This paper describes a detailed study into the unsteady boundary layer behaviour in two high lift and one ultra high lift Rolls-Royce Deutschland LP turbines. The objectives of the paper are to show that high lift and ultra high-lift concepts have been successfully incorporated into the design of these new LP turbine profiles.Measurements from surface mounted hot film sensors were made in full size, cold flow test rigs at the altitude test facility at Stuttgart University. The LP turbine blade profiles are thought to be state of the art in terms of their lift and design philosophy. The two high lift profiles represent slightly different styles of velocity distribution. The first high-lift profile comes from a two stage LP turbine (the BR710 cold-flow, high-lift demonstrator rig). The second high-lift profile tested is from a three-stage machine (the BR715 LPT rig). The ultra-high lift profile measurements come from a redesign of the BR715 LP turbine: this is designated the BR715UHL LP turbine. This ultra high-lift profile represents a 12% reduction in blade numbers compared to the original BR715 turbine.The results from NGV2 on all of the turbines show "classical" unsteady boundary layer behaviour. The measurements from NGV3 (of both the BR715 and BR715UHL turbines) are more complicated, but can still be broken down into classical regions of wake-induced transition, natural transition and calming. The wakes from both upstream rotors and NGVs interact in a complicated manner, affecting the suction surface boundary layer of NGV3. This has important implications for the prediction of the flows on blade rows in multistage environments.

In modern gas turbines hot section components, the over tip leakage (OTL) flow that occurs between the stationary casing and rotating tip of a shroudless HP turbine is still a considerable source of loss of performance. The principal means of reducing this loss have been to minimise the tip gap and/or to apply a rotating shroud to the rotor. Tip clearance control systems continue to improve, but a practical limit on tip gap remains. Winglets have been identified by a number of researchers as having potential, but none have yet to enter commercial service. Harvey & Ramsden [1] analysed a novel design of one, which indicated that it could significantly reduce OTL loss. This paper presents the design of such a winglet as applied to the rotor blade of a research high pressure turbine carried out as part of the ANTLE (Advanced Near Term Low Emissions) technology demonstrator programme. The use of Computational Fluid Dynamics (CFD) calculations in the design process is discussed. In particular, the use of coarse meshes and idealised geometries, for computational speed, did involve some compromise with accuracy. Results from high speed model rig testing of this research turbine are presented. The turbine efficiency was measured for three different tip gaps over a range of conditions. In addition detailed measurements of the flow field were taken, principally exit area traverses and rotor surface static pressures. These experimental results are very encouraging and show a high potential for further development. Part II of this paper presents a post-test re-analysis of the rig results using the state of the art Rolls-Royce in-house CFD code HYDRA, good agreement being found between the two.

The original LP turbine of the BR715 engine featured “High Lift” blading, which achieved a 20-percent reduction in aerofoil numbers compared to blading with conventional levels of lift, reported in Cobley et al. (1997). This paper describes the design and test of a re-bladed LP turbine with new “Ultra High Lift” aerofoils, achieving a further reduction of approximately 11 percent in aerofoil count and significant reductions in turbine weight. The design is based on the successful cascade experiments of Howell et al. (2000) and Brunner et al. (2000). Unsteady wake-boundary layer interaction on these low-Reynolds-number aerofoils is of particular importance in their successful application. Test results show the LP turbine performance to be in line with expectation. Measured aerofoil pressure distributions are presented and compared with the design intent. Changes in the turbine characteristics relative to the original design are interpreted by making reference to the detailed differences in the two aerofoil design styles.

This paper presents a study of the performance of a high-lift profile for low pressure turbines at Reynolds numbers lower than in previous investigations. By following the results of Coull et al. (2008 on the design of high-lift airfoils, the profile is forward loaded. The separate and combined effects of roughness and wake passing are compared. On a front loaded blade, the effect of incidence becomes more important and the consequences in terms of cascade losses, is evaluated. The experimental investigation was carried out in the high speed wind tunnel of Whittle Laboratory, University of Cambridge. This is a closed-circuit continuous wind tunnel where the Reynolds number and Mach number can be fixed independently. The unsteadiness caused by wake passing in front of the blades is reproduced using a wake generator with rotating bars. The results confirm that the beneficial effect of unsteadiness on losses is present even at the lowest Reynolds number examined ͑Re 3 ϭ 20,000͒. This beneficial effect is reduced at positive incidence. With a front loaded airfoil and positive incidence, the transition occurs on the suction side close to the leading edge and this results in higher losses. This has been found valid for the entire Reynolds range investigated ͑20,000Յ Re 3 Յ 140,000͒. Roughening the surface also had a beneficial effect on the losses but this effect vanishes at the lower Reynolds numbers, i.e., ͑Re 3 Յ 30,000͒, where the surface becomes hydraulically smooth. The present study suggests that a blade with as-cast surface roughness has a lower loss than a polished one.

The original LP turbine of the BR715 engine featured "High Lift" blading, which achieved a 20% reduction in aerofoil numbers compared to blading with conventional levels of lift -reported in Cobley et al. (1997). This paper describes the design and test of a re-bladed LP turbine with new "Ultra High Lift" aerofoils, achieving a further reduction of approximately 11% in aerofoil count and significant reductions in turbine weight. The design is based on the successful cascade experiments of Howell et al. (2000) and Brunner et al. (2000). Unsteady wake -boundary layer interaction on these low Reynolds number aerofoils is of particular importance in their successful application. Test results show the LP turbine performance to be in line with expectation. Measured aerofoil pressure distributions are presented and compared with the design intent. Changes in the turbine characteristics relative to the original design are interpreted by making reference to the detailed differences in the two aerofoil design styles. Abbreviations BLboundary layer HL High Lift Mn Mach-number Re Reynolds-number Sr Strouhal-number Sr=f*l/Cax UHL Ultra High Lift Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 06/16/2015 Terms of Use: http://asme.org/terms