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Flow Investigation through a Curved Square S-Duct
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This paper presents the results of an experimental work with measurement of wall static pressure of 45°/45° S shaped curved duct. An S shaped duct is widely used in aircraft intakes, gas turbines. The test ducts are made up of transparent perspex sheets to facilitate the flow visualization study. The duct have inlet to exit area ratio of 1.0 with centerline distance of 0.75m. The inlet aspect ratio of the test duct has been fixed at 1.0 with inlet width 100mm. The velocities for the proposed investigations are to be measured by using calibrated Pitot tube. Wall pressures are measured with the help of inclined manometer with the inclination of 35°. The main purpose of this investigation is to show the development of secondary flow which happens when flow takes place through the bend in the curvature. This secondary flow arises as a result of centrifugal force acting when the flow moves through the bend. The investigation is carried out at three different velocities 20 m/s, 40 m/s, 60 m/s. The distribution of normalized pressure which is the ratio of static pressure to the dynamic pressure is mapped and shown in the form of contours by using the software package SURFER. The trend of wall static pressure development on the walls of S shaped duct shows that as the flow proceeds towards the curvature and there exists a high pressure gradient between the outside face and inside face due the centrifugal force acting at the curvature. This shows the bulk shifting of flow towards outside face. This is due to the generation of secondary motion in a plane perpendicular to the primary flow. This gradient becomes zero at the inflexion plane. After the inflexion, the change of curvature causes a reverse trend in the wall static pressure growth leading to the probable development of pair of contra-rotating vortices as a result of secondary motion with opposite sense of rotation compared to the first half of the bend.
Keywords
45°/45° S Shaped Curved Duct, Secondary Flow, Contra-Rotating Vortices, SURFER.
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