Numerical Study of Counter Jet Formed by Impinging Jets in Cross-Flow and its Effect on Mixing

2017 ◽  
Author(s):  
Thomas A. Epalle ◽  
Fabien Gaugain ◽  
Vincent Melot ◽  
Nasser Darabiha ◽  
Olivier Gicquel
Keyword(s):  
Numerical Study ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Passive Scalar ◽  
Impinging Jets ◽  
Mean Velocity ◽  
Plane Flow ◽  
Flow Mixing ◽  
Mixing Chambers

In this paper we will numerically analyse flow mixing in multiple jets in a crossflow. The system comprises a row of six radially-distributed injectors around the main pipe. The configuration represents mixing zones in industrial systems where a counter jet can be formed in the injection plane. Flow mixing can be modified as a result of geometry and injection velocities. We propose a simple model to describe the counter jet length as a function of injection flow characteristics. We also develop empirical laws to help engineers design practical test facilities. We then vary the velocity ratio to obtain both impinging and non-impinging jets in the injection plane. The focus is mainly on flow characteristics around the radial injection plane in the case of impinging jets, examining the mixing quality and efficiency by introducing a passive scalar discharge in a nitrogen flow. The mean velocity and width of the counter jet are finally analyzed by changing the injection velocities. These results are compared to those of non-impinging jets. It is found that the non-impinging jet configurations are convenient for short length mixing chambers, while the impinging ones should be considered in the case of longer mixing chambers.

Turbulent Wake of a Stack and the Influence of Velocity Ratio

2006 ◽  
Author(s):  
M. S. Adaramola ◽  
D. Sumner ◽  
D. J. Bergstrom
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Reynolds Shear Stress ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Turbulent Wake ◽  
Mean Velocity ◽  
Distinct Structure ◽  
Flow Reynolds Number ◽  
Cross Flow Velocity

The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake of a cylindrical stack of AR = 9 was investigated with two-component thermal anemometry. The cross-flow Reynolds number was ReD = 2.3×104, the jet Reynolds number ranged from Red = 7×103 to 4.6×104, and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-height ratio of δ/H = 0.5 at the location of the stack. The flow around the stack was broadly classified into three flow regimes depending on the value of R, which were the downwash (R < 0.5), cross-wind dominated (0.5 < R < 1.5), and jet-dominated (R > 1.5) regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields.

scholarly journals Effects of Nozzle Pressure Ratio and Nozzle-to-Plate Distance to Flowfield Characteristics of an Under-Expanded Jet Impinging on a Flat Surface

Aerospace ◽  
2019 ◽  
Vol 6 (1) ◽  
pp. 4 ◽  
Author(s):  
Duy Thien Nguyen ◽  
Blake Maher ◽  
Yassin Hassan
Keyword(s):  
Vector Fields ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Impinging Jets ◽  
Central Plane ◽  
Mean Velocity ◽  
Image Velocimetry ◽  
Nozzle Pressure ◽  
Pod Analysis ◽  
Impingement Surface

The current work experimentally investigates the flowfield characteristics of an under-expanded turbulent jet impinging on a solid surface for various nozzle-to-plate distances 2.46 D j , 1.64 D j , and 0.82 D j ( D j is the jet hydraulic diameter), and nozzle pressure ratios (NPRs) ranging from 2 to 2.77 . Planar particle image velocimetry (PIV) measurements were performed in the central plane of the test nozzle and near the impingement surface. From the obtained PIV velocity vector fields, flow characteristics of under-expanded impinging jets, such as mean velocity, root-mean-square fluctuating velocity, and Reynolds stress profiles, were computed. Comparisons of statistical profiles obtained from PIV velocity measurements were performed to study the effects of the impingement surface, nozzle-to-plate distances, and NPRs to the flow patterns. Finally, proper orthogonal decomposition (POD) analysis was applied to the velocity snapshots to reveal the statistically dominant flow structures in the impinging jet regions.

scholarly journals An Experimental and Numerical Study of Heat Transfer From Arrays of Impinging Jets With Surface Ribs

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Sebastian Spring ◽  
Yunfei Xing ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Cross Flow ◽  
Impinging Jets ◽  
Separation Distance ◽  
Distance Measures ◽  
Impingement Plate ◽  
Roughness Elements ◽  
Staggered Arrangement ◽  
The Heat Transfer Coefficient

A combined experimental and numerical investigation of the heat transfer characteristics within arrays of impinging jets with rib-roughened surfaces is presented. Two configurations are considered: One with an inline arrangement of jets and ribs oriented perpendicular to the direction of cross-flow and one with a staggered arrangement of jets and broken ribs aligned with the direction of cross-flow. For both cases, the jet Reynolds number is 35,000, the separation distance measures H/D = 3, the spent air is routed through one exit contributing to the maximum cross-flow condition, and the rib height and width is both 1 D. The experiments are carried out in perspex models using the transient liquid crystal method. Local jet temperatures are measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. In addition to the measurements, a numerical analysis using the commercial CFD software package ANSYSCFX is conducted. Heat transfer predictions are compared with those obtained from experiments with regards to local distributions as well as averaged quantities. A good overall agreement is found but discrepancies for local values need to be accepted. The present investigation also emphasizes that configurations including rib roughness elements should be compared based on the amount of transferred heat flux in order to account for the area enlarging effect. This allows a correct evaluation of the thermal performance.

