An Experimental Investigation of the Turbulence Structure of a Lifted H2/N2 Jet Flame in a Vitiated Co-Flow

Abstract

Measurements of mean velocity components, turbulent intensity, and Reynolds shear stress are presented in a turbulent lifted H 2 /N 2 jet flame as well as non-reacting air jet issuing into a vitiated co-flow by laser doppler velocimetry (LDV) technique. The objectives of this paper are to obtain a velocity data base missing in the previous experiment data of the Dibble burner and so provide initial and flow field data for evaluating the validity of various numerical codes describing the turbulent partially premixed flames on this burner. It is found that the potential core is shortened due to the high ratio of jet density to co-flow density in the non-reacting cases. However, the existence of flame suppressed turbulence in the upstream region of the jet dominates the length of potential core in the reacting cases. At the centreline, the normalized axial velocities in the reacting cases are higher than the non-reacting cases, and the relative turbulent intensities of the reacting flow are smaller than in the non-reacting flow, where a self-preserving behaviour for the relative turbulent intensities exists at the downstream region. The profiles of mean axial velocity in the lifted flame distribute between the non-reacting jet and non-premixed flame both in the axial and radial distributions. The radial distributions of turbulent kinetic energy in the lifted flames exhibit a change in distributions indicating the difference of stabilisation mechanisms of the two lifted flame. The experimental results presented will guide the development of an improved modelling for such flames. Nomenclature r radial distance (mm) x axial distance from the burner exit (mm) d nozzle exit diameter (mm) u mean local fluid axial velocity (m/s) v mean local fluid radial velocity (m/s) U 1 co-flow velocity (m/s) U 0 jet velocity at nozzle exit (m/s) U excess fluid velocity (U = u − U 1 ) (m/s) U m the maximum value of U (m/s) u axial velocity fluctuation (m/s) 62 Z. WU ET AL. v radial velocity fluctuation (m/s) u vReynolds shear stress (m 2 /s 2 ) k turbulence kinetic energy, k = (u 2 + 2v 2 )/3 T mean local temperature (K) Q fluid flow rate (slm) b radial distance at which excess velocity is half value of U m (mm) s offset distance of U m from the real centre (mm) H liftoff height (mm) Y mole fraction TP thermal power (kJ/s) ρ density (kg/m 3 ) ReReynolds number equivalence ratio

RANS modelling of a lifted H2/N2 flame using an unsteady flamelet progress variable approach with presumed PDF

“…This paper is a contribution to UFPV modelling with presumed PDF in a RANS framework. In order to deal with realistic conditions while involving a small number of chemical species, we consider a steady lifted H 2 /N 2 turbulent jet flame in a coflow of hot products at atmospheric pressure (the vitiated co-flow burner developed by Dibble and co-workers), first measured at Berkeley university by Cabra et al [16,17] and later at Sydney university at different operating conditions [18,19]. This flame has mainly been modelled in a RANS framework using transported PDF methods with different mixing models [16,[20][21][22][23][24][25][26][27][28].…”

Simulation study on spray combustion mechanism of diesel–gasoline blend fuels

“…A PDF approach implemented with more detailed chemical models was again applied to calculate the detailed flame structure of turbulent lifted H 2 /N 2 jet flame in the Dibble burner by Masri et al [8], where it was found that the flame appears largely controlled by chemical kinetics and hence stressing the importance of chemical kinetics in this flow configuration and develop numerical indicators for identifying the behavior that the stabilization region of these flames undergo a transition from auto-ignition to premixed flame propagation. Soon afterward simulation by Cao and Pope [9][10][11] using the joint velocity-turbulence frequency-composition PDF method for a turbulent lifted H 2 /N 2 jet flame in a vitiated http co-flow gives better agreement with the measurements by Wu et al [5] than previous composition PDF calculations by Masri et al More recently a simulation using Conditional Moment Closure (CMC) by Patwardhan et al [12]shows a good prediction liftoff generally agrees with experimental data, as well as joint-PDF results and provides details of the conditional mean scalars in the mixture fraction space, and removes approximations associated with the molecular mixing model used in the PDF method. A combined Large Eddy Simulation-Conditional Moment Closure (LES-CMC) approach by Salvador and Andreas [13] allowed a clear distinction of different prevailing stabilization mechanisms was applied to Dibble burner and accurately predicts the competition between turbulence and chemistry during the auto-ignition process, the dynamics of turbulent flame propagation can be captured though the dynamics of the extinction process are not approximated well under certain conditions.…”

“…A large number of experimental data on temperature and component distribution of the H 2 /N 2 jet flame was accumulated. A laser doppler velocimeter was employed by Wu et al [5] to supplement the experimental data of velocity field of the burner. The testing perimeters are shown in Table 1.…”

“…The flame of blend fuel spray is a typical lift-off flame, and many researchers have investigated the structure of lifted flames to understand the mechanisms responsible for the lift-off phenomenon [3][4][5][6][7]. A PDF approach implemented with more detailed chemical models was again applied to calculate the detailed flame structure of turbulent lifted H 2 /N 2 jet flame in the Dibble burner by Masri et al [8], where it was found that the flame appears largely controlled by chemical kinetics and hence stressing the importance of chemical kinetics in this flow configuration and develop numerical indicators for identifying the behavior that the stabilization region of these flames undergo a transition from auto-ignition to premixed flame propagation.…”

Experimental study on multi-point autoignition characteristics and influence factors of diesel spray in a controllable active thermo-atmosphere

“…delay. At the same time, as the coflow temperature decreases, the Reynolds number of the coflow enlarges [21] . The penetration rate, Reynolds number, turbulent kinetic energy and turbulent dissipation of the coflow increase due to the decrease in the evaporation rate.…”