Coupled aeropropulsive design optimisation of a boundary-layer ingestion propulsor

Abstract

Airframe–propulsion integration concepts that use boundary-layer ingestion (BLI) have the potential to reduce aircraft fuel burn. One concept that has been recently explored is NASA’s STARC-ABL aircraft configuration, which offers the potential for fuel burn reduction by using a turboelectric propulsion system with an aft-mounted electrically driven BLI propulsor. So far, attempts to quantify this potential fuel burn reduction have not considered the full coupling between the aerodynamic and propulsive performance. To address the need for a more careful quantification of the aeropropulsive benefit of the STARC-ABL concept, we run a series of design optimisations based on a fully coupled aeropropulsive model. A 1D thermodynamic cycle analysis is coupled to a Reynolds-averaged Navier–Stokes simulation to model the aft propulsor at a cruise condition and the effects variation in propulsor design on overall performance. A series of design optimisation studies are performed to minimise the required cruise power, assuming different relative sizes of the BLI propulsor. The design variables consist of the fan pressure ratio, static pressure at the fan face, and 311 variables that control the shape of both the nacelle and the fuselage. The power required by the BLI propulsor is compared with a podded configuration. The results show that the BLI configuration offers 6–9% reduction in required power at cruise, depending on assumptions made about the efficiency of power transmission system between the under-wing engines and the aft propulsor. Additionally, the results indicate that the power transmission efficiency directly affects the relative size of the under-wing engines and the aft propulsor. This design optimisation, based on computational fluid dynamics, is shown to be essential to evaluate current BLI concepts and provides a powerful tool for the design of future concepts.

Performance bookkeeping for aircraft configurations with fuselage wake-filling propulsion integration

“…Drag and thrust were calculated as net forces integrated over aircraft and propulsion system surfaces, respectively. The overall net force in axial direction was determined as the sum of the integrated pressure and viscous forces over all body surfaces and the pressure and momentum flux contributions on the fan face and fan exit [65][66][67][68]. In a similar manner, Ordaz et al carried out an adjoint-based numerical design and optimization of BLI concepts (NASA STARC-ABL and MTA450-business jet with aft fan) with the objective of minimized flow distortion at the propulsor [69,70].…”

A Review of Concepts, Benefits, and Challenges for Future Electrical Propulsion-Based Aircraft

“…However, the improvements achieved from the propulsion efficiency and drag reduction must compensate for the weight penalty of the electric drive system components, and the additional BLI propulsor fan, and inefficiency from the added components to achieve a net system level benefit. The study performed by Gray et al [83] on STARC-ABL emphasizes the coupling effects of electrical drivetrain efficiency on the sizing and performance of the propulsion system. In a similar line, a partially distributed hybrid electric small regional 50 passenger aircraft showed high reliance on the transmission system efficiency parameter and on the specific power of the electrical system [84].…”

“…This platform enables coupled integration of different discipline models coded in several programming languages with various levels of fidelity into a single analysis tool. The framework uses a gradient based approach with analytic derivatives and uses in-house solvers and optimization methods to address the optimization problem [83,156]. Gray et al [83] used this platform for coupled aero-propulsive interactions to examine an optimized split ratio in the shaft power for different powertrain drive transmission efficiency values.…”

“…The framework uses a gradient based approach with analytic derivatives and uses in-house solvers and optimization methods to address the optimization problem [83,156]. Gray et al [83] used this platform for coupled aero-propulsive interactions to examine an optimized split ratio in the shaft power for different powertrain drive transmission efficiency values. The platform uses ADFlow computational fluid dynamics (CFD) solver to solve the Reynolds-averaged Navier Stokes (RANS) equations and the PyCycle-1-D propulsion analysis tool for generating the adjoint analytic derivative.…”

How Certain Physical Considerations Impact Aerostructural Wing Optimization

“…OpenMDAO was developed at NASA Glenn and uses the modular analysis and unified derivatives theory to allow for modular construction and execution of complicated models [20]. OpenMDAO has been used to optimize a variety of problems, including wind turbines [21,22], boundary layer ingestion aircraft [23,24], thermodynamic engine cycles [25,26], and coupled thermal-mission problems [6,27].…”