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The effect on non-uniform surface roughness on the aerodynamics of a turbine blade is investigated. Surface roughness on airfoils has a significant impact on total energy loss due to skin friction and typically leads to an increased thermal loading. In the present research project, investigations are supposed to be carried out experimentally. For this a blade must be designed, which accommodates the contradictory requirements of aerodynamics and manufacturing the sections of surface roughness. A fully automatic design process based on a genetic algorithm is developed and results are shown. The designed blade sufficiently fulfills the given requirements. A numerical study, using a low-Reynolds approach, is performed to investigate the influence of non-uniform roughness applied to different positions on the suction side of a high pressure turbine blade. It is shown that roughness applied at the leading and trailing edge does not significantly influence the flow whereas roughness at 20% cord length and at midchord induce transition. Especially surface roughness at 20% chord length shows a strong correlation to the change of total pressure loss.

In order to gain in cycle efficiency, turbine inlet temperatures tend to rise, posing the challenge for designers to cool components more effectively. Purge flow injection through the rim seal is regularly used in gas turbines to limit the ingestion of hot air in the cavities and prevent overheating of the disks and shaft bearings. The interaction of the purge air with the main flow and the static pressure field of the blade rows results in a non-homogenous distribution of coolant on the passage endwall which poses questions on its effect on endwall heat transfer. A novel measurement technique based on infrared thermography has been applied in the rotating axial turbine research facility LISA of the Laboratory for Energy Conversion (LEC) of ETH Zürich. A 1.5 stage configuration with fully three-dimensional airfoils and endwall contouring is integrated in the facility. The effect of different purge air mass flow rates on the distribution of the heat transfer quantities has been observed for the rated operating condition of the turbine. Two-dimensional distributions of Nusselt number and adiabatic wall temperature show that the purge flow affects local heat loads. It does so by acting on the adiabatic wall temperature on the suction side of the passage until 30% of the axial extent of the rotor endwall. This suggests the possibility of effectively employing purge air also as rotor platform coolant in this specific region. The strengthening of the secondary flows due to purge air injection is observed, but plays a negligible role in varying local heat fluxes. For one test case, experimental data is compared to high-fidelity, unsteady Reynolds-Averaged Navier–Stokes simulations performed on a model of the full 1.5 stage configuration.

Roughened aeroengine blade surfaces lead to increased friction losses and reduced efficiency of the individual blades. The surface roughness also affects the wake flow of the blade and thus the inflow conditions for the subsequent compressor or turbine stage. To investigate the impact of surface roughness on a turbulent blade wake, we conducted velocity field measurements by means of stereo particle image velocimetry in the wake of a roughened turbine blade in a linear cascade wind tunnel. The turbine blade was roughened at different chordwise locations. The influence of the chordwise location of the added surface roughness was examined by comparing their impact on the width and depth of the wake and, the positions and distribution of vortical structures in the wake. Additionally, the friction loss coefficients for different surface roughness positions were estimated directly from the velocity field.

This paper shows the effect of local surface roughness on the aerodynamic loss behavior of a turbine blade. Non-contact measurements of the surface roughness of turbine blades of a jet engine are conducted. The roughness is quantitatively characterised using a shape and density parameter to parametrise the topology and the average roughness height. An experimental investigation in a linear cascade wind tunnel is conducted in order to identify the contributions of pressure-and friction-losses of the measured surfaces to the overall profile loss increase due to local surface roughness. The results show that the change of profile losses due to local surface roughness is significant. The change in losses is dependent on the roughness height, as well as of the position on the blade of the roughness and the condition of the boundary layer behind. The local pressure gradient at and downstream of the surface roughness is identified as the main influencing parameter besides the roughness height.