RANS Study of Hydrogen-Air Turbulent Non-Premixed Flames

Ischia, June, 27-30 - 2010
Figure 3 shows results performed with URANS simulations for the three different injection
velocities configurations. For each of them gravity effect was considered by comparing
simulations with the gravity force included (on the left of each couple) and not (on the right).
These first results can be summarized with three mean features:
flame length increases when the inlet velocity increases,
gravity field makes the flame shorter,
but this effect is more evident for low injection velocities.
Physics interpretation of this behavior can be found recalling Froude number definition and
considering that increasing inlet velocity means increasing initial momentum flux with
respect to buoyant forces (i.e. Froude number): flame length (associated with the momentum
flux) increases. The second feature can be interpreted intuitively: gravity force acts opposing
to the flow motion and the flame is strongly affected due to the low hydrogen density value.
4. Temperature and velocity fields
Thermal field analysis, predicted by URANS simulations, show a well anchored flame with
the combustion initially limited to the thin shear layer where hydrogen and air mix. A cold
zone (blue depicted) can be identified, where only fuel exists and is generally called inertial or
potential core. Maximum temperature is reached on the axis, on a location increasing as
velocity injection increases. Buoyancy effects are evidenced by the presence of external
vortices at low axial locations. Fig. 6 shows instantaneous temperature fields comparing the
case with gravity force included with the one in absence of gravity.
Fig. 4
Instantaneous temperature fields for the three different cases: on the left is depicted
the case with .
5. Flame – vortex interaction
An instantaneous iso-temperature color visualization of the computed flame (U H2 = 106 m/s, no
gravity) is shown in Fig. 5a. It should be pointed out that no artificial perturbations were intro-
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