Low Pressure Turbine Pressure Side Aerodynamics

Introduction

Instantaneous streamlines and entropy contours from a 2D unsteady simulation

In order to reduce the weight and cost of modern civil aircraft engines, manufacturers often use thin, solid blades in the LP turbine. These blades commonly have a velocity ‘spike’ near the leading edge and an adverse pressure gradient along the pressure surface fore-blade. Under these conditions, the pressure surface boundary layer can separate near the leading edge and reattach as far back as mid-chord (figure 1). The resulting separation bubble can be strongly unsteady and contribute significantly to the loss generated by the blade.

The traditional approach of the aerodynamicist to this problem has been to increase the leading edge radius and thicken the blade profile. Inevitably, the profile either becomes heavier (if the section is solid) or more expensive to fabricate (if thick hollow profiles are used). Both of these options are undesirable to the engine manufacturer, and other possibilities are therefore sought.

Ideally, we would like to retain thin, solid profiles and devise ways of reducing the loss produced by the pressure surface separation. Therefore, this research is concerned with three questions: How much loss do these separations create? Why do they create this loss? How could the loss produced be reduced whilst retaining thin profiles?

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Howard Hodson and Michael Brear

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