A Novel Approach to Evaluate the Benefits of Casing Treatment in Axial Compressors

Guillaume Legras,Nicolas Gourdain,Lionel Castillon,Xavier Ottavy,Isabelle Trébinjac

doi:10.1155/2012/975407

Abstract

Passive control devices based on casing treatments have already shown their capability to improve the flow stability in axial compressors. However, their optimization remains complex due to a partial understanding of the related physical mechanisms. In order to quantitatively assess the interaction between slots and the blade tip flow, the present paper develops a novel analysis methodology based on a control-volume approach located in the rotor tip region. This methodology may be used for analyzing the casing treatment based on both axi- and non-axisymmetric slots design. The second issue of the paper focuses on the application of the current approach to better understand the effects of axi- and non-axisymmetric grooves in three different axial compressors which differ by the flow regime (subsonic/transonic) and the smooth casing shape (cylindrical/concave). Numerical simulations are performed, and results of the current approach with and without casing treatments are compared.

Highlights

Today, it is mandatory for compressor designers to improve performance in terms of efficiency and operating range characterized by the stall margin at low mass flow rate
The application of the current methodology applied on the near casing flow region can be useful to ascertain the flow mechanisms, to quantify the fluxes and to understand why the implementation of casing treatment (CT) is nonefficient in the NASA Rotor 37
By differentiating the terms between the axial outlet and inlet of the control volume (i.e., [(ρWz2Az)outlet −inlet]) and assuming that Wz is mainly positive in the volume, a negative force corresponds to a deceleration of the flow

Summary

Introduction

It is mandatory for compressor designers to improve performance in terms of efficiency and operating range characterized by the stall margin at low mass flow rate. Stall prevention techniques must be used, and one promising technology known to bring substantial stability for tip critical compressor rotor is casing treatment (CT) [1]. This passive control device consists of slots within the rotor casing and presents various types of geometries: circumferential grooves [2,3,4,5,6,7,8,9], nonaxisymmetric slot-type CT [10,11,12,13,14] and self-recirculating flow channels [15,16,17], and honeycomb [18].

Results

Discussion

Conclusion