Research On The Characteristics Of Flow And Heat Transfer In Rotor-stator Cavity Conjugated Mainstream With Sealing In Rim

In aeroengine air system,the cooling air is usually extracted from the compressor stage to turbine disk cavity with radical blow cooling.Too much cooling air leakage will reduce the average temperature of the hot gas and thus reduce the thermal efficiency of the engine.Therefore,the rim seal is usually installed between the rotor and stator disk to reduce the leakage of cooling air.Meanwhile,rim seal also plays a role in preventing the hot gas ingestion from mainstream into the turbine disk cavity.In this paper,the numerical,theoretical and experimental studies were carried out from two aspects: flow and heat transfer of the disk cavity,leakage and sealing characteristics of rim seal.In this paper,the influences of dimensionless secondary flow rate,rotating Reynolds number and rim structure parameters on the flow and heat transfer characteristics of rotor-stator disk cavity were obtained by using conjugate heat transfer numerical method.It was found that the relative scale of rotating Reynolds number and dimensionless secondary flow rate is the decisive factor to control the heat transfer of the rotating disk.Therefore,the Nusselt number of heat transfer in the disk cavity can be expressed as a function of "absolute velocity" of the fluid in the disk cavity.The one-dimensional model of the temperature distribution of the disk was established with the outer annular conjugate heat transfer conditions based on theoretical analysis method.The effects of dimensionless secondary flow rate,rotating/mainstream Reynolds number and rim structure parameters on rim seal leakage and sealing characteristics were obtained by using rotating2 D axisymmetric numerical method.It was found that both increasing rotating Reynolds number and increasing mainstream Reynolds number will reduce the sealing efficiency,but the influence of mainstream Reynolds number and rotating Reynolds number on sealing efficiency is fettered.For the sealing structure of single/double sealing rings,the inner ring rim seal structure and the bite rim seal structure were improved and designed respectively.The influences of dimensionless secondary flow rate,rotating/mainstream Reynolds number and guide vane structure parameters on rim seal leakage and sealing characteristics were explored by using periodic numerical method.It was suggested that there are two forms of external induced ingestion: The mainstream flow separate and decelerate at the trailing edge of guide vane and increase the pressure thus inducing host gas ingestion;the mainstream flow impact the outer edge of the disk with velocity stagnation pressure thus inducing host gas ingestion.Because of the radial positive pressure gradient in the disk cavity,the hot gas is concentrated on high radius but not deep into low radius with externally induced.A theoretical model for hot gas ingestion was established on the basis of refining the previous results.By assuming that the radial pressure gradient caused by the disk-cavity swirl is linear,three key factors affecting ingestion were obtained: internal and external pressure difference,secondary swirl pressure and mainstream swirl pressure;furthermore,assuming that the secondary swirl pressure is axial linear distribution,after obtaining the velocity profile by solving the pressure difference between the inside and outside of the seal ring,the ingress flow rate,the egress flow rate and the minimum flow rate were derived considering the tangential inhomogeneity of the mainstream.Besides,a program for predicting sealing efficiency is compiled in C language.Finally,the leakage characteristics of four kinds rim seal structures were studied experimentally,and the mainstream was heated.The results show that: The flow rate coefficients of four kinds of rim seals increase with the increase of secondary flow pressure ratio.With the increase of the rotating Reynolds number,the flow rate coefficients of four kinds of rim seals increase slightly.With the increase of the mainstream temperature,the secondary flow is heated by the heat transfer from the main flow through the disk,which increases the secondary flow temperature,increases the internal friction of the fluid and decreases the flow rate coefficients.This paper can provide technical guidance and application prospect support for advanced aeroengine air system design.