Boundary Layer Ingestion: Theoretical and Experimental Research:

by T. Hartuç

Institution: Delft University of Technology
Year: 2015
Keywords: Boundary Layer Ingestion; efficiency; propeller; wake ingestion; Particle Image Velocimetry
Record ID: 1254860
Full text PDF: http://resolver.tudelft.nl/uuid:7b305772-db45-431a-a431-3799e2cf0f20


In this thesis both Wake Ingestion (WI) and Boundary Layer Ingestion (BLI) configurations have been investigated and analyzed with respect to their application to aircraft design. WI and BLI in the context used here means positioning the engine such that it ingests boundary layer fluid for the purpose of saving shaft-power. This research compares propulsors in free-stream, WI and BLI configurations for their shaft-power savings. The power elements present in these configurations are identified theoretically using the Power Balance Method (PBM) and quantified experimentally by using Particle Image Velocimetry (PIV). Also, these different configurations are compared using non-dimensional parameters such as thrust-power coefficient and propeller efficiency. This is accomplished by integrating different instruments able to capture the relevant physical phenomena such as thrust, torque and Rotations Per Minute (RPM). These measurements are conducted in the low-speed wind-tunnel facility of Delft University of Technology. The aim is to experimentally quantify the increase in propeller efficiency for WI and BLI configurations. In order to properly compare the three configurations, these are tested in two different wind-tunnel conditions; ’equilibrium’ and ’constant-speed’. In the equilibrium case, propulsor thrust is set identical to body drag for varying wind-speeds whereas the constant-speed case requires the wind-speed to be fixed and propulsor thrust to vary. The main finding is that a propulsor in WI configuration saves 9% shaft-power w.r.t. an identical propulsor in free-stream configuration under identical net-force conditions. This power saving is more prominently present in BLI configuration where 18% power saving is measured. This measured power saving is due to the fact that the propulsor is immersed in the slower moving wake. The propulsive efficiency, which is different from propeller efficiency, can generate values that exceed 100% in WI and BLI configurations. Therefore, a different definition of efficiency for a wake ingested propulsor is introduced. Using this new definition, the propulsive efficiency does not exceed unity for perfect wake filling configurations. The PIV analysis on the identified power terms shows that a limited amount of wake power is available for performance enhancement. The analysis also showed that pressure plays a significant role in these tightly integrated configurations which cannot be ignored. This insight can be used for the development of WI and BLI applications. These applications are needed as a mean to reduce fuel consumption for future aircraft.