Some Aspects of Transonic Compressor Tandem Design

Abstract

The development of modern axial compressors has already reached a high level. Therefore an enlargement of the design space by means of new or advanced aerodynamic methods is necessary in order to achieve further enhancements of performance and efficiency. The tandem arrangement of profiles in a transonic compressor blade row is such a method. It is necessary to address the design aspects a bit more in detail in order to efficiently apply this blading concept to turbomachinery. Therefore, in the current study the known design aspects of tandem blading in compressors will be summed up under consideration of the aerodynamic effects and construction characteristics of a transonic compressor tandem. Based on this knowledge, a new transonic compressor tandem cascade (DLRTTC) with an inflow Mach number of 0.9 is designed using modern numerical methods and a multi objective optimization process. Three objective functions as well as three operating points are used in the optimization. Furthermore, both tandem blades and their arrangement are parameterized. From the resulting database of 1246 members a final best member is chosen as state-of-the-art design for further detailed investigation. The aim of the ensuing experimental and numerical investigation is to answer the question, whether the tandem cascade resulting from the modern design process fulfills the described design aspects and delivers the requested performance and efficiency criteria. The numerical simulations within the study are carried out with the DLR flow solver TRACE. The experiments are performed at the Transonic Cascade Wind Tunnel of DLR in Cologne. The inflow Mach number during the tests is 0.9 and the AVDR [1, 2] is adjusted to 1.3 (design value). Wake measurements with a 3-hole probe are carried out in order to determine the cascade performance. The experimental results show an increase in losses and a reduction of the cascade deflection by about 2 degrees compared to design concept. Nevertheless, the experimental and numerical results allow a good understanding of the aerodynamic effects. In addition, Planar PIV was applied in a single S1 plane located at midspan to capture the velocity field in the wake of blade 1 in order to analyze the wake flow in detail and describe its influence on the cascade deflection and loss behavior. Finally, an outlook will be given on what future tandem compressor research should be focused.

Aerodynamic optimization to tandem stators by using sweep and dihedral

“…Although small enhancement was obtained during optimizing blade shapes and resetting some blade design parameters, a much larger aerodynamic improvement did not occur. 10 Hence, the advantages of tandem blade design that tandem blade could outperform the traditional single blade at highly loaded conditions have already been confirmed. However, no more significant large improvement could be expected by just adjusting basic parameters of blade arrangements.…”

Low Reynolds Number Effect on Highly Loaded Compressor Stator Cascade

“…Under these conditions lower density causes higher kinematic viscosity resulting significant reduction of Reynolds number. At low Reynolds number conditions, the viscous losses dominate the flow which has a significant impact on the stability and operating range of the compressors [4].…”

Flow physics of highly loaded tandem compressor cascade with non-axisymmetric endwall profiling

“…Recently, McGlumhy et al 11 evaluated the flow mechanics of a tandem rotor in the rear stages of a core compressor, which showed that the F blade acted in a similar manner to a conventional rotor, whereas the R blade tended to be more 3D and non-uniform. Hergt et al 12 studied some aspects of the design of tandem cascade under transonic operating condition. Basic design recommendations were extracted from open literature and optimization of a transonic compressor tandem cascade was performed, which resulted in a highly loaded, high efficient tandem compressor cascade and showed a good agreement with the recommended design aspects.…”

“…Hergt et al. 12 studied some aspects of the design of tandem cascade under transonic operating condition. Basic design recommendations were extracted from open literature and optimization of a transonic compressor tandem cascade was performed, which resulted in a highly loaded, high efficient tandem compressor cascade and showed a good agreement with the recommended design aspects.…”