Abstr:Annular compressor cascade with tip clearance
Application Area 6: Turbomachinery Internal Flows
Application Challenge AC6-05
Abstract
This application challenge deals with the flow prediction in the stationary annular compressor cascade with rotating hub that has been installed at the Laboratory of Thermal Turbomachinery of the National Technical University of Athens (NTUA/LTT). The cascade has been designed for studying the tip-clearance effects in annular cascades at high but subsonic Mach numbers. The test cascade simulates the flow through a rear stage blading of an axial, high-pressure compressor where the tip-clearance effects have the greater influence on the flow structure. Therefore it contributes to the research community original experimental data on a high-speed machine, alleviating the lack of detailed measurements in such configurations. The test cascade has been designed by SNECMA, in the course of a European funded project set up for studying tip-clearance effects in axial compressors ("Advanced Civil Core Compressor Aerodynamics," AER2-CT92-0039, 1/1/1993-30/9/1996).
To provide as a complete a set of flow field data as possible, measurements accounting for the cascade performance have been performed using 5-hole probes and detailed measurements inside the blade passage have been carried out using both 5-hole probes and a three-dimensional Laser Doppler Velocimetry system. Measurements and complementary numerical calculations have been performed twice, in the context of two European funded research projects ("Advanced Civil Core Compressor Aerodynamics" and "Assessment of the Physical Processes and Code Evaluation for Turbomachinery Flows," BRPR-CT97-0610 1/1/1998-31/8/2000). Different solution methods, a significant number of turbulence models and numerous grids have been used in the calculations; nevertheless they all feature an incapability of reproducing the physical patterns downstream of the blade, despite their success in reproducing them in the blade passage. The measurements presented herein have been performed under the contractual obligations of the second research project mentioned above. The computations that accompany them have been obtained using a multi-domain, pressure-based, three-dimensional Navier-Stokes solver incorporating a high-Reynolds-number k-ε turbulence model.
While many studies have been performed to investigate the effects of tip-clearance flows on the performance of axial compressors and to study the structure of the corresponding flow field, there has been a lack of detailed measurements on high-speed machines. The tip-clearance flows are not only important because of their contribution to the overall losses of a turbomachine, but they also play an important role in determining the useful flow range of a compressor, i.e. its stability limits. The test rig described herein provides the possibility of experimentally studying the tip-clearance effects in a compressible, high-speed flow configuration. Thus, it contributes original data in this area for the first time, since detailed measurements were available only in incompressible flow configurations up to now. Experimental work providing such information for tip-clearance effects in rear stages of high-pressure compressors has been performed in close collaboration with industrial partners. Since, possibilities for simulating tip-clearance effects through numerical flow models exist nowadays, the main purpose of the experimental facility described herein was to provide data for validating the results from the computational procedures and to allow the improvement of the theoretical modelling.
Contributors: Dr. E.S. Politis; Prof. K.D. Papailiou - NTUA