Research presented in this thesis focuses on the development of a novel, open-source, automated, and fully parametric non-axisymmetric turbomachinery aero-design-optimization system, NAX. This research forms a part of a collaboration between NASA Glenn Research Center and University of Cincinnati for the development of a Boundary Layer Ingestion based Turbo-electric propulsion system under the NASA N+3 initiative.
For the present design, a 1.5 stage aft-mounted Tail Cone Thruster (TCT) unit is considered to ingest the boundary layer flow from the air-frame to increase the overall propulsion efficiency of the aircraft. This results in circumferential distortion (r, θ)in total pressure, swirl, and meridional flow (PT, α,ϕ) at the TCT inlet. at the TCT inlet. These non-uniformities causes partial off-design operation of the TCT and a significant departure in its component efficiency and aero-mechanics integrity.
A key feature of the NAX design system is its capability to allow for the design/optimize of spanwise (r) and/or circumferentially (θ) non-axisymmetric 3D blade shapes. It uses a harmonics-based design space parametrization, which offers an extended control in r, θ on blade parameters like blade angles, sweep, lean, chord, and thickness distribution. These non-uniformities (Σ ai sin(θ + ϕi)) can be controlled by modifying the magnitude and phase (i) at arbitrary span. NAX is demonstrated with the Inlet Guide Vanes (IGV) for TCT propulsor. This non-axisymmetric IGV is optimized to reduce the downstream rotor incidence and increase IGV performance under 2D distortion. A novel approach of transforming relative flow angle ( β) from IGV to rotor frame of reference is used to include the uncoupled rotor effects in the optimization of IGV.
The typical multi-fidelity design framework is used to develop TCT using a PT radial distortion at throughflow level and then further optimized for 2D distortion at 3D levels. For design process verification, a manual design is first created using only first mode (a1, ♓) of circumferential variation of IGV trailing edge angle as input (15% span). A least-squares method (NL2SOL) was then employed using the first mode (a1, ♓) at 5 spans. Finally, Genetic Algorithm (GA) was used with 2 modes (a1,2,♓,2) at span 0, 15 % and 1 mode at the other 3 spans to optimize IGV and reduce stage losses (ζ). Using NAX design system an overall reduction in harmonic content was achieved, 48% using GA (hub), 41% using GA (span 20%) and 57% using NL2SOL (span 45 %). Swirl, static pressure propagation, and work input at the rotor inlet are also explained, validating the choice of ( β) for optimization. Finally, a Finally, a non-axiIGV- axi rotor configuration is optimized for performance at near-stall (≅ 1% increase in η) and design-point using Multi-objective GA (MOGA).This demonstrates the efficacy of NAX-Optimization system for multi-row turbomachinery design.
The NAX development and design/optimization framework have enabled a new dimensionality (θ) into the definition of 6 blade design parameters in harmonics based turbomachinery design space. NAX capabilities can be used for non-axisymmetric end-wall designs, OGV/pylons, and non-axisymmetric volute designs.