# Thrust and Drag Evaluation of Boundary Layer Ingesting Aircraft Propulsion

[Examensarbete på avancerad nivå]

As EU has set a goal to reduce aircraft CO2 and NOx emissions by 75% and 90% respectively by year 2050 both relative the levels in 2000[4], more fuel-efficient aircraft are needed. In that pursuit the fan pressure ratio is decreasing and bypass ratio is increasing. However, the benefit of increasing bypass ratio can be eliminated due to increased weight and drag, due to an increased engine size. Another possibility to improve efficiency is to add an fan in the rear-end of the aircraft. The fan would ingested the boundary layer (BLI) and give more thrust for a given power input and therefore increase the propulsive efficiency. To evaluate the potential benefits of BLI fans without investigating a large number of possible installation geometries a thermodynamic performance method needs to be created and validated. Such a method can be used to see the effects of different fan sizes or fan pressure ratios. In this thesis performance calculations are based on a corrected inlet momentum, here called the equivalent velocity bookkeeping method. The performance calculations are validated against flow calculations for axi-symmetric geometries of a fuselage and fan installation. The flight altitude, speed, fan size and fan operating conditions were varied to study the accuracy the method. A new definition of velocity is needed due to the velocity at the entry of the fan is lower due to boundary layer. The new velocity is called the equivalent velocity. To design the nacelle an CST-curve method was used. The CST-method is basically an fourth-order polynomial. Also an method is needed to be able to calculate an nacelle drag, the method is based on drag calculation on a flat plate and weighting both the freestream and boundary layer pressure. The aircraft of interest is an A320 which is translated to an two-dimensional axisymmetric design. Furthermore the design method of the fuselage is varied if the fan is included or not. When no fan is included the CST-method is used if fan included an polynomial was made. The concept of validating is divided in to two parts. The first is to validate by iterating varies input values to give an net force equal to that of CFD, the second validation is that from an clean aircraft get an net force equal that of CFD. This thesis showed that method created could estimate the net force from an clean fuselage within 80 N this after accounting for an thrust coefficient and error made when calculating the impulse at the inlet. The method to calculate the drag was also sufficient to use from an fuselage as this resulted in a difference of around 7 N.

**Nyckelord: **CST-curve, Boundary layer ingestion, Equivalent velocity

Publikationen registrerades 2018-08-21. Den ändrades senast 2018-09-20

CPL ID: 255712

Detta är en tjänst från **Chalmers bibliotek
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