Experimental investigation and design of a shape-variable compressor cascade

Abstract

The design of jet engine compressor blading always implies a compromise between design and off-design operation. The reason for this is a fixed blade geometry which has to be operated over a wide range of operating conditions. Consequently, maximum achievable efficiencies at design operation are limited by off-design requirements, e.g. a certain stall margin. The corresponding paper describes an approach using shape-variable blades equipped with integrated Macro Fiber Composite actuators on the blade’s suction and pressure sides. By applying a voltage to these actuators it is possible to increase and to decrease the blade stagger angle and therefore the blade turning. Compared to a conventional fixed blade profile the actuated design thus is adaptable within a certain range to the actual flow conditions. The first part of the paper describes the geometry and structure of the shape-variable blades for use in a compressor cascade experiment. In the next part the three-dimensional deformation behavior of all manufactured blades at different shape conditions is characterized with a photogrammetric measurement system called ATOS. The first results without aerodynamic loads show an average displacement at the trailing edge of approximately Δz≈0.9 mm compared to the non-actuated condition. This corresponds to an average outlet angle variation of approximately ∆κ2≈±1°. The third part of the paper presents the results of the low speed cascade experiment using a full actuated cascade. On the one hand the objective is to determine the influence of blade actuation on aerodynamic characteristics such as flow outlet angle, total pressure loss and pressure distributions. On the other hand optical blade displacement measurements are used to investigate combined 2D- and 3D-deformation effects of blade actuation in conjunction with aerodynamic loads. For these measurements the ATOS system is used, too. The wake evaluations show that maximum blade actuation leads to flow outlet angle deviations up to ± 1° which can be described by an almost linear shift of the cascade performance without changing the loss distribution significantly. Furthermore, for the chosen profile this margin is approximately constant over the operating range.