The study of rake angle impact of peripheral part of the working blade on the efficiency of high-pressure and high-speed centrifugal compressors for prospective small-sized turboprop and turbo-shaft engines

Aeronautical and Space-Rocket Engineering


DOI: 10.34759/vst-2022-2-95-106

Аuthors

Sinyakin V. P.*, Ravikovich Y. A.**, Nesterenko V. G.***

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: vlad.siniy1996@yandex.ru
**e-mail: yurav@mai.ru, yr@mai.ru
***e-mail: valerynesterenk@yandex.ru

Abstract

The article being presented proposes the structure of the impeller peripheral part of the high-pressure single-stage centrifugal compressor with high degree pressure ratio of πκ* = 0.9 and η ≈ 0.78, which allows reducing gas overflowing from the concave side to the convex side of the blade in its opened radial gap, as well as efficiency increasing of this compressor stage. With this end in view, the impeller end surface is bent relative to the radial direction rather than having radial direction.

As is known, the opened gap in the centrifugal compressor is much more meaningful due to its large outstretch compared to the outstretch of radial gap above the impeller of axis compressor. This efficiency reduction is being aggravated also by the fact that pressure difference in the radial gap above the impeller of the high-pressure compressor under consideration is essentially higher, and, hence, there is larger overflowing of the air being compressed from the concave side to the convex side of the blade. Installing covering disk, fixed on the high-pressure compressor impellers end butts does not solve the problem.

Firstly, in the presence of easily worn-out coating applied on the stator housing above the blades end butts, the high-pressure impeller runs with small values of the radial gap, which, in itself, reduces the air overflowing in the radial gap. Secondly, the so-called secondary airflow the concave side to the convex side of the blade passage appears on the inner side of the covering disk. This unordered secondary airflow transfers to the reverse convex side of the channel and moves along the height into the depth of the channel, which distorts significantly the computed trajectory of its flowing as well as computed exit angles from the impeller and compressed air inlet to the vaned or slot diffusor. The area of variously directed airflows shifting and their intermixing appears, which leads to the centrifugal compressor efficiency reduction.

Computational studies of seventeen options of the working blades design of a high-pressure centrifugal compressor with various angles of inclination of the peripheral part of the working blades were conducted. The inclination angle value varied herewith in the range from αrk= –40 to αrk= +40°. The step value of the slope changing was 5°. Geometric models of the centrifugal wheel were developed in the Ansys system. The two-dimensional model was created using the Vista CCD program, and a three-dimensional geometric model was created based on the results of the two-dimensional calculation and optimized in BladeGen.

The isentropic and polytropic efficiency of this centrifugal compressor demonstrate significant increase of about 0.2% for every 5° up to the point corresponding to the model with αrk= +35 . Further, the efficiency growth in the computational domain decreases. Thus, the article demonstrates that there is a range of values of the inclination angles of the working blades in their end part, where gas flowing in the radial gap is reduced, and is a significant gain in compressor efficiency is obtained.

Keywords:

centrifugal compressor, pressure ratio, temperature increase degree, isentropic efficiency, polytropic efficiency, turboprop engine, turboshaft engine

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