Conditioned structure functions in turbulent hydrogen/air flames
Artikel i vetenskaplig tidskrift, 2022

Direct numerical simulation data obtained from two turbulent, lean hydrogen-air flames propagating in a box are analyzed to explore the influence of combustion-induced thermal expansion on turbulence in unburned gas. For this purpose, Helmholtz-Hodge decomposition is applied to the computed velocity fields. Subsequently, the second-order structure functions conditioned to unburned reactants are sampled from divergence-free solenoidal velocity field or irrotational potential velocity field, yielded by the decomposition. Results show that thermal expansion significantly affects the conditioned potential structure functions not only inside the mean flame brushes, but also upstream of them. Upstream of the flames, first, transverse structure functions for transverse potential velocities grow with distance r between sampling points more slowly when compared to the counterpart structure functions sampled from the entire or solenoidal velocity field. Second, the former growth rate depends substantially on the distance from the flame-brush leading edge, even at small r. Third, potential root-mean- square (rms) velocities increase with decreasing distance from the flame-brush leading edge and are comparable with solenoidal rms velocities near the leading edge. Fourth, although the conditioned axial and transverse potential rms velocities are always close to one another, thus, implying isotropy of the potential velocity field in unburned reactants; the potential structure functions exhibit a high degree of anisotropy. Fifthl thermal expansion effects are substantial even for the solenoidal structure functions and even upstream of a highly turbulent flame. These findings call for development of advanced models of turbulence in flames, which allow for the discussed thermal expansion effects.

Turbulent combustion

Helmholtz-Hodge decomposition

Thermal expansion

Structure functions

Författare

Vladimir Sabelnikov

ONERA Centre de Palaiseau

Andrei Lipatnikov

Chalmers, Mekanik och maritima vetenskaper, Förbränning och framdrivningssystem

Nikitin Nikolay

Moscow State University

F. E. Fernandez-Perez

King Abdullah University of Science and Technology (KAUST)

Hong Im

King Abdullah University of Science and Technology (KAUST)

Physics of Fluids

1070-6631 (ISSN) 1089-7666 (eISSN)

Vol. 34 8 085103

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Fundament

Grundläggande vetenskaper

Ämneskategorier

Strömningsmekanik och akustik

DOI

10.1063/5.0096509

Mer information

Senast uppdaterat

2022-08-19