Experimental and Numerical Analysis of Cavity/Mean-Flow Interaction in Low Pressure Axial Flow Turbines

The increasing performance of modern aeroengines led the research towards the optimization of machine components not deeply analyzed in the past.In this context,the mechanisms driving the interaction process between the secondary flows evolving at the hub of low-pressure turbines with the rotor-stator cavity systems have been poorly investigated in the literature.In this work,an experimental and numerical analysis of the interaction between the endwall near wall flow and the leakage flow of a real cavity system is presented.The experimental results were carried out in the annular low-pressure axial flow turbine of the University of Genova.Experimental blade loading and pressure distributions into the cavity,as well as the measured total pressure loss coefficient,have been used for a proper validation of CFD results.Both steady and unsteady calculations were carried out through the commercial solver Numeca.Particularly,several numerical approaches have been tested into this work:RANS,Non Linear Harmonic(NLH),and URANS.The most promising CFD techniques have been firstly identified by comparison with experimental results and then systematically employed to extend the analysis of secondary flow-cavity flow interaction to positions and quantities not available from the experiments.Losses characterizing the mean flow-cavity flow interaction process will be shown to cover a great amount of the overall stage losses and should be properly accounted for the design of future optimized cavity configurations.

Aerodynamic and heat transfer performances of a highly loaded transonic turbine rotor with upstream generic rim seal cavity

In turbine disk cavity,rim seals are fitted between the stator and its adjacent rotor disk.A coolant air injected through the turbine disk cavity to prevent the ingress of mainstream hot gases.The purpose of this paper is to investigate numerically the effect of the upstream purge flow on the aero and thermal performances of a high pressure turbine rotor.The investigations are conducted on a generic rim seal cavity inspired from a realistic turbofan engine.Four purge fractions(PF)equal to 0.2%,0.5%,1.0%and 1.5%of the mainstream are considered.The simulations are done by solving the three-dimensional Reynolds averaged Navier-Stokes and energy transport equations.The results include the effect of the PF on the cooling effectiveness,the sealing effectiveness,the secondary flows with losses and the heat transfer behavior,within the cavity and across the rotor passage.The low PF of 0.2%provided a low cooling effectiveness,a moderate sealing effectiveness and minimum losses.The high PF of 1.5%gave a high cooling effectiveness,a best sealing effectiveness and maximum losses.The medium PF of 1.0%supplied a compromise between the aerodynamic and thermal design needs with good cooling and sealing efficiencies and a tolerable level of losses.