Geometrical model of surface groove based on micro-segment combination for dry gas seal and its parameter influence

doi:10.11949/0438-1157.20210788

Abstract

Abstract:

To solve the problem that the existing dry gas seal surface groove type line equations are not strong enough in geometrical characterization ability and not unified in the geometrical parameter definition, a generalized logarithmic spiral groove geometrical model based on the combination of radial micro-segments to represent arbitrary shape lines is proposed. The generalized logarithmic spiral groove geometrical parameter definition is given, and the steady-state performance of the generalized spiral groove and the typical spiral groove dry gas seal under different pressure and rotating speed conditions, such as the opening force, film stiffness, and leakage rate, are compared. The research focuses on the influence of the two characteristic features, including the generalized spiral angle distribution and the circumferential deflection of profile line, on the performance of the dry gas seal, and the optimal shape of the generalized spiral groove is obtained based on different objective functions. The results show that the profile shape of the upstream side wall of the groove has a significant impact on various steady-state performance parameters, while the profile shape of the downstream side wall only has a significant impact on the leakage rate and film stiffness. The typical logarithmic spiral groove is exactly a kind of surface groove with strong hydrodynamic and hydrostatic effect. It is difficult to significantly increase the load-carrying capacity of the gas film by relying solely on profile optimization of the surface groove. However, optimization of the generalized helix angle distribution under low-pressure and high-speed condition, and proper design of the profile circumferential deflection under high-pressure and low-speed condition are expected to improve the film stiffness and stiffness-leakage ratio of dry gas seals.

Key words: dry gas seal, generalized spiral groove, micro-segment combination, film stiffness

摘要：

为解决现有干气密封端面型槽型线方程表征能力不强和结构参数定义体系不统一的问题，提出了一种基于径向微段组合以表征任意形状型线的广义对数螺旋槽结构模型。给出了广义对数螺旋槽结构参数定义体系，对比了不同压力和速度条件下广义螺旋槽与经典螺旋槽干气密封的开启力、气膜刚度和泄漏率等稳态性能，重点研究了广义螺旋角分布和型线周向偏转两个特征量对干气密封性能的影响，基于不同目标函数获得了广义螺旋槽的最优形状。结果表明：型槽上游侧壁型线形状对各项稳态性能参数均有显著影响，而下游侧壁型线形状仅对泄漏率和气膜刚度影响显著；经典对数螺旋槽是一种流体动静压效应很强的端面结构，单纯依靠型线优化难以使气膜承载力显著提高，不过在低压高速条件下优化广义螺旋角分布，在高压低速条件下合适设置型线周向偏转有望提高干气密封的气膜刚度和刚漏比。

关键词: 干气密封, 广义螺旋槽, 微段组合, 气膜刚度

CLC Number:

TH 117.2

Chen YU,Jinbo JIANG,Wenjing ZHAO,Jiyun LI,Xudong PENG,Yuming WANG. Geometrical model of surface groove based on micro-segment combination for dry gas seal and its parameter influence[J]. CIESC Journal, 2021, 72(10): 5294-5309.

于辰,江锦波,赵文静,李纪云,彭旭东,王玉明. 基于微段组合的干气密封端面型槽结构模型及其参数影响[J]. 化工学报, 2021, 72(10): 5294-5309.

Figures/Tables 18

Fig.1 Schematic diagram of some typical dry gas seal surface groove structure

Fig.2 Generalized logarithmic spiral groove dry gas seal and profile parameter definition diagram

Table 1 Discontinuous deflection and slotting angle of unidirectional generalized spiral groove

偏转角情况	型槽结构	槽根周向夹角θ_g
θ₁>0，θ₂<0		θ_h
θ₁<0，θ₂>0		θ_h(1-\|θ₂\|-\|θ₁\|)
θ₁<0，θ₂<0		θ_h(1-\|θ₁\|)
θ₁>0，θ₂>0		θ_h(1-\|θ₂\|)

Fig.3 Radial distribution of generalized spiral angle based on hyperelliptic curve

Table 2 The influence of generalized spiral groove structure parameters on the shape of groove

几何参数		形状演变
广义螺旋角分布	进口螺旋角β₁
	转折螺旋角β₂
	出口螺旋角β₃
	上游超椭圆系数n₁
	下游超椭圆系数n₂
极角分布	迎风侧偏角系数α₂
极角分布	背风侧偏角系数α₁

Table 3 Corresponding characteristic parameters of generalized spiral groove shape

型槽类型	型槽图例	广义螺旋角分布	周向极角分布	具体参数
流道等宽槽				β₁=β₂=β₃=15°； α₁=α₂=0；n₁=1, n₂=1
流道渐扩槽				β₁=10°, β₂=25°, β₃=40°； α₁=α₂=0；n₁=1, n₂=1
流道渐缩槽				β₁=40°, β₂=25°, β₃=10°；α₁=α₂=0；n₁=1, n₂=1
先扩后缩槽				β₁=10°, β₂=40°, β₃=10°；α₁=α₂=0；n₁=1, n₂=1
先缩后扩槽				β₁=40°, β₂=10°, β₃=40°；α₁=α₂=0；n₁=1, n₂=1
人字槽^[6]				β₁=15°, β₂=90°, β₃=165°；α₁=α₂=0；n₁=0.1, n₂=0.1
多翼槽				β₁=β₂=β₃=15°； α₁=0, α₂=0.5；n₁=1, n₂=1

Fig.4 Flow chart for solving gas film pressure and steady-state sealing performance of dry gas seal

Table 4 Operating conditions and structural parameter default values of dry gas seal

名称与单位	数值	名称与单位	数值
密封端面外径，r_o /mm	37.5	背风侧偏转角系数，α₁	0
密封端面内径，r_i/mm	29.5	迎风侧偏转角系数，α₂	0
螺旋槽数，N_g	12	气膜厚度，h₀/μm	3.0
周向槽宽比，δ	0.5	气体黏度， μ/(mPa·s)	0.0186
径向槽长比， γ₁	0.6	环境压力， p_a /MPa	0.10
上游槽长比，γ₂	0.5	内径侧压力，p_i/MPa	0.10
槽深， h_g/μm	5.0	外径侧压力，p_o/MPa	0.50
上游超椭圆系数，n₁	1.0	密封端面平均线速度，v/(m·s^-1)	100
下游超椭圆系数，n₂	1.0

Fig.5 The influence of the number of radial segments on the performance of generalized spiral groove seal

Fig.6 The influence of generalized spiral angle on the performance of generalized spiral groove seal

Fig.7 The influence of inlet spiral angle and outlet sprial angle on the steady-state performance of dry gas seals (β2=30°)

Fig.8 The influence of the hyperelliptic coefficient of upstream and downstream grooves on the steady-state performance of gas seals

Table 5 The sealing performance change rate corresponding to the characteristic parameters of the upstream and downstream grooves

密封性能	上游槽		下游槽
密封性能	β₁	n₁	β₃	n₂
开启力 F_o	5.48%	2.95%	1.45%	0.24%
泄漏率 q	6.42%	3.21%	6.77%	2.33%
气膜刚度 k_z	35.33%	10.70%	11.52%	4.00%

Fig.9 Performance parameter increment ratio of generalized spiral groove dry gas seal under different working conditions

Fig.10 Optimal structure of two spiral grooves under different objective functions and working conditions

Fig.11 Optimal structure of two spiral grooves under different objective functions and working conditions

Fig.12 The influence of circumferential deflection on the performance of dry gas seal at high speed and low pressure

Fig.13 The influence of circumferential deflection on the performance of dry gas seal at high pressure and low speed

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