Passive flow control in square duct and 90° elbow with circular turbulator at certain gaps

The ducting system has considerable energy losses in a high building. Pressure drop in ducting caused by friction loss, separation loss, and secondary flow. The high-pressure drop leads to an increased amount of energy consumption required. The method identified in reducing this energy loss is by using passive flow control. This study aims to identify the characteristics of the fluid in the ducting with variations in the circular turbulator gap. The variation of the gap between circular turbulator and inner of 90° elbows (g/Dh) is 0.01 - 0.05. The ducting model used is a square duct with a hydraulic diameter of 125 mm. Ducting consists upstream duct of 7Dh, Circular turbulator (CT) with a diameter of 12.5 mm, elbow with a curvature ratio (Rc/Dh) of 1.5, and a downstream duct of 15Dh. Tests are carried out at Reynolds numbers (ReDh) 3.97 × 104, 8.74 × 104, and 13.5 × 104. The results showed that the addition of circular turbulator g/Dh = 0.02 reduced the overall pressure drop by 20.52 %. While g/Dh = 0.04 and 0.05 can increase pressure drop. The addition of CT can form a shear layer that has a higher turbulence intensity (TI) so that it can fight adverse pressure or delay flow separation due to the inner of 90° elbow. The use of CT with g/Dh = 0.02 can increase TI by 30.92 %. While the ducting without CT only produces turbulence intensity of 18.02%. The use of CT with g/Dh = 0.01, 0.03, 0.04 and 0.05 found a decrease in turbulence intensity of 13.17 %, 15.95 %, 15.89 % and 8.51 % respectively.