A Study of Existing Multistage Transonic Axial Compressor Design for Surge Margin Improvement

The design of multistage axial flow compressors has been revolutionised in recent years by the development of three dimensional multistage viscous calculations (CFD) and the availability of the computational power to allow these methods to be used extensively in design process. Such a multistage turbomachinery was used to redesign the existing three stage transonic compressor for improved aerodynamic performance in terms of SM limit. The redesign activity of compressor configuration was carried out as surge margin obtained with hardware testing of existing machinery was not sufficient to meet the desired design goals. The higher limit of surge margin in accordance with design specification is required to maintain the successful and stable operation of aircraft engine. As at stall point of compressor, aerodynamic instabilities would be initiated resulting surge or rotating stall which potentially leading to a complete mechanical failure of the compression system as well as of the whole engine. Maximizing the SM of multistage compressors is particularly a complex process especially alongwith achieving higher efficiency. Outlined in this paper are the details of how advanced design techniques were incorporated using traditional 2D and CFD methods into redesign activities for compressor performance improvement. The approach used in this work was to modify compressor annulus flowpath and rotor and stator blade geometries based on output of 2D calculations and 3D N-S analysis for SM enhancement of existing design. While carrying out redesign activities for compressor, the constraints of retaining existing inlet and outlet flow area, axial length as well as design parameters i.e. inlet mass flow, rotational speed and operating point pressure ratio were taken care. The advanced design techniques like 3D blading, wide chord blade performance and many others were studied in detailed manner for incorporating them into compressor redesign procedure. Simultaneous resigned compressor configuration based on in-house design procedure showed improvement of SM by 17% at design speed with maintaining mentioned design constraints. Subsequently, the detailed analysis was also performed at off design speeds to have satisfactory performance.