scholarly journals Simultaneous temperature, mixture fraction and velocity imaging in turbulent flows using thermographic phosphor tracer particles

2012 ◽  
Vol 20 (20) ◽  
pp. 22118 ◽  
Author(s):  
Benoit Fond ◽  
Christopher Abram ◽  
Andrew L Heyes ◽  
Andreas M Kempf ◽  
Frank Beyrau
Keyword(s):  
Turbulent Flows ◽  
Mixture Fraction ◽  
Velocity Imaging ◽  
Tracer Particles ◽  
Thermographic Phosphor

A Method to Obtain Planar Mixture Fraction Statistics in Turbulent Flows Seeded With Tracer Particles

2011 ◽  
Author(s):  
M. Pernpeintner ◽  
M. Lauer ◽  
C. Hirsch ◽  
T. Sattelmayer
Keyword(s):  
Turbulent Flows ◽  
Particle Density ◽  
Scattered Light ◽  
Mixture Fraction ◽  
Light Sheet ◽  
Piv Measurements ◽  
Experimental Procedure ◽  
Free Jet ◽  
Tracer Particles ◽  
Inversion Procedure

We present a new method to obtain the mixture fraction probability density functions (PDF) of turbulent mixing in planar sections of a flow field which is seeded with PIV tracer particles. We derive a model how the observed scattered light obtained locally in a laser light sheet results from the local mixture fraction PDF and the particle density PDF. From this model we develop an analytical as well as a numerical inversion procedure that allows the deconvolution of the mixture fraction PDF from the light intensity PDF using the measured seeding PDF. We explain the experimental procedure necessary to apply the new technique on the example of a turbulent free jet. The results of both the analytical and the numerical method are compared and the method is then validated against the literature data. Since the method seems applicable whenever PIV measurements can be made it bears high potential for combustor development as it allows to obtain mixing statistics using basically the same measurement hardware.

A General Closure Model for the Time-Averaged Radiative Transfer Equation in Turbulent Flows

2010 ◽  
Author(s):  
Pedro J. Coelho
Keyword(s):  
Radiative Transfer ◽  
Turbulent Flows ◽  
Radiation Intensity ◽  
Transfer Equation ◽  
Radiative Transfer Equation ◽  
Mixture Fraction ◽  
Joint Probability ◽  
Turbulent Fluctuations ◽  
Proposed Model ◽  
Local Properties

The time-averaged form of the radiative transfer equation (RTE) includes emission and absorption correlations that need to be modeled. There is no general formulation to estimate the absorption coefficient-radiation intensity correlation, which is generally neglected (optically thin fluctuation approximation–OTFA). Here, a model to compute this correlation, as well as the other correlations in the time-averaged form of the RTE, is described. The formulation is based on the solution of two additional differential equations. The unclosed correlations in these equations are estimated assuming that the joint probability density function (pdf) of the radiation intensity and mixture fraction is a two-dimensional clipped Gaussian distribution. The model is applied to a turbulent jet diffusion flame, and a preliminary assessment of the model is reported. It is shown that fluctuations of the radiation intensity, caused by turbulence, imply the existence of a correlation between the radiation intensity and local properties. The assumption of the shape of the joint pdf of mixture fraction and radiation intensity yields satisfactory predictions if the turbulent fluctuations are moderate, but becomes inaccurate near the flame edge where turbulent fluctuations are very large. Nevertheless, the present results suggest that the proposed model may yield better predictions than the OTFA.

