Part of the life cycle of many industrial gas turbines often includes one or more performance uprates, typically defined by an increase in pressure ratio and/or firing temperature. In the process the hot section is usually only minimally modified due to cost and schedule limitations. As a result, the turbine section may operate at off-design with the last stage being most impacted. The exhaust system is thereby subjected to variations in inlet flow conditions, specifically the velocity and the flow angle, which adversely affect pressure recovery and impact overall engine performance. Similar variation in turbine exhaust inlet flow conditions arise for industrial two-shaft engines with power turbines operating at a wide range of speeds.
This paper describes studies completed using a quarter-scaled rig to assess the impact of turbine exit swirl and strut angular positioning on a turbine exhaust system that features an integral diffuser-collector. Advanced testing methods as well as flow visualization techniques are applied to ascertain exhaust performance for a range of inlet conditions aerodynamically matched to flow exiting an industrial gas turbine. Computational Fluid Dynamics (CFD) was extensively used to complement testing with the aim to ascertain the design phase and off-design performance prediction capability of modern day numerical tools.
A prototype code to facilitate reduced-order modeling of propeller inflow distortion noise was completed and successfully validated during our 6-month Phase I project. The “Installed Propeller Noise Model” code (IPNM) accepts both aircraft wing/tail surface geometry input or prescribed propeller inflow data via CFD solution or other means. During Phase II, the IPNM code will be developed in a deliverable software tool to the Army. Maturation of the IPNM noise modeling code will be enhanced by experimental measurements of propeller blade loads on rotating through inflow distortion generated by upstream airfoils. In addition, hot film flow measurements in the upstream propeller potential field will lend understanding to the inflow-propeller blade load coupling and associated noise generation.
Analysis and testing were conducted to optimize an axial diffuser–collector gas turbine exhaust. Two subsonic wind tunnel facilities were designed and built to support this program. A 1/12th 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 3.4105. A 1/4th geometric scale test rig was designed and built to validate the data in the 1/12th 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. Multihole pneumatic pressure probes, particle image velocimetry (PIV), and surface oil flow visualization were 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 þ0.07 (experimental result) above the baseline geometry. The optimized performance, first measured at 1/12th scale and obtained using computational fluid dynamics (CFD) was validated at the full scale Reynolds number.
Techsburg was honored to be selected as one of 24 small businesses across the country to receive a Northrop Grumman World Class Team Supplier Award. The awards were presented December 3, 2014 at a Northrop Grumman luncheon in Springfield, Virginia, and Techsburg chairman Dr. Wing Ng was on hand to gratefully receive the award. Techsburg is currently supporting Northrop Grumman with analysis and testing for a variety of platforms.