Experimental Verification for Acoustic Damping Enhancement by Gaps in Injector-Formed Baffles

The effect of baffle gaps on the damping enhancement of a liquid rocket engine combustor has been elucidated through a series of tests, which include cold acoustic tests under both atmospheric and simulated viscous conditions and simulated combustion tests. The injector-formed baffles, which consist of an array of protruded coaxial injectors, were found to have a much greater acoustic damping effect than conventional planar baffles. For several axial baffle lengths, an optimal acoustic damping capacitance has been achieved at a 0.1 ∼ 0.2 mm baffle gap. The reason there exists an optimal baffle gap is thought to be mainly due to the viscous dissipation at the surface of the injector-formed baffles. Consequently, the axial baffle length can be reduced by taking advantage of the optimal baffle gap, providing a possible solution to the thermal cooling problem persistent with the baffle. Moreover, these optimum characteristics can provide some guidelines for manufacturing and assembling of the baffled injectors in rocket combustors.