In many technical applications gas has to be injected at a dedicated location. The pressure ratio can be supercritical which means that speed of sound is achieved in the nozzle.
The following application shows the time-dependent methane injection into a vessel where the mass flow rate as a function of time was computed for different needle/needle seat geometries (only one geometry shown here). The pressure at the inlet and the outlet were kept constant.
The following figure shows the needle, the needle seat and the inlet and the outlet boundaries.
The flow field through the nozzle was monitored and is shown in the following video:
Due to the high pressure ratio shock waves have been observed downstream of the nozzle exit. A very fine mesh was used to resolve these shock waves.
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