Scaled-Model Testing of Rotor Hub Root-End Airfoil Shapes
Open Access
- Author:
- Tierney, Charles John
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 16, 2019
- Committee Members:
- Sven Schmitz, Thesis Advisor/Co-Advisor
- Keywords:
- Helicopter
Rotor Hub
Flow
Drag
Prediction - Abstract:
- In order to extend the boundaries of helicopter performance and increase forward-flight speed, it is necessary to reduce the drag on the rotor hub, which can account for as much as 30% of the total parasite drag on the helicopter. Currently, there is limited experimental data available to predict the drag force on new hub configurations. The purpose of this testing is to create a database of lift and drag at various angles of attack to aid in hub design and hub drag prediction. Testing was conducted in the 12 inch-diameter water tunnel at ARL Penn State on four shapes - DBLN 526, 4:1 Ellipse, 3.25:1 Rectangle, and a new Optimized Cambered Shape (OCS) designed at UT Knoxville. Load cell data for lift and drag were obtained for angles of attack from approximately −5◦ to 5◦ at Reynolds numbers from 3.1 ×10^5 to 6.2 ×10^5. Drag data were also calculated using a control volume analysis and PIV velocity fields taken in the wake of the airfoils. The highest Cd were calculated for the 4:1 Ellipse and OCS in reverse flow. Drag coefficients calculated for the OCS in forward flow were comparable to the DBLN 526. The highest magnitude CL were measured for the DBLN 526, OCS in reverse flow, and 4:1 Ellipse, while low-magnitude CL is observed over the tested range of angles of attack for the OCS in forward flow. CD Reynolds number sensitivity was similar between the DBLN 526 and the 4:1 Ellipse, while CD for the OCS is much more sensitive to Reynolds number in reverse flow than in forward flow. A low-order BEM drag prediction model used the drag coefficient data from this testing to estimate the drag on a "Low-Drag Hub" designed at Penn State. The BEM prediction code produced 2/rev drag harmonics twice that observed in the experimental data for the low-drag hub but underpredicted the 4/rev drag harmonic by approximately 40%. The prediction code fails to capture higher-frequency content (6/rev, 8/rev, etc.). Results are plotted and tabulated for use in future hub drag prediction toolset.