Experimental study of rotor/body aerodynamic interactions

Bi, Naipei; Leishman, J. Gordon

doi:10.2514/3.45938

Cited by 25 publications

(8 citation statements)

References 6 publications

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“…The present paper is concerned with boundary-layer separation and ejection of secondary vorticity induced by a vortex located near a circular cylinder, where the vortex axis is nominally orthogonal to the cylinder axis and the vortex core radius is much less than the cylinder diameter. This problem is particularly representative of rotorcraft aerodynamic problems, where impact of rotor tip vortices on the vehicle empennage, airframe and tail section during hover and low-speed flight causes strong impulsive forces and moments on the vehicle (Sheridan & Smith 1980;Bi & Leishman 1990;Bi, Leishman & Crouse 1993). Vortex-cylinder interaction is also important in problems such as turbulence-wall interaction in marine cable boundary layers (Neves, Moin & Moser 1994) and unsteady loading in an array of parallel cylinders owing to vortices shed from upstream cylinders, such as occurs in offshore platform risers, groups of tall buildings, and heat exchanger tube bundles (Rockwell 1998).…”

Section: Introductionmentioning

confidence: 99%

Simulation of normal vortex–cylinder interaction in a viscous fluid

Gossler

Marshall

2001

J. Fluid Mech.

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A computational study of three-dimensional vortex–cylinder interaction is reported for the case where the nominal orientation of the cylinder axis is normal to the vortex axis. The computations are performed using a new tetrahedral vorticity element method for incompressible viscous fluids, in which vorticity is interpolated using a tetrahedral mesh that is refit to the Lagrangian computational points at each timestep. Fast computation of the Biot-Savart integral for velocity is performed using a box-point multipole acceleration method for distant tetrahedra and Gaussian quadratures for nearby tetrahedra. A moving least-square method is used for differentiation, and a flux-based vorticity boundary condition algorithm is employed for satisfaction of the no-slip condition. The velocity induced by the primary vortex is obtained using a filament model and the Navier–Stokes computations focus on development of boundary-layer separation from the cylinder and the form and dynamics of the ejected secondary vorticity structure. As the secondary vorticity is drawn outward by the vortex-induced flow and wraps around the vortex, it has a substantial effect both on the essentially inviscid flow field external to the boundary layer and on the cylinder surface pressure field. Cases are examined with background free-stream velocity oriented in the positive and negative directions along the cylinder axis, with free-stream velocity normal to the cylinder axis, and with no free-stream velocity. Computations with no free-stream velocity and those with free-stream velocity tangent to the cylinder axis exhibit similar secondary vorticity structures, consisting of a vortex loop (or hairpin) that wraps around the primary vortex and is attached to the cylinder boundary layer at two points. Computations with free-stream velocity oriented normal to the cylinder axis exhibit secondary vorticity structure of a markedly different character, in which the secondary eddy remains close to the cylinder boundary and has a quasi-two-dimensional form for an extended time period.

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Section: Introductionmentioning

confidence: 99%

Simulation of normal vortex–cylinder interaction in a viscous fluid

Gossler

Marshall

2001

J. Fluid Mech.

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“…This strength is relatively large, and from a fundamental point of view it is natural to inquire how the present results will be modified with a weaker vortex. It is also useful to point out that the configuration of the rotorcraft experiments at Maryland (Bi & Leishman 1990) may, to a first approximation, be modelled by merely switching the sign of the circulation (Affes & Conlisk 1993). In this case, an eruptive region is likely to form just ahead of the main vortex with the evolution of the secondary flow being similar.…”

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confidence: 99%

The boundary-layer flow due to a vortex approaching a cylinder

1994

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The three-dimensional unsteady boundary layer induced by a vortex filament moving outside a circular cylinder is considered. In the present paper, we focus attention on the situation where the inviscid flow is fully three-dimensional but is symmetric with respect to the top centreline of the cylinder. The motion of the vortex toward the cylinder leads to separation of the boundary layer; in the present work a large unsteady adverse pressure gradient develops as well. Results for the three-dimensional streamlines, the vorticity distribution, and the velocity component normal to the cylinder indicate the presence of a region of unsteady three-dimensional secondary flow structure of rather complex shape located deep within the boundary layer. Within this three-dimensional secondary flow the fluid is progressively squeezed into a narrow region under the main vortex and it is expected that a local three-dimensional jet will develop sending boundary-layer fluid out into the main stream. It is pointed out that such three-dimensional eruptive behaviour has been observed in experiments. The results indicate the development of a three-dimensional singularity in the boundary-layer equations.

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“…Two primary design constraints are imposed by the dimensions of wind tunnel test section and the available hub components. The Glenn L. Martin Wind Tunnel in the University of Maryland has a test section of 3:3528 2:3622 m. The model rotor diameter is typically restricted to 45-55% of the wind tunnel width to avoid interference effects [29]. This translates to a maximum rotor diameter of 1.5088 to 1.8440 m. The existing articulated hub is a four-bladed, fully articulated rotor system with coincident flap and lead-lag hinges offset 0.054 m. The smaller the rotor radius the larger the effective hinge offset.…”

Section: Determination Of Rotor Parametersmentioning

confidence: 99%

Development of Mach Scale Rotors with Tailored Composite Coupling for Vibration Reduction

Jin

Nagaraj

Chopra

et al. 2006

Journal of Aircraft

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This paper presents the design, structural and aeroelastic analyses, fabrication, and structural tests of Mach-scale articulated composite rotors with tailored flap-bending/torsion couplings for vibration reduction. The rotor design was nominally based on the UH-60 Black Hawk rotor. A new fabrication process was developed to manufacture Mach-scale composite tailored blade. Five sets of Mach-scale composite tailored rotors were successfully fabricated in-house, including a baseline rotor without coupling, two rotors with uniform spanwise flap-bending/torsion couplings, and two rotors with spanwise segmented flap-bending/torsion couplings. Bench-top and nonrotating dynamic tests were performed to verify the structural analysis of these composite tailored blades. The measured results correlated well with predictions. Comprehensive aeroelastic analysis (using University of Maryland Advanced Rotorcraft Code) of these Mach-scale composite tailored rotors indicated that blade elastic flap-bending/ torsion couplings can significantly impact rotor vibration characteristics. It was shown that spanwise segmented flapbending/torsion couplings can provide larger rotor vibration reduction than uniform spanwise couplings.

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Experimental study of rotor/body aerodynamic interactions

Cited by 25 publications

References 6 publications

Simulation of normal vortex–cylinder interaction in a viscous fluid

Simulation of normal vortex–cylinder interaction in a viscous fluid

The boundary-layer flow due to a vortex approaching a cylinder

Development of Mach Scale Rotors with Tailored Composite Coupling for Vibration Reduction

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