New Hybrid Method for Predicting the Flowfields of Helicopter Rotors

Zhao, Qijun; Xu, Guohua; Zhao, Jiupeng

doi:10.2514/1.14863

Cited by 27 publications

(5 citation statements)

References 8 publications

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“…Because it is difficult to measure the pressure coefficient (Cp) distributions of the airfoil in the dynamic stall experiment by using the PIV technology, the CFD method 24 is employed to obtain the Cp of the airfoil under dynamic stall conditions. The unsteady RANS equations is employed as the governing equations for predicting the airfoil flowfield, and the cell center scheme is employed for spatial discretization of convective fluxes and viscous fluxes based on the embedded grids, and the highly efficient implicit scheme of LU-SGS is adopted for temporal discretization.…”

Section: Experiments and Cfd Simulation On A Trailing-edge Vortex Of Airfoilmentioning

confidence: 99%

Modification of Leishman–Beddoes model incorporating with a new trailing-edge vortex model

Wang

Zhao

2014

Proceedings of the Institution of Mechanical Engineers, Part G:

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The Leishman-Beddoes (L-B) model for airfoil dynamic stall is widely used in both helicopter rotor and wind turbine aerodynamics because it has fewer parameters and specific physical conceptions. However, in some cases of airfoil dynamic stall, the differences between the calculated results and experimental data are obvious, especially for the reattachment of airfoil dynamic stall. In order to observe the characteristics of dynamic stall about rotor airfoil, some dynamic stall experiments by PIV technology and CFD simulations based on RANS equations are accomplished. As a result, a trailing-edge vortex is observed which is not considered in the present L-B models. To consider the effect of this trailing-edge vortex on the unsteady aerodynamic characteristic, a new model of trailing-edge vortex is presented in this paper. In this method, the normal force induced by trailing-edge vortex is calculated by a similar methodology as leadingedge vortex, and the moment is modified due to the trailing-edge vortex. Consequently, the aerodynamic loads calculated by the modified L-B model at different reduced frequencies, Mach numbers, and airfoils are closer to the experimental data in the reattachment of dynamic stall. Therefore, it is demonstrated that the new trailing-edge vortex model further reflects the essence of trailing-edge vortex during the process of dynamic stall.

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Section: Experiments and Cfd Simulation On A Trailing-edge Vortex Of Airfoilmentioning

confidence: 99%

Modification of Leishman–Beddoes model incorporating with a new trailing-edge vortex model

Wang

Zhao

2014

Proceedings of the Institution of Mechanical Engineers, Part G:

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“…Xu et al [34] using SST k-ω turbulence model to calculate the near-ground flow field of UAV, the results showed that the velocity of the rotor increased first and then decreased, and the maximum velocity appeared near y/R=0.8. Xue et al [33] , Yang et al [36] , Zheng et al [37] , Wu et al [38] and Zhao et al [39] simulated the downwash airflow distribution in the helicopter flow field, the general trend of wind speed change in the same radial direction was determined as follows: wind speed first changed from small to large, then from large to small, the maximum wind speed was below the 3/4 rotor radius. Compared with the previous research results, the conclusions of each study are consistent in the trend of velocity distribution of the downwash field under the rotor, while the peak velocity position is slightly different.…”

Section: Discussionmentioning

confidence: 99%

Distribution regularity of downwash airflow under rotors of agricultural UAV for plant protection

