AEROMECHANICS OF A DOUBLE ANHEDRAL TIP COMPOSITE ROTOR: EXPERIMENT AND MODELING
| dc.contributor.advisor | Datta, Anubhav AD | en_US |
| dc.contributor.author | Chi, Cheng | en_US |
| dc.contributor.department | Aerospace Engineering | en_US |
| dc.contributor.publisher | Digital Repository at the University of Maryland | en_US |
| dc.contributor.publisher | University of Maryland (College Park, Md.) | en_US |
| dc.date.accessioned | 2022-09-16T05:35:38Z | |
| dc.date.available | 2022-09-16T05:35:38Z | |
| dc.date.issued | 2022 | en_US |
| dc.description.abstract | This thesis investigates the performance and loads on a double-anhedral tip modern composite rotor. Double anhedral tips are a recent introduction in rotors with no research data available for understanding their behavior or modeling them adequately. The objectives were to bridge these gaps. Both experimental and analytical methods were employed to fulfill the objectives systematically. Double anhedral blades of 5.6-ft diameter were designed and fabricated. The blades had a uniform VR-7 airfoil profile, a D-spar, $-16^\circ$ twist, a $5^{\circ}$ dihedral from $80\%$R to $95\%$R and a $15^{\circ}$ anhedral from $95\%$R to the tip. The blades were built in-house using IM7/8552 graphite/epoxy prepreg weave. They were instrumented for strains and structural loads measurement. A two-bladed hingeless hub was designed and fabricated for the vacuum chamber to measure rotating frequencies (fan plot). The hover tests were performed on the Alfred Gessow Rotorcraft Center Mach-scaled four-bladed hingeless rig. Tests were carried out up to tip Mach number of 0.6 over a collective range of $0^{\circ}$ to $10^{\circ}$. The rotor performance, blade structural loads, pitch link loads, and surface strains were measured. A double anhedral tip is a 3-D structure. Accordingly, a 3-D model was developed with CATIA (CAD), Cubit (hexahedral meshing), and X3D (aeromechanics). The 3-D CAD was constructed with guidance from Boeing to ensure the geometry was representative of a modern rotor yet generic enough to be open source for U.S. Gov-industry-academia joint study. The meshing used 27-node solid hexahedral elements, as needed by X3D. The pitch bearing was modeled with a joint commanded by control input. In total there were 3427 elements and approximately 100,000 degrees of freedom. Properties of the composite plies were acquired through in-house four-point bending coupon tests. The aerodynamic model used in-house CFD extracted C-81 decks and a lifting line with a refined free wake. The data acquired from tests were used to validate the model. A 3-D model of a straight blade was also developed as a baseline for comparison. These models have the same external and internal structure except for the tip. By comparing the behavior of the analytical models, insights were gained on the impacts of a double anhedral tip on the structural dynamics and aeromechanics in hover and forward flight. The local center of gravity offset at the tip appeared to make the blade softer. No performance gain was predicted in hover, however, the static flap, lag, and torsion moments at the root all decreased due to the vertical center of gravity offset in the tip portion. Strong 3-D strain patterns and multiple strain concentrations at the tip were predicted. In forward flight, the 4/rev vibratory vertical hub load and hub moments were predicted to increase by $15\%$ and $100\%$ respectively at tip speed ratio 0.1. Higher 1/rev oscillatory flap bending moment and 2/rev oscillatory lag bending moments were also predicted. The key conclusion is that the vertical center of gravity of the double anhedral tip can have significant ramifications on blade loads - reducing the static loads while increasing oscillatory harmonics particularly vibratory harmonics in forward flight. Systematic wind-tunnel tests are needed in future to dissect these effects. This thesis laid the foundations of that future through blade fabrication, vacuum and hover testing. | en_US |
| dc.identifier | https://doi.org/10.13016/jsqg-agtc | |
| dc.identifier.uri | http://hdl.handle.net/1903/29157 | |
| dc.language.iso | en | en_US |
| dc.subject.pqcontrolled | Aerospace engineering | en_US |
| dc.subject.pquncontrolled | 3-D modeling | en_US |
| dc.subject.pquncontrolled | Aeromechanic analysis | en_US |
| dc.subject.pquncontrolled | Composite rotor | en_US |
| dc.subject.pquncontrolled | Double anhedral tip | en_US |
| dc.subject.pquncontrolled | Rotor experiments | en_US |
| dc.title | AEROMECHANICS OF A DOUBLE ANHEDRAL TIP COMPOSITE ROTOR: EXPERIMENT AND MODELING | en_US |
| dc.type | Dissertation | en_US |
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