The Experimental Studies of Improving the Aerodynamic Performance of a Turbine Exhaust System

Analysis and testing was conducted to optimize an axial diffuser-collector gas turbine exhaust. Two subsonic wind tunnel facilities were designed and built to support this program. A 1/12^th scale test rig enabled rapid and efficient evaluation of multiple geometries. This test facility was designed to run continuously at an inlet Mach number of 0.41 and an inlet hydraulic diameter-based Reynolds number of 3.4 × 10⁵. A 1/4^th geometric scale test rig was designed and built to validate the data in the 1/12^th scale rig. This blow-down rig facilitated testing at a nominally equivalent inlet Mach number, while the Reynolds number was matched to realistic engine conditions via back pressure. Multi-hole pneumatic pressure probes, particle image velocimetry and surface oil flow visualization was deployed in conjunction with computational tools to explore physics-based alterations to the exhaust geometry. The design modifications resulted in a substantial increase in the overall pressure recovery coefficient of +0.07 (experimental result) above the baseline geometry. The optimized performance, first measured at 1/12^th scale and obtained using CFD was validated at the full scale Reynolds number.