Boundary-Layer Ingestion Key To MIT/NASA D8 Hopes

By Guy Norris, Graham Warwick
Source: Aviation Week & Space Technology

In addition, the combination of low thrust and high pressure ratio for an ultra-high-bypass D8 engine points to a decrease in compressor-exit corrected flow, which implies very small high-pressure compressor blade heights. “They could be 0.5 inches in height or smaller, and that will mean it will be hard to hold clearances,” Hathaway says. “We have research ongoing into how to mitigate those losses. We have to start looking at novel architectures when we look at small blades.”

But Uranga points out the D8 configuration could provide substantial fuel-burn reductions through boundary-layer ingestion even with existing engine technology.

“Small cores are not on the critical path,” says Greitzer. “The BLI benefit is completely decoupled from the core, and only the fan is the issue. But we have done some work on the behavior of turbomachinery in that flow regime, and Pratt & Whitney has conceptual designs for engines that have different architectures and thus different mechanical parameters in small sizes.”

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