Abstract
In order to investigate the part clearance leakage flow field through a variable area nozzle turbine (VANT), an experimental setup of the annular sector cascade (ASC) with eight numbers of passages is being developed. The second stage low-pressure turbine stator from Energy Efficient Engine proposed by Pratt and Whitney was selected and modified for the VANT concept. The intermediate turbine duct (ITD) – connecting the high-pressure turbine with the low-pressure turbine was inevitable to be incorporated between the wind tunnel and ASC test section for the following reasons: a) ITD will ensure the geometric continuity on the hub and casing end-walls, and b) it will provide realistic entry flow field with radial pressure gradient. The diverging shape of the ITD with continuously increasing mean radius imposes a major challenge to achieving the required inlet flow angle with periodicity at the entry of the ASC. Hence, the present study focuses on the challenging work of modifying the existing annular ITD to achieve the required inlet flow for ASC. The various geometries of the ITD, including different flow control methods, were numerically analyzed using commercial software ANSYS CFX®. The flow field of the numerical simulations at multiple locations was analyzed using flow angle and its distribution, velocity streamlines, static pressure recovery coefficient, and total pressure loss coefficient. It was found that the IGVs direct the flow through the ITD, and approximately the required flow condition with periodicity was achieved at the entry of the test vane cascade. As an active flow control method, an opening slot was modelled on the casing end-wall at the upstream region of the test vane cascade. However, the numerical analysis shows an adverse effect on the flow angle distribution at the entry of the cascade. The change in axial spacing between IGVs and the test vane cascade shows a negligible effect on the cascade entry flow field.
