scholarly journals 2D PIV Measurement of Twin Buoyant Jets in Wavy Cross-Flow Environment

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 399 ◽  
Author(s):  
Zhenshan Xu ◽  
Ebenezer Otoo ◽  
Yongping Chen ◽  
Hongwei Ding
Keyword(s):  
Current Velocity ◽  
Near Field ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Buoyant Jets ◽  
Flow Environment ◽  
Piv Measurement ◽  
Jet Trajectory ◽  
Twin Jets ◽  
Effluent Discharge

The multiport diffuser effluent discharge facilities constructed beneath the coastal waters were simplified in the laboratory as twin buoyant jets in a wavy cross-flow environment. The near-field flow structure of twin jets was studied by series of experiments conducted in a physical wave–current flume. The particle image velocimetry (PIV) system was used to measure the velocity field of the jets in various cross-flow-only and wavy cross-flow environments. By means of flow visualization, the distinctive “effluent cloud” (EC) phenomenon was clearly observed and the jet penetration height was found to be notably increased compared with that of cross-flow-only environment at the downstream position. It was found that the wave-to-current velocity ratio Rwc is a very important parameter for effluent discharge. A new characteristic velocity uch and the corresponding characteristic length scale lmb for twin buoyant jets in the wavy cross-flow environment were defined. Using curve-fitting, a new equation to estimate the effects of the jet-to-current velocity ratio (Rjc), wave-to-current velocity ratio (Rwc) and Strouhal number (St) on the jet trajectory were derived to enhance understanding the physical processes underpinning the rise and the dilution of buoyant jets, which is critical to the design of discharge facilities.

An Experimental Characterization of the Interaction Between Two Tandem Planar Jets in a Crossflow

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Kun Zhao ◽  
Patrick N. Okolo ◽  
Yong Wang ◽  
John Kennedy ◽  
Gareth J. Bennett
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Near Field ◽  
Mean Flow ◽  
Piv Measurement ◽  
Jet Trajectory ◽  
The Mean ◽  
Pod Analysis ◽  
Particle Imaging ◽  
Quantitative Definition

This study reports an experimental investigation of two planar jets in a crossflow in a tandem arrangement. Tests were conducted in an open-jet wind tunnel facility using two-dimensional (2D)-particle imaging velocimetry (PIV) measurement. Using the terminology in the dual jets in a quiescent ambient, the mean flow field of the crossflow arrangement was divided into a converging region, a merging region, and a combined region. An approach to determining the range of these three regions was proposed based on the mean characteristics of horizontal velocity profiles of the flow field, validated by the experimental data. The momentum-dominated near field (MDNF) for the rear jet in the dual-jet configuration was recognized using the horizontal offset of mean jet trajectory, which accordingly gives a quantitative definition of the MDNF range. Discussions were made on the effects of different parameters on the three regions and MDNF. Finally, snapshot proper orthogonal decomposition (POD) analysis was conducted, characterizing the coherent structures of the flow field, particularly the large-scale vortices. It was observed that the large-scale vortices mainly occur in the shear layers of the jets and their occurrence is affected by the parameters of the jets. In addition, compared with the single-jet configuration, the introduction of the front jet was found to contribute to the occurrence and development of the large-scale vortices.

Dynamics of Large-Scale Structures for Jets in a Crossflow

1998 ◽  
Author(s):  
Frank Muldoon ◽  
Sumanta Acharya
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Computational Study ◽  
Near Field ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leeward Side ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Scale Structures

Results of a three dimensional unsteady computational study of a row of jets injected normal to a cross-flow are presented with the aim of understanding the dynamics of the large scale structures in the region near the jet. The jet to cross-flow velocity ratio is .5. A modified version of the computer program (INS3D) which utilizes the method of artificial compressibility is used for the computations. Results obtained clearly indicate that the near field large scale structures are extremely dynamical in nature, and undergo breakup and reconnection processes. The dynamical near field structures identified include the counter rotating vortex pair (CVP), the horseshoe vortex, wake vortex, wall vortex and the shear layer vortex. The dynamical features of these vortices are presented in this paper. The CVP is observed to be a convoluted structure interacting with the wall and horseshoe vortices. The shear layer vortices are stripped by the crossflow, and undergo pairing and stretching events in the leeward side of the jet. The wall vortex is reoriented into the upright wake system. Comparison of the predictions with mean velocity measurements is made. Reasonable agreement is observed.

scholarly journals Near-field dynamics of parallel twin jets in cross-flow

2017 ◽  
Vol 29 (3) ◽  
pp. 035103 ◽  
Author(s):  
B. Zang ◽  
T. H. New
Keyword(s):  
Near Field ◽  
Cross Flow ◽  
Twin Jets

DIRECT NUMERICAL SIMULATION OF MULTIPLE JETS IN CROSS-FLOW

2009 ◽  
Vol 23 (03) ◽  
pp. 249-252 ◽  
Author(s):  
YUFENG YAO
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Industrial Applications ◽  
Complex Flow ◽  
Vortex Pairs ◽  
Multiple Jets ◽  
Twin Jets ◽  
Complex Flow Structure

