CUED Publications database

Experimental investigation of a vortex-generator-controlled intermediate turbine duct under the influence of rotating wakes

Steiner, M and Göttlich, E and Spataro, R and Heitmeir, F (2014) Experimental investigation of a vortex-generator-controlled intermediate turbine duct under the influence of rotating wakes. In: UNSPECIFIED.

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The bypass ratio of modern turbofan needs to be increased in order to improve engine specific fuel consumption (SFC). This leads to the development of low-pressure turbines running at lower rotational speed but with larger diameters. The aerodynamics of the intermediate turbine duct connecting the high-pressure and the low-pressure stages plays then a major role. The duct will have to be designed not only with a higher inlet/outlet diameter change, but also shortening its axial length in order to allow for weight saving. This current trend induces an increasing aggressiveness in the design of such s-shaped intermediate turbine diffusers, where the aerodynamics is pushed to its limit such that end wall boundary layers could destabilise and separation can occur. This paper focuses on one super-aggressive configuration for turbine transition ducts. Such design was carried out to investigate the effectiveness of flow control systems on a baseline layout intended to fully separate. The duct was tested in an annular cascade under engine realistic inflow conditions. The wakes of the high-pressure turbine are simulated by means of a spoke wheel with applied rods located upstream the duct. Low profile vortex generators were also applied upstream the separation line (downstream of the inner part of first duct bend) in order investigate their effects the boundary layer stability. Since such devices are very sensitive to their inflow condition, in this study the effect of the upstream spoke wheel rod passing frequency was investigated. Oil flow visualisation techniques were applied and measurements such as static pressure distributions along the inner and outer walls and five-hole probes were performed. The results hereby presented were obtained in a newly designed annular cascade located at Graz University of Technology. The investigation outcomes are in line with what previously observed in the high speed turbine test rig present in the same laboratory. Such results confirm the importance of the upstream structure unsteadiness scales on the diffusing duct performance. Whenever the spoke wheel passing frequency is kept low and therefore the inlet unsteadiness, flow control devices such as the vortex generators could actually delay the flow separation. As soon as the upstream unsteadiness level raises reaching engine realistic levels, these devices are seen worsening the flow behaviour.

Item Type: Conference or Workshop Item (UNSPECIFIED)
Divisions: Div A > Turbomachinery
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 19:05
Last Modified: 01 Aug 2017 03:02