Effect of nozzle geometry and semi-confinement on the potential core of a turbulent axisymmetric free jet

1996 ◽  
Vol 23 (2) ◽  
pp. 155-162 ◽  
Author(s):  
S. Ashforth-Frost ◽  
K. Jambunathan
Keyword(s):  
Nozzle Geometry ◽  
Potential Core ◽  
Free Jet

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.

Total Temperature Based Correction of the Turbulence Production in Hot Jets

2017 ◽  
Author(s):  
Jens Truemner ◽  
Christian Mundt
Keyword(s):  
Shear Layers ◽  
Efficiency Gain ◽  
Potential Core ◽  
Production Term ◽  
Turbofan Engines ◽  
Free Jet ◽  
Rans Models ◽  
Total Temperature ◽  
Turbulence Production ◽  
Good Agreement

Comparisons with experiments have shown that RANS models tend to underpredict the mixing process in shear layers with strong temperature gradients. In the modeling of jet engine’s exhaust systems this leads to an overpredicted potential core length and underestimated turbulence intensity in the free jet. In addition, the calculated efficiency gain is lower than indicated by measurements in mixed turbofan engines. Based on the findings from scale-resolving simulations a correction to the turbulence production term is proposed and compared with two NASA-experiments on hot jets. This correction is implemented in a Reynolds-stress and a k-ε model. The results are in very good agreement with the experimental data.

Characteristics of a co-flowing jet with varying lip thickness and constant bypass ratio

2019 ◽  
Vol 91 (9) ◽  
pp. 1205-1213 ◽  
Author(s):  
Naren Shankar R. ◽  
Kevin Bennett S.
Keyword(s):  
Design Methodology ◽  
Critical Value ◽  
Commercial Aircraft ◽  
Critical Limit ◽  
Potential Core ◽  
Content Type ◽  
Free Jet ◽  
The Past ◽  
Bypass Ratio ◽  
Practical Implications

Purpose Subsonic commercial aircraft operate with turbo-fan engines that operate with moderate bypass ratio (BR) co-flowing jets (CFJ). This study aims to analyse CFJ with constant BR 6.3 and varying primary nozzle lip thickness (LT) to find a critical LT in CFJ below which mixing enhances and beyond which mixing inhibits. Design/methodology/approach CFJ were characterized with a constant BR of 6.3 and varying lip thicknesses. A single free jet with a diameter equal to that of a primary nozzle of the co-flowing jet was also studied for comparison. Findings The results show that within a critical limit, the mixing enhanced with an increase in LT. This was signified by a reduction in potential core length (PCL). Beyond this limit, mixing inhibited leading to the elongation of PCL. This limit was controlled by parameters such as LT and magnitude of BR. Practical implications The BR value of CFJ in the present study was 6.3. This lies under the moderate BR value at which subsonic commercial turbofan operates. Hence, it becomes impervious to study its mixing behavior. Originality/value This is the first effort to find the critical value of LT for a constant BR for compressible co-flow jets. The CFJ with moderate BR and varying LT has not been studied in the past. The present study focuses on finding a critical LT below which mixing enhances and above which mixing inhibits.

Effects of nozzle geometry on kinetics in free-jet expansions

1984 ◽  
Vol 88 (20) ◽  
pp. 4474-4478 ◽  
Author(s):  
Hylton R. Murphy ◽  
David R. Miller
Keyword(s):  
Nozzle Geometry ◽  
Free Jet

Characteristics of a co-flowing jet with varying lip thickness and constant velocity ratio

2020 ◽  
Vol 92 (4) ◽  
pp. 633-644
Author(s):  
Naren Shankar R. ◽  
Kevin Bennett S. ◽  
Dilip Raja N. ◽  
Sathish Kumar K.
Keyword(s):  
Constant Velocity ◽  
Velocity Ratio ◽  
Critical Limit ◽  
Potential Core ◽  
Content Type ◽  
Free Jet ◽  
Current Scenario ◽  
Wake Zone ◽  
Bypass Ratio ◽  
Practical Implications

Purpose This study aims to analyze co-flowing jets (CFJs) with constant velocity ratio (VR) and varying primary nozzle lip thickness (LT) to find a critical LT in CFJs below which mixing enhances and beyond which mixing inhibits. Design/methodology/approach CFJs were characterized with a constant VR and varying LTs. A single free jet with a diameter equal to that of a primary nozzle of the CFJ was used for characteristic comparison. Numerical simulation is carried out and is validated with the experimental results. Findings The results show that within a critical limit, the mixing enhanced with an increase in LT. This was signified by a reduction in potential core length (PCL). Beyond this limit, mixing inhibited leading to the elongation of PCL. This limit was controlled by parameters such as LT and constant VR. A new region termed as influential wake zone is identified. Practical implications In this study, the VR is maintained constant and bypass ratio (BR) was varied from low value to very high values. Presently, subsonic commercial turbo fan operates under low to ultra-high BR. Hence the present study becomes vital to the current scenario. Originality/value To the best of the authors’ knowledge, this is the first effort to find the critical value of LT for a constant VR for compressible co-flow jets. The CFJs with constant VR and varying LT have not been studied in the past. The present study focuses on finding a critical LT below which mixing enhances and above which mixing inhibits.

