Tip Vortex Conservation on a Helicopter Main Rotor Using Vortex-Adapted Chimera Grids

Dietz, Markus; Keßler, Manuel; Krämer, Ewald; Wagner, Siegfried

doi:10.2514/1.28643

Cited by 22 publications

(12 citation statements)

References 11 publications

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“…The adapted grid technique is commonly used to reduce numerical dissipation. Lately, a vortex-adapted grid using a chimera technique [2] has been applied to conserve tip vortices of the rotor in forward flight. These high-order schemes were also used to avoid dissipation problems.…”

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confidence: 99%

Numerical Simulation of Rotor Using Coupled Computational Fluid Dynamics and Free Wake

Wie

Kwon

et al. 2010

Journal of Aircraft

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Rotor aerodynamics is governed by wake behavior. Particularly, aerodynamic performance in the hovering flight condition is determined by the structure and the strength of the wake. In this paper, rotating blades were simulated using a tightly coupled computational fluid dynamics and time-marching free-wake method in hovering and forward flight. The rotating blades and a flowfield near the rotor are calculated by the computational fluid dynamics, and the strength and motions of the wake are simulated with the time-marching free-wake method. A moving overset grid technique is applied to consider rotor motions during hovering and forward flight. Inflow and outflow conditions in the computational fluid dynamics domain are provided from an induced flow rate by the time-marching free-wake method at each time step. The strength of the trailed vortices is determined from a sectional lift calculated in the rotating blade, which is computed using the computational fluid dynamics. The present coupled method was compared with other inflow and outflow conditions, such as source-sink and Riemann-invariant conditions. To investigate the robustness of the present method, grid-size effects were also tested in large and small background grid systems. Nomenclature a = distance between velocity position and vortex filament a c = vortex core radius a 1 = speed of soundMach number, R=a 1 R = rotor radius r = spanwise distance along rotor y = wake node position = flapping angle = vortex circulation strength bound = bound vortex circulation strength trailed = trailed vortex circulation strength = pitch angle = azimuth angle

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confidence: 99%

Numerical Simulation of Rotor Using Coupled Computational Fluid Dynamics and Free Wake

Wie

Kwon

et al. 2010

Journal of Aircraft

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“…In other words, the specific structural property will get more influenced when the Pearson coefficient departs from one and approaches zero. Note that a retrimming is used throughout the sensitivity study for realistic analysis results [19]. Figure 20 shows the Pearson correlation coefficients describing the overall sensitivity of blade elastic property changes on section airloads (Fig.…”

Section: Sensitivity Of Blade Structural Propertiesmentioning

confidence: 99%

Study on Blade Property Measurement and Its Influence on Air/Structural Loads

et al. 2015

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In this study, the structural properties of Second Higher-Harmonic Aeroacoustic Rotor Test blades are determined using state-of-the-art test techniques. The measurement includes bending and torsion stiffnesses, section geometric offsets, and mass and inertia properties. Several Second Higher-Harmonic Aeroacoustic Rotor Test blades, including the original instrumented blade used for the wind-tunnel test campaign in 2001, as stated by Yu et al. ) are used for the activity. A finite element-based cross-section analysis combined with an x-ray computer tomography technique is employed for the cases where no mechanical measurement is available or attempted. The resulting structural properties are correlated against the earlier estimated values, which have extensively been used in the literature for the validation of the Second Higher-Harmonic Aeroacoustic Rotor Test rotor. A substantial deviation is observed between the present measurement and the earlier property result. The comprehensive rotor dynamics analysis is performed to quantify the impact of the measured blade properties on the aeromechanics behavior of the rotor. The location of the center of gravity is demonstrated to be the most influential factor affecting the deviation and the sensitivity of the aeroelastic response of the rotor. Nomenclature C T = thrust coefficient; T∕ρRΩ 2 πR 2 c = chord, m EA = axial stiffness, N EI β = flap-bending stiffness, N · m 2 EI ζ = chord-bending stiffness, N · m 2 GJ = torsion stiffness, N · m 2 I θ = polar mass moment of inertia per length, kg · m M = hover tip Mach number R = rotor radius, m T = applied torque, N · m α s = shaft tilt angle, deg μ = advance ratio ρ = air density, kg∕m 3 Ω = rotor nominal speed, rad∕s

