Coherent structure characteristics of the swirling flow during turbulent mixing in a multi-inlet vortex reactor

2021 ◽  
Vol 33 (6) ◽  
pp. 065119
Author(s):  
Emmanuel Hitimana ◽  
Rodney O. Fox ◽  
James C. Hill ◽  
Michael G. Olsen
Keyword(s):  
Coherent Structure ◽  
Turbulent Mixing ◽  
Swirling Flow ◽  
Structure Characteristics ◽  
Vortex Reactor

scholarly journals Turbulent mixing in the confined swirling flow of a multi‐inlet vortex reactor

AIChE Journal ◽  
2016 ◽  
Vol 63 (6) ◽  
pp. 2409-2419 ◽  
Author(s):  
Zhenping Liu ◽  
Emmanuel Hitimana ◽  
Michael G. Olsen ◽  
James C. Hill ◽  
Rodney O. Fox
Keyword(s):  
Turbulent Mixing ◽  
Swirling Flow ◽  
Vortex Reactor

A Batchelor Vortex Model for Mean Velocity of Turbulent Swirling Flow in a Macroscale Multi-Inlet Vortex Reactor

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Zhenping Liu ◽  
Rodney O. Fox ◽  
James C. Hill ◽  
Michael G. Olsen
Keyword(s):  
Reynolds Number ◽  
Simple Model ◽  
Velocity Field ◽  
Swirling Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Mean Velocity ◽  
Vortex Model ◽  
Nonlinear Curve Fitting ◽  
Image Velocimetry ◽  
Vortex Reactor

The velocity field in a macroscale multi-inlet vortex reactor (MIVR) used in “flash nanoprecipitation (FNP)” process for producing functional nanoparticles was investigated using stereoscopic particle image velocimetry (SPIV). Based on the experimental data, a simple model was proposed to describe the average velocity field within the reactor. In the model, the axial and azimuthal velocities could be well described by the combination of two coflowing Batchelor vortices. In this model, six dimensionless coefficients are identified by nonlinear curve fitting, and their dependence on Reynolds number can be linearly described. This simple model is able to accurately predict the mean velocity field within the confined turbulent swirling flow based purely on Reynolds number.

A ‘turbulent spot’ in an axisymmetric free shear layer. Part 2

1980 ◽  
Vol 98 (1) ◽  
pp. 97-135 ◽  
Author(s):  
A. K. M. F. Hussain ◽  
S. J. Kleis ◽  
M. Sokolov
Keyword(s):  
Time Series ◽  
Reynolds Stress ◽  
Coherent Structure ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Layer ◽  
Turbulent Mixing Layer ◽  
Phase Average ◽  
Background Turbulence ◽  
Stream Functions

The mechanics of a spark-induced coherent structure (called a ‘spot’) in the turbulent mixing layer of a 12.7 cm diameter incompressible air jet has been investigated through phase-locked measurements at three streamwise stations. Phase averages have been obtained from 200 realizations of X-wire (time-series) data after these are optimally time-aligned with respect to one another through an iterative process of maximization of cross-correlation of individual realizations with the ensemble average. Realizations that are grossly out of alignment owing to turbulence-induced distortions have been rejected; the rejection ratio increases with increasing radial position. Data include phase-average time series of background turbulence intensities, coherent and background Reynolds stresses, vorticity and intermittency at different transverse positions. Spatial distributions of these properties over the extent of the spot have been presented as contour maps. The computed pseudo-stream-functions have been compared with the phase-average streamlines inferred from the measured distributions of the velocity vector. Comparison with the phase-average intermittency contours show that the pseudo-stream-functions are reliable and, even though the integration involved produces smoothed-out stream functions, are most useful in deducing the structure dynamics and its convection velocity.The spark-induced spot is an elongated large-scale coherent vortical structure spanning the entire thickness of the mixing layer, which moves downstream at a convection velocity of about 0.68Ue. The dynamics of the turbulent mixing layer spot, whose signature is buried in the large-amplitude background fluctuations, is much more complicated than that of the boundary-layer spot. The spot transports jet-core fluid outwards at its front and entrains ambient fluid primarily at its back; the outward-momentum transport dominates the inward transport. The Reynolds stress contribution by the spot structure is noticeably larger than that due to the background turbulence. The coherent structure vorticity is significantly modified by the structure-induced organization of the background Reynolds stress at the locations of ‘saddle points’ of the latter's distribution. The vorticity, intermittency and other turbulence measures, zone averaged over the extent of the spot, compare well with the time-average values, thus suggesting that the spark-induced ‘spot’ is probably not different from a naturally occurring large-scale coherent structure.

Research on the flame structure characteristics and NOx pathways of low swirl combustion

2021 ◽  
pp. 095441002110161
Author(s):  
Zhibo Cao ◽  
Yinli Xiao ◽  
Xin Ming ◽  
Wenyan Song
Keyword(s):  
Flow Field ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Flame Structure ◽  
Chemical Reactor ◽  
Flame Zone ◽  
Structure Characteristics ◽  
Swirl Combustion ◽  
Dynamics Simulations ◽  
Reactor Network

Low swirl combustion (LSC) technology has the advantage of ultralow NOx emissions, which is of great significance to the development of low-emission gas turbine engines in the future. To investigate the flow field and flame structure characteristics of LSC, a test rig of low swirl burner was designed and developed. Particle image velocimetry measurement results show that the location and size of the recirculation zone are different, and the flow field shows typical “W”- and “U”-shaped distributions under various swirling flow conditions. The self-luminous results of LSC show that there are three flame modes including attached flame, “W”-shaped flame, and “U”-shaped flame. To deeply understand NOx generation pathways, a chemical reactor network model was developed based on experiments and computational fluid dynamics simulations, and the effects of premixed gas components on NOx pathways were calculated by using Chemkin software. It was verified that the NOx production of the CH4 mixture mixed with H2, N2, and CO2 was mainly formed by the thermal NO pathway in the recirculation zone. The increase of H2 promotes the generation of NNH-type NOx in the main flame zone and inhibits prompt NOx. The addition of N2 and CO2 greatly promotes the generation of prompt NOx and at the same time inhibits NNH-type NOx. In addition, there is little prompt NOx formation in the post-flame zone.

Sign in / Sign up

Export Citation Format

Share Document