Reactive front propagation in turbulence

The relation between the propagation velocity of a thin flame and the turbulence intensity of the ambient flow is largely debated in the literature, giving rise to various parametrisations (e.g. [1-5]).

According to Damk ̈ohler’s analysis [1], based on the Huygens propagation model, a flame front propagates with a constant normal velocity even when wrinkled by turbulence. However, experiments using exothermic combustion reactions deviate from this model. The analysis of these experiments is complicated by the intermingling of turbulent and thermal effects, limiting potential improvement of the flame propagation parameterisation.

To test and improve Damk ̈ohler’s original theory, an autocatalytic chemical reaction is extensively studied experimentally and numerically. Analogous to a combustion reaction, it produces a thin reactive front separating the reactants from the products in an aqueous medium. Yet, this autocatalytic front does not show significant compressibility or thermal effects, and propagates at a much smaller velocity, hence facilitating metrology.  Accordingly, it allows to quantify the specific influence of turbulence on the speed and shape of the front in a refined framework.

In our experimental set-up, turbulence is generated by a system of oscillating grids establishing a homogeneous and isotropic turbulence in a closed water tank. Coupled measurements of PIV and LIF allow to follow, simultaneously, the velocity field and the propagation of the front.

In this presentation, the characteristics of the grid turbulence as well as the laminar propagation of the chemical reaction are first discussed and an estimated propagation law including the influence of chemical kinetics along with turbulence and its limitations are analyzed.

References

[1] Damköhler, G. Turbulence's influence on flame speed (1912).

[2] Schelkin K.I., Zhur. Techn. Fiz. 520 (no. 1110) (1943).

[3] Clavin, P. & Williams. F. A. Theory of premixed-flame propagation in turbulence (1979).

[4] Klimov, A.M. Interplay of hydrodynamics and chemistry in turbulent flames (1983).

[5]Gülder, ̈O. L. Turbulent flame propagation models for combustion regimes (1991).