Experimental Boundary Layer Study on Hovering Rotors

Tanner, W. H.; Yaggy, P. F.

doi:10.4050/jahs.11.22

Cited by 22 publications

(4 citation statements)

References 4 publications

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“…Observations from experimental campaigns conducted by Tanner and Yaggy, [17], and by McCroskey [18], for hover and forward flight, support this approach by demonstrating airflow patterns on the surface of the rotor blades that were mainly 2D. In airflow regions away from the blade tip, boundary layer growth was observed to be almost exclusively 2D in both rotating and stationary frames, with rotational effects having only a minor influence on cross-flow.…”

Section: Introductionmentioning

confidence: 80%

Ice Accretion Effects on Helicopter Rotor Performance, via Multibody and CFD Approaches

Kelly¹,

Habashi²,

Quaranta³

et al. 2018

Journal of Aircraft

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Section: Introductionmentioning

confidence: 80%

Ice Accretion Effects on Helicopter Rotor Performance, via Multibody and CFD Approaches

Kelly¹,

Habashi²,

Quaranta³

et al. 2018

Journal of Aircraft

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“…This action is considered to be similar to that reported by Tanner and Yaggy as being the result of the radial inflow on the upper surface induced by the tip vortex. 10 As the pitch angle is increased, the tip vortex is strengthened, thereby increasing the inward flow at the blade tip.…”

Section: =5°mentioning

confidence: 99%

Boundary-layer discontinuity on a helicopter rotor blade in hovering

Velkoff

Blaser

Jones

1971

Journal of Aircraft

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To synthesize the three-arc trajectory, draw a unity circle Ci tangent to both C 0 arid C/ as in Fig. 8b. The center of Ci is the intersection of two arcs which are two radii from C 0 and C f , respectively. By using different combinations of initial and final circles in this construction, up to eight such centers can be found. At most, two of these can be used to draw circles that form confluent three-arc trajectories and that contain angles of more than TT radians. The shortest of these two is another feasible optimum trajectory.To construct the four-arc trajectory, denote by P m the midpoint of the line connecting the center of the circles C 0 and C f . Draw a unity circle Ci tangent to C 0 with center at the intersection of two arcs, the first arc being two radii from C 0 and the second arc one radius from P m , as illustrated in Fig. 8c. Similarly, draw a second circle (7 2 tangent to both the final circle C/ and the circle C\. This procedure guarantees that the two-interior arcs of the four-arc trajectory are of equal length. At most, two four-arc trajectories with interior arcs containing angles of more than TT radians can be drawn by using different combinations of initial and final circles.This concludes the construction of all feasible optimum trajectories. The globally optimum trajectory can now be determined by comparing the length of all feasible optimum trajectories, and choosing the one with the shortest arc length.An experimental study was conducted using flow visualization techniques to investigate the nature of the boundary layer on a model helicopter rotor. Hovering and forward flight data were obtained; however, efforts were concentrated on hovering when unanticipated boundary-layer behavior was revealed. The primary flow visualization technique involved the use of ammonia injected into the boundary layer at the leading edge. The blade surface was chemically coated, and as the ammonia moved with the local airflow, it formed a trace on the surface indicative of the boundary-layer flow. The hovering traces initially moved chordwise along the surface, and then abruptly turned outward. A short distance later, the traces moved inward and then continued aft along the blade in a somewhat diffuse pattern. Similar traces were found over wide ranges of pitch angles and rotor speeds. It is hypothesized that a standing laminar separation bubble exists on the blade surface aft of the peak pressure position. No indication of any separation bubbles could be found on the forward flight traces. Nomenclature c = blade chord length LI = separation point 1/2 = reattachment point P = pressure coefficient AP = differential pressure q = dynamic pressure, pF 2 /2 r = radius to local blade section R = blade radius si = stagnation point preceding the separation bubble «2 = stagnation point following the separation bubble V -flight speed Presented as Paper 69-197 at the AIAA/AHS VTOL Research

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“…17 The transition lines determined by the acenaphthene were verified by heated film skin-friction gages, following Bellhouse and Schultz. 18…”

Section: Introductionmentioning

confidence: 99%

Crossflow and Unsteady Boundary-Layer Effects on Rotating Blades

Dwyer

Aiccroskey

1971

AIAA Journal

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knowing the effective elastic and damping properties of the materials over a sufficiently large frequency range the speed and attenuation of the pulses can be predicted using the linear theory of viscoelasticity.Material dispersion appears to be relatively insignificant in glass-epoxy and boron-epoxy samples below 0.25 mHz, although further research in this area is needed. Ultrasonic methods have been shown to provide a useful way of studying dispersion in composite materials.In this paper attention has been restricted to disturbances propagating in the direction of the reinforcing filaments. A complete characterization of the dynamic behavior of unidirectional fiber-reinforced materials requires a knowledge of the remaining four dynamic moduli (assuming transverse isotropy). Hence additional testing is needed.Laminar viscous flow on propellers and helicopter rotors lias been studied for a wide variety of blade shapes and environments. The significance of crossflow and unsteady effects has been assessed, and the physical processes which influence the primary flow around the blade have been explained. Special attention has been devoted to those terms in the differential equations that change the boundary-layer structure from that of two-dimensional steady flow. Detailed analyses and calculations reveal that large rotational effects are limited to the immediate vicinity of the rotor hub, while the unsteady and yawed-wing effects of forward flight are important over most of the blade surface. However, chordwise pressure gradients tend to predominate over rotational and unsteady velocity effects for blunt bodies or thin airfoils at large angles of attack. Experimental results for laminar separation and transition support these predictions.

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Experimental Boundary Layer Study on Hovering Rotors

Cited by 22 publications

References 4 publications

Ice Accretion Effects on Helicopter Rotor Performance, via Multibody and CFD Approaches

Ice Accretion Effects on Helicopter Rotor Performance, via Multibody and CFD Approaches

Boundary-layer discontinuity on a helicopter rotor blade in hovering

Crossflow and Unsteady Boundary-Layer Effects on Rotating Blades

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