Experimental investigation of tandem rotor under clean and radially distorted inflows

Amit Kumar, A.M. Pradeep ^*

Department of Aerospace Engineering, Indian Institute of Technology Bombay, Mumba, 400076, India

Abstract: With increasing emphasis on renewable sources of energy, the gas turbine engine faces several challenges in evolving its design, to remain relevant. Compressor is one of the main components, which accounts for one-third of the engine length. Compressor designers have been exploring different ideas to achieve maximum pressure rise with minimum number of stages required. Tandem blading is one such novel design that has demonstrated higher diffusion capability than a single rotor blade.  A single blade, with a higher diffusion factor, carries the risk of flow separation against the adverse pressure gradient of the compressor flow. In the tandem blading concept, a single blade is split into forward and aft blade.  The gap that is created between the forward and aft blade, serves as a mechanism to energize the sluggish flow over the aft blade suction surface, which in turn helps in mitigating the flow separation. The present experimental work is aimed at exploring the feasibility of a tandem rotor in an axial flow compressor under the clean and radially distorted inflows. Steady and unsteady experimental results of the tandem rotor are included in this paper. The stage performance characteristics, variation of total pressure, flow coefficient, and exit flow angle along the blade span for clean and distorted flow is included in this paper. Some results of a steady Reynolds-averaged Navier-Stokes simulation are also included to give some insight into the complex flow field of the tandem rotor. Wavelet transform, fast Fourier Transform analysis, and visual inspection of casing pressure traces are used to analyze the unsteady result of the tandem rotor in clean and distorted flow. The tandem rotor is able to achieve its design pressure ratio and has a stall margin of 9% under the clean flow condition. Initially, stall appears as a low-intensity spike for all the cases, which turns into a long length-scale disturbance within three rotor revolutions. A modal wave of low frequency is also observed under clean and distorted inflows.

Keywords: Tandem rotor; Axial overlap and percentage pitch; Radially distorted inflows; Diffusion factor; Stall; Aerodynamics of compressor blade

https://doi.org/10.1016/j.jppr.2021.05.004