Session: 31-06 Tandem Design

Paper Number: 127650

127650 - Numerical Investigation of the Effect of Diffusion Factor Variation on the Performance of Single-Row and Tandem Bladings in Low-Speed Axial Compressor Stages 

To make aircraft engines more fuel-efficient, the design of modern axial compressors has primarily followed two paths. First, there is the drive to reduce the compressor's weight. This can be achieved by decreasing the number of compressor stages while maintaining the same compressor total pressure ratio. The second approach is to increase the compressor's total pressure ratio, thus increasing the engine's thermal efficiency without making the compressor heavier. In either case, both strategies put more load on each stage within the compressor.

The stability of the boundary layer around an aerofoil dictates its loading limits and off-design behavior. Previous research has indicated that using tandem blade configurations can be a solution to achieve higher blade loadings compared to conventional single aerofoil configurations. In tandem configurations, a fresh and more stable boundary layer around the rear aerofoil is introduced, allowing for higher blade turnings in tandem aerofoils and, consequently, higher stage loadings. However, it's important to note that adding a second aerofoil to a row and increasing stage loadings leads to a more complex secondary flow field and results in higher losses than conventional stages.

Conventional single aerofoil designs have been well-studied over the years, and the most efficient designs can be plotted in the “Smith Chart” (work coefficient vs. flow coefficient). It was shown that the most efficient designs are found only in a narrow range with low work coefficients and high through-flow coefficients. Tandem configurations aim to shift the area of high efficiency towards higher work coefficients, thus allowing for higher stage loadings.

A prior study found that tandem stages excel in efficiency when DeHaller numbers are low. However, this comparison was made under strict design conditions, leading to suboptimal diffusion factors for various designs and making it hard to compare their off-design performance. This limitation is what the current paper aims to address by studying the effects of varying the diffusion factor and ensuring that the off-design behavior is comparable.

The 3.5-stage low-speed axial research compressor at the Institute of Turbomachinery and Flight Propulsion at the TUM sets this study's geometrical and aerodynamic baseline. The first 1.5 stages of this compressor will be redesigned, either considering a set-up of IGV, single rotor, and single stator or asset-up of IGV, tandem rotor, and tandem stator. The numerical analyses are based on the throughflow – B2B coupled quasi 3D design process.

This paper's findings will deepen future designers' insights on how and when to apply tandem aerofoil configurations in axial compressor stages. Additionally, these findings will enable designers to anticipate the benefits of tandem aerofoil configurations compared to single aerofoil configurations concerning their design point.

Presenting Author: Philipp von Jeinsen Technical University of Munich

Presenting Author Biography: Philipp von Jeinsen finished his studies in aerospace engineering at the Technical University of Berlin in 2019 after being a working student at Rolls Royce in Dahlewitz for one year. Since February 2020, he has been working as a Ph.D. student and research associate at the Institute for Turbomachinery and Flight Propulsion at the Technical University of Munich, focusing on unconventional designs of highly loaded axial compressor rotors.

Authors:

Philipp von Jeinsen Technical University of Munich
Samuele Giannini Technical University of Munich
Volker Gümmer Technical University of Munich