The Effect To The Boundary Of Low Pressure Turbine By The Potential Flow Coupled With The Wakes

Turbofan engines with large bypass ratios are used in modern civil aviation aircraft.The number of low-pressure turbine(LPT)stages and the number of blades are usually large in order to drive large-scale fans to obtain greater thrust.LPT have become an important factor limiting the thrust-to-weight ratio of aeroengines.There are two main ways to reduce the weight of the turbine under the premise of ensuring the efficiency of the low-pressure turbine.One is to reduce the number of blades and the number of stages.But the reverse pressure gradient on the suction side makes the laminar flow easier to separate as the blade load increases.The second solution is to shorten the blade row spacing and reduce the weight of aeroengines by reducing the weight of lowpressure turbine casings and low-pressure shafts.The potential flow generated by the downstream blades will spread to the upstream blade channel,enhancing the unsteadiness of the flow inside the turbine as the axial distance decreases.Focusing on the T106A blade profile,the effects of the upstream wake,downstream potential flow,and upstream wake coupled with downstream potential flow on the boundary layer of low-pressure turbine are respectively studied in this thesis.The CFX software was used to perform the LES numerical simulation.In addition,the experimental verification was completed by the low-speed cascade wind tunnel.Aiming at the aerodynamic problems in the design of high-load blades for low-pressure turbines,the following three aspects of work have been carried out:(1)The position and size of the separation bubbles at the trailing edge of the T106 A blade suction surface were studied under steady flow conditions.On this basis,the influence of the downstream potential flow simulated by the round bars on the upstream cascade channel is studied.The downstream potential flow has an important influence on the upper blade suction surface layer.Both the pressure gradient and the velocity of the boundary layer periodically fluctuate under the periodic sweep of the round bars,which affects the length,maximum thickness and reattachment position of the separation bubble at the trailing edge of the suction surface.(2)The effect of upstream wake sweep on the flow of the suction surface attached to the surface layer was studied.On the one hand,the streaks produced by the trailing edge of wake at the leading edge of the blade due to the "shearing and shadowing" effect were found,and the process of streak generation and development was analyzed.On the other hand,the wake center impacts the trailing edge of the suction surface and interacts with the separation bubble,triggering the wake-induced transition process.(3)On the basis of studying the separate effects of the downstream potential field and the upstream wake,the influence of the wake coupled potential flow on the boundary layer flow is studied.The transport process of the upstream wake is affected by the periodically changing pressure gradient driven by the downstream forces,and finally affects the interaction process of the wake and the boundary layer.The downstream potential flow affects the wake shape and the timing of the interaction between the wake and the boundary layer,as well as the wake induced transition process.The influence of the boundary layer flow on the loss is judged by analyzing the boundary layer shape factor and momentum thickness.