Direct numerical simulation has been performed to study flow interactions in multiple jets in cross-flow. Configurations considered are twin jets side-by-side and triple jets in tandem. Computations are carried out at the jet to cross-flow velocity ratio of 2.5 and the Reynolds number 225 based on the free-stream quantities and the jet width D . For twin jets, results show that in the vicinity of jet exits, the merging of two counter rotating vortex pairs (CRVP) is strongly dependent on the gap of two jets. Downstream in the far-field, a large single CRVP dominates. The simulation is in qualitatively good agreement with the experimental findings by other researchers. For triple jets, more complicated flow structures are revealed, in which a total of three vortex pairs has been identified, but none of them is dominating. The observations of complex flow structure could assistant relevant industrial applications.

Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

Turbulence of vertical round buoyant jets in a cross flow

2004 ◽  
pp. 1167-1174 ◽  
Author(s):  
M Meftah ◽  
A Petrillo ◽  
P Davies ◽  
D Malcangio ◽  
M Mossa
Keyword(s):  
Cross Flow ◽  
Buoyant Jets

scholarly journals Numerical Simulation of Propagation Characteristics of Hazardous Noxious Substances Spilled from Transport Ships

2018 ◽  
Vol 8 (12) ◽  
pp. 2409 ◽  
Author(s):  
Chan Ho Jeong ◽  
Min Kyu Ko ◽  
Moonjin Lee ◽  
Seong Hyuk Lee
Keyword(s):  
Current Velocity ◽  
Propagation Velocity ◽  
Near Field ◽  
Navier Stokes ◽  
Surface Model ◽  
Least Squares Regression ◽  
Propagation Characteristics ◽  
Ansys Fluent ◽  
Dimensional Simulation ◽  
Noxious Substances

This study numerically investigates the propagation characteristics of hazardous noxious substances (HNSs) spilled from transport ships and suggests the metal model for predicting the HNS propagation velocity varied with the current velocity and HNS density. The commercial computational fluid dynamics (CFD) code ANSYS FLUENT (V. 17.2) was used for two-dimensional simulation based on the Reynolds-averaged Navier–Stokes (RANS) equation together with the standard k–ε model. The scalar transport equation was also solved to estimate the spatial and transient behaviors of HNS. The main parameters to analyze the near-field propagation characteristics of HNSs spilled from the ship were layer thickness, HNS concentration, and propagation velocity. It was found that advection becomes more dominant in propagating an HNS layer that becomes thinner as the current velocity increases. When the current velocity increased beyond a certain level (~0.75 m/s), the mixing effect made the HNS layer less dense but thicker. Consequently, lower-density HNS causes increased HNS concentrations at sea level. As the current velocity increased, the concentration distribution became homogeneous regardless of HNS density. In particular, the second-order response surface model provided for three variables on the basis of the numerical results for 15 cases with the use of the general least-squares regression method, showing a good fit. This model would be useful in estimating the propagation velocity of HNS spilled from a ship.

scholarly journals Real-Time Monitoring of Jet Trajectory during Jetting Based on Near-Field Computer Vision

Sensors ◽  
2019 ◽  
Vol 19 (3) ◽  
pp. 690 ◽  
Author(s):  
Jinsong Zhu ◽  
Wei Li ◽  
Da Lin ◽  
Ge Zhao
Keyword(s):  
Computer Vision ◽  
Prediction Model ◽  
Real Time ◽  
Processing Time ◽  
Near Field ◽  
Image Correction ◽  
Noise Elimination ◽  
Sensor Device ◽  
Jet Trajectory ◽  
Novel Method

A novel method of near-field computer vision (NFCV) was developed to monitor the jet trajectory during the jetting process, which was used to precisely predict the falling point position of the jet trajectory. By means of a high-resolution webcam, the NFCV sensor device collected near-field images of the jet trajectory. Preprocessing of collected images was carried out, which included squint image correction, noise elimination, and jet trajectory extraction. The features of the jet trajectory in the processed image were extracted, including: start-point slope (SPS), end-point slope (EPS), and overall trajectory slope (OTS) based on the proposed mean position method. A multiple regression jet trajectory range prediction model was established based on these trajectory characteristics and the reliability of the model was verified. The results show that the accuracy of the prediction model is not less than 94% and the processing time is less than 0.88s, which satisfy the requirements of real-time online jet trajectory monitoring.

Twin jets in cross-flow

2011 ◽  
Vol 66 (12) ◽  
pp. 2616-2626 ◽  
Author(s):  
V.S. Naik-Nimbalkar ◽  
A.D. Suryawanshi ◽  
A.W. Patwardhan ◽  
I. Banerjee ◽  
G. Padmakumar ◽  
...  
Keyword(s):  
Cross Flow ◽  
Twin Jets
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