Axial Compressor Mean-Line Analysis: Choking Modelling and Fully-Coupled Integration in Engine Performance Simulations

Abstract

A mean-line compressor performance calculation method is presented that covers the entire operating range, including the choked region of the map. It can be directly integrated into overall engine performance models, as it is developed in the same simulation environment. The code materializing the model can inherit the same interfaces, fluid models, and solvers, as the engine cycle model, allowing consistent, transparent, and robust simulations. In order to deal with convergence problems when the compressor operates close to or within the choked operation region, an approach to model choking conditions at blade row and overall compressor level is proposed. The choked portion of the compressor characteristics map is thus numerically established, allowing full knowledge and handling of inter-stage flow conditions. Such choking modelling capabilities are illustrated, for the first time in the open literature, for the case of multi-stage compressors. Integration capabilities of the 1D code within an overall engine model are demonstrated through steady state and transient simulations of a contemporary turbofan layout. Advantages offered by this approach are discussed, while comparison of using alternative approaches for representing compressor performance in overall engine models is discussed.

Aero-Engine Preliminary Design Optimization and Operability Studies Supported by a Compressor Mean-Line Design Module

“…For predicting the flow ( . m, T 0 , p 0 ) across any blade row and for estimating the required geometry, MLDC employs the same computational building blocks as those used in MLAC [9], i.e., the Blade Row Module (BRM) and the Inter-Volume Module (IVM). Figure 1 illustrates the blade row modelling concept through BRMs and IVMs.…”

“…For choke, the methodology presented by the authors in [9] for MLAC is also applied in MLDC. For stall, an approach similar to the one presented in [9] for choke was formulated, where appropriate indices (I) quantifying how far the operation of any individual blade row is from stall were defined. For the definition of these indices, the user has a number of different possibilities:…”

“…For the compressor to operate stably, stall indices must be positive (I ≥ 0). As is the case with choke modelling [9], an overall stall index is defined, which is the minimum value between the stall indices of all blade rows. The minimum stall index is used as an indication of the row which is more likely to stall first.…”

“…MLDC is developed in the same modelling environment as conventional 0D engine components, thus using the same interface, fluid and thermodynamic functions and numerical routines while inheriting directly the basic modelling equations of 0D general purpose turbomachinery components. It uses the same fluid models, thermodynamic functions, blade models, loss models, and numerical schemes as those employed in the Mean-Line Analysis Code (MLAC) for compressor off-design performance predictions described previously by the authors [9]. Thus, MLDC produces compressor geometries, which can then be used by MLAC to generate consistent performance maps.…”

Improvement of the Parallel Compressor Model and Application to Inlet Flow Distortion

“…It can be combined with extra data and enriched in many ways. However, in addition to improving the modeling of individual components, a major perspective to increase the level of accuracy in global performance prediction remains the coupling of such an aerodynamic method with a performance tool at the system level, as recently illustrated by Pokhrel et al [41], Lopez de Vega et al [42] or Kolias et al [43], so that aircraft design can beneficiate from an improved modeling of the propulsive subsystem, even for complex innovative configurations.…”