scholarly journals On the spectra of nozzle-exit velocity disturbances in initially nominally turbulent, transitional jets

2011 ◽  
Vol 23 (9) ◽  
pp. 091702 ◽  
Author(s):  
Christophe Bogey ◽  
Olivier Marsden ◽  
Christophe Bailly
Keyword(s):  
Nozzle Exit ◽  
Exit Velocity ◽  
Nozzle Exit Velocity

scholarly journals Stochastic Simulation of Soot Formation Evolution in Counterflow Diffusion Flames

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Xiao Jiang ◽  
Kun Zhou ◽  
Ming Xiao ◽  
Ke Sun ◽  
Yu Wang
Keyword(s):  
Nozzle Exit ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Hydrocarbon Fuels ◽  
Number Density ◽  
Exit Velocity ◽  
Soot Particles ◽  
Counterflow Diffusion Flames ◽  
Nozzle Exit Velocity

Soot generally refers to carbonaceous particles formed during incomplete combustion of hydrocarbon fuels. A typical simulation of soot formation and evolution contains two parts: gas chemical kinetics, which models the chemical reaction from hydrocarbon fuels to soot precursors, that is, polycyclic aromatic hydrocarbons or PAHs, and soot dynamics, which models the soot formation from PAHs and evolution due to gas-soot and soot-soot interactions. In this study, two detailed gas kinetic mechanisms (ABF and KM2) have been compared during the simulation (using the solver Chemkin II) of ethylene combustion in counterflow diffusion flames. Subsequently, the operator splitting Monte Carlo method is used to simulate the soot dynamics. Both the simulated data from the two mechanisms for gas and soot particles are compared with experimental data available in the literature. It is found that both mechanisms predict similar profiles for the gas temperature and velocity, agreeing well with measurements. However, KM2 mechanism provides much closer prediction compared to measurements for soot gas precursors. Furthermore, KM2 also shows much better predictions for soot number density and volume fraction than ABF. The effect of nozzle exit velocity on soot dynamics has also been investigated. Higher nozzle exit velocity renders shorter residence time for soot particles, which reduces the soot number density and volume fraction accordingly.

scholarly journals Near-Field Flow Structure and Entrainment of a Round Jet at Low Exit Velocities: Implications on Microclimate Ventilation

Computation ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 100
Author(s):  
Alan Kabanshi
Keyword(s):  
Flow Structure ◽  
Nozzle Exit ◽  
Near Field ◽  
Jet Flow ◽  
Field Vector ◽  
Statistical Characteristics ◽  
Round Jets ◽  
Nozzle Exit Velocity ◽  
Development And Validation ◽  
Ventilation Systems

This paper explores the flow structure, mean/turbulent statistical characteristics of the vector field and entrainment of round jets issued from a smooth contracting nozzle at low nozzle exit velocities (1.39–6.44 m/s). The motivation of the study was to increase understand of the near field and get insights on how to control and reduce entrainment, particularly in applications that use jets with low-medium momentum flow like microclimate ventilation systems. Additionally, the near field of free jets with low momentum flow is not extensively covered in literature. Particle image velocimetry (PIV), a whole field vector measurement method, was used for data acquisition of the flow from a 0.025 m smooth contracting nozzle. The results show that at low nozzle exit velocities the jet flow was unstable with oscillations and this increased entrainment, however, increasing the nozzle exit velocity stabilized the jet flow and reduced entrainment. This is linked to the momentum flow of the jet, the structure characteristics of the flow and the type or disintegration distance of vortices created on the shear layer. The study discusses practical implications on microclimate ventilation systems and at the same time contributes data to the development and validation of a planned computational turbulence model for microclimate ventilation.

scholarly journals Effects of nozzle-exit boundary-layer profile on the initial shear-layer instability, flow field and noise of subsonic jets

2019 ◽  
Vol 876 ◽  
pp. 288-325 ◽  
Author(s):  
Christophe Bogey ◽  
Roberto Sabatini
Keyword(s):  
Boundary Layer ◽  
Velocity Profile ◽  
Shear Layer ◽  
Nozzle Exit ◽  
Momentum Thickness ◽  
Shear Layer Instability ◽  
Instability Waves ◽  
Exit Velocity ◽  
Exit Boundary ◽  
Boundary Layer Profile

