MODAL TRANSITIONS IN ROTATING DETONATION ROCKET ENGINES

Various modal transitions within a rotating detonation rocket engine (RDRE) are investigated in detail within this experimental study. Using direct high-speed visible imaging along with a recently developed processing technique, detonation mode transition events are captured and analyzed with a focus on quantifying the unsteady wave propagation behavior during a modal shift. Specifically, three transition types are discussed including a rotational direction reversal where the number of waves is held constant, an increase in the number of detonation waves, as well as a decrease in the number of waves. The rotational direction reversal exhibits intermittent counter-propagating wave behavior, which eventually results in the opposing set of waves overtaking the dominant set. The ascending and descending modal transitions are attributed to significant galloping-type detonation propagation that grows in severity for the descending shifts and decays during the ascending transitions. In general, the exponential growth/decay rate alpha(avg,pk) of the angular separation associated with the wave pairs delta theta is larger for the ascending transitions than descending, where the higher wave mode is more stable (i.e., delta theta' averages 8 degrees for the three-wave mode and 39 degrees for the two-wave mode). Also, the ma vi mu in peak-to-peak delta theta' amplitude for the wave pairs separating the threshold between the two- and three-wave modes is on average 135-138 degrees and U-wv(1)/(U) over bar (wv) equals 24% for these two transition types. In total, this work provides notable insight into modal behavior that can affect the stability of RDRE's.