Frequency spectra of reactant fluctuations in turbulent flows

1993 ◽  
Vol 246 ◽  
pp. 489-502 ◽  
Author(s):  
George Kosály
Keyword(s):  
Turbulent Flows ◽  
Cross Correlation ◽  
Mixture Fraction ◽  
Spectral Characteristics ◽  
Mixing Layer ◽  
Correlation Coefficients ◽  
Frequency Spectra ◽  
Fast Chemistry ◽  
Limiting Values ◽  
Intermediate Rate

Bilger, Saetran & Krishnamoorthy (1991) give measured values of the variance, cross-correlation coefficient, autospectra, coherence and phase shift of the reactant concentration fluctuations for an irreversible second-order reaction in an incompressible turbulent scalar mixing layer. The present paper approaches the interpretation of the measured data by evaluating the above quantities in the frozen (slow) and equilibrium (fast) chemistry limits. We assume that the limiting values bracket the corresponding intermediate rate data.The analysis leads to values that correspond with the measured variances and correlation coefficients. The paper offers simple procedures for experimenters to evaluate the fast chemistry limit of the spectral characteristics from the measured mixture fraction fluctuations. The investigation of the limiting spectra suggests that, in the frequency region considered in the Bilger et al. measurements, the shape of the autospectrum is quite insensitive to the chemistry rate. The cross-spectrum is much more sensitive to the chemistry than the autospectrum. The analysis predicts correctly that the coherence decreases with increasing frequency while the phase stays equal to π until the decrease of the coherence leads to indeterminate phase results.

scholarly journals Three-dimensional temperature and velocity measurements in fluids using thermographic phosphor tracer particles

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Moritz Stelter ◽  
Fabio J. W. A. Martins ◽  
Frank Beyrau ◽  
Benoît Fond
Keyword(s):  
Gas Flow ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Fluid Temperature ◽  
Velocity Measurements ◽  
Tomographic Piv ◽  
Tracer Particles ◽  
Thermographic Phosphor ◽  
Wide Range ◽  
Ratio Imaging

Many flows of technical and scientific interest are intrinsically three-dimensional. Extracting slices using planar measurement techniques allows only a limited view into the flow physics and can introduce ambiguities while investigating the extent of 3D regions. Nowadays, thanks to tremendous progress in the field of volumetric velocimetry, full 3D-3C velocity information can be gathered using tomographic PIV or PTV hence eliminating many of these ambiguities (Discetti and Coletti, 2018; Westerweel et al., 2013). However, for scalar quantities like temperature, 3D measurements remain challenging. Previous approaches for coupled 3D thermometry and velocimetry combined astigmatism PTV with encapsulated europium chelates particles (Massing et al., 2018) or tomographic PIV with thermochromic liquid crystals particles (Schiepel et al., 2021). Here we present a new technique based on solid thermographic phosphor tracer particles, which have been extensively used for planar fluid temperature and velocity measurements (Abram et al., 2018) and are applicable in a wide range of temperatures. The particles are seeded into a gas flow where their 3D positions are retrieved by triangulation from multiple views and their temperatures are derived from two-colour luminescence ratio imaging. In the following, the experimental setup and key processing steps are described before a demonstration of the concept in a turbulent heated jet is shown.

scholarly journals Lagrangian Statistics of Heat Transfer in Homogeneous Turbulence Driven by Boussinesq Convection

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 127
Author(s):  
Jane Pratt ◽  
Angela Busse ◽  
Wolf-Christian Müller
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Turbulent Flows ◽  
Statistical Approach ◽  
Homogeneous Turbulence ◽  
Turbulent Convection ◽  
Clear Trend ◽  
Tracer Particles ◽  
Non Gaussian ◽  
Natural Settings

The movement of heat in a convecting system is typically described by the nondimensional Nusselt number, which involves an average over both space and time. In direct numerical simulations of turbulent flows, there is considerable variation in the contributions to the Nusselt number, both because of local spatial variations due to plumes and because of intermittency in time. We develop a statistical approach to more completely describe the structure of heat transfer, using an exit-distance extracted from Lagrangian tracer particles, which we call the Lagrangian heat structure. In a comparison between simulations of homogeneous turbulence driven by Boussinesq convection, the Lagrangian heat structure reveals significant non-Gaussian character, as well as a clear trend with Prandtl number and Rayleigh number. This has encouraging implications for simulations performed with the goal of understanding turbulent convection in natural settings such as Earth’s atmosphere and oceans, as well as planetary and stellar dynamos.

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