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 Lift Offset Rotor: Hover and Wind Tunnel Testing

2019 ◽  
Vol 64 (2) ◽  
pp. 1-12 ◽  
Author(s):  
Christopher G. Cameron ◽  
Jayant Sirohi
Keyword(s):  
Wind Tunnel ◽  
Scale Model ◽  
Wind Tunnel Testing ◽  
Forward Flight ◽  
Maximum Increase ◽  
Bladed Rotor ◽  
Advance Ratio ◽  
Thrust And Torque ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The results of hover and wind tunnel tests of a reduced-scale, model rotor operating with lift offset are presented. The two-bladed rotor had a diameter of 2.03 m and constant cross section untwisted blades. Measurements include steady and vibratory hub loads, as well as control angles and pushrod loads. The rotor system was tested in hover and at advance ratios between 0.21 and 0.53, at collective pitches ranging from 3° to 10°, achieving blade loadings in excess of 0.10. At each forward flight operating condition, sweeps of lift offset up to 15% were performed. In forward flight, the rotor effective lift-to-drag ratio was found to increase with increasing advance ratio and lift offset, with a maximum increase of 40% compared to the zero lift offset case. Vibratory loads increased with advance ratio, with the largest loads in the two- and four-per-revolution harmonics. Lift offset is shown to modify vibratory hub forces and moments transmitted to the fixed frame, increasing vibratory rolling and pitching moments while decreasing vibratory thrust and torque.

scholarly journals Geometry Design of Coaxial Rigid Rotor in High-Speed Forward Flight

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Bo Wang ◽  
Xin Yuan ◽  
Qi-jun Zhao ◽  
Zheng Zhu
Keyword(s):  
High Speed ◽  
Reverse Flow ◽  
Geometrical Parameters ◽  
Rigid Rotor ◽  
Forward Flight ◽  
Geometry Design ◽  
Coaxial Rotor ◽  
Flow Field Characteristics ◽  
Speed Level ◽  
Blade Tip

The aerodynamic performance analysis and blade planform design of a coaxial rigid rotor in forward flight were carried out utilizing CFD solver CLORNS. Firstly, the forward flow field characteristics of the coaxial rotor were analyzed. Shock-induced separation occurs at the advancing side blade tip and severe reverse flow occurs at the retreating side blade root. Then, the influence of geometrical parameters of the coaxial rigid rotor on forward performance was investigated. Results show that swept-back tip could reduce the advancing side compressibility drag and elliptic shape of blade planform could optimize the airload distribution at high advance ratio flights. A kind of blade planform combining swept-back tapered tip and nonlinear chord distribution was optimized to improve the rotor efficiency for a given high-speed level flight based on geometric parameter studies. The optimized coaxial rotor increases lift-to-drag ratio by 30% under the design conditions.

Aerodynamic performance of a small-scale tilt rotor: Numerical simulation and experiment in steady state

2020 ◽  
pp. 095440622095035
Author(s):  
Haitao Yang ◽  
Wei Xia ◽  
Kun Wang ◽  
Shuling Hu
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Tilt Angle ◽  
High Speed ◽  
Aerodynamic Performance ◽  
Small Scale ◽  
Thrust Coefficient ◽  
Wind Tunnel Tests ◽  
Advance Ratio

The present work studies the aerodynamic performance of a small-scale rotor in tilting transition states through wind tunnel tests and numerical simulations. Firstly, the test platform for the rotor aerodynamics is built up, and the Computational Fluid Dynamics (CFD) model of flow field around the rotors is established based on the multiple reference frame method. Secondly, the effects of flow velocity, tilt angle and advance ratio on the aerodynamic performance of the rotor are investigated using both the numerical simulation and the wind tunnel test. It is found that for the Model 8038 rotor with maximum effeciency of 0.567 at advance ratio of 0.43, the rotor thrust coefficient increases with the increase of the Reynolds number. At Reynolds number of 410 thousand to 820 thousand, the thrust coefficient increases slightly with the increase of the rotating speed. The results also show that the thrust coefficient decreases with the increase of the advance ratio. With high-speed airflow and relatively low-speed rotation, “windmill” phenomenon is found in the experiment. The tilting of the rotor from level flight to hovering increases the thrust coefficient. Highly dependency of the tilt angle on the thrust coefficients at given advance ratios is found in the wind tunnel tests.

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.

Experimental investigations of flow over NACA airfoils 0021 and 4412 of wind turbine blades with and without Tubercles

2021 ◽  
pp. 0309524X2110071
Author(s):  
Usman Butt ◽  
Shafqat Hussain ◽  
Stephan Schacht ◽  
Uwe Ritschel
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Wind Turbine ◽  
Critical Region ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Wind Turbine Blades

Experimental investigations of wind turbine blades having NACA airfoils 0021 and 4412 with and without tubercles on the leading edge have been performed in a wind tunnel. It was found that the lift coefficient of the airfoil 0021 with tubercles was higher at Re = 1.2×105 and 1.69×105 in post critical region (at higher angle of attach) than airfoils without tubercles but this difference relatively diminished at higher Reynolds numbers and beyond indicating that there is no effect on the lift coefficients of airfoils with tubercles at higher Reynolds numbers whereas drag coefficient remains unchanged. It is noted that at Re = 1.69×105, the lift coefficient of airfoil without tubercles drops from 0.96 to 0.42 as the angle of attack increases from 15° to 20° which is about 56% and the corresponding values of lift coefficient for airfoil with tubercles are 0.86 and 0.7 at respective angles with18% drop.

Sign in / Sign up

Export Citation Format

Share Document