1+1/2对转涡轮高压动叶叶顶间隙变化规律及影响作用

Investigation on the Tip Clearance Variation of the High Pressure Rotor Blade of a Vaneless Counter-Rotating Turbine

为阐明1+1/2对转涡轮高压动叶叶顶间隙高度在变工况时的变化规律,以涡轮流场和高压动叶为整体进行气热双向耦合计算,根据所得温度场对叶片进行热弹单向耦合计算,获取了叶片形变量。不同于常规亚音速涡轮动叶的间隙变化规律,1+1/2对转涡轮高压动叶在较高转速和膨胀比的工况范围内,随着膨胀比降低,前缘间隙高度保持不变,而尾缘间隙高度以二次曲线规律减小。这是由于该工况范围内高压动叶流场展向全超音堵塞,喉道上游流场不受膨胀比变化影响,下游流场的温度随膨胀比减小而升高。相应地,叶片喉道前部温度不变、后部温度升高,导致前缘叶高不变、尾缘因热膨胀伸长。为避免尾缘间隙减小引起碰磨,根据叶片尾缘形变特点增大了设计点的尾缘间隙高度,导致设计工况时叶片后部间隙泄漏流射流速度增大、剪切作用增强,泄漏流流量和损失增加。为保证工作安全的同时提高涡轮效率,有必要发展前、尾缘叶顶间隙独立控制方法,使变工况时前、尾缘的叶顶间隙高度皆在合理范围内。

In order to illuminate the tip clearance variation of the high pressure rotor blade of a vaneless counter-rotating turbine at off-design conditions, the fluid region and the solid region are taken as one single domain to calculate the temperature distribution with aero-thermal interaction simulation, and then the blade deformation is gained by thermal-elastic interaction simulation. At conditions with high rotating speed and expansion ratio, as the expansion ratio decreases, the blade tip clearance height at leading edge remains unchanged, and that at trailing edge shows a quadratic decrease, differing from the blade tip clearance variation of a conventional subsonic turbine. The reason is that the flow of the high pressure rotor is transonic and choked at those conditions, leading to that the fluid and solid temperature upstream of the throat is not affected by the varied expansion ratio, and that downstream of the throat increases as the expansion ratio decreases. The blade height at leading edge keeps constant, and that at trailing edge rises due to thermal expansion. A larger blade tip clearance height at trailing edge is designed at the design condition to account for the blade deformation, resulting in the larger outflow velocity and the stronger shear strength of the tip clearance leakage flow. More tip clearance leakage flow and more flow losses are generated. In order to improve the turbine performance with safety, it is necessary to develop a method to control the blade tip clearance height at leading edge and trailing edge respectively and keep the tip clearance height reasonable at off-design conditions.