Abstract
The flowfield inside the second solid stage of the European launch vehicle VEGA is
simulated with a full 3D unsteady flow solver in order to characterize the unsteadinesses,
aero-acoustics and dynamics loads resulting from the growth of complex vorticity patterns
in the internal flow of the aft-finocyl solid rocket motor. The analysis considers different
configurations during the firing of the solid stage: the first one corresponds to an advanced
stage of combustion, when the aft-part of the propellant grain is almost completely burnt
out and the aft-end cavity is almost empty of propellant; the second one corresponds to
an early stage of combustion, with a large burning surface and a small internal volume
available for the flow. The first configuration is computed for different motor geometrical
conditions: a symmetric case, a case with an imposed small angle of nozzle gimbaling and
a case with an imposed propellant grain offset with respect to motor assembly. The second
configuration is analyzed considering a small angle of nozzle gimbaling. The rotation of the
gimbaled nozzle, as well as the propellant grain offset are imposed in such a way to remove
any symmetry in the motor geometry.
The motor configuration advanced into the firing shows the presence of low-level limit
cycle oscillations of the flowfield at high frequency, resulting into the generation of lateral
force oscillations of the order of one percentage of the generated thrust. This peculiar
behavior is not altered by the perturbation of the motor geometry due to the imposed
nozzle gimbaling; whereas it is slightly modified in terms of lower characteristic frequencies
and lower amplitude of the oscillations, for the case with the imposed propellant grain
offset. The presence of such flowfield fluctuations is caused by the onset of unstable sound
generating vortical structures along the motor axis, that produce pressure fluctuations and
that are coupled with acoustic waves. The motor configuration early into the firing, instead,
does not show any significant of flow instability.
Anno
2014
Tipo pubblicazione
Altri Autori
A. Di Mascio
E. Cavallini
B. Favini
A. Neri
E. Cavallini
B. Favini
A. Neri
Titolo Volume
Proceedings of 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference