The Design Of Blade Profile At High Exit Mach Number

Nowadays, under the background of improving thrust-weight ratio and thermalefficiency, the development of minimum stage for high pressure turbine is one ofthe trends for turbine. Taking the limit factors into consideration, like bladematerials, manufacturing processes and operating life, the only way to realize thesingle stage highly loaded turbine is probably to continuously improve the turbineoutlet Mach number.According to the difference in the form of cascade passage, the modernaviation turbine cascade can be divided into two kinds: convergent-divergent typeand convergent type. The highest Mach number in the flow field of practicalaero-engine turbine is usually in the range of1.2to1.3, according to relevantreferences, it is necessary to adopt using convergent-divergent form cascades toget a higher exit Mach number. However, it has a negligible influence to studyconvergent-divergent type cascade that researching the convergent type cascadeinto depth and finding the main reasons which cause greater losses with the higherexit Mach number.The present paper takes the above purposes as a starting point, and theresearch objects are the convergent form blade profile in the mid-diameter of anaero-engine as well as its modification convergent-divergent form bladeprofile. The study analyzes the two cascades through the evolution of the shockwave system, one-dimensional parameters, the total pressure loss the base pressureand so on. The specific main research content in this paper is listed as follows:First of all, this paper analyzes the basic flow field of convergent cascade atsubsonic, transonic and supersonic conditions, it is helpful to have a betterunderstanding the evolution of the shock wave and expansion wave systems. Thispaper also puts emphasis on studying the reason why convergent cascade can’tapply to high outlet Mach number condition from the perspective of loss es. Basedthe same blade profile, two-dimensional slice cascade and three-dimensional planecascade are respectively studied under the same boundary conditions and the gridnodes distribution(expect for the spanwise grid distribution).Secondly, This paper studies the effects of cascade geometry and workingparameters on the convergent cascades. Cascades geometrical parameters haschosen the parameters which have a greater impact on the airfoil near the trailingedge, including backward curved angle, trailing edge wedge angle, trailing edgerelative thickness. Cascades working parameters has chosen incidence angle as a research variable.In addition, this paper studies the variation of the convergent-divergentcascades’ properties with exit Mach number, and analyzes the cascade losses withdifferent back pressure. The backward curved angle has a critical influence on theflow field of convergent-divergent cascade, it is also studied in this paper.At last, this paper studies the effect of the ratio of inscribed circle diameter atthe cascade throat to the inscribed circle diameter at the outlet of the passage onthe flow field, this parameter plays a positive role for understanding the flow fieldinside the cascade.Currently, the literatures about studying these two forms cascades deeply arerelatively rare. This paper lays the foundation and provides some basis thataccumulating experience in related areas and designing a better performanceairfoil more quickly after analyzing the flow field and blade profile losses b etweenthe two forms cascades.