DEVELOPMENT OF BLADE PROFILES FOR LOW-PRESSURE TURBINE APPLICATIONS

This paper describes a program of work, largely experimental, which wa s undertaken with the objective of developing an improved blade profil e for the low-pressure turbine in aero-engine applications. Preliminar y experiments were conducted using a novel technique. An existing casc ade of datum blades was modified to enable the pressure distribution o n the suction surface of one of the blades to be altered. Various mean s, such as shaped inserts, an adjustable flap at the trailing edge, an d changing stagger were employed to change the geometry of the passage . These experiments provided boundary layer and lift data for a wide r ange of suction surface pressure distributions. The data were then use d as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades to simulate the effect of the incoming wakes from the previous blade row in a multista ge turbine environment. Results are presented for two improved profile s that are compared with a datum representative of current practice. T he experimental results include loss measurements by wake traverse, su rface pressure distributions, and boundary layer measurements. The cas cades were operated over a Reynolds number range from 0.7 x 10(5) to 4 .0 x 10(5). The first profile is a ''laminar flow'' design that was in tended to improve the efficiency at the same lending as the datum. The other is a more highly loaded blade profile intended to permit a redu ction in blade numbers. The more highly loaded profile is the most pro mising candidate for inclusion in future designs. It enables blade num bers to be reduced by 20 percent, without incurring any efficiency pen alty. The results also indicate that unsteady effects must be taken in to consideration when selecting a blade profile for the low-pressure t urbine.