刷式密封吹下效应诱发机理流固耦合数值研究

分析了刷式密封吹下效应理论模型,建立基于arbitrary Lagrange-Euler(ALE)流固耦合方法的刷式密封吹下效应三维瞬态数值模型,在验证数值模型准确性的基础上,分别研究了刷丝轴向、径向和截面变形特性,量化分析了刷丝径向吹下量,揭示了刷式密封吹下效应诱发机理。研究表明:刷式密封吹下效应会减小刷丝径向间隙,考虑吹下效应可以更加准确地计算泄漏量。刷式密封吹下效应是伴随刷丝扰动的非定常变形形式,刷丝自由端相比于后挡板径向中部和末端的刷丝截面,其吹下效应和刷丝扰动均较强。随着进出口压比的增加,刷式密封刷丝在具有更大径向吹下量的同时也伴随着更强的刷丝扰动,在研究工况下,2、3和4进出口压比下的刷丝束中部刷丝最大径向吹下量分别为0.004、0.010 mm和0.019 mm。刷丝具有一定的周向倾角和刷丝束区域的径向压力梯度是诱发刷式密封吹下效应的初始条件,且刷丝间的法向正压力和切向摩擦力会进一步影响吹下效应。增大刷丝周向倾角可以减弱刷式密封吹下效应。 

Numerical investigation on induced mechanism of blow-down effect of brush seals with fluid-structure interaction

The theoretical model of blow-down effect of brush seals was analyzed. The three-dimensional transient numerical model of blow-down effect of brush seals based on arbitrary Lagrange-Euler（ALE） fluid-structure interaction method was established. The axial, radial and sectional deflection characteristics of bristles were studied respectively. The radial blow-down displacements of bristles were analyzed quantitatively, and the induced mechanism of blow-down effect of brush seals was revealed. The results showed that the leakage can be calculated more accurately with consideration of blow-down effect, because the bristle radial clearance was reduced by blow-down effect. Blow-down effect of brush seals presented an unsteady deflection with bristle oscillation. Compared with bristle cross section in the radial middle and end position of backing plate, blow-down effect and bristle oscillation of bristle tip were stronger. Bristles had more radial blow-down displacements and stronger bristle oscillation with the increase of inlet-outlet pressure ratio. When the inlet-outlet pressure ratio was 2, 3 and 4, the maximum radial blow-down displacement of bristles in the middle of bristle pack was 0.004, 0.010 mm and 0.019 mm, respectively, under the studied condition. The initial condition for the bristles with a certain circumferential lay angle and the radial pressure gradient in bristle pack contributed to the induced blow-down effect, and blow-down effect was further influenced by the normal pressure and the tangential friction between bristles. Blow-down effect of brush seals can be weakened by increasing the circumferential lay angle.