Air Jets to Modulate Flow in a Nozzle Vane Passage Within a Linear Cascade

In gas turbines, it is difficult to effectively incorporate variable geometry within the pressurized hot section of the engine. To avoid using complex mechanical linkages that may wear and leak, an approach using pneumatic actuation with air jets can be deployed eliminating the need for any internal moving parts. An application for an internal pneumatic actuator was conceived and studied. After initial conceptual assessment and CFD analysis of air jets within a turbine nozzle vane passage, a linear cascade rig was assembled to validate and demonstrate the modulation of flow capacity within a nozzle vane passage using the jet flow. This paper will explain the concept, reflect on the supportive analysis demonstrating feasibility, and will show test results from the linear cascade rig. The additive manufactured test section, method, and instrumentation is described including the various configurations evaluated. Data show that flow capacity can be altered with the injection of air at high momentum flux ratios upstream of the throat plane. Incurred pressure losses are sufficiently small to favor integration in engine for cycle thermal efficiency increases at part load operation. Parameters investigated include total pressure losses, flow reduction, flow angle and momentum flux ratio. Geometry variations assessed included hole positioning relative to nozzle throat, injection hole designs. Airfoil geometry was representative of a center section of a low-pressure turbine. Also included is the detailed normalized data analysis and conclusions.