EXPERIMENTAL OFF-DESIGN INVESTIGATION OF UNSTEADY SECONDARY FLOW PHENOMENA IN A THREE-STAGE AXIAL COMPRESSOR AT 100% NOMINAL SPEED

Andreas Bohne

andreas. bohne@web. de

Reinhard Niehuis

Institute of Jet Propulsion and Turbomachinery RWTHAachen University D-52056 Aachen, Germany niehuis@ist. rwth-aachen. de

Abstract This paper deals with unsteady measurements in a high-speed three-stage ax­ial compressor with inlet guide vanes (IGV) and controlled diffusion airfoils (CDA) at off-design conditions. The compressor under consideration exhibits design features of real industrial compressors. The main emphasis is put on the experimental investigation of two operating points at 100% nominal speed. The first one represents design conditions whereas the second one is the last stable operating point near the surge margin. Probe traverses, with a high resolution both in space and time, show the significant potential upstream inflience of the blades dependent on varying operating conditions. Besides that, the structure of the rotor tip clearance fbw changes with further throttling of the compres­sor. Dynamic pressure transducers on the casing show the appearance of both spiral-type – and bubble-type-vortices as these are described by Furukawa et al. (2000). The convected wakes of the airfoils strongly inflience the fl>w field downstream, and the varying incidence even causes flictuating fl>w separations in the blade rows downstream.

Keywords: Axial Compressor, Multistage, Unsteady Flow, Off-Design, Experimental Inves­

tigation

369

K. C. Hall et al. (eds.),

Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines, 369-380. © 2006 Springer. Printed in the Netherlands.

Glossary

In the field of multistage compressor development, remarkable effort is spent to achieve higher efficiencies and wider operating ranges. In order to consider all relevant aspects of the highly complex three-dimensional fbw within the design process, especially viscous and unsteady fbw phenomena, highly-sophisticated and well-calibrated design tools are essential. The devel­opment of reliable design tools, however, requires detailed experimental data of all relevant ft>w phenomena in adequate multistage components. The highly three-dimensional flow in turbomachines features complex unsteady flow phe­nomena due to the existence of stationary and rotating blade rows. These ef­fects vary depending on different aerodynamic loading and different throttling of the compressor respectively. With a higher loading, the boundary layers enlarge, resulting in wider wakes, which do strongly influence the blade rows downstream. Due to varying incidence, the intensity and structure of the tip clearance ft>w changes. Besides that, the potential upstream infhence of both rotor and stator blades increases with higher aerodynamic loading. In a multi­stage environment, these phenomena do not only influence the generating blade row, but the entire flow field of the compressor, known as stage interaction.