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Jet in Crossflow Dispersion

In many industrial applications fuel is injected into a channel and transported downstream to inlet valves or burning chambers. There are two main goals for such applications from an engineering point of view:

1. The injected fuel (e.g. methane) should form a homogeneous mixture with the crossflow (typically air).

2. If the fuel injection is unsteady (like for piston engines) the time scale of the mixture process and gas transport should be as close to the activation time of the injection valve as possible. This ensures that the amount of fuel mass flow keeps synchronized with the cycle times of inlet valves or the ignition pulses.

Within a long term project on pulverized coal injection (PCI) with voestalpine Donawitz we investigated a particle jet in crossflow (see previous annual reports) with steady state boundary conditions. We now adapted our wind tunnel facility for pulsed jet experiments of a gas jet in crossflow. The idea was to implement a similar way of post processing like for the PCI project. This kind of data analysis allows a direct comparison of experimental results and CFD simulations to analyze temporal and spatial distribution of the injected gas. Instead of solid particles we used oil droplets as tracer particles.

The CFD simulations were done in OpenFOAM with the incompressible pimpleFoam solver and a LES turbulence model. The qualitative agreement of experimental results and CFD simulations is very good (Fig.1). The data processing method is robust enough to handle poor image quality and noise in the experimental results and delivers a very good quantitative agreement of the temporal and spatial gas dispersion (Fig.2).

Fig. 1: Example of high jet momentum case (experiment on the left, CFD simulation on the right)

Fig. 2: Temporal distribution of the mixing process of the injected fluid mass. The black lines mark the activation time (10ms) of the valve. (experiment on the left, CFD simulation on the right).

(Stefan Puttinger, Gijsbert Wierink)