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“…The laminar separation bubbles (LSB) [14] and strong rotational flow are usually induced by small rotors causing complicated flow phenomena. Computational fluid dynamics (CFD) and analytical approaches are frequently utilised for these cases [15][16][17][18][19][20][21][22][23]. CFD has a fidelity performance to predict the rotary wing flow, whereas the analytical approach is capable of solving the problem quickly.…”

Section: Nomenclaturementioning

confidence: 99%

Design of Test Benches for the Hovering Performance of Nano-Rotors

Liu

Moschetta

Chapman

et al. 2010

International Journal of Micro Air Vehicles

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With the reduction of rotor diameter and motor size, the hovering performance measurement becomes a challenge for rotary wing Nano Air Vehicles (NAVs). Conventional test benches for Micro Aerial Vehicles fail to measure some characteristics of Nano Air Vehicles. In this paper, five test benches with highly sensitive mechanisms were successively designed in order to measure the thrust and torque of nano-rotors simultaneously and respond to the change of variables rapidly with sufficient accuracy. A commercial micro brushless motor and a micro rotor were studied experimentally and computationally at a low Reynolds range from 4,000 to 19,000. Computational and experimental comparisons were carried out and the performance of the test benches was discussed. The analysis suggests that the thrust coefficients measured by each test bench vary little from each other, while the power coefficients present significant differences. Then the hovering performance of the micro rotor and power efficiency of the motor were studied. Degradation of motor efficiency and rotor figure of merit are observed with size reduction associated with NAV applications. [1][2][3][4][5]. At present, more complicated battlefield environments or civilian security situations force soldiers to implement MAVs in urban missions. Therefore, an ever-present need has emerged to improve MAV capabilities, enabling the timely collection of comprehensive intelligence information, particularly on the ground in urban terrain. However, current MAVs are too large to provide situational awareness to the users; consequently, even smaller Unmanned Air Vehicles (UAVs) are required to allow reconnaissance inside buildings, penetration of narrow entries and transmission of data without being detected. Therefore, NAVs [6] were proposed to fulfil such missions. Referring to the definition proposed by DARPA, a NAV is defined as a UAV whose maximum dimension should not exceed 3 inches (7.5 cm) and maximum weight should be less than 10 g. Because of the special requirement of this kind of aerial vehicle, it should be able to autonomously enter buildings, stare, spot targets and transmit data at a fairly low speed or hovering mode. Hence, compared with the conventional MAV, a NAV not only has a smaller size but also the requirement of a low-speed flight and hovering ability. Furthermore, it is expected that NAVs should have an endurance of 20 minutes to complete a recognition mission within a range of less than 1 km. Consequently, the propulsion efficiency becomes a quite important parameter for NAV design. In addition, hovering performance is always a bottleneck for the design of small unmanned air vehicles as a result of the degradation of the aerodynamic performance at low Reynolds numbers. Thus, the hovering performance of NAVs was investigated in this paper. NOMENCLATUREPresently, two concepts are predominately studied in the design of NAVs [7][8][9]. One is the rotary wing; the other is the flapping wing. Previous studies have shown that the rotary-wing conce...

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Tip Vortex Conservation on a Helicopter Main Rotor Using Vortex-Adapted Chimera Grids

Cited by 22 publications

References 11 publications

Numerical Simulation of Rotor Using Coupled Computational Fluid Dynamics and Free Wake

Numerical Simulation of Rotor Using Coupled Computational Fluid Dynamics and Free Wake

Study on Blade Property Measurement and Its Influence on Air/Structural Loads

Design of Test Benches for the Hovering Performance of Nano-Rotors

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