Liu

Zhang

et al. 2021

International Journal of Agricultural and Biological Engineering

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In the plant protection spray operation of UAVs, the process of droplet from formation to sedimentation target is affected by airflow, easy to form uneven deposition. Accurately description of rotor downwash flow field, clarification of velocity vector distribution at different heights of the UAV rotor flow field, simulation of the flow field with high precision, which are the prerequisites for accurately analyzing the droplet deposition distribution in rotor downwash flow field. Based on CFD method, the detail of rotor flow field was numerically calculated. Taking LTH-100 single-rotor agricultural UAV as the research object, the three-dimensional solid model of UAV was established, the Reynolds average N-S equation was used as the control equation and the RNG κ-ε as the turbulence model to simulate the flow field of UAV in hover and lateral wind conditions, the wind velocity distribution at different altitudes of rotor downwash flow field was studied. The simulation results of the hover state showed that: In the flow field, the peak velocity appears in a circular distribution below the distal axis of the rotor. With the decrease of height, the peak velocity distribution area showed a tendency to expand gradually after small shrinkage; When the distance from the rotor was not more than 1.5 m, the downwash flow field presented an axisymmetric distribution based on the rotor axis, and the variation rate of velocity in the peak velocity was basically the same, turbulence in downwash flow field made the flow field more complex when the distance from rotor was larger than 2.0 m. On this basis, the optimal flight altitude of UAV is 1.5 m. Wind velocity test of the flow field was carried out on a rotor test bench, wind velocities at four altitudes of 0.5 m, 1.0 m, 1.5 m and 2.0 m were measured to verify the coincidence between the simulated and measured values. The test results showed that: the relative error between the measured and simulated values at four measurement heights were between 0.382-0.524, and the overall average relative errors was 0.430, which verified the confidence level of simulated values for measured values. When the lateral wind velocity was 3 m/s, 4 m/s and 5 m/s, the simulation results showed that: The distribution trend of airflow velocity at the same altitude in lateral-wind flow field with different wind speeds was similar; When the lateral wind speed was 5 m/s, the coupling field formed by the lateral wind and rotor airflow cannot reach the height of 2 m below the rotor. The results of this study can provide more accurate environmental conditions for theoretical analysis of droplet deposition regularity in the flow field, and also provide methodological guidance for the related research on rotor flow field of multi-rotor UAV.

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“…To satisfy the requirement of OFV simulation, the far-field boundary of airfoil grids is fixed at 25 times the airfoil chord, and the y + of the grids near the wall surface is smaller than 1.2. In this research, the background grid is composed of 300 × 300 points with a far-field boundary of 50 c (airfoil chord), and the inverse map method [29] is employed in this code to search donor element. As shown in Figure 2, the oscillating velocity is simulated by moving the airfoil back and forth periodically [30,31].…”

Section: Numerical Simulation Methodsmentioning

confidence: 99%

Unsteady Aerodynamic Characteristics Simulations of Rotor Airfoil under Oscillating Freestream Velocity

Qing

Zhao

2020

Applied Sciences

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The dynamic stall characteristics of rotor airfoil are researched by employing unsteady Reynolds-Averaged Navier-Stokes (RANS) method under oscillating freestream velocity conditions. In order to simulate the oscillating freestream velocity of airfoil under dynamic stall conditions, the moving-embedded grid method is employed to simulate the oscillating velocity. By comparing the simulated dynamic stall characteristics of two-dimensional airfoil and three-dimensional rotor, it is indicated that the dynamic stall characteristics of airfoil under oscillating freestream velocity reflect the actual dynamic stall characteristics of rotor airfoil in forward flight more accurately. By comparing the simulated results of OA209 airfoil under coupled freestream velocity/pitching oscillation conditions, it is indicated that the dynamic stall characteristics of airfoil associate with the critical value of Cp peaks (i.e., the dynamic stall characteristics of OA209 airfoil would be enhanced when the maximum negative pressure is larger than −1.08, and suppressed when this value is smaller than −1.08). By comparing the characteristics of vortices under different oscillating velocities, it indicates that the dissipation rate of leading edge vortex presents as exponent characteristics, and it is not sensitive to different oscillating velocities.

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New Hybrid Method for Predicting the Flowfields of Helicopter Rotors

Cited by 27 publications

References 8 publications

Modification of Leishman–Beddoes model incorporating with a new trailing-edge vortex model

Modification of Leishman–Beddoes model incorporating with a new trailing-edge vortex model

Distribution regularity of downwash airflow under rotors of agricultural UAV for plant protection

Unsteady Aerodynamic Characteristics Simulations of Rotor Airfoil under Oscillating Freestream Velocity

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