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The ducting system has considerable energy losses in channeling cold air in a tall building. At the square elbow 90-degree, the pressure drop due to friction loss, separation loss, and secondary flow. An increase in pressure drop can increase the amount of energy consumption needed. 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 90-degree inner elbow (g/Dh) is 0.01 - 0.05. The ducting model used is a square duct with a hydraulic diameter of 125 mm. The results showed that the addition of circular turbulator g/Dh = 0.02 reduced the pressure drop by 20.52 percent. The use of circular turbulator on the 90-degree inner elbow causes the phenomenon of separating and reattaching. The shear layer deflected from the circular turbulator meets the free stream momentum so that it has high turbulence intensity. This fluid momentum reattaches the curved surface of the 90-degree inner elbows and can resist wall shear stress.