Prof. Jochen Fröhlich , Prof. Wolfgang Rodi , Prof. Ulrich Maas, Dr. Ping Wang, Dipl.-Ing. Manuel García-Villalba
LES of variable density turbulent axisymmetric jets
The turbulent flows with variable density exist widely in nature as well as in technical devices. Unlike the extensively studied turbulent flows with constant density, variable density turbulent flows are less well understood. The ability to predict the turbulent mixing in these variable density flows is vital for the modeling of the flow dynamics, and it is also a prerequisite for predicting the turbulent combustion. In order to perform a detailed validation of the in-house Finite Volume code LESOCC2C which is developed for simulating turbulent combustion, three cases of variable-density turbulent round jets discharging from a straight circular pipe into a weakly confined low-speed co-flowing air stream are simulated with LESOCC2C. The density ratios considered are 0.14 [Helium/air], 1.0 [air/air] and 1.52 [CO2/air], with Reynolds numbers of 7000, 21000 and 32000, respectively. Detailed comparisons of the statistics show good agreement with the corresponding experiments. The coherent structures of the three jets are also investigated by visualization of the iso-surface of pressure fluctuations and vorticities.
Fig. 1. Sketch of the computational domain.
Fig. 2. Iso-surfaces of pressure fluctuation, coloured by instantaneous streamwise velocity.
Fig. 3. Instantaneous mass fraction field. Back to top
DNS of laminar Bunsen flame
A one-week workshop was hold in Technical University of Dresden during 21st to 25th, January 2008. The collaboration among projects A5, A6 and B8 aims to jointly work on issues of turbulent premixed flames and in particular on the modeling of the flame profiles in a hierarchical way. Participants are: Prof. Jochen Fröhlich, Dr. Andreas Class, Dr. Ping Wang, Dr. Mickael Lecanu and Christian Bruzzese. According to work plan of the workshop, a laminar Bunsen premixed flame is computed by Dr. Ping Wang with LESOCC2C using direct numerical simulation (DNS). The chemistry is a 2-step scheme for lean CH4/air premixed flame. This computational result provides a quantitative database, which is being processed by Dr. Christian Bruzzese (A5). In next step, the hierarchical model will be implemented in LESOCC2C with G-equation model.
Fig. 1. Contours of flow variables: a) temperature, b) reaction progress rate, c) CO mass fraction, and d) u-velocity. Back to top
LES of turbulent swirling lean-premixed flame
The turbulent lean premixed flame propagating in an experimental burner (from project C1) is being studied, with large-eddy simulation (LES) employing the Thickened-Flame (TF) model for the reacting species. To simulate the lean premixed methane/air combustion, a two-step chemical scheme is used, which takes into account six species (CH4, O2, CO2, CO, H2O and N2) and two reactions:
CH4 1.5 O2
CO 2 H2O
CO 0.5 O2
Up to date, some preliminary results are obtained and shown in below. More computations are being performed for steady inflow cases as well as for oscillating inflow cases.
Fig. 1. Left: Instantaneous contours of the streamwise velocity u, right; reaction progress rate of reaction:
CH4 1.5 O2
CO 2 H2O
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Fig. 2. Snapshot of the instantaneous flame front (iso-surface of temperature T=900 K)