Aeromechanics Analysis of a Coaxial Rotor System in Hover and High-Advance-Ratio Forward Flight

2016 ◽  
Author(s):  
Roland Feil ◽  
Juergen Rauleder ◽  
Manfred Hajek
Keyword(s):  
Rotor System ◽  
Forward Flight ◽  
Coaxial Rotor ◽  
Advance Ratio

scholarly journals Wind Tunnel Studies on Hover and Forward Flight Performances of a Coaxial Rigid Rotor

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 205
Author(s):  
Chang Wang ◽  
Minqi Huang ◽  
Xianmin Peng ◽  
Guichuan Zhang ◽  
Min Tang ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Tilt Angle ◽  
Lift Coefficient ◽  
Rotor System ◽  
Rigid Rotor ◽  
Forward Flight ◽  
Coaxial Rotor ◽  
Advance Ratio ◽  
Hover Flight ◽  
Development Center

The aerodynamic performance of a reduced-scale coaxial rigid rotor system in hover and steady forward flights was experimentally investigated to gain insights into the effect of interference between upper and lower rotors and the influences of the advance ratio, shaft tilt angle and lift offset. The rotor system featured by 2 m-diameter, four-bladed upper and lower hingeless rotors and was installed in a coaxial rotor test rig. Experiments were conducted in the Φ3.2 m wind tunnel at China Aerodynamics Research and Development Center (CARDC). The rotor system was tested in hover states at collective pitches ranging from 0° to 13° and it was also tested in forward flights at advance ratios up to 0.6, with specific focus on the shaft tilt angle and lift offset sweeps. To ensure that the coaxial rotor was operating in a similar manner to that of the real flight, the torque difference was trimmed to zero in hover flight, whilst the constant lift coefficient was maintained in forward flight. An isolated single-rotor configuration test was also conducted with the same pitch angle setting in the coaxial rotor. The hover test results demonstrate that the figure of merit (FM) value of the lower rotor is lower than that of the upper rotor, and both are lower than that of the isolated single rotor. Moreover, the coaxial rotor configuration can contribute to better hover efficiency under the same blade loading coefficient (CT/σ). In forward flight, the effective lift-to-drag (L/De) ratio of the coaxial rigid rotor does not monotonously change as the advance ratio increases. Increases in the required power and drag in the case with a high advance ratio of 0.6 leads to the decreasing L/De ratio of the rotor. Meanwhile, the L/De ratio of the rotor is relatively high when the rotor shaft is tilted backward. The increasing lift offset tends to result in reduced required rotor power and an increase in the rotor drag. When the effect of the reduced rotor power is greater than that of the increased rotor drag, the L/De ratio increases as the lift offset increases. The L/De ratio can benefit significantly from lift offset at a high advance ratio, but it is much less influenced by lift offset at a low advance ratio. The forward performance efficiency of the upper rotor is poorer than that of the lower rotor, which is significantly different from the case in the hover flight.

Aeromechanics Analysis of a High-Advance-Ratio Lift-Offset Coaxial Rotor System

2019 ◽  
Vol 56 (1) ◽  
pp. 166-178 ◽  
Author(s):  
Roland Feil ◽  
Jürgen Rauleder ◽  
Christopher G. Cameron ◽  
Jayant Sirohi
Keyword(s):  
Rotor System ◽  
Coaxial Rotor ◽  
Advance Ratio

Performance and Loads of a Reduced-Scale Coaxial Counterrotating Rotor

2019 ◽  
Vol 64 (4) ◽  
pp. 1-15
Author(s):  
Christopher Cameron ◽  
Jayant Sirohi ◽  
Joseph Schmaus ◽  
Inderjit Chopra
Keyword(s):  
Rotor System ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Forward Flight ◽  
Blade Tip ◽  
Advance Ratio ◽  
Drag Ratio ◽  
Lift To Drag Ratio ◽  
Reduced Scale ◽  
Blade Tip Clearance

