off height as well as the spray pattern. Overall the spray droplets mean D32 and mean axial velocity were under-predicted, while the rms distribution matched reasonably well for the H1S1 flame. The mean flame brush lift-off height is estimated based on the statistically stationary mean flame brush and is estimated to be around 6 mm from the bluff-body base. Instantaneous local flame extinction is observed. The H1S2 flame, however, showed similar but slightly better match with the measurements for the mean spray data compared to the H1S1 flame, with slight under-prediction for D32 at Z = 10 mm and Z = 20 mm. Future work will investigate the sensitivity of the simulation to the spray boundary conditions and grid resolution.

Infusion Jet Flow Control in Neonatal Double Lumen Cannulae

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Reza Rasooli ◽  
Yahya Yıldız ◽  
Muhammad Jamil ◽  
Kerem Pekkan
Keyword(s):  
Clinical Success ◽  
Venous Blood ◽  
Clinical Intervention ◽  
Design Flow ◽  
Double Lumen ◽  
Potential Core ◽  
Flow Features ◽  
Velocity Decay ◽  
Site Access ◽  
The Right

Abstract Clinical success of extracorporeal membrane oxygenation (ECMO) depends on the proper venous cannulation. Venovenous (VV) ECMO is the preferred clinical intervention as it provides a single-site access by utilizing a VV double lumen cannula (VVDLC) with a higher level of mobilization and physical rehabilitation. Concurrent venous blood drainage and oxygenated blood infusion in the right atrium at the presence of the cannula makes the flow dynamics complex where potential mixing of venous and oxygenated blood can drastically decrease the overall performance of ECMO. There are no studies focusing on the neonatal and pediatric populations, in which the flow related effects are critical due to the small atrium size. In this study, fluid dynamics of infusion outflow jet for two commercially available neonatal VVDLC is analyzed using particle image velocimetry (PIV). Moreover, six new designs are proposed for the infusion channel geometry and compared. Important flow parameters such as flow turning angle (FTA), velocity decay, potential core, and turbulent intensity are investigated for the proposed models. The experiments showed that the outflow parameters of commercial cannulae such as FTA are strongly dependent on the operating Re number. This may result in a drastic efficiency reduction for cannula operating at off-design flow conditions. Moreover, the infusion outlet tip structure and jet internal guiding pathway (JIGP) was observed to greatly affect the outflow flow features. This is of paramount importance since the anatomical positioning of the cannula and the infusion outlet is strongly dependent on the outflow properties such as FTA.

scholarly journals Component Velocities and Turbulence Intensities within Ship Twin-Propeller Jet Using CFD and ADV

2020 ◽  
Vol 8 (12) ◽  
pp. 1025
Author(s):  
Yonggang Cui ◽  
Wei Haur Lam ◽  
How Tion Puay ◽  
Muhammad S. I. Ibrahim ◽  
Desmond Robinson ◽  
...  
Keyword(s):  
Axial Velocity ◽  
Linear Equations ◽  
Critical Position ◽  
Velocity Decay ◽  
Computational Fluid Dynamics Cfd ◽  
Jet Theory ◽  
Acoustic Doppler Velocimetry ◽  
Two Peaks ◽  
Jet Structure ◽  
Gaussian Normal Distribution

This study presents the decays of three components of velocity for a ship twin-propeller jet associated with turbulence intensities using the Acoustic Doppler Velocimetry (ADV) measurement and computational fluid dynamics (CFD) methods. Previous research has shown that a single-propeller jet consists of a zone of flow establishment and a zone of established flow. Twin-propeller jets are more complex than single-propeller jets, and can be divided into zones with four peaks, two peaks, and one peak. The axial velocity distribution is the main contributor and can be predicted using the Gaussian normal distribution. The axial velocity decay is described by linear equations using the maximum axial velocity in the efflux plane. The tangential and radial velocity decays show linear and nonlinear distributions in different zones. The turbulence intensity increases locally in the critical position of the noninterference zone and the interference zone. The current research converts the axial momentum theory of a single propeller into twin-propeller jet theory with a series of equations used to predict the overall twin-propeller jet structure.

The Influence of Aspect Ratio on Incompressible, Turbulent Flows From Rectangular Slots

1980 ◽  
Vol 31 (4) ◽  
pp. 285-305 ◽  
Author(s):  
G.F. Marsters ◽  
J. Fotheringham
Keyword(s):  
Aspect Ratio ◽  
Turbulent Flows ◽  
Turbulence Intensity ◽  
Three Dimensional ◽  
Thin Plates ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Contour Maps ◽  
Velocity Decay ◽  
Spreading Rates

SummaryJets issuing from rectangular slots cut in thin plates exhibit some unusual features, including unequal spreading rates in the spanwise and transverse directions, the appearance of velocity peaks near the “ends” of the jet and changing rates of centreline velocity decay in the downstream direction. This study examines the effects of aspect ratio on such flows. The flow field has been investigated using both total head tubes and hot wire anemometry. The results are presented in the form of three-dimensional plots of total pressure and contour maps of constant velocity, streamwise turbulence intensity and the Reynolds shear stresses. The decay of mean velocity and stream-wise turbulence intensity along the centreline are presented. The rates of spanwise spreading and the location of the velocity peaks at various downstream stations are discussed. If the aspect ratio is small enough, spanwise peaks in the mean velocity distribution are suppressed.

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