Effects of baffle on the acoustic mode characteristics of liquid rocket engine combustion chambers
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摘要:
通过采用声学有限元法，求解带有平均流源项的亥姆霍兹方程，进而在考虑燃烧室高温、平均流场因素基础上分析了隔板结构参数对液体火箭发动机燃烧室声学模态特性影响规律。结果表明：增加隔板数目或长度，均会降低燃烧室1阶切向模态的特征频率；存在最佳隔板数目4，使燃烧室1阶切向模态阻尼率最大；而隔板长度越长，1阶切向模态声压波腹的分布面积越小，阻尼率越大；隔板型式对燃烧室1阶切向模态特性影响较小。
Abstract:The Helmholtz equation with the mean flow source term was solved by the acoustic finite element method. Then, on the basis of considering the high temperature and average flow field of the combustion chamber, the influence of baffle structure parameters on the acoustic mode characteristics of the liquid rocket engine combustion chamber was analyzed. The results showed that: increasing the number or length of baffle reduced the eigenfrequency of the first-order tangential mode of the combustion chamber; when the number of baffle was 4, the damping rate of the first-order tangential mode of the combustion chamber was greatest; the longer length of the baffle indicated the smaller distribution area of the first-order tangential mode acoustic pressure and the larger damping rate; the type of baffle had an insignificant effect on the first-order tangential mode characteristics of the combustion chamber.
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Key words:
- baffle /
- liquid rocket engine /
- combustion chamber /
- acoustic mode characteristics /
- Helmholtz equation
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图 1 RD-170发动机燃烧室自由四面体网格示意图
Figure 1. Schematic diagram of the free tetrahedral mesh of the RD-170 engine combustion chamber
图 2 燃烧室前3阶切向模态声压分布云图
Figure 2. Sound pressure contours of first three orders tangential mode on the combustion chamber
图 3 燃烧室前3阶切向模态特征频率随隔板数目的变化趋势
Figure 3. Trend of the first three orders of tangential mode eigenfrequencies in the combustion chamber with the number of baffles
图 4 燃烧室前3阶切向模态阻尼率随隔板数目的变化趋势
Figure 4. Trend of the first three orders of tangential mode damping rates in the combustion chamber with the number of baffles
图 5 不同隔板数目下燃烧室1T模态声压分布云图
Figure 5. Sound pressure contours of 1T mode in the combustion chamber for different number of baffles
图 6 不同隔板数目下燃烧室2T(1)模态声压分布云图
Figure 6. Sound pressure contours of 2T(1) mode in the combustion chamber with different number of baffles
图 7 不同隔板数目下燃烧室3T模态声压分布云图
Figure 7. Sound pressure contours of 3T mode in the combustion chamber with different number of baffles
图 8 燃烧室前3阶切向模态特征频率随隔板长度的变化趋势
Figure 8. Trend of the first three orders of tangential mode eigenfrequency in the combustion chamber with the length of baffles
图 9 燃烧室前3阶切向模态阻尼率随隔板长度的变化趋势
Figure 9. Trend of the first three orders of tangential mode damping rates in the combustion chamber with the length of baffles
图 10 不同隔板长度下燃烧室1T模态声压分布云图
Figure 10. Sound pressure contours of 1T mode in the combustion chamber with different length of baffles
图 11 不同隔板长度下燃烧室2T(1)模态声压分布云图
Figure 11. Sound pressure contours of 2T(1) mode in the combustion chamber with different length of baffles
图 12 不同隔板长度下燃烧室3T模态声压分布云图
Figure 12. Sound pressure contours of 3T mode in the combustion chamber with different length of baffles
图 13 隔板2、隔板3结构示意图
Figure 13. Schematic diagram of the structure of Baffle 2 and Baffle 3
表 1 RD-170发动机燃烧室几何结构参数[11]
Table 1. Geometrical parameters of the RD-170engine combustion chamber[11]
mm 参数 数值 燃烧室直径 380 燃烧室圆柱段长度 490 喉部直径 235.6 隔板高度 40 隔板厚度 18.7 隔板轮毂直径 143 喷嘴直径 17.5 
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表 2 RD-170发动机燃烧室平均流场参数[12]
Table 2. Average flow field parameters in the RD-170 engine combustion chamber[12]
参数 燃烧室 喷嘴 压力/MPa 24.55 27.0 温度/K 3676.1 687.7 比热比 1.2 1.33 摩尔质量/（g/mol） 24.21 31.91 密度/（kg/m3） 19.45 150.7 声速/（m/s） 1231.9 487.5 速度/（m/s） 326.9 93.4
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表 3 RD-170发动机燃烧室主要声学模态的特征频率及阻尼率
Table 3. Eigenfrequencies and damping rates of the main acoustic modes of the RD-170 engine combustion chamber
模态 频率/Hz 阻尼率/（rad/s） 1L 1405.1 602.4 1T 1874.5 383.6 1L1T 2614.2 616.1 2T(1) 2958 700.8 2T(2) 2963.7 690.6 3T 3622.5 1387.8
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表 4 不同隔板型式下燃烧室前3阶切向模态的特征频率
Table 4. Eigenfrequencies of the first three orders of tangential modes of the combustion chamber with different type of baffles
模态 隔板1 隔板2 隔板3 特征频率/Hz 特征频率/Hz 变化幅度/% 特征频率/Hz 变化幅度/% 1T 1874.5 1860.5 −0.8 1887.3 0.7 2T(1) 2958 3075.2 4.0 3118 5.4 2T(2) 2963.7 3083.7 4.0 3125 5.4 3T 3622.5 3613.5 −0.2 3845.1 6.1
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表 5 不同隔板型式下燃烧室前3阶切向模态的阻尼率
Table 5. Damping rates of the first three orders of tangential modes of the combustion chamber with different type of baffles
模态 隔板1 隔板2 隔板3 阻尼率/（rad/s） 阻尼率/（rad/s） 变化幅度/% 阻尼率/（rad/s） 变化幅度/% 1T 383.6 403.6 5.2 400.0 4.3 2T(1) 700.8 909.6 30.8 760.6 8.5 2T(2) 690.6 918.7 33 753.1 9.1 3T 1387.8 1400.3 0.9 1186.4 −14.5
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