Flow Fields Study And Rotordynamic Analysis Of Labyrinth Seals

Labyrinth seals are widely used in the turbomachinary, for the virtues of stability, simple structure, and low maintenance costs. But some problems exist too, such as a larger leakage, which decrease the unit's efficiency. At some conditions it can cause vibration, which affects the unit's operating. In order to decrease the leakage and avoid the emergence of vibration, the influences of seals'geometries to leakage are investigated, and the shape of seals'cavity is improved. At last, rotor dynamic coefficients are studied.FLUENT , a popular CFD software, is used for the numerical simulation of flow fields and calculation of rotor forces. By the simulation of sudden-expansion flow, single cavity seal and two cavity seal, results are gained and then compared to experiment data or semi-empirical equation, which shows a good accordance. Based on these works, flux coefficient is calculated at different structure dimensions, such as tooth height, tooth distance, tooth width, tooth clearance to stator, and different tooth shapes are considered too. The study shows that the flux coefficient increase linearly with the increase of clearance and decrease with the increase of tooth distance. The leakage becomes smaller when the width of tooth tends to zero or with a sharp angle on the tooth tip. According to the numerical simulation result, both of the tooth shape and cavity shape are improved, which decreases the leakage evidently. Then three-dimensional flow field of labyrinth seals are simulated, and the influences of rotor's eccentricity, rotating speed, inlet circumferential velocity to flow field are analyzed.For the particularity of labyrinth seal, the rotordynamic coefficients are difficult to measure by experiment. Recently the two control volume model is used often, which is created by Childs, but this model are just suited to straight through seals, it is not appropriate when tooth with slop or interlocking tooth is concerned. While CFD method solves these problem, and the details of flow fields can be got. In this study, the scheme mentioned by J. Jeffery Moore and Y. Hsu is used, which assume the rotor whirls along a circle, and the radius is the rotor's eccentricity, this action is deal with by rotating reference frame in FLUENT. The influences of rotating speed, pressure drop and inlet circumferential velocity to rotordynamic coefficients are investigated. The results show that a reverse inlet swirl can enhance the rotor's stability.At last, the develop trend of labyrinth seal design is discussed, and the shortage of current rotordynamic coefficients'calculating method,including the error caused by the assumption of rotor's whirl orbit, while this can be solved by using the skill of sliding mesh or moving mesh. The coupling process of rotordynamic force and rotor's displacement can be simulated by the secondary develop of the CFD software.