Flow Characteristics of Contra- and Co-Rotating Swirler Arrangements of an Industrial Combustor

2014 ◽  
Author(s):  
X. Wu ◽  
E. R. Norster ◽  
Gang Xie
Keyword(s):  
Temperature Distribution ◽  
Numerical Model ◽  
Vortex Flow ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Outlet Temperature ◽  
Gas Turbine Combustor ◽  
Mean Velocity ◽  
Split Ratio ◽  
The Impact

This paper describes the investigation of the flow characteristics of two double radial inflow swirlers configured for use in a gas turbine combustor. The only difference between the two swirlers is in the contra- and co-rotating flow of air in the inner nozzle arrangement. The isothermal vortex flow field created by the double swirlers has been examined using numerical Model 1. The model also includes a cylinder reaction zone downstream of the swirler. The comparison of flow characteristics is carried out by examination of the spatial resolution of three mean velocity components. The contra- and co-rotating configurations show some discrepancy in terms of total loss factor and mass split ratio between the two swirlers. The comparison of flow fields also indicate that there is almost no remaining swirl further downstream in the contra-rotating configuration, while a significant amount of remaining swirl exists for the co-rotating option. The development of Model 1 to include a typical dilution zone and transition duct leads to numerical Model 2, which was used to investigate the impact on downstream mixing with the dilution air and the emerging temperature distribution at the transition duct exit. Comparing the temperature field for both configurations, the dilution effectiveness increases significantly with dilution jet penetration depth and reduces with spread along the circumferential direction. These effects lead to the central hot core persisting along the transition duct to the combustor outlet for the co-rotating option due to the combination of initial cross flow and a strong swirl, resulting in a considerable difference in the predicted outlet temperature distribution factors (OTDF) of 10.8% and 17.7% for the contra- and co-rotating arrangements, respectively.

Flow Characteristics of Swirling Coaxial Jets From Divergent Nozzles

1987 ◽  
Vol 109 (3) ◽  
pp. 275-282 ◽  
Author(s):  
T. Mahmud ◽  
J. S. Truelove ◽  
T. F. Wall
Keyword(s):  
Bituminous Coal ◽  
Static Pressure ◽  
Reverse Flow ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Aerodynamic Characteristics ◽  
Flow Zone ◽  
Mean Velocity ◽  
Coaxial Jets ◽  
Mass Flowrate

The aerodynamic characteristics of free, swirling, coaxial jets issuing from an air model of a typical burner for pulverized bituminous coal have been studied. Detailed measurements of mean velocity and static pressure have been obtained in the region near the nozzle exit. The boundary of the reverse-flow zone has been mapped and the recirculated-mass flowrate measured in order to quantify the effects of velocity ratio and swirl in the primary and secondary jets. The influence of burner geometry (divergent-nozzle length and centre-line blockage) has also been studied. The type of flow pattern is found to depend upon the level of swirl in the primary and secondary jets. The recirculated-mass flowrate is predominantly influenced by secondary swirl. The measurements have been compared with predictions obtained by numerical solution of the governing conservation equations in orthogonal curvilinear co-ordinates. The general features of the flows are adequately predicted although discrepancies in detail seem to indicate deficiencies in the turbulence model.

The Impact of Manifold-to-Orifice Turning Angle on Sharp-Edge Orifice Flow Characteristics in Both Cavitation and Noncavitation Turbulent Flow Regimes

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
W. H. Nurick ◽  
T. Ohanian ◽  
D. G. Talley ◽  
P. A. Strakey
Keyword(s):  
Dynamic Pressure ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Sharp Edge ◽  
Turning Angle ◽  
Design Engineers ◽  
Orifice Flow ◽  
The Impact ◽  
Insight Into

The approach taken was to analyze the results in a manner consistent with application by design engineers to new and existing applications, while providing some insight into the processes that are occurring. This paper deals with predicting the initiation of cavitation, cavitation impacts on the contraction coefficient (Cc), as well as noncavitation impacts on discharge coefficient (Cd) from L/D of five sharp-edge orifices over a turning angle range between 60 deg and 120 deg. The results show that in the cavitation regime, Cc is controlled by the cavitation parameter (Kcav), where the data follow the 1∕2 power with Kcav, and inception of cavitation occurs at a Kcav of 1.8. In the noncavitation regime for conditions where the cross velocity is 0 the data are consistent with the first order equation relating head loss (HL) to the dynamic pressure where KL is constant and is consistent with in-line orifices. Cross flow has a significant impact on loss coefficient and depends on both the turning angle and manifold inlet to orifice exit velocity ratio.