The results of hover and wind tunnel tests of a reduced-scale, closely spaced, rigid, coaxial counterrotating rotor system are presented, along with results from a comprehensive analysis. The system features two-bladed upper and lower rotors, 2.03 m in diameter, with uniform section, untwisted rotor blades. Measurements include upper and lower rotor steady and vibratory hub loads, as well as control angles and control loads. Blade tip clearance was measured using an optical sensor. The rotor system was tested in hover and at advance ratios between 0.21 and 0.53, at collective pitches ranging from 2° to 10° achieving blade loadings in excess of 0.10. At each forward flight operating condition, sweeps of lift offset up to 20% were performed, while selected test conditions were repeated at different rotor speeds and interrotor index angles. Hover tests showed that aerodynamic interaction between upper and lower rotors decreased individual rotor performance compared to isolated rotors and induced a four-per-revolution vibratory load corresponding to the blade passage frequency. In forward flight, the rotor effective lift-to-drag ratio was found to increase with increasing advance ratio and lift offset, resulting in a 30% improvement at 20% lift offset and 0.5 advance ratio. The lower coaxial rotor was found to operate at higher lift-to-drag ratio than the upper rotor, in contrast to the behavior in hover. Lift offset resulted in a decrease in blade tip clearance with a corresponding increase in rotor side force. Vibratory loads increased with advance ratio, with the largest loads in the two- and four-per-revolution harmonics. Lift offset, in conjunction with interrotor index angle, is shown to modify vibratory forces and moments transmitted to the fixed frame, increasing some force components while decreasing others.

Blade Passage Loads and Deformation of a Coaxial Rotor System in Hover

2019 ◽  
Vol 56 (6) ◽  
pp. 2144-2157 ◽  
Author(s):  
Daiju Uehara ◽  
Jayant Sirohi ◽  
Roland Feil ◽  
Jürgen Rauleder
Keyword(s):  
Rotor System ◽  
Blade Passage ◽  
Coaxial Rotor

scholarly journals Spectrum Analysis of a Coaxial Dual-Rotor System with Coupling Misalignment

2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Hongxian Zhang ◽  
Liangpei Huang ◽  
Xuejun Li ◽  
Lingli Jiang ◽  
Dalian Yang ◽  
...  
Keyword(s):  
Spectral Characteristics ◽  
Element Model ◽  
Rotor System ◽  
Harmonic Frequencies ◽  
Coaxial Rotor ◽  
Outer Rotor ◽  
Frequency Components ◽  
Harmonic Resonance ◽  
The Finite Element Model ◽  
Engine Rotor

The finite element model of a dual-rotor system was established by Timoshenko beam element. The dual-rotor system is a coaxial rotor whose supporting structure is similar to that of an aero-engine rotor system. The inner rotor is supported by three bearings, which makes it a redundantly supported rotor. The outer rotor connects the inner rotor by an intershaft bearing. The spectrum characteristics of the dual-rotor system under unbalanced excitation and misalignment excitation were analysed in order to study the influence of coupling misalignment of the inner rotor on the spectral characteristics of the rotor system. The results indicate that the vibration caused by the misaligned coupling of the inner rotor will be transmitted to the outer rotor through the intershaft bearing. Multiple harmonic frequency components, mainly 1x and 2x, will be excited by the coupling misalignment. The amplitudes of all harmonic frequencies increase with the misalignment in both the inner and outer rotors. The vibration level of the outer rotor affected by the misalignment is lower than that of the inner rotor because it is far from the misaligned coupling. Harmonic resonance occurs when any harmonic frequencies of the misalignment response coincide with a natural frequency of the system. In order to verify the theoretical model, experiments are performed on a test rig. Both the experimental and simulation results are in good accordance with each other.

Sensitivity Analysis and Uncertainty Quantification of a Coaxial Rotor System

2019 ◽  
Author(s):  
Phuriwat Anusonti-Inthra ◽  
Ethan Corle ◽  
Brendan Smith ◽  
Zackery Nieto
Keyword(s):  
Sensitivity Analysis ◽  
Uncertainty Quantification ◽  
Rotor System ◽  
Coaxial Rotor
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