Flow-Control-Enabled Aggressive Turbine Transition Ducts and Engine System Analysis

Abstract

A methodology for designing flow-control-enabled aggressive transition ducts and evaluating their system level benefits is presented. The present methodology consists of a novel approach of coupling a parametric transition duct geometry with a flow control model to optimize aggressive transition duct shapes to reduce and/or eliminate flow separations and maximize system performance. Without boundary layer control, the flow through these aggressive transition ducts is characterized by large pressure losses due to massive flow separation resulting in low system performance. Flow control has the potential to eliminate flow separation in these aggressive transition ducts and was included in the present study as an enabling technology. A hierarchy of high and low fidelity models was utilized to include the relevant system effects, capturing not only the performance of the transition duct itself, but also the impact of the exit flow from the transition duct on the low pressure turbine and the engine and aircraft performance. The methodology was used to maximize range with minimum fuel burn by evaluating a system defined by families of transition duct geometries with large radial offsets coupled with a meanline representation of a low pressure turbine. In this example aircraft and propulsion benefits include the elimination of a low pressure turbine stage, which in turn translates into significant weight savings and compactness, while maintaining or improving overall propulsion system performance. The analysis also provides a direction for future studies aimed at defining what the required transition duct radial offsets and the corresponding flow authority levels to achieve aircraft range and total fuel burn benefits are.