scholarly journals Effects of roof configuration on natural ventilation for an isolated building

2021 ◽  
Vol 15 (3) ◽  
pp. 8379-8389
Author(s):  
Lip Kean Moey ◽  
Man Fai Kong ◽  
Vin Cent Tai ◽  
Tze Fong Go ◽  
Nor Mariah Adam
Keyword(s):  
Kinetic Energy ◽  
Natural Ventilation ◽  
Velocity Ratio ◽  
Mixing Layer ◽  
Flow Characteristics ◽  
Mean Velocity ◽  
Gable Roof ◽  
Building Models ◽  
Large Vortex ◽  
Field Information

Numerical analyses based on CFD steady RANS were conducted to investigate the effects of roof configuration on wind-induced natural ventilation for an isolated roofed building. Gable roof and saltbox roof building models were tested with 15˚, 25˚, 35˚ and 45˚ roof pitch in present study. The flow field information and flow characteristics were obtained from the contours and plots generated by CFD. In accordance to the increment of roof pitch, the turbulence kinetic energy and mean velocity ratio show vigorous response. The flow separated at the windward corner do not reattach onto the roof, thus induced higher velocity gradient and form a large vortex at the roof ridge. The vortices behind then building caused by the flow separation at the roof ridge extend along the mixing layer and spread up to the roof. The pressure differences mainly rely on the roof shapes. Greater pressure differences between the upstream, interior and downstream was observed in saltbox roof cases. This is due to the extended roof height which boosted the impinging effect caused by the incoming wind. Generally, the saltbox roof configuration exhibit better performance than gable roof in terms of the measured parameters.

Aerodynamic Influence of Endwall Fences Located in the Vicinity of the Leading Edge-Endwall Junction of Nozzle Guide Vanes

2011 ◽  
Author(s):  
Zeki Ozgur Gokce ◽  
Cengiz Camci
Keyword(s):  
Total Pressure ◽  
Numerical Study ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Vertical Cylinder ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Horseshoe Vortices ◽  
Nozzle Guide

Secondary flow characteristics like horseshoe vortices and related total pressure losses decrease turbine efficiency. Computerized simulations of potentially favorable modifications in turbine systems could provide a fast, numerical and inexpensive method of evaluating their effects on flow properties: This paper consists of a comparative numerical study of the flow characteristics of a domain containing a vertical cylinder subjected to cross flow and upstream endwall modifications. Analyzing the flow around a turbine nozzle guide vane (NGV) could be simplified by modeling it as a vertical cylinder with a diameter proportional to the leading edge diameter of the blade, and adding upstream endwall fences of varying dimensions and alignments could attenuate the development of a horseshoe vortex. A commercial computational fluid dynamics (CFD) software package, Fluent, was used for the numerical analysis. To validate the modeling strategy, experimental data previously reported in the literature for conventional cylinders in cross flow were compared to the current predictions. A grid independence study was also performed. The lateral distance between the two legs of the horseshoe vortex downstream of the cylinder was decreased by 7% to 14%. All fence types effectively changed the location of the main horseshoe vortex roll-up. The height of the fence was more influential than the length of the fence in modifying flow characteristics. The existence of the fences slightly increased the mass-averaged total pressure loss far downstream of the cylinder; however, beneficial near-fence flow characteristics were observed in all cases. Also, it was noted that an endwall fence could possibly result in decreased interaction between the horseshoe vortices created by consecutive blades in a row of NGV blades, which would be expected to result in improved flow conditions within actual turbine passages.

A Numerical Study on the Flow Characteristics of Opposed Impinging Jets

2012 ◽  
Vol 516-517 ◽  
pp. 854-857
Author(s):  
Shu Xia Qiu ◽  
Ning Pang
Keyword(s):  
Unsteady Flow ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Impinging Jets ◽  
Mixing Efficiency ◽  
Fluid Temperature ◽  
Mixing Rate ◽  
Numerical Work ◽  
Mixing Performance ◽  
Flow Pulsations

Inspired by the increasing interests on mixing effectiveness of opposed impinging jets, a numerical work is carried out to study the flow characteristics. The fluid temperature is used as a passive tracer to evaluate the mixing rate in the current mathematical models. The effect of Reynolds number on the mixing performance is discussed. Furthermore, in order to enhance the mixing efficiency and reduce the energy cost, unsteady flow pulsations are induced at the jet inlets. The numerical results indicate that the mixing efficiency can be improved by the unsteady flow pulsations via adjusting the hydrodynamics characteristics in the opposed jets.

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