Investigation On The Unsteady Mechanisms Of Rim Seal Flow And The Control Methods Of Hot Gas Ingestion

With the increasing development of aircraft power,aero engines' traditional turbine design technology has been challenging to support the further improvement of engine performance.Therefore,the detailed design of turbine that considers multiple factors comprehensively has become a trend.The understanding and control of the unsteady characteristics of flow near rim seal to improve sealing efficiency have become a research hotspot,which is of essential value in both academic and engineering fields.The current paper investigates the high-pressure turbine front cavity in a certain type of turbofan engine using verified steady and unsteady CFD methods.The research objects including sealing effectiveness and unsteady flow characteristics of different rim seal structures under different working conditions.The current research involves pressure field,velocity field and sealing efficiency.A new rim seal structure,which means a new sealing air distribution method,is proposed,which intends to suppress the flow instabilities near rim seal to reduce hot gas ingestion and improve sealing efficiency.First,a simple axial rim seal model is simulated by verified RANS and URANS methods under three rotating speeds and three sealing flowrate conditions.The steady,unsteady time-averaged and transient results are compared and analyzed.Four essential parameters(sealing efficiency,swirl ratio,non-dimensional pressure coefficient along radial and circumferential direction)are investigated quantitatively.The differences between RANS and URANS methods are compared,the unsteady flow structure and pressure fluctuation at rim clearance and in disc cavity are obtained,and the gas ingestion mechanisms at high and low radial positions are explained respectively.Second,three different rim seal structures(axial,fish-mouth and double rim seal)are simulated by RANS and URANS methods.The four parameters mentioned above are studied quantitatively,and the differences in sealing effectiveness as well as unsteady flow characteristics between three sealing structures are analyzed.These differences explain why the complex sealing structure acquire higher sealing efficiency.Special focus goes to the "buffer cavity" formed by the sealing lips on rotating and stationary disk.The buffer and mixing effects of ingestion gas and sealing air are described.Third,based on the in-depth understanding of real flow conditions in aero engines,the current paper presents a new type of rim seal structure with circumferential-inclined auxiliary sealing holes in a high radial position.The sealing efficiency is improved by this redistribution of sealing air and optimized design of sealing air flow path.The mechanism of this new design method improving sealing efficiency is explained,and the influence of two important parameters(the intake angle of auxiliary sealing air and the sealing air distribution ratio)on sealing efficiency is studied.The conclusions obtained can strongly support the understanding of the complex flow mechanisms near rim seal structure,providing useful references for the design of a new rim seal structure,which gives possibilities to improve the rim seal efficiency as well as the whole engine efficiency.