The influence of the nozzle-exit boundary-layer profile on high-subsonic jets is investigated by performing compressible large-eddy simulations (LES) for three isothermal jets at a Mach number of 0.9 and a diameter-based Reynolds number of $5\times 10^{4}$, and by conducting linear stability analyses from the mean-flow fields. At the exit section of a pipe nozzle, the jets exhibit boundary layers of momentum thickness of approximately 2.8 % of the nozzle radius and a peak value of turbulence intensity of 6 %. The boundary-layer shape factors, however, vary and are equal to 2.29, 1.96 and 1.71. The LES flow and sound fields differ significantly between the first jet with a laminar mean exit velocity profile and the two others with transitional profiles. They are close to each other in these two cases, suggesting that similar results would also be obtained for a jet with a turbulent profile. For the two jets with non-laminar profiles, the instability waves in the near-nozzle region emerge at higher frequencies, the mixing layers spread more slowly and contain weaker low-frequency velocity fluctuations and the noise levels in the acoustic field are lower by 2–3 dB compared to the laminar case. These trends can be explained by the linear stability analyses. For the laminar boundary-layer profile, the initial shear-layer instability waves are most strongly amplified at a momentum-thickness-based Strouhal number $St_{\unicode[STIX]{x1D703}}=0.018$, which is very similar to the value obtained downstream in the mixing-layer velocity profiles. For the transitional profiles, on the contrary, they predominantly grow at higher Strouhal numbers, around $St_{\unicode[STIX]{x1D703}}=0.026$ and 0.032, respectively. As a consequence, the instability waves rapidly vanish during the boundary-layer/shear-layer transition in the latter cases, but continue to grow over a large distance from the nozzle in the former case, leading to persistent large-scale coherent structures in the mixing layers for the jet with a laminar exit velocity profile.

Quantitative Visualization of a Submerged Pseudoplastic Jet Using Particle Image Velocimetry

1995 ◽  
Vol 117 (3) ◽  
pp. 369-373 ◽  
Author(s):  
A. Shekarriz ◽  
J. R. Phillips ◽  
T. D. Weir
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Nozzle Exit ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Image Velocimetry ◽  
Close Observation ◽  
Quantitative Visualization ◽  
Nozzle Exit Velocity

A preliminary experimental study of a pseudoplastic jet flow is reported in this paper. The velocity field was measured using Particle Image Velocimetry. Unlike a Newtonian jet, the pseudoplastic jet was observed to experience a sudden drop in its velocity at a reproducible position downstream of the nozzle for the range of velocities examined. This position moved downstream with an increase in the nozzle exit velocity. The center-line streamwise velocity decayed as X–15 to X–30 within the terminating region of the jet for three different nozzle exit velocities of 2.43, 3.17, and 5.42 m/s. This decay is in contrast to X–1 decay for a turbulent or laminar Newtonian jet. The location of the terminating region did not appear to scale with Reynolds number, Plasticity number, or Hedstrom number. At Reynolds numbers of 3000 and 6400, the instantaneous streamwise velocity maps indicated that the flow was fairly laminar, with a sinuous instability appearing at the higher Reynolds number condition. Close observation of the jet indicated that local turbulence could exist within regions of high shear rate. Further detailed study is required to confirm this observation.

EFFECTS OF NOZZLE EXIT GEOMETRY ON SPRAY CHARACTERISTICS OF A BLURRY INJECTOR

2013 ◽  
Vol 23 (3) ◽  
pp. 193-209 ◽  
Author(s):  
Claudia Goncalves Azevedo ◽  
Jose Carlos de Andrade ◽  
Fernando de Souza Costa
Keyword(s):  
Nozzle Exit ◽  
Spray Characteristics

Disorganization of a hole tone feedback loop by an axisymmetric obstacle on a downstream end plate

2014 ◽  
Vol 757 ◽  
pp. 908-942 ◽  
Author(s):  
K. Matsuura ◽  
M. Nakano
Keyword(s):  
Nozzle Exit ◽  
Passive Control ◽  
Control Method ◽  
Three Dimensional ◽  
Acoustic Power ◽  
Shear Layers ◽  
Mean Velocity ◽  
End Plate ◽  
Air Jet ◽  
Practical Engineering

AbstractThis study investigates the suppression of the sound produced when a jet, issued from a circular nozzle or hole in a plate, goes through a similar hole in a second plate. The sound, known as a hole tone, is encountered in many practical engineering situations. The mean velocity of the air jet $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}u_0$ was $6\text {--}12\ \mathrm{m}\ {\mathrm{s}}^{-1}$. The nozzle and the end plate hole both had a diameter of 51 mm, and the impingement length $L_{im}$ between the nozzle and the end plate was 50–90 mm. We propose a novel passive control method of suppressing the tone with an axisymmetric obstacle on the end plate. We find that the effect of the obstacle is well described by the combination ($W/L_{im}$, $h$) where $W$ is the distance from the edge of the end plate hole to the inner wall of the obstacle, and $h$ is the obstacle height. The tone is suppressed when backflows from the obstacle affect the jet shear layers near the nozzle exit. We do a direct sound computation for a typical case where the tone is successfully suppressed. Axisymmetric uniformity observed in the uncontrolled case is broken almost completely in the controlled case. The destruction is maintained by the process in which three-dimensional vortices in the jet shear layers convect downstream, interact with the obstacle and recursively disturb the jet flow from the nozzle exit. While regions near the edge of the end plate hole are responsible for producing the sound in the controlled case as well as in the uncontrolled case, acoustic power in the controlled case is much lower than in the uncontrolled case because of the disorganized state.

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