scholarly journals Simulation of non-isothermal liquid sprays under large-scale turbulence

2021 ◽  
Vol 8 (2) ◽  
Author(s):  
A. Askarova ◽  
S. Bolegenova ◽  
Sh. Ospanova ◽  
N. Slavinskaya ◽  
A. Aldiyarova ◽  
...  
Keyword(s):  
Large Scale ◽  
Liquid Sprays ◽  
Scale Turbulence

scholarly journals Role of large-scale advection and small-scale turbulence on vertical migration of gyrotactic swimmers

2019 ◽  
Vol 4 (12) ◽  
Author(s):  
C. Marchioli ◽  
H. Bhatia ◽  
G. Sardina ◽  
L. Brandt ◽  
A. Soldati
Keyword(s):  
Vertical Migration ◽  
Large Scale ◽  
Small Scale ◽  
Scale Turbulence

Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method

2013 ◽  
Author(s):  
Scott Martin ◽  
Aleksandar Jemcov ◽  
Björn de Ruijter
Keyword(s):  
Turbulent Combustion ◽  
Large Scale ◽  
Reaction Rates ◽  
Moment Closure ◽  
Scalar Dissipation ◽  
Small Scale ◽  
Conditional Moment ◽  
Progress Variable ◽  
Conditional Moment Closure ◽  
Scale Turbulence

Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided. The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors.

A Novel Turbulent Aggregation Device for Flue Gas

2014 ◽  
Vol 955-959 ◽  
pp. 2425-2429 ◽  
Author(s):  
Yun Fei Li ◽  
Jian Guo Yang ◽  
Yan Yan Wang ◽  
Xiao Guo Wang
Keyword(s):  
Size Distribution ◽  
Flue Gas ◽  
Large Scale ◽  
Balance Model ◽  
Small Scale ◽  
Multiphase Model ◽  
Specific Performance ◽  
Particles Size Distribution ◽  
Scale Turbulence ◽  
Eulerian Multiphase Model

The purpose of this study is to construct a turbulent aggregation device which has specific performance for fine particle aggregation in flue gas. The device consists of two cylindrical pipes and an array of vanes. The pipes extending fully and normal to the gas stream induce large scale turbulence in the form of vortices, while the vanes downstream a certain distance from the pipes induce small one. The process of turbulent aggregation was numerically simulated by coupling the Eulerian multiphase model and population balance model together with a proposed aggregation kernel function taking the size and inertia of particles into account, and based on data of particles’ size distribution measured from the flue of one power plant. The results show that the large scale turbulence generated by pipes favours the aggregation of smaller particles (smaller than 1μm) notably, while the small scale turbulence benefits the aggregation of bigger particles (larger than 1μm) notably and enhances the uniformity of particle size distribution among different particle groups.

scholarly journals An overview of the effect of large-scale inhomogeneities on small-scale turbulence

2002 ◽  
Vol 14 (7) ◽  
pp. 2475 ◽  
Author(s):  
L. Danaila ◽  
F. Anselmet ◽  
R. A. Antonia
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Scale Turbulence

scholarly journals Observations of Turbulence in Free Atmosphere by Balloon-Borne Sensors

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3273
Author(s):  
Lesong Zhou ◽  
Zheng Sheng ◽  
Qixiang Liao
Keyword(s):  
Large Scale ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Sensor Data ◽  
Free Atmosphere ◽  
Height Range ◽  
High Latitude Region ◽  
Thorpe Scale ◽  
Scale Turbulence ◽  
Turbulence Parameters

In recent years, Thorpe analysis has been used to retrieve the characteristics of turbulence in free atmosphere from balloon-borne sensor data. However, previous studies have mainly focused on the mid-high latitude region, and this method is still rarely applied at heights above 30 km, especially above 35 km. Therefore, seven sets of upper air (>35 km) sounding data from the Changsha Sounding Station (28°12′ N, 113°05′ E), China are analyzed with Thorpe analysis in this article. It is noted that, in the troposphere, Thorpe analysis can better retrieve the turbulence distribution and the corresponding turbulence parameters. Also, because of the thicker troposphere at low latitudes, the values of the Thorpe scale L T and turbulent energy dissipation rate ε remain greater in a larger height range. In the stratosphere below the height of 35 km, the obtained ε is higher, and Thorpe analysis can only be used to analyze the characteristics of large-scale turbulence. In the stratosphere at a height of 35–40 km, because of the interference of sensor noise, Thorpe analysis can only help to retrieve the rough distribution position of large-scale turbulence, while it can hardly help with the calculation of the turbulence parameters.