Influence of Exhaust Nozzle Geometry on the Jet Potential Core Development

2015 ◽  
Vol 811 ◽  
pp. 145-151 ◽  
Author(s):  
Daniel Eugeniu Crunteanu ◽  
Valentin Ionut Misirliu ◽  
Oana Dumitrescu ◽  
Bogdan Gherman
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Boundary Conditions ◽  
Turbulence Model ◽  
Nozzle Geometry ◽  
Turbofan Engine ◽  
Potential Core ◽  
The Third ◽  
The Impact

In this paper, a numerical simulation was performed on a scale turbofan engine nozzle to asses the influence of two nozzle configurations over the flow performance while the nozzle is situated at a certain distance from the ground. The turbulence model chosen for this numerical simulation was SST k-ω to capture boundary layer detachment and jet attachment to the ground. For this analysis two different computational domains where considered, while for the third case, boundary conditions for secondary inlet where modified. To assess the impact of these geometry changes a comparison between cases is made at different location in the domain.

Experimental-Numerical Analysis of Turbulent Incompressible Isothermal Jets

2017 ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Mark Francis Tachie ◽  
Peter Vorobieff ◽  
Mikhail Koupriyanov
Keyword(s):  
Reynolds Number ◽  
Near Field ◽  
Turbulent Transport ◽  
Reynolds Numbers ◽  
Nozzle Geometry ◽  
System Response ◽  
Potential Core ◽  
Turbulence Structures ◽  
Round Jets ◽  
Core Length

An experimental investigation was conducted to study the effects of Reynolds number on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free equilateral triangular and round jets issuing from modified contoured nozzles (nozzles with sharp linear contractions). Detailed velocity measurements were made using a particle image velocimetry at Reynolds numbers of 6000, 10000, 13800 and 20000. Computational fluid dynamics (CFD) was also applied to understand the flow behaviors in different Reynolds numbers. We applied standard k-ε turbulence model in an axisymmetric domain to conduct the numerical simulation of the round jet cases. The potential core length was the system response quantity to evaluate our simulation against the experimental results. The geometrical comparative study shows enhanced mixing in the near field of the triangular jets compared to the round jets, regardless of Reynolds number. This conclusion is supported by shorter potential core length and faster growth of turbulence intensity on the centerline of the triangular jets. The obtained data in the round jets exhibit that the jet at the lowest Reynolds number has the most effective mixing with the ambient fluid, while increase in Reynolds number reduces the mixing performance. In the triangular jets almost there is no Reynolds number effect on the measured quantities including the length of the potential core, the decay rate and the axis-switching locations. The results revealed that the asymptotic values of the turbulence intensities on the jet centerline are not only independent of the Reynolds number but also they are the same for both the round and triangular jets. Due to the specific shape of the triangular nozzle, a skewed flow pattern is observed in the near field region in the major plane while the jet is absolutely symmetric in the minor plane. The turbulence structures in all the jets studied become larger as streamwise distance increases, while there is no considerable Reynolds number or nozzle geometry effects on the size of the structures on the jet centerline.

Nozzle Spraying Model of Combustion Thermal Spray

2013 ◽  
Vol 655-657 ◽  
pp. 211-217 ◽  
Author(s):  
Wen Liang Guo ◽  
Zheng Guo
Keyword(s):  
Turbulent Flows ◽  
High Speed ◽  
Numerical Solutions ◽  
Substrate Surface ◽  
Ccd Camera ◽  
Nozzle Geometry ◽  
Flame Spraying ◽  
Free Jet ◽  
Powder Particles ◽  
Mixing Length Theory

The flame used in combustion flame spraying is typical of a high-temperature free jet. The flow fields of free jets are multi-phase flows that couple the mass and heat transfer. The analytical and numerical solutions to turbulent flows are engineering approximations. This work uses Prandtle’s mixing-length theory to describe the flame spreading of free combustion spray jet and uses nozzle spray model to describe the distribution of the powder particles sprayed from powder nozzle to the substrate surface. The nozzle geometry and the parameters determine the distribution of the powder particles. The nozzle spray model has the same physical meaning with the jet spreading angle. Experimental measurements were carried by a high-speed CCD camera.

Jet Flow Control Using Semi-Circular Corrugated Tab

2018 ◽  
Vol 0 (0) ◽  
Author(s):  
Sathish Kumar K ◽  
Senthilkumar Chidambaram
Keyword(s):  
Experimental Validation ◽  
Jet Flow ◽  
Blockage Ratio ◽  
Potential Core ◽  
Convergent Nozzle ◽  
Jet Mixing ◽  
Free Jet ◽  
Core Length ◽  
The Relationship ◽  
Subsonic Jet

Abstract This investigation aims to present the jet mixing characteristics and thrust variations of the subsonic jet employed with plain triangular tab and semi-circular corrugated tab by numerical simulation. A triangular tab with semi-circular corrugations is used in this regard at the exit plane of a convergent nozzle, to study the behavior of the jet and its structure. The near jet flow field is studied for different Mach numbers of 0.6, 0.8 and 1, and the comparisons were done for the jet employed with plain triangular tab. To validate the numerical results, experimental validation is carried out for 0.6 Mach jet. The thrust and the potential core length of any jet depend mainly on the percentage of blockage ratio. Since the relationship between the thrust and blockage ratio is such that, the blockage ratio increases, the thrust and the potential core length decreases and vice-versa. The blockage ratio is kept 8.27 % for both the corrugated and plain triangular tabs. From the results, it is found that the Potential core length of the free jet is cut down to 66 % by the jet employed with plain triangular tab, whereas it is 64.5 % for the corrugated tab enabled jet. It is also concluded that the corrugated tab enhances the thrust by 4.43 % for the same blockage ratio and increases potential core length by 3.33 % when compared with the plain triangular tab. This increase in thrust is there by an added advantage of this investigation.

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