推力室状态对其声学振型及其阻尼特性的影响

为确定工程中冷态条件下获得的推力室声学特性能否表征真实条件下的声学特性,研究了冷态无流动、热态气相流动和湍流两相燃烧三种状态下推力室声学振型及其阻尼特性。在推力室稳态流场中的有限区域施加数值定容弹,激发其具有多模态声学振型的大幅值压力振荡,采用衰减时间和半带宽来定量评价所激发的不同声学振型压力振荡衰减快慢,进而获得其阻尼特性。在相同过载比的数值定容弹激励下,在冷态条件下能激发包含更多声学振型压力振荡,且该振荡衰减时间更长,相同振型压力振荡衰减比热态条件下慢。在冷态条件下,一阶切向振型振幅最大,为最容易被激发声学振型;一阶纵向振型半带宽最小,为最难衰减的振型。在热态条件下,一阶纵向振型为最容易激发声学振型,也为最难衰减声学振型。从所激发的主要振型及其相对衰减的快慢来看,冷态条件下获得的声学特性能够表征真实条件下的推力室的声学特征。

Effects of thrust chamber conditions on its acoustic modes and their damping characteristics

In order to determine whether acoustic characteristics obtained in cold case in engineering can represent those in actual cases, acoustic modes and their damping characteristics of thrust chamber were investigated under three conditions: cold case without flow, hot case with flow and turbulent two-phase reactive case. High-amplitude pressure oscillations featured with multi-mode acoustic characteristics were excited by imposing numerical constant-volume bomb into a limited region at the steady flow in a thrust chamber. The damping rate of pressure oscillation of each acoustic mode was evaluated by decay time and half-power bandwidth, thereby damping capacity of each acoustic mode was obtained. Results showed more acoustic modes were excited in cold case than those in two hot cases. The decay times in cold case were longer than those in two hot cases. Moreover, pressure oscillation of each mode in cold case decayed slower than that of the corresponding mode in two hot cases. For the cold case, the amplitude of the first tangential mode was the greatest for the most inspirable acoustic mode. The half-power bandwidth of the first longitudinal mode was the smallest for the most difficult mode to be attenuated. For the two hot cases, the first longitudinal mode was the most inspirable acoustic mode with greatest amplitude and the most difficult mode to be attenuated with smallest half-power bandwidth. Judging from main acoustic modes excited by numerical constant-volume bomb as well as relative damping characteristics, investigation on acoustic performance of thrust chamber in the cold case was reasonable to reveal the acoustic performance under the real condition.