Large Scale Turbulence Suppression Control for Direct Reduction of Aero-Optical Aberrations

2007 ◽  
Author(s):  
Fazlul Zubair ◽  
Aaron Freeman ◽  
Siarhei Piatrovich ◽  
Jennifer Shockro ◽  
Youssef Ibrahim ◽  
...  
Keyword(s):  
Large Scale ◽  
Direct Reduction ◽  
Optical Aberrations ◽  
Turbulence Suppression ◽  
Scale Turbulence

scholarly journals High-resolution large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere

2013 ◽  
Vol 13 (12) ◽  
pp. 31891-31932 ◽  
Author(s):  
R. Paoli ◽  
O. Thouron ◽  
J. Escobar ◽  
J. Picot ◽  
D. Cariolle
Keyword(s):  
Large Scale ◽  
Lower Stratosphere ◽  
Atmospheric Model ◽  
Large Eddy Simulations ◽  
Stratified Flows ◽  
Flow Topology ◽  
Upper Troposphere ◽  
Large Eddy ◽  
Scale Turbulence ◽  
The Impact

Abstract. Large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere (UTLS) are carried out and analyzed using the mesoscale atmospheric model Méso-NH. Different levels of turbulence are generated using a large-scale stochastic forcing technique that was especially devised to treat atmospheric stratified flows. The study focuses on the analysis of turbulence statistics, including mean quantities and energy spectra, as well as on a detailed description of flow topology. The impact of resolution is also discussed by decreasing the grid spacing to 2 m and increasing the number of grid points to 8×109. Because of atmospheric stratification, turbulence is substantially anisotropic, and large elongated structures form in the horizontal directions, in accordance with theoretical analysis and spectral direct numerical simulations of stably stratified flows. It is also found that the inertial range of horizontal kinetic energy spectrum, generally observed at scales larger than a few kilometers, is prolonged into the sub-kilometric range, down to the Ozmidov scales that obey isotropic Kolmorogov turbulence. The results are in line with observational analysis based on in situ measurements from existing campaigns.

scholarly journals Statistical Measurements of Dispersion Measure Fluctuations of FRBs

2021 ◽  
Vol 922 (2) ◽  
pp. L31
Author(s):  
Siyao Xu ◽  
David H. Weinberg ◽  
Bing Zhang
Keyword(s):  
Electron Density ◽  
Large Scale ◽  
Density Fluctuations ◽  
Clear Correlation ◽  
Dispersion Measure ◽  
Large Dispersion ◽  
Dispersion Measures ◽  
The Difference ◽  
Electron Density Fluctuations ◽  
Scale Turbulence

Abstract Extragalactic fast radio bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu & Zhang, but no clear correlation hinting toward large-scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM < 500 pc cm−3. A trend of nonconstant SF and nonzero correlation function (CF) at angular separations θ less than 10° is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at θ ≲ 10° can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of 100 Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.

A study of the role of radiative ignition in the propagation of large explosions

1983 ◽  
Vol 385 (1789) ◽  
pp. 373-387 ◽  
Keyword(s):  
Flame Front ◽  
Large Scale ◽  
Critical Energy ◽  
Flame Speed ◽  
Minimum Size ◽  
Absolute Minimum ◽  
Radiation Fluxes ◽  
Radiation Induced ◽  
Vapour Cloud ◽  
Scale Turbulence

We consider the hypothesis that the anomalously high rates of propagation of unconfined vapour cloud explosions are caused, or aggravated, by radiation-induced multi-point ignition due to small particles ahead of the main flame front. The mechanism by which loose agglomerates of fine fibres ignite at very low radiation fluxes is examined and the measured dependence of ignition lag on the level of radiation provides the basis for calculating maximum flame speed enhancement. It is shown that, for compact particles, there is an absolute minimum size for radiative ignition due to vaporization below the minimum critical energy and that fibrous aggregates are more likely to be raised and dispersed by convection than any solid particle capable of inducing ignition. Modelling the growth of such flames for various densities of igniting particles displays the development in time of a convoluted flame front with greatly increased surface area and rate of burning, resembling in appearance the consequences of large-scale turbulence. The effective flame speeds are of the order required to account for observed levels of damage, even when no other enhancement is considered; in fact the mechanism suggests that interaction with other proposed causes of flame speed enhancement is highly probable

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