DNS and Combined Laser Diagnostics of Turbulent Combustion

Abstract

With the developments of computer technologies, three-dimensional direct numerical simulations (DNS) of turbulent combustion have been realized with a detailed or reduced kinetic mechanism. The 3D DNS gives detailed information about turbulent flames, while there are few experimental techniques which have high accuracy enough to compare with DNS. In this paper, after showing summary of recent DNS of turbulent premixed flames, newly-developed laser diagnostics are presented. Simultaneous CH-OH planar laser induced fluorescence (PLIF) and stereoscopic particle image velocimetry (PIV) are used to investigate the local flame structure of the turbulent premixed flames. From CH-OH PLIF and PIV measurements, flame fronts are identified, and the curvature of the flame front and the tangential strain rate at the flame front are evaluated. The experimental results are compared with 3D DNS of hydrogen-air and methane-air turbulent premixed flames. The flame displacement speeds in turbulent premixed flames have been measured directly by the CH double-pulsed PLIF. Since the time interval of the successive CH PLIF can be selected arbitrarily, both of the large scale dynamics and local displacement of the flame front can be obtained. As an application of laser diagnostics for development of high-efficient and low-emission combustors, reconstruction of 3D flame structure is shown by using multiple-plane OH PLIF.

Extended LES-PaSR model for simulation of turbulent combustion

“…The concept is based on the ideas of Chomiak [16,17], later re¦ned by Magnussen and Ertesv' ag [13,18], which, in turn, are based on Batchelor and Townsend [19], suggesting that at high Re numbers, turbulent ¦ne structure is not uniformly distributed but concentrated in small isolated regions, whose volume is a small fraction of the total volume. This has recently been veri¦ed by DNS in nonreactive [20] and reactive [21,22] §ows.…”

“…Recent DNS of combustion (at moderate Re and Da numbers) (see, e. g., [21,22]) show a similar organization of the §ow, with ¦ne-structure vortices at the §ame being essentially parallel to the §ame whereas those behind the §ame are mostly perpendicular to the §ame. Figures 1a and 1b show the results in terms of vorticity and heat release structures from DNS of planar §ame propagation in homogeneous istotropic turbulence from Tanahashi et al [22]. The regions of high heat release and volumetric expansion are typically found to exist in tubular and sheet-like structures, distributed between the high and low intensity vortical regions bracketing the §ame.…”

“…Based on the relationship between ψ * i , ψ 0 i , and " ψ i and the nature of Eqs. (5) and (6), it becomes evident that ' [16,17], experimental (see, e. g., [35]), and computational (see, e. g., [21,22]) observations suggest that most exothermal reactions mainly occur in the ¦ne structures (see Fig. 1).…”

Numerical simulation of a backward-facing step combustor using reynolds-averaged navier–stokes / extended partially stirred reactor model

“…Later, this model has been re¦ned in [710]. The spatial no uniformity of the turbulent ¦ne structures has been veri¦ed by a direct numerical simulation in nonreactive [16] and reactive [17,18] §ows. The organization of the paper is as follows: the RANS/EPaSR model is presented in section 2.…”

Chemiluminescence Measurements of Laminar Premixed Ethylene/Air Flame at Low Pressure

“…Laser diagnostic techniques such as PLIF and CARS are widely used in combustion field (9) . But it is difficult to employ these techniques for practical scramjet, mainly because of the harsh working environments such as vibration and noises in scramjet experiments.…”